Kaitlin Kratter

Interests

Teaching

General Science Education, Astrophysics Theory

Research

Star and Planet Formation, Theoretical and Computational Astrophysics, Binary Stars, Accretion Disks, Stellar and Planetary Dynamics

Courses

Scholarly Contributions

Chapters

• Canup, R., Kratter, K., & Neveu, M. (2021). "On the Origin of the Pluto System". In The Pluto System After New Horizons(pp 475-506).
• Kratter, K. (2017). "Constraints from Planets in Binaries". In Astrophysics and Space Science Library.

Journals/Publications

• De Furio, M., Gardner, T., Monnier, J. D., Meyer, M. R., Kratter, K. M., Lanthermann, C., Anugu, N., Kraus, S., & Setterholm, B. R. (2025). The Small Separation A-star Companion Population: Tentative Signatures of Enhanced Multiplicity with Primary Mass. Astrophysical Journal, 990(Issue 1). doi:10.3847/1538-4357/adf3b1
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  We present updated results from our near-infrared long-baseline interferometry (LBI) survey to constrain the multiplicity properties of intermediate-mass A-type stars within 80 pc. Previous adaptive optics surveys of A-type stars are incomplete at separations
• Eastlund, C., Moe, M., Kratter, K. M., & Kounkel, M. (2025). New Insights into the T Tauri Binary Separation Distribution. Astrophysical Journal, 990(Issue 2). doi:10.3847/1538-4357/adf6bc
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  For three decades, adaptive optic surveys have revealed an excess of T Tauri binaries across a = 10-100 au in nearby star-forming regions compared to the field population of main-sequence (MS) stars. Such an excess requires that most stars are born in dense clusters and subjected to significant dynamical processing that disrupts such binaries across intermediate separations. However, we demonstrate that the apparent excess is due to an observational selection bias. Close binaries within a < 100 au clear out their dusty circumstellar disks on faster timescales compared to wide binaries and single stars. A magnitude-limited sample is therefore biased toward close binaries that have preferentially cleared out their obscuring disks. We reexamine the separation distribution of pre-MS binaries in low-density Taurus, moderately dense Upper Scorpius (Upper Sco), and the extremely dense Orion Nebula Cluster (ONC). By limiting the samples to primary spectral type/mass instead of magnitude, the artificial excess across a = 10-100 au disappears in all three environments. Across wider separations a = 100-4000 au, Taurus exhibits an excess of companions (mostly tertiaries), the ONC displays a deficit, and Upper Sco matches the field MS population. The field derives from an amalgam of all three environments, where Upper Sco corresponds to the average birth environment of solar-type stars. The total binary fraction within a < 10,000 au in Taurus is only 52% ± 7%, substantially lower than the 100% inferred from the biased observations and only slightly higher than the field MS value of 45%. N-body interactions preferentially disrupt outer tertiaries with only marginal dynamical processing of the inner binaries, especially those within a < 100 au.
• Generozov, A., Offner, S. S., Kratter, K. M., Perets, H. B., Guszejnov, D., & Grudić, M. Y. (2025). The bound origin of low-mass stellar binaries. Nature Astronomy. doi:10.1038/s41550-025-02686-5
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  Most main sequence stars, unlike our Sun, belong to multiple systems containing two or more stars. How and when these multiples come together and become bound is uncertain, as the earliest stages of star formation are difficult to resolve. Here we analyse simulations of star cluster formation in Milky Way-like conditions, including all key physics and stellar feedback mechanisms, to understand how multiple systems form. We show that ~70–80% of binaries are gravitationally bound from the moment the second star forms. Binaries evolve and accrete together, which will affect their planetary systems and chemical evolution. Half of the binaries are disrupted by the end of the star-formation epoch, such that ~40% of the final single stars belonged to a multiple at some point, with implications for the stellar initial mass function. Formation in multiples is the dominant mode of star formation, accounting for at least 57% of stars.
• Longarini, C., Price, D. J., Kratter, K. M., Lodato, G., & Clarke, C. J. (2025). Infall-driven gravitational instability in accretion discs. Monthly Notices of the Royal Astronomical Society, 541(Issue 2). doi:10.1093/mnras/staf1018
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  Gravitational instability (GI) is typically studied in cooling-dominated discs, often modelled using simplified prescriptions such as -cooling. In this paper, we investigate the onset and evolution of GI in accretion discs subject to continuous mass injection, combining 1D and 3D numerical simulations. We explore an alternative self-regulation mechanism in which mass replenishment drives the system toward marginal stability. In this regime, the disc establishes a steady-state disc-to-star mass ratio, balancing the mass transported to the central object with that added to the disc. Our 3D simulations reveal that the general scaling predicted from the linear theory are respected, however there are important difference compared to the cooling case in terms of morphology and pattern speed. Unlike the flocculent spirals seen in cooling-driven instability, the power is concentrated towards the dominant modes in infall-driven spirals. Additionally, spiral waves generate at the mass injection location, and propagate at constant pattern speed, unlike in the cooling case. This suggests a fundamental difference in how mass-regulated and cooling-regulated discs behave and transport angular momentum.
• Moe, M., Oey, M. S., Vargas-Salazar, I., & Kratter, K. M. (2025). The Close Binary Properties of Massive Stars across Different Environments within the LMC. Astrophysical Journal, 991(Issue 2). doi:10.3847/1538-4357/ae0034
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  We analyze 4859 O stars in the third phase of the Optical Gravitational Lensing Experiment photometric survey of the LMC, including 415 eclipsing binaries (EBs). After accounting for the geometrical probability of eclipses, the period distribution of O-type binaries across P = 2.5-200 days follows a power law flogP ∝ (logP)Π with Π = −0.34 ± 0.06, which is skewed toward shorter periods compared to Opik’s law (Π = 0). We divide our O stars into seven environments based on their clustering with B stars and other O stars. The EB fraction of O stars in young clusters is 10.2% ± 0.6%, which matches the 10.8% ± 2.1% for O stars in young Milky Way clusters. O stars in old clusters exhibit a lower EB fraction of 5.5% ± 0.9% due to the effects of binary evolution. O stars in young dense clusters, young sparse associations, and even low-mass clusters that formed in situ in the field have similar EB fractions. This uniformity suggests that the formation of close massive binaries depends on small-scale gas physics, e.g., fragmentation and migration within protostellar disks, whereas N-body interactions that scale with cluster density do not affect the close binary properties of massive stars that remain in clusters. Conversely, ejected O stars in the field exhibit a lower close binary fraction. The EB fractions of field walkaways (projected velocities vproj < 24.5 km s−1) and field runaways (vproj > 24.5 km s−1) are 7.3% ± 1.0% and 4.7% ± 1.0%, respectively. These values suggest that most field O stars were dynamically ejected via N-body interactions from their birth clusters, whereas field O stars that formed in situ or were kicked from supernova explosions in binaries contribute 17% and
• Sefilian, A. A., Kratter, K. M., Wyatt, M. C., Petrovich, C., Thébault, P., Malhotra, R., & Faramaz-Gorka, V. (2025). The vertical structure of debris discs and the role of disc gravity: a primer using a simplified model. Monthly Notices of the Royal Astronomical Society, 543(Issue 4). doi:10.1093/mnras/staf1555
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  Debris discs provide valuable insights into the formation and evolution of exoplanetary systems. Their structures are commonly attributed to planetary perturbations, serving as probes of as-yet-undetected planets. However, most studies of planet-debris disc interactions ignore the disc’s gravity, treating it as a collection of mass-less planetesimals. We develop a simplified analytical model as a primer to investigate how the vertical structure of a back-reacting debris disc responds to secular perturbations from an inner, inclined planet. Considering the disc’s axisymmetric potential, we identify two dynamical regimes: planetdominated and disc-dominated, which may coexist, separated by a secular-inclination resonance. In the planet-dominated regime (Md /mp ≪ 1), we recover the classical result: a transient warp propagates outward until the disc settles into a box-like structure centred around the planetary orbit’s initial inclination Ip(0), with a distance-independent aspect ratio H(R) ≈ Ip(0). In contrast, in the disc-dominated regime (Md /mp ⪰ 1), the disc exhibits dynamical rigidity, remaining thin and misaligned, with significantly suppressed inclinations and a sharply declining aspect ratio, H(R) ∝ Ip(0)R−7/2. In the intermediate regime (Md /mp ≲ 1), the system exhibits a secular-inclination resonance, leading to long-lived, warp-like structures and a bimodal inclination distribution, containing both dynamically hot and cold populations. We provide analytic formulae describing these effects as a function of system parameters. We also find that the vertical density profile is intrinsically non-Gaussian and recommend fitting observations with non-zero slopes of H(R). Our results may be used to infer planetary parameters and debris disc masses based on observed warps and scale heights, as demonstrated for HD 110058 and β Pic.
• Vargas-Salazar, I., Oey, M. S., Eldridge, J. J., Weisserman, D., Januszewski, H. C., Becker, J. C., Zazzera, S., Castro, N., Kim, Y., Kratter, K. M., Mateo, M., & Bailey, J. I. (2025). New Field OB and OBe Binaries of the SMC Wing: Observational Properties and Population Modeling. Astrophysical Journal, 988(Issue 2). doi:10.3847/1538-4357/ade523
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  We present a radial velocity (RV) survey of the field OB and OBe stars of the SMC Wing. We use multiepoch observations of 55 targets obtained with the Magellan Inamori-Magellan Aerial Camera and Spectrograph and M2FS multi-object spectrographs to identify single- and double-lined spectroscopic binaries. We also use TESS light curves to identify new eclipsing binary candidates. We find that 10 each of our 34 OB (29%) and 21 OBe (48%) stars are confirmed binaries, and at least ∼6 more are candidates. Using our RV measurements, we set constraints on the companion masses, and in some cases, on periods, eccentricities, and inclinations. The RV data suggest that OB binaries favor more circular orbits (mean eccentricity 〈e〉 = 0.08 ± 0.02), while OBe binaries are eccentric (〈e〉 = 0.45 ± 0.04). We identify two candidate black hole binaries, [M2002] 77616, and 81941. We use Binary Population and Spectral Synthesis to predict the frequencies of ejected OB and OBe stars and binaries, assuming OBe stars are binary mass gainers ejected by the companion supernova. We also predict the frequencies of black-hole, neutron-star, and stripped-star companions, and we model the distributions of primary and secondary masses, periods, eccentricities, and velocity distributions. The models are broadly consistent with the binary origin scenario for OBe stars, and predict an even larger number of post-supernova OB binaries. Comparison with the kinematics supports a significant contribution from dynamical ejections for both OB and OBe stars, although less so for binaries.
• Weible, G., Wagner, K., Stone, J., Ertel, S., Apai, D., Kratter, K., & Leisenring, J. (2025). Orbital and Atmospheric Modeling of H ii 1348B: An Eccentric Young Substellar Companion in the Pleiades. Astronomical Journal, 169(Issue 4). doi:10.3847/1538-3881/adadf6
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  Brown dwarfs with known physical properties (e.g., age and mass) are essential for constraining models of the formation and evolution of substellar objects. We present new high-contrast imaging observations of the circumbinary brown dwarf H ii 1348B—one of the few known substellar companions in the Pleiades cluster. We observed the system in the infrared L ′ band with the Large Binocular Telescope Interferometer in dual-aperture direct-imaging mode (i.e., with the two telescope apertures used separately) on 2019 September 18. The observations attained a high signal-to-noise ratio (SNR > 150) photometric detection and relative astrometry with uncertainties of ∼5 mas. This work presents the first model of the companion’s orbital motion using relative astrometry from five epochs across a total baseline of 23 yr. Orbital fits to the compiled data show the companion’s semimajor axis to be a = 14 0 − 30 + 130 au with an eccentricity of e = 0.7 8 − 0.29 + 0.12 . We infer that H ii 1348B has a mass of 60-63 ± 2 MJ from comparison to brown dwarf evolutionary models given the well-constrained distance and age of the Pleiades. No other objects were detected in the H ii 1348 system, and through synthetic planet injection and retrievals we establish detection limits at a cluster age of 112 ± 5 Myr down to ∼10-30 MJ for companions with projected separations of 21.5-280 au. With this work, H ii 1348B becomes the second directly imaged substellar companion in the Pleiades with measured orbital motion after HD 23514B.
• Duffell, P., Dittmann, A., Franchini, A., Kratter, K., Penzlin, A., Ragusa, E., Siwek, M., Tiede, C., Wang, H., Zrake, J., Dempsey, A., Haiman, Z., Lupi, A., Pirog, M., Ryan, G., & D’Orazio, D. (2024). The Santa Barbara Binary−disk Code Comparison. Astrophysical Journal, 970(2). doi:10.3847/1538-4357/ad5a7e
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  We have performed numerical calculations of a binary interacting with a gas disk, using 11 different numerical methods and a standard binary−disk setup. The goal of this study is to determine whether all codes agree on a numerically converged solution and to determine the necessary resolution for convergence and the number of binary orbits that must be computed to reach an agreed-upon relaxed state of the binary−disk system. We find that all codes can agree on a converged solution (depending on the diagnostic being measured). The zone spacing required for most codes to reach a converged measurement of the torques applied to the binary by the disk is roughly 1% of the binary separation in the vicinity of the binary components. For our disk model to reach a relaxed state, codes must be run for at least 200 binary orbits, corresponding to about a viscous time for our parameters, 0.2(a 2ΩB /ν) binary orbits, where ν is the kinematic viscosity. The largest discrepancies between codes resulted from the dimensionality of the setup (3D vs. 2D disks). We find good agreement in the total torque on the binary between codes, although the partition of this torque between the gravitational torque, orbital accretion torque, and spin accretion torque depends sensitively on the sink prescriptions employed. In agreement with previous studies, we find a modest difference in torques and accretion variability between 2D and 3D disk models. We find cavity precession rates to be appreciably faster in 3D than in 2D.
• Krapp, L., Garrido-Deutelmoser, J., Kratter, K., & Benítez-Llambay, P. (2024). A Fast Second-order Solver for Stiff Multifluid Dust and Gas Hydrodynamics. Astrophysical Journal, Supplement Series, 271(1). doi:10.3847/1538-4365/ad14f9
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  We present MDIRK: a multifluid second-order diagonally implicit Runge-Kutta method to study momentum transfer between gas and an arbitrary number (N) of dust species. The method integrates the equations of hydrodynamics with an implicit-explicit scheme and solves the stiff source term in the momentum equation with a diagonally implicit, asymptotically stable Runge-Kutta method (DIRK). In particular, DIRK admits a simple analytical solution that can be evaluated with O ( N ) operations, instead of standard matrix inversion, which is O ( N ) 3 . Therefore, the analytical solution significantly reduces the computational cost of the multifluid method, making it suitable for studying the dynamics of systems with particle-size distributions. We demonstrate that the method conserves momentum to machine precision and converges to the correct equilibrium solution with constant external acceleration. To validate our numerical method we present a series of simple hydrodynamic tests, including damping of sound waves, dusty shocks, a multifluid dusty Jeans instability, and a steady-state gas-dust drift calculation. The simplicity of MDIRK lays the groundwork to build fast high-order, asymptotically stable multifluid methods.
• Krapp, L., Kratter, K., Youdin, A., Masset, F., Armitage, P., & Benítez-Llambay, P. (2024). A Thermodynamic Criterion for the Formation of Circumplanetary Disks. Astrophysical Journal, 973(2). doi:10.3847/1538-4357/ad644a
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  The formation of circumplanetary disks is central to our understanding of giant planet formation, influencing their growth rate during the post-runaway phase and observability while embedded in protoplanetary disks. We use three-dimensional global multifluid radiation hydrodynamics simulations with the FARGO3D code to define the thermodynamic conditions that enable circumplanetary disk formation around Jovian planets on wide orbits. Our simulations include stellar irradiation, viscous heating, static mesh refinement, and active calculation of opacity based on multifluid dust dynamics. We find a necessary condition for the formation of circumplanetary disks in terms of a mean cooling time: When the cooling time is at least 1 order of magnitude shorter than the orbital timescale, the specific angular momentum of the gas is nearly Keplerian at scales of one-third of the Hill radius. We show that the inclusion of multifluid dust dynamics favors rotational support because dust settling produces an anisotropic opacity distribution that favors rapid cooling. In all our models with radiation hydrodynamics, specific angular momentum decreases as time evolves, in agreement with the formation of an inner isentropic envelope due to compressional heating. The isentropic envelope can extend up to one-third of the Hill radius and shows negligible rotational support. Thus, our results imply that young gas giant planets may host spherical isentropic envelopes, rather than circumplanetary disks.
• Reynolds, N., Tobin, J., Sheehan, P., Sadavoy, S., Looney, L., Kratter, K., Li, Z., Segura-Cox, D., & Kaib, N. (2024). The Disk Orientations of Perseus Protostellar Multiples at ∼8 au Resolution. Astrophysical Journal, 963(2). doi:10.3847/1538-4357/ad151d
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  We present a statistical characterization of circumstellar disk orientations toward 12 protostellar multiple systems in the Perseus molecular cloud using the Atacama Large Millimeter/submillimeter Array at Band 6 (1.3 mm) with a resolution of ∼25 mas (∼8 au). This exquisite resolution enabled us to resolve the compact inner-disk structures surrounding the components of each multiple system and to determine the projected 3D orientation of the disks (position angle and inclination) to high precision. We performed a statistical analysis on the relative alignment of disk pairs to determine whether the disks are preferentially aligned or randomly distributed. We considered three subsamples of the observations selected by the companion separations a < 100 au, a > 500 au, and a < 10,000 au. We found for the compact (500 au) subsample appears to be consistent with a distribution of 40%-80% preferentially aligned sources. Similarly, the full sample of systems with companions (a < 10,000 au) is most consistent with a fractional ratio of at most 80% preferentially aligned sources and rules out purely randomly aligned distributions. Thus, our results imply the compact sources (500 au) are statistically different.
• Smith, C., Moe, M., & Kratter, K. (2024). Spin-Orbit Alignment of Early-type Astrometric Binaries and the Origin of Slow Rotators. Astrophysical Journal, 975(1). doi:10.3847/1538-4357/ad6dd2
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  The spin-orbit alignment of binary stars traces their formation and accretion history. Previous studies of spin-orbit alignment have been limited to small samples, slowly rotating solar-type stars, and/or wide visual binaries that not surprisingly manifest random spin-orbit orientations. We analyze 917 Gaia astrometric binaries across periods P = 100-3000 days (a = 0.5-5 au) that have B8-F1 IV/V primaries (M 1 = 1.5-3 M ⊙) and measured projected rotational velocities v sin i. The primary stars in face-on orbits exhibit substantially smaller v sin i compared to those in edge-on orbits at the 6σ level, demonstrating significant spin-orbit alignment. The primaries in our astrometric binaries are rotating more slowly than their single-star or wide-binary counterparts and therefore comprise the slow-rotator population in the observed bimodal rotational velocity distribution of early-type stars. We discuss formation models of close binaries where some of the disk angular momentum is transferred to the orbit and/or secondary spin, quenching angular momentum flow to the primary spin. The primaries in astrometric binaries with small mass ratios q = M 2/M 1 < 0.3 possess even smaller v sin i, consistent with model predictions. Meanwhile, astrometric binaries with large eccentricities e > 0.4 do not display spin-orbit alignment or spin reduction. Using a Monte Carlo technique, we measure a spin-orbit alignment fraction of F align = 75% ± 5% and an average spin reduction factor of 〈S align〉 = 0.43 ± 0.04. We conclude that 75% of close A-type binaries likely experienced circumbinary disk accretion and probably formed via disk fragmentation and inward disk migration. The remaining 25%, mostly those with e > 0.4, likely formed via core fragmentation and orbital decay via dynamical friction.
• Kong, S., Arce, H., Tobin, J., Zhang, Y., Maureira, M., Kratter, K., & Pillai, T. (2023). Binary Formation in a 100 μm Dark Massive Core. Astrophysical Journal, 950(2). doi:10.3847/1538-4357/acd252
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  We report high-resolution ALMA observations toward a massive protostellar core C1-Sa (∼30 M ⊙) in the Dragon infrared dark cloud. At the resolution of 140 au, the core fragments into two kernels (C1-Sa1 and C1-Sa2) with a projected separation of ∼1400 au along the elongation of C1-Sa, consistent with a Jeans length scale of ∼1100 au. Radiative transfer modeling using RADEX indicates that the protostellar kernel C1-Sa1 has a temperature of ∼75 K and a mass of 0.55 M ⊙. C1-Sa1 also likely drives two bipolar outflows, one being parallel to the plane of the sky. C1-Sa2 is not detected in line emission and does not show any outflow activity but exhibits ortho-H2D+ and N2D+ emission in its vicinity; thus it is likely still starless. Assuming a 20 K temperature, C1-Sa2 has a mass of 1.6 M ⊙. At a higher resolution of 96 au, C1-Sa1 begins to show an irregular shape at the periphery, but no clear sign of multiple objects or disks. We suspect that C1-Sa1 hosts a tight binary with inclined disks and outflows. Currently, one member of the binary is actively accreting while the accretion in the other is significantly reduced. C1-Sa2 shows hints of fragmentation into two subkernels with similar masses, which requires further confirmation with higher sensitivity.
• Krapp, L., Ramos, X., Kratter, K., & Benítez-Llambay, P. (2023). RAM: Rapid Advection Algorithm on Arbitrary Meshes. Astrophysical Journal, 952(2). doi:10.3847/1538-4357/acd698
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  The study of many astrophysical flows requires computational algorithms that can capture high Mach number flows, while resolving a large dynamic range in spatial and density scales. In this paper we present a novel method, RAM: Rapid Advection Algorithm on Arbitrary Meshes. RAM is a time-explicit method to solve the advection equation in problems with large bulk velocity on arbitrary computational grids. In comparison with standard upwind algorithms, RAM enables advection with larger time steps and lower truncation errors. Our method is based on the operator splitting technique and conservative interpolation. Depending on the bulk velocity and resolution, RAM can decrease the numerical cost of hydrodynamics by more than one order of magnitude. To quantify the truncation errors and speed-up with RAM, we perform one- and two-dimensional hydrodynamics tests. We find that the order of our method is given by the order of the conservative interpolation and that the effective speed-up is in agreement with the relative increment in time step. RAM will be especially useful for numerical studies of disk−satellite interaction, characterized by high bulk orbital velocities and nontrivial geometries. Our method dramatically lowers the computational cost of simulations that simultaneously resolve the global disk and potential well inside the Hill radius of the secondary companion.
• Pauwels, T., Reggiani, M., Sana, H., Rainot, A., & Kratter, K. (2023). The multiplicity of massive stars in the Scorpius OB1 association through high-contrast imaging. Astronomy and Astrophysics, 678(Issue). doi:10.1051/0004-6361/202245324
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  Context. Despite past efforts, a comprehensive theory of massive star formation is still lacking. One of the most remarkable properties of massive stars is that almost all of them are found in binaries or higher-order multiple systems. Since multiplicity is an important outcome parameter of a star formation process, observations that cover the full companion mass ratio and separation regime are essential to constrain massive star formation theories. Aims. We aim to characterise the multiplicity properties of 20 OB stars (one of which turned out to be a foreground object) in the active star-forming region Sco OB1 in the separation range 0.15-6 (∼200-9000 AU), using high-contrast imaging observations. These observations enabled us to reach very large magnitude differences and explore an as of yet uncharted territory of companions around massive stars. Methods. We used VLT/SPHERE to simultaneously observe with IFS and IRDIS, obtaining high-contrast imaging observations that cover a field of view (FoV) of 1'73 × 1'73 in YJH bands and 11 × 12 5 in K1 and K2 bands, respectively. We extracted low-resolution IFS spectra of candidate companions within 0 85 and compared them with PHOENIX and ATLAS9 atmosphere models to obtain an estimate of their fundamental parameters. Furthermore, we retrieved an estimate of the mass and age of all sources in the larger IRDIS FoV. The observations reached contrast magnitudes of Δ K1 ∼ 13 on average, so we were able to detect sources at the stellar-substellar boundary. Results. In total, we detect 789 sources, most of which are likely background sources. Thirty objects that are estimated to be in the stellar mass regime have a 20% or lower probability of being spurious associations. We obtain SPHERE companion fractions of 2.3-±-0.4 and 4.1-±-0.8 for O- and B-type stars, respectively. Splitting the sample between more massive (> 20 M⊙) and less massive stars (< 20 M⊙), we obtain companion fractions of 2.3-±-0.4 and 3.9-±-0.7, respectively. Including all previously detected companions, we find a total multiplicity fraction of 0.89-±-0.07 for separations in the range of -0-12 000 AU. Conclusions. With SPHERE, we are probing an unexplored area in the magnitude versus separation diagram of companions, which is crucial to achieve a complete overview of the multiplicity properties of massive stars and ultimately improve our understanding of massive star formation.
• Shen, Y., Hwang, H., Oguri, M., Chen, N., Matteo, T., Ni, Y., Bird, S., Zakamska, N., Liu, X., Chen, Y., & Kratter, K. (2023). Statistics of Galactic-scale Quasar Pairs at Cosmic Noon. Astrophysical Journal, 943(1). doi:10.3847/1538-4357/aca662
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  The statistics of galactic-scale quasar pairs can elucidate our understanding of the dynamical evolution of supermassive black hole (SMBH) pairs, the duty cycles of quasar activity in mergers, or even the nature of dark matter, but they have been challenging to measure at cosmic noon, the prime epoch of massive galaxy and SMBH formation. Here we measure a double quasar fraction of ∼6.2 ± 0.5 × 10−4 integrated over ∼0.″3-3″ separations (projected physical separations of ∼3-30 kpc at z ∼ 2) in luminous (L bol > 1045.8 erg s−1) unobscured quasars at 1.5 < z < 3.5 using Gaia EDR3-resolved pairs around SDSS DR16 quasars. The measurement was based on a sample of 60 Gaia-resolved double quasars (out of 487 Gaia pairs dominated by quasar+star superpositions) at these separations, corrected for pair completeness in Gaia, which we quantify as functions of pair separation, magnitude of the primary, and magnitude contrast. The double quasar fraction increases toward smaller separations by a factor of ∼5 over these scales. The division between physical quasar pairs and lensed quasars in our sample is currently unknown, requiring dedicated follow-up observations (in particular, deep, subarcsecond-resolution IR imaging for the closest pairs). Intriguingly, at this point, the observed pair statistics are in rough agreement with theoretical predictions both for the lensed quasar population in mock catalogs and for dual quasars in cosmological hydrodynamic simulations. Upcoming wide-field imaging/spectroscopic space missions such as Euclid, CSST, and Roman, combined with targeted follow-up observations, will conclusively measure the abundances and host galaxy properties of galactic-scale quasar pairs, offset AGNs, and subarcsecond lensed quasars across cosmic time.
• Wagner, K., Stone, J., Skemer, A., Ertel, S., Dong, R., Apai, D., Spalding, E., Leisenring, J., Sitko, M., Kratter, K., Barman, T., Marley, M., Miles, B., Boccaletti, A., Assani, K., Bayyari, A., Uyama, T., Woodward, C., Hinz, P., , Briesemeister, Z., et al. (2023). Direct images and spectroscopy of a giant protoplanet driving spiral arms in MWC 758. Nature Astronomy, 7(10). doi:10.1038/s41550-023-02028-3
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  Understanding the driving forces behind spiral arms in protoplanetary disks remains a challenge due to the faintness of young giant planets. MWC 758 hosts such a protoplanetary disk with a two-armed spiral pattern that is suggested to be driven by an external giant planet. We present observations in the thermal infrared that are uniquely sensitive to redder (that is, colder, or more attenuated) planets than past observations at shorter wavelengths. We detect a giant protoplanet, MWC 758c, at a projected separation of roughly 100 au from the star. The spectrum of MWC 758c is distinct from the rest of the disk and consistent with emission from a planetary atmosphere with T eff = 500 ± 100 K for a low level of extinction (A V ≤ 30), or a hotter object with a higher level of extinction. Both scenarios are commensurate with the predicted properties of the companion responsible for driving the spiral arms. MWC 758c provides evidence that spiral arms in protoplanetary disks can be caused by cold giant planets or by those whose optical emission is highly attenuated. MWC 758c stands out both as one of the youngest giant planets known, and as one of the coldest and/or most attenuated. Furthermore, MWC 758c is among the first planets to be observed within a system hosting a protoplanetary disk.
• Zhang, Z., Bowler, B., Dupuy, T., Brandt, T., Brandt, G., Cochran, W., Endl, M., MacQueen, P., Kratter, K., Isaacson, H., Franson, K., Kraus, A., Morley, C., & Zhou, Y. (2023). The McDonald Accelerating Stars Survey: Architecture of the Ancient Five-planet Host System Kepler-444. Astronomical Journal, 165(2). doi:10.3847/1538-3881/aca88c
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  We present the latest and most precise characterization of the architecture for the ancient (≈11 Gyr) Kepler-444 system, which is composed of a K0 primary star (Kepler-444 A) hosting five transiting planets and a tight M-type spectroscopic binary (Kepler-444 BC) with an A-BC projected separation of 66 au. We have measured the system’s relative astrometry using the adaptive optics imaging from Keck/NIRC2 and Kepler-444 A’s radial velocities from the Hobby-Eberly Telescope and reanalyzed relative radial velocities between BC and A from Keck/HIRES. We also include the Hipparcos-Gaia astrometric acceleration and all published astrometry and radial velocities in an updated orbit analysis of BC’s barycenter. These data greatly extend the time baseline of the monitoring and lead to significant updates to BC’s barycentric orbit compared to previous work, including a larger semimajor axis ( a = 52.2 − 2.7 + 3.3 au), a smaller eccentricity (e = 0.55 ± 0.05), and a more precise inclination ( i = 85 .° 4 − 0 .° 4 + 0 .° 3 ). We have also derived the first dynamical masses of B and C components. Our results suggest that Kepler-444 A’s protoplanetary disk was likely truncated by BC to a radius of ≈8 au, which resolves the previously noticed tension between Kepler-444 A’s disk mass and planet masses. Kepler-444 BC’s barycentric orbit is likely aligned with those of A’s five planets, which might be primordial or a consequence of dynamical evolution. The Kepler-444 system demonstrates that compact multiplanet systems residing in hierarchical stellar triples can form at early epochs of the universe and survive their secular evolution throughout cosmic time.
• Anguiano, B., Badenes, C., Buttry, R., Carlberg, J. K., Daher, C. M., De Lee, N., Dixon, D., Godoy-Rivera, D., Hernández, J., Koposov, S. E., Kratter, K., Majewski, S., Moe, M., Nitschelm, C., Pinsonneault, M., Serna, J., Stassun, K. G., Stringfellow, G. S., Tayar, J., , Troup, N. W., et al. (2022). Stellar multiplicity and stellar rotation: insights from APOGEE. Monthly Notices of the Royal Astronomical Society, 512(2), 2051-2061. doi:10.1093/mnras/stac590
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  We measure rotational broadening in spectra taken by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey to characterise the relationship between stellar multiplicity and rotation. We create a sample of 2786 giants and 24 496 dwarfs with stellar parameters and multiple radial velocities from the APOGEE pipeline, projected rotation speeds \vsini\ determined from our own pipeline, and distances, masses, and ages measured by Sanders \& Das. We use the statistical distribution of the maximum shift in the radial velocities, \drvm, as a proxy for the close binary fraction to explore the interplay between stellar evolution, rotation, and multiplicity. Assuming that the minimum orbital period allowed is the critical period for Roche Lobe overflow and rotational synchronization, we calculate theoretical upper limits on expected \vsini\ and \drvm\ values. These expectations agree with the positive correlation between the maximum \drvm\ and \vsini\ values observed in our sample as a function of \logg. We find that the fast rotators in our sample have a high occurrence of short-period ($\log(P/\text{d})\lesssim 4$) companions. We also find that old, rapidly-rotating main sequence stars have larger completeness-corrected close binary fractions than their younger peers. Furthermore, rapidly-rotating stars with large \drvm\ consistently show differences of 1-10 Gyr between the predicted gyrochronological and measured isochronal ages. These results point towards a link between rapid rotation and close binarity through tidal interactions. We conclude that stellar rotation is strongly correlated with stellar multiplicity in the field, and caution should be taken in the application of gyrochronology relations to cool stars.
• Bonidie, V., Court, T., Daher, C., Fielder, C., Badenes, C., Newman, J., Moe, M., Kratter, K., Walker, M., Majewski, S., Hayes, C., Hasselquist, S., Stassun, K., Kounkel, M., Dixon, D., Stringfellow, G., Carlberg, J., Anguiano, B., De Lee, N., & Troup, N. (2022). Multiplicity Statistics of Stars in the Sagittarius Dwarf Spheroidal Galaxy: Comparison to the Milky Way. Astrophysical Journal Letters, 933(1). doi:10.3847/2041-8213/ac79af
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  We use time-resolved spectra from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) to examine the distribution of radial velocity (RV) variations in 249 stars identified as members of the Sagittarius (Sgr) dwarf spheroidal (dSph) galaxy by Hayes et al. We select Milky Way (MW) stars that have stellar parameters ( log(g), T eff, and [Fe/H] ) similar to those of the Sagittarius members by means of a k-d tree of dimension 3. We find that the shape of the distribution of RV shifts in Sgr dSph stars is similar to that measured in their MW analogs, but the total fraction of RV variable stars in the Sgr dSph is larger by a factor of 1/42. After ruling out other explanations for this difference, we conclude that the fraction of close binaries in the Sgr dSph is intrinsically higher than in the MW. We discuss the implications of this result for the physical processes leading to the formation of close binaries in dwarf spheroidal and spiral galaxies.
• De Furio, M., Gardner, T., Monnier, J., Meyer, M., Kratter, K., Schaefer, G., Anugu, N., Davies, C., Kraus, S., Lanthermann, C., Le Bouquin, J., & Ennis, J. (2022). The Small Separation A-star Companion Population: First Results with CHARA/MIRC-X. Astrophysical Journal, 941(2). doi:10.3847/1538-4357/aca1ad
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  We present preliminary results from our long-baseline interferometry (LBI) survey to constrain the multiplicity properties of intermediate-mass A-type stars within 80 pc. Previous multiplicity studies of nearby stars exhibit orbital separation distributions well fitted with a lognormal with peaks >15 au, increasing with primary mass. The A-star multiplicity survey of De Rosa et al., sensitive beyond 30 au but incomplete below 100 au, found a lognormal peak around 390 au. Radial velocity surveys of slowly rotating, chemically peculiar Am stars identified a significant number of very close companions with periods ≤5 days, ∼0.1 au, a result similar to surveys of O- and B-type primaries. With the improved performance of LBI techniques, we can probe these close separations for normal A-type stars where other surveys are incomplete. Our initial sample consists of 27 A-type primaries with estimated masses between 1.44 and 2.49 M ⊙ and ages 10-790 Myr, which we observed with the MIRC-X instrument at the CHARA Array. We use the open-source software CANDID to detect five companions, three of which are new, and derive a companion frequency of 0.19 − 0.06 + 0.11 over mass ratios of 0.25-1.0 and projected separations of 0.288-5.481 au. We find a probability of 10−6 that our results are consistent with extrapolations based on previous models of the A-star companion population over the mass ratios and separations sampled. Our results show the need to explore these very close separations to inform our understanding of stellar formation and evolution processes.
• Dupuy, T. J., Huber, D., Ireland, M. J., Kratter, K. M., Kraus, A. L., Mann, A. W., & Rizzuto, A. C. (2022). Orbital architectures of planet-hosting binaries – II. Low mutual inclinations between planetary and stellar orbits. Monthly Notices of the Royal Astronomical Society, 512(1), 648-660. doi:10.1093/mnras/stac306
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  Planet formation is often considered in the context of one circumstellar disc around one star. Yet, stellar binary systems are ubiquitous, and thus a substantial fraction of all potential planets must form and evolve in more complex, dynamical environments. We present the results of a 5 yr astrometric monitoring campaign studying 45 binary star systems that host Kepler planet candidates. The planet-forming environments in these systems would have literally been shaped by the binary orbits that persist to the present day. Crucially, the mutual inclinations of star-planet orbits can only be addressed by a statistical sample. We describe in detail our sample selection and Keck/NIRC2 laser guide star adaptive optics observations collected from 2012 to 2017. We measure orbital arcs, with a typical accuracy of ∼0.1 mas yr-1, that test whether the binary orbits tend to be aligned with the edge-on transiting planet orbits. We rule out randomly distributed binary orbits at 4.7σ, and we show that low mutual inclinations are required to explain the observed orbital arcs. If the stellar orbits have a field binary-like eccentricity distribution, then the best match to our observed orbital arcs is a distribution of mutual inclinations ranging from 0° to 30°. We discuss the implications of such widespread planet-binary alignment in the theoretical context of planet formation and circumstellar disc evolution.
• Gardner, T., Monnier, J., Fekel, F., Le Bouquin, J., Scovera, A., Schaefer, G., Kraus, S., Adams, F., Anugu, N., Berger, J., Ten Brummelaar, T., Davies, C., Ennis, J., Gies, D., Johnson, K., Kervella, P., Kratter, K., Labdon, A., Lanthermann, C., , Sahlmann, J., et al. (2022). ARMADA. II. Further Detections of Inner Companions to Intermediate-mass Binaries with Microarcsecond Astrometry at CHARA and VLTI. Astronomical Journal, 164(5). doi:10.3847/1538-3881/ac8eae
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  We started a survey with CHARA/MIRC-X and VLTI/GRAVITY to search for low-mass companions orbiting individual components of intermediate-mass binary systems. With the incredible precision of these instruments, we can detect astrometric "wobbles"from companions down to a few tens of microarcseconds. This allows us to detect any previously unseen triple systems in our list of binaries. We present the orbits of 12 companions around early F- to B-type binaries, 9 of which are new detections and 3 of which are first astrometric detections of known radial velocity (RV) companions. The masses of these newly detected components range from 0.45 to 1.3 M ⊙. Our orbits constrain these systems to a high astrometric precision, with median residuals to the orbital fit of 20-50 μas in most cases. For seven of these systems we include newly obtained RV data, which help us to identify the system configuration and to solve for masses of individual components in some cases. Although additional RV measurements are needed to break degeneracy in the mutual inclination, we find that the majority of these inner triples are not well aligned with the wide binary orbit. This hints that higher-mass triples are more misaligned compared to solar and lower-mass triples, though a thorough study of survey biases is needed. We show that the ARMADA survey is extremely successful at uncovering previously unseen companions in binaries. This method will be used in upcoming papers to constrain companion demographics in intermediate-mass binary systems down to the planetary-mass regime.
• Garrido-Deutelmoser, J., Petrovich, C., Krapp, L., Kratter, K., & Dong, R. (2022). Substructures in Protoplanetary Disks Imprinted by Compact Planetary Systems. Astrophysical Journal, 932(1). doi:10.3847/1538-4357/ac6bfd
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  The substructures observed in protoplanetary disks may be the signposts of embedded planets carving gaps or creating vortices. The inferred masses of these planets often fall in the Jovian regime despite their low abundance compared to lower-mass planets, partly because previous works often assume that a single substructure (a gap or vortex) is caused by a single planet. In this work, we study the possible imprints of compact systems composed of Neptune-like planets (∼10-30 M ⊕) and show that long-standing vortices are a prevalent outcome when their interplanetary separation (Δa) falls below ∼8 times H p - the average disk's scale height at the planet's locations. In simulations where a single planet is unable to produce long-lived vortices, two-planet systems can preserve them for at least 5000 orbits in two regimes: (i) fully shared density gaps with elongated vortices around the stable Lagrange points L 4 and L 5 for the most compact planet pairs (Δa ≲ 4.6 H p), and (ii) partially shared gaps for more widely spaced planets (Δa ∼4.6-8 H p) forming vortices in a density ring between the planets through the Rossby wave instability. The latter case can produce vortices with a wide range of aspect ratios down to ∼3 and can occur for planets captured into the 3:2 (2:1) mean-motion resonances for disks' aspects ratios of h ≳ 0.033 (h ≳ 0.057). We suggest that their long lifetimes are sustained by the interaction of spiral density waves launched by the neighboring planets. Overall, our results show that the distinguishing imprint of compact systems with Neptune-mass planets are long-lived vortices inside the density gaps, which in turn are shallower than single-planet gaps for a fixed gap width.
• Reggiani, M., Rainot, A., Sana, H., Almeida, L. A., Caballero-Nieves, S., Kratter, K., Lacour, S., Le Bouquin, J. B., & Zinnecker, H. (2022). Probing the low-mass end of the companion mass function for O-type stars. Astronomy and Astrophysics, 660(Issue). doi:10.1051/0004-6361/202142418
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  Context. Past observations of O-type stars in the Galaxy have shown that almost all massive stars are part of a binary or higher-order multiple system. Given the wide range of separations at which these companions are found, several observational techniques have been adopted to characterize them. Despite the recent advancements in interferometric and adaptive optics observations, contrasts greater than 4 in the H band have never been reached between 100 and 1000 mas. Aims. Using new adaptive optics (AO) assisted coronagraphic observations, we aim to study the multiplicity properties of a sample of 18 dwarf (or sub-giant) O stars in the galactic field and in OB associations to probe the existence of stellar companions in the angular separation range from 0. 3;15 to 6 down to very low mass ratios. Methods. We used VLT/SPHERE to observe simultaneously with the IRDIS and IFS sub-systems 18 O-type stars within 6 kpc and ages between 1 and 5 Myr. The IFS YJH band observations have allowed us to probe the presence of sub-solar companions in a 1.7 ×- 1.7 × field-of-view down to magnitude limits of I H = 10 at 0. ×4. In the wider 12 ×- 12 × IRDIS field-of-view, we reached contrasts of I K = 12 at 1 ×, enabling us to look for even fainter companions at larger angular separations and to probe the source density of the surrounding portion of the sky. Results. This paper presents five newly discovered intermediate (< 1 ×) separation companions, three of which are smaller than 0.2 M·. If confirmed by future analyses of proper motions, these new detections represent the lowest-mass companions ever found around O-type stars. Additionally, 29 other sources are found in the IRDIS field-of-view with spurious association probabilities smaller than 5%. Assuming that all sources detected within 1 × are physically bound companions, the observed (uncorrected for bias) fraction of companions for O-type stars between 150 and 900 mas is 0.39 ± 0.15, whereas it increases to 1.6 ± 0.3 in the separation range from 0. ×9 to 6 ×. Conclusions. These findings clearly support the notion that massive stars form almost exclusively in multiple systems, serving as proof of concept that supports the application of larger AO-assisted coronagraphic surveys as a crucial step in placing constraints on the multiplicity properties of massive star companions in regions of the parameter space that have previously gone unexplored. These results also demonstrate that the companion mass function is populated down to the lowest stellar masses.
• Tobin, J., Offner, S., Kratter, K., Megeath, S., Sheehan, P., Looney, L., Diaz-Rodriguez, A., Osorio, M., Anglada, G., Sadavoy, S., Furlan, E., Segura-Cox, D., Karnath, N., Van 'T Hoff, M., Van Dishoeck, E., Li, Z., Sharma, R., Stutz, A., & Tychoniec, Ł. (2022). The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars. V. A Characterization of Protostellar Multiplicity. Astrophysical Journal, 925(1). doi:10.3847/1538-4357/ac36d2
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  We characterize protostellar multiplicity in 20 Current address: Niels Bohr Institute, University of Copenhagen, Øster Voldgade 5a7, DK-1350, Copenhagen K, Denmark. the Orion molecular clouds using Atacama Large Millimeter/submillimeter Array 0.87 mm and Very Large Array 9 mm continuum surveys toward 328 protostars. These observations are sensitive to projected spatial separations as small as ∼20 au, and we consider source separations up to 104 au as potential companions. The overall multiplicity fraction (MF) and companion fraction (CF) for the Orion protostars are 0.30 ± 0.03 and 0.44 ± 0.03, respectively, considering separations from 20 to 104 au. The MFs and CFs are corrected for potential contamination by unassociated young stars using a probabilistic scheme based on the surface density of young stars around each protostar. The companion separation distribution as a whole is double peaked and inconsistent with the separation distribution of solar-type field stars, while the separation distribution of Flat Spectrum protostars is consistent solar-type field stars. The multiplicity statistics and companion separation distributions of the Perseus star-forming region are consistent with those of Orion. Based on the observed peaks in the Class 0 separations at ∼100 au and ∼103 au, we argue that multiples with separations 103 au to
• Bowler, B. P., Cochran, W. D., Endl, M., Franson, K., Brandt, T. D., Dupuy, T. J., MacQueen, P. J., Kratter, K. M., Mawet, D., & Ruane, G. (2021). "The McDonald Accelerating Stars Survey (MASS): White Dwarf Companions Accelerating the Sun-like Stars 12 Psc and HD 159062". aj, 161(3), 106.
• Bowler, B. P., Cochran, W. D., Endl, M., Franson, K., Brandt, T. D., Dupuy, T. J., MacQueen, P. J., Kratter, K. M., Mawet, D., & Ruane, G. (2021). The McDonald accelerating stars survey (MASS): White dwarf companions accelerating the sun-like stars 12 Psc and HD 159062. Astronomical Journal, 161(Issue 3). doi:10.3847/1538-3881/abd243
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  We present the discovery of a white dwarf companion to the G1 V star 12 Psc found as part of a Keck adaptive optics imaging survey of long-term accelerating stars from the McDonald Observatory Planet Search Program. Twenty years of precise radial-velocity monitoring of 12 Psc with the Tull Spectrograph at the Harlan J. Smith telescope reveals a moderate radial acceleration (~10 m s-1 yr -1), which together with relative astrometry from Keck/NIRC2 and the astrometric acceleration between Hipparcos and Gaia DR2 yields a dynamical mass of MB =0.605+0.021-0.022M⊙ for 12 Psc B, a semimajor axis of 40+2-4 au, and an eccentricity of 0.84 ± 0.08. We also report an updated orbital fit of the white dwarf companion to the metal-poor (but barium-rich) G9 V dwarf HD 159062 based on new radial-velocity observations from the High-Resolution Spectrograph at the Hobby-Eberly Telescope and astrometry from Keck/NIRC2. A joint fit of the available relative astrometry, radial velocities, and tangential astrometric acceleration yields a dynamical mass of MB = 0.609+0.010-0.011M⊙ for HD 159062 B, a semimajor axis of 60+5-7 au, and preference for circular orbits (e < 0.42 at 95% confidence). 12 Psc B and HD 159062 B join a small list of resolved Sirius-like benchmark white dwarfs with precise dynamical mass measurements which serve as valuable tests of white dwarf mass-radius cooling models and probes of AGB wind accretion onto their mainsequence companions.
• Bowler, B. P., Endl, M., Cochran, W. D., MacQueen, P. J., Crepp, J. R., Doppmann, G. W., Dulz, S., Brandt, T. D., Mirek Brandt, G., Li, Y., Dupuy, T. J., Franson, K., Kratter, K. M., Morley, C. V., & Zhou, Y. (2021). "The McDonald Accelerating Stars Survey (MASS): Discovery of a Long-period Substellar Companion Orbiting the Old Solar Analog HD 47127". apjl, 913(2), L26.
• Bowler, B., Cochran, W., Endl, M., Franson, K., Brandt, T., Dupuy, T., MacQueen, P., Kratter, K., Mawet, D., & Ruane, G. (2021). "VizieR Online Data Catalog: Radial velocities of 12 Psc and HD 159062 (Bowler+, 2021)". VizieR Online Data Catalog, J/AJ/161/106.
• Gardner, T., Monnier, J. D., Fekel, F. C., Schaefer, G., Johnson, K. J., Le Bouquin, J. B., Kraus, S., Anugu, N., Setterholm, B. R., Labdon, A., Davies, C. L., Lanthermann, C., Ennis, J., Ireland, M., Kratter, K. M., Ten Brummelaar, T., Sturmann, J., Sturmann, L., Farrington, C., , Gies, D. R., et al. (2021). ARMADA. I. Triple Companions Detected in B-type Binaries α Del and ν Gem. Astronomical Journal, 161(Issue 1). doi:10.3847/1538-3881/abcf4e
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  Ground-based optical long-baseline interferometry has the power to measure the orbits of close binary systems at ∼10 μas precision. This precision makes it possible to detect "wobbles"in the binary motion due to the gravitational pull from additional short-period companions. We started the ARrangement for Micro-Arcsecond Differential Astrometry (ARMADA) survey with the Michigan Infra-Red Combiner (MIRC)/MIRC-X instrument at the Center for High Angular Resoloution Astronomy (CHARA) array for the purpose of detecting giant planets and stellar companions orbiting individual stars in binary systems. We describe our observations for the survey, and introduce the wavelength calibration scheme that delivers precision at the tens of microarcseconds level for
• Gardner, T., Monnier, J. D., Fekel, F. C., Schaefer, G., Johnson, K. J., Le, B. J., Kraus, S., Anugu, N., Setterholm, B. R., Labdon, A., Davies, C. L., Lanthermann, C., Ennis, J., Ireland, M., Kratter, K. M., Ten, B. T., Sturmann, J., Sturmann, L., Farrington, C., , Gies, D. R., et al. (2021). "ARMADA. I. Triple Companions Detected in B-type Binaries {ensuremath{alpha} Del and ensuremath{nu} Gem}". aj, 161(1), 40.
• Hammer, M., Lin, M., Kratter, K. M., & Pinilla, P. (2021). "Which planets trigger longer lived vortices: low-mass or high-mass?". mnras, 504(3), 3963-3985.
• Kounkel, M., Covey, K. R., Stassun, K. G., Price-Whelan, A. M., Holtzman, J., Chojnowski, D., Longa-Pe{~na}, P., Rom{'an-Z'u~niga}, C. G., Hernandez, J., Serna, J., Badenes, C., De, L. N., Majewski, S., Stringfellow, G. S., Kratter, K. M., Moe, M., Frinchaboy, P. M., Beaton, R. L., Fern{'andez-Trincado}, J. G., , Mahadevan, S., et al. (2021). "Double-lined Spectroscopic Binaries in the APOGEE DR16 and DR17 Data". aj, 162(5), 184.
• Krapp, L., Kratter, K. M., & Youdin, A. N. (2021). "The 3D dust and opacity distribution of protoplanets in multi-fluid global simulations". arXiv e-prints, arXiv:2110.02428.
• Kratter, K. (2021). "Giant planet imaged orbiting two massive stars". nat, 600(7888), 227-228.
• Moe, M., & Kratter, K. M. (2021). "Impact of binary stars on planet statistics - I. Planet occurrence rates and trends with stellar mass". mnras, 507(3), 3593-3611.
• Reggiani, M., Rainot, A., Sana, H., Almeida, L., Caballero-Nieves, S. .., Kratter, K., Lacour, S., LeBouquin, J. -., & Zinnecker, H. (2021). "Probing the low-mass end of the companion mass function for O-type stars". arXiv e-prints, arXiv:2112.10831.
• Reynolds, N. K., Tobin, J. J., Sheehan, P., Sadavoy, S. I., Kratter, K. M., Li, Z., Chandler, C. J., Segura-Cox, D., Looney, L. W., & Dunham, M. M. (2021). "Kinematic Analysis of a Protostellar Multiple System: Measuring the Protostar Masses and Assessing Gravitational Instability in the Disks of L1448 IRS3B and L1448 IRS3A". apjl, 907(1), L10.
• Seligman, D. Z., Kratter, K. M., Garrett Levine, W., & Jedicke, R. (2021). A sublime opportunity: The dynamics of transitioning cometary bodies and the feasibility of in situ observations of the evolution of their activity. Planetary Science Journal, 2(Issue 6). doi:10.3847/psj/ac2dee
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  The compositional and morphological evolution of minor bodies in the solar system is primarily driven by the evolution of their heliocentric distances, as the level of incident solar radiation regulates cometary activity. We investigate the dynamical transfer of Centaurs into the inner solar system, facilitated by mean motion resonances with Jupiter and Saturn. The recently discovered object P/2019 LD2 will transition from the Centaur region to the inner solar system in 2063. In order to contextualize LD2, we perform N-body simulations of a population of Centaurs and Jupiter-family comets. Objects between Jupiter and Saturn with Tisserand parameter TJ ∼ 3 are transferred onto orbits with perihelia q < 4 au within the next 1000 yr with notably high efficiency. Our simulations show that there may be additional LD2-like objects transitioning into the inner solar system in the near future, all of which have low δV with respect to Jupiter. We calculate the distribution of orbital elements resulting from a single Jovian encounter and show that objects with initial perihelia close to Jupiter are efficiently scattered to q < 4 au. Moreover, approximately 55% of the transitioning objects in our simulated population experience at least one Jovian encounter prior to reaching q < 4 au. We demonstrate that a spacecraft stationed near Jupiter would be well positioned to rendezvous, orbit-match, and accompany LD2 into the inner solar system, providing an opportunity to observe the onset of intense activity in a pristine comet in situ. Finally, we discuss the prospect of identifying additional targets for similar measurements with forthcoming observational facilities.
• Seligman, D. Z., Kratter, K. M., Levine, W. G., & Jedicke, R. (2021). "A Sublime Opportunity: The Dynamics of Transitioning Cometary Bodies and the Feasibility of In Situ Observations of the Evolution of Their Activity". psj, 2(6), 234.
• Tobin, J., Sheehan, P., Megeath, S., Diaz-Rodriguez, A., Offner, S., Murillo, N., Hoff, M., Dishoeck, E., Osorio, M., Anglada, G., Furlan, E., Stutz, A., Reynolds, N., Karnath, N., Fischer, W., Persson, M., Looney, L., Li, Z. -., Stephens, I., , Chandler, C., et al. (2021). "VizieR Online Data Catalog: VANDAM survey of Orion protostars. II. (Tobin+, 2020)". VizieR Online Data Catalog, J/ApJ/890/130.
• Krapp, L., Youdin, A. N., Kratter, K. M., & Ben{'itez-Llambay}, P. (2020). "Dust settling instability in protoplanetary discs". mnras, 497(3), 2715-2729.
• Krumholz, M. R., Ireland, M. J., & Kratter, K. M. (2020). "Dynamics of small grains in transitional discs". mnras, 498(2), 3023-3042.
• Krumholz, M. R., Ireland, M. J., & Kratter, K. M. (2020). Dynamics of small grains in transitional discs. Monthly Notices of the Royal Astronomical Society, 498(Issue 2). doi:10.1093/mnras/staa2546
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  Transitional discs have central regions characterized by significant depletion of both dust and gas compared to younger, optically thick discs. However, gas and dust are not depleted by equal amounts: Gas surface densities are typically reduced by factors of ∼100, but small dust grains are sometimes depleted by far larger factors, to the point of being undetectable. While this extreme dust depletion is often attributed to planet formation, in this paper we show that another physical mechanism is possible: Expulsion of grains from the disc by radiation pressure. We explore this mechanism using 2D simulations of dust dynamics, simultaneously solving the equation of radiative transfer with the evolution equations for dust diffusion and advection under the combined effects of stellar radiation and hydrodynamic interaction with a turbulent, accreting background gas disc. We show that, in transition discs that are depleted in both gas and dust fraction by factors of ∼100-1000 compared to minimum mass Solar nebular values, and where the ratio of accretion rate to stellar luminosity is low (˙M/L ≲ 10-10 M⊙ yr-1, L⊙-1), radiative clearing of any remaining ∼0.5 μm and larger grains is both rapid and inevitable. The process is size-dependent, with smaller grains removed fastest and larger ones persisting for longer times. Our proposed mechanism thus naturally explains the extreme depletion of small grains commonly found in transition discs. We further suggest that the dependence of this mechanism on grain size and optical properties may explain some of the unusual grain properties recently discovered in a number of transition discs. The simulation code we develop is freely available.
• Mazzola, C. N., Badenes, C., Moe, M., Koposov, S. E., Kounkel, M., Kratter, K., Covey, K., Walker, M. G., Thompson, T. A., Andrews, B., Freeman, P. E., Anguiano, B., Carlberg, J. K., De, L., Frinchaboy, P. M., Lewis, H. M., Majewski, S., Nidever, D., Nitschelm, C., , Price-Whelan, A. M., et al. (2020). "The close binary fraction as a function of stellar parameters in APOGEE: a strong anticorrelation with {ensuremath{alpha} abundances}". mnras, 499(2), 1607-1626.
• Mu{~noz}, D. J., Lai, D., Kratter, K., & Miranda, R. (2020). "Circumbinary Accretion from Finite and Infinite Disks". apj, 889(2), 114.
• Petrovich, C., Mu{~noz}, D. J., Kratter, K. M., & Malhotra, R. (2020). "A Disk-driven Resonance as the Origin of High Inclinations of Close-in Planets". apjl, 902(1), L5.
• Petrovich, C., Muñoz, D. J., Kratter, K. M., & Malhotra, R. (2020). A disk-driven resonance as the origin of high inclinations of close-in planets. Astrophysical Journal Letters, 902(Issue 1). doi:10.3847/2041-8213/abb952
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  The recent characterization of transiting close-in planets has revealed an intriguing population of sub-Neptunes with highly tilted and even polar orbits relative to their host star’s equator. Any viable theory for the origin of these close-in, polar planets must explain (1) the observed stellar obliquities, (2) the substantial eccentricities, and (3) the existence of Jovian companions with large mutual inclinations. In this work, we propose a theoretical model that satisfies these requirements without invoking tidal dissipation or large primordial inclinations. Instead, tilting is facilitated by the protoplanetary disk dispersal during the late stage of planet formation, initiating a process of resonance sweeping and parametric instability. This mechanism consists of two steps. First, a nodal secular resonance excites the inclination to large values; then, once the inclination reaches a critical value, a linear eccentric instability is triggered, which detunes the resonance and ends inclination growth. The critical inclination is pushed to high values by general relativistic precession, making polar orbits an inherently post-Newtonian outcome. Our model predicts that polar, close-in sub-Neptunes coexist with cold Jupiters in low stellar obliquity orbits.
• Poovelil, V. J., Zasowski, G., Hasselquist, S., Seth, A., Donor, J., Beaton, R. L., Cunha, K., Frinchaboy, P. M., Garc{'ia-Hern'andez}, D., Hawkins, K., Kratter, K., Lane, R. R., & Nitschelm, C. (2020). "Open Cluster Chemical Homogeneity throughout the Milky Way". apj, 903(1), 55.
• Rainot, A., Reggiani, M., Sana, H., Bodensteiner, J., Gomez-Gonzalez, C., Absil, O., Christiaens, V., Delorme, P., Almeida, L., Caballero-Nieves, S. .., De Ridder, J., Kratter, K., Lacour, S., Le, B., Pueyo, L., & Zinnecker, H. (2020). "Carina High-contrast Imaging Project for massive Stars (CHIPS). I. Methodology and proof of concept on QZ Car ({ensuremath{equiv} HD 93206)}". aap, 640, A15.
• Smullen, R. A., Kratter, K. M., Offner, S. S., Lee, A. T., & Chen, H. H. (2020). "The highly variable time evolution of star-forming cores identified with dendrograms". mnras, 497(4), 4517-4534.
• Tobin, J. J., Sheehan, P. D., Megeath, S. T., D{'iaz-Rodr'iguez}, A. K., Offner, S. S., Murillo, N. M., Hoff, M. L., Dishoeck, E. F., Osorio, M., Anglada, G., Furlan, E., Stutz, A. M., Reynolds, N., Karnath, N., Fischer, W. J., Persson, M., Looney, L. W., Li, Z., Stephens, I., , Chandler, C. J., et al. (2020). "The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars. II. A Statistical Characterization of Class 0 and Class I Protostellar Disks". apj, 890(2), 130.
• Tobin, J. J., Sheehan, P. D., Reynolds, N., Megeath, S. T., Osorio, M., Anglada, G., D{'iaz-Rodr'iguez}, A. K., Furlan, E., Kratter, K. M., Offner, S. S., Looney, L. W., Kama, M., Li, Z., Hoff, M. L., Sadavoy, S. I., & Karnath, N. (2020). "The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars. IV. Unveiling the Embedded Intermediate-Mass Protostar and Disk within OMC2-FIR3/HOPS-370". apj, 905(2), 162.
• Vargas-Salazar, I., Oey, M., Barnes, J. R., Chen, X., Castro, N., Kratter, K. M., & Faerber, T. A. (2020). "A Search for In Situ Field OB Star Formation in the Small Magellanic Cloud". apj, 903(1), 42.
• Wyse, R. F., Moe, M., & Kratter, K. M. (2020). "The rich lack close neighbours: the dependence of blue-straggler fraction on metallicity". mnras, 493(4), 6109-6118.
• Dupuy, T. J., Brandt, T. D., Kratter, K. M., & Bowler, B. P. (2019). A Model-independent Mass and Moderate Eccentricity for ensuremath{beta} Pic b. apjl, 871(1), L4.
• Hammer, M., Pinilla, P., Kratter, K. M., & Lin, M. (2019). Observational diagnostics of elongated planet-induced vortices with realistic planet formation time-scales. mnras, 482(3), 3609-3621.
• Kollmeier, J. A., Anderson, L., Benson, A., Bogdanovic, T., Boylan-Kolchin, M., Bullock, J. S., Dave, R., Fraschetti, F., Fuller, J., Hopkins, P. F., Kaplinghat, M., Kratter, K., Lamberts, A., Miller, M. C., Owen, J. E., Phinney, E. S., Piro, A. L., Rix, H., Robertson, B., , Wetzel, A., et al. (2019). Astro2020 APC White Paper: Theoretical Astrophysics 2020-2030. arXiv e-prints, arXiv:1912.09992.
• Kounkel, M., Covey, K., Moe, M., Kratter, K. M., Su{'arez}, G., Stassun, K. G., Rom{'an-Z'u~niga}, C., {Hernand, e. J., Kim, J. S., Pe{~na, R. K., Roman-Lopes, A., Stringfellow, G. S., Jaehnig, K. O., Borissova, J., Tofflemire, B., Krolikowski, D., Rizzuto, A., Kraus, A., Badenes, C., , Longa-Pe{~na}, P., et al. (2019). Close Companions around Young Stars. aj, 157(5), 196.
• Kounkel, M., Covey, K., Moe, M., Kratter, K., Suarez, G., Stassun, K., Roman-Zuniga, C. .., {Hernand, e. J., Kim, J., Ramirez, K., Roman-Lopes, A. .., Stringfellow, G., O, J. K., Borissova, J., Tofflemire, B., Krolikowski, D., Rizzuto, A., Kraus, A., Badenes, C., , Longa-Pena, P. .., et al. (2019). VizieR Online Data Catalog: Close companions around young stars (Kounkel+, 2019). VizieR Online Data Catalog, J/AJ/157/196.
• Krumholz, M. R., Ireland, M. J., & Kratter, K. M. (2019). Dynamics of small grains in transitional discs. arXiv e-prints, arXiv:1912.06788.
• Lee, A. T., Offner, S. S., Kratter, K. M., Smullen, R. A., & Li, P. S. (2019). The Formation and Evolution of Wide-orbit Stellar Multiples In Magnetized Clouds. apj, 887(2), 232.
• Lee, A. T., Offner, S. S., Kratter, K. M., Smullen, R. A., & Li, P. S. (2019). The Formation and Evolution of Wide-orbit Stellar Multiples in Magnetized Clouds. Astrophysical Journal, 887(Issue 2). doi:10.3847/1538-4357/ab584b
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  Stars rarely form in isolation. Nearly half of the stars in the Milky Way have a companion, and this fraction increases in star-forming regions. However, why some dense cores and filaments form bound pairs while others form single stars remains unclear. We present a set of three-dimensional, gravo-magnetohydrodynamic simulations of turbulent star-forming clouds, aimed at understanding the formation and evolution of multiple-star systems formed through large-scale (⪆103 au) turbulent fragmentation. We investigate three global magnetic field strengths, with global mass-to-flux ratios of μ φ = 2, 8, and 32. The initial separations of protostars in multiples depend on the global magnetic field strength, with stronger magnetic fields (e.g., μ φ = 2) suppressing fragmentation on smaller scales. The overall multiplicity fraction (MF) is between 0.4 and 0.6 for our strong and intermediate magnetic field strengths, which is in agreement with observations. The weak field case has a lower fraction. The MF is relatively constant throughout the simulations, even though stellar densities increase as collapse continues. While the MF rarely exceeds 60% in all three simulations, over 80% of all protostars are part of a binary system at some point. We additionally find that the distribution of binary spin misalignment angles is consistent with a randomized distribution. In all three simulations, several binaries originate with wide separations and dynamically evolve to ≲102 au separations. We show that a simple model of mass accretion and dynamical friction with the gas can explain this orbital evolution.
• McCann, J., Murray-Clay, R. A., Kratter, K., & Krumholz, M. R. (2019). Morphology of Hydrodynamic Winds: A Study of Planetary Winds in Stellar Environments. apj, 873(1), 89.
• Moe, M., & Kratter, K. M. (2019). Impact of Binary Stars on Planet Statistics -- I. Planet Occurrence Rates, Trends with Stellar Mass, and Wide Companions to Hot Jupiter Hosts. arXiv e-prints, arXiv:1912.01699.
• Moe, M., Kratter, K. M., & Badenes, C. (2019). The Close Binary Fraction of Solar-type Stars Is Strongly Anticorrelated with Metallicity. apj, 875(1), 61.
• Stone, J., Skemer, A., Hinz, P., Bonavita, M., Kratter, K., Maire, A. -., Defrere, D., Bailey, V., Spalding, E., Leisenring, J., Desidera, S., Bonnefoy, M., Biller, B., Woodward, C., Henning, T., Skrutskie, M., Eisner, J., Crepp, J., Patience, J., , Weigelt, G., et al. (2019). VizieR Online Data Catalog: The LEECH exoplanet imaging survey (Stone+, 2018). VizieR Online Data Catalog, J/AJ/156/286.
• Sutherland, A. P., & Kratter, K. M. (2019). Instabilities in multiplanet circumbinary systems. mnras, 487(3), 3288-3304.
• Tobin, J. J., Kounkel, M., Offner, S., Sheehan, P., Johnstone, D., Megeath, S. T., Kratter, K. M., Stephens, I., Li, Z., Sadavoy, S., Looney, L., Green, J., Gutermuth, R., Fischer, W., Dunham, M. M., & Yang, Y. (2019). Astro2020 Science White Paper: The Formation and Evolution of Multiple Star Systems. arXiv e-prints, arXiv:1904.08442.
• Tobin, J. J., Megeath, S. T., Hoff, M. V., Díaz-Rodríguez, A. K., Reynolds, N., Osorio, M., Anglada, G., Furlan, E., Karnath, N., Offner, S. S., Sheehan, P. D., Sadavoy, S. I., Stutz, A. M., Fischer, W. J., Kama, M., Persson, M., Francesco, J. D., Looney, L. W., Watson, D. M., , Li, Z. Y., et al. (2019). The vla/alma nascent disk and multiplicity (vandam) survey of orion protostars. i. identifying and characterizing the protostellar content of the omc-2 fir4 and omc-2 fir3 regions. Astrophysical Journal, 886(Issue 1). doi:10.3847/1538-4357/ab498f
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  We present Atacama Large Millimeter/submillimeter Array (0.87 mm) and Very Large Array (9 mm) observations toward OMC-2 FIR4 and OMC-2 FIR3 within the Orion integral-shaped filament, thought to be two of the nearest regions of intermediate-mass star formation. We characterize the continuum sources within these regions on ∼40 au (0.″1) scales and associated molecular line emission at a factor of ∼30 better resolution than previous observations at similar wavelengths. We identify six compact continuum sources within OMC-2 FIR4, four in OMC-2 FIR3, and one additional source just outside OMC-2 FIR4. This continuum emission is tracing the inner envelope and/or disk emission on less than 100 au scales. HOPS-108 is the only protostar in OMC-2 FIR4 that exhibits emission from high-excitation transitions of complex organic molecules (e.g., methanol and other lines) coincident with the continuum emission. HOPS-370 in OMC-2 FIR3, with L ∼ 360 L o˙, also exhibits emission from high-excitation methanol and other lines. The methanol emission toward these two protostars is indicative of temperatures high enough to thermally evaporate it from icy dust grains; overall, these protostars have characteristics similar to hot corinos. We do not identify a clear outflow from HOPS-108 in 12CO, but we find evidence of interaction between the outflow/jet from HOPS-370 and the OMC-2 FIR4 region. A multitude of observational constraints indicate that HOPS-108 is likely a low- to intermediate-mass protostar in its main mass accretion phase and is the most luminous protostar in OMC-2 FIR4. The high-resolution data presented here are essential for disentangling the embedded protostars from their surrounding dusty environments and characterizing them.
• Tobin, J. J., Megeath, S. T., Hoff}, M., D{'iaz-Rodr'iguez}, A. K., Reynolds, N., Osorio, M., Anglada, G., Furlan, E., Karnath, N., Offner, S. S., Sheehan, P. D., Sadavoy, S. I., Stutz, A. M., Fischer, W. J., Kama, M., Persson, M., Di, F. J., Looney, L. W., Watson, D. M., , Li, Z., et al. (2019). The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars. I. Identifying and Characterizing the Protostellar Content of the OMC-2 FIR4 and OMC-2 FIR3 Regions. apj, 886(1), 6.
• Tobin, J., Kounkel, M., Offner, S., Sheehan, P., Johnstone, D., Megeath, S. T., Kratter, K. M., Stephens, I., Li, Z., Sadavoy, S., Looney, L., Green, J., Gutermuth, R., Fischer, W., Dunham, M. M., & Yang, Y. (2019). The Formation and Evolution of Multiple Star Systems. baas, 51(3), 187.
• Wagner, K., Apai, D., & Kratter, K. M. (2019). On the Mass Function, Multiplicity, and Origins of Wide-Orbit Giant Planets. arXiv e-prints, arXiv:1904.06438.
• Wagner, K., Apai, D., & Kratter, K. M. (2019). On the Mass Function, Multiplicity, and Origins of Wide-orbit Giant Planets. apj, 877(1), 46.
• Zhang, Y., Tan, J. C., Sakai, N., Tanaka, K. E., De, B., Liu, M., Beltr{'an}, M. T., Kratter, K., Mardones, D., & Garay, G. (2019). An Ordered Envelope-Disk Transition in the Massive Protostellar Source G339.88-1.26. apj, 873(1), 73.
• Zhang, Y., Tan, J. C., Tanaka, K. E., De, B., Liu, M., Beltr{'an}, M. T., Kratter, K., Mardones, D., & Garay, G. (2019). Dynamics of a massive binary at birth. Nature Astronomy, 224.
• Bowler, B. P., Dupuy, T. J., Endl, M., Cochran, W. D., MacQueen, P. J., Fulton, B. J., Petigura, E. A., Howard, A. W., Hirsch, L., Kratter, K. M., Crepp, J. R., Biller, B. A., Johnson, M. C., & Wittenmyer, R. A. (2018). Orbit and Dynamical Mass of the Late-T Dwarf GL 758 B. aj, 155(4), 159.
• Bowler, B., Dupuy, T., Endl, M., Cochran, W., MacQueen, P., Fulton, B., Petigura, E., Howard, A., Hirsch, L., Kratter, K., Crepp, J., Biller, B., Johnson, M., & Wittenmyer, R. (2018). "Orbit and Dynamical Mass of the Late-T Dwarf Gl 758 B". ArXiv e-prints.
• Bowler, B., Dupuy, T., Endl, M., Cochran, W., MacQueen, P., Fulton, B., Petigura, E., Howard, A., Hirsch, L., Kratter, K., Crepp, J., Biller, B., Johnson, M., & Wittenmyer, R. (2018). VizieR Online Data Catalog: RVs of the late-T dwarf GL 758 B host star (Bowler+, 2018). VizieR Online Data Catalog, J/AJ/155/159.
• Dupuy, T. J., Liu, M. C., Allers, K. N., Biller, B. A., Kratter, K. M., Mann, A. W., Shkolnik, E. L., Kraus, A. L., & Best, W. M. (2018). The Hawaii Infrared Parallax Program. III. 2MASS J0249-0557 c: A Wide Planetary-mass Companion to a Low-mass Binary in the ensuremath{beta} Pic Moving Group. aj, 156(2), 57.
• Dupuy, T. J., Liu, M. C., Allers, K. N., Biller, B. A., Kratter, K. M., Mann, A. W., Shkolnik, E. L., Kraus, A. L., & Best, W. M. (2018). The Hawaii Infrared Parallax Program. III. 2MASS J0249-0557 c: A Wide Planetary-mass Companion to a Low-mass Binary in the β Pic Moving Group. Astronomical Journal, 156(Issue 2). doi:10.3847/1538-3881/aacbc2
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  We have discovered a wide planetary-mass companion to the β Pic moving group member 2MASS J02495639-0557352 (M6 vl-g) using Canada-France-Hawaii Telescope/WIRCam astrometry from the Hawaii Infrared Parallax Program. In addition, Keck laser guide star adaptive optics aperture-masking interferometry shows that the host is itself a tight binary. Altogether, 2MASS J0249-0557ABc is a bound triple system with an 11.6+1.3 -1.0 Mjupobject separated by 1950 ±200 au (40″) from a relatively close (2.17 ±0.22 au, 0.″04) pair of 48+13 -12 Mjupand 44+14 -11 Mjupobjects. 2MASS J0249-0557AB is one of the few ultracool binaries to be discovered in a young moving group and the first confirmed in the β Pic moving group (22 ±6 Myr). The mass, absolute magnitudes, and spectral type of 2MASS J0249-0557 c (L2 vl-g) are remarkably similar to those of the planet β Pic b (L2, 13.0+0.4 -0.3 Mjup). We also find that the free-floating object 2MASS J2208+2921 (L3 vl-g) is another possible β Pic moving group member with colors and absolute magnitudes similar to β Pic b and 2MASS J0249-0557 c. β Pic b is the first directly imaged planet to have a "twin," namely an object of comparable properties in the same stellar association. Such directly imaged objects provide a unique opportunity to measure atmospheric composition, variability, and rotation across different pathways of assembling planetary-mass objects from the same natal material.
• Hammer, M., Kratter, K. M., Lin, M., & Pinilla, P. (2018). Observational diagnostics of elongated planet-induced vortices with realistic planet formation time-scales. Monthly Notices of the Royal Astronomical Society, 482(3), 3609-3621. doi:10.1093/mnras/sty2946
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  Gap-opening planets can generate dust-trapping vortices that may explain some of the latest discoveries of high-contrast crescent-shaped dust asymmetries in transition discs. While planet-induced vortices were previously thought to have concentrated shapes, recent computational work has shown that these features naturally become much more elongated in the gas when simulations account for the relatively long time-scale over which planets accrete their mass. In this work, we conduct two-fluid hydrodynamical simulations of vortices induced by slowly growing Jupiter-mass planets in discs with very low viscosity (α = 3 × 10-5). We simulate the dust dynamics for four particle sizes spanning 0.3 mm to 1 cm in order to produce synthetic ALMA images. In our simulations, we find that an elongated vortex still traps dust, but not directly at its centre. With a flatter pressure bump and disruptions from the planet's overlapping spiral density waves, the dust instead circulates around the vortex. This motion (1) typically carries the peak off-centre, (2) spreads the dust out over a wider azimuthal extent ≥180?, (3) skews the azimuthal profile towards the front of the vortex, and (4) can also create double peaks in newly formed vortices. In particular, we expect that the most defining observational signature, a peak offset of more than 30?, should be detectable > 30 per cent of the time in observations with a beam diameter of at most the planet's separation from its star.
• Moe, M., & Kratter, K. (2018). "Dynamical Formation of Close Binaries during the Pre-main-sequence Phase". apj, 854, 44.
• Moe, M., & Kratter, K. M. (2018). Dynamical Formation of Close Binaries during the Pre-main-sequence Phase. apj, 854(1), 44.
• Morrison, S. J., & Kratter, K. M. (2018). Gap formation in planetesimal discs via divergently migrating planets. Monthly Notices of the Royal Astronomical Society, 481(Issue 4). doi:10.1093/mnras/sty2657
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  While many observed debris discs are thought to have gaps suggestive of the presence of planets, direct imaging surveys do not find many high-mass planets in these systems. We investigate if divergent migration is a viable mechanism for forming gaps in young debris discs with planets of low enough mass to currently elude detection. We perform numerical integrations of planet pairs embedded in planetesimal discs to assess the conditions for which divergent, planetesimal-driven migration occurs and gaps form within the disc. Gap widths and the migration rate of planets within a pair depend on both disc mass and the degree to which the planets share disc material. We find that planet pairs with planets more massive than Neptune can produce gaps with widths similar to their orbit distance within 10 Myr at orbit separations probed by direct imaging campaigns. Pairs of migrating super-Earths likely cannot form observable gaps on the same time and distance scales, however. Inferring the responsible planet masses from these gaps while neglecting migration could overestimate the mass of planets by more than an order of magnitude.
• Morrison, S. J., & Kratter, K. M. (2018). Gap formation in planetesimal discs via divergently migrating planets. mnras, 481(4), 5180-5188.
• Segura-Cox, D. M., Looney, L. W., Tobin, J. J., Li, Z., Harris, R. J., Sadavoy, S., Dunham, M. M., Chandler, C., Kratter, K., P{'erez}, L., & Melis, C. (2018). The VLA Nascent Disk and Multiplicity Survey of Perseus Protostars (VANDAM). V. 18 Candidate Disks around Class 0 and I Protostars in the Perseus Molecular Cloud. apj, 866(2), 161.
• Stone, J. M., Skemer, A. J., Hinz, P. M., Bonavita, M., Kratter, K. M., Maire, A. L., Defrere, D., Bailey, V. P., Spalding, E., Leisenring, J. M., Desidera, S., Bonnefoy, M., Biller, B., Woodward, C. E., Henning, T., Skrutskie, M. F., Eisner, J. A., Crepp, J. R., Patience, J., , Weigelt, G., et al. (2018). The LEECH exoplanet imaging survey: Limits on planet occurrence rates under conservative assumptions. Astronomical Journal, 156(Issue 6). doi:10.3847/1538-3881/aaec00
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  We present the results of the largest L' (3.8 μm) direct imaging survey for exoplanets to date, the Large Binocular Telescope Interferometer Exozodi Exoplanet Common Hunt (LEECH). We observed 98 stars with spectral types from B to M. Cool planets emit a larger share of their flux in L' compared to shorter wavelengths, affording LEECH an advantage in detecting low-mass, old, and cold-start giant planets. We emphasize proximity over youth in our target selection, probing physical separations smaller than other direct imaging surveys. For FGK stars, LEECH outperforms many previous studies, placing tighter constraints on the hot-start planet occurrence frequency interior to ~20 au. For less luminous, cold-start planets, LEECH provides the best constraints on giant-planet frequency interior to ~20 au around FGK stars. Direct imaging survey results depend sensitively on both the choice of evolutionary model (e.g., hot- or coldstart) and assumptions (explicit or implicit) about the shape of the underlying planet distribution, in particular its radial extent. Artificially low limits on the planet occurrence frequency can be derived when the shape of the planet distribution is assumed to extend to very large separations, well beyond typical protoplanetary dust-disk radii (≤50 au), and when hot-start models are used exclusively. We place a conservative upper limit on the planet occurrence frequency using coldstart models and planetary population distributions that do not extend beyond typical protoplanetary dust-disk radii. We find that ≤90% of FGK systems can host a 7-10 MJupplanet from 5 to 50 au. This limit leaves open the possibility thatplanets in this range are common.
• Stone, J. M., Skemer, A. J., Hinz, P. M., Bonavita, M., Kratter, K. M., Maire, A., Defrere, D., Bailey, V. P., Spalding, E., Leisenring, J. M., Desidera, S., Bonnefoy, M., Biller, B., Woodward, C. E., Henning, T., Skrutskie, M. F., Eisner, J., Crepp, J. R., Patience, J., , Weigelt, G., et al. (2018). The LEECH Exoplanet Imaging Survey: Limits on Planet Occurrence Rates under Conservative Assumptions. aj, 156(6), 286.
• Tobin, J. J., Looney, L. W., Li, Z., Sadavoy, S. I., Dunham, M. M., Segura-Cox, D., Kratter, K., {Chand, l., Melis, C., Harris, R. J., & Perez, L. (2018). The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Perseus Protostars. VI. Characterizing the Formation Mechanism for Close Multiple Systems. apj, 867(1), 43.
• Tobin, J., Looney, L., Li, Z. -., {Chand, l. C., Dunham, M., Segura-Cox, D. .., Sadavoy, S., Melis, C., Harris, R., Kratter, K., & Perez, L. (2018). VizieR Online Data Catalog: Study of protostars in the Perseus molecular cloud (Tobin+, 2016). VizieR Online Data Catalog, J/ApJ/818/73.
• Tobin, J., Looney, L., Li, Z., Chandler, C., Dunham, M., Segura-Cox, D. .., Sadavoy, S., Melis, C., Harris, R., Kratter, K., & Perez, L. (2018). "VizieR Online Data Catalog: Study of protostars in the Perseus molecular cloud (Tobin+, 2016)". VizieR Online Data Catalog, 181.
• Tychoniec, L., Tobin, J. J., Karska, A., {Chand, l. C., Dunham, M. M., Harris, R. J., Kratter, K. M., Li, Z., Looney, L. W., Melis, C., P{'erez}, L. M., Sadavoy, S. I., Segura-Cox, D., & Dishoeck, E. F. (2018). The VLA Nascent Disk and Multiplicity Survey of Perseus Protostars (VANDAM). IV. Free-Free Emission from Protostars: Links to Infrared Properties, Outflow Tracers, and Protostellar Disk Masses. apjs, 238(2), 19.
• Tychoniec, L., Tobin, J., Karska, A., Chandler, C., Dunham, M., Harris, R., Kratter, K., Li, Z. -., Looney, L., Melis, C., Perez, L., Sadavoy, S., Segura-Cox, D. .., & Dishoeck, E. (2018). VizieR Online Data Catalog: VANDAM IV. Free-free emission from protostars (Tychoniec+, 2018). VizieR Online Data Catalog, J/ApJS/238/19.
• Baehr, H., Klahr, H., & Kratter, K. (2017). "The Fragmentation Criteria in Local Vertically Stratified Self-gravitating Disk Simulations". apj, 848, 40.
• Cox, E., Harris, R., Looney, L., Chiang, H., Chandler, C., Kratter, K., Li, Z., Perez, L., & Tobin, J. (2017). "Protoplanetary Disks in {$rho$ Ophiuchus as Seen from ALMA}". apj, 851, 83.
• Hammer, M., Kratter, K., & Lin, M. (2017). "Slowly-growing gap-opening planets trigger weaker vortices". mnras, 466, 3533-3543.
• MacGregor, M., Wilner, D., Czekala, I., Andrews, S., Dai, Y., Herczeg, G., Kratter, K., Kraus, A., Ricci, L., & Testi, L. (2017). "ALMA Measurements of Circumstellar Material in the GQ Lup System". apj, 835, 17.
• Macgregor, M., Wilner, D., Czekala, I., Andrews, S., Dai, Y., Herczeg, G., Kratter, K., Kraus, A., Ricci, L., & Testi, L. (2017). ALMA MEASUREMENTS of CIRCUMSTELLAR MATERIAL in the GQ LUP SYSTEM. Astrophysical Journal, 835(1). doi:10.3847/1538-4357/835/1/17
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  We present Atacama Large Millimeter/submillimeter Array observations of the GQ Lup system, a young Sun-like star with a substellar-mass companion in a wide-separation orbit. These observations of 870 μm continuum and CO J = 3-2 line emission with beam size ∼0.″3 (∼45 au) resolve the disk of dust and gas surrounding the primary star, GQ Lup A, and provide deep limits on any circumplanetary disk surrounding the companion, GQ Lup b. The circumprimary dust disk is compact with an FWHM of 59 ±12 au, while the gas has a larger extent with a characteristic radius of 46.5 ±1.8 au. By forward-modeling the velocity field of the circumprimary disk based on the CO emission, we constrain the mass of GQ Lup A to be M ∗ = (1.03 ±0.05) (d/156 pc) M o, where d is a known distance, and determine that we view the disk at an inclination angle of 60.°5 ±0.°5 and a position angle of 346° ±1°. The 3σ upper limit on the 870 μm flux density of any circumplanetary disk associated with GQ Lup b of
• Smullen, R., & Kratter, K. (2017). "The Fate of Debris in the Pluto-Charon System". mnras.
• Dupuy, T., Kratter, K., Kraus, A., Isaacson, H., Mann, A., Ireland, M., Howard, A., & Huber, D. (2016). "Orbital Architectures of Planet-hosting Binaries. I. Forming Five Small Planets in the Truncated Disk of Kepler-444A". apj, 817, 80.
• Dupuy, T., Kratter, K., Kraus, A., Isaacson, H., Mann, A., Ireland, M., Howard, A., & Huber, D. (2016). ORBITAL ARCHITECTURES of PLANET-HOSTING BINARIES. I. FORMING FIVE SMALL PLANETS in the TRUNCATED DISK of KEPLER-444A. Astrophysical Journal, 817(1). doi:10.3847/0004-637x/817/1/80
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  We present the first results from our Keck program investigating the orbital architectures of planet-hosting multiple star systems. Kepler-444 is a metal-poor triple star system that hosts five sub-Earth-sized planets orbiting the primary star (Kepler-444A), as well as a spatially unresolved pair of M dwarfs (Kepler-444BC) at a projected distance of 1.″8 (66 AU).We combine our Keck/NIRC2 adaptive optics astrometry with multi-epoch Keck/HIRES RVs of all three stars to determine a precise orbit for the BC pair around A, given their empirically constrained masses. We measure minimal astrometric motion (1.0 ± 0.6 mas yr?1, or 0.17 ± 0.10 km s?1), but our RVs reveal significant orbital velocity (1.7 ± 0.2 km s?1) and acceleration (7.8 ± 0.5 m s?1 yr?1). We determine a highly eccentric stellar orbit (e = 0.864 ± 0.023) that brings the tight M dwarf pair within 5.0-1.0 +0.9 AU of the planetary system. We validate that the system is dynamically stable in its present configuration via n-body simulations. We find that the A-BC orbit and planetary orbits are likely aligned (98%) given that they both have edge-on orbits and misalignment induces precession of the planets out of transit. We conclude that the stars were likely on their current orbits during the epoch of planet formation, truncating the protoplanetary disk at ≈2 AU. This truncated disk would have been severely depleted of solid material from which to form the total ≈1.5M? of planets. We thereby strongly constrain the efficiency of the conversion of dust into planets and suggest that the Kepler-444 system is consistent with models that explain the formation of most close-in Kepler planets in more typical, not truncated, disks.
• Kratter, K., & Lodato, G. (2016). "Gravitational Instabilities in Circumstellar Disks". araa, 54, 271-311.
• Lin, M., & Kratter, K. (2016). "On the Gravitational Stability of Gravito-turbulent Accretion Disks". apj, 824, 91.
• Lin, M., & Kratter, K. (2016). ON the GRAVITATIONAL STABILITY of GRAVITO-TURBULENT ACCRETION DISKS. Astrophysical Journal, 824(2). doi:10.3847/0004-637x/824/2/91
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  Low mass, self-gravitating accretion disks admit quasi-steady, "gravito-turbulent" states in which cooling balances turbulent viscous heating. However, numerical simulations show that gravito-turbulence cannot be sustained beyond dynamical timescales when the cooling rate or corresponding turbulent viscosity is too large. The result is disk fragmentation. We motivate and quantify an interpretation of disk fragmentation as the inability to maintain gravito-turbulence due to formal secondary instabilities driven by: (1) cooling, which reduces pressure support; and/or (2) viscosity, which reduces rotational support. We analyze the axisymmetric gravitational stability of viscous, non-adiabatic accretion disks with internal heating, external irradiation, and cooling in the shearing box approximation. We consider parameterized cooling functions in 2D and 3D disks, as well as radiative diffusion in 3D. We show that generally there is no critical cooling rate/viscosity below which the disk is formally stable, although interesting limits appear for unstable modes with lengthscales on the order of the disk thickness. We apply this new linear theory to protoplanetary disks subject to gravito-turbulence modeled as an effective viscosity, and cooling regulated by dust opacity. We find that viscosity renders the disk beyond ∼60 au dynamically unstable on radial lengthscales a few times the local disk thickness. This is coincident with the empirical condition for disk fragmentation based on a maximum sustainable stress. We suggest turbulent stresses can play an active role in realistic disk fragmentation by removing rotational stabilization against self-gravity, and that the observed transition in behavior from gravito-turbulent to fragmenting may reflect instability of the gravito-turbulent state itself.
• Morrison, S., & Kratter, K. (2016). "Orbital Stability of Multi-planet Systems: Behavior at High Masses". apj, 823, 118.
• Segura-Cox, D., Harris, R., Tobin, J., Looney, L., Li, Z., Chandler, C., Kratter, K., Dunham, M., Sadavoy, S., Perez, L., & Melis, C. (2016). "The VLA Nascent Disk and Multiplicity Survey: First Look at Resolved Candidate Disks around Class 0 and I Protostars in the Perseus Molecular Cloud". apjl, 817, L14.
• Segura-Cox, D., Harris, R., Tobin, J., Looney, L., Li, Z., Chandler, C., Kratter, K., Dunham, M., Sadavoy, S., Perez, L., & Melis, C. (2016). THE VLA NASCENT DISK and MULTIPLICITY SURVEY: FIRST LOOK at RESOLVED CANDIDATE DISKS AROUND CLASS 0 and i PROTOSTARS in the PERSEUS MOLECULAR CLOUD. Astrophysical Journal Letters, 817(2). doi:10.3847/2041-8205/817/2/l14
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  We present the first dust emission results toward a sample of seven protostellar disk candidates around Class 0 and I sources in the Perseus molecular cloud from the VLA Nascent Disk and Multiplicity (VANDAM) survey with ∼0.″05 or 12 AU resolution. To examine the surface brightness profiles of these sources, we fit the Ka-band 8 mm dust-continuum data in the u, v-plane to a simple, parametrized model based on the Shakura-Sunyaev disk model. The candidate disks are well-fit by a model with a disk-shaped profile and have masses consistent with known Class 0 and I disks. The inner-disk surface densities of the VANDAM candidate disks have shallower density profiles compared to disks around more evolved Class II systems. The best-fit model radii of the seven early-result candidate disks are Rc > 10 AU; at 8 mm, the radii reflect lower limits on the disk size since dust continuum emission is tied to grain size and large grains radially drift inwards. These relatively large disks, if confirmed kinematically, are inconsistent with theoretical models where the disk size is limited by strong magnetic braking to
• Smullen, R., Kratter, K., & Shannon, A. (2016). "Planet scattering around binaries: ejections, not collisions". mnras, 461, 1288-1301.
• Stone, J., Skemer, A., Kratter, K., Dupuy, T., Close, L., Eisner, J., Fortney, J., Hinz, P., Males, J., Morley, C., Morzinski, K., & Ward-Duong, K. (2016). ADAPTIVE OPTICS IMAGING of VHS 1256-1257: A LOW MASS COMPANION to A BROWN DWARF BINARY SYSTEM. Astrophysical Journal Letters, 818(1). doi:10.3847/2041-8205/818/1/L12
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  Recently, Gauza et al. reported the discovery of a companion to the late M-dwarf, VHS J125601.92-125723.9 (VHS 1256-1257). The companions absolute photometry suggests its mass and atmosphere are similar to the HR 8799 planets. However, as a wide companion to a late-type star, it is more accessible to spectroscopic characterization. We discovered that the primary of this system is an equal-magnitude binary. For an age ∼300 Myr the A and B components each have a mass of 64.6 -2.0+0.8 MJup, and the b component has a mass of 11.2-1.8+9.7, making VHS 1256-1257 only the third brown dwarf triple system. There exists some tension between the spectrophotometric distance of 17.2±2.6 pc and the parallax distance of 12.7±1.0 pc. At 12.7 pc VHS 1256-1257 A and B would be the faintest known M7.5 objects, and are even faint outliers among M8 types. If the larger spectrophotmetric distance is more accurate than the parallax, then the mass of each component increases. In particular, the mass of the b component increases well above the deuterium burning limit to ∼35 MJup and the mass of each binary component increases to 73-17+20 MJup. At 17.1 pc, the UVW kinematics of the system are consistent with membership in the AB Dor moving group. The architecture of the system resembles a hierarchical stellar multiple suggesting it formed via an extension of the star formation process to low masses. Continued astrometric monitoring will resolve this distance uncertainty and will provide dynamical masses for a new benchmark system.
• Stone, J., Skemer, A., Kratter, K., Dupuy, T., Close, L., Eisner, J., Fortney, J., Hinz, P., Males, J., Morley, C., Morzinski, K., & Ward-Duong, K. .. (2016). "Adaptive Optics imaging of VHS 1256-1257: A Low Mass Companion to a Brown Dwarf Binary System". apjl, 818, L12.
• Tobin, J., Kratter, K., Persson, M., Looney, L., Dunham, M., Segura-Cox, D. .., Li, Z., Chandler, C., Sadavoy, S., Harris, R., Melis, C., & P{'erez}, L. (2016). "A triple protostar system formed via fragmentation of a gravitationally unstable disk". nat, 538, 483-486.
• Tobin, J., Looney, L., Li, Z., Chandler, C., Dunham, M., Segura-Cox, D. .., Sadavoy, S., Melis, C., Harris, R., Kratter, K., & Perez, L. (2016). "The VLA Nascent Disk and Multiplicity Survey of Perseus Protostars (VANDAM). II. Multiplicity of Protostars in the Perseus Molecular Cloud". apj, 818, 73.
• Tobin, J., Looney, L., Li, Z., Chandler, C., Dunham, M., Segura-Cox, D., Sadavoy, S., Melis, C., Harris, R., Kratter, K., & Perez, L. (2016). THE VLA NASCENT DISK AND MULTIPLICITY SURVEY OF PERSEUS PROTOSTARS (VANDAM). II. MULTIPLICITY OF PROTOSTARS IN THE PERSEUS MOLECULAR CLOUD. Astrophysical Journal, 818(1). doi:10.3847/0004-637x/818/1/73
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  We present a multiplicity study of all known protostars (94) in the Perseus molecular cloud from a Karl G. Jansky Very Large Array survey at Ka-band (8 mm and 1 cm) and C-band (4 and 6.6 cm). The observed sample has a bolometric luminosity range between 0.1 Lȯ and ∼33 Lȯ, with a median of 0.7 Lȯ. This multiplicity study is based on the Ka-band data, having a best resolution of ∼0.″065 (15 au) and separations out to ∼43″ (10,000 au) can be probed. The overall multiplicity fraction (MF) is found to be 0.40 ± 0.06 and the companion star fraction (CSF) is 0.71 ± 0.06. The MF and CSF of the Class 0 protostars are 0.57 ± 0.09 and 1.2 ± 0.2, and the MF and CSF of Class I protostars are both 0.23 ± 0.08. The distribution of companion separations appears bi-modal, with a peak at ∼75 au and another peak at ∼3000 au. Turbulent fragmentation is likely the dominant mechanism on >1000 au scales and disk fragmentation is likely to be the dominant mechanism on
• Wagner, K., Apai, D., Kasper, M., Kratter, K., McClure, M., Robberto, M., & Beuzit, J. (2016). "Direct imaging discovery of a Jovian exoplanet within a triple-star system". Science, 353, 673-678.
• Wagner, K., Apai, D., Markus, K., Kratter, K., McClure, M., Robberto, M., & Beuzit, J. (2016). Direct imaging discovery of a Jovian exoplanet within a triple-star system. Science, 673, 353.
• Lee, K., Dunham, M., Myers, P., Tobin, J., Kristensen, L., Pineda, J., Vorobyov, E., Offner, S., Arce, H., Li, Z., Bourke, T., Jørgensen, J., Goodman, A., Sadavoy, S., Chandler, C., Harris, R., Kratter, K., Looney, L., Melis, C., , Perez, L., et al. (2015). MASS ASSEMBLY of STELLAR SYSTEMS and THEIR EVOLUTION with the SMA (MASSES). MULTIPLICITY and the PHYSICAL ENVIRONMENT in L1448N. Astrophysical Journal, 814(2). doi:10.1088/0004-637x/814/2/114
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  We present continuum and molecular line observations at 230 and 345 GHz from the Submillimeter Array (SMA) toward three protostars in the Perseus L1448N region. The data are from the large project "Mass Assembly of Stellar Systems and their Evolution with the SMA." Three dust continuum sources, Source B, Source NW, and Source A, are detected at both frequencies. These sources have corresponding emission peaks in C18O (J= 2 → 1), 13CO (J=2 → 1), and HCO+ (J=4 → 3), and have offsets with N2D+ (J=4 → 3) peaks. High angular resolution data from a complementary continuum survey with the Karl G. Jansky Very Large Array show that Source B is associated with three 8 mm continuum objects, Source NW with two, and Source A remains single. These results suggest that multiplicity in L1448N exists at different spatial scales from a few thousand AU to
• Mu~noz, D. J., Kratter, K., Vogelsberger, M., Hernquist, L., & Springel, V. (2015). Stellar orbit evolution in close circumstellar disc encounters. mnras, 446, 2010-2029.
• Sana, H., Le Bouquin, J., Lacour, S., Berger, J., Duvert, G., Gauchet, L., Norris, B., Olofsson, J., Pickel, D., Zins, G., Absil, O., Koter, A., Kratter, K., Schnurr, O., & Zinnecker, H. (2015). VizieR Online Data Catalog: SMaSH+: observations and companion detection (Sana+, 2014). VizieR Online Data Catalog, 221, 50015.
• Tobin, J. J., Dunham, M. M., Looney, L. W., Li, Z. Y., Chandler, C. J., Segura-cox, D., Sadavoy, S. I., Melis, C., Harris, R. J., Perez, L. M., Kratter, K., Jørgensen, J. K., Plunkett, A. L., & Hull, C. L. (2015). The VLA nascent disk and multiplicity (vandam) survey of perseus protostars. resolving the sub-arcsecond binary system in NGC 1333 IRAS2A. Astrophysical Journal, 798(Issue 1). doi:10.1088/0004-637x/798/1/61
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  We are conducting a Jansky Very Large Array (VLA) Ka -band (8 mm and 1 cm) and C-band (4 cm and 6.4 cm) survey of all known protostars in the Perseus Molecular Cloud, providing resolution down to ∼0″.06 and ∼0.0″.35 in the Ka band and C band, respectively. Here we present first results from this survey that enable us to examine the source NGC 1333 IRAS2A in unprecedented detail and resolve it into a protobinary system separated by 0″.621 ± 0″.006 (∼143 AU) at 8 mm, 1 cm, and 4 cm. These two sources (IRAS2A VLA1 and VLA2) are likely driving the two orthogonal outflows known to originate from IRAS2A. The brighter source IRAS2A VLA1 is extended perpendicular to its outflow in the VLA data, with a deconvolved size of 0″.055 (∼13AU), possibly tracing a protostellar disk. The recently reported candidate companions (IRAS2A MM2 and MM3) are not detected in either our VLA data, Combined Array for Research in Millimeter-wave Astronomy (CARMA) 1.3 mm data, or Submillimeter Array (SMA) 850 μm data. SMA CO (J = 3 → 2), CARMA CO (J = 2 → 1), and lower-resolution CARMA CO (J = 1 → 0) observations are used to examine the outflow origins and the nature of the candidate companions to IRAS2A VLA1. The CO (J = 3 → 2) and (J = 2 → 1) data show that IRAS2A MM2 is coincident with a bright CO emission spot in the east-west outflow, and IRAS2A MM3 is within the north-south outflow. In contrast, IRAS2A VLA2 lies at the east-west outflow symmetry point. We propose that IRAS2A VLA2 is the driving source of the east-west outflow and a true companion to IRAS2A VLA1, whereas IRAS2A MM2 and MM3 may not be protostellar.
• Tobin, J. J., Dunham, M. M., Looney, L. W., Li, Z., Chandler, C. J., Segura-Cox, D., Sadavoy, S. I., Melis, C., Harris, R. J., Perez, L. M., Kratter, K., Jorgensen, J. K., Plunkett, A. L., & Hull, C. L. (2015). The VLA Nascent Disk and Multiplicity (VANDAM) Survey of Perseus Protostars. Resolving the Sub-arcsecond Binary System in NGC 1333 IRAS2A. apj, 798, 61.
• Tripathi, A., Kratter, K., Murray-Clay, R., & Krumholz, M. (2015). Erratum: sIMULATED PHOTOEVAPORATIVE MASS LOSS from HOT JUPITERS in 3D (Astrophysical Journal (2015) 808:173). Astrophysical Journal, 811(2). doi:10.1088/0004-637x/811/2/159
• Tripathi, A., Kratter, K., Murray-Clay, R., & Krumholz, M. (2015). SIMULATED PHOTOEVAPORATIVE MASS LOSS from HOT JUPITERS in 3D. Astrophysical Journal, 808(2). doi:10.1088/0004-637x/808/2/173
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  Ionizing stellar photons heat the upper regions of planetary atmospheres, driving atmospheric mass loss. Gas escaping from several hot, hydrogen-rich planets has been detected using UV and X-ray transmission spectroscopy. Because these planets are tidally locked, and thus asymmetrically irradiated, escaping gas is unlikely to be spherically symmetric. In this paper, we focus on the effects of asymmetric heating on local outflow structure. We use the Athena code for hydrodynamics to produce 3D simulations of hot Jupiter mass loss that jointly model wind launching and stellar heating via photoionization. Our fiducial planet is an inflated, hot Jupiter with radius Rp = 2.14RJup and mass Mp = 0.53MJup. We irradiate the initially neutral, atomic hydrogen atmosphere with 13.6 eV photons and compute the outflows ionization structure. There are clear asymmetries in the atmospheric outflow, including a neutral shadow on the planets nightside. Given an incident ionizing UV flux comparable to that of the Sun, we find a steady-state mass loss rate of ∼2 × 1010 g s?1. The total mass loss rate and the outflow substructure along the substellar ray show good agreement with earlier 1D models, for two different fluxes. Our 3D data cube can be used to generate the outflows extinction spectrum during transit. As a proof of concept, we find absorption of stellar Lyα at Doppler-shifted velocities of up to ±50 km s?1. Our work provides a starting point for further 3D models that can be used to predict observable signatures of hot Jupiter mass loss.
• {Cox}, E., {Harris}, R., {Looney}, L., {Segura-Cox}, D., {Tobin}, J., {Li}, Z., {Tychoniec}, {., {Chandler}, C., {Dunham}, M., {Kratter}, K., {Melis}, C., {Perez}, L., , S. (2015). "{High-resolution 8 mm and 1 cm Polarization of IRAS 4A from the VLA Nascent Disk and Multiplicity (VANDAM) Survey}". apjl, 814, L28.
• {Kratter}, K. (2015). "{Star formation: Sibling rivalry begins at birth}". nat, 518, 173-174.
• {Lee}, K., {Dunham}, M., {Myers}, P., {Tobin}, J., {Kristensen}, L., {Pineda}, J., {Vorobyov}, E., {Offner}, S., {Arce}, H., {Li}, Z., {Bourke}, T., {J{o}rgensen}, J., {Goodman}, A., {Sadavoy}, S., {Chandler}, C., {Harris}, R., {Kratter}, K., {Looney}, L., {Melis}, C., , {Perez}, L., et al. (2015). "{Mass Assembly of Stellar Systems and Their Evolution with the SMA (MASSES). Multiplicity and the Physical Environment in L1448N}". apj, 814, 114.
• {Sallum}, S., {Follette}, K., {Eisner}, J., {Close}, L., {Hinz}, P., {Kratter}, K., {Males}, J., {Skemer}, A., {Macintosh}, B., {Tuthill}, P., {Bailey}, V., {Defr{`e}re}, D., {Morzinski}, K., {Rodigas}, T., {Spalding}, E., {Vaz}, A., , A. (2015). "{Accreting protoplanets in the LkCa 15 transition disk}". nat, 527, 342-344.
• {Tripathi}, A., {Kratter}, K., {Murray-Clay}, R., , M. (2015). "{Erratum: {ldquo}Simulated Photoevaporative Mass Loss from Hot Jupiters in 3D{rdquo} (2015, ApJ, 808, 173)}". apj, 811, 159.
• {Tripathi}, A., {Kratter}, K., {Murray-Clay}, R., , M. (2015). "{Simulated Photoevaporative Mass Loss from Hot Jupiters in 3D}". apj, 808, 173.
• Kratter, K. M., & Shannon, A. (2014). Planet packing in circumbinary systems. mnras, 437, 3727-3735.
• Mu~noz, D. J., Kratter, K., Springel, V., & Hernquist, L. (2014). Planet-disc interaction on a freely moving mesh. mnras, 445, 3475-3495.
• Sana, H., Le Bouquin, J. B., Lacour, S., Berger, J. P., Duvert, G., Gauchet, L., Norris, B., Olofsson, J., Pickel, D., Zins, G., Absil, O., De Koter, A., Kratter, K., Schnurr, O., & Zinnecker, H. (2014). Southern massive stars at high angular resolution: Observational campaign and companion detection. Astrophysical Journal, Supplement Series, 215(Issue 1). doi:10.1088/0067-0049/215/1/15
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  Multiplicity is one of the most fundamental observable properties of massive O-type stars and offers a promising way to discriminate between massive star formation theories. Nevertheless, companions at separations between 1 and 100 milliarcsec (mas) remain mostly unknown due to intrinsic observational limitations. At a typical distance of 2 kpc, this corresponds to projected physical separations of 2-200 AU. The Southern MAssive Stars at High angular resolution survey (SMaSH+) was designed to fill this gap by providing the first systematic interferometric survey of Galactic massive stars. We observed 117 O-type stars with VLTI/PIONIER and 162 O-type stars with NACO/Sparse Aperture Masking (SAM), probing the separation ranges 1-45 and 30-250 mas and brightness contrasts of ΔH < 4 and ΔH < 5, respectively. Taking advantage of NACO's field of view, we further uniformly searched for visual companions in an 8″ radius down to ΔH = 8. This paper describes observations and data analysis, reports the discovery of almost 200 new companions in the separation range from 1 mas to 8″ and presents a catalog of detections, including the first resolved measurements of over a dozen known long-period spectroscopic binaries. Excluding known runaway stars for which no companions are detected, 96 objects in our main sample (δ < 0°; H < 7.5) were observed both with PIONIER and NACO/SAM. The fraction of these stars with at least one resolved companion within 200 mas is 0.53. Accounting for known but unresolved spectroscopic or eclipsing companions, the multiplicity fraction at separation ρ < 8″ increases to f m = 0.91 ± 0.03. The fraction of luminosity class V stars that have a bound companion reaches 100% at 30 mas while their average number of physically connected companions within 8″ is f c = 2.2 ± 0.3. This demonstrates that massive stars form nearly exclusively in multiple systems. The nine non-thermal radio emitters observed by SMaSH+ are all resolved, including the newly discovered pairs HD 168112 and CPD-47°2963. This lends strong support to the universality of the wind-wind collision scenario to explain the non-thermal emission from O-type stars.
• Sana, H., Le Bouquin, J., Lacour, S., Berger, J., Duvert, G., Gauchet, L., Norris, B., Olofsson, J., Pickel, D., Zins, G., Absil, O., Koter, A., Kratter, K., Schnurr, O., & Zinnecker, H. (2014). Southern Massive Stars at High Angular Resolution: Observational Campaign and Companion Detection. apjs, 215, 15.
• Stassun, K. G., Scholz, A., Dupuy, T. J., & Kratter, K. M. (2014). The Impact of Chromospheric Activity on Observed Initial Mass Functions. apj, 796, 119.
• Stassun, K. G., Scholz, A., Dupuy, T. J., & Kratter, K. M. (2014). The impact of chromospheric activity on observed initial mass functions. Astrophysical Journal, 796(Issue 2). doi:10.1088/0004-637x/796/2/119
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  Using recently established empirical calibrations for the impact of chromospheric activity on the radii, effective temperatures, and estimated masses of active low-mass stars and brown dwarfs, we reassess the shape of the initial mass function (IMF) across the stellar/substellar boundary in the Upper Sco star-forming region (age 5-10 Myr). We adjust the observed effective temperatures to warmer values using the observed strength of the chromospheric Hα emission, and redetermine the estimated masses of objects using pre-main-sequence evolutionary tracks in the H-R diagram. The effect of the activity-adjusted temperatures is to shift the objects to higher masses by 3%-100%. While the slope of the resulting IMF at substellar masses is not strongly changed, the peak of the IMF does shift from 0.06 to 0.11 M . Moreover, for objects with masses ≲ 0.2 M , the ratio of brown dwarfs to stars changes from 80% to 33%. These results suggest that activity corrections are essential for studies of the substellar mass function, if the masses are estimated from spectral types or from effective temperatures.
• Harding, L. K., Hallinan, G., Konopacky, Q. M., Kratter, K. M., Boyle, R. P., Butler, R. F., & Golden, A. (2013). Spin-orbit alignment in the very low mass binary regime. The L dwarf tight binary 2MASSW J0746425+200032AB. aap, 554, A113.
• Welsh, W., Bloemen, S., Conroy, K., Doyle, L., Fabrycky, D. C., Ford, E. B., Haghighipour, N., Huber, D., Kane, S., Kirk, B., Kostov, V., Kratter, K., Mazeh, T., Orosz, J., Pepper, J., Prsa, A., Shporer, A., & Windmiller, G. (2013). Kepler's Unparalleled Exploration of the Time Dimension. ArXiv e-prints.
• Zhao, B., Li, Z., & Kratter, K. M. (2013). Effect of Magnetic Misalignment on Protobinary Evolution. ArXiv e-prints.
• Conroy, C., & Kratter, K. M. (2012). Runaway Stars and the Escape of Ionizing Radiation from High-redshift Galaxies. apj, 755, 123.
• Conroy, C., & Kratter, K. M. (2012). Runaway stars and the escape of ionizing radiation from high-redshift galaxies. Astrophysical Journal, 755(Issue 2). doi:10.1088/0004-637x/755/2/123
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  Approximately 30% of all massive stars in the Galaxy are runaways with velocities exceeding 30 km s-1. Their high speeds allow them to travel 0.1-1 kpc away from their birthplace before they explode at the end of their several Myr lifetimes. At high redshift, when galaxies were much smaller than in the local universe, runaways could venture far from the dense inner regions of their host galaxies. From these large radii, and therefore low column densities, much of their ionizing radiation is able to escape into the intergalactic medium. Runaways may therefore significantly enhance the overall escape fraction of ionizing radiation, f esc, from small galaxies at high redshift. We present simple models of the high-redshift runaway population and its impact on f esc as a function of halo mass, size, and redshift. We find that the inclusion of runaways enhances f esc by factors of ≈1.1-8, depending on halo mass, galaxy geometry, and the mechanism of runaway production, implying that runaways may contribute 50%-90% of the total ionizing radiation escaping from high-redshift galaxies. Runaways may therefore play an important role in reionizing the universe. © © 2012. The American Astronomical Society. All rights reserved..
• Kratter, K. M., & Perets, H. B. (2012). Star Hoppers: Planet Instability and Capture in Evolving Binary Systems. apj, 753, 91.
• Perets, H. B., & Kratter, K. M. (2012). The Triple Evolution Dynamical Instability: Stellar Collisions in the Field and the Formation of Exotic Binaries. apj, 760, 99.
• Perets, H. B., & Kratter, K. M. (2012). The triple evolution dynamical instability: Stellar collisions in the field and the formation of exotic binaries. Astrophysical Journal, 760(Issue 2). doi:10.1088/0004-637x/760/2/99
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  Physical collisions and close approaches between stars play an important role in the formation of exotic stellar systems. Standard theories suggest that collisions are rare, occurring only via random encounters between stars in dense clusters. We present a different formation pathway, the triple evolution dynamical instability (TEDI), in which mass loss in an evolving triple star system causes orbital instability. The subsequent chaotic orbital evolution of the stars triggers close encounters, collisions, exchanges between the stellar components, and the dynamical formation of eccentric compact binaries (including Sirius-like binaries). We demonstrate that the rate of stellar collisions due to the TEDI is approximately 10-4 yr-1 per Milky Way Galaxy, which is nearly 30 times higher than the total collision rate due to random encounters in the Galactic globular clusters. Moreover, we find that the dominant type of stellar collision is qualitatively different; most collisions involve asymptotic giant branch stars, rather than main sequence or slightly evolved stars, which dominate collisions in globular clusters. The TEDI mechanism should lead us to revise our understanding of collisions and the formation of compact, eccentric binaries in the field. © 2012. The American Astronomical Society. All rights reserved.
• Stassun, K. G., Kratter, K. M., Scholz, A., & Dupuy, T. J. (2012). An Empirical Correction for Activity Effects on the Temperatures, Radii, and Estimated Masses of Low-mass Stars and Brown Dwarfs. apj, 756, 47.
• Stassun, K. G., Kratter, K. M., Scholz, A., & Dupuy, T. J. (2012). An empirical correction for activity effects on the temperatures, radii, and estimated masses of low-mass stars and brown dwarfs. Astrophysical Journal, 756(Issue 1). doi:10.1088/0004-637x/756/1/47
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  We present empirical relations for determining the amount by which the effective temperatures and radii - and therefore the estimated masses - of low-mass stars and brown dwarfs are altered due to chromospheric activity. We base our relations on a large set of low-mass stars in the field with Hα activity measurements, and on a set of low-mass eclipsing binaries with X-ray activity measurements from which we indirectly infer the Hα activity. Both samples yield consistent relations linking the amount by which an active object's temperature is suppressed, and its radius inflated, to the strength of its Hα emission. These relations are found to approximately preserve bolometric luminosity. We apply these relations to the peculiar brown dwarf eclipsing binary 2M0535-05, in which the active, higher-mass brown dwarf has a cooler temperature than its inactive, lower-mass companion. The relations correctly reproduce the observed temperatures and radii of 2M0535-05 after accounting for the Hα emission; 2M0535-05 would be in precise agreement with theoretical isochrones were it is inactive. The relations that we present are applicable to brown dwarfs and low-mass stars with masses below 0.8 M ⊙ and for which the activity, as measured by the fractional Hα luminosity, is in the range -4.6 ≲ log L Hα/L bol ≲ - 3.3. We expect these relations to be most useful for correcting radius and mass estimates of low-mass stars and brown dwarfs over their active lifetimes (few Gyr) and when the ages or distances (and therefore luminosities) are unknown. We also discuss the implications of this work for improved determinations of young cluster initial mass functions. © © 2012. The American Astronomical Society. All rights reserved..
• Stassun, K. G., Kratter, K. M., Scholz, A., & Dupuy, T. J. (2012). Correcting for Activity Effects on the Temperatures, Radii, and Estimated Masses of Low-Mass Stars and Brown Dwarfs. ArXiv e-prints.
• Youdin, A. N., Kratter, K. M., & Kenyon, S. J. (2012). Circumbinary Chaos: Using Pluto's Newest Moon to Constrain the Masses of Nix and Hydra. apj, 755, 17.
• Kratter, K. M., & Murray-Clay, R. A. (2011). Fragment Production and Survival in Irradiated Disks: A Comprehensive Cooling Criterion. apj, 740, 1.
• Lin, M., Krumholz, M. R., & Kratter, K. M. (2011). Spin-down of protostars through gravitational torques. mnras, 416, 580-590.
• Kratter, K. M., Matzner, C. D., Krumholz, M. R., & Klein, R. I. (2010). On the Role of Disks in the Formation of Stellar Systems: A Numerical Parameter Study of Rapid Accretion. apj, 708, 1585-1597.
• Kratter, K. M., Matzner, C. D., Krumholz, M. R., & Klein, R. I. (2010). On the role of disks in the formation of stellar systems: A numerical parameter study of rapid accretion. Astrophysical Journal, 708(Issue 2). doi:10.1088/0004-637x/708/2/1585
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  We study rapidly accreting, gravitationally unstable disks with a series of idealized global, numerical experiments using the code ORION. Our numerical parameter study focuses on protostellar disks, showing that one can predict disk behavior and the multiplicity of the accreting star system as a function of two dimensionless parameters which compare the infall rate to the disk sound speed and orbital period. Although gravitational instabilities become strong, we find that fragmentation into binary or multiple systems occurs only when material falls in several times more rapidly than the canonical isothermal limit. The disk-to-star accretion rate is proportional to the infall rate and governed by gravitational torques generated by low-m spiral modes. We also confirm the existence of a maximum stable disk mass: disks that exceed ∼ 50% of the total system mass are subject to fragmentation and the subsequent formation of binary companions. © 2010. The American Astronomical Society. All rights reserved.
• Kratter, K. M., Murray-Clay, R. A., & Youdin, A. N. (2010). The Runts of the Litter: Why Planets Formed Through Gravitational Instability Can Only Be Failed Binary Stars. apj, 710, 1375-1386.
• Kratter, K. M., Murray-Clay, R. A., & Youdin, A. N. (2010). The runts of the litter: Why planets formed through gravitational instability can only be failed binary stars. Astrophysical Journal, 710(Issue 2). doi:10.1088/0004-637x/710/2/1375
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  Recent direct imaging discoveries suggest a new class of massive, distant planets around A stars. These widely separated giants have been interpreted as signs of planet formation driven by gravitational instability, but the viability of this mechanism is not clear-cut. In this paper, we first discuss the local requirements for fragmentation and the initial fragment mass scales. We then consider whether the fragment's subsequent growth can be terminated within the planetary mass regime. Finally, we place disks in the larger context of star formation and disk evolution models. We find that in order for gravitational instability to produce planets, disks must be atypically cold in order to reduce the initial fragment mass. In addition, fragmentation must occur during a narrow window of disk evolution, after infall has mostly ceased, but while the disk is still sufficiently massive to undergo gravitational instability. Under more typical conditions, disk-born objects will likely grow well above the deuterium burning planetary mass limit. We conclude that if planets are formed by gravitational instability, they must be the low-mass tail of the distribution of disk-born companions. To validate this theory, ongoing direct imaging surveys must find a greater abundance of brown dwarf and M-star companions to A stars. Their absence would suggest planet formation by a different mechanism such as core accretion, which is consistent with the debris disks detected in these systems. © 2010. The American Astronomical Society.
• Offner, S. S., Kratter, K. M., Matzner, C. D., Krumholz, M. R., & Klein, R. I. (2010). The Formation of Low-mass Binary Star Systems Via Turbulent Fragmentation. apj, 725, 1485-1494.
• Offner, S. S., Kratter, K. M., Matzner, C. D., Krumholz, M. R., & Klein, R. I. (2010). The formation of low-mass binary star systems via turbulent fragmentation. Astrophysical Journal, 725(Issue 2). doi:10.1088/0004-637x/725/2/1485
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  We characterize the infall rate onto protostellar systems forming in self-gravitating radiation-hydrodynamics simulations. Using two dimensionless parameters to determine the disks' susceptibility to gravitational fragmentation, we infer limits on protostellar system multiplicity and the mechanism of binary formation. We show that these parameters give robust predictions even in the case of marginally resolved protostellar disks.We find that protostellar systems with radiation feedback predominately form binaries via turbulent fragmentation, not disk instability, and predict that turbulent fragmentation is the dominant channel for binary formation for low-mass stars. We clearly demonstrate that systems forming in simulations including radiative feedback have fundamentally different parameters than those in purely hydrodynamics simulations. © 2010. The American Astronomical Society. All rights reserved.
• Kratter, K. M., Matzner, C. D., & Krumholz, M. R. (2008). Global Models for the Evolution of Embedded, Accreting Protostellar Disks. apj, 681, 375-390.
• Kratter, K. M., Matzner, C. D., & Krumholz, M. R. (2008). Global models for the evolution of embedded, accreting protostellar disks. Astrophysical Journal, 681(Issue 1). doi:10.1086/587543
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  Most analytic work to date on protostellar disks has focused on those in isolation from their environments. However, observations are now beginning to probe the earliest, most embedded phases of star formation, during which disks are rapidly accreting from their parent cores and cannot be modeled in isolation. We present a simple, one-zone model of protostellar accretion disks with high-mass infall rates. Our model combines a self-consistent calculation of disk temperatures with an approximate treatment of angular momentum transport via two mechanisms. We use this model to survey the properties of protostellar disks across a wide range of stellar masses and evolutionary times and make predictions for disks' masses, sizes, spiral structure, and fragmentation that will be directly testable by future large-scale surveys of deeply embedded disks. We define a dimensionless accretion-rotation parameter that, in conjunction with the disk's temperature, controls the disk evolution. We track the dominant mode of angular momentum transport and demonstrate that for stars with final masses greater than roughly one solar mass, gravitational instabilities are the most important mechanism as most of the mass accumulates. We predict that binary formation through disk fission, fragmentation of the disk into small objects, and spiral arm strength all increase in importance to higher stellar masses. © 2008. The American Astronomical Society. All rights reserved.
• Hinkley, S., Oppenheimer, B. R., Soummer, R., Sivaramakrishnan, A., Roberts, L. C., Kuhn, J., Makidon, R. B., Perrin, M. D., Lloyd, J. P., Kratter, K., & Brenner, D. (2007). Temporal Evolution of Coronagraphic Dynamic Range and Constraints on Companions to Vega. apj, 654, 633-640.
• Hinkley, S., Oppenheimer, B. R., Soummer, R., Sivaramakrishnan, A., Roberts, L. C., Kuhn, J., Makidon, R. B., Perrin, M. D., Lloyd, J. P., Kratter, K., & Brenner, D. (2007). Temporal evolution of coronagraphic dynamic range and constraints on companions to Vega. Astrophysical Journal, 654(Issue 1 I). doi:10.1086/509063
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  The major obstacle to the direct detection of companions to nearby stars is the overwhelming brightness of the host star. Current instruments employing the combination of adaptive optics (AO) and coronagraphy can typically detect objects within 2″ of the star that are ∼104-105 times fainter. Correlated speckle noise is one of the biggest obstacles limiting such high-contrast imaging. We have obtained a series of 284 8 s, AO-corrected, coronagraphically occulted H-band images of the star Vega at the 3.63 m AEOS telescope located on Haleakala, Hawaii. This data set is unique for studying the temporal behavior of speckle noise and represents the first time such a study on highly corrected coronagraphic AO images has been carried out in a quantitative way. We find the speckle pattern to be highly stable in both position and time in our data. This is due to the fact that the AO system corrects disturbances to the stellar wave front at the level where the instrumental wave front errors dominate. Because of this, we find that our detection limit is not significantly improved simply with increased exposure time alone. However, we are able to improve our dynamic range by 1.5-2 mag through subtraction of static/quasi-static speckles in two rotating frames: the telescope pupil frame and the deformable mirror frame. The highly stable nature of speckles will exist for any program using coronagraphy and high-order AO. Furthermore, from our data, we are able to constrain the mass of any purported companion to Vega to be less than ∼45MJ at 8 AU and less than ∼30MJ at 16 AU, radii not previously probed at these sensitivities. © 2007. The American Astronomical Society. All rights reserved.
• Kratter, K. M., Carter, L. M., & Campbell, D. B. (2007). An expanded view of Lada Terra, Venus: New Arecibo radar observations of Quetzalpetlatl Corona and surrounding flows. Journal of Geophysical Research (Planets), 112, 4008.
• Kratter, K. M., & Matzner, C. D. (2006). Fragmentation of massive protostellar discs. mnras, 373, 1563-1576.

Proceedings Publications

• Zariski, J., Kratter, K., Logsdon, S., Bender, C., Li, D., Schweiker, H., Rajagopal, J., McBride, B., & Hunting, E. (2024). Deep learning solutions to telescope pointing and guiding. In Software and Cyberinfrastructure for Astronomy VIII 2024, 13101.
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  The WIYN 3.5m Telescope at Kitt Peak National Observatory hosts a suite of optical and near-infrared instruments, including an extreme precision, optical spectrograph, NEID, built for exoplanet radial velocity studies. In order to achieve sub ms−1 precision, NEID has strict requirements on survey efficiency, stellar image positioning, and guiding performance, which have exceeded the native capabilities of the telescope’s original pointing and tracking system. In order to improve the operational efficiency of the telescope we have developed a novel telescope pointing system, built on a recurrent neural network, that does not rely on the usual pointing models (TPoint or other quasi-physical bases). We discuss the development of this system, how the intrinsic properties of the pointing problem inform our network design, and show preliminary results from our best models. We also discuss plans for the generalization of this framework, so that it can be applied at other sites.
• Best, W., Kraus, A., Allers, K., Biller, B., Bowler, B., Dupuy, T., Fontanive, C., Kratter, K., Lu, J., Offner, S., Reiter, M., & Rizzuto, A. (2021, jan). "Probing the Low-Mass End of the Initial Mass Function with an HST DASH Survey of Star-Forming Regions". In American Astronomical Society Meeting Abstracts, 53.
• Seligman, D., Kratter, K., Levine, W., & Jedicke, R. (2021, oct). "A Sublime Opportunity: In Situ Observations of The Onset of Intense Activity in Transitioning Cometary Bodies". In AAS/Division for Planetary Sciences Meeting Abstracts, 53.
• Best, W., Kraus, A., Allers, K., Biller, B., Bowler, B., Dupuy, T., Fontanive, C., Kratter, K., Lu, J., Offner, S., Reiter, M., & Rizzuto, A. (2020, jan). "Probing the Low-Mass End of the Initial Mass Function with an HST DASH Survey of Star-Forming Regions". In American Astronomical Society Meeting Abstracts #235, 235.
• Dupuy, T., Kraus, A., Kratter, K., Rizzuto, A., Prato, L., Mann, A., Ireland, M., & Huber, D. (2020, jan). "Which Binaries Foster Planet Formation and Survival?". In American Astronomical Society Meeting Abstracts #235, 235.
• Dupuy, T., Kraus, A., Kratter, K. M., Rizzuto, A., Mann, A., Ireland, M., & Huber, D. (2019, aug). Planetary-Stellar Orbit Alignment in Binary Systems. In AAS/Division for Extreme Solar Systems Abstracts, 51.
• Kollmeier, J., Anderson, L., Benson, A., Bogdanovi{'c}, T., Boylan-Kolchin, M., Bullock, J. S., Dav{'e}, R., Fuller, J., Hopkins, P., Kaplinghat, M., Kratter, K., Miller, M. C., Owen, J. E., Phinney, E. S., Piro, A. L., Rix, H., Robertson, B., Wheeler, C., Wetzel, A., , Youdin, A. N., et al. (2019, sep). Theoretical Astrophysics 2020-2030. In baas, 51.
• Kounkel, M., Covey, K., Moe, M., & Kratter, K. M. (2019, jan). Close companions to young stars. In American Astronomical Society Meeting Abstracts #233, 233.
• McCann, J., Murray-Clay, R., Krumholz, M., & Kratter, K. M. (2019, aug). Atmospheric escape: new windows, longer baselines and demographic influences. In AAS/Division for Extreme Solar Systems Abstracts, 51.
• Neveu, M., Canup, R., & Kratter, K. (2019, jul). On the Origin of the Pluto System. In Pluto System After New Horizons, 2133.
• Rainot, A., Reggiani, M., Sana, H., Gomez-Gonzalez, C. A., Absil, O., Christiaens, V., Delorme, P., Almeida, L., Caballero-Nieves, S., de Ridder, J., Kratter, K., Lacour, S., Le Bouquin, J. B., Pueyo, L., & Zinnecker, H. (2019). Towards constraints on massive galactic stars using VLT/SPHERE with high-contrast imaging. In EWASS 2019: Special Session 22 Stellar Multiplicity in the Gaia Era: Where do we Stand?, 90.
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  While the formation of massive stars remains heavily debated, it is nowadays clear that the formation scenarios need to account for the high-degree of multiplicity of these objects that has been observed by recent studies. Here we introduce the Carina High-contrast Imaging Project for massive Stars (CHIPS) that aims to obtain coronagraphic observations of massive stars in the Carina region using VLT/SPHERE. We illustrate the capabilities of SPHERE for massive stars by focusing on the QZ Car system. We detect 19 sources, most of them for the first time, within a 7x700field of view. We show that contrast better than 9 mag can be achieved at separation larger than 200 mas. We also investigate avenues to obtain a first characterisation of the detected sources by fitting their source energy distribution with pre-main sequence stellar atmosphere models.
• Sutherland, A. P., & Kratter, K. M. (2019, aug). Instabilities in Multi-Planet Circumbinary Systems. In AAS/Division for Extreme Solar Systems Abstracts, 51.
• Januszewski}, H., Castro, N., Oey, S., Becker, J., Kratter, K. M., Mateo, M., Sim{'on-D'iaz}, S., Bjorkman, J. E., Bjorkman, K., Sigut, A., Smullen, R., & Team, {. (2018, Jan). Kinematic Clues to OB Field Star Origins: Radial Velocities, Runaways, and Binaries. In American Astronomical Society Meeting Abstracts #231, 231.
• Monnier, J. D., Ireland, M., Kraus, S., Alonso-Herrero, A., Bonsor, A., Baron, F., Bayo, A., Berger, J., Boyajian, T., Chiavassa, A., Ciardi, D., Creech-Eakman, M., Wit, W., Defr{`ere}, D., Dong, R., Duch{^ene}, G., Espaillat, C., Gallenne, A. r., Gandhi, P., , Gonzalez, J., et al. (2018, Jul). Planet formation imager: project update. In Optical and Infrared Interferometry and Imaging VI, 10701.
• Oey, M., Barnes, J. R., Paggeot, K. J., Dorigo, J. J., Castro, N., Simon-Diaz, S., Kratter, K. M., Moe, M., & Szymanski, M. (2018, Jun). Further RIOTS4 Characterization of Field OB Stars in the SMC. In American Astronomical Society Meeting Abstracts #232, 232.
• Dupuy, T., Kraus, A., Kratter, K., & Prato, L. (2017, jan). "Orbital Architectures of Planet-Hosting Binaries: Testing Co-alignment". In American Astronomical Society Meeting Abstracts, 229.
• Guilfoil Cox, E., Looney, L., Harris, R., Dong, J., Segura-Cox, D. .., Tobin, J., Sadavoy, S., Li, Z., Dunham, M., Perez, L., Chandler, C., Kratter, K., Melis, C., & Chiang, H. (2017, jan). "An ALMA Survey of Planet Forming Disks in Rho Ophiuchus". In American Astronomical Society Meeting Abstracts, 229.
• Morrison, S., & Kratter, K. (2017, jan). "Forming Gaps in Debris Disks with Migrating Planets". In American Astronomical Society Meeting Abstracts, 229.
• Rainot, A., Sana, H., Gomez-Gonzalez, C., Absil, O., Delorme, P., Almeida, L., Caballero-Nieves, S. .., Kratter, K., Lacour, S., Le, B. J., Pueyo, L., & Zinnecker, H. (2017, nov). "CHIPS: The Carina High-contrast Imaging Project of massive Stars". In The Lives and Death-Throes of Massive Stars, 329.
• Tobin, J., Kratter, K., Persson, M., Looney, L., Dunham, M., Segura-Cox, D. .., Li, Z., Chandler, C., Sadavoy, S., Harris, R., Melis, C., & Perez, L. (2017, jan). "A Triple Protostar System in L1448 IRS3B Formed via Fragmentation of a Gravitationally Unstable Disk". In American Astronomical Society Meeting Abstracts, 229.
• Wilner, D., MacGregor, M., Czekala, I., Andrews, S., Dai, Y., Herczeg, G., Kratter, K., Kraus, A., Ricci, L., & Testi, L. (2017, jan). "ALMA Measurements of Circumstellar Material in the GQ Lup System". In American Astronomical Society Meeting Abstracts, 229.
• Crepp, J., Crass, J., King, D., Bechter, A., Bechter, E., Ketterer, R., Reynolds, R., Hinz, P., Kopon, D., Cavalieri, D., Fantano, L., Koca, C., Onuma, E., Stapelfeldt, K., Thomes, J., Wall, S., Macenka, S., McGuire, J., Korniski, R., , Zugby, L., et al. (2016, aug). "iLocater: a diffraction-limited Doppler spectrometer for the Large Binocular Telescope". In Ground-based and Airborne Instrumentation for Astronomy VI, 9908.
• Kraus, S., Monnier, J., Ireland, M., Duch{^ene}, G., Espaillat, C., H{"onig}, S., Juhasz, A., Mordasini, C., Olofsson, J., Paladini, C., Stassun, K., Turner, N., Vasisht, G., Harries, T., Bate, M., Gonzalez, J., Matter, A., Zhu, Z., Panic, O., , Regaly, Z., et al. (2016, aug). "Planet Formation Imager (PFI): science vision and key requirements". In Optical and Infrared Interferometry and Imaging V, 9907.
• Morrison, S., & Kratter, K. (2016, may). "Orbital Stability of High Mass Planetary Systems". In AAS/Division of Dynamical Astronomy Meeting, 47.
• Morrison, S., & Kratter, K. (2016, oct). "Forming Gaps in Debris Disks with Fewer Planets via Planet Migration". In AAS/Division for Planetary Sciences Meeting Abstracts, 48.
• Sallum, S., Eisner, J., Close, L., Hinz, P., Follette, K., Kratter, K., Skemer, A., Bailey, V., Briguglio, R., Defrere, D., Macintosh, B., Males, J., Morzinski, K., Puglisi, A., Rodigas, T., Spalding, E., Tuthill, P., Vaz, A., Weinberger, A., & Xomperio, M. (2016, aug). "Imaging protoplanets: observing transition disks with non-redundant masking". In Optical and Infrared Interferometry and Imaging V, 9907.
• Smullen, R., & Kratter, K. (2016, may). "The fate of debris in the Pluto-Charon system". In AAS/Division of Dynamical Astronomy Meeting, 47.
• {Dupuy}, T., , K. (2016, jan). "{Orbital Architectures of Planet-Hosting Binary Systems}". In American Astronomical Society Meeting Abstracts, 227.
• {Follette}, K., {Miller Close}, L., {Males}, J., {Macintosh}, B., {Sallum}, S., {Eisner}, J., {Kratter}, K., {Bailey}, V., {Defrere}, D., {Hinz}, P., {Morzinski}, K., {Rodigas}, T., {Skemer}, A., {Spalding}, E., {Tuthill}, P., {Vaz}, A., , A. (2016, jan). "{An Accreting Protoplanet: Confirmation and Characterization of LkCa15b}". In American Astronomical Society Meeting Abstracts, 227.
• {Guilfoil Cox}, E., {Harris}, R., {Looney}, L., {Segura-Cox}, D., {Tobin}, J., {Li}, Z., {Tychoniec}, L., {Chandler}, C., {Dunham}, M., {Kratter}, K., {Melis}, C., {Perez}, L., , S. (2016, jan). "{The Inferred Magnetic Field on 50 AU Scales Around IRAS 4A}". In American Astronomical Society Meeting Abstracts, 227.
• {Segura-Cox}, D., {Harris}, R., {Tobin}, J., {Looney}, L., {Li}, Z., {Chandler}, C., {Kratter}, K., {Dunham}, M., {Sadavoy}, S., {Perez}, L., , C. (2016, jan). "{The VLA Nascent Disk and Multiplicity Survey (VANDAM): Resolved Candidate Disks around Class 0 and I Protostars}". In American Astronomical Society Meeting Abstracts, 227.
• {Tobin}, J., {Looney}, L., {Li}, Z., {Chandler}, C., {Dunham}, M., {Segura-Cox}, D., {Sadavoy}, S., {Melis}, C., {Harris}, R., {Kratter}, K., , L. (2016, jan). "{Protostellar Multiplicity in Perseus Characterized by the VLA Nascent Disk and Multiplicity (VANDAM) Survey}". In American Astronomical Society Meeting Abstracts, 227.
• {Dupuy}, T., {Kratter}, K., {Kraus}, A., {Isaacson}, H., {Mann}, A., {Ireland}, M., {Howard}, A., , D. (2015, dec). "{Orbital Architectures of Planet-Hosting Binary Systems}". In AAS/Division for Extreme Solar Systems Abstracts, 3.
• {Follette}, K., {Close}, L., {Males}, J., {Macintosh}, B., {Sallum}, S., {Eisner}, J., {Kratter}, K., {Morzinski}, K., {Hinz}, P., {Weinberger}, A., {Rodigas}, T., {Skemer}, A., {Bailey}, V., {Vaz}, A., {Defrere}, D., {spalding}, e., , P. (2015, dec). "{An Accreting Protoplanet: Confirmation and Characterization of LkCa15b}". In AAS/Division for Extreme Solar Systems Abstracts, 3.
• {Morrison}, S., , K. (2015, dec). "{Orbital Stability of Multi-Planet Systems: Behavior at High Masses}". In AAS/Division for Extreme Solar Systems Abstracts, 3.
• {Smullen}, R., , K. (2015, dec). "{The Architecture of Circumbinary Systems}". In AAS/Division for Extreme Solar Systems Abstracts, 3.
• Bechter, E., Bechter, A., Crepp, J. R., Berg, M., Carroll, J., Collins, K., Corpuz, T., Ketterer, R., Kielb, E., Stoddard, R., Eisner, J., Gaudi, B. S., Hinz, P., Kratter, K., Macela, G., Quirrenbach, A., Skrutskie, M., Sozzetti, A., Woodward, C. E., & Zhao, B. (2014, mar). The iLocater Doppler Spectrometer. In Search for Life Beyond the Solar System. Exoplanets, Biosignatures amp Instruments, 3P.
• Crepp, J. R., Bechter, A., Bechter, E., Berg, M., Carroll, J., Collins, K., Corpuz, T., Ketterer, R., Kielb, E., Stoddard, R., Eisner, J. A., Gaudi, B. S., Hinz, P., Kratter, K. M., Macela, G., Quirrenbach, A., Skrutskie, M. F., Sozzetti, A., Woodward, C. E., & Zhao, B. (2014, jan). iLocater: A Diffraction-Limited Doppler Spectrometer for the Large Binocular Telescope. In American Astronomical Society Meeting Abstracts #223, 223, #348.20.
• Kratter, K. M., Shannon, A. B., Youdin, A., & Kenyon, S. (2014, may). Circumbinary Planetary Systems at Home and Abroad. In AAS/Division of Dynamical Astronomy Meeting, 45, #200.01.
• Segura-Cox, D., Tobin, J. J., Chandler, C. J., Dunham, M. M., Kratter, K. M., Li, Z., Looney, L., Melis, C., Perez, L. M., & Sadavoy, S. (2014, jan). The VLA Perseus Young Protostellar Disk and Multiplicity Survey: A First Look. In American Astronomical Society Meeting Abstracts #223, 223, #345.20.
• Zhao, B., Li, Z., & Kratter, K. M. (2014, jan). PROTOBINARY EVOLUTION DRIVEN BY MAGNETIC BRAKING. In American Astronomical Society Meeting Abstracts #223, 223, #214.07.
• Jumper, P., Kratter, K. M., Offner, S., & Fisher, R. T. (2013, jan). Understanding the Origin of Binary and Multiple Stellar Systems: Determining Fragmentation Criteria from Three-Dimensional Hydrodynamic Simulations of Star Formation with Supersonic Turbulence. In American Astronomical Society Meeting Abstracts #221, 221, #202.04.
• Kratter, K. M. (2013, oct). Planet Formation: Knowing the Progenitors and the Progeny. In New Horizons in Astronomy (BASH 2013), 13.
• Kratter, K. M., & Perets, H. (2013, jan). Planets in Evolved Binary Systems. In American Astronomical Society Meeting Abstracts #221, 221, #424.07.
• Stassun, K., Kratter, K. M., Scholz, A., & Dupuy, T. J. (2013, jan). An Empirical Correction for Activity Effects on the Temperatures, Radii, and Estimated Masses of Low-Mass Stars and Brown Dwarfs. In American Astronomical Society Meeting Abstracts #221, 221, #321.07.
• Tripathi, A., Kratter, K., Krumholz, M., & Murray-Clay, R. (2013, jul). Simulating Photoevaporative Mass Loss from Hot Jupiters in 3D. In Protostars and Planets VI Posters, 62.
• Kratter, K. M. (2012, dec). The Formation and Evolution of Massive Binaries. In Proceedings of a Scientific Meeting in Honor of Anthony F. J. Moffat, 465, 451.
• Kratter, K. M. (2011, sep). From Star Formation to Exoplanets. In AAS/Division for Extreme Solar Systems Abstracts, 2, 807.
• Kratter, K. M. (2011, sep). The Formation of Close Binaries. In Evolution of Compact Binaries, 447, 47.
• Murray-Clay, R., Kratter, K., & Youdin, A. (2011, sep). Core Accretion at Wide Separations: The Critical Role of Gas. In AAS/Division for Extreme Solar Systems Abstracts, 2, 804.
• Offner, S., Kratter, K. M., Matzner, C. D., Krumholz, M. R., & Klein, R. I. (2011, jan). The Turbulent Fragmentation Origin of Low-Mass Binary Star Systems. In American Astronomical Society Meeting Abstracts #217, 43, #258.10.
• Perets, H. B., & Kratter, K. M. (2011, sep). Formation of Compact Binaries in Destabilised Evolved Triples. In Evolution of Compact Binaries, 447, 61.
• Perets, H., Kratter, K., & Kenyon, S. (2011, sep). Planetary Dynamics and Evolution in Evolved Binary Systems. In AAS/Division for Extreme Solar Systems Abstracts, 2, 1507.
• Kratter, K. M. (2010, jan). The Role of Disks in the Formation of Stellar Systems. In American Astronomical Society Meeting Abstracts #215, 42, #374.01.
• Murray-Clay, R., Kratter, K., & Youdin, A. (2009, sep). Planet Formation at Wide Separations: Constraints from HR 8799. In AAS/Division for Planetary Sciences Meeting Abstracts #41, 41, #05.06.
• Kratter, K. M., & Matzner, C. D. (2008, may). Embedded, Accreting Disks in Massive Star Formation. In Massive Star Formation: Observations Confront Theory, 387, 262.
• Kratter, K. (2007, aug). Global Models for the Evolution of Embedded Accreting Protostellar Disk. In Star Formation, Then and Now, 44.
• Kratter, K. M., Dursi, L. J., & Pen, U. (2006, dec). Global Simulations of the Magnetorotational Instability in a Spherical Geometry. In American Astronomical Society Meeting Abstracts, 38, 1024.
• Soummer, R., Oppenheimer, B. R., Hinkley, S., Sivaramakrishnan, A., Makidon, R. B., Digby, A., Brenner, D., Kuhn, J., Perrin, M. D., Roberts, L. C., & Kratter, K. (2006). The Lyot project coronagraph: data processing and performance analysis. In EAS Publications Series, 22, 199-212.
• Kratter, K., & Matzner, C. (2005, dec). Massive protostellar disks: gravitational fragmentation?. In American Astronomical Society Meeting Abstracts, 37, #196.04.
• Kratter, K. M., Carter, L. M., & Campbell, D. B. (2004, nov). New Arecibo Radar Observations of Quetzalpetlatl Corona and Surroundings. In AAS/Division for Planetary Sciences Meeting Abstracts #36, 36, 1165.

Presentations

• Kratter, K. (2021, June). Multiplicity in Protostellar Disks. MIAPP. Munich (remote): LMU.
• Kratter, K. (2021, March). Stellar Companions from binaries to planets. UCSD/SDSU joint colloquiumUCSD.
• Kratter, K. (2020, April). The origin of binaries. Univ. of Pittsburgh Colloquium.
• Kratter, K. (2020, Octoer). Stellar Companions Across the Mass Ratio Spectrum. University of New Mexico Physics ColloquiumUNM.
• Kratter, K. (2018, January). Hydrodynamics of Star and Planet Formation. Applied Math Colloquium, UofA.
• Kratter, K. (2018, July). Unsolving problems in binary formation. Unsolved problems in Astrophysics. Budapest, Hungary.
• Kratter, K. (2018, June). Planets in hot star binaries. Planets around Hot Stars. Nashville, TN.
• Kratter, K. (2018, June). Theory overview of the hunt for young planets. Where are the baby Planets. Madrid, Spain.
• Kratter, K. (2018, November). Binaries in the big data era. CITA Seminar. Toronto, Canada.
• Kratter, K. (2018, October). Binary Stars and Planets in the Big Data Era. Carnegie Observatory Colloquium. Pasadena, CA.
• Kratter, K. (2018, September). Binary Star Formation. Stellar Birth and Death, GMT. Hawaii: GMTO.
• Kratter, K. (2018, Summer). Close binary formation. Mt. Stromlo Colloquium. Canberra, Australia.
• Kratter, K. (2017, April). Three puzzles in star and planet formation. Princeton Colloquium.
• Kratter, K. (2017, June). Unsolved problems in Planet Formation. Lund Colloquium. Lund, Sweden.
• Kratter, K. (2017, September). Three puzzles in Star and Planet Formation. CfA Colloquium.
• Kratter, K. (2015, April). Hertzberg Institute for Astrophysics Colloquium. Colloquium. Victoria, Canada: HIA.
• Kratter, K. (2015, July). Gravitational Instability and Planet Formation. Sagan Workshop, Invited Lecture.
• Kratter, K. (2015, July). Wide Orbit Planet Formation:. Sagan Workshop, Invited Lecture.
• Kratter, K. (2015, May). Planet in Binaires. Institute for Advanced Study Seminar.
• Kratter, K. (2014, April). Circumbinary Planetary systems at home and abroad. DDA Meeting. Philadelphia: DDA/ AAS.
• Kratter, K. (2014, April). The Formation of Herbig Ae/Be Stars. Herbig Ae/Be Stars, the Missing Link. Santiago, Chile: ESO.
• Kratter, K. (2014, August). Planet Formation including Binaries. Planets in relation to their Disks: ISSI Beijing. ISSI Beijing, China: ISSI Beijing, China.
• Kratter, K. (2014, Dec). Binaries and Planets. Colloquim. MIT: MIT.
• Kratter, K. (2014, Dec). Binaries and Planets. Colloquim. UMass Amherst: UMass Amherst.
• Kratter, K. (2014, February). Binaries and Planets. Colloquim. Flagstaff, AZ: Lowell Observatory.
• Kratter, K. (2014, July). Circumbinary Planets. Unsolved Problems in Astrophysics. Budapest, Hungary: Eotvos University, Budapest, Hungary.
• Kratter, K. (2014, June). Binary and Planet Formation around the Coolest Stars. Cool Stars 18. Flagstaff, AZ: Lowell Observatory.
• Kratter, K. (2014, Nov). Binaries and Planets. YCAA Seminar. Yale: Yale.
• Kratter, K. (2014, Sep). Binaries and Planets. Colloquium. University of Toronto: University of Toronto.

Others

• Best, W., Allers, K., Biller, B., Bowler, B., Dupuy, T. J., Fontanive, C., Kratter, K., Kraus, A. L., Lu, J. R., Morley, C., Offner, S., Reiter, M., Rizzuto, A., & Zhou, Y. (2021). "A Census to the Bottom of the IMF in Westerlund 2: Atmospheres, Disks, Accretion, and Demographics".
• Kratter, K. M. (2011). Accretion Disks and the Formation of Stellar Systems.