Orbital Architectures of Planet-Hosting Binaries: I. Forming Five Small Planets in the Truncated Disk of Kepler-444A

Creators: Dupuy, Trent J.; Kratter, Kaitlin M.; Kraus, Adam L.; Isaacson, Howard; Mann, Andrew W.; Ireland, Michael J.; Howard, Andrew W.; Huber, Daniel

Abstract

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^(+0.9)_(-1.0) 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 ≈1.5 M⊕ 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.

Additional Information

© 2016 The American Astronomical Society. Received 2015 November 3; accepted 2015 December 4; published 2016 January 22. Data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. This work was supported by a NASA Keck PI Data Award, administered by the NASA Exoplanet Science Institute. K.M.K. was supported by NSF AST-1410174. We thank Will Best for assistance with some Keck/NIRC2 observations. It is a pleasure to thank Joel Aycock, Carolyn Jordan, Jason McIlroy, Luca Rizzi, Terry Stickel, Hien Tran, and the Keck Observatory staff for assistance with our Keck AO observations. The HIRES data presented here were obtained in collaboration with Geoff Marcy. We also thank James R. A. Davenport for distributing his IDL implementation of the cubehelix color scheme (Green 2011). Our research has employed the 2MASS data products; NASA's Astrophysical Data System; and the SIMBAD database operated at CDS, Strasbourg, France. Finally, the authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Facility: Keck:II - (NGS AO - , NIRC2 - ), Keck:I(HIRES) - KECK I Telescope.

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Submitted - 1512.03428.pdf

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