Robert J. de Rosa, Stanford University
Eric L. Nielsen, Stanford University
Julien Rameau, Université Grenoble Alpes
Gaspard Duchêne, Université Grenoble Alpes
Alexandra Z. Greenbaum, University of Michigan, Ann Arbor
Jason J. Wang, California Institute of Technology
S. Mark Ammons, Lawrence Livermore National Laboratory
Vanessa P. Bailey, Jet Propulsion Laboratory
Travis Barman, The University of Arizona
Joanna Bulger, University Hawaii Institute for Astronomy
Jeffrey Chilcote, University of Notre Dame
Tara Cotten, University of Georgia
Rene Doyon, Institut de Recherche sur les Exoplanètes
Thomas M. Esposito, University of California, Berkeley
Michael P. Fitzgerald, University of California, Los Angeles
Katherine B. Follette, Amherst College
Benjamin L. Gerard, University of Victoria
Stephen J. Goodsell, Gemini Observatory
James R. Graham, University of California, Berkeley
Pascale Hibon, Gemini ObservatorySouthern Operations Center
Justin Hom, School of Earth and Space Exploration
Li Wei Hung, US National Park Service
Patrick Ingraham, Large Synoptic Survey Telescope
Paul Kalas, University of California, Berkeley
Quinn Konopacky, Center for Astrophysics & Space Sciences
James E. Larkin, University of California, Los Angeles
Bruce Macintosh, Stanford University
Jérôme Maire, Center for Astrophysics & Space Sciences
Franck Marchis, SETI Institute
Mark S. Marley, NASA Ames Research Center
Christian Marois, University of Victoria
Stanimir Metchev, Western University
Kimberly Ward-Duong, Amherst CollegeFollow
et al, Various Institutions

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Publication Title

Astrophysical Journal


The ∼500 Myr A2IV star HR 1645 has one of the most significant low-amplitude accelerations of nearby early-type stars measured from a comparison of the Hipparcos and Gaia astrometric catalogs. This signal is consistent with either a stellar companion with a moderate mass ratio (q ∼ 0.5) on a short period (P < 1 yr), or a substellar companion at a separation wide enough to be resolved with ground-based high-contrast imaging instruments; long-period equal-mass ratio stellar companions that are also consistent with the measured acceleration are excluded with previous imaging observations. The small but significant amplitude of the acceleration made HR 1645 a promising candidate for targeted searches for brown dwarf and planetary-mass companions around nearby, young stars. In this paper we explore the origin of the astrometric acceleration by modeling the signal induced by a wide-orbit M8 companion discovered with the Gemini Planet Imager, as well as the effects of an inner short-period spectroscopic companion discovered a century ago but not since followed up. We present the first constraints on the orbit of the inner companion, and demonstrate that it is a plausible cause of the astrometric acceleration. This result demonstrates the importance of vetting of targets with measured astrometric acceleration for short-period stellar companions prior to conducting targeted direct imaging surveys for wide-orbit substellar companions.










© 2019. The American Astronomical Society.


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