Detection of a Low-mass Stellar Companion to the Accelerating A2IV Star HR 1645
Duchêne, Gaspard; Esposito, Thomas M.; Hom, Justin; Oppenheimer, Rebecca; Kalas, Paul; De Rosa, Robert J.; Fitzgerald, Michael P.; Macintosh, Bruce; Metchev, Stanimir; Millar-Blanchaer, Maxwell A.; Nielsen, Eric L.; Pueyo, Laurent; Rantakyrö, Fredrik T.; Soummer, Remi; Barman, Travis; Graham, James R.; Marley, Mark S.; Song, Inseok; Marchis, Franck; Schneider, Adam C.; Wolff, Schuyler; Sivaramakrishnan, Anand; Marois, Christian; Chilcote, Jeffrey; Ward-Duong, Kimberly; Wang, Jason J.; Bailey, Vanessa P.; Ammons, S. Mark; Ren, Bin; Follette, Katherine B.; Bulger, Joanna; Cotten, Tara; Doyon, Rene; Goodsell, Stephen J.; Greenbaum, Alexandra Z.; Hibon, Pascale; Hung, Li-Wei; Ingraham, Patrick; Konopacky, Quinn; Larkin, James E.; Maire, Jérôme; Palmer, David; Patience, Jennifer; Poyneer, Lisa; Rajan, Abhijith; Rameau, Julien; Savransky, Dmitry; Thomas, Sandrine; Wallace, J. Kent; Wiktorowicz, Sloane; Gerard, Benjamin L.; Perrin, Marshall; Ruffio, Jean-Baptiste; Tallis, Melisa
United States, France, Canada, Chile, Netherlands
Abstract
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.