Detection of a Low-mass Stellar Companion to the Accelerating A2IV Star HR 1645
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.
- Publication:
-
The Astronomical Journal
- Pub Date:
- December 2019
- DOI:
- 10.3847/1538-3881/ab4ef7
- arXiv:
- arXiv:1910.10172
- Bibcode:
- 2019AJ....158..226D
- Keywords:
-
- Astrometry;
- Radial velocity;
- Close binary stars;
- Coronographic imaging;
- Visual binary stars;
- 80;
- 1332;
- 254;
- 313;
- 1777;
- Astrophysics - Solar and Stellar Astrophysics;
- Astrophysics - Earth and Planetary Astrophysics;
- Astrophysics - Instrumentation and Methods for Astrophysics
- E-Print:
- 14 pages, 9 figures. Accepted for publication in the Astronomical Journal