The Solar Neighborhood. XXX. Fomalhaut C
Abstract
LP 876-10 is a nearby active M4 dwarf in Aquarius at a distance of 7.6 pc. The star is a new addition to the 10 pc census, with a parallax measured via the REsearch Consortium On Nearby Stars (RECONS) astrometric survey on the Small and Moderate Aperture Research Telescope System's 0.9 m telescope. We demonstrate that the astrometry, radial velocity, and photometric data for LP 876-10 are consistent with the star being a third bound stellar component to the Fomalhaut multiple system, despite the star lying nearly 6° away from Fomalhaut A in the sky. The three-dimensional separation of LP 876-10 from Fomalhaut is only 0.77 ± 0.01 pc, and 0.987 ± 0.006 pc from TW PsA (Fomalhaut B), well within the estimated tidal radius of the Fomalhaut system (1.9 pc). LP 876-10 shares the motion of Fomalhaut within ~1 km s-1, and we estimate an interloper probability of ~10-5. Neither our echelle spectroscopy nor astrometry are able to confirm the close companion to LP 876-10 reported in the Washington Double Star Catalog (WSI 138). We argue that the Castor Moving Group to which the Fomalhaut system purportedly belongs, is likely to be a dynamical stream, and hence membership to the group does not provide useful age constraints for group members. LP 876-10 (Fomalhaut C) has now risen from obscurity to become a rare example of a field M dwarf with well-constrained age (440 ± 40 Myr) and metallicity. Besides harboring a debris disk system and candidate planet, Fomalhaut now has two of the widest known stellar companions.
- Publication:
-
The Astronomical Journal
- Pub Date:
- December 2013
- DOI:
- 10.1088/0004-6256/146/6/154
- arXiv:
- arXiv:1310.0764
- Bibcode:
- 2013AJ....146..154M
- Keywords:
-
- binaries: visual;
- stars: activity;
- stars: fundamental parameters;
- stars: individual: LP 876-10 Fomalhaut TW PsA;
- stars: rotation;
- Astrophysics - Solar and Stellar Astrophysics;
- Astrophysics - Earth and Planetary Astrophysics;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 43 pages, 5 figures, AJ, in press, emulateapj version can be downloaded at: http://www.pas.rochester.edu/~emamajek/fomc/index.html