HD 861 is a spectroscopic binary star system in the deep northern constellation of Cassiopeia. With an apparent magnitude of 6.622, the star is faintly visible to the naked eye under very dark skies and readily visible using binoculars.[8] It is located approximately 403 light-years (124 parsecs) distant according to Gaia EDR3parallax measurements, and is moving further away at a heliocentric radial velocity of 8.80 km/s.
Stellar properties
The primary star is a typical Am star, enriched in iron and especially so in barium but depleted in carbon, oxygen and calcium. At an age of 724 million (108.86) years, it is currently a main-sequence starfusinghydrogen into helium at its core. It will continue to do so for the next 320 million years until it runs out of core hydrogen at 1.05 billion (109.02) years old, at which point it will leave the main sequence and enter the subgiant phase.[4]
The orbital properties of the companion were first determined in 1971 by Acker, with an orbital period of 11.2153 days and an eccentricity of 0.22.[9] In 2002, however, Debernardi found an entirely different set of orbital parameters in his PhDthesis and also discovered the stellar spectra of the secondary star. This new orbit has a longer period of 15.9696 days and a lower eccentricity of 0.124. This was backed up by Budaj et al.,[10] who also independently found the secondary spectra and obtained a mass ratio between the two stars that agreed with Debernardi's research.[4]
^ abHøg, E.; et al. (February 2000). "The Tycho-2 Catalogue of the 2.5 Million Brightest Stars". Astronomy and Astrophysics. 355 (1): L27 –L30. Bibcode:2000A&A...355L..27H.
^Acker, A. (September 1971). "Orbital elements of the spectroscopic binaries HD 24733 and HD 861". Astronomy & Astrophysics (in French). 14: 189. Bibcode:1971A&A....14..189A.
^Budaj, J.; Iliev, I. Kh.; Fenovcik, M.; Barzova, I.; Richards, M. T.; Geordzheva, E. (12 March 2004). "Discovery of the Secondary in the Spectrum of the SB1 System HD 861". Information Bulletin on Variable Stars. 5509 (1). International Astronomical Union. Bibcode:2004IBVS.5509....1B. ISSN0374-0676.
