HD 861
Spectroscopic binary in the constellation Cassiopeia
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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 DR3 parallax measurements, and is moving further away at a heliocentric radial velocity of 8.80 km/s.
 | |
| Observation data Epoch J2000[1] Equinox J2000[1] | |
|---|---|
| Constellation | Cassiopeia[2] |
| Right ascension | 00h 13m 12.73037s[3] |
| Declination | +62° 02′ 27.1598″[3] |
| Apparent magnitude (V) | 6.622[4] |
| Characteristics | |
| Spectral type | A2m[5] + GV[6] |
| B−V color index | +0.208[4] |
| Astrometry | |
| Radial velocity (Rv) | 8.80±6.28[3] km/s |
| Proper motion (μ) | RA: 72.804[3] mas/yr Dec.: -19.171[3] mas/yr |
| Parallax (π) | 8.0883±0.0269 mas[3] |
| Distance | 403 ± 1 ly (123.6 ± 0.4 pc) |
| Absolute magnitude (MV) | 1.30 (A), 5.62 (B)[6] |
| Orbit[6] | |
| Primary | HD 861 A |
| Name | HD 861 B |
| Period (P) | 15.9696 d |
| Eccentricity (e) | 0.124 |
| Details[6] | |
| HD 861 A | |
| Mass | 2.04 M☉ |
| Radius | 2.775 ± 0.139[7] R☉ |
| Surface gravity (log g) | 4.00 cgs |
| Temperature | 8100 K |
| Metallicity [Fe/H] | 0.44 dex |
| Rotational velocity (v sin i) | 37 km/s |
| Age | 724 Myr |
| HD 861 B | |
| Mass | 0.95 M☉ |
| Surface gravity (log g) | 4.5 cgs |
| Temperature | 5500 K |
| Other designations | |
| AG+61°8, BD+61°16, GC 233, HD 861, HIP 1063, SAO 11044, PPM 12017, TIC 83612641, TYC 4018-687-1, GSC 04018-00687, 2MASS J00131272+6202271, Renson 130[1] | |
| Database references | |
| SIMBAD | HD 861 |
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 star fusing hydrogen 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.[6]
The secondary star is a G-type main-sequence star slightly less massive than the Sun and less than half as luminous.[6]
Orbit
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 PhD thesis 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.[6]
