Omicron Cassiopeiae
Star in the constellation Cassiopeia
From Wikipedia, the free encyclopedia
Omicron Cassiopeiae is a triple star system[7] in the constellation Cassiopeia. Its name is a Bayer designation that is Latinized from ο Cassiopeiae, and abbreviated Omicron Cas or ο Cas. This star is approximately 690 light-years (210 pc) 700 light-years from Earth, based on its parallax.[6] It is visible to the naked eye with a slightly variable apparent magnitude of about 4.5.
  | |
| Observation data Epoch J2000.0 Equinox ICRS | |
|---|---|
| Constellation | Cassiopeia |
| Right ascension | 00h 44m 43.519s[1] |
| Declination | +48° 17′ 03.73″[1] |
| Apparent magnitude (V) | 4.30 to 4.62[2] |
| Characteristics | |
| Spectral type | B3Ve (Aa) B7V (Ab2) B7V (Ab2)[3] |
| U−B color index | −0.53[4] |
| B−V color index | −0.06[4] |
| Variable type | γ Cas[2] |
| Astrometry | |
| Radial velocity (Rv) | −12.36±0.41[5] km/s |
| Proper motion (μ) | RA: +17.415 mas/yr[1] Dec.: −8.947 mas/yr[1] |
| Parallax (π) | 4.7046±0.4306 mas[6] |
| Distance | 690 ± 60 ly (210 ± 20 pc) |
| Absolute magnitude (MV) | −2.55 / 0.35[5] |
| Orbit[5] | |
| Primary | ο Cas Aa |
| Name | ο Cas Ab |
| Period (P) | 1031.55 d |
| Semi-major axis (a) | 0.0170±0.0006″ |
| Eccentricity (e) | 0 |
| Inclination (i) | 115.0±2.6° |
| Longitude of the node (Ω) | 267.3±0.8° |
| Periastron epoch (T) | 2452792.2±0.6 JD |
| Argument of periastron (ω) (secondary) | 0° |
| Semi-amplitude (K1) (primary) | 21.593±0.071 km/s |
| Orbit[3] | |
| Primary | Ab1 |
| Name | Ab2 |
| Period (P) | 11.66043 ± 0.000031 |
| Eccentricity (e) | 0 (fixed) |
| Periastron epoch (T) | 60529.5023 ± 0.0078 |
| Semi-amplitude (K1) (primary) | 75.79 ± 0.45 km/s |
| Semi-amplitude (K2) (secondary) | 81.47 km/s |
| Details[5] | |
| ο Cas Aa | |
| Mass | 6.07[3] M☉ |
| Radius | 8.0 R☉ |
| Surface gravity (log g) | 3.284[7] cgs |
| Temperature | 14,438[7] K |
| Rotational velocity (v sin i) | 208±13[7] km/s |
| ο Cas Ab1 | |
| Mass | 3.37 [3] M☉ |
| ο Cas Ab2 | |
| Mass | 3.26[3] M☉ |
| Other designations | |
| ο Cas, 22 Cassiopeiae, BD+47°183, FK5 25, HD 4180, HIP 3504, HR 193, SAO 36620, ADS 622, CCDM J00447+4817[8] | |
| Database references | |
| SIMBAD | ο Cas A |
| ο Cas B | |
The primary component, ο Cassiopeiae A, is a spectroscopic binary, and its close companion completes one orbit every 2.83 years (1,031.55 days). The system has also been resolved with interferometry.[5]
The primary of this spectroscopic binary is a blue-white B-type giant star.[9] It is classified as a Gamma Cassiopeiae variable and its brightness varies from magnitude 4.30 to 4.62. It is rotating at a speed of 249 km/s at its equator (close to its theoretical break-up velocity of 332 km/s),[7] although because the pole is inclined 36 degrees,[5] its projected rotational velocity is 208 km/s.[7] The nature of the secondary is not well known. Despite the fact that the secondary is 2.9 magnitudes dimmer than the primary, the secondary appears to have a mass similar to, or even larger than primary.[5] It is possible that the secondary is a pair of early A-type main-sequence stars.[5]
A more distant companion, ο Cassiopeiae B, lies 33.6 arcseconds away. It is an eleventh-magnitude, F-type main-sequence star.[9] Because it has a similar proper motion to the central system, it is assumed to be gravitationally bound.[10]