Omicron Cassiopeiae
| Observation data Epoch J2000.0 Equinox J2000.0 |
|
|---|---|
| Constellation | Cassiopeia |
| Right ascension | 00h 44m 43.51867s |
| Declination | +48° 17′ 03.7136″ |
| Apparent magnitude (V) | 4.50 |
| Characteristics | |
| Spectral type | B5IIIe |
| U−B color index | −0.53 |
| B−V color index | −0.06 |
| Variable type | γ Cas |
| Astrometry | |
| Radial velocity (Rv) | −12.36 ± 0.41 km/s |
| Proper motion (μ) |
RA: 18.84 mas/yr Dec.: -7.18 mas/yr |
| Parallax (π) | 4.64 ± 0.38mas |
| Distance | 700 ± 60 ly (220 ± 20 pc) |
| Absolute magnitude (MV) | −2.55 / 0.35 |
| Orbit | |
| Primary | ο Cas Aa |
| Companion | 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) | JD 2452792.2 ± 0.6 |
|
Argument of periastron (ω) (secondary) |
0° |
|
Semi-amplitude (K1) (primary) |
21.593 ± 0.071 km/s |
| Details | |
| ο Cas Aa | |
| Mass | 6.2 M☉ |
| Radius | 8.0 R☉ |
| Temperature | 14,000 K |
| Rotational velocity (v sin i) | 220 km/s |
| ο Cas Ab | |
| Mass | ~5 M☉ |
| Other designations | |
| Database references | |
| SIMBAD | ο Cas A |
| ο Cas B | |
Omicron Cassiopeiae (ο Cas, ο Cassiopeiae) is a triple star system in the constellation Cassiopeia. It is approximately 700 light-years from Earth, based on its parallax. It is visible to the naked eye with an apparent magnitude of 4.50.
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.
The primary of this spectroscopic binary is a blue-white B-type giant star. It is classified as a Gamma Cassiopeiae-type variable star and its brightness varies from magnitude 4.30 to 4.62. It is rotating at a speed of 375 km/s at its equator (close to its theoretical break-up velocity of 390 km/s), although because the pole is inclined 36 degrees, its projected rotational velocity is only 220 km/s. 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. It is possible that the secondary is a pair of early A-type main-sequence stars.
A more distant companion, ο Cassiopeiae B, lies 33.6 arcseconds away. It is an eleventh-magnitude, F-type main-sequence star. Because it has a similar proper motion to the central system, it is assumed to be gravitationally bound.
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