Omicron Cassiopeiae
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| 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 | B2-5III-Ve(shell)[2] |
| U−B color index | −0.53[3] |
| B−V color index | −0.06[3] |
| Variable type | γ Cas[2] |
| Astrometry | |
| Radial velocity (Rv) | −12.36±0.41[4] km/s |
| Proper motion (μ) | RA: +17.415 mas/yr[1] Dec.: −8.947 mas/yr[1] |
| Parallax (π) | 4.7046±0.4306 mas[5] |
| Distance | 690 ± 60 ly (210 ± 20 pc) |
| Absolute magnitude (MV) | −2.55 / 0.35[4] |
| Orbit[4] | |
| 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) | 2452792.2±0.6 JD |
| Argument of periastron (ω) (secondary) | 0° |
| Semi-amplitude (K1) (primary) | 21.593±0.071 km/s |
| Details[4] | |
| ο Cas Aa | |
| Mass | 6.2 M☉ |
| Radius | 8.0 R☉ |
| Surface gravity (log g) | 3.284[6] cgs |
| Temperature | 14,438[6] K |
| Rotational velocity (v sin i) | 208±13[6] km/s |
| ο Cas Ab | |
| Mass | ~5 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[7] | |
| Database references | |
| SIMBAD | ο Cas A |
| ο Cas B | |
Omicron Cassiopeiae is a triple star system[6] 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.[5] It is visible to the naked eye with a slightly variable apparent magnitude of about 4.5.
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.[4]
The primary of this spectroscopic binary is a blue-white B-type giant star.[8] 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),[6] although because the pole is inclined 36 degrees,[4] its projected rotational velocity is 208 km/s.[6] 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.[4] It is possible that the secondary is a pair of early A-type main-sequence stars.[4]
A more distant companion, ο Cassiopeiae B, lies 33.6 arcseconds away. It is an eleventh-magnitude, F-type main-sequence star.[8] Because it has a similar proper motion to the central system, it is assumed to be gravitationally bound.[9]
References
- ^ a b c Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
- ^ a b c Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
- ^ a b Johnson, H. L. (1966). "UBVRIJKL Photometry of the Bright Stars". Communications of the Lunar and Planetary Laboratory. 4: 99. Bibcode:1966CoLPL...4...99J.
- ^ a b c d e f g h i Koubský, P.; et al. (2010). "Properties and nature of Be stars. 28. Implications of systematic observations for the nature of the multiple system with the Be star o Cassiopeæ and its circumstellar environment". Astronomy and Astrophysics. 517: A24. Bibcode:2010A&A...517A..24K. doi:10.1051/0004-6361/201014477.
- ^ a b Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
- ^ a b c d e f Touhami, Y.; et al. (May 2013). "A CHARA Array Survey of Circumstellar Disks around Nearby Be-type Stars". The Astrophysical Journal. 768 (2). id. 128. arXiv:1302.6135. Bibcode:2013ApJ...768..128T. doi:10.1088/0004-637X/768/2/128.
- ^ "omi Cas". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2025-10-14.
- ^ a b Koubský, Pavel; et al. (2004). "The Be star omicron Cassiopeiae". IAU Colloq. 193: Variable Stars in the Local Group. 310: 387. Bibcode:2004ASPC..310..387K.
- ^ Pourbaix, D.; et al. (2004). "SB9: The ninth catalogue of spectroscopic binary orbits". Astronomy and Astrophysics. 424 (2): 727–732. arXiv:astro-ph/0406573. Bibcode:2004A&A...424..727P. doi:10.1051/0004-6361:20041213. S2CID 119387088.