Omicron Cassiopeiae

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ο Cassiopeiae
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Cassiopeia
Right ascension 00h 44m 43.51867s[1]
Declination +48° 17′ 03.7136″[1]
Apparent magnitude (V) 4.50[2]
Spectral type B5IIIe[2]
U−B color index −0.53[3]
B−V color index −0.06[3]
Variable type γ Cas
Radial velocity (Rv) −12.36 ± 0.41[4] km/s
Proper motion (μ) RA: 18.84[1] mas/yr
Dec.: -7.18[1] mas/yr
Parallax (π) 4.64 ± 0.38[1] mas
Distance 700 ± 60 ly
(220 ± 20 pc)
Absolute magnitude (MV) −2.55 / 0.35[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) JD 2452792.2 ± 0.6
Argument of periastron (ω)
Semi-amplitude (K1)
21.593 ± 0.071 km/s
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
22 Cas, BD+47° 183, FK5 25, HD 4180, HIP 3504, HR 193, SAO 36620, ADS 622, CCDM J00447+4817
Database references
ο Cas B
Map of the Bayer-designated stars in Cassiopeia. Omicron Cassiopeiae is circled.

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.[1] It is visible to the naked eye with an apparent magnitude of 4.50.[2]

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.[5] 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.[4] 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.[5] Because it has a similar proper motion to the central system, it is assumed to be gravitationally bound.[6]


  1. ^ a b c d e f van Leeuwen, F.; et al. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752Freely accessible. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. 
  2. ^ a b c "* omi Cas". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved December 27, 2016. 
  3. ^ 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. 
  4. ^ a b c d e f g h Koubský, P.; Hummel, C. A.; Harmanec, P.; Tycner, C.; Van Leeuwen, F.; Yang, S.; Šlechta, M.; Božić, H.; Zavala, R. T.; Ruždjak, D.; Sudar, D. (2010). "Properties and nature of Be stars". Astronomy and Astrophysics. 517: A24. Bibcode:2010A&A...517A..24K. doi:10.1051/0004-6361/201014477. 
  5. ^ a b Koubský, Pavel; Ak, Hasan; Harmanec, Petr; Yang, Stephenson; Božić, Hrvoje (2004). "The Be star omicron Cassiopeiae". Koubský, P., Ak, H., Harmanec, P., Yang, S., & Božić, H. 310: 387. Bibcode:2004ASPC..310..387K. 
  6. ^ Pourbaix, D.; et al. (2004). "SB9: The ninth catalogue of spectroscopic binary orbits". Astronomy and Astrophysics. 424 (2): 727. arXiv:astro-ph/0406573Freely accessible. Bibcode:2004A&A...424..727P. doi:10.1051/0004-6361:20041213.