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) 4.30 - 4.62[2]
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]
Radial velocity (Rv)−12.36 ± 0.41[4] km/s
Proper motion (μ) RA: 18.84[5] mas/yr
Dec.: -7.18[5] mas/yr
Parallax (π)4.7046 ± 0.4306[5] mas
Distance690 ± 60 ly
(210 ± 20 pc)
Absolute magnitude (MV)−2.55 / 0.35[4]
Primaryο Cas Aa
Companionο 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
Mass6.2 M
Radius8.0 R
Temperature14,000 K
Rotational velocity (v sin i)220 km/s
ο Cas Ab
Mass~5 M
Other designations
22 Cassiopeiae, 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 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.[6] 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 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.[6] Because it has a similar proper motion to the central system, it is assumed to be gravitationally bound.[7]


  1. ^ a b c Van Leeuwen, Floor (2007). "Validation of the new Hipparcos reduction". Astronomy & Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
  2. ^ 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.
  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 c 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.
  6. ^ a b Koubský, Pavel; Ak, Hasan; Harmanec, Petr; Yang, Stephenson; Božić, Hrvoje (2004). "The Be star omicron Cassiopeiae". 310: 387. Bibcode:2004ASPC..310..387K. Cite journal requires |journal= (help)
  7. ^ Pourbaix, D.; et al. (2004). "SB9: The ninth catalogue of spectroscopic binary orbits". Astronomy and Astrophysics. 424 (2): 727. arXiv:astro-ph/0406573. Bibcode:2004A&A...424..727P. doi:10.1051/0004-6361:20041213.