Omicron Cassiopeiae
Star in the constellation Cassiopeia
title: "Omicron Cassiopeiae" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["b-type-giants", "f-type-main-sequence-stars", "gamma-cassiopeiae-variable-stars", "spectroscopic-binaries", "triple-star-systems", "cassiopeia-(constellation)", "bayer-objects", "bright-star-catalogue-objects", "durchmusterung-objects", "flamsteed-objects", "henry-draper-catalogue-objects", "hipparcos-objects"] description: "Star in the constellation Cassiopeia" topic_path: "science/astronomy" source: "https://en.wikipedia.org/wiki/Omicron_Cassiopeiae" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0
::summary Star in the constellation Cassiopeia ::
| name = ο Cassiopeiae | image= |image=Cassiopeia IAU.svg|alt=|float=center|width=260 |label=|position=right |mark=Red circle.svg|mark_width=8|mark_link=ο Cas |x%=54.5|y%=72.1 | caption = Location of ο Cassiopeiae (circled) | epoch = J2000.0 | constell = Cassiopeia | ra = | dec = | appmag_v = | type = | class = B2-5III-Ve(shell) | b-v = −0.06 | u-b = −0.53 | variable = γ Cas | radial_v = | prop_mo_ra = +17.415 | prop_mo_dec = −8.947 | pm_footnote = | parallax = 4.7046 | p_error = 0.4306 | parallax_footnote = | absmag_v = −2.55 / 0.35 | reference = | primary = ο Cas Aa | name = ο Cas Ab | period_unitless = 1031.55 d | axis = 0.0170 | periastron = | inclination = 115.0 | node = 267.3 | eccentricity = 0 | periarg = 0 | k1 = 21.593 | source = | component1 = ο Cas Aa | mass = 6.2 | radius = 8.0 | temperature = 14,438 | luminosity = | gravity = 3.284 | metal_fe = | age_myr = | rotational_velocity = 208 | component2 = ο Cas Ab | mass2 = ~5 | names = | Simbad=omi+Cas | sn=ο Cas A | Simbad2=BD%2B47+183B | sn2=ο Cas B
Omicron Cassiopeiae is a triple star system 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 ly 700 light-years from Earth, based on its parallax. It is visible to the naked eye with a slightly variable apparent magnitude of about 4.5.
::figure[src="https://upload.wikimedia.org/wikipedia/commons/b/b9/OmicronCasLightCurve.png" caption="visual band]] [[light curve]] for Omicron Cassiopeiae, adapted from Koubský ''et al.'' (2010)"] ::
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 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), although because the pole is inclined 36 degrees, its projected rotational velocity is 208 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.
References
| title=SB9: The ninth catalogue of spectroscopic binary orbits | display-authors=1 | last1=Pourbaix | first1=D. | last2=Tokovinin | first2=A. A. | last3=Batten | first3=A. H. | last4=Fekel | first4=F. C. | last5=Hartkopf | first5=W. I. | last6=Levato | first6=H. | last7=Morrell | first7=N. I. | last8=Torres | first8=G. | last9=Udry | first9=S. | journal=Astronomy and Astrophysics | year=2004 | volume=424 | issue=2 | pages=727–732 | doi=10.1051/0004-6361:20041213 | arxiv=astro-ph/0406573 | bibcode=2004A&A...424..727P | s2cid=119387088}}
| bibcode=2010A&A...517A..24K|doi=10.1051/0004-6361/201014477 | title=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 | journal=Astronomy and Astrophysics|volume=517|pages=A24|year=2010 | last1=Koubský|first1=P.|last2=Hummel|first2=C. A.|last3=Harmanec|first3=P. | last4=Tycner|first4=C.|last5=Van Leeuwen|first5=F.|last6=Yang|first6=S. | last7=Šlechta|first7=M.|last8=Božić|first8=H.|last9=Zavala|first9=R. T. | last10=Ruždjak|first10=D.|last11=Sudar|first11=D.|doi-access=}}
| title=The Be star omicron Cassiopeiae | volume=310 | pages=387 | bibcode=2004ASPC..310..387K | last1=Koubský | first1=Pavel | last2=Ak | first2=Hasan | last3=Harmanec | first3=Petr | last4=Yang | first4=Stephenson | last5=Božić | first5=Hrvoje | journal=IAU Colloq. 193: Variable Stars in the Local Group | year=2004 }}
| bibcode=2009yCat....102025S | title=VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)|journal=VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S | volume=1|display-authors=etal|last1=Samus|first1=N. N. | last2=Durlevich|first2=O. V.|year=2009}}
| title=UBVRIJKL Photometry of the Bright Stars | last=Johnson | first=H. L. | journal=Communications of the Lunar and Planetary Laboratory | volume=4 | pages=99 | date=1966 | bibcode=1966CoLPL...4...99J }}
| title=A CHARA Array Survey of Circumstellar Disks around Nearby Be-type Stars | last1=Touhami | first1=Y. | last2=Gies | first2=D. R. | last3=Schaefer | first3=G. H. | last4=McAlister | first4=H. A. | last5=Ridgway | first5=S. T. | last6=Richardson | first6=N. D. | last7=Matson | first7=R. | last8=Grundstrom | first8=E. D. | last9=ten Brummelaar | first9=T. A. | last10=Goldfinger | first10=P. J. | last11=Sturmann | first11=L. | last12=Sturmann | first12=J. | last13=Turner | first13=N. H. | last14=Farrington | first14=C. | display-authors=1 | journal=The Astrophysical Journal | volume=768 | issue=2 | at=id. 128 | date=May 2013 | doi=10.1088/0004-637X/768/2/128 | arxiv=1302.6135 | bibcode=2013ApJ...768..128T }}
References
- "omi Cas".
- {{cite Gaia DR3. 390548351252549760
- {{cite DR2. 390548351252549760
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