Theta Circini

Theta Circini (θ Cir), is a binary star located in the southern constellation of Circinus, to the northwest of Alpha Circini.[5] It is faintly visible to the naked eye with an apparent visual magnitude of 5.110.[2] Based upon an annual parallax shift of 11.82 mas,[1] it is located at a distance of about 276 light years from the Sun.

θ Circini
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Circinus
Right ascension 14h 56m 43.987s[1]
Declination −62° 46′ 51.66″[1]
Apparent magnitude (V) 5.110[2] (5.90 + 5.90)[3]
Characteristics
Spectral type B3 Ve[4] (B2 + B2)[3]
B−V color index +0.00[2]
Variable type GCAS[5]
Astrometry
Proper motion (μ) RA: +102.65[1] mas/yr
Dec.: +9.35[1] mas/yr
Parallax (π)11.82 ± 0.30[1] mas
Distance276 ± 7 ly
(85 ± 2 pc)
Absolute magnitude (MV)−2.43/−2.43[3]
Orbit[4]
Period (P)39.62±0.78 yr
Semi-major axis (a)0.08564±0.00056″
Eccentricity (e)0.3014±0.0081
Inclination (i)153.3±2.0°
Longitude of the node (Ω)228.0±5.2°
Periastron epoch (T)1993.81±0.12
Argument of periastron (ω)
(secondary)		68.6±6.5°
Details
θ Cir A
Mass9.3±0.6[6] M☉
Surface gravity (log g)3.38[2] cgs
Temperature19,099[2] K
Rotational velocity (v sin i)195±13[7] km/s
Age27.1±6.1[6] Myr
Other designations
θ Cir, CD−62°891, HD 131492, HIP 73129, HR 5551, SAO 252965.[8]
Database references
SIMBADdata

This is an astrometric binary[9] star system with an orbital period of about 39.6 years, an eccentricity of 0.3, and a semimajor axis of 85.64 mas.[4] The pair show a combined stellar classification of B3 Ve,[4] which matches a B-type main sequence star.[4] The 'e' suffix on the class indicates this is a Be star. Alternate classifications include B4 Vnp[6] and B4npe,[4] with the 'n' indicating broad ("nebulous") absorption lines due to rotation and the 'p' meaning a chemically peculiar star. The two components appear to have similar visual magnitude, mass, and classification.[4] The system behaves as a Gamma Cassiopeiae variable[5] showing occasional outbursts of up to 0.27 in magnitude.[10]

References
  1. van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357.
  2. Soubiran, C.; et al. (June 2010), "The PASTEL catalogue of stellar parameters", Astronomy and Astrophysics, 515: A111, arXiv:1004.1069, Bibcode:2010A&A...515A.111S, doi:10.1051/0004-6361/201014247.
  3. Cvetkovic, Z.; Ninkovic, S. (June 2010), "On the Component Masses of Visual Binaries", Serbian Astronomical Journal, 180: 71–80, Bibcode:2010SerAJ.180...71C, doi:10.2298/SAJ1080071C.
  4. Mason, Brian D.; et al. (September 2010), "Binary Star Orbits. IV. Orbits of 18 Southern Interferometric Pairs", The Astronomical Journal, 140 (3): 735–743, Bibcode:2010AJ....140..735M, doi:10.1088/0004-6256/140/3/735.
  5. Arnold, H. J. P.; et al. (1999), The Photographic Atlas of the Stars, CRC Press, p. 176, ISBN 0750306548.
  6. Tetzlaff, N.; et al. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun", Monthly Notices of the Royal Astronomical Society, 410 (1): 190–200, arXiv:1007.4883, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x.
  7. Frémat, Y.; et al. (September 2005), "Effects of gravitational darkening on the determination of fundamental parameters in fast-rotating B-type stars", Astronomy and Astrophysics, 440 (1): 305–320, arXiv:astro-ph/0503381, Bibcode:2005A&A...440..305F, doi:10.1051/0004-6361:20042229.
  8. "tet Cir -- Be Star", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2017-01-18.
  9. Mason, Brian D.; et al. (July 1997), "A Speckle Survey of Southern Be Stars", Be Star Newsletter, 32: 9–10, Bibcode:1997BeSN...32....9M.
  10. Adelman, S. J.; et al. (December 2000), "On the Variability of O4-B5 Luminosity Class III-V Stars", Information Bulletin on Variable Stars (5008): 1, Bibcode:2000IBVS.5008....1A.
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