Theta Circini

θ Circini

A light curve for Theta Circini, plotted from Hipparcos data
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Circinus
Right ascension 14h 56m 43.987s
Declination −62° 46′ 51.66″
Apparent magnitude (V) 4.81 to 5.65 (5.90 + 5.90)
Characteristics
Spectral type B3 Ve (B2 + B2)
B−V color index +0.00
Variable type GCAS
Astrometry
Proper motion (μ) RA: +102.65 mas/yr
Dec.: +9.35 mas/yr
Parallax (π)11.82±0.30 mas
Distance276 ± 7 ly
(85 ± 2 pc)
Absolute magnitude (MV)−2.43/−2.43
Orbit
Period (P)38.2±0.2 yr
Semi-major axis (a)0.08808±0.00073″
Eccentricity (e)0.2775±0.0080
Inclination (i)146.8±1.8°
Longitude of the node (Ω)223.8±3.0°
Periastron epoch (T)1993.76±0.24
Argument of periastron (ω)
(secondary)		64.7±4.9°
Details
θ Cir A
Mass9.3±0.6 M☉
Surface gravity (log g)3.38 cgs
Temperature19,099 K
Rotational velocity (v sin i)195±13 km/s
Age27.1±6.1 Myr
Other designations
θ Cir, CD−62°891, HD 131492, HIP 73129, HR 5551, SAO 252965
Database references
SIMBADdata

Theta Circini (θ Cir), is a binary star located in the southern constellation of Circinus, to the northwest of Alpha Circini. Its name is a Bayer designation that is Latinized from θ Circini, and abbreviated Theta Cir or θ Cir. This system is faintly visible to the naked eye as a point of light with an apparent visual magnitude of about five. Based upon an annual parallax shift of 11.82 mas, it is located at a distance of about 276 light years from the Sun.

This is an astrometric binary star system with an orbital period of about 38.2 years, an eccentricity of 0.2775, and an angular semimajor axis of 0.08808". The pair show a combined stellar classification of B3 Ve, which matches a B-type main sequence star. The 'e' suffix on the class indicates this is a Be star. Alternate classifications include B4 Vnp and B4npe, 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. The system behaves as a Gamma Cassiopeiae variable showing occasional outbursts of up to 0.27 in magnitude.

References

  1. ↑ "Hipparcos Tools Interactive Data Access". Hipparcos. ESA. Retrieved 8 December 2021.
  2. 1 2 3 4 5 6 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, S2CID 18759600.
  3. ↑ "Theta Cir". International Variable Star Index. AAVSO. Retrieved 2026-05-17.
  4. 1 2 3 Cvetkovic, Z.; Ninkovic, S. (June 2010), "On the Component Masses of Visual Binaries", Serbian Astronomical Journal, 180 (180): 71–80, Bibcode:2010SerAJ.180...71C, doi:10.2298/SAJ1080071C.
  5. 1 2 3 4 5 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.
  6. 1 2 3 4 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, S2CID 118362423.
  7. 1 2 3 Arnold, H. J. P.; et al. (1999), The Photographic Atlas of the Stars, CRC Press, p. 176, ISBN 0750306548.
  8. 1 2 Mason, Brian D.; et al. (October 2023), "Speckle Interferometry at SOAR in 2022", The Astronomical Journal, 166 (4): 139, Bibcode:2023AJ....166..139M, doi:10.3847/1538-3881/acedaf, ISSN 0004-6256..
  9. 1 2 3 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, S2CID 118629873.
  10. ↑ 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, S2CID 19016751.
  11. ↑ "tet Cir", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2017-01-18
  12. ↑ Mason, Brian D.; et al. (July 1997), "A Speckle Survey of Southern Be Stars", Be Star Newsletter, 32: 9–10, Bibcode:1997BeSN...32....9M.
  13. ↑ Adelman, S. J.; et al. (December 2000), "On the Variability of O4-B5 Luminosity Class III-V Stars", Information Bulletin on Variable Stars, 5008 (5008): 1, Bibcode:2000IBVS.5008....1A.