Astronomy:Theta Circini

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Short description: Star in the constellation Circinus
θ Circini
ThetaCirLightCurve.png
A light curve for Theta Circini, plotted from Hipparcos data[1]
Observation data
Equinox J2000.0]] (ICRS)
Constellation Circinus
Right ascension  14h 56m 43.987s[2]
Declination −62° 46′ 51.66″[2]
Apparent magnitude (V) 5.110[3] (5.90 + 5.90)[4]
Characteristics
Spectral type B3 Ve[5] (B2 + B2)[4]
B−V color index +0.00[3]
Variable type GCAS[6]
Astrometry
Proper motion (μ) RA: +102.65[2] mas/yr
Dec.: +9.35[2] mas/yr
Parallax (π)11.82 ± 0.30[2] mas
Distance276 ± 7 ly
(85 ± 2 pc)
Absolute magnitude (MV)−2.43/−2.43[4]
Orbit[5]
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[7] M☉
Surface gravity (log g)3.38[3] cgs
Temperature19,099[3] K
Rotational velocity (v sin i)195±13[8] km/s
Age27.1±6.1[7] Myr
Other designations
θ Cir, CD−62°891, HD 131492, HIP 73129, HR 5551, SAO 252965.[9]
Database references
SIMBADdata

Theta Circini (θ Cir), is a binary star located in the southern constellation of Circinus, to the northwest of Alpha Circini.[6] It is faintly visible to the naked eye with an apparent visual magnitude of 5.110.[3] Based upon an annual parallax shift of 11.82 mas,[2] it is located at a distance of about 276 light years from the Sun.

This is an astrometric binary[10] star system with an orbital period of about 39.6 years, an eccentricity of 0.3, and a semimajor axis of 85.64 mas.[5] The pair show a combined stellar classification of B3 Ve,[5] which matches a B-type main sequence star.[5] The 'e' suffix on the class indicates this is a Be star. Alternate classifications include B4 Vnp[7] and B4npe,[5] 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.[5] The system behaves as a Gamma Cassiopeiae variable[6] showing occasional outbursts of up to 0.27 in magnitude.[11]

References

  1. ↑ "Hipparcos Tools Interactive Data Access". ESA. https://www.cosmos.esa.int/web/hipparcos/interactive-data-access. 
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, doi:10.1051/0004-6361:20078357, Bibcode: 2007A&A...474..653V. 
  3. ↑ 3.0 3.1 3.2 3.3 3.4 Soubiran, C. et al. (June 2010), "The PASTEL catalogue of stellar parameters", Astronomy and Astrophysics 515: A111, doi:10.1051/0004-6361/201014247, Bibcode: 2010A&A...515A.111S. 
  4. ↑ 4.0 4.1 4.2 Cvetkovic, Z.; Ninkovic, S. (June 2010), "On the Component Masses of Visual Binaries", Serbian Astronomical Journal 180 (180): 71–80, doi:10.2298/SAJ1080071C, Bibcode: 2010SerAJ.180...71C. 
  5. ↑ 5.0 5.1 5.2 5.3 5.4 5.5 5.6 Mason, Brian D. et al. (September 2010), "Binary Star Orbits. IV. Orbits of 18 Southern Interferometric Pairs", The Astronomical Journal 140 (3): 735–743, doi:10.1088/0004-6256/140/3/735, Bibcode: 2010AJ....140..735M. 
  6. ↑ 6.0 6.1 6.2 Arnold, H. J. P. et al. (1999), The Photographic Atlas of the Stars, CRC Press, p. 176, ISBN 0750306548, https://books.google.com/books?id=YjcvJUfnWBAC&pg=PA176. 
  7. ↑ 7.0 7.1 7.2 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, doi:10.1111/j.1365-2966.2010.17434.x, Bibcode: 2011MNRAS.410..190T. 
  8. ↑ 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, doi:10.1051/0004-6361:20042229, Bibcode: 2005A&A...440..305F. 
  9. ↑ "tet Cir -- Be Star", SIMBAD Astronomical Database (Centre de Données astronomiques de Strasbourg), http://simbad.u-strasbg.fr/simbad/sim-id?Ident=tet+Cir, retrieved 2017-01-18. 
  10. ↑ Mason, Brian D. et al. (July 1997), "A Speckle Survey of Southern Be Stars", Be Star Newsletter 32: 9–10, Bibcode: 1997BeSN...32....9M. 
  11. ↑ 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. 

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