Tau2 Capricorni

Tau2 Capricorni, Latinized from τ2 Capricorni, is a triple star[2] system in the constellation Capricornus. It is approximately 1,100 light years from Earth based on parallax. The system has a blue-white hue and a combined apparent visual magnitude of +5.20.[2] Because it is positioned near the ecliptic, τ2 Capricorni can be occulted by the Moon.[9]

For other stars with this Bayer designation, see τ Capricorni.
Tau2 Capricorni
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Capricornus
Right ascension  20h 39m 16.31779s[1]
Declination +14° 57′ 17.1352″[1]
Apparent magnitude (V) 5.20 (5.77 + 9.5 + 6.19)[2]
Characteristics
Spectral type B6III + ? + B6IV[2]
Astrometry
Radial velocity (Rv)−4.1±2.1[3] km/s
Proper motion (μ) RA: +2.62[1] mas/yr
Dec.: −19.46[1] mas/yr
Parallax (π)2.87 ± 0.65[1] mas
Distanceapprox. 1,100 ly
(approx. 350 pc)
Orbit[4]
Primaryτ2 Cap A
Companionτ2 Cap B
Period (P)420 yr
Semi-major axis (a)0.48″
Eccentricity (e)0.73
Inclination (i)75°
Longitude of the node (Ω)93.0°
Periastron epoch (T)1915.0
Argument of periastron (ω)
(secondary)		270°
Details
A
Mass5.01±0.35[5] M☉
Luminosity (bolometric)1,893[5] L☉
Surface gravity (log g)3.90[6] cgs
Temperature15,439[6] K
Metallicity [Fe/H]0.14[6] dex
Rotational velocity (v sin i)170[7] km/s
Other designations
τ2 Cap, 14 Capricorni, BD−15°5743, GC 28748, HD 196662, HIP 101923, HR 7889, SAO 163771, ADS 14099, CCDM J20392-1457, WDS J20393-1457[8]
Database references
SIMBADdata

The primary, component A, is a B-type giant with a stellar classification of B6III and an apparent magnitude of +5.8.[2] It has five[5] times the mass of the Sun and is spinning rapidly with a projected rotational velocity of 170 km/s.[7] The star is radiating 1,893[5] times the luminosity of the Sun from its photosphere at an effective temperature of 15,439 K.[6]

At an angular separation of only 0.34 arcseconds is the companion, component B, a B-type subgiant star with a class of B6IV[2] and an apparent magnitude of +6.3. These two stars orbit around their common centre of mass once every 420 years.[4] A possible third component with an apparent magnitude of +9.5,[2] detected by studying the star during occultation, is located 0.052 arcseconds away from the A component.[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. Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x.
  3. Kharchenko, N. V.; et al. (2007), "Astrophysical supplements to the ASCC-2.5: Ia. Radial velocities of ˜55000 stars and mean radial velocities of 516 Galactic open clusters and associations", Astronomische Nachrichten, 328 (9): 889, arXiv:0705.0878, Bibcode:2007AN....328..889K, doi:10.1002/asna.200710776.
  4. Hartkopf, W. I.; et al. (June 30, 2006), Sixth Catalog of Orbits of Visual Binary Stars, United States Naval Observatory, retrieved 2017-06-02.
  5. Hohle, M. M.; et al. (2010), "Masses and luminosities of O- and B-type stars and red supergiants", Astronomische Nachrichten, 331 (4): 349, arXiv:1003.2335, Bibcode:2010AN....331..349H, doi:10.1002/asna.200911355.
  6. Koleva, M.; Vazdekis, A. (February 2012), "Stellar population models in the UV. I. Characterisation of the New Generation Stellar Library", Astronomy & Astrophysics, 538: A143, arXiv:1111.5449, Bibcode:2012A&A...538A.143K, doi:10.1051/0004-6361/201118065.
  7. Abt, Helmut A.; et al. (2002), "Rotational Velocities of B Stars", The Astrophysical Journal, 573 (1): 359–365, Bibcode:2002ApJ...573..359A, doi:10.1086/340590.
  8. "tau Cap". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-08-30.
  9. Radick, R.; Lien, D. (August 1980), "Illinois occultation summary. I. 1977-1978", Astronomical Journal, 85: 1053–1061, Bibcode:1980AJ.....85.1053R, doi:10.1086/112767.
  10. Hoffleit, Dorrit; Jaschek, Carlos (1991), "The Bright star catalogue", New Haven, Bibcode:1991bsc..book.....H.
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