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]
| 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 mas[1] |
| Distance | approx. 1,100 ly (approx. 350 pc) |
| Orbit[4] | |
| Primary | τ2 Cap A |
| Companion | τ2 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 | |
| Mass | 5.01±0.35[5] M☉ |
| Luminosity (bolometric) | 1,893[5] L☉ |
| Surface gravity (log g) | 3.90[6] cgs |
| Temperature | 15,439[6] K |
| Metallicity [Fe/H] | 0.14[6] dex |
| Rotational velocity (v sin i) | 170[7] km/s |
| Other designations | |
| Database references | |
| SIMBAD | data |
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
edit- ^ a b c d e 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.
- ^ a b c d e f g 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, S2CID 14878976.
- ^ 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, S2CID 119323941.
- ^ a b Hartkopf, W. I.; et al. (June 30, 2006), Sixth Catalog of Orbits of Visual Binary Stars, United States Naval Observatory, archived from the original on 2017-04-30, retrieved 2017-06-02.
- ^ a b c d 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, S2CID 111387483.
- ^ a b c d 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, S2CID 53999614.
- ^ a b 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.
- ^ "tau Cap". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-08-30.
{{cite web}}: CS1 maint: postscript (link) - ^ 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.
- ^ Hoffleit, Dorrit; Jaschek, Carlos (1991), "The Bright star catalogue", New Haven, Bibcode:1991bsc..book.....H.