Tau Coronae Borealis

Tau Coronae Borealis, Latinized from τ Coronae Borealis, is a possible astrometric and spectroscopic binary star system in the northern constellation of Corona Borealis. It is visible to the naked eye with an apparent visual magnitude of 4.76.

Tau Coronae Borealis
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Corona Borealis
Right ascension  16h 08m 58.30151s[1]
Declination +36° 29′ 27.3740″[1]
Apparent magnitude (V) 4.76[2] (4.89 + 13.2)[3]
Characteristics
Spectral type K1 III-IV[4]
U−B color index +0.86[2]
B−V color index +1.01[2]
Astrometry
Radial velocity (Rv)−21.02±0.33[5] km/s
Proper motion (μ) RA: −37.02[1] mas/yr
Dec.: +340.44[1] mas/yr
Parallax (π)27.95 ± 1.24[1] mas
Distance117 ± 5 ly
(36 ± 2 pc)
Absolute magnitude (MV)+2.03[6]
Details[5]
Radius6 R☉
Luminosity16.2 L☉
Surface gravity (log g)3.1 cgs
Temperature4,742 K
Metallicity [Fe/H]−0.20 dex
Rotational velocity (v sin i)1.7 km/s
Other designations
τ CrB, 16 CrB, BD+36° 2699, HD 145328, HIP 79119, HR 6018, SAO 65108[7]
Database references
SIMBADdata

Tau CrB has a visible companion of visual magnitude 13.2 and they have been treated as a common proper motion pair.[8] As of 2014, the pair had an angular separation of 2.20 arc seconds along a position angle of 186°.[8] It has also been described as a spectroscopic binary, but there is no confirmation of this.[9] Due to an abnormal space motion, it has also been described as an astrometric binary although there is no orbit.[3]

Based upon an annual parallax shift of 27.95 mas as seen from Earth,[1] it is located about 117 light years from the Sun. At that distance, the visual magnitude of the system is diminished by an extinction factor of 0.04 due to interstellar dust.[10]

The primary component is a magnitude 4.89[3] K-type star with a stellar classification of K1 III-IV, having a spectrum that shows mixed traits of an evolved subgiant and giant star. It is catalogued as a red clump giant, which would indicate it is generating energy through helium fusion at its core.[11] The star has expanded to six times the Sun's radius and is radiating 16 times the solar luminosity from its photosphere at an effective temperature of 4,742 K.[5]

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. Nicolet, B. (1978), "Photoelectric photometric Catalogue of homogeneous measurements in the UBV System", Astronomy and Astrophysics Supplement Series, 34: 1–49, Bibcode:1978A&AS...34....1N.
  3. 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.
  4. Keenan, Philip C.; McNeil, Raymond C. (1989). "The Perkins Catalog of Revised MK Types for the Cooler Stars". The Astrophysical Journal Supplement Series. 71: 245. Bibcode:1989ApJS...71..245K. doi:10.1086/191373.
  5. Massarotti, Alessandro; et al. (January 2008), "Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity", The Astronomical Journal, 135 (1): 209–231, Bibcode:2008AJ....135..209M, doi:10.1088/0004-6256/135/1/209.
  6. Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015.
  7. "tau CrB". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-04-30.
  8. Mason, B. D.; et al. (2014), "The Washington Visual Double Star Catalog", The Astronomical Journal, 122 (6): 3466–3471, Bibcode:2001AJ....122.3466M, doi:10.1086/323920
  9. Hoffleit, D.; Warren, W. H. (1995). "VizieR Online Data Catalog: Bright Star Catalogue, 5th Revised Ed. (Hoffleit+, 1991)". VizieR On-line Data Catalog: V/50. Originally Published in: 1964BS....C......0H. 5050. Bibcode:1995yCat.5050....0H.
  10. Famaey, B.; et al. (January 2005), "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters", Astronomy and Astrophysics, 430 (1): 165–186, arXiv:astro-ph/0409579, Bibcode:2005A&A...430..165F, doi:10.1051/0004-6361:20041272.
  11. Alves, David R. (August 2000), "K-Band Calibration of the Red Clump Luminosity", The Astrophysical Journal, 539 (2): 732–741, arXiv:astro-ph/0003329, Bibcode:2000ApJ...539..732A, doi:10.1086/309278.
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