Tau Coronae Borealis

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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]
Spectral type K0 III-IV[4]
U−B color index +0.86[2]
B−V color index +1.01[2]
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]
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

Tau Coronae Borealis, Latinized from τ Coronae Borealis, is a probable astrometric binary[3] star system in the northern constellation of Corona Borealis. It is visible to the naked eye with a combined apparent visual magnitude of 4.76.[2] As of 2014, the pair had an angular separation of 2.20 arc seconds along a position angle of 186°.[8] 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.[9]

The brighter component is a magnitude 4.89[3] K-type star with a stellar classification of K0 III-IV,[4] having a spectrum that shows mixed traits of a 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.[10] 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] The secondary companion is a magnitude 13.2 star.[8]


  1. ^ a b c d e f 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. ^ a b c d 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. ^ a b c 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. ^ a b Eggen, O. J. (1962), "Space-velocity vectors for 3483 stars with proper motion and radial velocity", Royal Observatory Bulletin, 51, Bibcode:1962RGOB...51...79E.
  5. ^ a b c 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. ^ a b Mason, B. D.; et al. (2014), "The Washington Visual Double Star Catalog", The Astronomical Journal, 122: 3466–3471, Bibcode:2001AJ....122.3466M, doi:10.1086/323920
  9. ^ 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.
  10. ^ 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.