Tau Ursae Majoris

Tau Ursae Majoris (τ UMa) is the Bayer designation for a binary star in the northern circumpolar constellation of Ursa Major. It is visible to the naked eye, having an apparent visual magnitude of 4.66.[2] With an annual parallax shift of 25.82 mas,[1] it is located about 126 light years from the Sun. At that distance, the visual magnitude is diminished by an extinction factor of 0.19 due to interstellar dust.[9]

Tau Ursae Majoris
Location of τ Ursae Majoris (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Ursa Major
Right ascension  09h 10m 55.06553s[1]
Declination +63° 30′ 49.0553″[1]
Apparent magnitude (V) 4.66[2]
Characteristics
Spectral type kA5hF0mF5 II[3]
U−B color index +0.14[2]
B−V color index +0.35[2]
Astrometry
Radial velocity (Rv)−9.80±0.30[4] km/s
Proper motion (μ) RA: +102.37[1] mas/yr
Dec.: −63.55[1] mas/yr
Parallax (π)25.82 ± 0.54[1] mas
Distance126 ± 3 ly
(38.7 ± 0.8 pc)
Absolute magnitude (MV)+1.73[5]
Orbit[6]
Period (P)1,062.4 d
Eccentricity (e)0.48
Periastron epoch (T)2425721.6 JD
Argument of periastron (ω)
(secondary)		349.4°
Semi-amplitude (K1)
(primary)		3.9 km/s
Details
τ UMa A
Mass1.8±0.1[7] M☉
Luminosity16[8] L☉
Surface gravity (log g)3.86±0.43[9] cgs
Temperature7,343±100[9] K
Metallicity [Fe/H]+0.57±0.15[9] dex
Rotational velocity (v sin i)21[10] km/s
Other designations
τ UMa, 14 Ursae Majoris, BD+64°723, FK5 2727, HD 78362, HIP 45075, HR 3624, SAO 14796, WDS J09109+6331A[11]
Database references
SIMBADdata

This is a single-lined spectroscopic binary star system with an orbital period of 2.9 years and an eccentricity of 0.48.[6] The primary member, component A, is an evolved bright giant with a stellar classification of kA5hF0mF5 II.[3] This notation indicates the star's spectrum shows the calcium K lines of an A5 star, the hydrogen lines of an F0 star, and the metallic lines of an F5 star.[12] It is an evolved Am star of the ρ Puppis type, a class of evolved stars showing the Am chemical peculiarities.[13] It is located in the instability strip of the Hertzsprung–Russell diagram but is not thought to be variable.[7]

Naming

With φ, h, υ, θ, e, and f, it composed the Arabic asterism Sarīr Banāt al-Na'sh, the Throne of the daughters of Na'sh, and Al-Haud, the Pond.[14] According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Al-Haud were the title for seven stars : f as Alhaud I, this star (τ) as Alhaud II, e as Alhaud III, h as Alhaud IV, θ as Alhaud V, υ as Alhaud VI and φ as Alhaud VII .[15]

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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. Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV Data, SIMBAD, Bibcode:1986EgUBV........0M.
  3. Gray, R. O.; et al. (July 2006), "Contributions to the Nearby Stars (NStars) Project: spectroscopy of stars earlier than M0 within 40 pc-The Southern Sample", The Astronomical Journal, 132 (1): 161–170, arXiv:astro-ph/0603770, Bibcode:2006AJ....132..161G, doi:10.1086/504637.
  4. de Bruijne, J. H. J.; Eilers, A.-C. (October 2012), "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project", Astronomy & Astrophysics, 546: 14, arXiv:1208.3048, Bibcode:2012A&A...546A..61D, doi:10.1051/0004-6361/201219219, A61.
  5. 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.
  6. Pourbaix, D.; Tokovinin, A. A.; Batten, A. H.; Fekel, F. C.; Hartkopf, W. I.; et al. (2004), "SB9: The ninth catalogue of spectroscopic binary orbits", Astronomy & Astrophysics, 424 (2): 727, arXiv:astro-ph/0406573, Bibcode:2004A&A...424..727P, doi:10.1051/0004-6361:20041213.
  7. Burkhart, C.; et al. (January 2005), "The field Am and ρ Puppis-like stars: Lithium and heavier elements", Astronomy and Astrophysics, 429: 1043–1049, Bibcode:2005A&A...429.1043B, doi:10.1051/0004-6361:20040467.
  8. McDonald, I.; et al. (2012), "Fundamental Parameters and Infrared Excesses of Hipparcos Stars", Monthly Notices of the Royal Astronomical Society, 427 (1): 343–57, arXiv:1208.2037, Bibcode:2012MNRAS.427..343M, doi:10.1111/j.1365-2966.2012.21873.x.
  9. 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.
  10. Royer, F.; et al. (October 2002), "Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i", Astronomy and Astrophysics, 393: 897–911, arXiv:astro-ph/0205255, Bibcode:2002A&A...393..897R, doi:10.1051/0004-6361:20020943.
  11. "tau UMa". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-02-25.
  12. Gray, Richard O.; Corbally, J. (2009), Stellar Spectral Classification, Princeton University Press, p. 178, ISBN 0691125112.
  13. Zaremba, D. (1979), "On the determination of the stellar chemical composition. I - Tau UMa", Acta Astronomica, 29 (4): 573–586, Bibcode:1979AcA....29..573Z.
  14. Allen, Richard Hinckley (1899), Star-Names and Their Meanings, New York: G. E. Stechert, p. 442.
  15. Rhoads, Jack W. (November 15, 1971), Technical Memorandum 33-507-A Reduced Star Catalog Containing 537 Named Stars (PDF), Jet Propulsion Laboratory, California Institute of Technology.
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