Wikipedia

Sigma Tauri

Sigma Tauri (σ Tauri) is the Bayer designation for a pair of white-hued stars in the zodiac constellation of Taurus. The system is a visual double star, whose components are designated σ1 Tauri and σ2 Tauri, with the latter being the more northerly star.[15] The two are separated by 7.2[16] arcminutes on the sky and can be readily split with a pair of binoculars.[15] They have apparent visual magnitudes of +5.07[2] and +4.70,[3] respectively, which indicates they are both visible to the naked eye. Based upon parallax measurements, σ1 Tauri is about 147 light years from the Sun, while σ2 Tauri is 156 light years distant.

Sigma Tauri
Location of σ2 Tauri (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Taurus
σ1 Tau
Right ascension 04h 39m 09.22247s[1]
Declination +15° 47′ 59.5345″[1]
Apparent magnitude (V) 5.07[2]
σ2 Tau
Right ascension 04h 39m 16.50230s[1]
Declination +15° 55′ 04.7029″[1]
Apparent magnitude (V) 4.70[3]
Characteristics
σ1 Tau
Spectral type A4m[4]
U−B color index 0.190[2]
B−V color index 0.146[2]
σ2 Tau
Spectral type A5 Vn[5]
U−B color index +0.13[3]
B−V color index +0.14[3]
Astrometry
σ1 Tau
Radial velocity (Rv)+26.1±10.0[6] km/s
Proper motion (μ) RA: +41.91[1] mas/yr
Dec.: −66.88[1] mas/yr
Parallax (π)22.18 ± 0.93 mas[1]
Distance147 ± 6 ly
(45 ± 2 pc)
Absolute magnitude (MV)1.73[2]
σ2 Tau
Radial velocity (Rv)+40.8±1.2[6] km/s
Proper motion (μ) RA: +83.17[1] mas/yr
Dec.: −20.97[1] mas/yr
Parallax (π)20.97 ± 0.27 mas[1]
Distance156 ± 2 ly
(47.7 ± 0.6 pc)
Orbit[7]
Primaryσ1 Tau A
Companionσ1 Tau B
Period (P)38.951 d
Eccentricity (e)0.15
Longitude of the node (Ω)82°
Periastron epoch (T)2443094.319 JD
Semi-amplitude (K1)
(primary)		7.9 km/s
Details
σ1 Tau
Mass1.94[2] M☉
Luminosity14.7[8] L☉
Surface gravity (log g)4.08[2] cgs
Temperature8,470[2] K
Rotational velocity (v sin i)56.5±7.1[9] km/s
σ2 Tau
Mass1.71[10] M☉
Radius1.9[11] R☉
Luminosity22.5[8] L☉
Surface gravity (log g)3.96[10] cgs
Temperature8,165±278[10] K
Metallicity [Fe/H]0.10±0.11[12] dex
Rotational velocity (v sin i)128[5] km/s
Age258[10] Myr
Other designations
σ Tau, WDS J04393+1555
σ1 Tau: 91 Tauri, BD+15° 665, HD 29479, HIP 21673, HR 1478, SAO 94051[13]
σ2 Tau: 92 Tauri, BD+15° 666, FK5 2345, HD 29488, HIP 21683, HR 1479, SAO 94054[14]
Database references
SIMBADσ1 Tau
σ2 Tau

σ1 Tauri is a single-lined spectroscopic binary star system with an orbital period of 38.951 days and an eccentricity of 0.15. The visible component is an Am star with a stellar classification of A4m,[4] indicating it is chemically peculiar A-type star. It is spinning with a projected rotational velocity of 56.5 km/s.[9] The star has 1.9[2] times the mass of the Sun and is radiating 14.7[8] times the Sun's luminosity from its photosphere at an effective temperature of 8,470 K.[2] Although it lies in the general direction of the Hyades cluster, based on parallax measurements it has been excluded from the list of candidate members.[2]

σ2 Tauri is a solitary[17] A-type main sequence star with a stellar classification of A5 Vn.[5] The 'n' suffix indicates the lines are "nebulous" due to rapid rotation, and indeed it is spinning with a projected rotational velocity of 128 km/s.[5] The star is an estimated 258[10] million years old, with 1.7[10] times the mass of the Sun. It is radiating 22.5[8] times the Sun's luminosity from its photosphere at an effective temperature of around 8,165 K.[10] The star is considered a member of the Hyades cluster.[11]

In Chinese astronomy, σ2 Tauri is called 附耳, Pinyin: Fùěr, meaning Whisper, because this star is marking itself and stands alone in the Whisper asterism of the Net mansion (see : Chinese constellation).[18]

References

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  1. ^ a b c d e f g h i j 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.
  2. ^ a b c d e f g h i j k Iliev, I. Kh.; et al. (August 2006), "Abundance analysis of Am binaries and search for tidally driven abundance anomalies - II. HD861, HD18778, HD20320, HD29479, HD96528 and HD108651", Monthly Notices of the Royal Astronomical Society, 370 (2): 819–827, Bibcode:2006MNRAS.370..819I, doi:10.1111/j.1365-2966.2006.10513.x, S2CID 56133360.
  3. ^ a b c d Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99): 99, Bibcode:1966CoLPL...4...99J.
  4. ^ a b Cowley, A.; et al. (1969), "A study of the bright A stars. I. A catalogue of spectral classifications", Astronomical Journal, 74: 375–406, Bibcode:1969AJ.....74..375C, doi:10.1086/110819.
  5. ^ a b c d Royer, F.; et al. (February 2007), "Rotational velocities of A-type stars. III. Velocity distributions", Astronomy and Astrophysics, 463 (2): 671–682, arXiv:astro-ph/0610785, Bibcode:2007A&A...463..671R, doi:10.1051/0004-6361:20065224, S2CID 18475298.
  6. ^ a b 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, S2CID 59451347, A61.
  7. ^ Pourbaix, D.; et al. (2004), "SB9: The ninth catalogue of spectroscopic binary orbits", Astronomy and Astrophysics, 424 (2): 727–732, arXiv:astro-ph/0406573, Bibcode:2004A&A...424..727P, doi:10.1051/0004-6361:20041213, S2CID 119387088.
  8. ^ a b c d 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, S2CID 118665352.
  9. ^ a b Paunzen, E.; et al. (February 2013), "A photometric study of chemically peculiar stars with the STEREO satellites - II. Non-magnetic chemically peculiar stars", Monthly Notices of the Royal Astronomical Society, 429 (1): 119–125, arXiv:1211.1535, Bibcode:2013MNRAS.429..119P, doi:10.1093/mnras/sts318, S2CID 119231581.
  10. ^ a b c d e f g David, Trevor J.; Hillenbrand, Lynne A. (2015), "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets", The Astrophysical Journal, 804 (2): 146, arXiv:1501.03154, Bibcode:2015ApJ...804..146D, doi:10.1088/0004-637X/804/2/146, S2CID 33401607.
  11. ^ a b Pasinetti Fracassini, L. E.; et al. (February 2001), "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS)", Astronomy and Astrophysics, 367 (Third ed.): 521–524, arXiv:astro-ph/0012289, Bibcode:2001A&A...367..521P, doi:10.1051/0004-6361:20000451, S2CID 425754.
  12. ^ Soubiran, C.; et al. (June 2010), "The PASTEL catalogue of stellar parameters", Astronomy and Astrophysics, 515: A111, arXiv:1004.1069, Bibcode:2010A&A...515A.111S, doi:10.1051/0004-6361/201014247, S2CID 118362423.
  13. ^ "sig01 Tau". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-08-06.{{cite web}}: CS1 maint: postscript (link)
  14. ^ "sig02 Tau". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-08-06.{{cite web}}: CS1 maint: postscript (link)
  15. ^ a b Burnham, Robert (2013), Burnham's Celestial Handbook, volume 3: An Observer's Guide to the Universe Beyond the Solar System, Dover Books on Astronomy, vol. 3, Courier Corporation, p. 1825, ISBN 978-0486318035
  16. ^ O'Meara, Stephen James (2016), Deep-Sky Companions: The Caldwell Objects, Cambridge University Press, p. 195, ISBN 978-1107083974.
  17. ^ 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.
  18. ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 23 日
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