Tau Sagittarii

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Tau Sagittarii
Diagram showing star positions and boundaries of the Sagittarius constellation and its surroundings
Cercle rouge 100%.svg

Location of τ Sagittarii (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Sagittarius
Right ascension 19h 06m 56.40897s[1]
Declination –27° 40′ 13.5189″[1]
Apparent magnitude (V) +3.326[2]
Characteristics
Spectral type K1 III[3]
U−B color index +1.185[2]
B−V color index +1.170[2]
Astrometry
Radial velocity (Rv) +45.4[4] km/s
Proper motion (μ) RA: –50.61[1] mas/yr
Dec.: -249.80[1] mas/yr
Parallax (π) 26.82 ± 0.86[1] mas
Distance 122 ± 4 ly
(37 ± 1 pc)
Details
Radius 16[5] R
Surface gravity (log g) 2.75[6] cgs
Temperature 4,860[6] K
Metallicity [Fe/H] –0.23[6] dex
Other designations
τ Sagittarii, τ Sgr, Tau Sgr, 40 Sagittarii, CPD-27  6617, FK5 1496, GC 26291, HD 177716, HIP 93864, HR 7234, PPM 269078, SAO 187683.[7]

Tau Sagittarii (Tau Sgr, τ Sagittarii, τ Sgr) is a star in the southern zodiac constellation of Sagittarius.

Description[edit]

With an apparent visual magnitude of +3.3,[2] this is one of the brighter members of the constellation. The distance of this star from Earth is roughly 122 light-years (37 parsecs), based upon parallax measurements.[1]

This is a spectral type K1 giant star with 1.5 - 2 Solar masses. The stellar envelope is slightly cooler than the Sun, with an effective temperature of 4,860 K,[6] giving the star a light orange color. The interferometry-measured angular diameter of this star, after correcting for limb darkening, is 3.93 ± 0.04 mas,[8] which, at its estimated distance, equates to a physical radius of about 16 times the radius of the Sun.[5] Tau Sagittarii is a suspected double star although no companion has been confirmed yet. A lower metal content (Fe to H ratio is 70%) and a high peculiar velocity (64 km/s, 4x the local average) relative to the Sun suggest the star is a visitor from a different part of the Galaxy.

The Wow! signal[edit]

Tau Sagittarii is the closest visible star in the night sky to the origin of the 1977 Wow! signal, the only radio signal that has been received that may be a sign of extraterrestrial intelligence. The location of the signal was, in epoch J2000.0 coordinates:

Name and etymology[edit]

References[edit]

  1. ^ a b c d e f van Leeuwen, F. (November 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 Celis S., L. (October 1975), Photoelectric photometry of late-type variable stars, Astronomy and Astrophysics Supplement Series 22: 9–17, Bibcode:1975A&AS...22....9C 
  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. ^ Wilson, R. E. (1953). General Catalogue of Stellar Radial Velocities. Carnegie Institute of Washington D.C. Bibcode:1953GCRV..C......0W. 
  5. ^ a b Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library 1 (3 ed.), Birkhäuser, ISBN 3-540-29692-1 . The radius (R*) is given by:
    \begin{align} 2\cdot R_*
 & = \frac{(10^{-3}\cdot 37\cdot 3.93)\ \text{AU}}{0.0046491\ \text{AU}/R_{\bigodot}} \\
 & \approx 31.3\cdot R_{\bigodot}
\end{align}
  6. ^ a b c d Jones, K. L. et al. (June 1992), Spectroscopic investigation of cool giants and the authenticity of their reported microwave emission, Monthly Notices of the Royal Astronomical Society 256 (3): 535–544, Bibcode:1992MNRAS.256..535J 
  7. ^ HD 177716 -- High proper-motion Star, SIMBAD Astronomical Object Database (Centre de Données astronomiques de Strasbourg), retrieved 2012-02-12 
  8. ^ Richichi; Percheron, I.; Khristoforova, M. (February 2005), CHARM2: An updated Catalog of High Angular Resolution Measurements, Astronomy and Astrophysics 431: 773–777, Bibcode:2005A&A...431..773R, doi:10.1051/0004-6361:20042039 
  9. ^ "Sagittarius". deepsky.astroinfo.org. Retrieved 30 August 2008. 
  10. ^ skywatchers[dead link]
  11. ^ a b Allen, R. H. (1963). Star Names: Their Lore and Meaning (Reprint ed.). New York: Dover Publications Inc. p. 355. ISBN 0-486-21079-0. Retrieved 2012-09-04. 
  12. ^ Jack W. Rhoads - Technical Memorandum 33-507-A Reduced Star Catalog Containing 537 Named Stars, Jet Propulsion Laboratory, California Institute of Technology; November 15, 1971
  13. ^ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 11 日