Epoch J2000.0 Equinox J2000.0
|Right ascension||19h 06m 56.40897s|
|Declination||–27° 40′ 13.5189″|
|Apparent magnitude (V)||+3.326|
|Spectral type||K1 III|
|U−B color index||+1.185|
|B−V color index||+1.170|
|Radial velocity (Rv)||+45.4 km/s|
|Proper motion (μ)||RA: –50.61 mas/yr
Dec.: -249.80 mas/yr
|Parallax (π)||26.82 ± 0.86 mas|
|Distance||122 ± 4 ly
(37 ± 1 pc)
|Surface gravity (log g)||2.75 cgs|
|Metallicity [Fe/H]||–0.23 dex|
With an apparent visual magnitude of +3.3, 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.
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, 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, which, at its estimated distance, equates to a physical radius of about 16 times the radius of the Sun. 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
|This section does not cite any references or sources. (June 2015)|
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:
- Right ascension (on the positive horn): 19h 25m 31 ± 10s
- Right ascension (on the negative horn): 19h 28m 22 ± 10s
- Declination (the same for both horns): –26° 57 ± 20′
Name and etymology
- This star, together with :
- γ Sgr, δ Sgr, ε Sgr, ζ Sgr, λ Sgr, σ Sgr and φ Sgr, comprising the asterism Teapot.
- φ Sgr, ζ Sgr, χ Sgr and σ Sgr were Al Naʽām al Ṣādirah (النعم السادرة), the Returning Ostriches. According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Al Naʽām al Ṣādirah or Namalsadirah was originally the title for four stars: φ Sgr as Namalsadirah I, τ Sgr as Namalsadirah II, χ1 Sgr as Namalsadirah III and χ2 Sgr as Namalsadirah IV (except σ Sgr and ζ Sgr).
- ν Sgr, ψ Sgr, ω Sgr, 60 Sgr and ζ Sgr were Al Udḥiyy, the Ostrich's Nest.
- In Chinese, 斗 (Dǒu), meaning Dipper, refers to an asterism consisting of τ Sagittarii, φ Sagittarii, λ Sagittarii, μ Sagittarii, σ Sagittarii and ζ Sagittarii. Consequently, τ Sagittarii itself is known as 斗宿五 (Dǒu Sù wu, English: the Fifth Star of Dipper.)
- 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
- 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
- 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
- Wilson, R. E. (1953). General Catalogue of Stellar Radial Velocities. Carnegie Institute of Washington D.C. Bibcode:1953GCRV..C......0W.
- Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library 1 (3rd ed.), Birkhäuser, ISBN 3-540-29692-1. The radius (R*) is given by:
- 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
- "HD 177716 -- High proper-motion Star", SIMBAD Astronomical Object Database (Centre de Données astronomiques de Strasbourg), retrieved 2012-02-12
- Richichi, A.; 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
- "Sagittarius". deepsky.astroinfo.org. Retrieved 30 August 2008.
- skywatchers[dead link]
- 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.
- 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
- (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 11 日