Tau Sagittarii
  | |
| 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 mas[1] |
| Distance | 122 ± 4 ly (37 ± 1 pc) |
| Details | |
| Mass | 1.25[5] M☉ |
| Radius | 15.71[5] R☉ |
| Luminosity | 87.6[5] L☉ |
| Surface gravity (log g) | 2.15[5] cgs |
| Temperature | 4,459[5] K |
| Metallicity [Fe/H] | –0.27[5] dex |
| Rotational velocity (v sin i) | 1.04[6] km/s |
| Age | 7.91[5] Gyr |
| Other designations | |
| Database references | |
| SIMBAD | data |
Tau Sagittarii (Tau Sgr, τ Sagittarii, τ Sgr) is a star in the southern zodiac constellation of Sagittarius.
Description
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 about 1.25 M☉. The stellar envelope is slightly cooler than the Sun, with an effective temperature of 4,459 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,[7] which, at its estimated distance, equates to a physical radius of about 16 times the radius of the Sun.[8]
τ Sagittarii is a suspected double star although no companion has been confirmed yet. A lower metal content (Fe to H ratio is 54% lower than the sun's) and a high peculiar velocity (64 km/s, four times the local average) relative to the Sun suggest the star is a visitor from a different part of the Galaxy.[citation needed]
τ Sagittarii is a red clump giant, a star with similar mass to the sun which has exhausted its core hydrogen, passed through the red giant branch, and started helium fusion in its core.[9]
The Wow! signal
τ Sagittarii is the closest visible star in the night sky to the origin of the 1977 Wow! signal.[10]
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.[11][12]
- φ Sgr, ζ Sgr, χ Sgr and σ Sgr were Al Naʽām al Ṣādirah (النعم السادرة), the Returning Ostriches.[13] 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).[14]
- ν Sgr, ψ Sgr, ω Sgr, 60 Sgr and ζ Sgr were Al Udḥiyy, the Ostrich's Nest.[13]
- 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, Template:Lang-en.)[15]
References
- ^ 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
- ^ 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
- ^ 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.
- ^ a b c d e f g Reffert, Sabine; Bergmann, Christoph; Quirrenbach, Andreas; Trifonov, Trifon; Künstler, Andreas (2015). "Precise radial velocities of giant stars. VII. Occurrence rate of giant extrasolar planets as a function of mass and metallicity". Astronomy & Astrophysics. 574: A116. Bibcode:2015A&A...574A.116R. doi:10.1051/0004-6361/201322360.
- ^ Hekker, S.; Meléndez, J. (2007). "Precise radial velocities of giant stars. III. Spectroscopic stellar parameters". Astronomy and Astrophysics. 475 (3): 1003. Bibcode:2007A&A...475.1003H. doi:10.1051/0004-6361:20078233.
- ^ Richichi, A.; Percheron, I.; Khristoforova, M. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics, 431 (2): 773–777, Bibcode:2005A&A...431..773R, doi:10.1051/0004-6361:20042039
- ^ Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, vol. 1 (3rd ed.), Birkhäuser, ISBN 3-540-29692-1. The radius (R*) is given by:
- ^ Alves, David R. (2000). "K-Band Calibration of the Red Clump Luminosity". The Astrophysical Journal. 539 (2): 732. arXiv:astro-ph/0003329. Bibcode:2000ApJ...539..732A. doi:10.1086/309278.
- ^ http://www.news.com.au/technology/science/the-worlds-biggest-mysteries-scientists-still-cant-solve/story-fnjwl1aw-1227045377722
- ^ "Sagittarius". deepsky.astroinfo.org. Retrieved 30 August 2008.
- ^ skywatchers Archived May 17, 2007, at the Wayback Machine
- ^ 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.
- ^ 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
- ^ Template:Zh icon AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 11 日
