Tau Sagittarii
 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 | |
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 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.[citation needed]
The Wow! signal
Tau Sagittarii is the closest visible star in the night sky to the origin of the 1977 Wow! signal.[9]
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.[10][11]
- φ Sgr, ζ Sgr, χ Sgr and σ Sgr were Al Naʽām al Ṣādirah (النعم السادرة), the Returning Ostriches.[12] 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).[13]
- ν Sgr, ψ Sgr, ω Sgr, 60 Sgr and ζ Sgr were Al Udḥiyy, the Ostrich's Nest.[12]
- 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.)[14]
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 2.0 2.1 2.2 2.3 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 5.0 5.1 Lua error in package.lua at line 80: module 'strict' not found.. The radius (R*) is given by:
- ↑ 6.0 6.1 6.2 6.3 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ http://www.news.com.au/technology/science/the-worlds-biggest-mysteries-scientists-still-cant-solve/story-fnjwl1aw-1227045377722
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ skywatchers Archived May 17, 2007 at the Wayback Machine
- ↑ 12.0 12.1 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 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
