Tau Sagittarii
 Location of τ Sagittarii (circled) |
|
| Observation data Epoch J2000.0 Equinox J2000.0 |
|
|---|---|
| Constellation | Sagittarius |
| Right ascension | 19h 06m 56.40897s |
| Declination | –27° 40′ 13.5189″ |
| Apparent magnitude (V) | +3.326 |
| Characteristics | |
| Spectral type | K1 III |
| U−B color index | +1.185 |
| B−V color index | +1.170 |
| Astrometry | |
| Radial velocity (Rv) | +45.4 km/s |
| Proper motion (μ) |
RA: –50.61 mas/yr Dec.: -249.80 mas/yr |
| Parallax (π) | 26.82 ± 0.86mas |
| Distance | 122 ± 4 ly (37 ± 1 pc) |
| Details | |
| Mass | 1.25 M☉ |
| Radius | 15.71 R☉ |
| Luminosity | 87.6 L☉ |
| Surface gravity (log g) | 2.15 cgs |
| Temperature | 4,459 K |
| Metallicity [Fe/H] | –0.27 dex |
| Rotational velocity (v sin i) | 1.04 km/s |
| Age | 7.91 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.
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 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, which, at its estimated distance, equates to a physical radius of about 16 times the radius of the Sun.
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.
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.
τ Sagittarii is the closest visible star in the night sky to the origin of the 1977 Wow! signal.
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