Tau Draconis
Star in the constellation Draco
From Wikipedia, the free encyclopedia
Tau Draconis, Latinized from τ Draconis, is an astrometric binary[9] star system in the northern circumpolar constellation of Draco. The star is faintly visible to the naked eye, having an apparent visual magnitude of 4.45.[2] Based upon an annual parallax shift of 22.28 mas as measured from Earth,[1] it is located around 146 light years from the Sun. Its proper motion is propelling it across the sky at the rate of 0.176 arc seconds per year.[10]
 | |
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Draco |
| Right ascension | 19h 15m 33.05868s[1] |
| Declination | +73° 21′ 19.6769″[1] |
| Apparent magnitude (V) | 4.45[2] |
| Characteristics | |
| Spectral type | K2 III:[3] |
| U−B color index | +1.45[2] |
| B−V color index | +1.25[2] |
| Astrometry | |
| Radial velocity (Rv) | −33.70[3] km/s |
| Proper motion (μ) | RA: −115.29[1] mas/yr Dec.: +103.23[1] mas/yr |
| Parallax (π) | 22.28±0.50 mas[1] |
| Distance | 146 ± 3 ly (45 ± 1 pc) |
| Absolute magnitude (MV) | +1.19[4] |
| Details | |
| Mass | 1.25[3] M☉ |
| Luminosity | 48[3] L☉ |
| Surface gravity (log g) | 2.00[5] cgs |
| Temperature | 4,413±77[3] K |
| Metallicity [Fe/H] | 0.17±0.06[6] dex |
| Rotational velocity (v sin i) | 8[7] km/s |
| Age | 6.48[3] Gyr |
| Other designations | |
| τ Dra, 60 Dra, BD+73°857, FK5 729, HD 181984, HIP 94648, HR 7352, SAO 9366[8] | |
| Database references | |
| SIMBAD | data |
This is a K-type giant star with a stellar classification of K2 III:,[3] where the semi-colon indicates some uncertainty about its spectral value. It is considered metal-rich[6] star and is past the first dredge-up phase of its post-main sequence evolution, although it shows under-abundances of carbon and oxygen in its spectrum.[5] The star has 1.25[3] times the mass of the Sun and is an estimated 6.48[3] billion years old. It is radiating 48[3] times the solar luminosity from its enlarged photosphere at an effective temperature of 4,413 K.[3]