Tau1 Serpentis, Latinized from τ1 Serpentis, is a single[10] star in the Caput (Head) segment of the equatorial constellation of Serpens. It is a red hued star that is dimly visible to the naked eye with an apparent visual magnitude of 5.16.[3] Based upon parallax measurements, this star is located at a distance of approximately 990 light years from the Sun,[2] while it is drifting closer with a radial velocity of −16.5 km/s.[3]
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Serpens |
| Right ascension | 15h 25m 47.39664s[2] |
| Declination | +15° 25′ 40.9307″[2] |
| Apparent magnitude (V) | 5.16[3] (5.13 to 5.20)[4] |
| Characteristics | |
| Evolutionary stage | AGB[5] |
| Spectral type | M1III[6] |
| U−B color index | +1.95[7] |
| B−V color index | +1.650±0.006[3] |
| R−I color index | +1.04[7] |
| Astrometry | |
| Radial velocity (Rv) | −16.51±0.23[3] km/s |
| Proper motion (μ) | RA: −12.467[2] mas/yr Dec.: −7.740[2] mas/yr |
| Parallax (π) | 3.3030 ± 0.1988 mas[2] |
| Distance | 990 ± 60 ly (300 ± 20 pc) |
| Absolute magnitude (MV) | −1.45[3] |
| Details | |
| Radius | 99+7 −14[2] R☉ |
| Luminosity | 2,158±149[2] L☉ |
| Surface gravity (log g) | 1.07±0.18[8] cgs |
| Temperature | 3,954+309 −132[2] K |
| Metallicity [Fe/H] | 0.05±0.06[8] dex |
| Other designations | |
| Database references | |
| SIMBAD | data |
This object is an aging red giant star, currently on the asymptotic giant branch,[5] with a stellar classification of M1III.[6] Having exhausted the supply of hydrogen at its core, it has cooled and expanded until it now has around 99[2] times the girth of the Sun.[2] It is a suspected variable star with a brightness that has been measured varying from magnitude 5.13 down to 5.20.[4] The Hipparcos data for Tau1 Serpentis shows brightness variations with a period of 6.4675 days, and an amplitude of 0.0066 magnitudes.[11] The star is radiating 2,158[2] times the luminosity of the Sun from its swollen photosphere at an effective temperature of 3,954 K.[2]