Tau1 Serpentis

Tau¹ Serpentis, Latinized from τ¹ Serpentis, is a single^[11] 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]

For other stars with this Bayer designation, see Tau Serpentis.

τ¹ Serpentis

A light curve for Tau1 Serpentis, plotted from Hipparcos data[1]
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
Mass	2.3[8] M☉
Radius	99+7 −14[2] R☉
Luminosity	2,158±149[2] L☉
Surface gravity (log g)	1.07±0.18[9] cgs
Temperature	3,954+309 −132[2] K
Metallicity [Fe/H]	0.05±0.06[9] dex
Age	933[8] Myr
Other designations
τ1 Ser, 9 Serpentis, NSV 7074, BD+15°2858, FK5 570, GC 20740, HD 137471, HIP 75530, HR 5739, SAO 101545[10]
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 has around 99 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.^[12] The star is radiating 2,158 times the luminosity of the Sun from its swollen photosphere at an effective temperature of 3,954 K.^[2]