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τ¹ Serpentis
	; A light curve for Tau1 Serpentis, plotted from Hipparcos data
Observation data; Epoch J2000.0 Equinox J2000.0 (ICRS)
Constellation	Serpens
Right ascension	15h 25m 47.39664s
Declination	+15° 25′ 40.9307″
Apparent magnitude (V)	5.16 (5.13 to 5.20)
Characteristics
Evolutionary stage	AGB
Spectral type	M1III
U−B color index	+1.95
B−V color index	+1.650±0.006
R−I color index	+1.04
Astrometry
Radial velocity (Rv)	−16.51±0.23 km/s
Proper motion (μ)	RA: −12.467 mas/yr ; Dec.: −7.740 mas/yr
Parallax (π)	3.3030 ± 0.1988 mas
Distance	990 ± 60 ly ; (300 ± 20 pc)
Absolute magnitude (MV)	−1.45
Details
Radius	99+7; −14 R☉
Luminosity	2,158±149 L☉
Surface gravity (log g)	1.07±0.18 cgs
Temperature	3,954+309; −132 K
Metallicity [Fe/H]	0.05±0.06 dex
Other designations
	τ1 Ser, 9 Serpentis, NSV 7074, BD+15°2858, FK5 570, GC 20740, HD 137471, HIP 75530, HR 5739, SAO 101545
Database references
SIMBAD	data

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]

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]

References

^ "/ftp/cats/more/HIP/cdroms/cats". Centre de Données astronomiques de Strasbourg. Strasbourg astronomical Data Center. Retrieved 15 October 2022.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
^ ^a ^b ^c ^d ^e ^f Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
^ ^a ^b Samus', N. N; Kazarovets, E. V; Durlevich, O. V; Kireeva, N. N; Pastukhova, E. N (2017), "General catalogue of variable stars: Version GCVS 5.1", Astronomy Reports, 61 (1): 80, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085, S2CID 125853869.
^ ^a ^b Eggen, Olin J. (July 1992), "Asymptotic giant branch stars near the sun", Astronomical Journal, 104 (1): 275–313, Bibcode:1992AJ....104..275E, doi:10.1086/116239.
^ ^a ^b Cenarro, A. J.; et al. (July 2009), "Mg and TiO spectral features at the near-IR: spectrophotometric index definitions and empirical calibrations", Monthly Notices of the Royal Astronomical Society, 396 (4): 1895–1914, arXiv:0903.4835, Bibcode:2009MNRAS.396.1895C, doi:10.1111/j.1365-2966.2009.14839.x, S2CID 15729759.
^ ^a ^b Hoffleit, D.; Warren, Jr., W. H., "HR 5739", The Bright Star Catalogue (5th Revised ed.), retrieved 2019-10-17.
^ ^a ^b Prugniel, P.; et al. (2011), "The atmospheric parameters and spectral interpolator for the MILES stars", Astronomy & Astrophysics, 531: A165, arXiv:1104.4952, Bibcode:2011A&A...531A.165P, doi:10.1051/0004-6361/201116769, S2CID 54940439.
^ "tau01 Ser". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-10-17.
^ Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x, S2CID 14878976.
^ Koen, Chris; Eyer, Laurent (March 2002). "New periodic variables from the Hipparcos epoch photometry". Monthly Notices of the Royal Astronomical Society. 331 (1): 45–59. arXiv:astro-ph/0112194. Bibcode:2002MNRAS.331...45K. doi:10.1046/j.1365-8711.2002.05150.x. S2CID 10505995.