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11 Serpentis
Observation data; Epoch J2000 Equinox J2000
Constellation	Serpens
Right ascension	15h 32m 57.93765s
Declination	−01° 11′ 11.0412″
Apparent magnitude (V)	5.497
Characteristics
Evolutionary stage	horizontal branch
Spectral type	K0 III
B−V color index	1.092
Astrometry
Radial velocity (Rv)	−16.1±2.8 km/s
Proper motion (μ)	RA: −17.765 mas/yr ; Dec.: −42.217 mas/yr
Parallax (π)	12.0563 ± 0.1290 mas
Distance	271 ± 3 ly ; (82.9 ± 0.9 pc)
Absolute magnitude (MV)	0.83
Details
Mass	1.27±0.35 M☉
Radius	11 R☉
Luminosity	50 L☉
Surface gravity (log g)	2.48±0.11 cgs
Temperature	4,767±92 K
Metallicity [Fe/H]	−0.13 dex
Age	2.75+0.88; −0.66 Gyr
Other designations
	A1 Ser, 11 Ser, BD−00°2982, FK5 3226, GC 20896, HD 138562, HIP 76133, HR 5772, SAO 140596
Database references
SIMBAD	data

11 Serpentis is a single^[9] star in the constellation of Serpens, located 271 light years away from the Sun. It has the Bayer designation A¹ Serpentis,^[10] 11 Serpentis is the Flamsteed designation. This object is visible to the naked eye as a faint, orange-hued star with an apparent visual magnitude of 5.497.^[2] It is moving closer to the Earth with a heliocentric radial velocity of −16 km/s.^[4]

This is an aging giant star with a stellar classification of K0 III,^[3] a star that has used up its core hydrogen and has expanded. It is a red clump giant on the horizontal branch, which indicates it is generating energy through the fusion of helium at its core.^[2] 11 Serpentis is 2.75 billion years old with 1.3^[6] times the mass of the Sun and has 11^[7] times the Sun's radius. It is radiating 50^[7] times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,767 K.^[6]

References

^ ^a ^b ^c ^d ^e 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 Alves, David R. (August 2000), "K-Band Calibration of the Red Clump Luminosity", The Astrophysical Journal, 539 (2): 732–741, arXiv:astro-ph/0003329, Bibcode:2000ApJ...539..732A, doi:10.1086/309278, S2CID 16673121.
^ ^a ^b Houk, N.; Swift, C. (1999), "Michigan catalogue of two-dimensional spectral types for the HD Stars", Michigan Spectral Survey, 5, Ann Arbor, Michigan: Department of Astronomy, University of Michigan, Bibcode:1999MSS...C05....0H
^ ^a ^b de Bruijne, J. H. J.; Eilers, A.-C. (October 2012), "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project", Astronomy & Astrophysics, 546: 14, arXiv:1208.3048, Bibcode:2012A&A...546A..61D, doi:10.1051/0004-6361/201219219, S2CID 59451347, A61.
^ 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 ^c ^d ^e ^f Feuillet, Diane K.; et al. (2016), "Determining Ages of APOGEE Giants with Known Distances", The Astrophysical Journal, 817 (1): 40, arXiv:1511.04088, Bibcode:2016ApJ...817...40F, doi:10.3847/0004-637x/817/1/40, S2CID 118675933.
^ ^a ^b ^c ^d ^e Massarotti, Alessandro; et al. (January 2008), "Rotational and Radial Velocities for a Sample of 761 Hipparcos Giants and the Role of Binarity", The Astronomical Journal, 135 (1): 209–231, Bibcode:2008AJ....135..209M, doi:10.1088/0004-6256/135/1/209
^ "11 Ser". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-03-21.
^ Eggleton, P. P.; Tokovinin, A. A. (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
^ Hoffleit, D. (July 1979), "Discordances in Star Designations", Bulletin d'Information du Centre de Données Stellaires, 17 (17): 38, Bibcode:1979BICDS..17...38H