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31 Leonis
Observation data; Epoch J2000.0 Equinox J2000.0
Constellation	Leo
Right ascension	10h 07m 54.2701s
Declination	+09° 59′ 51.025″
Apparent magnitude (V)	4.39
Characteristics
Spectral type	K3.5 IIIb Fe-1:
B−V color index	1.447
Astrometry
Radial velocity (Rv)	+39.84±0.20 km/s
Proper motion (μ)	RA: −82.021 mas/yr ; Dec.: −64.844 mas/yr
Parallax (π)	11.0209 ± 0.1661 mas
Distance	296 ± 4 ly ; (91 ± 1 pc)
Absolute magnitude (MV)	−0.39
Details
Radius	33.9+0.7; −0.71 R☉
Luminosity	283±9 L☉
Surface gravity (log g)	1.42 cgs
Temperature	4066±28 K
Metallicity [Fe/H]	−0.02 dex
Rotational velocity (v sin i)	5.1 km/s
Other designations
	31 Leo, BD+10°2112, HD 87837, HIP 49637, HR 3980, SAO 98964
Database references
SIMBAD	data

31 Leonis is a binary star^[9] system in the equatorial constellation of Leo. The system is visible to the naked eye in unresolved form, having a combined apparent visual magnitude of 4.39.^[2] An estimated distance of around 300 light years is obtained from the annual parallax shift of 11.02 mas as seen from Earth's orbit.^[1] At the current distance, interstellar extinction between Earth and 31 Leo diminished the apparent brightness by 0.12 magnitudes.^[6] It is moving away from the Sun with a radial velocity of +39.8 km/s.^[5]

The primary member of 31 Leonis, component A, is an evolved K-type red giant^[10] with a stellar classification of K3.5 IIIb Fe-1:,^[3] where the suffix notation indicates an underabundance of iron in the spectrum. It has expanded to 34 times the Solar radius and is radiating around 283 times the Sun's luminosity from its photosphere at an effective temperature of 4,066 K.^[6] The magnitude 13.6 secondary, component B, lies at an angular separation of 7.9 arcseconds, as of 2008.^[9]

References

^ ^a ^b ^c ^d ^e ^f Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
^ ^a ^b ^c 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 Keenan, Philip C; McNeil, Raymond C (1989), "The Perkins catalog of revised MK types for the cooler stars", Astrophysical Journal Supplement Series, 71: 245, Bibcode:1989ApJS...71..245K, doi:10.1086/191373, S2CID 123149047.
^ ^a ^b 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, S2CID 121883397.
^ ^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.
^ ^a ^b ^c ^d ^e ^f Baines, Ellyn K.; Clark III, James H.; Schmitt, Henrique R.; Stone, Jordan M.; von Braun, Kaspar (2023-12-01), "33 New Stellar Angular Diameters from the NPOI, and Nearly 180 NPOI Diameters as an Ensemble", The Astronomical Journal, 166 (6): 268, Bibcode:2023AJ....166..268B, doi:10.3847/1538-3881/ad08be, ISSN 0004-6256.
^ Piau, L.; et al. (February 2011), "Surface convection and red-giant radius measurements", Astronomy and Astrophysics, 526: A100, arXiv:1010.3649, Bibcode:2011A&A...526A.100P, doi:10.1051/0004-6361/201014442, S2CID 118533297.
^ "31 Leo". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2018-02-18.
^ ^a ^b 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.
^ Wood, Brian E.; et al. (October 2016), "Hubble Space Telescope Constraints on the Winds and Astrospheres of Red Giant Stars", The Astrophysical Journal, 829 (2): 13, arXiv:1607.07732, Bibcode:2016ApJ...829...74W, doi:10.3847/0004-637X/829/2/74, S2CID 119258785, 74.