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Upsilon Leonis

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υ Leonis
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Leo
Right ascension 11h 36m 56.92983s[1]
Declination +00° 49′ 25.8758″[1]
Apparent magnitude (V) 4.33[2]
Characteristics
Spectral type G9 III[3]
U−B color index +0.76[2]
B−V color index +1.00[2]
Astrometry
Radial velocity (Rv)1.79±0.16[4] km/s
Proper motion (μ) RA: +1.76[1] mas/yr
Dec.: +43.37[1] mas/yr
Parallax (π)17.97 ± 0.22 mas[1]
Distance182 ± 2 ly
(55.6 ± 0.7 pc)
Absolute magnitude (MV)0.59[5]
Details
Mass2.58[5] M☉
Radius11[4] R☉
Luminosity56[4] L☉
Surface gravity (log g)2.7[4] cgs
Temperature4,842[4] K
Metallicity [Fe/H]–0.34[4] dex
Rotational velocity (v sin i)0.0[4] km/s
Age4.12±2.08[6] Gyr
Other designations
υ Leo, 91 Leo, BD−00°2458, FK5 437, HD 100920, HIP 56647, HR 4471, SAO 138298[7]
Database references
SIMBADdata

Upsilon Leonis (υ Leo) is a star in the zodiac constellation of Leo. It is visible to the naked eye with an apparent visual magnitude of 4.33.[2] The distance to this star, as determined using parallax measurements,[1] is about 182 light years. At that distance, the visual magnitude of the star is diminished by an estimated extinction factor of 0m.02 because of interstellar dust.[5]

With an age of around 4 billion years, this star has evolved into a G-type giant star with a stellar classification of G9 III.[3] It has 2.6 times the Sun's mass,[5] but has expanded to 11 times the solar radius and shines with 56 times the luminosity of the Sun at an effective temperature of 4,842 K.[4] The rate of rotation is too small to be measured, with a projected rotational velocity of 0.0 km/s.[4] The chemical abundance of elements other than hydrogen and helium, what astronomers term the star's metallicity, is less than half that in the Sun.[4] It is most likely a member of the galactic thin disk population.[6]

Planetary system

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In 2021, a gas giant planet was detected by radial velocity method.[8] In 2024, this object's true mass was measured using astrometry from the Gaia spacecraft. The method consists of taking the host star's RUWE level—an astrometirc indicator— from the astrometric solution. A large RUWE could imply that there is an unseen companion around the star, or that there are systematic calibration errors in the astrometric solution. Assuming the former scenario, the mass of Upsilon Leonis b is measured at 29.2 MJ, indicating that it is a brown dwarf, but the latter scenario is still a possibility, which means that this measured mass is likely an upper limit.[9]

The Upsilon Leonis planetary system[8]
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination Radius
b ≥0.51+0.06
−0.26[8] and ≤29.2[9] MJ 		1.18+0.11
−0.32 		385.2+2.8
−1.3 		0.320+0.134
−0.218 		— —

References

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  1. ^ a b c d e f van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357, S2CID 18759600.
  2. ^ a b c d Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV Data, SIMBAD, Bibcode:1986EgUBV........0M.
  3. ^ a b Buscombe, W. (1962), "Spectral classification of Southern fundamental stars", Mount Stromlo Observatory Mimeogram, 4: 1, Bibcode:1962MtSOM...4....1B.
  4. ^ a b c d e f g h i j 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.
  5. ^ a b c d Takeda, Yoichi; et al. (February 2005), "Stellar Parameters and Photospheric Abundances of Late-G Giants: Properties of the Targets of the Okayama Planet Search Program", Publications of the Astronomical Society of Japan, 57 (1): 109–125, Bibcode:2005PASJ...57..109T, doi:10.1093/pasj/57.1.109.
  6. ^ a b Soubiran, C.; et al. (March 2008), "Vertical distribution of Galactic disk stars. IV. AMR and AVR from clump giants", Astronomy and Astrophysics, 480 (1): 91–101, arXiv:0712.1370, Bibcode:2008A&A...480...91S, doi:10.1051/0004-6361:20078788, S2CID 16602121.
  7. ^ "* ups Leo". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2016-09-29.
  8. ^ a b c Teng, Huan-Yu; Sato, Bun'ei; Takarada, Takuya; Omiya, Masashi; Harakawa, Hiroki; Izumiura, Hideyuki; Kambe, Eiji; Takeda, Yoichi; Yoshida, Michitoshi; Itoh, Yoichi; Ando, Hiroyasu; Kokubo, Eiichiro (2022), "Regular radial velocity variations in nine G- and K-type giant stars: Eight planets and one planet candidate", Publications of the Astronomical Society of Japan, 74: 92–127, arXiv:2112.07169, doi:10.1093/pasj/psab112
  9. ^ a b Wallace, A. L.; Casey, A. R.; Brown, A. G. A.; Castro-Ginard, A. (2024-11-10). "Detection and Characterisation of Giant Planets with Gaia Astrometry". arXiv:2411.06705.
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