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Regulus

This article is about the star. For other uses, see Regulus (disambiguation).
Regulus
Location of Regulus (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Leo
Pronunciation UK: /ˈrɛɡˌjulʊs/ US: /ˈrɛɡˌjʊlʊsˌ/[1]
Regulus A
Right ascension 10h 08m 22.311s[2]
Declination +11° 58′ 01.95″[2]
Apparent magnitude (V) 1.40[3]
Regulus BC
Right ascension 10h 08m 12.8/14s[4]
Declination +11° 59′ 48″[4]
Apparent magnitude (V) 8.13[5]/13.50[5]
Characteristics
Regulus A
Evolutionary stage Subgiant
Spectral type B8 IVn[3]
U−B color index –0.36[6]
B−V color index –0.11[6]
Variable type Suspected[7]
Regulus BC
Evolutionary stage Main sequence
Spectral type K2 V[8] + M4 V[8]
U−B color index +0.51[6]
B−V color index +0.86[6]
Astrometry
A
Radial velocity (Rv)4.39±0.09[9] km/s
Proper motion (μ) RA: −248.73±0.35[2] mas/yr
Dec.: 5.59±0.21[2] mas/yr
Parallax (π)41.13 ± 0.35 mas[2]
Distance79.3 ± 0.7 ly
(24.3 ± 0.2 pc)
Absolute magnitude (MV)–0.57[10]
BC
Radial velocity (Rv)+6.72[11] km/s
Proper motion (μ) RA: −254.399±0.028[11] mas/yr
Dec.: 8.127±0.027[11] mas/yr
Parallax (π)41.2745 ± 0.0270 mas[11]
Distance79.02 ± 0.05 ly
(24.23 ± 0.02 pc)
Absolute magnitude (MV)6.20/11.56[12]
Orbit[9]
Primaryα Leo Aa (HD 87901 A)
Companionα Leo Ab (HD 87901 B)
Period (P)40.102±0.002 d
Semi-major axis (a)6.00±0.17 R☉ projected
Eccentricity (e)0 (assumed)
Semi-amplitude (K1)
(primary)		7.58±0.12 km/s
Details
α Leo A
Mass3.8[13] M☉
Radius4.16±0.08 (equatorial), 3.14±0.06 (polar)[14] R☉
Luminosity314±36[14] L☉
Surface gravity (log g)3.54±0.09[15] cgs
Temperature10,314 (equatorial), 15,400 (polar)[14] K
Metallicity [Fe/H]+0.21[16] dex
Rotation15.9 hours[14]
Rotational velocity (v sin i)318±8[17] km/s
Age≳1[18] Gyr
α Leo B
Mass0.8[19] M☉
Radius0.83[12] R☉
Luminosity0.50[19] L☉
Surface gravity (log g)4.4[19] cgs
Temperature4,885[19] K
Metallicity [Fe/H]−0.21[20] dex
α Leo C
Mass0.3[5] M☉
Radius0.37[12] R☉
Temperature3,242[12] K
Other designations
α Leonis, 32 Leonis, GJ 9316, HR 3982, ADS 7654, WDS J10084+1158
α Leo A: BD+12°2149, FK5 380, HD 87901, HIP 49669, SAO 98967, LTT 12716
α Leo B/C: BD+12°2147, HD 87884, SAO 98966, LTT 12714
Database references
SIMBADRegulus
BC

Regulus is the brightest object in the constellation Leo and one of the brightest stars in the night sky. It has the Bayer designation designated α Leonis, which is Latinized to Alpha Leonis, and abbreviated Alpha Leo or α Leo. Regulus appears singular, but is actually a quadruple star system composed of four stars that are organized into two pairs. The spectroscopic binary Regulus A consists of a blue-white main-sequence star and its companion, which has not yet been directly observed, but is probably a white dwarf. The system lies approximately 79 light years from the Sun.

HD 87884 is separated from Regulus by 176″ and is itself a close pair. Regulus, along with five slightly dimmer stars (Zeta Leonis, Mu Leonis, Gamma Leonis, Epsilon Leonis, and Eta Leonis) have collectively been called 'the Sickle', which is an asterism that marks the head of Leo.

  1. ^ "regulus". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
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