Regulus
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.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Leo |
| Pronunciation | UK: /ˈrɛɡˌjulʊs/ US: /ˈrɛɡˌjʊlʊsˌ/ |
| Regulus A | |
| Right ascension | 10h 08m 22.311s |
| Declination | +11° 58′ 01.95″ |
| Apparent magnitude (V) | 1.40 |
| Regulus BC | |
| Right ascension | 10h 08m 12.8/14s |
| Declination | +11° 59′ 48″ |
| Apparent magnitude (V) | 8.13/13.50 |
| Characteristics | |
| Regulus A | |
| Evolutionary stage | Subgiant |
| Spectral type | B8 IVn |
| U−B color index | –0.36 |
| B−V color index | –0.11 |
| Variable type | Suspected |
| Regulus BC | |
| Evolutionary stage | Main sequence |
| Spectral type | K2 V + M4 V |
| U−B color index | +0.51 |
| B−V color index | +0.86 |
| Astrometry | |
| A | |
| Radial velocity (Rv) | 4.39±0.09 km/s |
| Proper motion (μ) | RA: −248.73±0.35 mas/yr Dec.: 5.59±0.21 mas/yr |
| Parallax (π) | 41.13 ± 0.35 mas |
| Distance | 79.3 ± 0.7 ly (24.3 ± 0.2 pc) |
| Absolute magnitude (MV) | –0.57 |
| BC | |
| Radial velocity (Rv) | +6.72 km/s |
| Proper motion (μ) | RA: −254.399±0.028 mas/yr Dec.: 8.127±0.027 mas/yr |
| Parallax (π) | 41.2745 ± 0.0270 mas |
| Distance | 79.02 ± 0.05 ly (24.23 ± 0.02 pc) |
| Absolute magnitude (MV) | 6.20/11.56 |
| Orbit | |
| Primary | α Leo Aa (HD 87901 A) |
| Companion | α 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 | |
| Mass | 3.8 M☉ |
| Radius | 4.35±0.1 R☉ |
| Luminosity | 316.2±16.7 L☉ |
| Surface gravity (log g) | 3.54±0.09 cgs |
| Temperature | 11,668±195 K |
| Metallicity [Fe/H] | +0.21 dex |
| Rotation | 15.9 hours |
| Rotational velocity (v sin i) | 318±8 km/s |
| Age | ≳1 Gyr |
| α Leo B | |
| Mass | 0.8 M☉ |
| Radius | 0.83 R☉ |
| Luminosity | 0.50 L☉ |
| Surface gravity (log g) | 4.4 cgs |
| Temperature | 4,885 K |
| Metallicity [Fe/H] | −0.21 dex |
| α Leo C | |
| Mass | 0.3 M☉ |
| Radius | 0.37 R☉ |
| Temperature | 3,242 K |
| Other designations | |
| 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 | |
| SIMBAD | Regulus |
| BC | |
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.