Rho Leonis
Variable star in the constellation Leo
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Rho Leonis, also named Shaomin,[9] is a star in the zodiac constellation of Leo, and, like the prominent nearby star Regulus, is near the ecliptic. With an apparent visual magnitude of 3.9,[5] this star can be readily seen with the naked eye. Spectroscopic measurements give a distance estimate of about 2,930 light-years (900 parsecs) from the Earth.[7] Rho Leonis is an Alpha Cygni-type variable star, showing 0.032 magnitude brightness variations with a period of 3.427 days, in Hipparcos data.[10]
 | |
| Observation data Epoch J2000 Equinox ICRS | |
|---|---|
| Constellation | Leo |
| Right ascension | 10h 32m 48.67168s[1] |
| Declination | +09° 18′ 23.7094″[1] |
| Apparent magnitude (V) | 3.83 - 3.90[2] |
| Characteristics | |
| Evolutionary stage | Blue loop[3] |
| Spectral type | B1 Iab[4] |
| U−B color index | −0.945[5] |
| B−V color index | −0.153[5] |
| Variable type | α Cyg[2] |
| Astrometry | |
| Radial velocity (Rv) | +42.0[6] km/s |
| Proper motion (μ) | RA: −5.93±0.20 mas/yr[1] Dec.: −3.40±0.11 mas/yr[1] |
| Distance | 2,900±230 ly (900±70 pc)[7] |
| Absolute magnitude (MV) | −6.19±0.2[7] |
| Details | |
| Mass | 19.9±1.0[7] M☉ |
| Radius | 28±3[7] R☉ |
| Luminosity | 151,000+30,600 −25,500[7] L☉ |
| Surface gravity (log g) | 2.87±0.04[7] cgs |
| Temperature | 21,700±200[7] K |
| Metallicity [Fe/H] | −0.06[8] dex |
| Rotation | 12.5±0.7[3] days |
| Rotational velocity (v sin i) | 49.0±2.4[3] km/s |
| Age | 9.12+0.88 −0.91[7] Myr |
| Other designations | |
| Shaomin, ρ Leo, 47 Leo, BD+10 2166, FK5 396, HD 91316, HIP 51624, HR 4133, SAO 118355 | |
| Database references | |
| SIMBAD | data |
Nomenclature
ρ Leonis (Latinized to Rho Leonis, abbreviated ρ Leo, Rho Leo) is the star's Bayer designation.
Rho Leonis has the traditional Chinese name Shaomin (少民); it and ο Leonis (Taimin, 太民) are the two southernmost stars of the Xuanyuan (轩辕) constellation. The IAU Working Group on Star Names approved the name Shaomin for ρ Leonis on 18 July 2024 and it is now so entered in the IAU Catalog of Star Names; ο Leonis has the IAU-approved name Subra.[9]
Characteristics
The spectrum of Rho Leonis matches a stellar classification of B1 Iab,[4] with the 'Iab' luminosity class indicating that it is a supergiant star. Rho Leonis is a former red supergiant that shifted back to hotter temperatures, being in the evolutionary stage known as the blue loop.[3]
This is an enormous star with about 20 times the Sun's mass (M☉) and 28 times the Sun's radius (R☉). Rho Leonis is radiating about 150,000 times the Sun's luminosity (L☉) at an effective temperature of 21,700 K,[7] giving it the blue-white hue typical of a B-type star. A strong stellar wind is expelling mass from the outer envelope at a rate of 3.5×10−7 M☉ per year, or the equivalent of 1 M☉ every 2.8 million years.[12] The rotation rate is about once per 12.5 days. The star rotates at an angle of 21.7°+0.5°
−0.4° relative to Earth.[3]
Rho Leonis is classified as a runaway star, which means it has a peculiar velocity of at least 30 km s−1 relative to the surrounding stars. It has radial velocity of 42 km s−1 away from the Sun and a proper motion that is carrying it about 1.56 astronomical units per year, equivalent to 7 km s−1,[a] in a transverse direction. The star is situated about 2,300 light-years (710 parsecs) above the galactic plane.[13]
The star is 0.15 degree north of the ecliptic, so it can be occulted by the moon.[14] Unusual light variation during these occultations has been explained as the result of a possible close companion, which would be just over one magnitude fainter and separated by 0.01 arcsec.[15] It has not been detected by any other means although it should be easily detected with modern observations.[16] Speckle interferometry observations made during 2009 to 2023 did not detect the companion, strongly indicating that it does not exist.[17] However, there is evidence for a companion from spectroscopic observations, which could be interpreted as radial pulsations or the presence of a secondary star that periodically exchange mass with the primary and has its own circumstellar disk.[3]
Notes
- An Astronomical Unit (AU) is 1.5×108 km, while a year is 3.2×107 s. Thus, 1.56 AU/year = (1.56 AU/yr) × (1.5×108 km/AU) / (3.2×107 s/yr) = 7 km/s.