| Observation data EpochJ2000.0 EquinoxJ2000.0 (ICRS) | |
|---|---|
| Constellation | Leo |
| Right ascension | 09h 52m 45.81654s[1] |
| Declination | +26° 00′ 25.0319″[1] |
| Apparent magnitude (V) | 3.88[2] |
| Characteristics | |
| Evolutionary stage | Red giant branch[3] |
| Spectral type | K2 IIIb CN1 Ca1[4] |
| U−Bcolor index | +1.38[2] |
| B−Vcolor index | +1.23[2] |
| Astrometry | |
| Radial velocity (Rv) | 14.03±0.19[5] km/s |
| Proper motion (μ) | RA: −217.31[1]mas/yr Dec.: −54.26[1]mas/yr |
| Parallax (π) | 26.28±0.16 mas[1] |
| Distance | 124.1 ± 0.8 ly (38.1 ± 0.2 pc) |
| Absolute magnitude (MV) | +0.83[6] |
| Details | |
| Mass | 1.5±0.1[7] M☉ |
| Radius | 11.89±0.11[8] R☉ |
| Luminosity | 53±1[8] L☉ |
| Surface gravity (log g) | 2.43±0.06[8] cgs |
| Temperature | 4,519±23[8] K |
| Metallicity [Fe/H] | 0.27±0.03[8] dex |
| Rotational velocity (v sin i) | 4.5[5] km/s |
| Age | 3.35±0.70,[7] ~5.0[3] Gyr |
| Other designations | |
| Rasalas, Alshemali,μ Leo,24 Leonis,BD+26°2019,HD 85503,HIP 48455,HR 3905,SAO 81064[9] | |
| Database references | |
| SIMBAD | data |
Mu Leonis (μ Leonis, abbreviatedMu Leo,μ Leo), also namedRasalas/ˈræsəlæs/,[10][11] is astar in theconstellation ofLeo. Theapparent visual magnitude of this star is 3.88,[2] which is bright enough to be seen with the naked eye. Based upon an annualparallax shift of 0.02628 arc seconds as measured by theHipparcos satellite,[1] this system is 124light-years (38.1parsecs) from theSun. In 2014, anexoplanet was discovered to be orbiting the star.
μ Leonis (Latinised toMu Leonis) is the star'sBayer designation.
It bore the traditional namesRasalas andAlshemali, both abbreviations ofRas al Asad al Shamaliyy.[12] In 2016, theInternational Astronomical Union organized aWorking Group on Star Names (WGSN)[13] to catalogue and standardize proper names for stars. The WGSN approved the nameRasalas for this star on 12 September 2016 and it is now so included in the List of IAU-approved Star Names.[11]
Mu Leonis is an evolvedK-typered giant star with astellar classification ofK2 IIIb CN1 Ca1.[4] It is believed to be on thered giant branch, where it is fusing hydrogen into helium in a shell surrounding an inert helium core.[3] The trailing notation indicates that, for a star of its type, it has stronger than normalabsorption lines ofcyanogen andcalcium in itsspectrum.[14] It has around 1.5 times the Sun's mass[7] and is estimated to be 5 billion years old,[3] older than the Sun's age of 4.6 billion years. Usinginterferometry with theNavy Precision Optical Interferometer, itsdiameter was determined to be 11.8 times that of the Sun. Mu Leonis shines with 57 times the luminosity of the Sun from anouter atmosphere that has aneffective temperature of 4,606 K.[15]
In 2014 it was announced that Mu Leonis has a planetary companion that is at least 2.4 times as massive as Jupiter and orbits with a period of 358 days. This planet was detected by measuringradial velocity variations caused by gravitational displacement from the orbiting body.[7]
Later in 2024, a study usingastrometry from theGaia spacecraft find a mass of12.6 MJ, which the authors interpret as a likely upper limit, as the large level of RUWE in the astrometric solution—which could be caused by a companion around the star—might be just the result of systematic calibration errors. This indicate that Mu Leonis b lies in the planetary-mass regime and is not abrown dwarf.[16]
| Companion | Mass | Semimajor axis (AU) | Orbital period | Eccentricity | Discovery year |
| b | ≥2.4±0.4 and ≤12.6MJ | 1.1±0.1 | 357.8±1.2days | 0.09±0.06 | 2014 |
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