Mu Leonis (μ Leonis, abbreviated Mu Leo, μ Leo), also named Rasalas,[1] [2] is a star in the constellation of Leo. The apparent visual magnitude of this star is 3.88, which is bright enough to be seen with the naked eye. Based upon an annual parallax shift of 0.02628 arc seconds as measured by the Hipparcos satellite, this system is 38.1pc from the Sun. In 2014, an exoplanet was discovered to be orbiting the star.
μ Leonis (Latinised to Mu Leonis) is the star's Bayer designation.
It bore the traditional names Rasalas and Alshemali, both abbreviations of Ras al Asad al Shamaliyy. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalogue and standardize proper names for stars. The WGSN approved the name Rasalas for this star on 12 September 2016 and it is now so included in the List of IAU-approved Star Names.[2]
Mu Leonis is an evolved K-type red giant star with a stellar classification of . It is believed to be on the red 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 normal absorption lines of cyanogen and calcium in its spectrum. It has around 1.5 times the Sun's mass, but has expanded to around 14 times the Sun's radius. Mu Leonis shines with 63 times the luminosity of the Sun from an outer atmosphere that has an effective temperature of 4,436 K. It is around 3.35 billion years old, however research in 2018 suggested it could be around 5 billion years old, older than the Sun's 4.6 billion years old.
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 measuring radial velocity variations caused by gravitational displacement from the orbiting body.