Mu Centauri

Mu Centauri, Latinized from μ Centauri, is a third-magnitude star in the southern constellation of Centaurus. With the stars ν and φ Centauri, it marks what has been traditionally portrayed as "dextro Latere" (the right side) of the Centaur. The apparent visual magnitude of this star is 3.42,[2] making it one of the brighter members of the constellation. The distance to this star can be estimated directly using parallax measurements, which yield a value of roughly 510 light years (155 parsecs) from Earth.[1]

Mu Centauri

Location of μ Centauri (circled)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Centaurus
Right ascension	13h 49m 36.98863s[1]
Declination	−42° 28′ 25.4296″[1]
Apparent magnitude (V)	+3.42[2] (+2.75 to +3.25)[3]
Characteristics
Spectral type	B2 IV-Ve[4]
U−B color index	−0.854[2]
B−V color index	−0.205[2]
Variable type	γ Cas[3]
Astrometry
Radial velocity (Rv)	+9.1[5] km/s
Proper motion (μ)	RA: −24.25[1] mas/yr Dec.: −18.64[1] mas/yr
Parallax (π)	6.45 ± 0.16[1] mas
Distance	510 ± 10 ly (155 ± 4 pc)
Absolute magnitude (MV)	−2.48[6]
Details
Mass	9.1 ± 0.2[4] M☉
Radius	3.4 × 4.2[7] R☉
Luminosity	2,089[8] L☉
Surface gravity (log g)	3.95 (3.86–4.33)[7] cgs
Temperature	22,410[7] K
Rotational velocity (v sin i)	194[9] km/s
Age	19.8 ± 1.7[4] Myr
Other designations
μ Cen, CD−41°8172, FK5 508, HD 120324, HIP 67472, HR 5193, SAO 224471.
Database references
SIMBAD	data

The spectrum of Mu Centauri matches a stellar classification of B2 IV-Ve.[4] The 'e' suffix is used to mark the presence of emission lines, which indicates this is a Be star surrounded by a circumstellar disk of hot gas that was formed from material ejected from the star. Mu Centauri is a pulsating variable star that has multiple non-radial cycles with a primary period of 0.503 days. Three other pulsation cycles have a similar period, while two have a shorter interval of about 0.28 days. It undergoes outburst events that result in the transfer of additional material to the surrounding disk.[10] During these outbursts, the star can experience transient periodicities.[11] Mu Centauri is classified as a Gamma Cassiopeiae typevariable star and its brightness varies from magnitude +2.75 to +3.25.[3]

This star is spinning rapidly, with a projected rotational velocity of 194,[9] km s⁻¹ and is completing a full rotation in about 11.615 hours. The equatorial azimuthal velocity is around 85% of the critical velocity where the star would start to break up, resulting a pronounced equatorial bulge that is about 26% wider than the radius at the poles. Because of the oblate spheroidal shape of this star, the polar region is at a higher temperature than the equator—23,000 K versus 17,600 K respectively. Likewise, the gravitational force at the poles is greater than along the equator. The axis of rotation of the star is tilted by an angle of about (19 ± 3)° to the line of sight from the Earth.[8]

At an estimated age of nearly 20 million years,[4] this star is around 55–65% of the way through its evolutionary period on the main sequence of core hydrogen burning stars.[7] It has around nine[4] times the mass of the Sun and four[7] times the Sun's radius, but emits over 2,000[8] times as much energy as the Sun. The outer atmosphere has a mean effective temperature of 22,410 K,[7] giving the star a blue-white hue.[12]

This star is a proper motion member of the Upper-Centaurus Lupus sub-group in the Scorpius-Centaurus OB association, the nearest such co-moving association of massive stars to the Sun.[13]