Mu Centauri

Mu Centauri

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

Mu Centauri (μ Cen, 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.[1] The apparent visual magnitude of this star is 3.42, 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.

The spectrum of Mu Centauri matches a stellar classification of B2 IV-Ve. 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. During these outbursts, the star can experience transient periodicities. Mu Centauri is classified as a Gamma Cassiopeiae typevariable star and its brightness varies from magnitude +2.75 to +3.25.

This star is spinning rapidly, with a projected rotational velocity of 194, 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.

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

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.