Mu Centauri
Variable star in the constellation Centaurus
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Mu Centauri is a star in the southern constellation of Centaurus. Its name is a Bayer designation that is Latinized from μ Centauri, and abbreviated Mu Cen or μ Cen. With the stars ν and φ Centauri, it marks what has been traditionally portrayed as "dextro Latere" (the right side) of the Centaur.[11] The apparent visual magnitude of this star is 3.42,[3] 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.[2] It is drifting further away with a radial velocity of +9 km/s.[6]
  | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Centaurus[1] |
| Right ascension | 13h 49m 36.98863s[2] |
| Declination | −42° 28′ 25.4296″[2] |
| Apparent magnitude (V) | +3.42[3] (+2.92 to +3.49)[4] |
| Characteristics | |
| Spectral type | B2V:e[5] |
| U−B color index | −0.854[3] |
| B−V color index | −0.205[3] |
| Variable type | γ Cas[4] |
| Astrometry | |
| Radial velocity (Rv) | +9.2±2.7[6] km/s |
| Proper motion (μ) | RA: −24.25[2] mas/yr[2] Dec.: −18.64 mas/yr[2] |
| Parallax (π) | 6.45±0.16 mas[2] |
| Distance | 510 ± 10 ly (155 ± 4 pc) |
| Absolute magnitude (MV) | −2.48[1] |
| Details | |
| Mass | 9.1±0.2[7] M☉ |
| Radius | 4.21 (equatorial) 3.4±0.3 (polar)[8] R☉ |
| Luminosity | 2,090[8] L☉ |
| Surface gravity (log g) | 3.86 (equatorial) 4.33 (polar)[8] cgs |
| Temperature | 17,600 (equatorial) 23,200±200 (polar)[8] K |
| Rotation | 11.615 hours[8] |
| Rotational velocity (v sin i) | 194[9] km/s |
| Age | 19.8±1.7[7] Myr |
| Other designations | |
| μ Cen, CD−41°8172, FK5 508, HD 120324, HIP 67472, HR 5193, SAO 224471[10] | |
| Database references | |
| SIMBAD | data |
The spectrum of Mu Centauri is considered to be a standard for a B2 Be star with the stellar classification of B2V:e.[5] The 'e' suffix is used to mark the presence of emission lines, caused 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.[13] During these outbursts, the star can experience transient periodicities.[14] Mu Centauri is classified as a Gamma Cassiopeiae type variable star and its brightness varies from magnitude +2.92 to +3.49.[4]
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,[7] this star is around 55–65% of the way through its evolutionary period on the main sequence of core hydrogen burning stars.[15] It has around nine[7] times the mass of the Sun and four[15] 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,[15] giving the star a blue-white hue.[16]
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.[17]