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.[1] 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]
The spectrum of Mu Centauri is considered to be a standard for a B2 Be star with the stellar classification of B2V:e.[4] 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.[12] During these outbursts, the star can experience transient periodicities.[13] Mu Centauri is classified as a Gamma Cassiopeiae typevariable star and its brightness varies from magnitude +2.92 to +3.49.[3]
This star is spinning rapidly, with a projected rotational velocity of 194,[10] 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.[9]
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.[8] It has around nine[7] times the mass of the Sun and four[8] times the Sun's radius, but emits over 2,000[9] times as much energy as the Sun. The outer atmosphere has a mean effective temperature of 22,410 K,[8] giving the star a blue-white hue.[14]
^ abMorgan, W. W; Abt, Helmut A; Tapscott, J. W (1978). "Revised MK Spectral Atlas for stars earlier than the sun". Williams Bay: Yerkes Observatory. Bibcode:1978rmsa.book.....M.
^Evans, D. S. (June 20–24, 1966), Batten, Alan Henry; Heard, John Frederick (eds.), "The Revision of the General Catalogue of Radial Velocities", Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30, vol. 30, University of Toronto: International Astronomical Union, p. 57, Bibcode:1967IAUS...30...57E
^ abcRivinius, Th.; et al. (April 2001), "Stellar and circumstellar activity of the Be star mu Centauri. III. Multiline nonradial pulsation modeling", Astronomy and Astrophysics, 369: 1058–1077, Bibcode:2001A&A...369.1058R, doi:10.1051/0004-6361:20010185
^ abBernacca, P. L.; Perinotto, M. (1970). "A catalogue of stellar rotational velocities". Contributi Osservatorio Astronomico di Padova in Asiago. 239 (1). Bibcode:1970CoAsi.239....1B.
^Rivinius, Th.; et al. (May 1998), "Stellar and circumstellar activity of the Be star MU Centauri. I. Line emission outbursts", Astronomy and Astrophysics, 333: 125–140, Bibcode:1998A&A...333..125R
^de Geus, E. J.; de Zeeuw, P. T.; Lub, J. (June 1989), "Physical parameters of stars in the Scorpio-Centaurus OB association", Astronomy and Astrophysics, 216 (1–2): 44–61, Bibcode:1989A&A...216...44D