Astronomy:Mu Centauri

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Short description: Variable star in the constellation Centaurus
Mu Centauri
Location of μ Centauri (circled)
Observation data
Equinox J2000.0]] (ICRS)
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][2] mas/yr
Dec.: −18.64[2] mas/yr
Parallax (π)6.45 ± 0.16[2] mas
Distance510 ± 10 ly
(155 ± 4 pc)
Absolute magnitude (MV)−2.48[1]
Details
Mass9.1±0.2[7] M☉
Radius4.21 (equatorial)
3.4±0.3 (polar)[8] R☉
Luminosity2,090[8] L☉
Surface gravity (log g)3.86 (equatorial)
4.33 (polar)[8] cgs
Temperature17,600 (equatorial)
23,200±200 (polar)[8] K
Rotation11.615 hours[8]
Rotational velocity (v sin i)194[9] km/s
Age19.8±1.7[7] Myr
Other designations
μ Cen, CD−41°8172, FK5 508, HD 120324, HIP 67472, HR 5193, SAO 224471[10]
Database references
SIMBADdata

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]

A visual band light curve for Mu Centauri, plotted from data published by Aguayo et al. (2018)[12]

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]

References

  1. ↑ 1.0 1.1 Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters 38 (5): 331. doi:10.1134/S1063773712050015. Bibcode: 2012AstL...38..331A.  XHIP record for this object at VizieR.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, doi:10.1051/0004-6361:20078357, Bibcode: 2007A&A...474..653V. 
  3. ↑ 3.0 3.1 3.2 3.3 Gutierrez-Moreno, Adelina; Moreno, Hugo (June 1968), "A photometric investigation of the Scorpio-Centaurus association", Astrophysical Journal Supplement 15: 459, doi:10.1086/190168, Bibcode: 1968ApJS...15..459G. 
  4. ↑ 4.0 4.1 4.2 Samus, N. N. et al. (2017), "General Catalogue of Variable Stars", Astronomy Reports, 5.1 61 (1): 80–88, doi:10.1134/S1063772917010085, Bibcode: 2017ARep...61...80S. 
  5. ↑ 5.0 5.1 Morgan, W. W. et al. (1978), "Revised MK Spectral Atlas for stars earlier than the sun", Williams Bay: Yerkes Observatory, Bibcode: 1978rmsa.book.....M. 
  6. ↑ 6.0 6.1 Gontcharov, G. A. (2006), "Pulkovo compilation of radial velocities for 35495 stars in a common system", Astronomy Letters 32 (11): 759–771, doi:10.1134/S1063773706110065, Bibcode: 2006AstL...32..759G. 
  7. ↑ 7.0 7.1 7.2 7.3 Tetzlaff, N. et al. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun", Monthly Notices of the Royal Astronomical Society 410 (1): 190–200, doi:10.1111/j.1365-2966.2010.17434.x, Bibcode: 2011MNRAS.410..190T. 
  8. ↑ 8.0 8.1 8.2 8.3 8.4 8.5 8.6 Rivinius, 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, doi:10.1051/0004-6361:20010185, Bibcode: 2001A&A...369.1058R. 
  9. ↑ 9.0 9.1 Bernacca, P. L.; Perinotto, M. (1970), "A catalogue of stellar rotational velocities", Contributi Osservatorio Astronomico di Padova in Asiago 239 (1), Bibcode: 1970CoAsi.239....1B. 
  10. ↑ "mu Cen". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=mu+Cen. 
  11. ↑ Star Catalogue of Ptolemy, http://astro.isi.edu/reference/almagest.html, retrieved 2007-11-15. 
  12. ↑ Aguayo, G. et al. (October 2018), "Multi-epoch L-band Spectroscopy of the Be Star μ Centauri Prior to Outburst", The Astronomical Journal 156 (4): 174, doi:10.3847/1538-3881/aad5db, Bibcode: 2018AJ....156..174A. 
  13. ↑ 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. 
  14. ↑ Rivinius, Th. et al. (November 2003), "Non-radially pulsating Be stars", Astronomy and Astrophysics 411 (2): 229–247, doi:10.1051/0004-6361:20031285, Bibcode: 2003A&A...411..229R. 
  15. ↑ 15.0 15.1 15.2 Zorec, J. et al. (October 2005), "On the evolutionary status of Be stars. I. Field Be stars near the Sun", Astronomy and Astrophysics 441 (1): 235–248, doi:10.1051/0004-6361:20053051, Bibcode: 2005A&A...441..235Z. 
  16. ↑ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html, retrieved 2012-01-16. 
  17. ↑ de Geus, E. J. et al. (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. 



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