Alpha Muscae

Coordinates: Sky map 12h 37m 11.08s, −69° 08′ 07.9″
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Alpha Muscae
Musca IAU.svg
Red circle.svg
Location of α Muscae (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Musca
Right ascension 12h 37m 11.01789s[1]
Declination –69° 08′ 08.0332″[1]
Apparent magnitude (V) +2.69[2]
Spectral type B2 IV–V[3]
U−B color index −0.854[2]
B−V color index −0.219[2]
Variable type β Cep[4]
Radial velocity (Rv)+13[5] km/s
Proper motion (μ) RA: −40.20[1] mas/yr
Dec.: −12.80[1] mas/yr
Parallax (π)10.34 ± 0.11 mas[1]
Distance315 ± 3 ly
(97 ± 1 pc)
Absolute magnitude (MV)–2.2[6]
Mass8.8±0.1[3] M
Radius4.8[7] R
Luminosity4,000[6] L
Surface gravity (log g)4.06[6] cgs
Temperature21,400[6] K
Rotational velocity (v sin i)114[8] km/s
Age18.3±3.2[3] Myr
Other designations
α Mus, CD−68 1104, CPD−68 1702, FK5 474, HD 109668, HIP 61585, HR 4798, SAO 251974[9]
Database references

Alpha Muscae, Latinized from α Muscae, is a star in the southern circumpolar constellation of Musca. With an apparent visual magnitude of +2.7,[2] it is the brightest star in the constellation. The distance to this star has been determined using parallax measurements, giving an estimate of about 315 light-years (97 parsecs) from Earth.[1]

With a stellar classification of B2 IV-V,[3] this star appears to be in the process of evolving away from the main sequence of stars like the Sun and turning a subgiant star, as the supply of hydrogen at its core becomes exhausted. It is larger than the Sun, with nearly nine[3] times the mass and almost five[7] times the radius. This star is radiating around 4,000[6] times as much luminosity as the Sun from its outer atmosphere at an effective temperature of 21,400 K,[6] giving it the blue-white hue of a B-type star.[10]

A light curve for Alpha Muscae, plotted from TESS data[11]

Alpha Muscae appears to be a Beta Cephei variable star. Telting and colleagues report it as a Beta Cephei with a high degree of confidence as they found regular pulsations in its spectrum in a high-resolution spectroscopy study published in 2006,[4] although Stankov and Handler (2005) listed it as a poor or rejected candidate in their Catalog of Galactic β Cephei Stars.[8] The International Variable Star Index lists it as a Beta Cephei variable which varies in brightness from magnitude 2.68 to 2.73, with a period of 2.17 hours.[12] Alpha Muscae is rotating rapidly with a projected rotational velocity of 114 km s−1[8] and has an estimated age of about 18 million years.[3]

This star is a proper motion member of the Lower Centaurus–Crux sub-group in the Scorpius–Centaurus OB association, the nearest such association of co-moving massive stars to the Sun.[6] Alpha Muscae has a peculiar velocity of 10 km s−1, which, while high, is not enough for it to be considered a runaway star.[3]


  1. ^ a b c d e f van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357, S2CID 18759600
  2. ^ a b c d Gutierrez-Moreno, Adelina; Moreno, Hugo (June 1968), "A photometric investigation of the Scorpio-Centaurus association", Astrophysical Journal Supplement, 15: 459, Bibcode:1968ApJS...15..459G, doi:10.1086/190168
  3. ^ a b c d e f g Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (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, arXiv:1007.4883, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x, S2CID 118629873
  4. ^ a b Telting, J. H.; et al. (June 2006), "A high-resolution spectroscopy survey of β Cephei pulsations in bright stars", Astronomy and Astrophysics, 452 (3): 945–953, Bibcode:2006A&A...452..945T, doi:10.1051/0004-6361:20054730
  5. ^ 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, University of Toronto: International Astronomical Union, 30: 57, Bibcode:1967IAUS...30...57E
  6. ^ a b c d e f g 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
  7. ^ a b Underhill, A. B.; et al. (November 1979), "Effective temperatures, angular diameters, distances and linear radii for 160 O and B stars", Monthly Notices of the Royal Astronomical Society, 189 (3): 601–605, Bibcode:1979MNRAS.189..601U, doi:10.1093/mnras/189.3.601
  8. ^ a b c Stankov, Anamarija; Handler, Gerald (June 2005), "Catalog of Galactic β Cephei Stars", The Astrophysical Journal Supplement Series, 158 (2): 193–216, arXiv:astro-ph/0506495, Bibcode:2005ApJS..158..193S, doi:10.1086/429408, S2CID 119526948
  9. ^ "HD 109668 -- Variable Star of Beta Cep type", SIMBAD Astronomical Database, retrieved 2007-01-29
  10. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on November 8, 2004, retrieved 2012-01-16
  11. ^ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 8 December 2021.
  12. ^ "alf Mus". The International Variable Star Index. AAVSO. Retrieved 16 December 2022.