Alpha Muscae

Alpha Muscae
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]
Characteristics
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]
Astrometry
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]
Details
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
SIMBADdata

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]

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