Alpha Muscae

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]

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]
Distance	315 ± 3 ly (97 ± 1 pc)
Absolute magnitude (MV)	−2.2[6]
Details
Mass	8.8±0.1[3] M☉
Radius	5.22 ± 0.06[7][a] R☉
Luminosity	4,270±100[7] L☉
Surface gravity (log g)	4.06[6] cgs
Temperature	20,400[7] K
Rotational velocity (v sin i)	114[8] km/s
Age	18.3±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
SIMBAD	data

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 5.2 times the radius.^[a] This star is radiating around 4,300 times as much luminosity as the Sun from its outer atmosphere at an effective temperature of 20,400 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]

Notes

1. Calculated, using the Stefan-Boltzmann law and the star's effective temperature and luminosity, with respect to the solar nominal effective temperature of 5,772 K:$${\displaystyle {\sqrt {{\biggl (}{\frac {5,772}{20,400}}{\biggr )}^{4}\cdot 10^{3.63}}}=5.22\ R_{\odot }.}$$