S Muscae

S Muscae is a classical (δ) Cepheid variable star in the constellation Musca about 2,600 light years away.

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

S Muscae

Location of S Muscae (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Musca
Right ascension	12h 12m 47.01834s[1]
Declination	−70° 09′ 06.4363″[1]
Apparent magnitude (V)	6.394[2] (5.89 - 6.49[3])
Characteristics
Spectral type	F6Ib (F6-G0[3]) + B5V[4]
U−B color index	+0.66[5]
B−V color index	+1.00[5]
Variable type	δ Cepheid[3]
Astrometry
Radial velocity (Rv)	−1.91[6] km/s
Proper motion (μ)	RA: −7.79[1] mas/yr Dec.: −0.60[1] mas/yr
Parallax (π)	1.99±0.84 mas[1]
Distance	863[2] pc
Absolute magnitude (MV)	−4.01[7]
Orbit[7][8]
Period (P)	504.9 ± 0.07
Semi-major axis (a)	794 AU
Eccentricity (e)	0.08 ± 0.002
Inclination (i)	32 ± 1°
Semi-amplitude (K1) (primary)	14.7 ± 0.2 km/s
Details
Mass	6.2[7] M☉
Radius	65.1[2] R☉
Luminosity	3,467[7] L☉
Metallicity	+0.18[9]
companion
Mass	5.3[7] M☉
Temperature	17,000[10] K
Other designations
S Mus, HR 4645, SAO 251791, CD−69°977, GSC 09231-00752, HD 106111, GC 16679, HIP 59551, AAVSO 1207-69
Database references
SIMBAD	data

S Muscae is a yellow supergiant ranging between spectral types F6Ib and G0Ib and magnitudes 5.89 to 6.49 over a period of 9.66 days.^[3] It is a luminous star around six times as massive as the Sun and 65.1 times the radius of the Sun. It is a binary star with a blue-white main sequence star companion likely to be of spectral type B3V to B5V with a mass of just over five solar masses,^[12] one of the hottest and brightest companions of a Cepheid known. The two stars orbit each other every 505 days.^[13]

S Muscae has been found to lie within the faint star cluster ASCC 69.^[14]