Iota Mensae

Iota Mensae is a single star about 880 light years away in the faint constellation Mensa. It has a very slightly variable apparent magnitude of 6.0, making it visible with the naked eye under good skies.

A light curve for Iota Mensae plotted from TESS data^[11]

ι Mensae

Location of ι Mensae (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Mensa
Right ascension	05h 35m 36.1787s[1]
Declination	−78° 49′ 15.129″[1]
Apparent magnitude (V)	6.00 - 6.05[2]
Characteristics
Spectral type	B8 III[3]
B−V color index	−0.022[4]
Variable type	Ellipsoidal?[2]
Astrometry
Radial velocity (Rv)	12.6±4.3[5] km/s
Proper motion (μ)	RA: +5.547[1] mas/yr[1] Dec.: +25.710[1] mas/yr[1]
Parallax (π)	3.7076±0.1819 mas[1]
Distance	880 ± 40 ly (270 ± 10 pc)
Absolute magnitude (MV)	−1.03[6]
Details
Mass	3.6[1] M☉
Radius	9.5[1] R☉
Luminosity	301[1] L☉
Surface gravity (log g)	3.4[7] cgs
Temperature	11,272±264[8] K
Metallicity [Fe/H]	+0.13[9] dex
Age	203[1] Myr
Other designations
ι Men, CD−78°216, HD 38602, HIP 26264, HR 1991, SAO 256214[10]
Database references
SIMBAD	data

Iota Mensae has a spectral type of B8III, indicating that it has exhausted hydrogen at its core and expanded away from the main sequence. It is about 3.6 times the mass (M_☉), 301 times as luminous, and has swollen to 9.5 times the radius of the Sun (R_☉). It is calculated to be 314 million years old.

It has been catalogued as a chemically peculiar star with abnormally strong lines of silicon in its spectrum but this classification is now considered doubtful.^[12] Its brightness varies by a few hundredths of a magnitude. Its period was initially measured at 2.6 days,^[13] but this is now considered to be a period of 5.3 days with primary and secondary minima of a similar depth. The variability is thought to be due to the rotation of the star.^[2]