Alpha Monocerotis

Alpha Monocerotis, Latinised from α Monocerotis, is the Bayer designation for a star in the equatorial constellation of Monoceros. It can be viewed with the naked eye, having an apparent visual magnitude of 3.94.^[2] Despite being labeled "alpha", it is not the brightest star in the constellation; Beta Monocerotis is.^[10] Based upon an annual parallax shift of 22.4 mas as seen from Earth,^[1] it is located 146 light-years away from the Sun. The star is moving away from the Sun with a radial velocity of +11.7 km/s.^[5]

α Monocerotis

Location of α Monocerotis (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Monoceros
Right ascension	07h 41m 14.832s[1]
Declination	−09° 33′ 04.08″[1]
Apparent magnitude (V)	3.94[2]
Characteristics
Evolutionary stage	red clump[3]
Spectral type	G9.5 III-IIIb Fe-0.5[4]
B−V color index	1.022[2]
Astrometry
Radial velocity (Rv)	11.66±0.06[5] km/s
Proper motion (μ)	RA: −74.989 mas/yr[1] Dec.: −19.838 mas/yr[1]
Parallax (π)	22.3839±0.1348 mas[1]
Distance	145.7 ± 0.9 ly (44.7 ± 0.3 pc)[1]
Absolute magnitude (MV)	0.71±0.08[6]
Details
Mass	2.25±0.13[5] M☉
Radius	10.42±0.12[7] R☉
Luminosity	63.7±1.3[7] L☉
Surface gravity (log g)	2.79±0.04[5] cgs
Temperature	5049±32[7] K
Metallicity [Fe/H]	−0.04±0.03[5] dex
Rotation	326 days[8]
Rotational velocity (v sin i)	0.92±0.45[5] km/s
Age	890±180[5] Myr
Other designations
α Mon, 26 Monocerotis, BD−09°2172, HD 61935, HIP 37447, HR 2970, SAO 134986[9]
Database references
SIMBAD	data

The stellar classification of G9.5 III-IIIb Fe-0.5^[4] indicates this is an evolved giant star of type G, which means the hydrogen has been depleted at its core and the outer envelope has expanded and cooled. The 'Fe−0.5' notation indicates the spectrum displays a slight underabundance of iron relative to other stars of this temperature. It is a red clump giant, which means it is generating energy through helium fusion at its core.^[3] At the age of 890 million years, this yellow-hued star has an estimated 2.2 times the mass of the Sun^[5] and 10 times the Sun's radius.^[7] It is spinning sedately with a rotation period of about 326 days.^[8]