51 Orionis

This article is about b Orionis; it is not to be confused with β (beta) Orionis.

51 Orionis is a single^[10] star in the equatorial constellation of Orion.^[9] It has the Bayer designation b Orionis, while 51 Orionis is the Flamsteed designation. This object is visible to the naked eye as a faint, orange-hued star with an apparent visual magnitude of 4.90.^[2] It is located approximately 299 light-years away from the Sun based on parallax,^[1] and is drifting further away with a radial velocity of +88 km/s.^[4]

51 Orionis

Location of 51 Orionis (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Orion
Right ascension	05h 42m 28.63240s[1]
Declination	+01° 28′ 28.6714″[1]
Apparent magnitude (V)	4.90[2]
Characteristics
Spectral type	K1III[3]
U−B color index	+1.06[2]
B−V color index	+1.17[2]
Astrometry
Radial velocity (Rv)	+87.55[4] km/s
Proper motion (μ)	RA: −54.741[1] mas/yr Dec.: −14.732[1] mas/yr
Parallax (π)	10.9178±0.2225 mas[1]
Distance	299 ± 6 ly (92 ± 2 pc)
Absolute magnitude (MV)	0.13[5]
Details
Mass	1.11[5] M☉
Radius	19.3+0.4 −1.0[1] R☉
Luminosity	132±3[1] L☉
Surface gravity (log g)	2.24[6] cgs
Temperature	4,458+92 −51[1] K
Metallicity [Fe/H]	−0.45[6] dex
Rotational velocity (v sin i)	1.1[7] km/s
Age	4.06[8] Gyr
Other designations
b Ori, 51 Ori, BD+01°1105, FK5 2427, GC 7136, HD 37984, HIP 26885, HR 1963, SAO 113056[9]
Database references
SIMBAD	data

This is an aging giant star with a stellar classification of K1III,^[3] having exhausted the supply of hydrogen at its core and expanded to 19 times the Sun's radius.^[1] It is four^[8] billion years old with 1.11^[5] times the mass of the Sun. The star is radiating 132^[1] times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,458 K.^[1]