Phi1 Orionis

For other stars with this Bayer designation, see Phi Orionis.

Phi¹ Orionis is a binary star system in the constellation Orion, positioned less than a degree to the south of Meissa.^[10] It is visible to the naked eye with an apparent visual magnitude of 4.42.^[2] The distance to this system, based upon an annual parallax shift of 3.0 mas,^[1] is around 1,090 light-years.

φ¹ Orionis

φ1 (circled) in the constellation Orion
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Orion
Right ascension	05h 34m 49.23804s[1]
Declination	+09° 29′ 22.4878″[1]
Apparent magnitude (V)	4.42[2]
Characteristics
Spectral type	B0 III[3]
U−B color index	−0.97[2]
B−V color index	−0.15[2]
Astrometry
Radial velocity (Rv)	+33.2[4] km/s
Proper motion (μ)	RA: +0.27[1] mas/yr Dec.: −2.26[1] mas/yr
Parallax (π)	3.00±0.25 mas[1]
Distance	1,090 ± 90 ly (330 ± 30 pc)
Absolute magnitude (MV)	−3.53±0.30
Orbit[5]
Period (P)	3,068.03 d
Eccentricity (e)	0.22
Periastron epoch (T)	2418051.8 JD
Argument of periastron (ω) (secondary)	105°
Semi-amplitude (K1) (primary)	13.3 km/s
Details[6]
Mass	15.5±1.1 M☉
Radius	6.3±1.0 R☉
Luminosity	28,840 L☉
Surface gravity (log g)	4.05±0.10 cgs
Temperature	30,000±300 K
Rotational velocity (v sin i)	20[7] km/s
Age	7.2±0.8[8] Myr
Other designations
φ1 Ori, 37 Orionis, BD+09°877, FK5 208, HD 36822, HIP 26176, HR 1876, SAO 112914.[9]
Database references
SIMBAD	data

φ¹ Orionis with nebulosity west of φ² Orionis and south of λ Orionis

This is a single-lined^[6] spectroscopic binary star system with an orbital period of 3,068 days and an eccentricity of 0.22.^[5] It is a member of the young Lambda Orionis cluster^[11] and is roughly 7 million years old.^[8] The primary component is a B-type giant star with a stellar classification of B0 III.^[3] It has over 15 times the mass of the Sun and around 6.3 times the Sun's radius.^[6] Nothing is known about the secondary companion. It does not contribute a significant amount of light to the combined spectrum.^[6]