Chi1 Orionis

Chi¹ Orionis (χ¹ Ori, χ¹ Orionis) is a star about 28 light years away.^[1] It is in the constellation Orion, where it can be seen in the tip of the hunter's upraised club.^[11]

A light curve for Chi¹ Orionis, plotted from TESS data.^[12] The 5.5 day period derived by Stępień and Geyer is marked in red.

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

Chi¹ Orionis A

Star map of the Bayers Stars in Orion. Chi1 Orionis is indicated.
Observation data Epoch J2000      Equinox J2000
Constellation	Orion
Right ascension	05h 54m 22.96136s[1]
Declination	+20° 16′ 34.5194″[1]
Apparent magnitude (V)	4.38 - 4.41[2]
Characteristics
Spectral type	G0 V[3]
U−B color index	+0.07[4]
B−V color index	+0.59[4]
Variable type	RS CVn[2]
Astrometry
Radial velocity (Rv)	−15.42[1] km/s
Proper motion (μ)	RA: −179.014 mas/yr[1] Dec.: −90.73 mas/yr[1]
Parallax (π)	114.9497±0.528 mas[1]
Distance	28.4 ± 0.1 ly (8.70 ± 0.04 pc)
Absolute magnitude (MV)	4.82±0.005[5]
Orbit[6]
Period (P)	5156.291±2.508 d
Semi-major axis (a)	89.662±0.880 mas
Eccentricity (e)	0.452±0.002
Inclination (i)	95.937±0.790°
Longitude of the node (Ω)	126.360±0.593°
Periastron epoch (T)	2451468.2±3.083 JD
Argument of periastron (ω) (secondary)	111.527±0.230°
Semi-amplitude (K1) (primary)	1.876±0.003 km/s
Details
primary
Mass	1.01[7] M☉
Radius	0.983±0.01[8] R☉
Luminosity	1.042±0.042[8] L☉
Surface gravity (log g)	4.47±0.02[8] cgs
Temperature	5,883±63[8] K
Metallicity [Fe/H]	−0.03±0.01[8] dex
Rotation	5.2 days[9]
Rotational velocity (v sin i)	8.7[7] km/s
Age	300–400[10] Myr
companion
Mass	0.15[7] M☉
Age	70-130[7] Myr
Other designations
54 Ori, Gl 222, HR 2047, BD+20°1162, HD 39587, LTT 11743, GCTP 1354.00, SAO 77705, HIP 27913
Database references
SIMBAD	data

χ¹ Ori is a G0V star.^[7] It is listed in the General Catalog of Variable Stars as an RS Canum Venaticorum variable, varying between visual magnitude 4.38 and 4.41.^[2] Stępień and Geyer measured its period to be 5.5 days.^[13]

χ¹ Ori has a faint companion with a mass estimated at 15% of the mass of the Sun, and an orbital period of 14.1 years. The companion orbits an average distance of 6.1 AU from the primary, but has a fairly high orbital eccentricity, ranging from 3.3 AU out to 8.9 AU from the primary. Because of this red dwarf companion, the likelihood of habitable planets in this system is low. It is thought that the companion is a red dwarf still contracting towards the main sequence.^[7]

A necessary condition for the existence of a planet in this system are stable zones where the object can remain in orbit for long intervals. For hypothetical planets in a circular orbit around the individual members of this star system, this maximum orbital radius is computed to be 1.01 AU for the primary and 0.41 AU for the secondary. (Note that the orbit of the Earth is 1 AU from the Sun.) A planet orbiting outside of both stars would need to be at least 18.4 AU distant.^[14]

χ¹ Ori is a candidate stream star member of the Ursa Major Moving Group, although there is some evidence to the contrary.^[9]

See also

• List of star systems within 25–30 light-years