Chi1 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
Declination	+20° 16′ 34.5194″
Apparent magnitude (V)	4.38 - 4.41
Characteristics
Spectral type	G0 V
U−B color index	+0.07
B−V color index	+0.59
Variable type	RS CVn
Astrometry
Radial velocity (Rv)	−15.42 km/s
Proper motion (μ)	RA: −179.014 mas/yr ; Dec.: −90.73 mas/yr
Parallax (π)	114.9497 ± 0.528 mas
Distance	28.4 ± 0.1 ly ; (8.70 ± 0.04 pc)
Absolute magnitude (MV)	4.82±0.005
Orbit
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 M☉
Radius	0.983±0.01 R☉
Luminosity	1.042±0.042 L☉
Surface gravity (log g)	4.47±0.02 cgs
Temperature	5,883±63 K
Metallicity [Fe/H]	−0.03±0.01 dex
Rotation	5.2 days
Rotational velocity (v sin i)	8.7 km/s
Age	300–400 Myr
companion
Mass	0.15 M☉
Age	70-130 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

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.

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]

References

^ ^a ^b ^c ^d ^e ^f Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
^ ^a ^b ^c "khi 1 Ori". General Catalog of Variable Stars. Sternberg Astronomical Institute. Retrieved 29 December 2022.
^ Keenan, Philip C.; McNeil, Raymond C. (1989). "The Perkins catalog of revised MK types for the cooler stars". The Astrophysical Journal Supplement Series. 71: 245. Bibcode:1989ApJS...71..245K. doi:10.1086/191373. S2CID 123149047.
^ ^a ^b Hoffleit, Dorrit; Jaschek, Carlos (1991). "The Bright star catalogue". New Haven, Conn.: Yale University Observatory, 5th Rev.ed. Bibcode:1991bsc..book.....H.
^ Park, Sunkyung; et al. (2013). "Wilson-Bappu Effect: Extended to Surface Gravity". The Astronomical Journal. 146 (4): 73. arXiv:1307.0592. Bibcode:2013AJ....146...73P. doi:10.1088/0004-6256/146/4/73. S2CID 119187733.
^ Han, Inwoo; Gatewood, George (2002). "A Precise Orbit Determination of χ¹Orionis from Astrometric and Radial Velocity Data". Publications of the Astronomical Society of the Pacific. 114 (792): 224–228. Bibcode:2002PASP..114..224H. doi:10.1086/338367. S2CID 122100081.
^ ^a ^b ^c ^d ^e ^f König, B.; Fuhrmann, K.; Neuhäuser, R.; Charbonneau, D.; Jayawardhana, R. (2002). "Direct detection of the companion of chi ¹ Orionis". Astronomy and Astrophysics. 394. arXiv:astro-ph/0209404. Bibcode:2002A&A...394L..43K. doi:10.1051/0004-6361:20021377. S2CID 10411048.
^ ^a ^b ^c ^d ^e Soubiran, C.; Creevey, O. L.; Lagarde, N.; Brouillet, N.; Jofré, P.; Casamiquela, L.; Heiter, U.; Aguilera-Gómez, C.; Vitali, S.; Worley, C.; de Brito Silva, D. (2024-02-01). "Gaia FGK benchmark stars: Fundamental Teff and log g of the third version". Astronomy and Astrophysics. 682: A145. arXiv:2310.11302. Bibcode:2024A&A...682A.145S. doi:10.1051/0004-6361/202347136. ISSN 0004-6361. Chi1 Orionis' database entry at VizieR.
^ ^a ^b Maldonado, J.; et al. (October 2010). "A spectroscopy study of nearby late-type stars, possible members of stellar kinematic groups". Astronomy and Astrophysics. 521: A12. arXiv:1007.1132. Bibcode:2010A&A...521A..12M. doi:10.1051/0004-6361/201014948. S2CID 119209183.
^ Mamajek, Eric E.; Hillenbrand, Lynne A. (November 2008). "Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics". The Astrophysical Journal. 687 (2): 1264–1293. arXiv:0807.1686. Bibcode:2008ApJ...687.1264M. doi:10.1086/591785. S2CID 27151456.
^ Jim Kaler. "Chi-1 Orionis". Retrieved 2022-12-29.
^ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 28 December 2022.
^ Stępień, K.; Geyer, E. (May 1996). "Rotation of solar-like main sequence stars". Astronomy and Astrophysics Supplement. 117: 83–91. Bibcode:1996A&AS..117...83S. doi:10.1051/aas:1996141.
^ Jaime, Luisa G.; et al. (December 2012). "Regions of dynamical stability for discs and planets in binary stars of the solar neighbourhood". Monthly Notices of the Royal Astronomical Society. 427 (4): 2723–2733. arXiv:1208.2051. Bibcode:2012MNRAS.427.2723J. doi:10.1111/j.1365-2966.2012.21839.x. S2CID 118570249.