Chi Aurigae

Chi Aurigae is a binary star system in the northern constellation of Auriga. Its name is a Bayer designation that is Latinized from χ Aurigae, and abbreviated Chi Aur or χ Aur. This star is visible to the naked eye with an apparent visual magnitude of 4.74.^[2] The brightness of the star is diminished by 1.26 in magnitude from extinction caused by intervening gas and dust.^[5] It is a member of the Aur OB1 association of co-moving stars.^[5]

Chi Aurigae

The location of χ Aurigae (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Auriga
Right ascension	05h 32m 43.67437s[1]
Declination	+32° 11′ 31.2805″[1]
Apparent magnitude (V)	4.74[2]
Characteristics
Spectral type	B5 Iab[3]
U−B color index	−0.44[2]
B−V color index	+0.32[2]
Astrometry
Radial velocity (Rv)	7.27±5.21[1] km/s
Proper motion (μ)	RA: −0.812 mas/yr[1] Dec.: −3.15 mas/yr[1]
Parallax (π)	0.9087±0.1906 mas[1]
Distance	3,910±420 ly (1,200±130 pc)[4]
Absolute magnitude (MV)	−6.4[5]
Orbit[5]
Period (P)	676.85 ± 0.21 d
Eccentricity (e)	0.116 ± 0.048
Longitude of the node (Ω)	181.7° ± 24.3°
Periastron epoch (T)	2422754.2 ± 46.1 HJD
Semi-amplitude (K1) (primary)	22.0 ± 2.9 km/s
Details
Mass	21.1±0.2[4] M☉
Radius	68±8[4] R☉
Luminosity	190,500+49,300 −39,200[4] L☉
Surface gravity (log g)	2.11±0.06[4] cgs
Temperature	14,600±300[4] K
Rotational velocity (v sin i)	40[6] km/s
Age	8.7[4] Myr
Other designations
χ Aur, 25 Aurigae, BD+32°1024, GC 6849, HD 36371, HIP 25984, HR 1843, SAO 58164, PPM 70517[7]
Database references
SIMBAD	data

Chi Aurigae is a single-lined spectroscopic binary with an orbital period of 676.85 d and an eccentricity of 0.116.^[5] The primary component of this system is a supergiant star with a stellar classification of B5 Iab.^[3] It is over 190,000 times more luminous, around 20 times more massive and around 70 times larger than the Sun. The photosphere has an effective temperature of 14,600 K.^[4] Its stellar wind is causing mass loss at the rate of (0.38–0.46)×10⁻⁹ solar masses per year, or the equivalent of the Sun's mass every 2.4 billion years.^[8]

The distance of Chi Aurigae is determined at 3,900 light-years based on spectroscopic observations.^[4] Parallax measurements by the Hipparcos spacecraft were unsuccessful because the parallax error was bigger than the value itself,^[9] while the Gaia spacecraft measured the parallax with a 22% error, giving a distance of 3,590±750 ly.^[1]