9 Aurigae

Location of 9 Aurigae (circled)
Observation data Epoch J2000      Equinox ICRS
Constellation	Auriga
9 Aurigae A
Right ascension	05h 06m 40.63060s[1]
Declination	+51° 35′ 51.7990″[1]
Apparent magnitude (V)	4.93 - 5.03[2]
9 Aurigae B
Right ascension	05h 06m 41.12083s[3]
Declination	+51° 35′ 53.2333″[3]
Apparent magnitude (V)	12.2[4]
9 Aurigae C
Right ascension	05h 06m 49.17489s[5]
Declination	+51° 36′ 34.5112″[5]
Apparent magnitude (V)	9.49[6]
Characteristics
A
Evolutionary stage	main sequence[1]
Spectral type	F2V[7]
U−B color index	−0.01[8]
B−V color index	+0.34[8]
Variable type	γ Dor[9]
Astrometry
A
Radial velocity (Rv)	−0.47±0.57[1] km/s
Proper motion (μ)	RA: −28.557[1] mas/yr Dec.: −171.822[1] mas/yr
Parallax (π)	37.0551±0.1371 mas[1]
Distance	88.0 ± 0.3 ly (26.99 ± 0.10 pc)
B
Proper motion (μ)	RA: −54.582[3] mas/yr Dec.: −156.009[3] mas/yr
Parallax (π)	37.0796±0.0631 mas[3]
Distance	88.0 ± 0.1 ly (26.97 ± 0.05 pc)
C
Radial velocity (Rv)	−1.88±0.17[5] km/s
Proper motion (μ)	RA: −32.386[5] mas/yr Dec.: −173.026[5] mas/yr
Parallax (π)	37.2115±0.0184 mas[5]
Distance	87.65 ± 0.04 ly (26.87 ± 0.01 pc)
Orbit[10]
Period (P)	391.7 d
Eccentricity (e)	0.37
Semi-amplitude (K1) (primary)	5.8 km/s
Details
A
Mass	1.97[4] M☉
Radius	1.56[9] R☉
Luminosity	6.042[11] L☉
Surface gravity (log g)	4.07[9] cgs
Temperature	7,023[9] K
Metallicity [Fe/H]	−0.12[9] dex
Rotational velocity (v sin i)	21.0[9] km/s
B
Mass	0.49[4] M☉
Temperature	4,947[12] K
C
Mass	0.751[13] M☉
Radius	0.756[13] R☉
Luminosity	0.162[14] L☉
Temperature	4,633[14] K
Other designations
V398 Aur, BD+51°1024, GJ 187.2, GJ 9174, HD 32537, HIP 23783, HR 1637, SAO 25019
Database references
SIMBAD	9 Aur A
	9 Aur B
	9 Aur C

9 Aurigae (9 Aur) is a star system in the constellation Auriga. It has an apparent magnitude of about 5, making it visible to the naked eye in many suburban skies.^[15] Parallax estimates made by the Hipparcos spacecraft put it at about 86 light-years (26 parsecs) from the Solar System,^[16] although individual Gaia Data Release 3 parallaxes place all three components at 88 light-years.

Kevin Krisciunas and Edward Francis Guinan discovered that the star is a variable star in 1990.^[18] It is a well-studied Gamma Doradus variable,^[9] and was one of the first stars to be so-classified.^[19] This star type varies in luminosity due to non-radial pulsations.^[19] Its apparent magnitude varies from 4.93 to 5.03 over a period of 1.25804 days.^[2] For that reason it was given the variable star designation V398 Aurigae in 1995.^[2][20]

9 Aurigae is a multiple star system. The naked-eye component A is a single-lined spectroscopic binary. Only the signature of an F-type main-sequence star can be seen in the spectrum, but the periodic Doppler shift of the absorption lines demonstrates that there is a hidden companion in a 391.7-day orbit. The gravitational interaction of the two bodies produces variations in their respective motions, which is what creates the Doppler shift.^[10]

Four other companions to 9 Aurigae are listed in multiple star catalogs.^[21][22] The closest companion is a 12th-magnitude red dwarf 5″ away.^[9] Ninety arcseconds away is component C, a 9th-magnitude star with a spectral class of K5Ve,^[23] which may also be a spectroscopic binary.^[4] Further separated still is a 14th-magnitude star, component D, proposed to be a more distant red giant,^[24] although Gaia astrometry places it at a similar distance and with a similar proper motion.^[25] The most widely separated companion is component E, a distant, unrelated star.^[24][26]

References