9 Aurigae

Location of 9 Aurigae (circled)
Observation data Epoch J2000       Equinox J2000
Constellation	Auriga
Right ascension	05h 06m 40.62967s [1]
Declination	+51° 35′ 51.8025″ [1]
Apparent magnitude (V)	4.93 - 5.03 [2]
Characteristics
Spectral type	F2V [3]
U−B color index	-0.03 [4]
B−V color index	+0.34 [4]
Variable type	γ Dor [5]
Astrometry
A
Radial velocity (Rv)	−0.47±0.57 [6] km/s
Proper motion (μ)	RA: −28.557 [6]  mas/ yr Dec.: −171.822 [6]  mas/ yr
Parallax (π)	37.0551 ± 0.1371  mas [6]
Distance	88.0 ± 0.3  ly (26.99 ± 0.10  pc)
B
Proper motion (μ)	RA: −54.582 [7]  mas/ yr Dec.: −156.009 [7]  mas/ yr
Parallax (π)	37.0796 ± 0.0631  mas [7]
Distance	88.0 ± 0.1  ly (26.97 ± 0.05  pc)
C
Radial velocity (Rv)	−1.88±0.17 [7] km/s
Proper motion (μ)	RA: −32.386 [8]  mas/ yr Dec.: −173.026 [8]  mas/ yr
Parallax (π)	37.2115 ± 0.0184  mas [8]
Distance	87.65 ± 0.04  ly (26.87 ± 0.01  pc)
Orbit [9]
Period (P)	391.7  d
Eccentricity (e)	0.37
Semi-amplitude (K1) (primary)	5.8 km/s
Details
A
Mass	1.97 [10]  M☉
Radius	1.56 [5]  R☉
Luminosity	6.042 [11]  L☉
Surface gravity (log g)	4.07 [5]  cgs
Temperature	7,023 [5]  K
Metallicity [Fe/H]	−0.12 [5]  dex
Rotational velocity (v sin i)	21.0 [5] km/s
B
Mass	0.49 [10]  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 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 Auriga (constellation). 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, ^[1] although individual Gaia Data Release 3 parallaxes place all three components at 88 light years.

It is a well-studied Gamma Doradus variable, ^[5] and was one of the first stars to be so-classified. ^[17] This star type varies in luminosity due to non-radial pulsations. ^[17] Its apparent magnitude varies from 4.93 to 5.03 over a period of 1.25804 days. ^[2] For that reason it has been given the variable star designation V398 Aurigae. ^[2]

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. ^[9]

Four other companions to 9 Aurigae are listed in multiple star catalogs. ^{[18] [19]} The closest companion is a 12th-magnitude red dwarf 5 ″ away. ^[5] 90″ away is component C, a 9th-magnitude star with a spectral class of K5Ve, ^[20] which may also be a spectroscopic binary. ^[10] Further-separated still is a 14th-magnitude star, component D, proposed to be a more distant red giant, ^[21] although Gaia astrometry places it at a similar distance and with a similar proper motion. ^[22] The most widely-separated companion is component E, a distant unrelated star. ^{[21] [23]}