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.[13] Parallax estimates made by the Hipparcos spacecraft put it at about 85.7 light-years (26.3 parsecs) from the solar system.[1]

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
Radial velocity (Rv)	-0.90 ± 0.3[6] km/s
Proper motion (μ)	RA: -30.49[1] mas/yr Dec.: -172.89[1] mas/yr
Parallax (π)	38.04 ± 0.34 mas[1]
Distance	85.7 ± 0.8 ly (26.3 ± 0.2 pc)
Orbit[7]
Period (P)	391.7 d
Eccentricity (e)	0.37
Semi-amplitude (K1) (primary)	5.8 km/s
Details
A
Mass	1.97[8] M☉
Radius	1.56[5] R☉
Luminosity	6.042[9] 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[8] M☉
Temperature	4,947[10] K
C
Mass	0.751[11] M☉
Radius	0.756[11] R☉
Luminosity	0.162[12] L☉
Temperature	4,633[12] 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

It is a well-studied Gamma Doradus variable,[5] and was one of the first stars to be so-classified.[15] This star type varies in luminosity due to non-radial pulsations.[15] 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.[7]

Four other companions to 9 Aurigae are listed in multiple star catalogs,[16][17] all thought to be common proper motion companions at the same distance from us as 9 Aurigae.[7][10][12][18] 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,[19] which may also be a spectroscopic binary.[8] Further-separated still is a 14th-magnitude star, component D, thought to be a more distant red giant.[20][18] The most widely-separated companion is component E, another distant star.[20][21]

References

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