Rho Aurigae

Not to be confused with R Aurigae.

Rho Aurigae is a binary star system in the northern constellation of Auriga. Its name is a Bayer designation that is Latinized from ρ Aurigae, and abbreviated Rho Aur or ρ Aur. This system is faintly visible to the naked eye with an apparent visual magnitude of +5.22.^[2] Judging by parallax measurements, this system is approximately 630 light-years (190 parsecs) distant from the Earth, give or take a 20-light-year margin of error.^[1] It is drifting further away from the Sun with a radial velocity of +16 km/s.^[4]

ρ Aurigae

Location of ρ Aurigae (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Auriga
Right ascension	05h 21m 48.417s[1]
Declination	+41° 48′ 16.46″[1]
Apparent magnitude (V)	+5.22[2]
Characteristics
Spectral type	B5 V[3]
U−B color index	−0.57[2]
B−V color index	−0.14[2]
Astrometry
Radial velocity (Rv)	+16.3±2.2[4] km/s
Proper motion (μ)	RA: +15.053 mas/yr[1] Dec.: −37.695 mas/yr[1]
Parallax (π)	5.2029±0.1327 mas[1]
Distance	630 ± 20 ly (192 ± 5 pc)
Orbit[5]
Period (P)	34.49321±0.00057 d
Eccentricity (e)	0.104±0.019
Periastron epoch (T)	47962.5±2.0 JD
Argument of periastron (ω) (secondary)	3.4±12.0°
Semi-amplitude (K1) (primary)	39.8±0.8 km/s
Details
ρ Aur A
Mass	5–7[5] M☉
Radius	3.2–3.4[6] R☉
Rotational velocity (v sin i)	55[7] km/s
ρ Aur B
Mass	2–4[5] M☉
Other designations
ρ Aurigae, 20 Aurigae, BD+41 1162, FK5 2400, GC 6556, HD 34759, HIP 25048, HR 1749, SAO 40269, PPM 48030[8]
Database references
SIMBAD	data

ρ Aurigae is a single-lined spectroscopic binary system; the presence of a companion object is revealed by shifts in the stellar spectrum. The pair orbit each other with a period of 34.49 days and an orbital eccentricity of 0.10.^[5]

The primary component of this system is a B-type main-sequence star defined as a standard star for the stellar classification of B5 V.^[3] The deduced mass of the secondary and the lack of evidence for it in the spectrum suggest it may be a B- or A-type star somewhat less luminous than the primary.^[5]

Name

In Chinese, 咸池 (Xián Chí), meaning Pool of Harmony, refers to an asterism consisting of ρ Aurigae, λ Aurigae and HD 36041.^[9] Consequently, the Chinese name for ρ Aurigae itself is 咸池一 (Xián Chí yī, English: the First Star of Pool of Harmony).^[10]