RT Aurigae

RT Aurigae

Template:Location mark Location of RT Aur (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Auriga
Right ascension	Template:RA
Declination	Template:DEC
Apparent magnitude (V)	5.75 (5.00 - 5.82)
Characteristics
Spectral type	F8Ib (F4Ib - G4Ib)
U−B Template:Engvar	0.5
B−V Template:Engvar	0.74
Variable type	δ Cep
Astrometry
Radial velocity (Rv)	20.30 km/s
Proper motion (μ)	RA: −0.492 mas/yr Dec.: −13.441 mas/yr
Parallax (π)	1.8153±0.1222 mas
Distance	1,540 ly (473 pc)
Absolute magnitude (MV)	−3.09
Details
Mass	4.4 Template:Solar mass
Radius	Template:Val Template:Solar radius
Luminosity	Template:Val Template:Solar luminosity
Surface gravity (log g)	1.42 cgs
Temperature	Template:Val K
Metallicity	0.1
Rotational velocity (v sin i)	8.8 km/s
Age	85 Myr
Metallicity [Fe/H]	{{{metal_fe2}}} dex
Other designations
48 Aurigae, HD 45412, BD+30°1238, HIP 30827, SAO 59128, HR 2332
Database references
SIMBAD	data
Data sources:
Hipparcos Catalogue, CCDM (2002), Bright Star Catalogue (5th rev. ed.)

RT Aurigae (RT Aur, 48 Aurigae) is a yellow supergiant variable star in the constellation Auriga, about 1,500 light years from Earth. Although its brightness is variable, it as consistently visible to the naked eye under good observing conditions.

File:RTAurLightCurve.png

A visual band light curve for RT Aurigae, adapted from Kiss (1998)

RT Aurigae is an F to G type Classical Cepheid variable which varies from magnitude +5.00 to +5.82 with a period of 3.728309 days. The variability was discovered in 1905, by an English schoolmaster and amateur astronomer, Thomas Hinsley Astbury. It was quickly recognised as a member of the class of Cepheid variables, but their nature was not understood at that time. Radial velocity changes were detected corresponding to the brightness variations, but the idea that these were caused by stellar pulsations and temperature changes was largely dismissed in favour of orbital motions of a binary star. More accurate observations eventually proved beyond doubt that the brightness variations were caused by pulsations in the atmospheres of the stars, with the stars being smallest and hottest near maximum brightness.

RT Aurigae has been suspected to be a spectroscopic binary system, but this has not been confirmed. The strongest evidence was found in 2013 using CHARA array optical interferometry. The companion would be 6.7 magnitudes fainter than the supergiant primary, cooler and fainter than an F0 main sequence star. The two stars are separated by 2.1 milli-arc seconds.