12 Aurigae is a Be star in the northern constellation Auriga. It lies below the normal limit for visibility to the naked eye, having an apparent visual magnitude of 6.988. It lacks a designation from the Hipparcos catalogue. It is located just under half a degree north of Capella.
Assigned spectral classes for 12 Aurigae vary greatly from B2 to B5 and the luminosity class from V (main sequence) to Ia (luminous supergiant). Its spectrum shows prominent emission lines, but the spectrum is complicated by the appearance of sharp shell components to some of the spectral lines.[1] The colour of the star as shown by the B-V and U-B colour indices is not consistent with an early B spectral class,[2] leading to many estimates of its effective temperature that are much lower than expected for a B-class star. The expected temperature for a B5 spectral type would be,[3] but most sources assign a temperature of around . Other properties also vary between different sources, for example the bolometric luminosity derived from the distance and temperature is, while it is when derived by fitting the spectral energy distribution.[4] A calculation of the stellar properties assuming the maximum possible interstellar extinction in the direction of 12 Aurigae results in a temperature of and a luminosity of, although it is strongly noted that the likely extinction is much lower.[4]