12 Aurigae

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. 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, 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 $100$, but most sources assign a temperature of around $15,400 K$. 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. A calculation of the stellar properties assuming the maximum possible interstellar extinction in the direction of 12 Aurigae results in a temperature of $8,000 K$ and a luminosity of, although it is strongly noted that the likely extinction is much lower.