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.[9] 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,[10] leading to many estimates of its
effective temperature that are much lower than expected for a B-class star.[6][4] The expected temperature for a B5 spectral type would be 15,400
K,[11] but most sources assign a temperature of around 8,000 K.[6][4] Other properties also vary between different sources, for example the
bolometric luminosity derived from the distance and temperature is 25
L☉,[6] while it is 635 L☉ when derived by fitting the
spectral energy distribution.[5] A calculation of the stellar properties assuming the maximum possible
interstellar extinction in the direction of 12 Aurigae results in a temperature of 14,336 K and a luminosity of 8,092 L☉, although it is strongly noted that the likely extinction is much lower.[5]
