Eps Aur spectral classification

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Robin Leadbeater

Eps Aur is not really a good choice as a reference star. It is a famous long period eclipsing binary but is not particularly typical even outside eclipse.  Using Brian Skiff’s huge database of published spectral classifications


we can see it has been classified as anything from F4i to A8i.  (A hotter star would be better as it would have fewer lines)

It is also a pulsating variable star and shows varying  H alpha in emission for reasons which are not exactly clear. The spectrum also has significant interstellar lines so the continuum shape may be affected by interstellar extinction.   Main sequence (luminosity class v) stars are generally a better choice as reference stars as they are less likely to be variable and more likely to be  typical of their spectral classification though this cannot be guaranteed unless (like the MILES stars) there is a reliable calibrated spectrum for it.