AX Persei – a symbiotic binary star
AX Per is an eclipsing symbiotic binary star comprising a cool M-type giant and a white dwarf with an orbital period of 680 days. The giant star emits a wind, some of which accretes onto the white dwarf raising its temperature. The hot white dwarf ionises the circumstellar matter in the binary giving rise to strong nebular emission lines of hydrogen and helium. As the light curve shows, AX Per is currently in an active phase with a V magnitude of around 10.7.
This flux calibrated spectrum was taken on 31 March 2016 with a LISA spectrograph on a C11 scope. It shows emission lines of the hydrogen Balmer series (Hα to Hδ) and helium (HeI and HeII) with some forbidden oxygen lines ([OIII]). These sit on top of the spectrum of the red giant which rises towards the red end. The white dwarf is too hot to emit much light in the visible spectrum. The lighter spectrum (with flux scale on the RHS) is a 10x magnification to expand the weaker lines.