Nova Cas 2021 remarkable spectral evolution

Forums Variable Stars Nova Cas 2021 Nova Cas 2021 remarkable spectral evolution

Hugh Allen

Yes Mike, the HeI emission has returned amongst a few other significant changes in this wonderful nova. I’ve captured a dozen spectra since Mar 22, here’s an offset relative flux plot of a few of them showing the disappearnce and then return of the HeI emission:

I’ve also been monitoring the expansion velocity. Until May 24 it was showing a perhaps expected gradual decline, but then briefly increased in my spectrum of May 24 around the time the nova began to brighten again. My latest spectrum from last night May 30 suggests the decline in expansion velocity has resumed accompanied by a strengthening again of the P Cygni profiles:

The spectrum is dominated by the overwhelming relative brightness of the H alpha emission line. Here is the spectrum from May 24:

A truly remarkable object and great fun to follow in a spectroscope!