Gamma Cassiopeiae is the prototype of a class of rapidly spinning stars. These stars are rotating so fast that they are on the verge of tearing themselves apart. The material these stars eject forms an equatorial ring around the star, which as it cools, can cause the star’s brightness to fade. These stars can not only display changes in magnitude, but will also display changes in spectral type, colour, temperature and diameter.
Gamma Cassiopeiae is a B0 sub-giant, with bright hydrogen lines, which were first observed by Father Secchi in 1866. Before 1910, it had a magnitude of 2.25, which slowly rose to 1.75 by 1936. Then, in April of 1937, it showed a rapid increase to magnitude 1.6, before returning to its original magnitude of 2.25 by the end of that year.
It then faded to magnitude 3.0 by 1940, before slowly rising to magnitude 2.5 by 1954. It then rose still further, so by 1975 it was at magnitude 2.2. It has stayed at about this magnitude up to the present day. Over the past few years, Gamma Cassiopeiae has only displayed some flickering between magnitude 2.2 and 2.0.
Gamma Cassiopeiae used to be on the SPA programme, but was dropped, as it rarely shows much in the way of variation. However, as the central star in the big ‘W’ of Cassiopeia, it has the advantage of been easy to find and visible all year round from the UK. It’s always worth taking a moment to look at Gamma Cassiopeiae when you’re out observing, as you never know what it may do.
