I have outlined the evidence which points to the possibility of a connection between the LBV variations of on time scales of tens of years and the shell phase of Cas in the period 1933 - 1942. A recent mechanism proposed by Stothers and Chin (1993, 1994, 1995) seems to be capable of explaining these variations in the LBVs. However it will not work for the shell phase of Cas.
Photospheric variability is common in many Be stars. Perhaps very infrequently a non-linear amplification occurs, resulting in the ejection of a significant amount of matter into the line of sight, a super, Cen-like process, possibly? If the matter is sufficiently optically thick, it may behave as a false photosphere simulating a cooler, less dense atmosphere. Superficially such variations in Cas may appear similar to those in LBVs, although they have arisen from different physical causes.
© European Southern Observatory (ESO) 1997