Photometry of yellow semiregular variables - {rho} Cassiopeiae

The variable yellow hypergiant Rho Cas has been observed photoelectrically since 1978 (since 1983 by members of the American Association of Variable Star Observers). Analysis of all available observations indicates at least one significant period, P = 298.5 d, which is apparently constant since 1963. The effect of shell ejections on the light curve makes it difficult to identify other periods, and assess their significance. The color curves of Rho Cas became significantly redder in the late 1970s; this change, however, was not reflected by any long-term trend in the V-curve. It seems that the best explanation for this observation is that it is a consequence of a temperature (and also mean spectral type) change of the star occurring at constant luminosity. It is argued that the behavior of Rho Cas is best explained by assuming that it is still before the red supergiant phase in its evolution.