1994A&A...291..226L

We checked the hypothesis that the yellow hypergiant ρ Cas is pulsating radially, by the application of an improved Baade-Wesselink test, in which the effective temperature during an interval of 178 days in 1970 is determined from an analysis of five stellar spectra. We assume that the changing atmospherical circumstances can be represented by various static Kurucz models over the pulsation period. The changing effective temperature, combined with the radial velocity and luminosity data, yields that radial pulsations are only possible if the star would have a radius of 2000±200R_☉, while the best value is rather 400R_☉. The conclusion is supported by the study of allowed wave motions, which also excludes radial pulsations. An investigation of the evolution of splitted absorption profiles during this pulsation cycle combined with the radial velocity curve reveals that line doubling in ρ Cas is produced by a narrow emission line superimposed on a single broad absorption line instead of being produced by radially propagating shock waves. We conclude that ρ Cas was pulsating non-radially in 1970. Byproducts of the investigation are determinations of the variation of the microturbulent velocity (ranging between 11.1 and 13.5km/s) and of the effective acceleration of gravity.