THE PULSATING YELLOW SUPERGIANT V810 CENTAURI

The F8 Ia supergiant V810 Centauri is part of a longterm high-precisio n photometric monitoring program on long period variables started twen ty years ago. Time series analysis of this unique set of 500 data poin ts, spanning almost fifteen years in the homogeneous Geneva photometri c system, is presented. Cluster membership, physical parameters and ev olutionary status of the star are reinvestigated. Radial velocity data do not support the cluster membership to Stock 14. Ultraviolet and op tical spectrophotometry is combined with optical and infrared photomet ry to evaluate the physical parameters of the yellow supergiant (T-eff = 5970 K, M-bol = -8.5, R = 420 R-.) and of its B0 III companion. Fro m theoretical stellar evolutionary tracks, an initial mass of similar to 25 M-. is estimated for V810 Cen, which is actually at the end of i ts first redward evolution. V810 Cen is a multi-periodic small amplitu de variable star, whose amplitudes are variable with time. The period of the main mode, similar to 156 d, is in agreement with the Period-Lu minosity-Colour relation for supergiants. This mode is most probably t he fundamental radial one. According to the theoretical pulsation peri ods for the radial modes, calculated from a linear non-adiabatic analy sis, the period of the observed second mode, similar to 107 d, is much too long to correspond to the first radial overtone. Thus, this secon d mode could be a non-radial p-mode. Other transient periods are obser ved, in particular at similar to 187 d. The length of this period sugg ests a non-radial g-mode. Then, the complex variability of V810 Cen co uld be due to a mixing of unstable radial and non-radial p- and g-mode s.