THE EC-14026 STARS - V - THE PULSATION PERIODS OF PB-8783

PB 8783 is a member of the newly discovered class of pulsating sdB sta rs, the EC 14026 stars. The potential of the pulsations of these stars as diagnostic probes of their interiors can only be realized fully by intensive campaigns of multisite time series photometry. To this end we have undertaken a campaign spanning 2 weeks and involving data from five different sites. 183 h of data were obtained. Frequency analysis yielded at least 11 pulsation periods in seven discrete groups betwee n 94 and 136 s. Three of the periods in one specific group are equally spaced in frequency, with a spacing of 0.94 mu Hz. The frequency spac ings amongst the members of other groups are similar to this. A rotati on period of similar to 12 d is implied. A general scheme for identify ing the observed modes is suggested. The periods from a detailed model are in good overall agreement with the observed periods, but some dif ficulties remain. Three additional periods in the range 61-63 s, and w ith very low amplitude, were also found. No convincing interpretation of these could be devised.