TIME-RESOLVED PHOTOMETRY OF BN AND BU CANCRI, 2-DELTA SCUTI STARS IN THE PRAESEPE CLUSTER - 4TH PHOTOMETRY CAMPAIGN OF THE STEPHI NETWORK

The fourth photometry campaign of the STEPHI network was carried out i n January 1992. On this occasion, the 6 Scuti-like stars BN Cnc and BU Cnc were simultaneously monitored during a three-week, three-continen tal run. Six and five frequency peaks are unambiguously detected for B U Cnc and BN Cnc, respectively. Some additional frequency peaks, with confidence levels between 50% and 60% are also reported. Both stars be long to the Praesepe open cluster, thus they should have almost the sa me age and primeval chemical composition. Consequently, their differen ces in the frequency spectrum might be merely due to the distinct mass es of the star pair. Some asteroseismic implications will be also disc ussed.