Photometry and asteroseismology of δ Scuti stars in Praesepe

We discuss observations and seismic analyses for three multi-periodic δ Scuti stars in the Praesepe cluster: BU, BN and BV Cnc. For two stars (BU and BN Cnc) we re-analyse published photoelectric photometry and show that using statistical weights results in a dramatic reduction in the noise level. We detect seven frequencies in BU Cnc and eight in BN Cnc, with three of the latter being previously unknown. We also present new time-series CCD observations of BN and BV Cnc that successfully demonstrate high-precision differential photometry on strongly defocussed images. The observations show that BV Cnc is a multi-periodic variable, with at least four oscillation frequencies. Finally, we compare the observed oscillation frequencies in the three stars with models and derive luminosities, effective temperatures and masses.