New β Cephei stars in the young open cluster NGC 637

Context. Studying stellar pulsations in open clusters offers the possibility of performing ensemble asteroseismology. The reasonable assumption that the cluster members have the same age, distance, and overall metallicity aids in the seismic modelling process and tightly constrains it. Therefore it is important to identify open clusters with many pulsators.
Aims: New pulsating stars of the β Cephei type were searched for among the members of the open cluster NGC 637.
Methods: Thirty-one hours of time-resolved V filter CCD photometry were obtained.
Results: The measurements confirmed two previously known variables, and revealed three new β Cephei stars and one more candidate. All four pulsators have sufficiently large amplitudes for easy mode identification and are multiperiodic.
Conclusions: With four certain pulsating members, NGC 637 is now among the open clusters that are richest in β Cephei stars. It is thus an excellent target for ensemble asteroseismology, and to examine the differences between pulsating and apparently constant stars in the β Cephei domain.

Photometric lightcurves are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/533/A70