THE EC-14026 STARS - XI - FEIGE-48 - A LINK IN ITS CLASS

Rapid oscillations in the sdB star Feige 48 have been discovered. The frequency spectrum reveals at least four periods in a narrow interval from 340 to 380 s. The oscillation amplitude is typically a few per ce nt, but this star shows perhaps the most dramatic amplitude variabilit y from night to night of any of the known sdB pulsators (EC 14026 star s). Analysis of multicolour absolute photometry, as well as low- and i ntermediate-dispersion spectroscopy, yields an effective temperature o f 28 900 +/- 300 K and log g = 5.45 +/- 0.05. Feige 48 is thus the coo lest EC 14026 star. Its intermediate gravity and intermediate period s uggest the existence of a period-gravity correlation, and unite the ma jority of the EC 14026 stars with the extreme object, PG 1605+072. The narrow frequency intervals in which the pulsations of Feige 48 and ot her EC 14026 stars fall suggest a narrow bandpass for the excitation m echanism.