bump Cepheid

A bump Cepheid is a Delta Cephei star (classical Cepheid) that has a bump in its light curve. The light curves of Delta Cephei stars are asymmetrical, with a rapid rise to maximum light and a slower fall. The form of the light curve changes with period in a systematic way known as the Hertzsprung progression. A bump appears on the descending branch of the light curve of stars with periods of about a week and is found at earlier phases in stars of successively longer periods so that the bump is near maximum light in stars of 10-day period, which may show a double maximum. The bump falls on the rising branch in stars of longer period. Stars of the shortest or longest periods have smooth light curves. The amplitude of the pulsation increases slowly with period up to about 10 days, where there is a drop in amplitude; it then increases more rapidly to longer periods. The bumps may represent an echo of the surface pulsation from the deep interior; an alternative explanation is that they result from a resonance when the second overtone period is about one-half of the fundamental period.