TU Cassiopeiae periods and amplitudes

Abstract

Light-curve observations of the double-mode Cepheid TU Cas obtained by 10 different groups of observers on several photometric systems over a time span of 67 years have been carefully studied to determine the fundamental and first-overtone periods and their amplitudes on the V magnitude scale. The presence of a second-overtone radial pulsation is discussed, and it is concluded that a previous detection of this mode was spurious because of the lack of a proper zero-point corretion for two groups of observations. It is possible that the amplitude of one of the two modes varies during the entire observing period, with the fundamental-mode amplitude constant at 0.69 +- 0.03 and the overtone amplitude decreasing from 0.4 to 0.25 mag. If this Cepheid displays the two pulsation modes because it is mode switching, this switching time scale may be less than a few hundred years.