1997A&A...324..566B

A coordinated photometric campaign at five observatories to monitor the suspected brightness variations of the early-F star HD 108100 was undertaken by the DSN (Delta Scuti Network) and WET (Whole Earth Telescope). 288 hours of high-quality observations during a 58 day time span led to the discovery of two frequencies of 1.32 and 1.40c/d with V amplitudes of 0.010 and 0.007mag. The detection of both frequencies is statistically significant with amplitude signal/noise ratios of 18 and 12. The light variations are accompanied by v-y color variations of 0.005 and 0.003mag, respectively. The variability of HD 108100 is typical of the new class of γ Dor variables. We also derive amplitude ratios and phase differences between the light curves at different wavelengths. These are consistent with g-mode pulsation of l=1, but not l=2. The observed periods can be fit by two modes with successive radial orders of n∼19. Studies of the δ Scuti star 4 CVn from 1970 to 1976 reported the existence of unusually low frequencies of 1.3 and 1.4c/d. These frequencies can now be traced back to HD 108100, the single comparison star used in these studies. Consequently, 4 CVn should no longer be regarded as an example of a star exhibiting both δ Scuti type pulsation (acoustic modes of mixed character) and γ Dor variability (gravity modes of high order). An analysis of unpublished data from 1970 to 1976 shows that the amplitudes associated with the two frequencies of HD 108100 are variable and that the two frequencies can appear to switch their power.