During observing run XCOV7 of the WET (Whole Earth Telescope, R. E. Nather et al. 1990, ApJ 361, 309) network devoted to the recently discovered dwarf nova 1H0857-242 one of the recommended comparison stars, CoD -24o 7599, turned out to be variable. As a result CoD -24o 7599 was chosen as a second target object. After 11 days of high-speed photometry observations, 110.8 hours of Johnson B measurements had been obtained. Including some overlaps, a duty cycle of 40 % was achieved, resulting in the excellent spectral window shown in the upper panel of the figure.
The subsequent panels show the power spectrum and its appearance after the removal of two, three, four, ... seven simultaneously determined frequencies. These seven frequencies are located in the range between 27.0 to 38.1 cycles/day with amplitudes between 2 and 11 mmag, yielding amplitude signal-to-noise ratios larger than 6. However, additional frequencies may still be present, but their S/N lower than 4 does not allow regarding them to be certain. A term f8 = 2f1 also exceeds the noise level of the amplitude spectrum by more than a factor of 4 in the corresponding frequency domain. The calculated 8-frequency fit reflects the observed light curve well within 5.0 mmag per single measurement.
A low-resolution spectrogram kindly supplied by Beverley J. Wills shows that CoD -24o 7599 is an A star, together with the size of the pulsation frequencies we can conclude that it is also a d Scuti variable. Because of the close frequency spacing purely radial pulsation can be ruled out.
A detailed paper authored by G. Handler, M. Breger, D. J. Sullivan, A. J. van der Peet, J. C. Clemens, D. O'Donoghue, A.-L. Chen, A. Kanaan, C. Sterken, C. F. Claver, K. L. Krisciunas, S. J. Kleinman, D. T. Wickramasinghe, J. L.Provencal, R. E.Nather, E. L. Robinson, D. E. Winget, M. A. Barstow and D. A. H. Buckley will be submitted to Astronomy & Astrophysics.
sperl@astro.ast.univie.ac.at