Nonradial pulsation of the unevolved hot (gamma) scuti star cd-24 7599 discovered with the whole earth telescope

Abstract

We report a frequency analysis of the δ Scuti star CD-24°7599 and the discovery that it pulsates nonradially with at least 7 frequencies between 27.01 and 38.11 cycles per day (312 to 441 μHz). These results are based on 116.7 hours of photometric data obtained with the Whole Earth Telescope network. New uvbyβ photometry implies that the star is unevolved and located near the observed hot border of the classical instability strip. We give arguments for interpreting the pulsation periods in terms of low-order low-degree nonradial p-modes. Rotational m-mode splitting is likely. Few radial modes could also be present. The rich modal content and unevolved state of CD-24°7599 emphasize its importance for δ Scuti star asteroseismology. We detect linear combination frequencies of the pulsation modes with the highest photometric amplitudes and suggest they are not normal modes excited by resonance.