Strong interactions between g- and p-modes in the hybrid γ Doradus-δ Scuti CoRoT star ID 105733033

Context. The presence of stellar p- and g-modes allows us to test stellar structure models in great detail from the core to the envelope. As the driving mechanisms are not yet fully understood, the first important step is to provide clear evidence of these pulsation modes. Aims. Recent space missions have confirmed that the gamma Doradus and the delta Scuti observational instability strips overlap and consequently that many stars may be hybrids. CoRoT ID105733033 is an excellent example of these hybrid pulsators as it shows g- and p-modes with almost similar amplitudes in two clearly distinct frequency domains. We present a detailed frequency analysis of the CoRoT star ID105733033, which is obtained with a classical Fourier analysis. Methods. After removing residual instrumental effects from the CoRoT light curve of N2 level, frequencies with an amplitude as small as 0.1 mmag were determined with Period04 and SigSpec up to 50 d(-1), although if deemed necessary lower amplitudes and higher frequencies were also investigated. The frequency spectrum of CoRoT ID105733033 clearly consists of two distinct ranges, which are typical of gamma Doradus and delta Scuti pulsation. Focus was placed on the identification of linear combinations and frequencies due to the coupling between gamma Doradus and delta Scuti modes. Results. We detect 198 gamma Doradus type frequencies in the range [0.25; 4]d(-1), of which 180 are not combination frequencies, and 24 of them are separated by a constant period-interval Delta P = 0.03074 d. According to the asymptotic theory, these 24 frequencies correspond to a series of g-modes of the same l-degree and different radial orders n. We also detect 246 delta Scuti type frequencies in the range [10.1; 63.4] d(-1). The dominant frequency F = 12.6759 d(-1) was identified as the fundamental radial mode. Our most noteworthy result is that all the main gamma Doradus frequencies f(i) are also detected in the d Scuti domain as F +/- f(i) with four times smaller amplitudes. Once these frequencies were removed, only 59 can be considered as individual d Scuti frequencies. Conclusions. A coupling between g- and p-modes is proposed to be a tool for detecting g-modes in the Sun, but this coupling has never yet been observed. Our present study may be valuable input to theoretical studies, addressing the mutual influence of g- and p-mode cavities and the deviation from classical theory. Furthermore, we identify a sequence of g-modes belonging to the same l but with consecutive orders n.