Non-radial pulsations in the γ Doradus star HD 195068

Abstract

We present high resolution spectroscopic observations of the γ Doradus star HD 195068. About 230 spectra were collected over 2 years. Time series analysis performed on radial velocity data shows a main peak at 1.61 d -1 , a frequency not yet detected in photometry. The Hipparcos photometric 1.25 d -1 frequency is easily recovered as is 1.30 d -1 while the third photometric frequency, 0.97 d -1 , is only marginally present. The good quality of our data, which includes 196 spectra collected over seven consecutive nights, shows that both the 1.61 d -1 and intermediate 1.27 d -1 (mixture of 1.25 and 1.30 d -1 ) frequencies are present in the line profile variations. Using the Fourier-Doppler Imaging (FDI) method, the variability associated with 1.61 d -1 can be successfully modeled by a non-radial pulsation mode $\ell=5\pm 1$, $|m|=4\pm 1$. For the intermediate frequency 1.27 d -1 we deduce $\ell=4\pm 1$, $|m|=3\pm 1$. Evidence that the star is not pulsating in the radial mode ($\ell=0$) rules out a previous classification as an RR Lyrae type star. We investigate the time variability of FDI power spectra concluding that the observed temporal variability of modes can be explained by a beating phenomenon between closely spaced frequencies of two non-radial modes. The distribution of the oscillation power within the line profile indicates that there is a significant tangential velocity component of oscillations characteristic of high radial order gravity modes which are predicted to be observed in γ Doradus type stars.