ZZ Ceti stars of the southern ecliptic hemisphere re-observed by TESS

Abstract

Context. In 2020, a publication presented the first-light results for 18 known ZZ Ceti stars observed by the TESS Space Telescope during the first survey observations of the southern ecliptic hemisphere. However, in the meantime, new measurements have become available from this field, in many cases with the new, 20 s ultrashort cadence mode. Aims. We investigated the similarities and differences in the pulsational behaviour of the observed stars between the two observational seasons, and searched for new pulsation modes for asteroseismology. Methods. We performed Fourier analysis of the light curves using the standard pre-whitening process, and compared the results with frequencies obtained from the earlier data. Utilising the 2018 version of the White Dwarf Evolution Code, we also performed an asteroseismic analysis of the different stars. We searched for models with seismic distances in the vicinity of the Gaia geometric distances. Results. We detected several new possible pulsation modes of the studied pulsators. In the case of HE 0532-5605, we found a similar brightening phase to the one presented in the 2020 first-light paper, which means this phenomenon is recurring. Therefore, HE 0532-5605 appears to be a new outbursting DAV star. We also detected a lower-amplitude brightening phase in the star WD J0925+0509. However, this case has proven to be the result of the passage of a Solar System object in the foreground. We accept asteroseismic model solutions for six stars.