G 207-9 and LP 133-144: light curve analysis and asteroseismology of two ZZ Ceti stars

TL;DR

This study presents new pulsation modes and asteroseismic analysis of two ZZ Ceti stars, G 207-9 and LP 133-144, revealing their internal properties and rotation periods through light curve analysis.

Contribution

The paper reports the discovery of new pulsation modes and triplet structures in two ZZ Ceti stars, enhancing understanding of their internal structure and rotation.

Findings

Five and three new pulsation modes identified for G 207-9 and LP 133-144.

Triplet frequency structures in LP 133-144 indicate a rotation period of approximately 42 hours.

Asteroseismic models suggest effective temperatures and masses consistent with or slightly larger than spectroscopic estimates.

Abstract

G 207-9 and LP 133-144 are two rarely observed ZZ Ceti stars located in the middle and close to the blue edge of the ZZ Ceti instability domain, respectively. We aimed to observe them at least during one observing season at Konkoly Observatory with the purpose of extending the list of known pulsation modes for asteroseismic investigations and detect any significant changes in their pulsational behaviour. We determined five and three new normal modes of G 207-9 and LP 133-144, respectively. In LP 133-144, our frequency analysis also revealed that at least at three modes there are actually triplets with frequency separations of ~4 microHz. The rotational period of LP 133-144 based on the triplets is ~42 h. The preliminary asteroseismic fits of G 207-9 predict Teff=12 000 or 12 400 K and M*=0.855-0.870 MSun values for the effective temperature and mass of the star, depending on the assumptions on the spherical degree (l) values of the modes. These results are in agreement with the spectroscopic determinations. In the case of LP 133-144, the best-fitting models prefer Teff=11 800 K in effective temperature and M*>=0.71 MSun stellar masses, which are more than 0.1 MSun larger than the spectroscopic value.