Orbital periods of cataclysmic variables identified by the SDSS. IV. SDSS J220553.98+115553.7 has stopped pulsating

TL;DR

This study investigates the pulsation behavior of the white dwarf in the cataclysmic variable SDSS J220553.98+115553.7, finding no detectable pulsations despite previous observations, and discusses potential reasons for this change.

Contribution

It provides the first detailed time-series spectroscopy and photometry of this system, revealing the absence of expected pulsations and exploring possible explanations for this change.

Findings

Spectroscopic orbital period of 82.825 min determined.

No pulsations detected at the previous amplitude levels.

Possible cooling or surface changes may explain pulsation cessation.

Abstract

We present time-series VLT spectroscopy and NTT photometry of the cataclysmic variable SDSS J220553.98+115553.7, which contains a pulsating white dwarf. We determine a spectroscopic orbital period of 82.825 +/- 0.089 min from velocity measurements of the Halpha emission line. A period analysis of the light curves reveals a dominant periodicity at 44.779 +/- 0.038 min which is not related to the spectroscopic period. However, the light curves do not exhibit a variation at any frequency which is attributable to GW Lib type pulsations, to a detection limit of 5 mmag. This non-detection is in contrast to previous studies which have found three pulsation frequencies with amplitudes of 9 to 11 mmag at optical wavelengths. Destructive interference and changes to the thermal properties of the driving layer in direct response to accretion can be ruled out as causes of the non-detection. Alternatively, it is feasible that the object has cooled out of the instability strip since a previous (unobserved) dwarf nova superoutburst. This would be the first time this behaviour has been seen in a cataclysmic variable pulsator. Another possibility is that changes in the surface characteristics, possibly induced by accretion phenomena, have modified the surface visibility of the pulsation modes. Further observations, particularly improved constraints on the timescale for changes in the mode spectrum, are needed to distinguish among possible explanations.