Journal Article

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

John Southworth, D. M. Townsley and B. T. Gänsicke

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 388, issue 2, pages 709-715
Published in print August 2008 | ISSN: 0035-8711
Published online July 2008 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2008.13433.x
Orbital periods of cataclysmic variables identified by the SDSS – IV. SDSS J220553.98+115553.7 has stopped pulsating

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We present time-series Very Large Telescope (VLT) spectroscopy and New Technology Telescope (NTT) photometry of the cataclysmic variable SDSS J220553.98+115553.7, which contains a pulsating white dwarf. We determine a spectroscopic orbital period of Porb= 82.825 ± 0.089 min from velocity measurements of the Hα emission line. A period analysis of the light curves reveals a dominant periodicity at Pphot= 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 9–11 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 time-scale for changes in the mode spectrum, are needed to distinguish among possible explanations.

Keywords: binaries: close; binaries: spectroscopic; stars: dwarf novae; stars: individual: SDSS J220553.98+115553.7; novae, cataclysmic variables; white dwarfs

Journal Article.  4639 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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