Orbital periods of cataclysmic variables identified by the SDSS – IV. SDSS J220553.98+115553.7 has stopped pulsating |
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| Authors: | John Southworth D M Townsley B T Gänsicke |
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| Institution: | Department of Physics, University of Warwick, Coventry CV4 7AL;Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL 60637, USA;Joint Institute for Nuclear Astrophysics, University of Chicago, Chicago, IL 60637, USA |
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| Abstract: | 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 P orb= 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 P phot= 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. |
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| Keywords: | binaries: close binaries: spectroscopic stars: dwarf novae stars: individual: SDSS J220553 98+115553 7 novae cataclysmic variables white dwarfs |
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