A ZZ Ceti white dwarf in SDSS J133941.11+484727.5

Radboud University Nijmegen, Nymegen, Gelderland, Netherlands
Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.11). 10/2005; 365(3). DOI: 10.1111/j.1365-2966.2005.09781.x
Source: arXiv


We present time-resolved spectroscopy and photometry of the cataclysmic variable (CV) SDSS J133941.11+484727.5 (SDSS 1339)
which has been discovered in the Sloan Digital Sky Survey (SDSS) Data Release 4. The orbital period determined from radial
velocity studies is 82.524(24) min, close to the observed period minimum. The optical spectrum of SDSS 1339 is dominated to
90 per cent by emission from the white dwarf (WD). The spectrum can be successfully reproduced by a three-component model
(white dwarf, disc, secondary) with TWD=12 500 K for a fixed log g= 8.0, d= 170 pc, and a spectral type of the secondary later than M8. The mass-transfer rate corresponding to the optical luminosity
of the accretion disc is very low, ≃ 1.7 × 10−13M⊙ yr−1. Optical photometry reveals a coherent variability at 641 s with an amplitude of 0.025 mag, which we interpret as non-radial
pulsations of the white dwarf. In addition, a long-period photometric variation with a period of either 320 or 344 min and
an amplitude of 0.025 mag is detected, which bears no apparent relation with the orbital period of the system. Similar long-period
photometric signals have been found in the CVs SDSS J123813.73-033933.0, SDSS J204817.85-061044.8, GW Lib and FS Aur, but
so far no working model for this behaviour is available.

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Available from: S. C. C. Barros, Oct 17, 2012
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    ABSTRACT: The number of discovered non-radially pulsating white dwarfs (WDs) in cataclysmic variables (CVs) is increasing rapidly by the aid of the Sloan Digital Sky Survey (SDSS). We performed photometric observations of two additional objects, SDSS J133941.11+484727.5 (SDSS 1339), independently discovered as a pulsator by Gansicke et al., and SDSS J151413.72+454911.9, which we identified as a CV/ZZ Ceti hybrid. In this Letter we present the results of the remote observations of these targets performed with the Nordic Optical Telescope (NOT) during the Nordic-Baltic Research School at Moletai Observatory, and follow-up observations executed by NOT in service mode. We also present 3 candidates we found to be non-pulsating. The results of our observations show that the main pulsation frequencies agree with those found in previous CV/ZZ Ceti hybrids, but specifically for SDSS 1339 the principal period differs slightly between individual observations and also from the recent independent observation by Gansicke et al. Analysis of SDSS colour data for the small sample of pulsating and non-pulsating CV/ZZ Ceti hybrids found so far, seems to indicate that the r-i colour could be a good marker for the instability strip of this class of pulsating WDs.
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