Article

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

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

ABSTRACT

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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##### Article: Pulsational Instabilities in Accreting White Dwarfs
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ABSTRACT: (Abridged) The Cataclysmic Variable (CV) population harbors a diverse range of donor stars and accreting white dwarfs (WDs). A range of WD masses is expected, from low mass Helium core WDs, to massive WDs which have previously accreted at rates high enough for Hydrogen to burn steadily. Furthermore, a wide range of Helium enrichment is expected in the accreted material depending on the degree to which the donor star is evolved. We investigate the impact of this diversity on the range of effective temperatures ($T_{\rm eff}$) for which g-modes are unstable. The critical $T_{\rm eff}$ below which modes are unstable ("blue edge") depends on both surface gravity, $g$, and He abundance, $Y$. The Hydrogen/first Helium ionization instability strip is more sensitive to $g$ than $Y$. We find that (for solar composition envelopes), relative to a fiducial WD mass $0.6 M_\odot$, the blue edge for a $0.4 M_\odot$ He core WD shifts downward by $\approx 1000 {\rm K}$, while that for a massive $\approx 1.2 M_\odot$ WD shifts upward by $\approx 2000 {\rm K}$. The second Helium ionization instability strip exhibits strong dependences on both $g$ and $Y$. Surprisingly, increasing $Y$ by only 10% relative to solar creates an instability strip near $15,000 {\rm K}$. Hence CV's below the period gap with evolved donor stars of $Y\ga 0.4$ may have an "intermediate" instability strip well outside of the isolated DA and DB variables. This "intermediate" instability strip also occurs for low mass He WD with solar composition envelopes. The lack of pulsations in CV's with $T_{\rm eff}$ in the pure Hydrogen ZZ Ceti instability strip is also easily explained. Comment: submitted to ApJL. 3 figures
Preview · Article · Apr 2006 · The Astrophysical Journal
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##### Article: New Pulsating White Dwarfs in Cataclysmic Variables
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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 Gänsicke 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 Molėtai Observatory, and follow-up observations executed by NOT in service mode. We also present three 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 Gänsicke 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.
Full-text · Article · Jun 2006 · Monthly Notices of the Royal Astronomical Society
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##### Article: VLT/FORS spectroscopy of faint cataclysmic variables discovered by the Sloan Digital Sky Survey
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ABSTRACT: We present medium-resolution VLT/FORS2 spectroscopy of six cataclysmic variables discovered by the Sloan Digital Sky Survey. We determine orbital periods for SDSS J023322.61+005059.5 (96.08 +/- 0.09 min), SDSS J091127.36+084140.7 (295.74 +/- 0.22 min), SDSS J103533.02+055158.3 (82.10 +/- 0.09 min), and SDSS J121607.03+052013.9 (most likely 98.82 +/- 0.16 min, but the one-day aliases at 92 min and 107 min are also possible) using radial velocities measured from their H_alpha and H_beta emission lines. Three of the four orbital periods measured here are close to the observed 75--80 min minimum period for cataclysmic variables, indicating that the properties of the population of these objects discovered by the SDSS are substantially different to those of the cataclysmic variables found by other means. Additional photometry of SDSS J023322.61+005059.5 reveals a periodicity of approximately 60 min which we interpret as the spin period of the white dwarf, suggesting that this system is an intermediate polar with a low accretion rate. SDSS J103533.02+055158.3 has a period right at the observed minimum value, a spectrum dominated by the cool white dwarf primary star and exhibits deep eclipses, so is an excellent candidate for an accurate determination of the parameters of the system. The spectroscopic orbit of SDSS J121607.03+052013.9 has a velocity amplitude of only 13.8 +/- 1.6 km/s, implying that this system has an extreme mass ratio. From several physical constraints we find that this object must contain either a high-mass white dwarf or a brown-dwarf-mass secondary component or both. Comment: 15 pages, 13 figures, accepted for publication by MNRAS. Data are available at http://www.astro.keele.ac.uk/~jkt/ and will be lodged with CDS
Full-text · Article · Sep 2006 · Monthly Notices of the Royal Astronomical Society