Abstract
Context: KUV 05134+2605 is one of the 21 pulsating DB white dwarfs (V777 Her or DBV variables) known so far. The detailed investigation of the short-period and low-amplitude pulsations of these relatively faint targets requires considerable observational efforts from the ground, long-term single-site or multisite observations. The observed amplitudes of excited modes undergo short-term variations in many cases, which makes the determination of pulsation modes difficult. Methods: We re-analysed the data already published, and collected new measurements. We compared the frequency content of the different datasets from the different epochs and performed various tests to check the reliability of the frequency determinations. The mean period spacings were investigated with linear fits to the observed periods, Kolmogorov-Smirnov and Inverse Variance significance tests, and Fourier analysis of different period sets, including a Monte Carlo test simulating the effect of alias ambiguities. We employed fully evolutionary DB white dwarf models for the asteroseismic investigations. Results: We identified 22 frequencies between 1280 and 2530 microHz. These form 12 groups, which suggests at least 12 possible frequencies for the asteroseismic investigations. Thanks to the extended observations, KUV 05134+2605 joined the group of rich white dwarf pulsators. We identified one triplet and at least one doublet with a ~9 microHz frequency separation, from which we derived a stellar rotation period of 0.6 d. We determined the mean period spacings of ~31 and ~18 s for the modes we propose as dipole and quadrupole, respectively. We found an excellent agreement between the stellar mass derived from the l=1 period spacing and the period-to-period fits, all providing M_* = 0.84-0.85 M_Sun solutions. Our study suggests that KUV 05134+2605 is the most massive amongst the known V777 Her stars.
Highlights
The discovery of the first pulsating DB-type white dwarf (GD 358 or V777 Her) was not serendipitous: it was the result of a dedicated search for unstable modes in these stars, driven by the partial ionization of the atmospheric helium (Winget et al 1982)
We constructed the list of frequencies considered as real by applying the following rules: (1) for the Konkoly2007 frequencies, we considered a frequency as real if it was detected at least with a 75 percent success rate in at least in two test cases
(2) For the other datasets, we considered a frequency as real if it was found with at least a 75 percent success rate in the corresponding test data
Summary
The discovery of the first pulsating DB-type white dwarf (GD 358 or V777 Her) was not serendipitous: it was the result of a dedicated search for unstable modes in these stars, driven by the partial ionization of the atmospheric helium (Winget et al 1982). Tables of the photometric time series are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/570/A116 was proposed by the modelling results of Van Grootel et al (2013) Except for their similar driving mechanism and surface composition, they are completely different: they likely have a binary origin, their cores are dominated by helium, and they pulsate with longer periods associated to g-modes than the ZZ Ceti stars (Hermes et al 2013). The most famous example is the so-called sforzando effect observed in GD 358 This star showed a high-amplitude sinusoidal light variation for a short period of time instead of the non-linear variability observed just a day before (Kepler et al 2003; Provencal et al 2009). We discuss our findings and the results on the asteroseismic investigations based on the set of pulsation modes
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