Revealing the pulsational properties of the V777 Herculis star KUV 05134+2605 by its long-term monitoring^⋆

¹ Konkoly Observatory, MTA CSFK, Konkoly Thege M. u. 15-17, 1121 Budapest, Hungary
e-mail: bognar@konkoly.hu
² Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Argentina
³ Consejo Nacional de Investigaciones Científicas y Ténicas (CONICET), Argentina
⁴ Instituto de Física, Universidade Federal do Rio Grande do Sul, 91501-900 Porto-Alegre, RS, Brazil
⁵ Department of Astronomy, Eötvös Loránd University, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary

Received: 4 March 2014
Accepted: 11 August 2014

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 multi-site observations. The observed amplitudes of excited modes undergo short-term variations in many cases, which makes determining pulsation modes difficult.

Aims. We aim to determine the pulsation frequencies of KUV 05134+2605, find regularities between the frequency and period components, and perform an asteroseismic investigation for the first time.

Methods. We re-analysed the published data 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 with a Fourier analysis of different period sets, including a Monte Carlo test that simulated 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 μHz. 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 μHz frequency separation, from which we derived a stellar rotation period of 0.6 d. We determined the mean period spacings of ≈ 31 s and 18 s for the modes we propose as dipole and quadrupole. 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_⊙ solutions. Our study suggests that KUV 05134+2605 is the most massive amongst the known V777 Her stars.