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

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 = 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.

A Deep Test of Radial Differential Rotation in a Helium-atmosphere White Dwarf.I. Discovery of Pulsations in PG 0112+104

“…Similarly, for the = 2 modes we observe ∆Π 2 = 22.1 ± 2.0 s. The ratio expected for ∆Π 1 /∆Π 2 from theory is √ 3, and we find 1.80 ± 0.18, within expectations. While neither value puts strong constraints on the stellar parameters, the relatively large period spacings suggest a relatively low-mass DBV, using the models published in Bognár et al (2014): < 0.57 M if T eff > 30,000 K, as suggested by spectroscopy.…”

Pulsating white dwarfs: new insights

“…The second asteroseismological approach for WDs was developed at La Plata Observatory and is based on non-static WD evolutionary models that result from the complete evolution of the progenitor stars. This method has been already applied to GW Virginis stars (see, e.g., Córsico et al, 2007aCórsico et al, ,b, 2008Córsico et al, , 2009aCalcaferro et al, 2016, and references therein), to DBV WDs (see, e.g., Córsico et al, 2012aCórsico et al, , 2014Bognár et al, 2014), and recently to ELMV stars (Calcaferro et al, 2017b(Calcaferro et al, , 2018b. Regarding ZZ Ceti stars, this approach has been employed by Romero et al (2012Romero et al ( , 2013Romero et al ( , 2017.…”

G 207-9 and LP 133-144: light-curve analysis and asteroseismology of two ZZ Ceti stars

“…Our purposes are to examine the short-term variability of pulsation modes in amplitude and phase, and to obtain precise periods for asteroseismic investigations. We have already published our findings on two cool ZZ Ceti stars (KUV 02464+3239, Bognár et al 2009 andGD 154, Paparó et al 2013), one ZZ Ceti located in the middle of the instability strip (GD 244; Bognár et al 2015), and the DBV type KUV 05134+2605 (Bognár et al 2014). With the observations of G 207-9 and LP 133-144, we extended our scope of investigations to higher effective temperatures in the DAV instability domain.…”