Related papers: A puzzling periodicity in the pulsating DA white d…
The pulsating hydrogen atmosphere white dwarf star G 117-B15A has been observed since 1974. Its main pulsation period at 215.19738823(63) s, observed in optical light curves, varies by only (5.12+/-0.82)x10^{-15} s/s and shows no glitches,…
White dwarfs are well studied objects. The relative simplicity of their physics allows to obtain very detailed models which can be ultimately compared with their observed properties. Among white dwarfs there is a specific class of stars,…
We present time-resolved spectrophotometry of the pulsating DA white dwarf G 29-38. As in previous broad-band photometry, the light curve shows the presence of a large number of periodicities. Many of these are combination frequencies,…
We present time-series VLT spectroscopy and NTT photometry of the cataclysmic variable SDSS J220553.98+115553.7, which contains a pulsating white dwarf. We determine a spectroscopic orbital period of 82.825 +/- 0.089 min from velocity…
We report the detection of periodic variations on the T_eff ~32 000 K DA white dwarf star HE 1017-1352. We obtained time series photometry using the 4.1 m SOAR telescope on three separate nights for a total of 16.8 h. From the frequency…
Some cataclysmic variables show short-period ($\sim$200 to $\sim$2000 s) light variations, which are attributable to nonradial pulsations of the accreting primary white dwarf. We regard these periodic variations as r-mode (global…
Non-radial pulsations have been identified in a number of accreting white dwarfs in cataclysmic variables. These stars offer insight into the excitation of pulsation modes in atmospheres with mixed compositions of hydrogen, helium, and…
With 10m class telescopes as well as with time-tagging detectors on board of HST and FUSE, the analysis of time-resolved spectra for pulsating white dwarfs becomes feasible. We present simulated time-resolved spectra for the hot pulsating…
We have obtained time-resolved ultraviolet spectroscopy for the pulsating DAV stars G226-29 and G185-32, and for the pulsating DBV star PG1351+489 with the Hubble Space Telescope Faint Object Spectrograph, to compare the ultraviolet to the…
We report the most rapid rate of period change measured to date for a pulsating DA (hydrogen atmosphere) white dwarf (WD), observed in the 292.9 s mode of WD 0111+0018. The observed period change, faster than 10^{-12} s/s, exceeds by more…
In this paper we derive a bound on the rate of change of the gravitational constant G coming from the pulsating white dwarf G117-B15A. This star is a ZZ Ceti pulsator extensively studied with astroseismological techniques for last three…
We present a detailed analysis of time-resolved optical spectra of the ZZ Ceti white dwarf, HS 0507+0434B. Using the wavelength dependence of observed mode amplitudes, we deduce the spherical degree, l, of the modes, most of which have l=1.…
We report our measurement of the rate of change of period with time dP/dt for the 215 s periodicity in the pulsating white dwarf G 117-B15A, the most stable optical clock known. After 31 years of observations, we have finally obtained a 4…
We employ a state-of-the-art asteroseismological model of G117-B15A, the archetype of the H-rich atmosphere (DA) white dwarf pulsators (also known as DAV or ZZ Ceti variables), and use the most recently measured value of the rate of period…
We report on our findings of the bright, pulsating, helium atmosphere white dwarf GD 358, based on time-resolved optical spectrophotometry. We identify 5 real pulsation modes and at least 6 combination modes at frequencies consistent with…
We present a follow-up analysis of the unique magnetic luminosity-variable carbon-atmosphere white dwarf SDSS J142625.71+575218.3. This includes the results of some 106.4 h of integrated light photometry which have revealed, among other…
The standard theory of pulsations deals with the frequencies and growth rates of infinitesimal perturbations in a stellar model. Modes which are calculated to be linearly driven should increase their amplitudes exponentially with time; the…
Hydrogen atmosphere pulsating white dwarfs, also known as DAV stars, are the most abundant type of pulsating white dwarfs. High-temperature DAV stars exhibit in general a small number of pulsation modes and stable frequencies. G132-12 is…
The pulsating DA white dwarfs are the coolest degenerate stars that undergo self-driven oscillations. Understanding their interior structure will help to understand the previous evolution of the star. To this end, we report the analysis of…
The location of the red edge of the ZZ Ceti instability strip is defined observationally as being the lowest temperature for which a white dwarf with a H-rich atmosphere (DA) is known to exhibit periodic brightness variations. Whether this…