Related papers: Constraints on 12C(alpha,gamma)16O from White Dwar…
For many years, astronomers have promised that the study of pulsating white dwarfs would ultimately lead to useful information about the physics of matter under extreme conditions of temperature and pressure. In this paper we finally make…
White dwarf asteroseismology offers the opportunity to probe the structure and composition of stellar objects governed by relatively simple physical principles. The observational requirements of asteroseismology have been addressed by the…
Due to a new global analysis method, it is now possible to measure the internal composition of pulsating white dwarf stars, even with relatively simple theoretical models. The precise internal mixture of carbon and oxygen is the largest…
During helium burning in the core of a red giant, the relative rates of the 3&alpha and ^{12}C(&alpha,&gamma)^{16}O reactions largely determine the final ratio of carbon to oxygen in the resulting white dwarf star. The uncertainty in the…
Recent determinations of the internal composition and structure of two helium-atmosphere variable white dwarf stars, GD 358 and CBS 114, have led to conflicting implied rates for the ^{12}C(alpha,gamma)^{16}O reaction. If we assume that…
Pulsating white dwarfs provide constraints to the evolution of progenitor stars. We revise He-burning stellar models, with particular attention to core convection and to its connection with the nuclear reactions powering energy generation…
We seek signatures of the current experimental $^{12}$C$(\alpha,\gamma)^{16}$O reaction rate probability distribution function in the pulsation periods of carbon-oxygen white dwarf models. We find that adiabatic g-modes trapped by the…
We investigate the evolution of cooling helium atmosphere white dwarfs using a full evolutionary code, specifically developed for following the effects of element diffusion and gravitational settling on white dwarf cooling. The major…
We report new infrared spectroscopic observations of cool DQ white dwarfs by using Coolspec on the 2.7m Harlan-Smith Telescope. DQs have helium-rich atmospheres with traces of molecular carbon thought to be the result of convective…
Reliable modeling of the atmospheres of cool white dwarfs is crucial for understanding the atmospheric evolution of these stars and for accurate white dwarfs cosmochronology. Over the last decade {\it ab initio} modeling entered many…
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 have identified seven independent pulsation modes in the helium-atmosphere variable (DBV) white dwarf star CBS 114, based on 65 hours of time-resolved CCD photometry from the 0.75-m telescope at SAAO. We interpret these pulsations as…
We present preliminary results of an experimental study exploring helium at photospheric conditions of white dwarf stars. These data were collected at Sandia National Laboratories' Z-machine, the largest x-ray source on earth. Our helium…
White dwarf asteroseismology offers the opportunity to probe the structure and composition of stellar objects governed by relatively simple physical principles. The observational requirements of asteroseismology have been addressed by the…
We consider the combined effects that overshooting and the $^{12}$C($\alpha$, $\gamma$)$^{16}$O reaction rate have on variable white dwarf stellar models. We find that carbon-oxygen white dwarf models continue to yield pulsation signatures…
One of the largest uncertainties in stellar evolutionary computations is the accuracy of the considered reaction rates. The 12C(alpha,gamma)16O reaction is particularly important for the study of low- and intermediate-mass stars as it…
We present a new method that investigates the evolutionary history of the pulsating DB white dwarf GD358 using asteroseismology. This is done considering the internal C/O profile, which describes the relative abundances of carbon and oxygen…
Here, we present near-infrared spectroscopic observations of 15 helium atmosphere, metal-rich white dwarfs obtained at the NASA Infrared Telescope Facility. While a connection has been demonstrated between the most highly polluted, hydrogen…
White dwarf photospheric parameters are usually obtained by means of spectroscopic or photometric analysis. These results are not always consistent with each other, with the published values often including just the statistical…
We determine the phase diagram for dense carbon/ oxygen mixtures in White Dwarf (WD) star interiors using molecular dynamics simulations involving liquid and solid phases. Our phase diagram agrees well with predictions from Ogata et al. and…