We present full evolutionary calculations appropriate for the study of hydrogen-rich DA white dwarfs. This is done by evolving dwarf progenitors from zero age main sequence, through core hydrogen burning phase, helium phase and thermally pulsing asymptotic giant branch to stage. Complete sequences are computed a wide range stellar masses two different metallicities: Z=0.01, which representative solar neighborhood, Z=0.001, old systems, like globular clusters. During cooling stage we compute...

Ultra-massive white dwarfs are powerful tools to study various physical processes in the Asymptotic Giant Branch (AGB), type Ia supernova explosions and theory of crystallization through dwarf asteroseismology. Despite interest these dwarfs, there few evolutionary studies literature devoted them. Here, we present new ultra-massive sequences that constitute an improvement over previous ones. In sequences, take into account for first time process phase separation expected during stage by...

Abstract Using archival Hubble Space Telescope observations, we report the discovery of four variable low-mass white dwarfs (WDs; 0.18 M ⊙ ≤ 0.5 ) in globular cluster NGC 6397. One source exhibits a periodic optical modulation 5.21 ± 0.02 hr, which interpret as potentially due to rotation magnetic helium core WD (He WD). This makes this candidate second He 6397, and one few WDs with measured period. The other three candidates show aperiodic variability, change magnitude ranging from ∼0.11...

We present evolutionary calculations and colors for massive white dwarfs with oxygen-neon cores masses between 1.06 1.28 Mo. The stages computed cover the luminosity range from log(L/Lo) approx. 0.5 down to -5.2. Our cooling sequences are based on that take into account chemical composition expected dwarf progenitors burned carbon in partially degenerate conditions. use of detailed non-gray model atmospheres provides us accurate outer boundary conditions our evolving models at low effective...

The present work is designed to explore the evolution of helium-core white dwarf (HeWD) stars for case metallicities much lower than solar one (Z=0.001 and Z=0.0002). Evolution followed in a self-consistent way with predictions detalied new non-grey atmospheres, time-dependent element diffusion history progenitor. Reliable initial models low mass HeWDs are obtained by applying loss rates 1msun stellar model. angular momentum caused gravitational wave emission magnetic wind braking...

We present full evolutionary calculations appropriate for the study of hot hydrogen-deficent DO white dwarfs, PG 1159 stars, and DB dwarfs. White dwarf sequences are computed a wide range stellar masses helium envelopes on basis complete treatment history progenitors including core hydrogen burning phases, thermally-pulsing AGB phase, born-again episode that is responsible deficiency. also provide colors magnitudes new $T_{\rm eff} < 40 000$ K, where NLTE effects not dominant. These an...

Abstract We present a set of full evolutionary sequences for white dwarfs with hydrogen-deficient atmospheres. take into account the history progenitor stars, all relevant energy sources involved in cooling, element diffusion very outer layers, and boundary conditions provided by new detailed non-gray dwarf model atmospheres pure helium composition. These are based on most up-to-date physical inputs. Our calculations extend down to low effective temperatures, ∼2500 K, provide homogeneous...

The purpose of this work is to explore the evolution helium-core white dwarf stars in a self-consistent way with predictions detailed non-grey model atmospheres and element diffusion. To end, we consider models stellar masses 0.406, 0.360, 0.327, 0.292, 0.242, 0.196 0.169 M⊙ follow their from end mass-loss episodes, during pre-white evolution, down very low surface luminosities.

The structural properties of single component fluids hard hyperspheres in odd space dimensionalities $d$ are studied with an analytical approximation method that generalizes the Rational Function Approximation earlier introduced study hard-sphere [S. B. Yuste and A. Santos, Phys. Rev. A {\bf 43}, 5418 (1991)]. theory makes use exact form radial distribution function to first order density extends it finite by assuming a rational for defined Laplace space, coefficients being determined simple...

A recently derived method [R. D. Rohrmann and A. Santos, Phys. Rev. E 76, 051202 (2007)] to obtain the exact solution of Percus-Yevick equation for a fluid hard spheres in (odd) d dimensions is used investigate convergence properties resulting virial series. This done both compressibility routes, which coefficients B(j) are expressed terms set (d-1)/2 coupled algebraic equations become nonlinear d>/=5. Results have been up d=13. confirmation alternating character series d>/=5, due existence...

Motivated by the recent detection of single and binary He-core white dwarfs in metal-rich clusters, we present a full set evolutionary calculations colors appropriate for study such dwarfs. The paper is also aimed at investigating whether stable hydrogen burning may constitute main source energy massive resulting from high-metallicity progenitors. White dwarf sequences are derived taking into account history progenitor stars with supersolar metallicities. We incorporate self-consistent,...

White dwarf evolution is essentially a gravothermal cooling process, which,for cool white dwarfs, sensitively depends on the treatment of outer boundary conditions. We provide detailed conditions appropriate for computing dwarfs employing non-gray model atmospheres pure H composition. also explore impact times different assumptions energy transfer in atmosphere dwarfs. Detailed are computed taken into account non-ideal effects gas equation state and chemical equilibrium, collision-induced...

We examine the emergent fluxes from helium-core white dwarfs following their evolution end of pre-white dwarf stages down to advanced cooling stages. For this purpose, we include a detailed treatment physics atmosphere, particularly an improved representation state gas by taking into account non-ideal effects according so-called occupation probability formalism. The present calculations also incorporate hydrogen-line opacity Lyman, Balmer and Paschen series, pseudo-continuum absorptions new...

Kowalski & Saumon identified the missing absorption mechanism in observed spectra of cool white dwarf stars as Lyman α red wing formed by collisions between atomic and molecular hydrogen successfully explained entire many DA-type dwarfs. Owing to important astrophysical implications this issue, we present here an independent assessment process. For purpose, compute free–free quasi-molecular due with H H2 within one-perturber, quasi-static approximation. Line cross-sections are obtained using...

Mixtures of hard hyperspheres in odd space dimensionalities are studied with an analytical approximation method. This technique is based on the so-called Rational Function Approximation and provides a procedure for evaluating equations state, structure factors, radial distribution functions, direct correlations functions additive mixtures any number components arbitrary odd-dimension space. The method gives exact solution Ornstein--Zernike equation coupled Percus--Yevick closure, thus...

The chemical potentials of multicomponent fluids are derived in terms the pair correlation functions for arbitrary number components, interaction potentials, and dimensionality. formally exact result is particularized to hard-sphere mixtures with zero or positive nonadditivity. As a simple application, three-dimensional additive from Percus-Yevick theory associated equation state obtained. This chemical-route shown be more accurate than virial state. An interpolation between...

Iglesias et al. showed that the Rayleigh scattering from helium atoms decreases by collective effects in atmospheres of cool white dwarf stars. Their study is here extended to consider an accurate evaluation atomic polarizability and density involved cross-section over a wide density–temperature region. The dynamic dipole ground state determinated with oscillator-strength distribution approach. spectral oscillator strength considered includes most significant single doubly excited...

We present a detailed calculation of model atmospheres for DA white dwarfs. Our atmosphere code solves the structure in local thermodynamic equilibrium with standard partial linearization technique, which takes into account energy transfer by radiation and convection. This incorporates recent improved extended data base collision-induced absorption molecular hydrogen. analyse emergent flux range 2500Teff60 000 K 6.5log g9.0. Bolometric correction colour indices are provided subsample grid....

A selection of 17 stars in the Sloan Digital Sky Survey, previously identified as DC-class white dwarfs (WDs), has been reported to show spectra very close blackbody radiation wavelength range from ultraviolet infrared. Because absence lines and other details their spectra, surface gravity these objects poorly constrained, effective temperatures have determined by fits continuum spectrum using pure helium atmosphere models. We computed model atmospheres with H/He mixtures used Gaia DR2...

ABSTRACT We report a peculiar variable blue star in the globular cluster (GC) NGC 6397, using Hubble Space Telescope optical imaging. Its position colour–magnitude diagrams and its spectrum are consistent with this being helium-core white dwarf (He WD) binary system. The light curve shows periodicity at 18.5 h. argue that is due to rotation of WD possibly magnetic spots on surface WD. This would make object first candidate He any GC, detached system GC one few WDs known period nature....

We argue that NSV 11749, an eruption observed in the early twentieth century, was a rare event known as "very late thermal pulse" (VLTP). To support our argument we compare lightcurve of 11749 with those two bonafide VLTP objects to date, V4334 Sgr and V605 Aql, predicted by state art stellar evolution models. Next, explore IPHAS 2MASS catalogues for possible counterparts eruption. Our analysis shows scenario outperforms all other proposed scenarios explanation 11749. identify IPHAS/2MASS...

Structural and thermodynamic properties of multicomponent hard-sphere fluids at odd dimensions have recently been derived in the framework rational function approximation (RFA) [Rohrmann Santos, Phys. Rev. E \textbf{83}, 011201 (2011)]. It is demonstrated here that RFA technique yields exact solution Percus-Yevick (PY) closure to Ornstein-Zernike (OZ) equation for binary mixtures arbitrary dimensions. The proof relies mainly on Fourier transforms $\hat{c}_{ij}(k)$ direct correlation...

The coupling-parameter method, whereby an extra particle is progressively coupled to the rest of particles, applied sticky-hard-sphere fluid obtain its equation state in so-called chemical-potential route ($\ensuremath{\mu}$ route). As a consistency test, results for one-dimensional sticky particles are shown be exact. Results corresponding three-dimensional case (Baxter's model) derived within Percus-Yevick approximation by using different prescriptions dependence interaction potential on...

New spectra have been obtained for the pole-on Be star HR 5223 (HD 120991) using Far Ultraviolet Satellite Explorer (FUSE). We give a complete description of far-UV spectral range (920 to 1180 Å). The are affected by strong blends with interstellar lines and molecular bands that also significantly lower energy distribution star. produce synthetic spectrum medium (ISM) determine column densities several elements (H2, H i, N O i ...) seen towards disentangle components due ISM, photosphere...