Related papers: How an overweight and rapidly rotating PG 1159 sta…

We examine a recently-proposed evolutionary scenario that could explain the existence of the low-mass, helium-enriched PG1159 stars. We assess the overstability of pulsation g-modes of stellar models as evolution proceeds along the PG1159…

Seismological observations with the Whole Earth Telescope (WET) allow the determination of the subsurface compositional structure of white dwarf stars. The hot DO PG 1159 has a helium surface layer with a mass of 0.001 Msun, while the…

We present full evolutionary calculations appropriate to post-AGB PG1159 stars for a wide range of stellar masses. We take into account the complete evolutionary stages of PG1159 progenitors starting from the Zero Age Main Sequence. We…

PG1159 stars are hot, hydrogen-deficient (pre-) white dwarfs with atmospheres mainly composed of helium, carbon, and oxygen. The unusual surface chemistry is the result of a late helium-shell flash. Observed element abundances enable us to…

Hot, compact, hydrogen-deficient pre-white dwarfs (pre-WDs) with effective temperatures of Teff > 70,000 K and a surface gravity of 5.0 < log g < 7.0 are rather rare objects despite recent and ongoing surveys. It is believed that they are…

To improve the understanding of the pulsational instabilities of some of the PG1159-type pre-white dwarfs we performed detailed stability analyses on helium star evolutionary models. With the canonical chemical compositions, pulsational…

We present evidence that PG1159 stars could harbour He--rich envelopes substantially thinner than those predicted by current evolutionary models with current estimates of mass loss, which may be attributable to an extensive mass--loss…

This paper is designed to explore the formation and evolution of hydrogen-deficient post-AGB white dwarfs. To this end, we compute the complete evolution of an initially 2.7 M_sun star from the zero-age main sequence through the thermally…

We present high-resolution VLT spectra of a new helium-rich DO white dwarf and a new PG1159 star, which we identified in the ESO SPY survey. We performed NLTE model atmosphere analyses and found that the PG1159 star is a low-gravity,…

We present full evolutionary calculations appropriate for the study of hot hydrogen-deficent DO white dwarfs, PG 1159 stars, and DB white dwarfs. White dwarf sequences are computed for a wide range of stellar masses and helium envelopes on…

We present asteroseismological inferences on RX J2117.1+3412, the hottest known pulsating PG1159 star. Our results are based on full PG1159 evolutionary models recently presented by Miller Bertolami & Althaus (2006). We performed extensive…

We present high-resolution VLT spectra of a new DO white dwarf and a new PG1159 star, which we identified in the ESO SPY survey. The PG1159 star is a low-gravity, extremely hot (Teff=160,000 K, log g=6) star, having a C/He dominated…

We have detected three new hydrogen-deficient (H < 0.001 mass fraction) pre-white dwarfs (WDs) with helium-dominated atmospheres. The first object is a relatively cool PG1159 star (effective temperature Teff = 72,000 K) that has the lowest…

We reexamine the theoretical instability domain of pulsating PG1159 stars (GW Vir variables). We performed an extensive g-mode stability analysis on PG1159 evolutionary models with stellar masses ranging from 0.530 to 0.741 Mo for which the…

Context: The Sloan Digital Sky Survey Data Release 4 has provided spectra of several new PG 1159 stars and DO white dwarfs. This increase in known hot H-deficient compact objects significantly improves the statistics and helps to…

Recently a new class of hot subluminous stars strongly enriched in C and O have been discovered (CO-sdOs). These stars show abundances very similar to those observed in PG1159 stars but at lower temperatures. Moreover, it has been recently…

Up to 98% of all single stars will eventually become white dwarfs - stars that link the history and future evolution of the Galaxy, and whose previous evolution is engraved in their interiors. Those interiors can be studied using…

We have used phase-resolved high-resolution images and low resolution spectra taken at the ESO Very Large Telescope, to study the properties of the low-mass Helium White Dwarf companion to the millisecond pulsar \psr (hereafter COM…

The helium-atmosphere (DB) white dwarfs are commonly thought to be the descendants of the hotter PG 1159 stars, which initially have uniform He/C/O atmospheres. In this evolutionary scenario, diffusion builds a pure He surface layer which…

Helium rich subdwarf O stars (sdOs) are hot compact stars in a pre-white dwarf evolutionary state. Most of them have effective temperatures and surface gravities in the range Teff = 40,000-50,000 K and log g = 5.5-6.0. Their atmospheres are…