Related papers: Are sdAs helium core stars?
We present a detailed calculation of model atmospheres for DA white dwarfs. Our atmosphere code solves the atmosphere structure in local thermodynamic equilibrium with a standard partial linearization technique, which takes into account the…
In young dense clusters repeated collisions between massive stars may lead to the formation of a very massive star (above 100 Msun). In the past the study of the long-term evolution of merger remnants has mostly focussed on collisions…
Elements heavier than hydrogen and helium, collectively termed metals, were created inside stars and dispersed through space at the final stages of stellar evolution. The relative amounts of different isotopes (variants of the same element…
Dark Stars are stellar objects made (almost entirely) of hydrogen and helium, but powered by the heat from Dark Matter annihilation, rather than by fusion. They are in hydrostatic and thermal equilibrium, but with an unusual power source.…
We have found a new evolutionary path to Type Ia supernovae (SNe Ia) which has been overlooked in previous work. In this scenario, a carbon-oxygen white dwarf (C+O WD) is originated, not from an asymptotic giant branch star with a C+O core,…
Studies by Lada (2010) and Heiderman (2010) have suggested that star formation mostly occurs above a threshold in gas surface density Sigma of Sigma_c = 120 Msun pc^{-2} (A_K = 0.8). Heiderman infer a threshold by combining low-mass…
We analyse the properties of three unusual dwarf galaxies in the Centaurus A group discovered with the HIPASS survey. From their optical morphology they appear to be low surface brightness dwarf spheroidals, yet they are gas-rich…
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…
The recent discovery of examples of intermediate-mass helium stars have offered new insights into interacting binaries. These observations will allow significant improvements in our understanding of helium stars. However, in the creation of…
A large number of low-mass (< 0.20 M_sun) helium white dwarfs (He WDs) have recently been discovered. The majority of these are orbiting another WD or a millisecond pulsar (MSP) in a close binary system; a few examples are found to show…
We present theoretical analysis on old white dwarf stars with \emph{some} hydrogen, that possess a mass of surface hydrogen from $1\times10^{-11}M_{\sun}$ to $1\times10^{-7}M_{\sun}$. The evolution of such objects is complicated by…
Many characteristics of dwarf carbon stars are broadly consistent with a binary origin, including mass transfer from an evolved companion. While the population overall appears to have old-disc or halo kinematics, roughly 2$\,$per cent of…
Recent UV observations of the most massive Galactic globular clusters show a significant population of hot stars below the zero-age HB (``blue hook'' stars), which cannot be explained by canonical stellar evolution. Stars which suffer…
Some globular clusters host multiple stellar populations with different chemical abundance patterns. This is particularly true for $\omega$ Centauri, which shows clear evidence of a helium- enriched sub-population characterized by a helium…
We present the results of a spectral analysis of a large sample of subdwarf B stars selected from follow-up observations of candidates from the Hamburg Quasar Survey. Fundamental parameters (effective temperature, gravity, and helium…
A photometric and spectroscopic analysis of 152 cool white dwarf stars is presented. The discovery of 7 new DA white dwarfs, 2 new DQ white dwarfs, 1 new magnetic white dwarf, and 3 weak magnetic white dwarf candidates, is reported, as well…
Pulsating low-mass white dwarf stars are white dwarfs with stellar masses between 0.30~M$_{\odot}$ and 0.45~M$_{\odot}$ that show photometric variability due to gravity-mode pulsations. Within this mass range, they can harbour both a…
White dwarfs with helium-dominated atmospheres comprise approximately 20% of all white dwarfs. Among the open questions are the total masses and the origin of the hydrogen traces observed in a large number and the nature of the deficit of…
The mixing of material from stellar convective cores into their adjacent radiative layers has been a matter of long-standing debate. Pulsating subdwarf B stars offer excellent conditions to advance our understanding of this problem. In this…
We have presented 309 new white-dwarf (WD) + main-sequence (MS) star binaries identified from the Sloan Digital Sky Survey (SDSS) Tenth Data Release (DR10). The majority of them consist of a white dwarf and a low-mass secondary (typically M…