Related papers: Do Hydrogen-deficient Carbon Stars have Winds?
Mid-infrared arcs of dust emission are often seen near ionizing stars within HII regions. A possible explanations for these arcs is that they could show the outer edges of asymmetric stellar wind bubbles. We use two-dimensional,…
The effects of gravitational settling and radiative levitation in the stellar atmospheres and envelopes of subdwarf B (sdB) stars strongly depend on the presence of weak winds. In the paper the existence of weak radiatively driven winds is…
Hydrogen-deficient central stars of planetary nebula such as Wolf-Rayet and PG1159 central stars and some weak emission line stars are primarily composed of helium and carbon. This abundance is well explained by a scenario where a single…
The surface abundances of extreme helium (EHe) and R Coronae Borealis (RCB) stars are discussed in terms of the merger of a carbon-oxygen white dwarf with a helium white dwarf. The model is expressed as a linear mixture of the individual…
We report the detection, from observations using the James Clerk Maxwell Telescope, of CO J $=$ 3$\to$ 2 transition lines in six carbon stars, selected as members of the Galactic Halo and having similar infrared colors. Just one Halo star…
We analysed UV FUSE, IUE, and HST/STIS spectra of five of the hottest [WCE]-type central stars of planetary nebulae: NGC 2867, NGC 5189, NGC 6905, Pb 6, and Sand 3. The analysis leveraged on our grid of CMFGEN synthetic spectra, which…
We are conducting a high-resolution follow-up of candidate EMP stars extracted from the Sloan Digital Sky Survey (SDSS; York et al. 2000) using UVES at the VLT. Three of the programme stars, SDSS J0912+0216, SDSS J1036+1212 and SDSS…
Neutral fluorine (F I) lines are identified in the optical spectra of several R Coronae Borealis stars (RCBs) at maximum light. These lines provide the first measurement of the fluorine abundance in these stars. Fluorine is enriched in some…
There are strong observational indications that the dense slow winds of cool luminous AGB stars are driven by radiative pressure on dust grains which form in the extended atmospheres resulting from pulsation-induced shocks. For carbon…
Atmospheric parameters for hot DB (helium atmosphere) white dwarfs near effective temperatures of 25000K are extremely difficult to determine from optical spectroscopy. This is particularly unfortunate, because this is the range of variable…
The connection between helium-rich hot subdwarfs of spectral types O and B (He-sdB) has been relatively unexplored since the latter were found in significant numbers in the 1980's. In order to explore this connection further, we have…
Abundances of lithium, heavy elements and carbon isotope ratios have been derived in 12 J-type galactic carbon stars. The abundance analysis shows that in these stars the abundances of s-process elements with respect to the metallicity are…
We report the first detection of new dust formation in an SC star. The prototype of the SC stars, UY Cen, underwent a decline of 2 magnitudes in the V-band. The SC stars show pulsational variations and have 60 micron excesses indicating…
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…
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…
This paper presents the initial results of a multi-site photometric programme to examine the extraordinary behaviour displayed by 18 R Coronae Borealis (RCB) stars in the Magellanic Clouds (MCs). RCB stars exhibit a unique variability…
Using a radiative transfer code (DUSTY) parameters of the circumstellar dust shells of 15 hot post-AGB stars have been derived. Combining the optical, near and far-infrared (ISO, IRAS) data of the stars, we have reconstructed their spectral…
Surface abundances of 14 (11 majority class and 3 minority class) R Coronae Borealis stars (RCBs) along with the final flash object, V4334 Sgr (Sakurai's object) are revised based on their carbon abundances measured from the observed C2…
Dwarf carbon (dC) stars, main sequence stars showing carbon molecular bands, were initially thought to be an oxymoron since only AGB stars dredge carbon into their atmospheres. Mass transfer from a former AGB companion that has since faded…
Infrared carbon stars without visible counterparts are generally known as extreme carbon stars. We have selected a subset of these stars with absorption features in the 10-13 $\mu$m range, which has been tentatively attributed to silicon…