Related papers: Improved helium line formation for EHe stars
The study of Stark broadening of neutral helium lines, despite significant advances over recent decades, has not led to updated large grids of helium line profiles relevant to the spectroscopic study of helium-rich stars. While the…
Hot subdwarfs represent a group of low-mass helium-burning stars formed through binary-star interactions and include some of the most chemically-peculiar stars in the Galaxy. Stellar evolution theory suggests that they should have…
A high resolution (R = 110.000), very high S/N (>600) spectrum of the metal-poor turnoff star G271-162 has been obtained in connection with the commissioning of UVES at VLT/Kueyen. Using both 1D hydrostatic and 3D hydrodynamical model…
We calculate a grid of spherically symmetric OB stellar atmospheres at low metallicities, including both non-local thermodynamic equilibrium (NLTE) and metal line blanketing effects. This is done to assess the uncertainties in helium…
The measurement of oxygen lines in metal-poor unevolved stars, in particular near-UV OH lines, can provide invaluable information on the properties of the Early Galaxy. Near-UV OH lines constitute an important tool to derive oxygen…
Current three-dimensional (3D) hydrodynamical model atmospheres together with NLTE spectrum synthesis, permit to derive reliable atomic and isotopic chemical abundances from high-resolution stellar spectra. Not much is known about the…
The Galactic evolution of copper remains poorly understood, partly due to the strong departures from local thermodynamic equilibrium (LTE) affecting Cu I lines. A key source of uncertainty in non-LTE modelling is the treatment of inelastic…
The [Ba/Eu] abundance ratio is commonly adopted as a tracer of the relative contributions of the slow (s) and rapid (r) neutron-capture processes. However, at [Fe/H] < -2 dex, Ba can be produced efficiently by both processes, rendering…
We explore the response of the He II 304 {\AA} and He I 584 {\AA} line intensities to electron beam heating in solar flares using radiative hydrodynamic simulations. Comparing different electron beams parameters, we found that the…
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…
Aims: Aluminium is a key element to constrain the models of the chemical enrichment and the yields of the first supernovae. But obtaining precise Al abundances in extremely metal-poor (EMP) stars requires that the non-LTE effects be…
Aluminium abundances of B-type stars were spectroscopically determined in order to get information about the galactic gas composition at the time of their formation. For this purpose, two AlII lines at 6243 and 4663A were employed. The…
We report a photometric and spectroscopic study of the hot extreme helium star LSS 5121. We found photometric variability, but no period was evident in its periodogram. This is consistent with the previous proposal, based on spectral line…
The Lyman and Werner band systems of deuterated molecular hydrogen (HD) occur in the far UV range below 1200 A. The high sensitivity of the FUSE mission can give access, at moderate resolution, to hot stars shining through translucent…
The formation of lithium lines in the atmosphere of C-rich giants is discussed. LTE and NLTE approximations are used to model lithium lines in the spectra of super Li-rich AGB stars. The system of equations of the statistical balance of…
It is generally accepted that the atmospheres of cool/lukewarm stars of spectral types A and later are described well by LTE model atmospheres, while the O-type stars require a detailed treatment of NLTE effects. Here model atmosphere…
HD 140283 is a reference subgiant that is metal poor and confirmed to be a very old star. The abundances of this type of old star can constrain the nature and nucleosynthesis processes that occurred in its (even older) progenitors. The…
One of the major tasks in interpretation of data from large-scale stellar surveys is to determine the fundamental atmospheric parameters such as effective temperature, surface gravity, and metallicity. In most on-going and upcoming…
Aims. We gathered about 100 high-resolution spectra of three typical HgMn (mercury-manganese) stars, HD 11753, HD 53244, and HD 221507, to search for slowly pulsating B-like pulsations and surface inhomogeneous distribution of various…
Context: Recently, the He I triplet at 10830 \r{A} has been rediscovered as an excellent probe of the extended and possibly evaporating atmospheres of close-in transiting planets. This has already resulted in detections of this triplet in…