Related papers: Distorted surfaces of magnetic helium-peculiar sta…
Chemically peculiar stars present spectral and photometric variability with a single period. In the oblique rotator model, the non homogeneous distribution of elements on the stellar surface is at the origin of the observed variations. As…
A fraction of the extreme horizontal branch stars of globular clusters exhibit a periodic light variability that has been attributed to rotational modulation caused by surface spots. These spots are believed to be connected to inhomogeneous…
The light curves of magnetic, chemically peculiar stars typically show periodic variability due to surface spots that in most cases can be modeled by low-order harmonic expansion. However, high-precision satellite photometry reveals tiny…
The spectral and magnetic properties and variability of the B2Vnp emission-line magnetosphere star HR7355 were analyzed. The object rotates at almost 90% of the critical value, meaning it is a magnetic star for which oblateness and gravity…
The amplitude and morphology of light curves of solar-like stars change substantially with increasing rotation rate: brightness variations get amplified and become more regular, which has so far not been explained. We develop a modelling…
High-resolution UV spectra, obtained with HST and FUSE, enable us to analyse hot hydrogen-rich central stars in detail. Up to now, optical hydrogen and helium lines have been used to derive temperature and surface gravity. Those lines,…
Context: The presence of heavier chemical elements in stellar atmospheres influences the spectral energy distribution (SED) of stars. An uneven surface distribution of these elements, together with flux redistribution and stellar rotation,…
The discovery of exotic abundances, chemical inhomogeneities, and weak magnetic fields on the surface of late B-type primaries in spectroscopic binaries has important implications not only for our understanding of the formation mechanisms…
Electrons on the helium surface display sharp resonant absorption lines related to the transitions between the subbands of quantized motion transverse to the surface. A magnetic field parallel to the surface strongly affects the absorption…
The magnetic star HD 21699 possesses a unique magnetic field structure where the magnetic dipole is displaced from the centre by 0.4 +/- 0.1 of the stellar radius (perpendicularly to the magnetic axis), as a result, the magnetic poles are…
Diffusion of elements in the atmosphere and envelope of a star can drastically alter its surface composition, leading to extreme chemical peculiarities. We consider the case of hot subdwarfs, where surface helium abundances range from…
We show that element diffusion can produce large fluctuations in the initial helium abundance of the star-forming clouds. Diffusion time-scale, which in stars is much larger than the Hubble time, can fall below 10^8 years in the neutral gas…
There is growing observational evidence for some kind of interaction between stars and close-in extrasolar giant planets. Shkolnik et al. reported variability in the chromospheric Ca H and K lines of HD 179949 and upsilon And that seemed to…
Early-type B stars with strong magnetic fields and rapid rotation form centrifugal magnetospheres (CMs), as the relatively weak stellar wind becomes magnetically confined and centrifugally supported above the Kepler co-rotation radius. CM…
The important result achieved in our recent study of a large sample of HgMn stars using UVES at the VLT and FEROS at the ESO 2.2m telescope is the finding that most HgMn stars exhibit spectral variability of various chemical elements,…
Context. Classical chemically peculiar stars exhibit atmospheres that are often structured by the effects of atomic diffusion. As a result of these elemental diffusion and horizontal abundance variations, photospheric temperature varies at…
In helioseismology, there is a well-known offset between observed and computed oscillation frequencies. This offset is known to arise from improper modeling of the near-surface layers of the Sun, and a similar effect must occur for models…
I summarize the results of 15 years of research on the surface abundances of stars in globular clusters. Globular-cluster stars afford a unique view of the physical processes that shape the surface abundances of stars on and beyond the…
The existence of dark radiation that is completely decoupled from the standard model in the early Universe leaves open the possibility of an associated dark radiation isocurvature mode. We show that the presence of dark radiation…
Stars consume hydrogen in their interiors but, generally speaking, their surfaces continue to contain some 70% hydrogen (by mass) throughout their lives. Nevertheless, many types of star can be found with hydrogen-deficient surfaces, in…