Context. Observations of hydrogen Balmer lines in solar flares remain an important source of information on flare processes in the chromosphere during the impulsive phase of flares. The intensity profiles of optically thick hydrogen lines are determined by the temperature, density, and ionisation structure of the flaring atmosphere, by the plasma velocities and by the velocity distribution of p...

BL Lacertae was the target of an extensive multiwavelength monitoring campaign in the second half of 2000. The campaign had revealed optical and X-ray intraday variability on time scales of ∼ 1.5 hours and evidence for significant spectral variability both at optical and X-ray frequencies. During the campaign, BL Lacertae was observed in two different activity states: A quiescent state with rel...

Aims. We study the emission and absorption of CO ro-vibrational lines in the spectra of intermediate mass pre-main-sequence stars with the aim to determine both the spatial distribution of the CO gas and its physical properties. We also aim to correlate CO emission properties with disk geometry. Methods. Using high-resolution spectra containing fundamental and first overtone CO ro-vibrational e...

In this paper the two-dimensional structure of protoplanetary disks around Herbig Ae/Be stars is studied. This is done by constructing a self-consistent model based on 2-D radiative transfer coupled to the equation of vertical hydrostatics. As a simplifying assumption a grey opacity is used. It is found that the disk can adopt four different structures, dependent on the surface density distribu...