Context: Inversion techniques are the most powerful methods to obtain information about the thermodynamical and magnetic properties of solar and stellar atmospheres. In the recent years, we have witnessed the development of highly sophisticated inversion codes that are now widely applied to spectro-polarimetric observations. The majority of these

We present spectroscopy of the Hα emision line in the X-ray transient V4 04 Cyg. Along with the spectroscopy, simultaneus photometry was used in order t o renormalize the spectra to agree with the photometry, giving us spectrophotom etric data. We have found evidence to show the presence of flares in both the l ine and continuum on a time-scale

Since the discovery of the first brown dwarfs (Tiede 1; Rebolo et al. 1995, Gliese 229B; Nakajima et al. 1995) the complement of identified brown dwarfs has grown to over 700. Yet our understanding of these cool objects is still somewhat lacking. Current models struggle to reproduce the observed variation in photometric and spectroscopic properties

We have used the Chandra X-ray Observatory to observe the following six black hole X-ray transients in quiescence: GRO J0422+32 (orbital period Porb=5.1 hr), A0620--00 (Porb=7.8 hr), GS2000+25 (Porb=8.3 hr), 4U1543--47 (Porb=27.0 hr), GRO J1655--40 (Porb=62.9 hr), GS2023+338 (Porb=155 hr). Previous to these Chandra observations there was only a

Blazars are active galactic nuclei, which are powerful sources of radiation whose central engine is located in the core of the host galaxy. Blazar emission is dominated by non-thermal radiation from a jet that moves relativistically towards us, and therefore undergoes Doppler beaming. This beaming causes flux enhancement and contraction of the

We present the detailed spectral analysis of a sample of M33 B-type supergiant stars, aimed at the determination of their fundamental parameters and chemical composition. The analysis is based on a grid of non-LTE metal line-blanketed model atmospheres including the effects of stellar winds and spherical extension computed with the code FASTWIND