Carrying out detailed analyses on massive blue stars further than the Milky Way is a demanding task, however it is feasible and the best way to comprehend the stellar evolution in environments with different metallicity. We present the first quantitative study performed on a massive blue star sample belonging to NGC~55, about 1.9 Mpc away. The

Atmospheric extinction data covering a long period are analysed. We present infrared atmospheric extinction in the J, H and K bands obtained at the Teide Observatory from 1989 to 1997. We find high-quality statistical values, similar to those of other good sites, such as Mauna Kea. We devote special attention to the study of the dependence of the

Context. Open clusters are ideal test particles for studying the chemical evolution of the Galactic disc. However, the number and accuracy of existing high-resolution abundance determinations, not only of [Fe/H], but also of other key elements, remains largely insufficient. Aims: We attempt to increase the number of Galactic open clusters that have

Aims.We used the UVES spectrograph (VLT-UT2 telescope) to obtain high-resolution spectra of 6 stars hosting transiting planets, namely for OGLE-TR-10, 56, 111, 113, 132, and TrES-1. These spectra are now used to derive and discuss the chemical abundances for C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, and Zn. Methods: .Abundances

Context: The young σ Orionis cluster is an important location for studying the formation and evolution of stars, brown dwarfs, and planetary-mass objects. Its metallicity, although it is a fundamental parameter, has not been well determined yet. Aims: We present the first determination of the metallicity of nine young late-type stars in σ Orionis

Using spectroscopic data presented in Magrini et al. (cite{m03}), we have analyzed with the photoionization code CLOUDY 94.00 (Ferland et al. cite{ferland}) 11 Planetary Nebulae belonging to the spiral galaxy M 33. Central star temperatures and nebular parameters have been determined. In particular the chemical abundances of He/H, O/H, N/H, Ar/H