R. Cabanac

Early-type stars observed in the ESO UVES Paranal Observatory Project - I. Interstellar Na I UV, Ti II and Ca II K observations

We present an analysis of interstellar Na I (λair = 3302.37 and 3302.98 A), Ti II (λair = 3383.76 A) and Ca II K( λair = 3933.66 A) absorption features for 74 sightlines towards O- and B-type stars in the Galactic disc. The data were obtained from the Ultraviolet and Visual Echelle Spectrograph Paranal Observatory Project, at a spectral resolution of 3.75 km s −1 and with mean signal-to-noise ratios per pixel of 260, 300 and 430 for the Na I ,T iII and Ca II observations, respectively. Interstellar features were detected in all but one of the Ti II sightlines and all of the Ca II sightlines. The dependence of the column density of these three species with distance, height relative to the Galactic plane, H I column density, reddening and depletion relative to the solar abundance has been investigated. We also examine the accuracy of using the Na I column density as an indicator of that for H I. In general, we find similar strong correlations for both Ti and Ca, and weaker correlations for Na. Our results confirm the general belief that Ti and Ca occur in the same regions of the interstellar medium (ISM) and also that the Ti II/Ca II ratio is constant over all parameters. We hence conclude that the absorption properties of Ti and Ca are essentially constant under the general ISM conditions of the Galactic disc.

A Fresh View of Henize 2-10 with VLT NAOS-CONICA*

We present high-resolution observations of Henize 2-10 in Ks (2.2 μm), L (3.8 μm), and M (4.8 μm) bands. These allow us, for the first time, to track accurately the structures at the heart of the galaxy from the optical to the radio. All radio knots previously observed can now be associated with L- and Ks-emitting regions. This implies a revision of their physical nature. Instead of highly extinguished ultradense H II regions, we propose that two of the five radio knots are either supernova remnants or normal H II regions, while the remaining three are bona fide ultradense H II regions, although less obscured than previously thought.

Abundance analysis of 5 early-type stars in the young open cluster IC 2391

Aims. It is unclear whether chemically peculiar stars of the upper main sequence represent a class completely distinct from normal A-type stars, or whether there exists a continuous transition from the normal to the most peculiar late F- to early B-type stars. A systematic abundance analysis of open cluster early-type stars would help to relate the observed differences of the chemical abundances of the photospheres to other stellar characteristics, without being concerned by possible different original chemical composition. Furthermore, if a continuous transition region from the very peculiar to the so called normal A–Fxa0stars exists, it should be possible to detect objects with mild peculiarities. Methods. As a first step of a larger project, an abundance analysis of 5xa0F–A type stars in the young cluster ICu20092391u2000was performed using high resolution spectra obtained with the UVES instrument of the ESO VLT. Results. Our targets seem to follow a general abundance pattern: close to solar abundance of the light elements and iron peak elements, heavy elements are slightly overabundant with respect to the sun, similar to what was found in previous studies of normal field A-type stars of the galactic plane. We detected a weakly chemically peculiar star, HDu200974044. Its element pattern contains characteristics of CP1 as well as CP2 stars, enhanced abundances of iron peak elements and also higher abundances ofxa0Sc, Y, Ba and Ce. We did not detect a magnetic field in this star (detection limit was 2u2009kG). We also studied the star SHJMu20092, proposed as a pre-main sequence object in previous works. Using spectroscopy we found a high surface gravity, which suggests that the star is very close to the ZAMS.