[en] The λ 6708 doublet of interstellar Li I has been observed at high spectral resolution (3.km s^-1) and very good signal to noise ratio (∼ 4000) towards δ Sco and ζ Oph. Using a profile fitting method, we derive for the first time outside the solar system a ⁷Li/⁶Li ratio of 38 for a diffuse cloud in front of ζ Oph. Even the lower limit of the error bar is incompatible with the ratio measured in meteorites and is not explained by recent models of galactic evolution. The existence of a local inhomogeneity is suggested. Finally, as for other alkalis, lithium is depleted on to dust grains in the diffuse interstellar medium

[en] The study of the interstellar medium toward epsilon Per, a moderately reddened (E_B-V = 0.1) B0.5 star, through the analysis of H I, D I, H₂, N I, O I, and Ar I absorption features, revealed the following structure of the line of sight: (1) a main interstellar, cold (Tapprox.100 K; b = 2.9 km s^-1) component, (2) a weak (approx.1% of the main one) probably cold component, and (3) a weak (also approx.1% of the main one) and hot component (Tapprox.8000 K). All three components have normal abundances. Comparison with ground-based observations or other UV studies reveals the presence on the line of sight of an H II region not detected in the neutral species observed in this study. High-velocity H I gas is also detected, located either in the interstellar medium or very likely in the stellar wind for the blue-shifted components. One of these features is blended with the deuterium lines and therefore obscures our D/H evaluation. All we can say is that the data are compatible with a D/H ratio equal to 1.5 x 10^-5. This blended feature proved to vary by at least a factor of 3 in column density within few hours, a result which sustains our interpretation of the stellar wind origin of the blueshifted high-velocity H I component. However, the alternative interpretation of a high D/H (approx.10^-4) value is also compatible with our data

[en] The interstellar medium on the γ Cas line of sight is studied through the observations of O I, H₂, H I, D I, and Ar absorption features with the Copernicus satellite. By using the velocity structure of the line of sight previously determined through atomic nitrogen, we demonstrate that these neutrals are located in the same physical regions and that the O I and Ar I abundances could be solar, on the average, relative to N I in all components. We also reevaluated the D/H ratio: (1.3 +- 0.25) x 10^-5. The 1066.660 A Ar I line profile is contaminated by an unidentifited line, already detected in the spectrum of zeta Pup. Furthermore, we report a peculiar behavior of the Ar I abundance in the different components, possibly associated with high-velocity interstellar gas present on that line of sight

[en] Observations of interstellar nitrogen absorption features in the spectrum of the star γ Cas with the Copernicus satellite were performed. Because of the large range in f-value for the lines observed, it is possible to accurately determine the structure of the line of sight. We find four components at LSR velocities around -24.6 km s^-1 (component A), -17.1 km s^-1 (component B), -7.8 km s^-1 (component C), and +1.3 km s^-1 (component D). Through the comparison with H I absorption lines and ground-based observations, we show that the main component (B), which contains about 97% of the total nitrogen column density, is warm (Tapprox.1200 K). We also demonstrate that N I is, on average, not depleted on the line of sight

[en] The IRAS star β Pictoris is still the only one around which a disk made of both dust and gas has been detected. Spectroscopic observations of β Pic have revealed that some metallic absorption lines present redshifted additional components which strongly variate with time. This has been interpreted as the result of the infall of small evaporating cometary-like bodies toward the star. To improve this model, a theoretical description of such an event has been purchased. Numerical simulations of such infalling bodies have been able to reproduce quite faithfully the observed behaviour of some metallic ions, and we have explained the observed difference between these behaviours by means of radiation pressure. Some constraints on the orbits of the bodies have been deduced by through the simulations which should be related to a possible interpretation concerning β Pic's disk

[en] We report the results of a systematic search for β Pic-like stars, undertaken at ESO, CFHT and OHP. The candidate stars, either IRAS excess stars or shell stars, are investigated by means of high resolution spectroscopy in the CaII and NaI lines, which in the case of β Pic, are very peculiar. We present the observations and show that among the selected stars, few do show spectral similarities with β Pic. Some interesting cases, HR10, HR2174, HR9043 and HR6519 are discussed

[en] A general presentation of astrophysical observations in the ultraviolet is given. First the particular nature of ultraviolet studies is emphasised. This is followed by a brief historical presentation of some of the typical instrumentation used. Then, in the framework of galactic observations, some of the most important results obtained concerning the physics of planetary, solar, stellar and interstellar media are presented. (author)

[en] The study of deuterium in the direction of epsilonPer has revealed a time variation of the observed DI absorption feature. To explain this variation we suppose that HI material is present in the stellar wind producing the narrow absorption features observed on the blue wing of the Lyman lines. In consequence it appears that deuterium absorption lines may sometimes be contaminated by high-velocity HI present in stellar winds. Reviewing the previously published deuterium abundance determinations, it is shown that a correlation seems to exist between the stellar luminosity class and the D/H values, the lowest D/H value corresponding to the more evolved stars. The conclusion is that the local interstellar deuterium abundance is more probably of the order of 5x10^-₆ rather than 2x10^-₅ as previously thought. (orig.)