The following document lists the file abstract/ALECAVEL_GAS_DISC.abs
from catalogue VI/111.
A plain copy of the file
(without headers/trailers) may be downloaded.
One of the major discoveries made by IRAS was the finding of disc of dust particles around a number of main sequence stars. These stars may not only be surrounded by dust particles, but also by gas discs. Indeed, in the case of Beta Pictoris strong stable and variable redshifted absorption features are detected due to the absorption of the star light passing through a gaseous disc seen nearly edge on. After an extensive ground-based search of such gaseous discs, from a sample of about 50 stars, few revealed absorption features similar to Beta Pictoris ones (stable as well as variable). But the origin of this gas and the evolution of such discs are not well understood. The observations made in absorption however detect only the part of the disc just along the line of sight. The strength of the ISO observations in the contrary is to sample the whole gas distribution around the star whatever the tilt of the disc on the line of sight is. The observations of the infrared emission lines will allow to determine the composition and eventually the ionization state of these gaseous component of the discs. Since the composition is related to the history of the matter with N/C and N/O ratio or the proportion of these volatile elements compared to those of refractory. This will be check by measuring C/Fe or O/Fe ratio. The new information given by ISO will allow to distinguish between primordial gas with cosmic characteristics and gas replenished by evaporating bodies. The observations of the stars proposed here will thus improve our knowledge of the possible presence of large bodies around stars.