The following document lists the file abstract/CGRADY_HAE2BPIC.abs
from catalogue VI/111.
A plain copy of the file
(without headers/trailers) may be downloaded.
Since its discovery by IRAS, the uniqueness and evolutionary state of the beta Pictoris disk have been topics of lively discussion. While detailed studies of beta Pic have revealed the presence of a cleared inner region, with implications for planet formation, and the presence of accreting gas tentatively associated with comet-like bodies, observations of other systems, particularly younger ones, are needed to obtain a better understanding of the evolutionary history of the beta Pic system. During the past 2 years we have identified a number of PMS Herbig Ae/Be stars which are viewed through a significant portion of their circumstellar dust disks, and which exhibit accreting gas similar to, but higher in accretion rate than beta Pic. The available data suggest a correlation between the signatures of mass accretion, the prominence of optical indicators of dust in close proximity to the star, mass return to the ISM, and the shape of the IR spectral energy distribution. The spectroscopy suggests that signatures of accreting volatile gases disappear prior to the refractory species. The optical/UV data give no information on volatile molecules or ices, and thus do not sample the species which are most characteristic of a proto-planetary disk in its earliest evolutionary phases. The time scale for volatile depletion is a critical parameter in planetary formation models, and constrains the mass of any gas giant which can be formed in a planetary system. The mid-IR spectrum, as sampled by the ISO SWS, is rich in bands from volatile molecules which are expected to be abundant in proto-planetary disks, PAH features, sampling small organic grains, silicate bands sampling the refractory grains which are expected to be most important close to the stars, and ice features. Acquisition of a homogeneous sample of low resolution spectra for a group of Herbig Ae/Be stars chosen to span a range in age and degree of central clearing, together with a range in spectral type will permit us to constrain the time available for gas giant formation, and hence the expected planetary masses, more stringently than current estimates which are based on the disappearance of the dust disk.