The following document lists the file abstract/PJENNISK_DENSE_CL.abs
from catalogue VI/111.
A plain copy of the file
(without headers/trailers) may be downloaded.
ISO-LWS offers the unique possibility to measure the emission spectrum of quiescent dense cloud dust in the 43-196 micron range. In the dense cloud environment, the dust will show a number of broad emission bands due to water (43-90 micron) and other small molecules that are frozen on the grain surfaces. In addition, PAH emission bands may be present that originate from the outer regions of the cloud. We propose to observe these bands as a function of the total extinction in the line of sight, which is a measure of depth in the cloud. The sight lines chosen are towards background field K-giant stars. These stars have little to no detectable emission in the LWS wavelength range but a strong blackbody continuum at wavelengths less than about 20 micron. This continuum has been used in ground-based observations as a background source to observe the 3.07 micron water ice band and the 4.7 micron C=O band in absorption. The water ice band is typically much stronger per unit Av in these lines of sight than in the spectra of embedded infrared sources and the CO band is always present beyond a threshold of extinction. Therefore, the lines of sight to these stars have probably best been characterised as quiescent. Because the visual extinction along the line of sight to these stars is so well defined, they provide an opportunity to study grain mantle formation, the occurrence of UV photolysis products, and the weakening of the radiation field as manifested in PAH related features with depth in the cloud. It can be tested if the 45 micron water band or any other band contributes significantly to the IRAS 60 micron passband and perhaps signs of crystallinity in the water ice band can be detected that will provide insight into the thermal evolution of volatile grain mantles.