The following document lists the file abstract/NEVANS_WARMH2.abs
from catalogue VI/111.
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===================================================================== ==> In this proposal, more time is being requested for NEVANS.PHOTOION ===================================================================== In this proposal, we continue and extend the ISO open-time project NEVANS. PHOTOION, to study the physical and chemical conditions in the peripheries of star-forming clouds. Specifically, using studies from the ground, we have chosen outlying regions of the L1630, S140, and IC5146 molecular clouds, which have modest extinction (Av = 5 - 15) and density (n = 1000/cm^3). Regions like these include most of the mass in the interstellar medium, but their properties and role in star formation are poorly known. We are testing these regions for evidence of a distributed mode of star formation. Using IRAS data, we define 1-D positional cuts (see figures in the paper version), which have a range in intensity of the interstellar radiation field (Go = 10 - 170). In NEVANS. PHOTOION, we proposed to observe the [CII] line at 157 microns and the [OI] lines at 63 microns toward the outskirts of S140 and IC5146 by using LWS. Though the LWS software has yet to be released, we have used the ISO First-Look tool to examine the preliminary data on S140 we have received. We see good detections of both 157 and 63 micron lines, and the line intensities are roughly consistent with the models. Our initial analysis indicates that further observations will allow a detailed comparison with the models and improve our understanding of these regions. We propose to observe the rotational lines of H_2 at 28.221, 17.035, 9.665 microns, and rovibrational lines 1-0 O(3) at 2.80 microns toward these clouds using SWS, as they directly probe the total amount of warm gas in the PDR. These lines, together with the FIR continuum spectrum and lines from LWS, will allow us to test PDR models in regimes where they have not previously been tested and, together with our ground-based studies, to pin down the physical and chemical conditions in these regions. Knowledge of these conditions will allow us to test tracers of hydrogen column density, chemistry in cloud "edges", and McKee's theory that star formation is regulated by photoionization.