Other
Scientific paper
May 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006sptz.prop30167n&link_type=abstract
Spitzer Proposal ID #30167
Other
Scientific paper
We propose to carry out Spitzer/IRS observations of interstellar hydrogen deuteride (HD). The proposed program follows up our recent detection of the HD R(3) and R(4) transitions at 28.50 and 23.04 microns in Spitzer observations of shocked molecular gas in the supernova remnant IC443C; as well as tentative detections of warm HD in the Herbig-Haro objects HH54 and HH7, and in the star-forming region GGD37 (Cepheus A West). Using integration times a factor of 14 - 60 larger than the short integrations we have obtained to date, we expect to obtain signal-to-noise ratios sufficient to confirm and map the HD emission in HH54, HH7, and GGD37. These data will provide a more precise measurement of the HD R(4)/R(3) ratio in all four sources, allowing us to model the non-LTE excitation of HD reliably and determine the HD abundance and gas density. In addition to the Long-High observations needed to measure HD R(3) and R(4), we will carry out Short-Low observations of the H2 S(2) through S(7) lines in GGD37; these observations - which are already in hand for the other three sources - are essential to measure the column density of warm H2 in the source, without which the HD/H2 abundance ratio cannot be determined. The results of this investigation will greatly expand the sample of interstellar gas clouds in which the HD abundance has been measured, observations prior to Spitzer having only identified HD in a single source (the Orion Molecular Cloud). The results will have important implications for our understanding of the chemistry of deuterium-bearing molecules, and of the evolution of the elemental abundance of deuterium in our Galaxy.
Bergin Edwin
Forrest Bill
Green Joel
Melnick G. G.
Neufeld David
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