HD 112 mu m in absorption and extreme CO depletion in a cold molecular cloud

Details HD 112 mu m in absorption and extreme CO depletion in a cold molecular cloud HD 112 mu m in absorption and extreme CO depletion in a cold molecular cloud

Feb 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002a%26a...383l...9c&link_type=abstract

Astronomy and Astrophysics, v.383, p.L9-L13 (2002)

Astronomy and Astrophysics

Astrophysics

7

Ism: Abundances, Ism: Lines And Bands, Ism: Molecules, Ism: Clouds, Ism: Individual Objects: W49, Infrared: Ism, Radio Lines: Ism

Scientific paper

We present ISO-LWS observations at high spectral resolution (R ~ 104) towards a cold molecular cloud in the line of sight of W49. The HD ground state transition at 112 mu m is detected, showing the first observation of this line in absorption outside the solar system. The 112 mu m absorption depth gives a straightforward measure of the lower limit of the cloud's HD column density, N(HD) > 8 x 1018 cm-2. We also mapped the same line of sight in the 12CO (2-1) and (3-2), and 13CO (2-1) transitions at the CSO, and in the C18O and C17O (1-0) and (2-1) transitions at the IRAM 30-m. From these observations we derive an upper limit to the CO column density, N(CO) < 7 x 1017 cm-2. Assuming a standard CO abundance (1 x 10-4) would imply a [D]/[H] abundance two orders of magnitude larger than the average [D]/[H] value observed in the solar neighborhood. The alternative explanation that we defend here is that CO is highly depleted (by a factor 100) in this cloud. This is the first measurement of such a depletion factor in a relatively massive cold molecular cloud ( ~ 103 Msun). Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands and the UK) with the participation of ISAS and NASA.

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