Astronomy and Astrophysics, volume 471, 849-863 (2007/9-1)
A survey of [D2CO]/[H2CO] and [N2D+]/[N2H+] ratios towards protostellar cores.
ROBERTS H. and MILLAR T.J.
Abstract (from CDS):
We use observations and models of molecular D/H ratios to probe the physical conditions and chemical history of the gas and to differentiate between gas-phase and grain-surface chemical processing in star forming regions. As a follow up to previous observations of HDCO/H2
CO and DCN/HCN ratios in a selection of low-mass protostellar cores, we have measured D2
CO and N2
ratios in these same sources. For comparison, we have also measured N2
ratios towards several starless cores and have searched for N2
and deuterated formaldehyde towards hot molecular cores (HMCs) associated with high mass star formation. We compare our results with predictions from detailed chemical models, and to other observations made in these sources. Towards the starless cores and low-mass protostellar sources we have found very high N2
fractionation, which suggests that the bulk of the gas in these regions is cold and heavily depleted. The non-detections of N2
in the HMCs indicate higher temperatures. We did detect HDCO towards two of the HMCs, with abundances 1-3% of H2
CO. These are the first detections of deuterated formaldehyde in high mass sources since Turner (1990ApJ...362L..29T
) measured HDCO/H2
CO and D2
CO towards the Orion Compact Ridge.
ISM: molecules - ISM: clouds - ISM: abundances - stars: formation - astrochemistry
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