Formaldehyde and methanol deuteration in protostars: fossiles from a past fast high density pre-collapse phase

Abstract

Extremely high deuteration of several molecules have been observed around low mass protostars since a decade. Among them, formaldehyde and methanol present particularly high deuteration, with observations of abundant doubly and triply deuterated forms. Both species are thought to be mainly formed on interstellar grains during the low temperature and dense pre-collapse phase by H and D atom additions on the iced CO. We present here a theoretical study of the formaldehyde and methanol deuteration obtained with our gas-grain model, GRAINOBLE. This model takes into account the multilayer nature of the mantle and explores the robustness of the results against the uncertainties of poorly constrained chemical and surface model parameters. The comparison of the model predictions with the observations leads to two major results: i) the observed high deuteration is obtained during the last phase of the pre-collapse stage, when the density reaches 5 10^6 cm^-3, and this phase is fast, lasting only several thousands years. ii) D and H abstraction and substitution reactions are crucial in making up the observed deuteration ratios; This work shows the power of chemical composition as a tool to reconstruct the past history of protostars.

7 pages and 4 figures, accepted in The Astrophysical Journal Letters (14th February 2012)

References in corpus (9)

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• Chemical survey of Class I protostars with the IRAM-30m
• Successive deuteration in low-mass star-forming regions: the case of D${}_2$-methanol (CHD${}_2$OH) in IRAS 16293-2422
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• Modelling Deuterated Isotopologues of Methanol toward the Pre-Stellar Core L1544
• Imaging the water snowline in a protostellar envelope with H${}^{13}$CO${}^{+}$
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• FAUST XVII: Super deuteration in the planet forming system IRS 63 where the streamer strikes the disk
• Tracing the atomic nitrogen abundance in star-forming regions with ammonia deuteration
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• The L1157-B1 astrochemical laboratory: testing the origin of DCN
• Upper limit for the D2H+ ortho-to-para ratio in the prestellar core 16293E (CHESS)
• First detection of CHD${}_2$OH towards pre-stellar cores
• Deuterated Formaldehyde in the low mass protostar HH212
• Gas vs. solid phase deuterated chemistry: HDCO and D${}_2$CO in massive star-forming regions
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• FAUST X: Formaldehyde in the Protobinary System [BHB2007] 11: Small Scale Deuteration
• Pristine ices in a planet-forming disk revealed by heavy water
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• A survey of HDCO and D${}_2$CO towards Class 0/I proto-brown dwarfs
• Broadband infrared spectroscopy of methanol isotopologues in pure, H2O-rich, and CO-rich ice analogues
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• Hunting pre-stellar cores with APEX: overview
• Singly- and doubly-deuterated formaldehyde in massive star-forming regions