Query : 2001A&A...372..998C

2001A&A...372..998C - Astronomy and Astrophysics, volume 372, 998-1004 (2001/6-4)

Extended D2CO emission: The smoking gun of grain surface-chemistry.


Abstract (from CDS):

We present new observations of the H2CO and D2CO emission around IRAS16293-2422, a low mass protostar in the ρ Ophiuchus complex. Bright H2CO and D2CO emission is detected up to 40'' from the center, corresponding to a linear distance of ∼5000AU. The derived H2CO abundance profile has two jumps at r≤150AU and r≤700AU, where the dust temperature reaches 100K and 50K respectively. The measured [D2CO]/[H2CO] abundance ratio in the envelope is between 0.03 and 0.16, an extremely high value. We demonstrate that the present new observations can only be explained if the D2CO (and H2CO) are formed during the previous cold pre-collapse phase, stored in the grain mantles, and released in the gas phase during the pre-collapse phase. We consider the two main competing theories for mantle formation, i.e. pure accretion against grain surface chemistry, and we conclude that the former theory cannot explain the present observations, whereas grain active chemistry very naturally does. We found that the mantles are evaporated because of the thermal heating of the grains by the central source and that in the outer cold envelope H2CO and D2CO molecules are embedded in CO-rich mantles which sublimate when the dust is warmer than 25K. Finally, the present day H2CO and D2CO abundances very probably reflect the mantle composition. We argue that mantles have likely formed in an onion-like structure with the innermost ice layers more enriched in H2CO molecules and we give estimates of the CO hydrogenation efficiency across the envelope and/or in different ices.

Abstract Copyright:

Journal keyword(s): ISM: abundances - ISM: molecules - stars: formation - ISM: individual: IRAS 16293-2422

Simbad objects: 5

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Number of rows : 5
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
1 LDN 1544 DNe 05 04 16.6 +25 10 48           ~ 832 0
2 NAME [BM89] L1544 cor 05 04 22.5 +25 11 36           ~ 436 1
3 NAME Ophiuchus Molecular Cloud SFR 16 28 06 -24 32.5           ~ 3532 1
4 IRAS 16293-2422 cor 16 32 22.56 -24 28 31.8           ~ 1219 1
5 LDN 1689N DNe 16 32 25.96 -24 28 46.2           ~ 115 0

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