Query : 2017A&A...602L...3Z

2017A&A...602L...3Z - Astronomy and Astrophysics, volume 602, L3-3 (2017/6-1)

Gas versus solid-phase deuterated chemistry: HDCO and D2CO in massive star-forming regions.


Abstract (from CDS):

Context. The formation of deuterated molecules is favoured at low temperatures and high densities. Therefore, the deuteration fraction (Dfrac) is expected to be enhanced in cold, dense prestellar cores and to decrease after protostellar birth. Previous studies have shown that the deuterated forms of species such as N2H+ (formed in the gas phase) and CH3OH (formed on grain surfaces) can be used as evolutionary indicators and to constrain their dominant formation processes and timescales.
Aims. Formaldehyde (H2CO) and its deuterated forms can be produced both in the gas phase and on grain surfaces. However, the relative importance of these two chemical pathways is unclear. Comparison of the deuteration fraction of H2CO with respect to that of N2H+, NH3, and CH3OH can help us to understand its formation processes and timescales.
Methods. With the new SEPIA Band 5 receiver on APEX, we have observed the J=3-2 rotational lines of HDCO and D2CO at 193GHz and 175GHz toward three massive star-forming regions hosting objects at different evolutionary stages: two high-mass starless cores (HMSC), two high-mass protostellar objects (HMPOs), and one ultracompact HII region (UC HII). By using previously obtained H2CO J=3-2 data, the deuteration fractions HDCO/H2CO and D2CO/HDCO are estimated.
Results. Our observations show that singly deuterated H2CO is detected toward all sources and that the deuteration fraction of H2CO increases from the HMSC to the HMPO phase and then sharply decreases in the latest evolutionary stage (UCHII). The doubly deuterated form of H2CO is detected only in the earlier evolutionary stages, with D2CO/H2CO showing a pattern that is qualitatively consistent with the pattern of HDCO/H2CO, within current uncertainties.
Conclusions. Our initial results show that H2CO may display a similar Dfrac pattern as that of CH3OH in massive young stellar objects. This finding suggests that solid-state reactions dominate its formation.

Abstract Copyright: © ESO, 2017

Journal keyword(s): astrochemistry - ISM: molecules - stars: formation - radio lines: ISM - radio lines: ISM

Simbad objects: 7

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Number of rows : 7
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2021
1 GAL 174.20-00.08 Cld 05 30 45.9 +33 47 56           ~ 186 2
2 IRAS 05358+3543 mul 05 39 10.4 +35 45 19           ~ 139 1
3 NAME IRAS 05358+3543 mm mm 05 39 13.0 +35 45 54           ~ 4 0
4 NAME Mon R2 HII 06 07 47.58 -06 22 42.6           ~ 674 2
5 GAL 005.88-00.41 HII 18 00 30.388 -24 04 00.20           ~ 307 0
6 NGC 7129 OpC 21 42 56 +66 06.2     11.5     ~ 238 0
7 NAME NGC 7129 FIR 2 IR 21 44 01.5 +66 03 40           ~ 88 0

    Equat.    Gal    SGal    Ecl

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