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29 March 2024 |
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The L1157-B1 astrochemical laboratory: testing the origin of DCN | G. Busquet
; F. Fontani
; S. Viti
; C. Codella
; L. Podio
; B. Lefloch
; M. Benedettini
; C. Ceccarelli
; | Date: |
27 Jun 2017 | Abstract: | L1157-B1 is the brightest shocked region of the large scale molecular
outflow, considered the prototype of chemically rich outflows, being the ideal
laboratory to study how shocks affect the molecular gas. Several deuterated
molecules have been previously detected with the IRAM 30m, most of them formed
on grain mantles and then released into the gas phase due to the shock. We aim
to investigate observationally the role of the different chemical processes at
work that lead to formation the of DCN and test the predictions of the chemical
models for its formation. We performed high angular resolution observations
with NOEMA of the DCN(2-1) and H13CN(2-1) lines to compute the deuterated
fraction, Dfrac(HCN).We detected emission of DCN(2-1) and H13CN(2-1) arising
from L1157-B1 shock. Dfrac(HCN) is ~4x10$^{-3}$ and given the uncertainties, we
did not find significant variations across the bow-shock. Contrary to HDCO, for
which its emission delineates the region of impact between the jet and the
ambient material, DCN is more widespread and not limited to the impact region.
This is consistent with the idea that gas-phase chemistry is playing a major
role in the deuteration of HCN in the head of the bow-shock, where HDCO is
undetected as it is a product of grain-surface chemistry. The spectra of DCN
and H13CN match the spectral signature of the outflow cavity walls, suggesting
that their emission result from shocked gas. The analysis of the time dependent
gas-grain chemical model UCL-CHEM coupled with a C-type shock model shows that
the observed Dfrac(HCN) is reached during the post-shocked phase, matching the
dynamical timescale of the shock. Our results indicate that the presence of DCN
in L1157-B1 is a combination of gas-phase chemistry that produces the
widespread DCN emission, dominating in the head of the bow-shock, and
sputtering from grain mantles toward the jet impact region. | Source: | arXiv, 1706.8834 | Services: | Forum | Review | PDF | Favorites |
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