J/MNRAS/500/4901 Deuterated methanol in comet 67P/C-G (Drozdovskaya+, 2021)
Prestellar grain-surface origins of deuterated methanol in comet
67P/Churyumov-Gerasimenko.
Drozdovskaya M.N., Schroeder I I.R.H.G., Rubin M., Altwegg K.,
van Dishoeck E.F., Kulterer B.M., De Keyser J., Fuselier S.A., Combi M.
<Mon. Not. R. Astron. Soc., 500, 4901-4920 (2021)>
=2021MNRAS.500.4901D 2021MNRAS.500.4901D (SIMBAD/NED BibCode)
ADC_Keywords: Comets ; Molecular data ; Interstellar medium ;
Star Forming Region
Keywords: astrochemistry - comets: general -
comets: individual: 67P/Churyumov-Gerasimenko - ISM: molecules
Abstract:
Deuterated methanol is one of the most robust windows astrochemists
have on the individual chemical reactions forming deuterium-bearing
molecules and the physicochemical history of the regions where they
reside. The first-time detection of mono- and di-deuterated methanol
in a cometary coma is presented for comet 67P/Churyumov-Gerasimenko
using Rosetta-ROSINA data. D-methanol (CH3OD and CH2DOH combined)
and D2-methanol (CH2DOD and CHD2OH combined) have an abundance
of 5.5+/0.46 and 0.00069±0.00014 per cent relative to normal
methanol. The data span a methanol deuteration fraction (D/H ratio) in
the 0.71-6.6 per cent range, accounting for statistical corrections
for the location of D in the molecule and including statistical error
propagation in the ROSINA measurements. It is argued that cometary
CH2DOH forms from CO hydrogenation to CH3OH and subsequent H-D
substitution reactions in CH3-R. CHD2OH is likely produced from
deuterated formaldehyde. Meanwhile, CH3OD and CH2DOD could form
via H-D exchange reactions in OH-R in the presence of deuterated water
ice. Methanol formation and deuteration is argued to occur at the same
epoch as D2O formation from HDO, with formation of mono-deuterated
water, hydrogen sulphide, and ammonia occurring prior to that. The
cometary D-methanol/methanol ratio is demonstrated to agree most
closely with that in prestellar cores and low-mass protostellar
regions. The results suggest that cometary methanol stems from the
innate cold (10-20K) prestellar core that birthed our Solar system.
Cometary volatiles individually reflect the evolutionary phases of
star formation from cloud to core to protostar.
Description:
The ROSINA Double Focusing Mass Spectrometer (DFMS) has a high-mass
resolution of m/Δm=3000 for a m/z (mass-to-charge ratio) of 28
at 1 per cent of the peak height (Balsiger et al.
2007SSRv..128..745B 2007SSRv..128..745B). Its main detector, the MCP/LEDA, is a
position-sensitive imaging detector that is a stack of two
micro-channel plates (MCPs) arranged in Chevron configuration,
followed by two independent rows (Rows A and B) of 512 anodes on a
linear electron detector array (LEDA). For the measurement mode
discussed in this paper, spectra around each integer mass are obtained
consecutively every 30s (10s for adjusting voltages and 20s of
integration time).
Quantities of methanol and its isotopologues from star-forming regions
to comets used to construct Figs 2-4 and B1-B3 are tabulated in Table
D2 alongside their respective references. The full descriptions of the
probed locations in each source can be found in the corresponding
publications, as well as the beam sizes of the observations, and
assumptions about the source sizes. The isotopic ratios used in the
various publications are given in Table D1.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tabled1.dat 98 43 Carbon and oxygen isotopic ratios used in the
literature for derivation of methanol column
densities
tabled2.dat 177 141 Column densities in cm-2 of CH3OH, CH2DOH,
and CH3OD in star-forming regions and comets
used to construct Figs 2-4 and B1-B3
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Byte-by-byte Description of file: tabled1.dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- Isotope Carbon or oxygen ratio
(12C/13C or 16O/18O)
9- 11 I3 --- Ratio Isotopic ratio
13- 28 A16 --- Name Source name
30- 33 I4 pc Dist ? Galactocentric distance
35- 38 F4.1 pc e_Dist ? Error on Dist
40- 98 A59 --- Ref Reference for the source and the distance
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Byte-by-byte Description of file: tabled2.dat
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Bytes Format Units Label Explanations
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1- 21 A21 --- Name Source name
23- 60 A38 --- Position Source location (1)
62 A1 --- l_CH3OH Limit flag on CH3OH
64- 71 E8.3 cm-2 CH3OH Column density of CH3OH
73 A1 --- l_CH2DOH Limit flag on CH2DOH
75- 82 E8.3 cm-2 CH2DOH ? Column density of CH2DOH
84 A1 --- l_CH3OD Limit flag on CH3OD
86- 93 E8.3 cm-2 CH3OD ? Column density of CH3OD
95- 153 A59 --- Ref Reference
155- 177 A23 --- Comment Reason for exclusion (2)
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Note (1): When either 13CH3OH or CH183OH is specified in brackets in
the 'Position' column that is an indicator that an isotopologue was
used to determine the column density of normal methanol.
When a reference is made to a temperature in K in this column, it
refers to an assumption that has been made about the adopted
excitation temperatures. P04 and J18 refer to two different partition
functions for CH3OD used in Taquet et al. (2019A&A...632A..19T 2019A&A...632A..19T,
Cat. J/A+A/632/A19)
Note (2): If a value appeared only in Figures B1-B3 and not in Figures 2-4,
which contain only the most-reliable interstellar methanol
observations, then the last column states the reason for that (see
Section 3.3 of the article for more details)
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 12-Oct-2023