J/A+A/667/A136 Methanol deuteration in high-mass protostars (Van Gelder+, 2022)
Methanol deuteration in high-mass protostars.
Van Gelder M.L., Jaspers J., Nazari P., Ahmadi A., Van Dishoeck E.F.,
Beltran M.T., Fuller G.A., Sanchez-monge A., Schilke P.
<Astron. Astrophys., 667, A136 (2022)>
=2022A&A...667A.136V 2022A&A...667A.136V (SIMBAD/NED BibCode)
ADC_Keywords: Masers ; Interstellar medium ; Millimetric/submm sources
Keywords: ISM: abundances
Abstract:
The deuteration of molecules forming in the ices such as methanol
(CH3OH) is sensitive to the physical conditions during their
formation in dense cold clouds and can be probed through observations
of deuterated methanol in hot cores.
The aim is to determine the D/H ratio of methanol for a large sample
of 99 high-mass protostars and to link this to the physical conditions
during the formation of methanol in the prestellar phases.
Observations with the Atacama Large Millimeter/submillimeter Array
(ALMA) containing transitions of CH3OH, CH2DOH, CHD2OH,
13CH3OH, and CH318OH are investigated. The column densities of
CH2DOH, CHD2OH, and CH3OH are determined for all sources, where
the column density of CH3OH is derived from optically thin 13C and
18O isotopologues. Consequently, the D/H ratio of methanol is
derived taking statistical effects into account.
Singly deuterated methanol (CH2DOH) is detected at the 3σ
level toward 25 of the 99 sources in our sample of the high-mass
protostars. Including upper limits, the <D/H>CH3OH ratio inferred
from NCH2DOH/NCH3OH was derived for 38 of the 99 sources and
varies between ∼10-3-10-2. Including other high-mass hot cores from
the literature, the mean methanol D/H ratio is 1.1±0.7x10-3. This
is more than one order of magnitude lower than what is seen for
low-mass protostellar systems (2.2±1.2x10-2). Doubly deuterated
methanol (CHD2OH) is detected at the 3σ level toward 11 of the
99 sources. Including upper limits for 15 sources, the <D/H>CH2DOH
ratios derived from NCH2DOH/NCH2DOH are more than two orders of
magnitude higher than <D/H>CH3OH with an average of 2.0±0.8x10-1
which is similar to what is found for low-mass sources. Comparison
with literature GRAINOBLE models suggests that the high-mass
prestellar phases are either warm (>20K) or live shorter than the
free-fall timescale. In contrast, for low-mass protostars, both a low
temperature of <15K and a prestellar phase timescale longer than the
free-fall timescale are necessary.
The <D/H>CH3OH ratio drops by more than an order of magnitude
between low-mass and high-mass protostars due to either a higher
temperature during the prestellar phases or shorter prestellar phases.
However, successive deuteration toward CHD2OH seems equally
effective between low-mass and high-mass systems.
Description:
The dataset analyzed in this work was taken from the ALMA Evolutionary
study of High Mass Protocluster Formation in the Galaxy (ALMAGAL)
survey (2019.1.00195.L; PI: S. Molinari) that targeted over 1000 dense
clumps with M>500M☉ based on the Herschel Hi-Gal survey
The derived column densities of all isotopologues are presented in
Table B.1 for the reported excitation temperature.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tableb1.dat 181 99 Column densities of 13CH3OH, CH318OH,
CH3OH, CH2DOH, and CHD2OH and
derived methanol D/H ratios
--------------------------------------------------------------------------------
Byte-by-byte Description of file:tableb1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 20 A20 --- Source Source name
22- 23 I2 h RAh Right ascension (J2000) (1)
25- 26 I2 min RAm Right ascension (J2000) (1)
28- 32 F5.2 s RAs Right ascension (J2000) (1)
34 A1 --- DE- Declination sign (12000) (1)
35- 36 I2 deg DEd Declination (12000) (1)
38- 39 I2 arcmin DEm Declination (12000) (1)
41- 45 F5.2 arcsec DEs Declination (12000) (1)
47- 50 F4.2 arcsec phibeam Beam size
52- 54 I3 K Tex Excitation temperature
55 A1 --- n_Tex [3] Note on Tex (2)
56 A1 --- l_N13CH3OH Limit flag on N13CH3OH
57- 64 E8.3 cm-2 N13CH3OH 13CH3OH column density (3)
66- 72 E7.2 cm-2 e_N13CH3OH ? 13CH3OH column density error
74 A1 --- l_NCH318OH Limit flag on NCH318OH
75- 81 E7.2 cm-2 NCH318OH CH318OH column density (3)
83- 89 E7.2 cm-2 e_NCH318OH ? CH318OH column density error
91 A1 --- l_NCH3OH Limit flag on NCH3OH
92- 98 E7.2 cm-2 NCH3OH CH3OH column density or lower limit of
CH3OH column density (4)
100-106 E7.2 cm-2 e_NCH3OH ? CH3OH column density error
107 A1 --- --- [-]
108-115 E8.3 cm-2 NCH3OHu ? Upper limit of NCH3OH interval (4)
117 A1 --- l_NCH2DOH Limit flag on NCH2DOH
118-124 E7.2 cm-2 NCH2DOH CH2DOH column density (3)
126-132 E7.2 cm-2 e_NCH2DOH ? CH2DOH column density error
134 A1 --- l_NCHD2OH Limit flag on NCHD2OH
135-141 E7.2 cm-2 NCHD2OH CHD2OH column density (3)
143-149 E7.2 cm-2 e_NCHD2OH ? CHD2OH column density error
151 A1 --- l_<D/H>1 Limit flag on <D/H>CH3OH
152-158 E7.2 --- <D/H>1 ?=- <D/H>CH3OH using Eq. (2) of the paper
160-166 E7.2 --- e_<D/H>1 ? <D/H>1 error
167 A1 --- l_<D/H>2 Limit flag on <D/H>CH3OH
168-173 E6.2 --- <D/H>2 ?=- <D/H>CH3OH using Eq. (3)of the paper
176-181 E6.2 --- e_<D/H>2 ? <D/H>2 error
--------------------------------------------------------------------------------
Note (1): The coordinates mark the position from which the spectra were
extracted
Note (2): Tex is set to 150K for deuterated isotopologues and to 100K for
the other isotopologues.
Note (3): All column densities are derived for the reported Tex and assuming the
source size is equal to the size of the beam (i.e., beam dilution = 1).
Note (4): The column density of CH3OH is derived from the and 13CH3OH
isotopologues when these are detected. If neither isotopologue is detected but
CH3OH is, a range in column densities is presented where the lower limit it
the column density derived from CH3OH and the upper limit is scaled from
the upper limit on 13CH3OH. If CH3OH itself is also not detected,
an upper limit is directly derived from its spectrum.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 21-Feb-2023