J/A+A/682/A8 H-MM1 and Oph D deuterated ammonia spectra (Harju+, 2024)
Nuclear spin ratios of deuterated ammonia in prestellar cores.
LAsMA observations of H-MM1 and Oph D.
Harju J., Pineda J.E., Sipila O., Caselli P., Belloche A., Wyrowski F.,
Riedel W., Redaelli E., Vasyunin A.I.
<Astron. Astrophys. 682, A8 (2024)>
=2024A&A...682A...8H 2024A&A...682A...8H (SIMBAD/NED BibCode)
ADC_Keywords: Molecular clouds ; Spectra, millimetric/submm
Keywords: astrochemistry - ISM: molecules - ISM: individual objects: H-MM1 -
ISM: individual objects: Oph DC
Abstract:
We determine the ortho/para ratios of NH2D and NHD2 in two dense,
starless cores, where their formation is supposed to be dominated by
gas-phase reactions, which, in turn, is predicted to result in
deviations from the statistical spin ratios. The Large APEX
sub-Millimeter Array (LAsMA) multibeam receiver of the Atacama
Pathfinder EXperiment (APEX) telescope was used to observe the
prestellar cores H-MM1 and Oph D in Ophiuchus in the ground-state
lines of ortho and para NH2D and NHD2. The fractional abundances
of these molecules were derived employing 3D radiative transfer
modelling, using different assumptions about the abundance profiles as
functions of density. We also ran gas-grain chemistry models with
different scenarios concerning proton or deuteron exchanges and
chemical desorption from grains to find out if one of these models can
reproduce the observed spin ratios. The observationally deduced
ortho/para ratios of NH2D and NHD2 are in both cores within 10% of
their statistical values 3 and 2, respectively, and taking 3-sigma
limits, deviations from these of about 20% are allowed. Of the
chemistry models tested here, the model that assumes proton hop (as
opposed to full scrambling) in reactions contributing to ammonia
formation, and a constant efficiency of chemical desorption, comes
nearest to the observed abundances and spin ratios. The nuclear spin
ratios derived here are in contrast with spin-state chemistry models
that assume full scrambling in proton donation and hydrogen
abstraction reactions leading to deuterated ammonia. The efficiency of
chemical desorption influences strongly the predicted abundances of
NH3, NH2D, and NHD2, but has a lesser effect on their ortho/para
ratios. For these the proton exchange scenario in the gas is decisive.
We suggest that this is because of rapid re-processing of ammonia and
related cations by gas-phase ion-molecule reactions.
Description:
The data consist of 80 FITS spectra, presenting the oNH2D(1-0),
pNH2D(1-0), oNHD2(1-0), and pNHD2 lines towards 7 positions in
H-MM1 and 13 positions in OphD. In fact the mentioned four lines are
contained in the same spectral band of the receiver, but for the
convenience of the user, four separate files have been written out,
with different reference frequencies and line names in the FITS
header. Then, when the spectra are read in Class (using the command
fits read <file_name>), the lines appear at the correct LSR velocity
(around 4 km/s). Use, for example, the commands "set unit velocity",
"set mode x -10 20" to zoom to the line . The last 8 characters of the
file name (before the extension .fit) give the offset in arcseconds
from the map centre.
The central positions are H-MM1: (16:27:58.5, -24:33:40);
Oph D: (16:28:30.2, -24:18:42), J2000. The size of each file is 265K.
Objects:
-------------------------------------------------
RA (2000) DE Designation(s)
-------------------------------------------------
16 27 58.5 -24 33 40 H-MM1 = [MAN98] H-MM1
16 28 30.2 -24 18 42 Oph D = NAME Ophiuchus D
-------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
list.dat 148 80 List of fits spectra
fits/* . 80 Individual of fits spectra
--------------------------------------------------------------------------------
Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 24 I5 --- Nx Number of pixels along X-axis
26- 48 A23 "datime" Obs.date Observation date
50- 61 E12.6 Hz bFREQ Lower value of frequency interval
63- 73 E11.6 Hz BFREQ Upper value of frequency interval
75- 81 F7.1 Hz dFREQ Frequency resolution
83- 85 I3 Kibyte size Size of FITS file
87-108 A22 --- FileName Name of FITS file, in subdirectory fits
110-148 A39 --- Title Title of the FITS file
--------------------------------------------------------------------------------
Acknowledgements:
Jorma Harju, jorma.harju(at)helsinki.fi
(End) Patricia Vannier [CDS] 17-Nov-2023