J/A+A/634/A115 Orion B9 dense cores H2D+ spectra (Miettinen, 2020)
APEX observations of ortho-H2D+ towards dense cores in the Orion B9
filament.
Miettinen O.
<Astron. Astrophys. 634, A115 (2020)>
=2020A&A...634A.115M 2020A&A...634A.115M (SIMBAD/NED BibCode)
ADC_Keywords: Molecular clouds ; Radio lines ; Spectra, millimetric/submm
Keywords: astrochemistry - stars: formation - stars: protostars -
ISM: individual objects: Orion B9
Abstract:
We aim to determine the ortho-H2D+ properties (e.g. column density
and fractional abundance with respect to H2) in a sample of dense
cores in the Orion B9 star-forming filament, and to compare those with
the previously determined source characteristics, in particular with
the gas kinetic temperature, [N2D+]/[N2H+] deuterium
fractionation, and level of CO depletion. We used the Atacama
Pathfinder EXperiment (APEX) telescope to observe the 372GHz
o-H2D+(11,0-11,1) line towards three prestellar cores and three
protostellar cores in Orion B9. We also employed our previous APEX
observations of C17O, C18O, N2H+, and N2D+ line emission,
and 870 micron dust continuum emission towards the target sources. The
o-H2D+(11,0-11,1) line was detected in all three prestellar
cores, but in _nly one of the protostellar cores. The corresponding
o-H2D+ abundances were derived to be ~(12-30)x10-11 and
∼6x10-11. Two additional spectral lines, DCO+(5-4) and
N2H+(4-3), were detected in the observed frequency bands with high
detection rates of 100% and 83%. We did not find any significant
correlations among the explored parameters, although our results are
mostly consistent with theoretical expectations. Also, the Orion B9
cores were found to be consistent with the relationship between the
o-H2D+ abundance and gas temperature obeyed by other low-mass
dense cores. The o-H2D+ abundance was found to decrease as the
core evolves. The o-H2D+ abundances in the Orion B9 cores are in
line with those found in other low-mass dense cores and larger than
derived for high-mass star-forming regions. The higher o-H2D+
abundance in prestellar cores compared to that in cores hosting
protostars is to be expected from chemical reactions where higher
concentrations of gas-phase CO and elevated gas temperature accelerate
the destruction of H2D+. The validity of using the
[o-H2D+]/[N2D+] abundance ratio as an evolutionary indicator,
which has been proposed for massive clumps, remains inconclusive when
applied for the target cores. Similarly, the behaviour of the
[o-H2D+]/[DCO+] ratio as the source evolves was found to be
ambiguous. Still larger samples and observations of additional
deuterated species are needed to explore these potential evolutionary
indicators further. The low radial velocity of the line emission from
one of the targeted prestellar cores, SMM 7 (∼3.6km/s versus the
systemic Orion B9 velocity of ∼9km/s), suggests that it is a chance
superposition seen towards Orion B9. Overall, as located in a dynamic
environment of the Orion B molecular cloud, the Orion B9 filament
provides an interesting target system to investigate the
deuterium-based chemistry, and further observations of species like
para-H2D+ and D2H+ would be of particular interest.
Description:
APEX o-H2D+(11,0-11,1) spectra at 372 GHz towards six dense
cores in Orion B9. The spectra were reduced using the GILDAS/CLASS90
software package, and saved in the FITS format. Note that also the
N2H+(4-3) transition lies at the observed upper frequency sideband
(372.7GHz). The spectra were smoothed once, and their intensity scale
is that of the main-beam brightness temperature scale.
Objects:
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RA (2000) DE Designation(s)
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05 42 27.68 -01 20 01.0 i05399 = IRAS 05399-0121
05 43 03.06 -01 16 29.2 i05405 = IRAS 05405-0117
05 42 30.5 -01 20 45 ssm 1 = [MHH2009c] SMM 1
05 42 44.4 -01 16 03 ssm 3 = [MHH2009c] SMM 3
05 43 05.1 -01 18 38 ssm 6 = [MHH2009c] SMM 6
05 43 22.1 -01 13 46 ssm 7 = [MHH2009c] SMM 7
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 156 6 List of fits spectra
fits/* . 6 Individual fits spectra
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See also:
J/A+A/538/A137 : Orion B9 dense cores maps (Miettinen+, 2012)
Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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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- 57 F8.5 GHz bFreq Lower value of relative frequency interval
59- 65 F7.5 GHz BFreq Upper value of relative frequency interval
67- 72 I6 Hz dFreq Frequency resolution
74- 76 I3 Kibyte size Size of FITS file
78- 88 A11 --- FileName Name of FITS file, in subdirectory fits
90-156 A67 --- Title Title of the FITS file
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Acknowledgements:
Oskari Miettinen, oskari.miettinen(at)aka.fi
(End) Oskari Miettinen [Academy of Finland], Patricia Vannier [CDS] 10-Jan-2020