J/A+A/655/A86 PILS-Cygnus. observations of CygX-N30 (van der Walt +, 2021)
Protostellar Interferometric Line Survey of the Cygnus X region (PILS-Cygnus).
First results: observations of CygX-N30.
van der Walt S.J., Kristensen L.E., Jorgensen J.K., Calcutt H.,
Manigand S., el Akel M., Garrod R.T., Qiu K.
<Astron. Astrophys. 655, A86 (2021)>
=2021A&A...655A..86V 2021A&A...655A..86V (SIMBAD/NED BibCode)
ADC_Keywords: Interstellar medium ; Millimetric/submm sources ; Abundances ;
Spectra, millimetric/submm; Stars, early-type; YSOs
Keywords: astrochemistry - stars: protostars - ISM: molecules -
ISM: individual objects: W75N(B) - submillimeter: ISM
Abstract:
Complex organic molecules (COMs) are commonly detected in and near
star-forming regions. However, the dominant process in the release of
these COMs from the icy grains -- where they predominately form -- to
the gas phase is still an open question.
We investigate the origin of COM emission in a high-mass protostellar
source, CygX-N30 MM1, through high-angular-resolution interferometric
observations over a continuous broad frequency range.
We used 32 GHz Submillimeter Array (SMA) observations with continuous
frequency coverage from 329 to 361GHz at an angular resolution of
∼1'' to do a line survey and obtain a chemical inventory of the
source. The line emission in the frequency range was used to determine
column densities and excitation temperatures for the COMs. We also
mapped out the intensity distribution of the different species.
We identified approximately 400 lines that can be attributed to 29
different molecular species and their isotopologues. We find that the
molecular peak emission is along a linear gradient, and coincides with
the axis of red- and blue- shifted H2CO and CS emission. Chemical
differentiation is detected along this gradient, with the O-bearing
molecular species peaking towards one component of the system and the
N- and S-bearing species peaking towards the other. The chemical
gradient is offset from but parallel to the axis through the two
continuum sources. The inferred column densities and excitation
temperatures are compared to other sources where COMs are abundant.
Only one deuterated molecule is detected, HDO, while an upper limit
for CH2DOH is derived, leading to a D/H ratio of <0.1%.
We conclude that the origin of the observed COM emission is probably a
combination of the young stellar sources along with accretion of
infalling material onto a disc-like structure surrounding a young
protostar and located close to one of the continuum sources. This disc
and protostar are associated with the O-bearing molecular species,
while the S- and N- bearing species on the other hand are associated
with the other continuum core, which is probably a protostar that is
slightly more evolved than the other component of the system. The low
D/H ratio likely reflects a pre- stellar phase where the COMs formed
on the ices at warm temperatures (∼30K), where the deuterium
fractionation would have been inefficient. The observations and
results presented here demonstrate the importance of good frequency
coverage and high angular resolution when disentangling the origin of
COM emission.
Description:
Molecular transitions detected towards CygX-N30 MM1. The listed line
transitions are from best fit line models obtained using the software
package CASSIS, on the spectrum taken at the position of peak emission
of CH3OH (position 2 in Fig. 12). The model parameters are listed
in Table 6. Only transitions above 10K are listed (∼3σ),
corresponding to about 1.0Jy/beam.
Objects:
-------------------------------------------------------
RA (2000) DE Designation(s)
-------------------------------------------------------
20 38 36.39 +42 37 34.1 CygX-N30 MM1 = [S2001] MM 1
-------------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table8.dat 83 488 Molecular line transitions
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Byte-by-byte Description of file:table8.dat
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Bytes Format Units Label Explanations
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1- 10 F10.6 GHz Freq Line peak frequency
14- 30 A17 --- Mol Molecular formula
33- 57 A25 --- Trans Quantum number (J{Ka, Kc, F})
60- 66 F7.2 K Eup/kB Upper level energy
70- 74 F5.2 0.0001s-1 Aij Einstein A coefficient
78- 83 F6.2 --- Opacity ?=- Line opacity (τ)
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Acknowledgements:
Sarel J. van der Walt, sarel.vanderwalt(at)nbi.ku.dk
(End) Patricia Vannier [CDS] 08-Sep-2021