J/A+A/662/A32 G328.2551-0.5321 APEX spectrum (Bouscasse+, 2022)
Sulphur-rich cold gas around the hot core precursor G328.2551-0.5321. An APEX
unbiased spectral survey of the 2 mm, 1.2 mm, and 0.8 mm atmospheric windows.
Bouscasse L., Csengeri T., Belloche A., Wyrowski F., Bontemps S.,
Guesten R., Menten K.M.
<Astron. Astrophys. 662, A32 (2022)>
=2022A&A...662A..32B 2022A&A...662A..32B (SIMBAD/NED BibCode)
ADC_Keywords: YSOs ; Interstellar medium ; Spectroscopy
Keywords: stars: massive - astrochemistry - stars: protostars -
lines: identification - stars: formation - ISM: molecules
Abstract:
During the process of star formation, the dense gas undergoes
significant chemical evolution leading to the emergence of a rich
variety of molecules associated with hot cores and hot corinos.
However, the physical conditions and the chemical processes involved
in this evolution are poorly constrained; the early phases of emerging
hot cores in particular represent an unexplored territory. Aims. We
provide here a full molecular inventory of a massive protostellar core
that is proposed to represent a precursor of a hot core. We
investigate the conditions for the molecular richness of hot cores. We
performed an unbiased spectral survey towards the hot core precursor
associated with clump G328.2551-0.5321 between 159GHz and 374GHz,
covering the entire atmospheric windows at 2mm, 1.2mm, and 0.8mm.
To identify the spectral lines, we used rotational diagrams and
radiative transfer modelling assuming local thermodynamical
equilibrium. We detected 39 species plus 26 isotopologues, and were
able to distinguish a compact (∼2"), warm inner region with a
temperature, T, of ∼100K, a colder, more extended envelope with T∼20K,
and the kinematic signatures of the accretion shocks that have
previously been observed with ALMA. We associate most of the emission
of the small molecules with the cold component of the envelope, while
the molecular emission of the warm gas is enriched by complex organic
molecules (COMs). We find a high abundance of S-bearing molecules in
the cold gas phase, including the molecular ions HCS+ and SO+. The
abundance of sulphur-bearing species suggests a low sulphur depletion,
with a factor of >1%, in contrast to low-mass protostars, where the
sulphur depletion is found to be stronger. Similarly to other hot
cores, the deuterium fractionation of small molecules is low, showing
a significant difference compared to low-mass protostars. We find a
low isotopic ratio in particular for 12C/13C of ∼30, and
32S/34S of ∼12, which are about two times lower than the values
expected at the galactocentric distance of G328.2551-0.5321. We
identify nine COMs (CH3OH, CH3OCH3, CH3OCHO, CH3CHO,
HC(O)NH2, CH3CN, C2H5CN, C2H3CN, and CH3SH) in the warm
component of the envelope, four in the cold gas, and four towards the
accretion shocks. The presence of numerous molecular ions and high
abundance of sulphur-bearing species originating from the undisturbed
gas may suggest a contribution from shocked gas at the outflow cavity
walls. The molecular composition of the cold component of the envelope
is rich in small molecules, while a high abundance in numerous species
of COMs suggests an increasing molecular complexity towards the warmer
regions. The molecular composition of the warm gas is similar to that
of both hot cores and hot corinos, but the molecular abundances are
closer to the values found towards hot corinos than to values found
towards hot cores. Considering the compactness of the warm region and
its moderate temperature, we suggest that thermal desorption has not
been completed towards this object yet, representing an early phase of
the emergence of hot cores.
Description:
These are the corresponding spectra published in the paper.
G328.2551-0.5321 has been observed with APEX. We present here the
final spectra.
Objects:
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RA (2000) DE Designation(s)
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15 57 59.75 -53 58 00.4 G328.2551-0.5321 = [CUS2014] G328.2551-0.5321
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 122 1 Spectrum information
fits/* . 1 Spectrum in fits
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See also:
J/A+A/617/A89 : G328.2551-0.5321 ALMA images (Csengeri+, 2018)
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- 25 I6 --- Nx Number of pixels along X-axis
27- 49 A23 "datime" Obs.date Observation date
51- 56 I6 MHz bFreq Lower value of frequency interval
58- 63 I6 MHz BFreq Upper value of frequency interval
65- 70 I6 Hz dFreq Frequency resolution
72- 74 I3 Kibyte size Size of FITS file
76- 91 A16 --- FileName Name of FITS file, in subdirectory fits
93-122 A30 --- Title Title of the FITS file
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Acknowledgements:
Laure Bouscasse, lbouscasse(at)mpifr-bonn.mpg.de
(End) Patricia Vannier [CDS] 05-May-2022