J/A+A/632/A57 G328.2551-0.5321 spectra (Csengeri+, 2019)
Search for high-mass protostars with ALMA revealed up to kilo-parsec scales
(SPARKS).
II. Complex organic molecules in accretion shocks around a hot core precursor.
Csengeri T., Belloche A., Bontemps S., Wyrowski F., Menten K.M.,
Bouscasse L.
<Astron. Astrophys. 632, A57 (2019)>
=2019A&A...632A..57C 2019A&A...632A..57C (SIMBAD/NED BibCode)
ADC_Keywords: Radio sources ; YSOs ; Interstellar medium ; Spectroscopy
Keywords: astrochemistry - stars: massive - stars: formation -
submillimeter: ISM - ISM: molecules
Abstract:
Classical hot cores are rich in molecular emission, and they show a
high abundance of complex organic molecules (COMs). The emergence of
molecular complexity that is represented by COMs, in particular, is
poorly constrained in the early evolution of hot cores.
We put observational constraints on the physical location of COMs in a
resolved high-mass protostellar envelope associated with the
G328.2551-0.5321 clump. The protostar is single down to 400au
scales and we resolved the envelope structure down to this scale.
High angular resolution observations using the Atacama Large
Millimeter Array allowed us to resolve the structure of the inner
envelope and pin down the emission region of COMs. We use local
thermodynamic equilibrium modelling of the available 7.5GHz bandwidth
around 345GHz to identify the COMs towards two accretion shocks and a
selected position representing the bulk emission of the inner
envelope. We quantitatively discuss the derived molecular column
densities and abundances towards these positions, and use our line
identification to qualitatively compare this to the emission of COMs
seen towards the central position, corresponding to the protostar and
its accretion disk.
We detect emission from 10 COMs, and identify a line of deuterated
water (HDO). In addition to methanol (CH3OH), methyl formate
(CH3OCHO) and formamide (HC(O)NH2) have the most extended
emission. Together with HDO, these molecules are found to be
associated with both the accretion shocks and the inner envelope,
which has a moderate temperature of Tkin∼110K. We find a significant
difference in the distribution of COMs. O-bearing COMs, such as ethanol,
acetone, and ethylene glycol are almost exclusively found and show a
higher abundance towards the accretion shocks with Tkin∼180K. Whereas
N-bearing COMs with a CN group, such as vinyl and ethyl cyanide peak
on the central position, thus the protostar and the accretion disk.
The molecular composition is similar towards the two shock positions,
while it is significantly different towards the inner envelope,
suggesting an increase in abundance of O-bearing COMs towards the
accretion shocks.
We present the first observational evidence for a large column density
of COMs seen towards accretion shocks at the centrifugal barrier at
the inner envelope. The overall molecular emission shows increased
molecular abundances of COMs towards the accretion shocks compared to
the inner envelope. The bulk of the gas from the inner envelope is
still at a moderate temperature of Tkin∼110K, and we find that the
radiatively heated inner region is very compact (<1000au). Since the
molecular composition is dominated by that of the accretion shocks and
the radiatively heated hot inner region is very compact, we propose
this source to be a precursor to a classical, radiatively heated hot
core. By imaging the physical location of HDO, we find that it is
consistent with an origin within the moderately heated inner envelope,
suggesting that it originates from sublimation of ice from the grain
surface and its destruction in the vicinity of the heating source has
not been efficient yet.
Description:
These are the spectra of the three positions published in the paper.
Objects:
---------------------------------------------
RA (2000) DE Designation(s)
---------------------------------------------
15 58 00.05 -53 57 57.8 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 157 3 List of fits spectra
fits/* . 3 Individual spectra
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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- 24 I5 --- Nx Number of pixels along X-axis
26- 35 A10 "date" Obs.date Observation date
37- 44 F8.4 GHz bFREQ Lower value of frequency interval
46- 52 F7.5 GHz BFREQ Upper value of frequency interval
54- 59 I6 Hz dFREQ Frequency resolution
61- 62 I2 Kibyte size Size of FITS file
64- 80 A17 --- FileName Name of FITS file, in subdirectory fits
82-157 A76 --- Title Title of the FITS file
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Acknowledgements:
Timea Csengeri, timea.csengeri(at)u-bordeaux.fr
References:
Csengeri et al., Paper I 2018A&A...617A..89C 2018A&A...617A..89C, Cat. J/A+A/617/A89
(End) Patricia Vannier [CDS] 19-Nov-2019