J/A+A/641/A54 Complex organic molecules in high-mass SFRs (Coletta+, 2020)
Evolutionary study of complex organic molecules in high-mass star-forming
regions.
Coletta A., Fontani F., Rivilla V.M., Mininni C., Colzi L.,
Sanchez-Monge A., Beltran M.T.
<Astron. Astrophys. 641, A54 (2020)>
=2020A&A...641A..54C 2020A&A...641A..54C (SIMBAD/NED BibCode)
ADC_Keywords: Star Forming Region ; Spectroscopy ; Radio lines
Keywords: stars: formation - radio lines: ISM - ISM: molecules
Abstract:
We have studied four complex organic molecules (COMs), the
oxygen-bearing methyl formate (CH3OCHO) and dimethyl ether
(CH3OCH3) as well as the nitrogen-bearing formamide (NH2CHO) and
ethyl cyanide (C2H5CN), towards a large sample of 39 high-mass
star-forming regions representing different evolutionary stages, from
early to evolved phases. We aim to identify potential correlations and
chemical links between the molecules and to trace their evolutionary
sequence through the star formation process. We analysed spectra
obtained at 3, 2, and 0.9mm with the IRAM-30m telescope. We derived
the main physical parameters for each species by fitting the molecular
lines. We compared them and evaluated their evolution while also
taking several other interstellar environments into account.
We report detections in 20 sources, revealing a clear dust absorption
effect on column densities. Derived abundances range between
∼10-10-10-7 for CH3OCHO and CH3OCH3, ∼10-12-10-10 for
NH2CHO, and ∼10-11-10-9 for C2H5CN. The abundances of
CH3OCHO, CH3OCH3, and C2H5CN are very strongly correlated (r≥0.92)
across 4 orders of magnitude.We note that CH3OCHO and CH3OCH3
show the strongest correlations in most parameters, and a nearly
constant ratio (1) over a remarkable 9 orders of magnitude in
luminosity for the following wide variety of sources: pre-stellar to
evolved cores, low- to high-mass objects, shocks, Galactic clouds, and
comets. This indicates that COMs chemistry is likely early developed
and then preserved through evolved phases. Moreover, the molecular
abundances clearly increase with evolution, covering 6 orders of
magnitude in the luminosity/mass ratio. We consider CH3OCHO and
CH3OCH3 to be most likely chemically linked. They could, for
example, share a common precursor, or be formed one from the other.
Based on correlations, ratios, and the evolutionary trend, we propose
a general scenario for all COMs, involving a formation in the cold,
earliest phases of star formation and a following increasing
desorption with the progressive thermal and shock-induced heating of
the evolving core.
Description:
Reduced spectra of the high-mass star-forming regions shown in
the paper, obtained with the EMIR receivers E0 (3mm band), E1 (2mm),
and E3 (0.9mm), and the fast fourier transform spectrometers FTS50
(50khz freq.res.) and FTS 200 (200khz freq.res) at the IRAM-30m
telescope during August 2014, June 2015, and December 2016. Spectra
were reduced with the CLASS software from the GILDAS package. Each
table corresponds to a spectral window within the waveband indicated
in the file name, observed towards the relative source. In each table,
the first column represents frequency (in GHz), the second column is
the source spectrum (main beam temperature, in K), the third column is
the LTE model of the spectrum (in K) obtained with a non-linear
least-squares fitting performed on the emission lines of the molecule
shown in the file name: MF is methyl formate (CH3OCHO), DE is dimethyl
ether (CH3OCH3), F is formamide (NH2CHO), EC is ethyl cyanide
(C2H5CN).
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
list.dat 112 15 List of spectra
sp/* . 15 Individual spectra
--------------------------------------------------------------------------------
Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 15 A15 --- Name Name
17- 18 I2 h RAh Right ascension (J2000)
20- 21 I2 min RAm Right ascension (J2000)
23- 26 F4.1 s RAs Right ascension (J2000)
28 A1 --- DE- Declination sign (J2000)
29- 30 I2 deg DEd Declination (J2000)
32- 33 I2 arcmin DEm Declination (J2000)
35- 36 I2 arcsec DEs Declination (J2000)
38- 62 A25 --- FileName Name of the spectrum file in subdirectory sp
64-112 A49 --- Title Title of the spectrum
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Byte-by-byte Description of file: sp/*
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 13 F13.9 GHz Freq Frequency
15- 28 E14.8 K Tmb Main beam temperature from source spectrum
30- 50 E21.16 K LTE LTE model of the spectrum
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Acknowledgements:
Alessandro Coletta, alessandro.coletta(at)stud.unifi.it
(End) Patricia Vannier [CDS] 01-Jul-2020