J/A+A/633/A120 SgrB2(M) 13CCC and C13CC spectra (Giesen +, 2020)
First detection of the carbon chain molecules 13CCC and C13CC
towards SgrB2(M).
Giesen T.F., Mookerjea B., Fuchs G.W., Breier A.A., Witsch D., Simon R.,
Stutzki J.
<Astron. Astrophys. 633, A120 (2020)>
=2020A&A...633A.120G 2020A&A...633A.120G (SIMBAD/NED BibCode)
ADC_Keywords: Star Forming Region ; Interstellar medium ; Spectroscopy
Keywords: ISM: molecules - submillimeter: ISM - molecular processes
Abstract:
Carbon molecules and their 13C-isotopologues can be used to
determine the 12C/13C abundance ratios in stellar and interstellar
objects. C3 is a pure carbon chain molecule found in star forming
regions and in stellar shells of carbon-rich late-type stars. Latest
laboratory data of 13C-isotopologues of C3 allow a selective search
for the mono-substituted species 13CCC and C13CC based on accurate
ro-vibrational frequencies. Our aim was to provide the first detection
of the 13C-isotopologues ^13CCC and C13CC in space and to derive
the 12C/ 13C ratio of interstellar gas in the massive star-forming
region SgrB2(M) near the Galactic Center. We used the heterodyne
receivers GREAT and upGREAT on board SOFIA to search for the
ro-vibrational transitions Q(2) and Q(4) of 13CCC and C13CC at
1.9THz along the line of sight towards SgrB2(M). In addition, to
determine the local excitation temperature we analyzed data from nine
ro-vibrational transitions of the main isotopologue CCC in the
frequency range between 1.6-1.9THz which were taken from the Herschel
Science Data Archive. We report the first detection of the
isotopologues 13CCC and C13CC. For both species the ro-vibrational
absorption lines Q(2) and Q(4) have been identified, primarily arising
from the warm gas physically associated with the strong continuum
source SgrB2(M). From the available CCC ro-vibrational transitions we
derived a gas excitation temperature of Tex=44.4+4.7-3.9K and a
total column density of N(CCC)=3.88+0.39-0.35x1015cm^-2..
Assuming the excitation temperatures of C13CC and 13CCC to be the
same as for CCC, we obtained column densities of the
13C-isotopologues of N(C13CC)=2.1+0.9-0.6_x1014cm-2 and
N(13CCC)=2.4+1.2-0.8x1014cm-2. The derived 12C/13C
abundance ratio in the C3 molecules is 20.5±4.2, which is in
agreement with the elemental ratio of 20, typically observed in
SgrB2(M). However, we find the N(13CCC)/N(C13CC) ratio to be
1.2±0.1, which is shifted from the statistically expected value of
2. We propose that the discrepant abundance ratio arises due to the
the lower zero-point energy of C13CC which makes position- exchange
reaction converting C13CC to C13CC energetically favorable.
Description:
The observed spectra as presented in Figures 1 and 3 of the paper
are provided in FITS format with the intensity (in K) being the
continuum subtracted main beam temperature.
Objects:
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RA (2000) DE Designation(s)
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17 47 20.5 -28 23 06 SgrB2(M) = NAME Sgr B2(M)
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 158 12 List of fits spectra
fits/* . 12 Individual fits spectra
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See also:
J/A+A/559/A47 : Sgr B2(N) and Sgr B2(M) IRAM 30m line survey (Belloche+, 2013)
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- 61 E12.6 Hz bFREQ Lower value of frequency interval
63- 73 E11.6 Hz BFREQ Upper value of frequency interval
75- 85 E11.6 Hz dFREQ Frequency resolution
87- 89 I3 Kibyte size Size of FITS file
91-112 A22 --- FileName Name of FITS file, in subdirectory fits
114-158 A45 --- Title Title of the FITS file
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Acknowledgements:
Bhaswati Mookerjea, bhaswati(at)tifr.res.in
(End) Patricia Vannier [CDS] 22-Nov-2019