J/A+A/612/A117 CO isotopes towards Galactic YSOs and HII regions (Areal+, 2018)
Exploring the 13CO/C18O abundance ratio towards Galactic young stellar
objects and HII regions.
Areal M.B., Paron S., Celis Pena M., Ortega M.E.
<Astron. Astrophys., 612, A117 (2018)>
=2018A&A...612A.117A 2018A&A...612A.117A (SIMBAD/NED BibCode)
ADC_Keywords: YSOs ; H II regions ; Carbon monoxide ; Abundances
Keywords: ISM: abundances - ISM: molecules - Galaxy: abundances -
H II regions - stars: formation
Abstract:
Aims. Determining molecular abundance ratios is important not only for
the study of Galactic chemistry, but also because they are useful to
estimate physical parameters in a large variety of interstellar medium
environments. One of the most important molecules for tracing the
molecular gas in the interstellar medium is CO, and the 13CO/C18O
abundance ratio is usually used to estimate molecular masses and
densities of regions with moderate to high densities. Nowadays isotope
ratios are in general indirectly derived from elemental abundances
ratios. We present the first 13CO/C18O abundance ratio study
performed from CO isotope observations towards a large sample of
Galactic sources of different natures at different locations. Methods.
To study the 13CO/C18O abundance ratio, we used 12CO J=3-2 data
obtained from the CO High-Resolution Survey, 13CO and C18O J=3-2
data from the 13CO/C18O (J=3-2) Heterodyne Inner Milky Way Plane
Survey, and some complementary data extracted from the James Clerk
Maxwell Telescope database. We analyzed a sample of 198 sources
composed of young stellar objects (YSOs), and HII and diffuse HII
regions as catalogued in the Red MSX Source Survey in
27.5°≤l≤46.5° and |b|<0.5°. Results. Most of the
analyzed sources are located in the galactocentric distance range
4.0-6.5kpc. We found that YSOs have, on average, lower 13CO/C18O
abundance ratios than HII and diffuse HII regions. Taking into account
that the gas associated with YSOs should be less affected by the
radiation than in the case of the others sources, selective far-UV
photodissociation of C18O is confirmed. The 13CO/C18O abundance
ratios obtained in this work are systematically lower than those
predicted from the known elemental abundance relations. These results
will be useful in future studies of molecular gas related to YSOs and
HII regions based on the observation of these isotopes.
Description:
The data of the CO isotopes were extracted from two public databases
performed with the 15m James Clerk Maxwell Telescope (JCMT) in Hawaii.
The 12CO J=3-2 data were obtained from the CO High-Resolution Survey
(COHRS) with an angular and spectral resolution of 14" and 1km/s (see
Dempsey et al., 2013ApJS..209....8D 2013ApJS..209....8D). The data of the other CO
isotopes were obtained from the 13CO/C18O (J=3-2) Heterodyne Inner
Milky Way Plane Survey (CHIMPS), which have an angular and spectral
resolution of 15" and 0.5km/s (Rigby et al., 2016MNRAS.456.2885R 2016MNRAS.456.2885R).
Taking into account that the CHIMPS survey covers the Galactic region
in 27.5°<l<46.5° and |b|≤0.5°, we selected all sources
catalogued as YSOs, and selected HII and diffuse HII regions lying in
this area from the Red MSX Source Survey (Lumsden et al., 2013, Cat.
J/ApJS/208/11), which is the largest statistically selected catalogue
of young massive protostars and HII regions to date.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 97 114 Line parameters for the CO isotopes
tablea2.dat 51 114 Results
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See also:
J/ApJS/208/11 : The Red MSX Source Survey: massive protostars (Lumsden+, 2013)
Byte-by-byte Description of file: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Seq Sequential number
5- 22 A18 --- Source Source name (GLLL.llll+BB.bbbbA),
24- 34 A11 --- Type Source type (G1)
36- 38 F3.1 kpc Dgal Galactocentric distance
40- 44 F5.1 km/s v12 Central LSR velocity of 12CO line
46- 49 F4.1 km/s dv12 LSR velocity of 12CO line dispersion
51- 54 F4.1 K Tmb12 Peak main brightness temperature of
12CO line (1)
56- 60 F5.1 km/s v13 Central LSR velocity of 13CO line
62- 65 F4.1 km/s dv13 LSR velocity of 13CO line dispersion
67- 70 F4.1 K Tmb13 Peak main brightness temperature of
13CO line (1)
72- 76 F5.1 K.km/s I13 Velocity-integrated line emission of 13CO (2)
78- 82 F5.1 km/s v18 LSR velocity of C18O line
84- 86 F3.1 km/s dv18 LSR velocity of C18O line
88- 91 F4.1 K Tmb18 Peak main brightness temperature of
C18O line (1)
93- 97 F5.1 K.km/s I18 Velocity-integrated line emission of C18O (2)
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Note (1): In the case of 12CO and 13CO, the typical errors (the formal
1σ value for the model of the Gaussian line shape) in Tmb are between
5% and 10%, while the typical error in this parameter for C18O ranges from
10% to 20%.
Note (2): The integrated line emission has typical errors of 5-10% and 10-20%
for 13CO and C18O, respectively.
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Byte-by-byte Description of file: tablea2.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq Sequential number
5- 15 A11 --- Type Source type (G1)
17- 19 F3.1 kpc Dgal Galactocentric distance
21- 24 F4.1 --- I13/I18 Integrated line ratio, 13CO/C18O
26- 29 F4.1 K Tex Excitation temperature
31- 33 F3.1 --- tau13 Optical depth of 13CO
35- 38 F4.1 10+16cm-2 N13 Column density of 13CO
40- 42 F3.1 --- tau18 Optical depth of C18O
44- 46 F3.1 10+16cm-2 N18 Column density of C18O
48- 51 F4.1 --- N13/N18 Abundance ratio, N(13CO)/N(C16O)
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Global notes:
Note (G1): Source type from Red MSX Source Survey (HII, YSO, diffuse HII).
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 08-Aug-2018