J/ApJS/249/6 Galactic interstellar ratio 18O/17O. I. (Zhang+, 2020)
A systematic observational study on Galactic interstellar ratio 18O/17O.
I. C18O and C17O J=1-0 data analysis.
Zhang J.S., Liu W., Yan Y.T., Yu H.Z., Liu J.T., Zheng Y.H., Romano D.,
Zhang Z.-Y., Wang J.Z., Chen J.L., Wang Y.X., Zhang W.J., Lu H.H.,
Chen L.S., Zou Y.P., Yang H.Q., Wen T., Lu F.S.
<Astrophys. J. Suppl. Ser., 249, 6 (2020)>
=2020ApJS..249....6Z 2020ApJS..249....6Z
ADC_Keywords: Carbon monoxide; Molecular clouds; Milky Way
Keywords: Interstellar molecules ; Radio sources ; Isotopic abundances ;
Galaxy chemical evolution ; Milky Way evolution
Abstract:
The interstellar oxygen isotopic ratio of 18O/17O can reflect the
relative amount of the secular enrichment by ejecta from high-mass
versus intermediate-mass stars. Previous observations found a Galactic
gradient of 18O/17O, i.e., low ratios in the Galactic center and
large values in the Galactic disk, which supports the inside-out
formation scenario of our Galaxy. However, there are not many observed
objects and, in particular, there are not many at large galactocentric
distances. For this reason, we started a systematic study on Galactic
interstellar 18O/17O, through observations of C18O and C17O
multi-transition lines toward a large sample of 286 sources (at least
one order of magnitude larger than previous ones), from the Galactic
center region to the far outer Galaxy (∼22kpc). In this article, we
present our observations of J=1-0 lines of C18O and C17O, with the
12m antenna of the Arizona Radio Observatory (ARO 12m) and the
Institut de Radio Astronomie Millimetrique (IRAM) 30m telescopes.
Among our IRAM 30m sample of 50 targets, we detected successfully both
C18O and C17O 1-0 lines for 34 sources. Similarly, our sample of
260 targets for ARO 12m observations resulted in the detection of both
lines for 166 sources. The C18O optical depth effect on our ratio
results, evaluated by fitting results of C17O spectra with hyperfine
components (assuming τC18O=4τC17O) and our radiative
transfer and excitation model nonlocal thermodynamic equilibrium
(non-LTE) model calculation for the strongest source, was found to be
insignificant. Beam dilution does not seem to be a problem either,
which was supported by the fact that there is no systematic variation
between the isotopic ratio and the heliocentric distance, and ratios
are consistently measured from two telescopes for most of those
detected sources. With this study we obtained 18O/17O isotopic
ratios for a large sample of molecular clouds with different
galactocentric distances. Our results, though there are still very few
detections made for sources in the outer Galaxy, confirm the apparent
18O/17O gradient of 18O/17O=(0.10±0.03)RGC+(2.95±0.30),
with a Pearson's rank correlation coefficient of R=0.69. This is
supported by the newest Galactic chemical evolution model including
the impact of massive stellar rotators and novae.
Description:
The C18O and C17O J=1-0 lines were observed from June 29 to 2016
July 1, with the Institut de Radio Astronomie Millimetrique (IRAM) 30m
single dish telescope, at the Pico Veleta Observatory (Granada, Spain).
The center frequencies were set at 109.782182 and 112.359277GHz for
the C18O and C17O, respectively, with a corresponding beam size
of ∼23".
With the IRAM 30m we observed 50 sources of our sample. The parameters
of their observations are summarized in Table 1.
Other observations of the J=1-0 lines of C18O and C17O were also
carried out using the Arizona Radio Observatory (ARO) 12m telescope on
Kitt Peak, Tuscon, AZ, USA, with a corresponding beam size of ∼64".
Observations were performed remotely from Guangzhou University, China,
in 2016 November and December, 2017 January, November, and December,
and 2018 May and December.
Table 1 presents the parameters of the observational results of ARO
for the sample of 260 sources, including 24 sources observed by both
IRAM 30m and ARO 12m telescopes.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
sources.dat 40 286 List of sources observed by ARO 12m and IRAM 30m
telescopes; table added by CDS
table1.dat 99 626 Isotopic ratios of large sample of molecular clouds
table2.dat 69 28 Comparisons of ARO 12m and IRAM 30m observation
results for 7 sources with both C18O and
C17O detections
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See also:
J/A+AS/80/149 : IRAS Sources behind the Solar circle (WB89) (Wouterloot+ 1989)
J/A+A/430/549 : C18O/C17O near rho Oph (Wouterloot+, 2005)
J/ApJ/724/748 : Galactic anticenter PNe and oxygen abundance (Henry+, 2010)
J/MNRAS/403/1413 : Updated stellar yields from AGB models (Karakas, 2010)
J/A+A/554/A55 : C18O(1-0) and N2H+(1-0) in L1495/B213 (Hacar+, 2013)
J/ApJ/783/130 : Parallaxes of high mass star forming regions (Reid+, 2014)
J/ApJS/219/28 : C18O/C17O ratios in the Galactic center (Zhang+, 2015)
J/ApJS/237/13 : Yields of 13-120M☉ massive stars (Limongi+, 2018)
Byte-by-byte Description of file: sources.dat
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Bytes Format Units Label Explanations
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1- 14 A14 --- Name Source Name
16- 17 I2 h RAh Hour of Right Ascension (J2000)
19- 20 I2 min RAm Minute of Right Ascension (J2000)
22- 26 F5.2 s RAs Second of Right Ascension (J2000)
28- 28 A1 --- DE- Sign of the Declination (J2000)
29- 30 I2 deg DEd Degree of Declination (J2000)
32- 33 I2 arcmin DEm Arcminute of Declination (J2000)
35- 40 F6.3 arcsec DEs Arcsecond of Declination (J2000)
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 14 A14 --- Name Source Name
15 A1 --- m_Name Velocity component of the source
17- 17 I1 --- Flag [0/1] 1=absorption features close to the
emission in the spectra
19- 19 A1 --- f_Name Flags on individual sources (1)
21- 22 I2 h RAh ? Hour of Right Ascension (J2000) (2)
24- 25 I2 min RAm ? Minute of Right Ascension (J2000)
27- 31 F5.2 s RAs ? Second of Right Ascension (J2000)
33- 33 A1 --- DE- Sign of the Declination (J2000) (2)
34- 35 I2 deg DEd ? Degree of Declination (J2000) (2)
37- 38 I2 arcmin DEm ? Arcminute of Declination (J2000)
40- 45 F6.3 arcsec DEs ? Arcsecond of Declination (J2000)
47- 51 F5.2 kpc Rgc [0/22.7]? Galactocentric distance
53- 57 F5.2 kpc Dist [0.1/14.2]? Heliocentric distance (2)
59- 62 A4 --- Tel Telescope used ("ARO" or "IRAM")
64- 67 A4 --- Line Molecular species ("C17O" or "C18O")
69- 73 F5.3 K rms [0.006/0.3]? Root-Mean-Square value in Tmb
75- 79 F5.2 K.km/s I-Tmb [0.06/70.1]? Integrated line intensity
of C18O and C17O
81- 84 F4.2 K.km/s e_I-Tmb [0.01/1.2]? Uncertainty in I-Tmb
86- 89 F4.2 K Tpeak [0.03/8.1]? Line peak values
91- 94 F4.2 --- Ratio [2.3/7.1]? Frequency-corrected abundance ratio
96- 99 F4.2 --- e_Ratio [0.04/2.2]? Uncertainty in Ratio
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Note (1): Flags on individual sources as follows:
a = For the Galactic center source 1.3 Complex, its broad component
(∼50-80km/s) was not detected and the results given here are for
one detected strong narrow component (~-22km/s, not used for our
analysis), which should arise from the local gas, due to its smaller
linewidth and larger abundance ratio than typical GC sources
(Zhang+ 2015, J/ApJS/219/28);
b = For those sources with two velocity components, the abundance ratio
is given separately;
c = For those 6 sources with low S/N (≤3) C17O spectra, their abundance
ratios were not given.
Note (2): Positions and distances are given only for the first entry in a block
of source observations.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 14 A14 --- Name Source Name
16- 19 A4 --- Tel Telescope used ("ARO" or "IRAM")
21- 24 A4 --- Line Molecular species ("C17O" or "C18O")
26- 26 A1 --- f_Line Flag on Line
28- 32 F5.3 K rms [0.008/0.2] Root-Mean-Square value in Tmb
34- 38 F5.2 K.km/s I-Tmb [0.07/48.5] Integrated line intensity
of C18O and C17O
40- 43 F4.2 K.km/s e_I-Tmb [0.01/0.3] Uncertainty in I-Tmb
45- 48 F4.2 K Tpeak [0.03/7.4] Line peak values
50- 54 F5.2 kpc Rgc [4.8/13.5]? Galactocentric distance
56- 59 F4.2 kpc Dist [1.17/8.2]? Heliocentric distance
61- 64 F4.2 --- Ratio [2.3/5]? frequency-corrected abundance ratio
66- 69 F4.2 --- e_Ratio [0.05/0.7]? Uncertainty in Ratio
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 16-Sep-2020