A Systematic Observational Study on Galactic Interstellar Ratio 18O/17O. II. C18O and C17O J=2-1 Data Analysis
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| Format: | Preprint |
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2023
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| _version_ | 1866915640630050816 |
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| author | Zou, Y. P. Zhang, J. S. Henkel, C. Romano, D. Liu, W. Zheng, Y. H. Yan, Y. T. Chen, J. L. Wang, Y. X. Zhao, J. Y. |
| author_facet | Zou, Y. P. Zhang, J. S. Henkel, C. Romano, D. Liu, W. Zheng, Y. H. Yan, Y. T. Chen, J. L. Wang, Y. X. Zhao, J. Y. |
| contents | To investigate the relative amount of ejecta from high-mass versus intermediate-mass stars and to trace the chemical evolution of the Galaxy, we have performed with the IRAM 30m and the SMT 10m telescopes a systematic study of Galactic interstellar 18O/17O ratios toward a sample of 421 molecular clouds, covering a galactocentric distance range of 1-22 kpc. The results presented in this paper are based on the J=2-1 transition and encompass 364 sources showing both C18O and C17O detections. The previously suggested 18O/17O gradient is confirmed. For the 41 sources detected with both facilities, good agreement is obtained. A correlation of 18O/17O ratios with heliocentric distance is not found, indicating that beam dilution and linear beam sizes are not relevant. For the subsample of IRAM 30 m high-mass star-forming regions with accurate parallax distances, an unweighted fit gives 18O/17O = (0.12+-0.02)R_GC+(2.38+-0.13) with a correlation coefficient of R = 0.67. While the slope is consistent with our J=1-0 measurement, ratios are systematically lower. This should be caused by larger optical depths of C18O 2-1 lines, w.r.t the corresponding 1-0 transitions, which is supported by RADEX calculations and the fact that C18O/C17O is positively correlated with 13CO/C18O. After considering optical depth effects with C18O J=2-1 reaching typically an optical depth of 0.5, corrected 18O/17O ratios from the J=1-0 and J=2-1 lines become consistent. A good numerical fit to the data is provided by the MWG-12 model, including both rotating stars and novae. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2311_00547 |
| institution | arXiv |
| publishDate | 2023 |
| record_format | arxiv |
| spellingShingle | A Systematic Observational Study on Galactic Interstellar Ratio 18O/17O. II. C18O and C17O J=2-1 Data Analysis Zou, Y. P. Zhang, J. S. Henkel, C. Romano, D. Liu, W. Zheng, Y. H. Yan, Y. T. Chen, J. L. Wang, Y. X. Zhao, J. Y. Astrophysics of Galaxies To investigate the relative amount of ejecta from high-mass versus intermediate-mass stars and to trace the chemical evolution of the Galaxy, we have performed with the IRAM 30m and the SMT 10m telescopes a systematic study of Galactic interstellar 18O/17O ratios toward a sample of 421 molecular clouds, covering a galactocentric distance range of 1-22 kpc. The results presented in this paper are based on the J=2-1 transition and encompass 364 sources showing both C18O and C17O detections. The previously suggested 18O/17O gradient is confirmed. For the 41 sources detected with both facilities, good agreement is obtained. A correlation of 18O/17O ratios with heliocentric distance is not found, indicating that beam dilution and linear beam sizes are not relevant. For the subsample of IRAM 30 m high-mass star-forming regions with accurate parallax distances, an unweighted fit gives 18O/17O = (0.12+-0.02)R_GC+(2.38+-0.13) with a correlation coefficient of R = 0.67. While the slope is consistent with our J=1-0 measurement, ratios are systematically lower. This should be caused by larger optical depths of C18O 2-1 lines, w.r.t the corresponding 1-0 transitions, which is supported by RADEX calculations and the fact that C18O/C17O is positively correlated with 13CO/C18O. After considering optical depth effects with C18O J=2-1 reaching typically an optical depth of 0.5, corrected 18O/17O ratios from the J=1-0 and J=2-1 lines become consistent. A good numerical fit to the data is provided by the MWG-12 model, including both rotating stars and novae. |
| title | A Systematic Observational Study on Galactic Interstellar Ratio 18O/17O. II. C18O and C17O J=2-1 Data Analysis |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2311.00547 |