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arXiv 2007.00361astro-ph.GA
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银河系星际比18 O/17 O:I的系统观测研究C18O和C17O J=1-0数据分析

A systematic observational study on Galactic interstellar ratio 18O/17O: I. C18O and C17O J=1-0 data analysis

J. S. Zhang, W. Liu, Y. T. Yan, H. Z. Yu, J. T. Liu, Y. H. Zheng, D. Romano, Z. -Y. Zhang, J. Z. Wang, J. L. Chen, Y. X. Wang, W. J. Zhang, H. H. Lu, L. S. Chen… 展开作者

J. S. Zhang, W. Liu, Y. T. Yan, H. Z. Yu, J. T. Liu, Y. H. Zheng, D. Romano, Z. -Y. Zhang, J. Z. Wang, J. L. Chen, Y. X. Wang, W. J. Zhang, H. H. Lu, L. S. Chen, Y. P. Zou, H. Q. Yang, T. Wen, F. S. Lu

摘要:

星际氧同位素比值18 O/17 O可以反映出高质量恒星和中等质量恒星喷出物长期富集的相对量。以前的观测发现银河系的18 O/17 O梯度,即,银河系中心的比率较低,而银河系盘中的值较大,这支持了我们银河系由内而外形成的假设。然而,观察到的物体并不多,特别是在大的银河系中心距离上。因此,我们开始了对银河系星际18 O/17 O的系统研究,通过对从银河系中心区域到远外星系(~22 kpc)的286个源(至少比以前的大一个数量级)的大样本的C18 O和C17 O多跃迁线的观测。本文介绍了我们用ARO 12 m和IRAM 30 m望远镜对C ~(18)O和C ~(17)O的J=1-0谱线的观测结果。我们成功地检测到C18 O和C17 O 1-0线的34个源中,我们的IRAM 30米样品的50个目标和166个源中,我们的ARO 12米样品的260个目标。C18 O光学深度对我们的比值结果的影响,通过C17 O光谱与超精细成分的拟合结果和我们的RADEX非LTE模型计算的最强源进行评估,被认为是微不足道的。光束稀释似乎也不是一个问题,这是由同位素比率和日心距离之间没有系统变化的事实支持的,并且对于大多数被探测到的来源,两台望远镜的测量比率一致。虽然对外星系源的探测仍然很少,但我们的结果证实了~(18)O/~(17)O的表观梯度为~(18)O/~(17)O =(0.10+-0.03)R_GC+(2.95+-0.30),Pearson秩相关系数R = 0.69。这是由最新的银河系化学演化模型支持的,包括大质量恒星旋转体和新星的影响。

英文摘要:

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 insideout formation scenario of our Galaxy. However, the observed objects are not many and, in particular, not so many at large galactocentric distances. Thus 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 (~22 kpc). Here we present our observations of J=1-0 lines of C18O and C17O, with the ARO12m and the IRAM 30m telescope. We detected successfully both C18O and C17O 1-0 lines for 34 sources among our IRAM30m sample of 50 targets and for 166 sources among our ARO12m sample of 260 targets. The C18O optical depth effect on our ratio results, evaluated by fitting results of C17O spectra with hyperfine components and our RADEX 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 of no systematic variation between the isotopic ratio and the heliocentric distance, and consistent measured ratios from two telescopes for most of those detected sources. 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)R_GC+(2.95+-0.30), with a Pearson's rank correlation coefficient R = 0.69. This is supported by the newest Galactic chemical evolution model including the impact of massive stellar rotators and novae.

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