银河系中心人马座B2延展包层的硫同位素观测
Sulphur isotopes toward Sagittarius B2 extended envelope in the Galactic Center
AI总结：
本文通过对银河系中心Sgr B2的硫同位素高灵敏度成图观测，精确测得32S/34S和34S/33S比值，证实32S/34S向银心递减趋势终止，揭示银心大质量恒星形成率下降。
摘要：
同位素比值是探测恒星核合成和化学演化的有效工具。我们利用IRAM 30米望远镜对银河系中心巨分子云人马座B2（Sgr B2）进行了OCS、OC34S、O13CS和OC33S的J=7-6转动跃迁的高灵敏度成图观测。选择光学薄且无污染谱线的位置来确定硫同位素比值。利用OCS和OC34S谱线得到32S/34S比值为17.1±0.9，而34S/33S比值6.8±1.9则直接由OC34S和OC33S的积分强度比导出。基于对32S/34S比值的独立且精确的测量，我们的结果证实了32S/34S比值向银河系中心递减趋势的终止，表明银河系中心大质量恒星的形成有所下降。
英文摘要：
The isotopic ratios are good tools for probing the stellar nucleosynthesis and chemical evolution. We performed high-sensitivity mapping observations of the J=7-6 rotational transitions of OCS, OC34S, O13CS, and OC33S toward the Galactic Center giant molecular cloud, Sagittarius B2 (Sgr B2) with IRAM 30m telescope. Positions with optically thin and uncontaminated lines are chosen to determine the sulfur isotope ratios. A 32S/34S ratio of 17.1\pm0.9 was derived with OCS and OC34S lines, while 34S/33S ratio of 6.8\pm1.9 was derived directly from integrated intensity ratio of OC34S and OC33S. With independent and accurate measurements of 32S/34S ratio, our results confirm the termination of the decreasing trend of 32S/34S ratios toward the Galactic Center, suggesting a drop in the production of massive stars at the Galactic centre.
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