论文标题
硫和碳同位素朝向银河中心云
Sulphur and carbon isotopes towards Galactic centre clouds
论文作者
论文摘要
测量同位素比是一种敏感技术，用于获取有关恒星核合成和化学演化的信息。我们介绍了我们银河系中央区域的星际介质中碳和硫丰度的测量。选定的目标是 +50km/s云和几个L.O.S.朝向SGR B2（n）的云。朝着 +50km/s的云倾向，我们观察了CS，C34S，13C，C33S和13C34S的J = 2-1旋转过渡，以及IRAM-30M望远镜的CS和C34的J = 3-2过渡，以及J = 6-5的C34S和13C的j = 6-5转换。在SGR B2（n）的包膜中观察到Cs，C34s，13C和13C34的J = 2-1旋转过渡，在L.O.S.中也观察到CS和C34的J = 2-1旋转转变。朝向SGR B2（n）的云，全部吸收。在 +50km/s云中，我们得出了一个12c13c同位素比为〜22.1，其导致测量的13C/C34S线强度比为32S/34S的比率为16.3 +3.0-2.4。我们还直接从两个同位素学13C和13C34S得出32S/34s同位素比，这分别为+50km/s云B2（N）的独立32S/34S估计为16.3+2.1.1.7和17.9+-5.0。我们还获得了+50 km/s云中〜4.3的34S/33S比率。先前的研究观察到接近银河系中心时32S/34S同位素比的趋势下降。我们的结果表明，至少在半乳酸的距离为130-30+60 pc的情况下，这种趋势的终止。这与基于12C/13C，14N/15N和18O/17O同位素比的发现不同，在该发现中，观察到上述趋势继续延伸到中央分子区域。这可以表明与最近的金属性梯度研究相同的线路，在银河中心的大量恒星产生下降，并为与银河系和恒星进化模型进行比较开放了工作。
Measuring isotopic ratios is a sensitive technique used to obtain information on stellar nucleosynthesis and chemical evolution. We present measurements of the carbon and sulphur abundances in the interstellar medium of the central region of our Galaxy. The selected targets are the +50km/s Cloud and several l.o.s. clouds towards Sgr B2(N). Towards the +50km/s Cloud, we observed the J=2-1 rotational transitions of CS, C34S, 13CS, C33S, and 13C34S, and the J=3-2 transitions of CS and C34S with the IRAM-30m telescope, as well as the J=6-5 transitions of C34S and 13CS with the APEX 12m telescope, all in emission. The J=2-1 rotational transitions of CS, C34S, 13CS, and 13C34S were observed with ALMA in the envelope of Sgr B2(N), with those of CS and C34S also observed in the l.o.s. clouds towards Sgr B2(N), all in absorption. In the +50km/s Cloud we derive a 12C13C isotopic ratio of ~22.1, that leads, with the measured 13CS/C34S line intensity ratio, to a 32S/34S ratio of 16.3+3.0-2.4. We also derive the 32S/34S isotopic ratio more directly from the two isotopologues 13CS and 13C34S, which leads to an independent 32S/34S estimation of 16.3+2.1-1.7 and 17.9+-5.0 for the +50km/s Cloud and Sgr B2(N), respectively. We also obtain a 34S/33S ratio of ~4.3 in the +50 km/s Cloud. Previous studies observed a decreasing trend in the 32S/34S isotopic ratios when approaching the Galactic centre. Our result indicates a termination of this tendency at least at a galactocentric distance of 130-30+60 pc. This is at variance with findings based on 12C/13C, 14N/15N and 18O/17O isotope ratios, where the above-mentioned trend is observed to continue right to the central molecular zone. This can indicate a drop in the production of massive stars at the Galactic centre, in the same line as recent metallicity gradient studies, and opens the work towards a comparison with Galactic and stellar evolution models.
