Chemistry and rotational excitation of O_2 in interstellar clouds. II. The 16O^18O isotopomer
Chemistry and rotational excitation of O_2 in interstellar clouds. II. The 16O^18O isotopomer
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星际云中 O_2 的化学和旋转激发。
DOI：
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发表时间：
1997
期刊：
影响因子：
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通讯作者：
L. Pagani
中科院分区：
文献类型：
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作者：
P. Maréchal;Y. Viala;L. Pagani
尽管分子氧O2被预测为星际气体的重要成分，但在银河系星际云中尚未观察到它。虽然我们银河系正在进行的O2观测项目必须使用平流层气球或卫星，但几个团队已经尝试用地面望远镜观察它的同位素16O18O。本文利用包含18O和13C同位素反应的星际云化学模型，通过非LTE计算16O18O的旋转布居，预测了从地面可观测到的3条16O18O线，即234、298和402 GHz谱线的强度。这些预测与Maréchal等人获得的上限进行了比较。(1997a)和Pagani等人获得的初步检测结果。(1993)驶向L134N。我们发现，在今天的接收器中，只有234 GHz的谱线是可以观测到的，而且我们所报道的强上限与标准的稳态模型不兼容。需要笨拙、高(0.7)C/O比或其他非标准模型来解释我们的观察结果。讨论了~(18)O同位素分馏的结果。
Although molecular oxygen O2 is predicted to be an important constituent of the interstellar gas, it has not yet been observed in Galactic interstellar clouds. While ongoing O2 observation projects in our Galaxy have to use stratospheric balloons or satellites, several teams have already tried to observe its isotopomer 16O18O with ground-based telescopes. In this paper, a chemical model of interstellar clouds including 18O and 13C isotopic reactions with a non-LTE calculation of 16O18O rotational population has been used to predict the intensity of the 3 16O18O lines observable from the ground, namely the 234, 298 and 402 GHz lines. These predictions are compared to the upper limits obtained by Maréchal et al. (1997a) and to the tentative detection obtained by Pagani et al. (1993) towards L134N. We show that only the 234 GHz line is observable with today’s receivers and that the strong upper limits we have reported are not compatible with a standard steady-state model. Clumpiness, high (0.7) C/O ratio or other non-standard models are required to explain our observations. The consequence of the 18O isotopic fractionation is also discussed.