Low upper limits on the O2 abundance from the Odin satellite
Low upper limits on the O2 abundance from the Odin satellite
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DOI：
10.1051/0004-6361:20030344
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发表时间：
2003-05-01
影响因子：
6.5
通讯作者：
Wilson, CD
中科院分区：
文献类型：
--
作者：
Pagani, L;Olofsson, AOH;Wilson, CD
这是第一次，在我们的银河系中进行搜索，以寻找连接到O-2基态的119 GHz过渡，使用Odin卫星。Odin配备了灵敏的3 mm接收器（T-sys（SSB）= 600 K），已经达到了前所未有的O2丰度上限，特别是在寒冷的乌云中，487 GHz跃迁中涉及的激发态能级预计不会被大量填充。在这里，我们报告了十几个来源的上限。在冷的暗云中，我们将公布的SWAS上限提高了一个数量级以上，在一半的源中达到N（O-2）/N（H-2）小于或等于10（-7）。虽然标准的化学模型明确排除了这些新的限制，我们的研究结果是兼容的几个最近的研究，得出较低的O-2丰度。金匠等人（2002）最近报告了一个SWAS试验性探测，在约10'× 14'的7个波束的组合中，在外流机翼中O-2向rho Oph A的487 GHz跃迁。在短暂的（1.3小时的积分时间）和部分覆盖的SWAS区域（约65%，如果我们排除他们的中心位置），我们没有检测到相应的119 GHz线。我们对O-2柱密度的3 σ上限是7.3 × 10（15）cm（-2）。我们目前不能排除SWAS信号大部分位于9'奥丁光束之外并逃脱了我们灵敏的探测器的可能性。
For the first time, a search has been conducted in our Galaxy for the 119 GHz transition connecting to the ground state of O-2, using the Odin satellite. Equipped with a sensitive 3 mm receiver (T-sys(SSB) = 600 K), Odin has reached unprecedented upper limits on the abundance of O2, especially in cold dark clouds where the excited state levels involved in the 487 GHz transition are not expected to be significantly populated. Here we report upper limits for a dozen sources. In cold dark clouds we improve upon the published SWAS upper limits by more than an order of magnitude, reaching N(O-2)/N(H-2) less than or equal to 10(-7) in half of the sources. While standard chemical models are definitively ruled out by these new limits, our results are compatible with several recent studies that derive lower O-2 abundances. Goldsmith et al. (2002) recently reported a SWAS tentative detection of the 487 GHz transition of O-2 in an outflow wing towards rho Oph A in a combination of 7 beams covering approximately 10' X 14'. In a brief (1.3 hour integration time) and partial covering of the SWAS region (approximate to65% if we exclude their central position), we did not detect the corresponding 119 GHz line. Our 3 sigma upper limit on the O-2 column density is 7.3 X 10(15) cm(-2). We presently cannot exclude the possibility that the SWAS signal lies mostly outside of the 9' Odin beam and has escaped our sensitive detector.