The 12 C/ 13 C ratio has been measured toward a sample of planetary nebulae (PNe) using millimeter observations of CO, HCN, HNC, CN, and other species, conducted with the 12 m antenna and the Submillimeter Telescope of the Arizona Radio Observatory. The observed nebulae spanned the entire lifetime of PNe, from ∼900 to 12,000 yr, and include well-known objects such as NGC 7293 (Helix), NGC 6720 (Ring), and NGC 2440, as well as relatively unexplored nebulae (M3–28, M2–48, and M3–55). In most cases, multiple molecules and transitions were used in the ratio determination, resulting in the most accurate values available to date, with 10%–40% uncertainties. The ratios found were unexpectedly low, lying in the range 12 C/ 13 C ∼1.0 ± 0.7–13.2 ± 4.9, with an average value of 3.7—drastically less than found in the envelopes of C-rich AGB stars, and, in some cases, lower than the minimum value achieved in equilibrium CNO burning. Such low values are e...

中文翻译：

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行星状星云中的碳同位素比：13 C的意外增强

通过使用12 m天线和亚利桑那射电天文台的亚毫米望远镜进行的CO，HCN，HNC，CN和其他物种的毫米波观测，已对行星状星云（PNe）样品测量了12 C / 13 C比。 。观测到的星云跨越了PNe的整个生命，从约900年到12,000 yr，包括著名的天体，例如NGC 7293（Helix），NGC 6720（Ring）和NGC 2440，以及相对未探索的星云（M3– 28，M2-48和M3-55）。在大多数情况下，比率确定中使用了多个分子和离子对，因此可以得出迄今为止最准确的值，不确定性为10％至40％。发现的比率出乎意料的低，在12 C / 13 C〜1.0±0.7–13.2±4.9范围内，平均值为3.7，大大低于富含C的AGB恒星包壳中的比率，并且，在某些情况下，低于平衡CNO燃烧所达到的最小值。如此低的值是...