Hyung S, Aller L H
Department of Astronomy, University of California, Los Angeles, CA 90024-1562, USA.
Proc Natl Acad Sci U S A. 1993 Jan 15;90(2):413-7. doi: 10.1073/pnas.90.2.413.
Observations of two dense compact planetary nebulae secured with the Hamilton Echelle spectrograph at Lick Observatory combined with previously published UV spectra secured with the International Ultraviolet Explorer enable us to probe the electron densities and temperatures (plasma diagnostics) and ionic concentrations in these objects. The diagnostic diagrams show that no homogenous model will work for these nebulae. NGC 6572 may consist of an inner torordal ring of density 25,000 atoms/cm3 and an outer conical shell of density 10,000 atoms/cm3. The simplest model of IC 4997 suggests a thick inner shell with a density of about 107 atoms/cm3 and an outer envelope of density 10,000 atoms/cm3. The abundances of all elements heavier than He appear to be less than the solar values in NGC 6572, whereas He, C, N, and O may be more abundant in IC 4997 than in the sun. IC 4997 presents puzzling problems.
利用利克天文台的汉密尔顿阶梯光栅光谱仪对两个致密的行星状星云进行观测，并结合此前用国际紫外探测器获得的已发表紫外光谱，这使我们能够探测这些天体中的电子密度和温度（等离子体诊断）以及离子浓度。诊断图表明，没有一个均匀模型适用于这些星云。NGC 6572可能由一个密度为25,000个原子/立方厘米的内部环形环和一个密度为10,000个原子/立方厘米的外部锥形壳组成。IC 4997最简单的模型表明，它有一个密度约为10⁷个原子/立方厘米的厚内壳和一个密度为10,000个原子/立方厘米的外壳。在NGC 6572中，所有比氦重的元素的丰度似乎都低于太阳值，而在IC 4997中，氦、碳、氮和氧可能比太阳中更丰富。IC 4997存在一些令人困惑的问题。
