Flux ratio of HNC/HCN plotted against nebular age. Magenta points are PNe observed by Schmidt & Ziurys (2017a). Their sample encompasses objects with an age range half that of the PN included in our study. Linear regression identified a correlation of r = 0.496 with a linear slope of m = 0.019, or an increase in the ratio of HNC/HCN of 0.019 kyr−1.
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