Sampling molecular gas in the Helix planetary nebula: Variation in HNC/HCN with UV flux

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Table 4.

Average line ratios from PDR Meudon code.

	Model set 1	Model set 2			Observed ratio
Pressure (K cm⁻³)	10⁷	5 × 10⁷	10⁶	10⁵
UV Field: 0.14 pc	0.64	0.48			0.46–0.48
UV Field: 0.35 pc	0.48		0.55		0.64
UV Field: 0.44 pc	0.46			0.73	0.66–1.11

Notes. Average value of the HNC/HCN line ratio from Meudon PDR models (Fig. 9). The observed ratios for Helix positions with similar UV field strengths (see Table 3) are presented in the right-most column.

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