Presentation #351.02 in the session Planetary Nebulae, Supernova Remnants — iPoster Session.
Young planetary nebulae that have evolved in the last few thousands of years are very dense, with densities of up to 105 cm-3. Collision-excited [SII] lines have been instrumental in determining the densities of Jupiter-Io in the solar system, stars, gas nebulae, HII regions, and active galactic nuclei (AGN). So far, the [SII] 6716 and 6731 lines that are observed in the ionized or neutral hydrogen region are known to have densities in the ranges of 100 — 8000 cm-3, limited by their critical low densities (Osterbrock 1989; Osterbrock & Ferland 2006). Meanwhile, Keenan et al. (1996, K96) showed that these metastable (1) 2D0–4S0(6716 Å, 6731 Å) transition lines can form in a high-density zone of up to 105 cm-3, due to the contribution from (2) another metastable state through a 2P0–4S0(4069 Å, 4076 Å) transition that can occur under high densities. We compared the density diagnostic diagrams from CLOUDY (Ferland et al. 2017) and K96 for the [SII] 6716 to 6731 ratio for a temperature of 10,000 K, which have been applied to planetary nebula NGC 7009: The two main shells of NGC 7009 appear to have densities of 10,000 cm-3 or higher.