2024MNRAS.528.4228R

Spectrophotometric data of the young planetary nebula M 3-27, from 2004 to 2021, are presented and discussed. We corroborate that the H I Balmer lines present features indicating they are emitted by the central star, therefore He I lines were used to correct line fluxes by effects of reddening. Important variability on the nebular emission lines between 1964 and 2021, probably related to density changes in the nebula, is reported. Diagnostic diagrams to derive electron temperatures and densities have been constructed. The nebula shows a very large density contrast with an inner density of the order of 10⁷ cm^–3 and an outer density of about 10³-10⁴ cm^–3. With these values of density, electron temperatures of 16 000-18 000 K have been found from collisionally excited lines. Because the central star emits in the H⁺ lines, ionic abundances relative to He⁺ were calculated from collisionally excited and recombination lines, and scaled to H⁺ by considering that He⁺/H⁺ = He/H = 0.11. Abundance discrepancy factor (O⁺²) values were also determined. Total abundance values obtained indicate sub-solar abundances, similar to what is found in other comparable objects like IC 4997.