Near-infrared observations of AFGL 618. II. The atomic spectrum

We measured the 0.84-1.35 μm spectrum for the eastern lobe and the 0.40-0.68 μm spectra for both lobes of the proto - planetary nebula AFGL 618. These rich emission spectra are highlighted by strong forbidden lines. We have compiled an extensive line list from these spectra, including many identifications in the poorly explored 1.0-1.35 μm region. The atomic line ratios indicate that there is both high- and low-temperature gas in the lobes. The apparently shock-excited hotter gas has an electron temperature of T_e ≈ 25,000 K and an electron density of n_e ≈ 8000 cm^-3; the cooler gas has T_e ≈ 10,000 K and n_e ≈ 1600 cm^-3. We used line strengths to determine the filling factors of these two components and found that the cool component fills most of the visible lobes. We compare our results with previous work.