Spectroscopic mapping of the planetary nebula NGC 6302

Abstract

Context. Most spectroscopic studies of planetary nebulae (PNe) are based on data from specific parts of the objects. Considering the high complexity of their morphological structures, integrated or average values across an observed region can only provide limited information of their ionic, density, and temperature structures. Aims. We investigate the spatial variation of the physical and chemical properties of NGC 6302, a high-ionization PNe, with a complex bipolar structure. Methods. Spatially resolved long-slit spectroscopic data were obtained from 11 parallel and equally spaced directions over the nebula. Maps of emission line fluxes, line ratios, electron temperature T e , electron density N e , and ionic abundances (He+ , He2+ , N0 , N+ , O0 , O+ , O2+ , S+ , S2+ , Ne2+ , Ar2+ , Ar3+ , and Ar4+ relative to H+ ) were constructed with a spatial resolution of 1.45″ × 1″ for a large portion of the nebula over an area of 11″ × 250″. Electron densities were estimated from the [S ii] λ 6716/λ 6731 and [Ar iv] λ 4711/λ 4740 line ratios, and electron temperatures were estimated from the [O iii] (λ 4959 + λ 5007)/λ 4363 and [N ii] (λ 6548 + λ 6584)/λ 5755 ratios. Integrated spectra were also obtained and 142 lines were identified. Results. The electron density maps show a peaked distribution, with the densest area at the circumstellar region, reaching N e ≈ 40 000 cm-3 , and decreasing to N e ≤ 1000 cm-3 at the lobes. Knots were observed in the N e (S ii) map, with 2000 cm-3 e . The N e (Ar iv) map suggests the presence of an inner region with N e ≈ 20 000 cm-3 that extends from the center through the east lobe. A homogeneous temperature distribution was found for both T e (O iii) and T e (N ii). Small temperature fluctuations on the plane of the sky of and were estimated. Conclusions. In general, the total abundances obtained are similar to the maximum found in the ionic abundance maps of the dominant ionic species. This demonstrates the potential of spatially resolved abundance studies for establishing lower limits of the total abundances based on ionic abundances, for checking the ionization correlation factors, and in some cases, for determining the total abundances directly from maps of ionic abundances.