Hugo E. Schwarz

Three-Dimensional Photoionization Structure and Distances of Planetary Nebulae. I. NGC 6369

Continuing our series of papers on the three-dimensional (3D) structures of and accurate distances to planetary nebulae (PNe), we present our study of the planetary nebula NGC 6781. For this object, we construct a 3D photoionization model and, using the constraints provided by observational data from the literature, we determine the detailed 3D structure of the nebula, the physical parameters of the ionizing source, and the first precise distance. The procedure consists of simultaneously fitting all the observed emission-line morphologies, integrated intensities, and the two-dimensional (2D) density map from the [S II] line ratios to the parameters generated by the model, and in an iterative way obtaining the best fit for the central star parameters and the distance to NGC 6781, obtaining values of 950 ± 143 pc and 385 L☉ for the distance and luminosity of the central star, respectively. Using theoretical evolutionary tracks of intermediate and low-mass stars, we derive the mass of the central star of NGC 6781 and its progenitor to be 0.60 ± 0.03 M☉ and 1.5 ± 0.5 M☉, respectively.

Hα Morphological Classification of Planetary Nebulae

Using the data from the catalogue of PNe images of Schwarz et al. (1992), we have classified 255 nebulae into 5 morphological groups. The images were taken through a filter centred on the Ha line and included the [NII]6583 line. Most of the observations were made with the 3.5m ESO NTT during commissioning time. The main groups are called: stellar (st), irregular (i), elliptical (e), bipolar (b), and point-symmetric (p). The ellipticals are subdivided into: simple (e), multiple event (em), and inner structure (es) types. The bipolars into: simple (b), and multiple event (bm). The point-symmetric objects into: simple (p), and multiple events (pm).

Point Symmetry in Planetary Nebulae

We present narrow band images and spectra illustrating the morphological and kinematical characteristics of a new class of planetary nebulae. It consists of all those objects in the catalogue by Schwarz et al. (1992) whose morphology shows no other symmetries than point-reflection about the central source. This peculiar shape is often determined by pairs of ansae or blobs separated from the central body of the nebula. The kinematical data show both low (e.g. IC 4634) and high (He 2–186; V exp > 135 km s-1) velocity outflows.