3-D Photoionization Structure and Distances of Planetary Nebulae III. NGC 6781

Abstract

Continuing our series of papers on the three-dimensional (3-D) structures of and accurate distances to Planetary Nebulae (PNe), we present our study of the planetary nebula NGC6781. For this object we construct a 3-D photoionization model and, using the constraints provided by observational data from the literature we determine the detailed 3-D structure of the nebula, the physical parameters of the ionizing source and the first precise distance. The procedure consists in simultaneously fitting all the observed emission line morphologies, integrated intensities and the 2-D density map from the [SII] line ratios to the parameters generated by the model, and in an iterative way obtain the best fit for the central star parameters and the distance to NGC6781, obtaining values of 950+-143pc and 385 Lsun 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 NGC6781 and its progenitor to be 0.60+-0.03 Msun and 1.5+-0.5 Msun respectively.

arXiv comment16 pp, 6 figues, 2 tables, submitted to the ApJ

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• Three-dimensional chemically homogeneous and bi-abundance photoionization models of the "super-metal-rich" planetary nebula NGC 6153
• The Herschel Planetary Nebula Survey (HerPlaNS) I. Data Overview and Analysis Demonstration with NGC 6781
• The Herschel Planetary Nebula Survey (HerPlaNS) - a comprehensive dusty photoionization model of NGC6781
• 3-D Photoionization Structure and Distances of Planetary Nebulae IV. NGC 40
• Extended Structures of Planetary Nebulae Detected in H${}_2$ Emission
• Observations and three-dimensional ionization structure of the planetary nebula SuWt 2
• Physico-chemical spectroscopic mapping of the planetary nebula NGC 40 and the 2D_NEB, a new 2D algorithm to study ionised nebulae
• Distance mapping applied to four well-known planetary nebulae and a nova shell
• Scaling for the intensity of radiation in spherical and aspherical planetary nebulae
• Optical and Mid-Infrared Observations of the Planetary Nebula NGC 6781
• H$\alpha$ fluxes and extinction distances for planetary nebulae in the IPHAS survey of the Northern Galactic Plane
• Herschel observations of planetary nebulae