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Galaxies 2019, 7(1), 10;

Understanding the Spatial Distributions of the Ionic/Atomic/Molecular/Dust Components in PNe

Department of Physics & Astronomy, University of Denver, 2112 E. Wesley Ave., Denver, CO 80208, USA
Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei 10617, Taiwan
Current address: Okayama Observatory, Kyoto University, Honjo, Kamogata, Asakuchi, Okayama 719-0232, Japan.
Author to whom correspondence should be addressed.
Received: 4 December 2018 / Revised: 28 December 2018 / Accepted: 29 December 2018 / Published: 4 January 2019
(This article belongs to the Special Issue Asymmetric Planetary Nebulae VII)
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Planetary nebulae (PNe) are often recognized as the hallmark of compact H ii regions in the Universe. However, there exist dusty neutral regions extending beyond the central ionized region. We demonstrate that such dusty neutral regions (also known as photo-dissociation regions, or PDRs) around the central ionized region are significant parts of PNe in terms of energetics and mass. We do so by using our latest dusty photoionization model of NGC 6781 (of 13 parameters) based on one of the most comprehensive panchromatic data sets ever assembled for a PN encompassing from X-ray to radio (of 136 constraining data, including 19 flux densities, 78 line fluxes, and 37 band fluxes). We find that NGC 6781, evolved out of a 2.25–3.0 M star located 460 pc away from us, possesses a massive concentration of neutral gas (molecular hydrogen) just beyond the central ionized region and that the amount of ionized gas in NGC 6781 is only 22% of the observationally accounted amount of matter in the circumstellar environment, which itself does not even account for the amount of mass presumably ejected by the central star during the last thermal pulse event according to the latest evolutionary models. This means that the observed nebula in this PN is only the tip of the iceberg. View Full-Text
Keywords: dust; extinction; ISM: abundances; planetary nebulae: individual (NGC 6781) dust; extinction; ISM: abundances; planetary nebulae: individual (NGC 6781)

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Ueta, T.; Otsuka, M.; The HerPlaNS consortium. Understanding the Spatial Distributions of the Ionic/Atomic/Molecular/Dust Components in PNe. Galaxies 2019, 7, 10.

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