The Herschel Planetary Nebula Survey (HerPlaNS): A Comprehensive Dusty Photoionization Model of NGC6781

Abstract

We perform a comprehensive analysis of the planetary nebula (PN) NGC 6781 to investigate the physical conditions of each of its ionized, atomic, and molecular gas and dust components and the object's evolution, based on panchromatic observational data ranging from UV to radio. Empirical nebular elemental abundances, compared with theoretical predictions via nucleosynthesis models of asymptotic giant branch (AGB) stars, indicate that the progenitor is a solar-metallicity, 2.25 − 3.0 M ⊙ initial-mass star. We derive the best-fit distance of 0.46 kpc by fitting the stellar luminosity (as a function of the distance and effective temperature of the central star) with the adopted post-AGB evolutionary tracks. Our excitation energy diagram analysis indicate high excitation temperatures in the photodissociation region (PDR) beyond the ionized part of the nebula, suggesting extra heating by shock interactions between the slow AGB wind and the fast PN wind. Through iterative fitting using the Cloudy code with empirically-derived constraints, we find the best-fit dusty photoionization model of the object that would inclusively reproduce all of the adopted panchromatic observational data. The estimated total gas mass (0.41 M ⊙ ) corresponds to the mass ejected during the last AGB thermal pulse event predicted for a 2.5 M ⊙ initial-mass star. A significant fraction of the total mass (about 70 %) is found to exist in the PDR, demonstrating the critical importance of the PDR in PNe that are generally recognized as the hallmark of ionized/H

Extended Structures of Planetary Nebulae Detected in H2 Emission∗

“…At the distance to NGC 6781 (0.46-0.72 kpc, Frew et al 2016;Otsuka et al 2017), the pixel size 0 3 of CFHT WIRCam corresponds to 138-216 au (2.06-3.23×10 15 cm), which is comparable to the sizes of the H 2 clumps in NGC 2346 (112-238 au, Manchado et al 2015). For the more distant PN Sh 1-89 (1.85 kpc), the pixel size of WIRCam corresponds to 555 au (or 8.30×10…”

“…The locations of our targets in the Hertzsprung-Russell (H-R) diagram are shown in Figure 26, where the post-AGB evolutionary tracks calculated by Vassiliadis & Wood (1994) are presented. The effective temperatures and luminosities (as well as the uncertainties) of the PN central stars were adopted from the literature (Zhang & Kwok 1993;van Hoof et al 2000van Hoof et al , 2010Stanghellini et al 2002;Sabbadin et al 2004;Wesson & Liu 2004;Walsh et al 2016;Otsuka et al 2017). According to their locations in the H-R diagram, the central stars of our sample might be separated into two main groups: those already on the cooling track (NGC 6720, NGC 6772, NGC 6781, NGC 6894, NGC 7048, Sh 1-89), and those whose temperatures are still increasing (Hb 12,NGC 6543,NGC 6826,NGC 7009).…”

Physical properties of the fluorine and neutron-capture element-rich PN Jonckheere 900

“…Assuming that Cl is the sum of Cl +,2+,3+,4+ , we determine ICF(Cl) = 1.06 ± 0.06 from Ar/(Ar + + Ar 2+ + Ar 3+ ). As the fractional ionic stages of Si, P, and K are similar to that of S in the model of Otsuka et al (2017), we adopt ICF(Si) of 10.16 ± 2.88 from the S/S + ratio; ICF(P) is 1.70 ± 0.09 from the S/(S + + S 2+ ) ratio; and ICF(K) = 4.96 ± 0.23 from the Ar/Ar 3+ ratio, respectively. ICF(Fe) of 11.96 ± 0.55 corresponds to the O/O + .…”

Herschel Planetary Nebula Survey (HerPlaNS)★: hydrogen recombination laser lines in Mz 3

“…The optical to MIR HRL emission of regular PNe and H ii Regions can usually be well fitted by the calculated emission for an optically thin gas dominated by spontaneous emission (Osterbrock & Ferland 2006). We attempted to fit the Mz 3 observed HRL ratios curve using the emissivities provided by Storey & Hummer (1995).…”