OH${}^{+}$ emission from cometary knots in planetary nebulae

Abstract

We model the molecular emission from cometary knots in planetary nebulae (PNe) using a combination of photoionization and photodissociation region (PDR) codes, for a range of central star properties and gas densities. Without the inclusion of ionizing extreme ultraviolet (EUV) radiation, our models require central star temperatures $T_{\ast }$ to be near the upper limit of the range investigated in order to match observed H${}_2$ and OH${}^{+}$ surface brightnesses consistent with observations - with the addition of EUV flux, our models reproduce observed OH${}^{+}$ surface brightnesses for $T_{\ast }\ge 100\mathrm{kK}$. For $T_{\ast }<80\mathrm{kK}$, the predicted OH${}^{+}$ surface brightness is much lower, consistent with the non-detection of this molecule in PNe with such central star temperatures. Our predicted level of H${}_2$ emission is somewhat weaker than commonly observed in PNe, which may be resolved by the inclusion of shock heating or fluorescence due to UV photons. Some of our models also predict ArH${}^{+}$ and HeH${}^{+}$ rotational line emission above detection thresholds, despite neither molecule having been detected in PNe, although the inclusion of photodissociation by EUV photons, which is neglected by our models, would be expected to reduce their detectability.

arXiv commentAccepted by MNRAS, 11 pages, 15 figures. Author accepted manuscript. Accepted on 24/04/18. Deposited on 27/04/18

References in corpus (35)

• The UMIST database for astrochemistry 2012
• A Unified Representation of Gas-Phase Element Depletions in the Interstellar Medium
• Diagnostics of irradiated gas in galaxy nuclei. I: A Far-ultraviolet and X-ray dominated region code
• New models for the evolution of Post-Asymptotic Giant Branch stars and Central Stars of Planetary Nebulae
• Post-Asymptotic Giant Branch Evolution of Low- and Intermediate-Mass Stars. Preliminary Results
• Black hole accretion and star formation as drivers of gas excitation and chemistry in Mrk231
• Solar System Abundances of the Elements
• Mocassin: A fully three-dimensional Monte Carlo photoionization code
• A grid of synthetic ionizing spectra for very hot compact stars from NLTE model atmospheres
• The dusty MOCASSIN: fully self-consistent 3D photoionisation and dust radiative transfer models
• Detection of a Noble Gas Molecular Ion, {36}ArH^+, in the Crab Nebula
• The cosmic ray ionization rate in the Galactic disk, as determined from observations of molecular ions
• Ubiquitous argonium (ArH${}^{+}$) in the diffuse interstellar medium -- a molecular tracer of almost purely atomic gas
• Molecular line intensities as measures of cloud masses - I. Sensitivity of CO emissions to physical parameter variations
• X-ray enabled MOCASSIN: a 3D code for photoionized media
• Investigating the Near-Infrared Properties of Planetary Nebula II. Medium Resolution Spectra
• First interstellar detection of OH+
• Chemistry in Cosmic-Ray Dominated Regions (CRDRs)
• Knots in the Helix Nebula found in H2
• Analysis of Far-UV Data of Central Stars of Planetary Nebulae: Occurrence and Variability of Stellar Winds
• Morphology and Composition of the Helix Nebula
• Spatially extended OH+ emission from the Orion Bar and Ridge
• Photodissociation of interstellar ArH+
• H${}_2$ in low-ionization structures of planetary nebulae
• Determination of the Physical Conditions of the Knots in the Helix Nebula from Optical and Infrared Observations
• The Herschel Planetary Nebula Survey (HerPlaNS) I. Data Overview and Analysis Demonstration with NGC 6781
• VLT / Infrared Integral Field Spectrometer Observations of Molecular Hydrogen Lines in the Knots in the Planetary Nebula NGC 7293 (the Helix Nebula)
• The Herschel Planetary Nebula Survey (HerPlaNS) - a comprehensive dusty photoionization model of NGC6781
• Modelling the ArH${}^{+}$ emission from the Crab Nebula
• Molecular Hydrogen in the Ionized Region of Planetary Nebulae
• Molecular chemistry and the missing mass problem in PNe
• H2 infrared line emission from the ionized region of planetary nebulae
• Herschel Planetary Nebula Survey (HerPlaNS) - First Detection of OH+ in Planetary Nebulae
• Herschel spectral-mapping of the Helix Nebula (NGC 7293): Extended CO photodissociation and OH+ emission
• Modelling the Warm H2 Infrared Emission of the Helix Nebula Cometary Knots

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