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OH+ emission from cometary knots in planetary nebulae

Priestley, F D and Barlow, M J 2018. OH+ emission from cometary knots in planetary nebulae. Monthly Notices of the Royal Astronomical Society 478 (2) , pp. 1502-1511. 10.1093/mnras/sty1099

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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* to be near the upper limit of the range investigated in order to match observed H2 and OH+ surface brightnesses consistent with observations – with the addition of EUV flux, our models reproduce observed OH+ surface brightnesses for T* ≥ 100 kK. For T* < 80 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 H2 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.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Publisher: Oxford University Press
ISSN: 0035-8711
Date of First Compliant Deposit: 6 August 2019
Date of Acceptance: 24 April 2018
Last Modified: 06 Aug 2019 11:15
URI: http://orca.cf.ac.uk/id/eprint/124712

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