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PAH chemistry and IR emission from circumstellar disks

Visser, R. and Geers, V. C. and Dullemond, C. P. and Augereau, J.-C. and Pontoppidan, K. M. and van Dishoeck, E. F. (2007) PAH chemistry and IR emission from circumstellar disks. Astronomy and Astrophysics, 466 (1). pp. 229-241. ISSN 0004-6361. http://resolver.caltech.edu/CaltechAUTHORS:20091201-100041767

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Abstract

Aims. The chemistry of, and infrared (IR) emission from, polycyclic aromatic hydrocarbons (PAHs) in disks around Herbig Ae/Be and T Tauri stars are investigated. PAHs can exist in different charge states and they can bear different numbers of hydrogen atoms. The equilibrium (steady-state) distribution over all possible charge/hydrogenation states depends on the size and shape of the PAHs and on the physical properties of the star and surrounding disk. Methods. A chemistry model is created to calculate the equilibrium charge/hydrogenation distribution. Destruction of PAHs by ultraviolet (UV) photons, possibly in multi-photon absorption events, is taken into account. The chemistry model is coupled to a radiative transfer code to provide the physical parameters and to combine the PAH emission with the spectral energy distribution (SED) from the star+disk system. Results. Normally hydrogenated PAHs in Herbig Ae/Be disks account for most of the observed PAH emission, with neutral and positively ionized species contributing in roughly equal amounts. Close to the midplane, the PAHs are more strongly hydrogenated and negatively ionized, but these species do not contribute to the overall emission because of the low UV/optical flux deep inside the disk. PAHs of 50 carbon atoms are destroyed out to 100 AU in the disk's surface layer, and the resulting spatial extent of the emission does not agree well with observations. Rather, PAHs of about 100 carbon atoms or more are predicted to cause most of the observed emission. The emission is extended on a scale similar to that of the size of the disk, with the short-wavelength features less extended than the long-wavelength features. For similar wavelengths, the continuum emission is less extended than the PAH emission. Furthermore, the emission from T Tauri disks is much weaker and concentrated more towards the central star than that from Herbig Ae/Be disks. Positively ionized PAHs are predicted to be largely absent in T Tauri disks because of the weaker radiation field.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1051/0004-6361:20066829DOIArticle
http://www.aanda.org/index.php?option=article&access=doi&doi=10.1051/0004-6361:20066829PublisherArticle
ORCID:
AuthorORCID
Pontoppidan, K. M.0000-0001-7552-1562
van Dishoeck, E. F.0000-0001-7591-1907
Additional Information:© 2007 ESO. Received 28 November 2006; accepted 19 January 2007. The authors are grateful to Xander Tielens and Steven Doty for stimulating discussions. Astrochemistry in Leiden is supported by an NWO Spinoza Grant and a NOVA grant, and by the European Research Training Network “The Origin of Planetary Systems” (PLANETS, contract number HPRN-CT-2002-00308). Support for KMP was provided by NASA through Hubble Fellowship grant #01201.01 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555.
Funders:
Funding AgencyGrant Number
Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)UNSPECIFIED
Nederlandse Onderzoekschool voor de Astronomie (NOVA)UNSPECIFIED
European Research Training NetworkHPRN-CT-2002-00308
NASA Hubble Fellowship01201.01
NASANAS 5-26555
Subject Keywords:astrochemistry; circumstellar matter; planetary systems: protoplanetary disks; infrared: general
Issue or Number:1
Record Number:CaltechAUTHORS:20091201-100041767
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20091201-100041767
Official Citation:PAH chemistry and IR emission from circumstellar disks R. Visser, V. C. Geers, C. P. Dullemond, J.-C. Augereau, K. M. Pontoppidan and E. F. van Dishoeck A&A 466 (1) 229-241 (2007) DOI: 10.1051/0004-6361:20066829
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:16849
Collection:CaltechAUTHORS
Deposited By: Jason Perez
Deposited On:03 Dec 2009 22:18
Last Modified:22 Aug 2017 20:21

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