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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 358542.0, MPI für Astronomie / Publikationen_mpia
PAH chemistry and IR emission from circumstellar disks
Authors:Visser, R.; Geers, V. C.; Dullemond, C. P.; Augereau, J. C.; Pontoppidan, K. M.; van Dishoeck, E. F.
Date of Publication (YYYY-MM-DD):2007
Title of Journal:Astronomy and Astrophysics
Start Page:229
End Page:241
Audience:Not Specified
Abstract / Description: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.<BR /> 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.<BR /> 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
Free Keywords:astrochemistry; circumstellar matter; planetary systems: protoplanetary disks; infrared: general
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie

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