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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 358622.0, MPI für Astronomie / Publikationen_mpia
Modeling Spitzer observations of VV Ser. II. An extended quantum-heated nebula and a disk shadow
Authors:Pontoppidan, K. M.; Dullemond, C. P.; Blake, G. A.; Evans, N. J.; Geers, V. C.; Harvey, P. M.; Spiesman, W.
Date of Publication (YYYY-MM-DD):2007
Title of Journal:The Astrophysical Journal
Start Page:991
End Page:1000
Audience:Not Specified
Abstract / Description:We present mid-infrared Spitzer IRAC and MIPS images of the UX Orionis star VV Ser and the surrounding cloud. The 5.6-70 mum images show bright, localized, and nebulous emission extended over 4' centered on VV Ser. This nebulosity is due to transiently heated grains excited by UV photons emitted by VV Ser. Imprinted on the nebulosity is a wedge-shaped dark band, centered on the star. We interpret this as the shadow cast by the inner regions of a near-edge-on disk, allowing the PAHs to be excited only outside of this shadow. We extend an axisymmetric radiative transfer model of the VV Ser disk described in a companion paper to include quantum-heated PAH molecules and very small grains (VSGs) in the thermal cooling approximation. The presence of a disk shadow strongly constrains the inclination as well as the position angle of the disk. The nebulosity at 5.6-8.0 mum and the 2175 Å absorption feature seen in an archival spectrum from the IUE can be fit using only PAHs, consistent with the main carrier of the 2175 Å feature being due to the graphite-like structure of the PAHs. The PAH component is found to be relatively smoothly distributed in the cloud, while the population of VSGs emitting at 20-70 mum is strongly concentrated ~50'' to the southeast of VV Ser. Depending on the adopted PAH opacity, the abundance of PAHs in the surrounding cloud is constrained to 5%+/-2% of the total dust mass. Although relatively rare, quantum-heated nebulosities surrounding single, well-defined stars are well-suited for gaining unique insights into the physics of very small particles in molecular clouds.
Free Keywords:Accretion; Accretion Disks; Stars: Circumstellar Matter; Infrared: Stars; Stars: Pre-Main-Sequence; Stars: Formation
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
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