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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 308752.0, MPI für Astronomie / Publikationen_mpia
C2D Spitzer-IRS spectra of disks around T Tauri stars. II. PAH emission features
Authors:Geers, V. C.; Augereau, J. C.; Pontoppidan, K. M.; Dullemond, C. P.; Visser, R.; Kessler-Silacci, J. E.; Evans, N. J.; van Dishoeck, E. F.; Blake, G. A.; Boogert, A. C. A.; Brown, J. M.; Lahuis, F.; Merín, B.
Date of Publication (YYYY-MM-DD):2006
Journal Abbrev.:Astronomy and Astrophysics
Start Page:545
End Page:556
Audience:Not Specified
Abstract / Description:Aims.We search for Polycyclic Aromatic Hydrocarbon (PAH) features towards young low-mass (T Tauri) stars and compare them with surveys of intermediate mass (Herbig Ae/Be) stars. The presence and strength of the PAH features are interpreted with disk radiative transfer models exploring the PAH feature dependence on the incident UV radiation, PAH abundance and disk parameters.<BR /> Methods: .Spitzer Space Telescope 5-35 mum spectra of 54 pre-main sequence stars with disks were obtained, consisting of 38 T Tauri, 7 Herbig Ae/Be and 9 stars with unknown spectral type.<BR /> Results: .Compact PAH emission is detected towards at least 8 sources of which 5 are Herbig Ae/Be stars. The 11.2 mum PAH feature is detected in all of these sources, as is the 6.2 mum PAH feature for the 4 sources for which short wavelength data are available. However, the 7.7 and 8.6 mum features appear strongly in only 1 of these 4 sources. Based on the 11.2 mum feature, PAH emission is observed towards at least 3 T Tauri stars, with 14 tentative detections, resulting in a lower limit to the PAH detection rate of 8%. The lowest mass source with PAH emission in our sample is <ASTROBJ>T Cha</ASTROBJ> with a spectral type G8. All 4 sources in our sample with evidence for dust holes in their inner disk show PAH emission, increasing the feature/continuum ratio. Typical 11.2 mum line intensities are an order of magnitude lower than those observed for the more massive Herbig Ae/Be stars. Measured line fluxes indicate PAH abundances that are factors of 10-100 lower than standard interstellar values. Conversely, PAH features from disks exposed to stars with T_eff&leq; 4200 K without enhanced UV are predicted to be below the current detection limit, even for high PAH abundances. Disk modeling shows that the 6.2 and 11.2 mum features are the best PAH tracers for T Tauri stars, whereas the 7.7 and 8.6 mum bands have low feature over continuum ratios due to the strongly rising silicate emission.<BR />
Free Keywords:stars: pre-main sequence; planetary systems: protoplanetary disks; circumstellar matter; astrochemistry; ISM: molecules
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
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