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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 358747.0, MPI für Astronomie / Publikationen_mpia
Spatial separation of small and large grains in the transitional disk around the young star <ASTROBJ>IRS 48</ASTROBJ>
Authors:Geers, V. C.; Pontoppidan, K. M.; van Dishoeck, E. F.; Dullemond, C. P.; Augereau, J. C.; Merín, B.; Oliveira, I.; Pel, J. W.
Date of Publication (YYYY-MM-DD):2007
Title of Journal:Astronomy and Astrophysics
Start Page:L35
End Page:L38
Audience:Not Specified
Abstract / Description:Aims.We present spatially resolved mid-infrared images of the disk surrounding the young star <ASTROBJ>IRS 48</ASTROBJ> in the Ophiuchus cloud complex. The disk exhibits a ring-like structure at 18.7 mum, and is dominated by very strong emission from polycyclic aromatic hydrocarbons at shorter wavelengths. This allows a detailed study of the relative distributions of small and large dust grains.<BR /> Methods: Images of <ASTROBJ>IRS 48</ASTROBJ> in 5 mid-infrared bands from 8.6 to 18.7 mum as well as a low resolution N-band spectrum are obtained with VLT-VISIR. Optical spectroscopy is used to determine the spectral type of the central star and to measure the strength of the Halpha line.<BR /> Results: The 18.7 mum ring peaks at a diameter of 110 AU, with a gap of ~60 AU. The shape of the ring is consistent with an inclination of i = 48° ± 8°. In contrast, the 7.5-13 mum PAH emission bands are centered on the source and appear to fill the gap within the ring. The measured PAH line strengths are 10-100× stronger than those typically measured for young M0 stars and can only be explained with a high PAH abundance and/or strong excess optical/UV emission. The morphology of the images, combined with the absence of a silicate emission feature, imply that the inner disk has been cleared of micron-sized dust but with a significant population of PAHs remaining. We argue that the gap can be due to grain growth and settling or to clearing by an unseen planetary or low-mass companion. <ASTROBJ>IRS 48</ASTROBJ> may represent a short-lived transitional phase from a classical to a weak-line T Tauri star.<BR /> Based on observations obtained at the European Southern Observatory, Paranal, Chile, within the observing program 075.C-0211, and observations obtained with the WHT operated on the island of La Palma by the Isaac Newton Group.
Free Keywords:stars: pre-main sequence; stars: planetary systems: protoplanetary disks; stars: circumstellar matter; astrochemistry; stars: individual: <ASTROBJ>IRS 48</ASTROBJ>
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie

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