DUST PROPERTIES AND DISK STRUCTURE OF EVOLVED PROTOPLANETARY DISKS IN Cep OB2: GRAIN GROWTH, SETTLING, GAS AND DUST MASS, AND INSIDE-OUT EVOLUTION

Aurora Sicilia-Aguilar (Lead / Corresponding author), Thomas Henning, Cornelis P. Dullemond, Nimesh Patel, Attila Juhasz, Jeroen Bouwman, Bernhard Sturm

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Abstract

We present Spitzer/Infrared Spectrograph spectra of 31 T Tauri stars (TTS) and IRAM/1.3 mm observations for 34 low-and intermediate-mass stars in the Cep OB2 region. Including our previously published data, we analyze 56 TTS and 3 intermediate-mass stars with silicate features in Tr 37 (similar to 4 Myr) and NGC 7160 (similar to 12 Myr). The silicate emission features are well reproduced with a mixture of amorphous (with olivine, forsterite, and silica stoichiometry) and crystalline grains (forsterite, enstatite). We explore grain size and disk structure using radiative transfer disk models, finding that most objects have suffered substantial evolution (grain growth, settling). About half of the disks show inside-out evolution, with either dust-cleared inner holes or a radially dependent dust distribution, typically with larger grains and more settling in the innermost disk. The typical strong silicate features nevertheless require the presence of small dust grains, and could be explained by differential settling according to grain size, anomalous dust distributions, and/or optically thin dust populations within disk gaps. M-type stars tend to have weaker silicate emission and steeper spectral energy distributions than K-type objects. The inferred low dust masses are in a strong contrast with the relatively high gas accretion rates, suggesting global grain growth and/or an anomalous gas-to-dust ratio. Transition disks in the Cep OB2 region display strongly processed grains, suggesting that they are dominated by dust evolution and settling. Finally, the presence of rare but remarkable disks with strong accretion at old ages reveals that some very massive disks may still survive to grain growth, gravitational instabilities, and planet formation.
Original languageEnglish
Article number39
Number of pages35
JournalAstrophysical Journal
Volume742
Issue number1
DOIs
Publication statusPublished - 3 Nov 2011

Keywords

  • open clusters and associations: individual (Cep OB2) protoplanetary disks stars: late-type stars: pre-main sequence T-TAURI STARS SPITZER-SPACE-TELESCOPE SPECTRAL ENERGY-DISTRIBUTIONS INTERSTELLAR SILICATE MINERALOGY INFRARED SPECTROGRAPH SURVEY GIANT PLANET FORMATION YOUNG STELLAR OBJECTS HERBIG AE/BE SYSTEMS MAIN-SEQUENCE STARS NE-II EMISSION

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