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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 358651.0, MPI für Astronomie / Publikationen_mpia
Abundant crystalline silicates in the disk of a very low mass star
Authors:Merín, B.; Augereau, J. C.; van Dishoeck, E. F.; Kessler-Silacci, J.; Dullemond, C. P.; Blake, G. A.; Lahuis, F.; Brown, J. M.; Geers, V. C.; Pontoppidan, K. M.; Comerón, F.; Frasca, A.; Guieu, S.; Alcalá, J. M.; Boogert, A. C. A.; Evans, N. J.; D'Alessio, P.; Mundy, L. G.; Chapman, N.
Date of Publication (YYYY-MM-DD):2007
Title of Journal:The Astrophysical Journal
Start Page:361
End Page:367
Audience:Not Specified
Abstract / Description:We announce the discovery of SST-Lup3-1, a very low mass star close to the brown dwarf boundary in Lupus III with a circum(sub)stellar disk, discovered by the ``Cores to Disks'' Spitzer Legacy Program from mid-infrared, with very conspicuous crystalline silicate features in its spectrum. It is the first of such objects with a full 5-35 mum spectrum taken with the IRS, and it shows strong 10 and 20 mum silicate features with high feature-to-continuum ratios and clear crystalline features out to 33 mum. The dust in the disk upper layer has a crystalline silicate grain fraction between 15% and 33%, depending on the assumed dust continuum. The availability of the full Spitzer infrared spectrum allows an analysis of the dust composition as a function of temperature and position in the disk. The hot (~300 K) dust responsible for the 10 mum feature consists of a roughly equal mix of small (~0.1 mum) and large (~1.5 mum) grains, whereas the cold (~70 K) dust responsible for the longer wavelength silicate features contains primarily large grains (>1 mum). Since the cold dust emission arises from deeper layers in the inner (<3 AU) disk as well as from the surface layers of the outer (3-5 AU) disk, this provides direct evidence for combined grain growth and settling in the disk. The inferred crystalline mass fractions in the two components are comparable. Since only the inner 0.02 AU of the disk is warm enough to anneal the amorphous silicate grains, even the lowest fraction of 15% of crystalline material requires either very efficient mixing or other formation mechanisms. Based partly on observations obtained at the ESO NTT at La Silla (Chile) for program 276.C5031.
Free Keywords:Stars: Circumstellar Matter; stars: individual (SST-Lup3-1); Stars: Low-Mass; Brown Dwarfs
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
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