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Grain growth across protoplanetary discs: 10 μm silicate feature versus millimetre slope

Lommen, D. J. P. and van Dishoeck, E. F. and Wright, C. M. and Maddison, S. T. and Min, M. and Wilner, D. J. and Salter, D. M. and van Langevelde, H. J. and Bourke, T. L. and van der Burg, R. F. J. and Blake, G. A. (2010) Grain growth across protoplanetary discs: 10 μm silicate feature versus millimetre slope. Astronomy and Astrophysics, 515 . Art. No. A77. ISSN 0004-6361.

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Context. Young stars are formed with dusty discs around them. The dust grains in the disc are originally of the same size as interstellar dust, i.e., of the order of 0.1 μm. Models predict that these grains will grow in size through coagulation. Observations of the silicate features around 10 and 20 μm are consistent with growth from submicron to micron sizes in selected sources whereas the slope of the spectral energy distribution (SED) at mm and cm wavelengths traces growth up to mm sizes and larger. Aims. We here look for a correlation between these two grain growth indicators. Methods. A large sample of T-Tauri and Herbig-Ae/Be stars, spread over the star-forming regions in Chamaeleon, Lupus, Serpens, Corona Australis, and the Gum nebula in Vela, was observed with the Spitzer Space Telescope at 5–13 μm, and a subsample was observed with the SMA, ATCA, CARMA, and VLA at mm wavelengths. We complement this subsample with data from the literature to maximise the overlap between μm and mm observations and search for correlations in the grain-growth signatures. Synthetic spectra are produced to determine which processes may produce the dust evolution observed in protoplanetary discs. Results. Dust disc masses in the range <1 to 7 × 10^(-4) M_☉ are obtained. The majority of the sources have a mm spectral slope consistent with grain growth. There is a tentative correlation between the strength and the shape of the 10-μm silicate feature and the slope of the SED between 1 and 3 mm. The observed sources seem to be grouped per star-forming region in the 10-μm-feature vs. mm-slope diagram. The modelling results show that, if only the maximum grain size is increased, first the 10-μm feature becomes flatter and subsequently the mm slope becomes shallower. To explain the sources with the shallowest mm slopes, a grain size distribution shallower than that of the interstellar medium is required. Furthermore, the strongest 10-μm features can only be explained with bright (L ~ 6 L_☉), hot (T_(eff) = 4000 K) central stars. Settling of larger grains towards the disc midplane results in a stronger 10-μm feature, but has a very limited effect on the mm slope. Conclusions. A tentative correlation between the strength of the 10-μm feature and the mm slope is found, which would imply that the inner and outer disc evolve simultaneously. Dust with a mass dominated by large, ~mm-sized, grains is required to explain the shallowest mm slopes. Other processes besides grain growth, such as the clearing of an inner disc by binary interaction, may also be responsible for the removal of small grains. Observations with future telescopes with larger bandwidths or collecting areas are required to provide the necessary statistics to study these processes of disc and dust evolution.

Item Type:Article
Related URLs:
URLURL TypeDescription
van Dishoeck, E. F.0000-0001-7591-1907
Wilner, D. J.0000-0003-1526-7587
Blake, G. A.0000-0003-0787-1610
Additional Information:© 2010 EDP Sciences. Received: 19 August 2009; Accepted: 18 March 2010. We are indebted to Kees Dullemond for the use of his RADMC and RAYTRACE codes and to Stephen Bourke for help with AIPS. A special thanks to the ATNF and SMA staff for assistance with the observations. Ruud Visser’s help on all things computer is greatly appreciated and Carsten Dominik is thanked for his useful comments. Partial support for this work was provided by a Netherlands Research School For Astronomy network 2 grant, and by a Netherlands Organisation for Scientific Research Spinoza grant. C.M.W. acknowledges financial support from an ARC Australian Research Fellowship, Discovery Project DP0345227. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France.
Funding AgencyGrant Number
Nederlandse Onderzoekschool voor de Astronomie (NOVA)UNSPECIFIED
Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)UNSPECIFIED
Australian Research CouncilDP0345227
Subject Keywords:accretion, accretion disks; circumstellar matter; stars: pre-main sequence; stars: formation
Record Number:CaltechAUTHORS:20100818-103844238
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Official Citation:Grain growth across protoplanetary discs: 10 μm silicate feature versus millimetre slope D. J. P. Lommen, E. F. van Dishoeck, C. M. Wright, S. T. Maddison, M. Min, D. J. Wilner, D. M. Salter, H. J. van Langevelde, T. L. Bourke, R. F. J. van der Burg and G. A. Blake A&A 515 A77 (2010) DOI: 10.1051/0004-6361/200913150
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:19495
Deposited By: Jason Perez
Deposited On:18 Aug 2010 23:42
Last Modified:09 Mar 2020 13:19

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