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Published April 2016 | Published + Submitted
Journal Article Open

Multiwavelength analysis for interferometric (sub-)mm observations of protoplanetary disks: Radial constraints on the dust properties of protoplanetary disks


Context. The growth of dust grains from sub-μm to mm and cm sizes is the first step towards the formation of planetesimals. Theoretical models of grain growth predict that dust properties change as a function of disk radius, mass, age, and other physical conditions. High angular resolution observations at several (sub-)mm wavelengths constitute the ideal tool with which to directly probe the bulk of dust grains and to investigate the radial distribution of their properties. Aims. We lay down the methodology for a multiwavelength analysis of (sub-)mm and cm continuum interferometric observations to self-consistently constrain the disk structure and the radial variation of the dust properties. The computational architecture is massively parallel and highly modular. Methods. The analysis is based on the simultaneous fit in the uv-plane of observations at several wavelengths with a model for the disk thermal emission and for the dust opacity. The observed flux density at the different wavelengths is fitted by posing constraints on the disk structure and on the radial variation of the grain size distribution. Results. We apply the analysis to observations of three protoplanetary disks (AS 209, FT Tau, DR Tau) for which a combination of spatially resolved observations in the range ~0.88 mm to ~10 mm is available from SMA, CARMA, and VLA. In these disks we find evidence of a decrease in the maximum dust grain size, a_(max), with radius. We derive large a_(max) values up to 1 cm in the inner disk 15 AU ≤ R ≤ 30 AU and smaller grains with a_(max) ~ 1 mm in the outer disk (R ≳ 80 AU). Our analysis of the AS 209 protoplanetary disk confirms previous literature results showing amax decreasing with radius. Conclusions. Theoretical studies of planetary formation through grain growth are plagued by the lack of direct information on the radial distribution of the dust grain size. In this paper we develop a multiwavelength analysis that will allow this missing quantity to be constrained for statistically relevant samples of disks and to investigate possible correlations with disk or stellar parameters.

Additional Information

© 2016 ESO. Received 22 September 2015. Accepted 16 December 2015. M.T. and L.T. acknowledge support by the DFG cluster of excellence Origin and Structure of the Universe (http://www.universe-cluster.de). A.I. acknowledges support from the NSF award AST-1109334/1535809 and from the NASA Origins of Solar Systems program through the award number NNX14AD26G. The fits have been carried out on the computing facilities of the Computational Center for Particle and Astrophysics (C2PAP) as part of the approved project "Dust evolution in protoplanetary disks". M.T. and L.T. are grateful for the experienced support from F. Beaujean (C2PAP). M.T. thanks I. Jimenez-Serra, P. Papadopoulos, C. Manara and L. Loreta for the precious support throughout this work. Figures have been generated using the Python-based matplotlib package (Hunter 2007). Staircase plots of PDFs have been generated with a user-modified version of the Pythonbased triangle package (Foreman-Mackey et al. 2014). Plots of the residuals have been generated with APLpy, an open-source plotting package for Python hosted at http://aplpy.github.com. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France. This work was partly supported by the Italian Ministero dell´ Istruzione, Università e Ricerca through the grant Progetti Premiali 2012 – iALMA (CUP 52I13000140001).

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