Multiwavelength analysis for interferometric (sub-)mm observations of protoplanetary disks

Radial constraints on the dust properties and the disk structure

¹ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
e-mail: mtazzari@eso.org
² Excellence Cluster Universe, Boltzmannstr. 2, 85748 Garching, Germany
³ INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁴ Universitats-Sternwarte München, Scheinerstraße 1, 81679 München, Germany
⁵ Dublin Institute for Advanced Studies, School of Cosmic Physics, 31 Fitzwilliam Place, Dublin 2, Ireland
⁶ Department of Physics and Astronomy, Rice University, 6100 Main Street, Houston, TX, 77005, USA
⁷ National Radio Astronomy Observatory, PO Box O, Socorro, NM 87801, USA
⁸ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
⁹ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
¹⁰ Korea Astronomy and Space Science Institute, 776 Daedeok-daero, Yuseong-gu, 34055 Daejeon, Republic of Korea
¹¹ Joint ALMA Observatory (JAO), Av. Alonso de Cordova 3107, Vitacura, Santiago, Chile
¹² Institute for Theoretical Astrophysics, Heidelberg University, Albert-Ueberle-Strasse 2, 69120 Heidelberg, Germany
¹³ Department of Astronomy, California Institute of Technology, MC 249-17, Pasadena, CA 91125, USA
¹⁴ Department of Astronomy, University of Maryland, College Park, MD 20742, USA
¹⁵ Department of Astronomy, University of Michigan, 830 Dennison Building, 500 Church Street, Ann Arbor, MI 48109, USA
¹⁶ School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, KY16 9SS, UK
¹⁷ Jet Propulsion Laboratory, California Institute of Technology Pasadena, CA 91109, USA
¹⁸ The Netherlands Institute for Radio Astronomy (ASTRON), 7990 Dwingeloo, The Netherlands

Received: 22 September 2015
Accepted: 16 December 2015

Abstract

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 a_max 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.