Physical properties of dusty protoplanetary disks in Lupus: evidence for viscous evolution?

¹ Institute of Astronomy, University of Cambridge, Madingley Road, CB3 0HA, Cambridge, UK
e-mail: mtazzari@ast.cam.ac.uk
² European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
e-mail: mtazzari@eso.org
³ Excellence Cluster Universe, Boltzmannstr. 2, 85748 Garching, Germany
⁴ INAF–Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁵ School of Cosmic Physics, Dublin Institute for Advanced Studies, 31 Fitzwilliams Place, 2 Dublin, Ireland
⁶ Institute for Astronomy, University of Hawaii at Manoa, 2680 Woodlawn dr., Honolulu, HI, 96822, USA
⁷ Joint ALMA Observatory, Av. Alonso de Córdova 3107, Vitacura, Santiago, Chile
⁸ Leiden Observatory, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
⁹ Scientific Support Office, Directorate of Science, European Space Research and Technology Centre (ESA/ESTEC), Keplerlaan 1, 2201AZ Noordwijk, The Netherlands
¹⁰ Max-Plank-Institut für Extraterrestrische Physik, Giessenbachstraße 1, 85748 Garching, Germany

Received: 29 March 2017
Accepted: 5 July 2017

Abstract

Context. The formation of planets strongly depends on the total amount as well as on the spatial distribution of solids in protoplanetary disks. Thanks to the improvements in resolution and sensitivity provided by ALMA, measurements of the surface density of mm-sized grains are now possible on large samples of disks. Such measurements provide statistical constraints that can be used to inform our understanding of the initial conditions of planet formation.

Aims. We aim to analyze spatially resolved observations of 36 protoplanetary disks in the Lupus star forming complex from our ALMA survey at 890 μm, aiming to determine physical properties such as the dust surface density, the disk mass and size, and to provide a constraint on the temperature profile.

Methods. We fit the observations directly in the uv-plane using a two-layer disk model that computes the 890 μm emission by solving the energy balance at each disk radius.

Results. For 22 out of 36 protoplanetary disks we derive robust estimates of their physical properties. The sample covers stellar masses between ~0.1 and ~ 2 M_⊙, and we find no trend in the relationship between the average disk temperatures and the stellar parameters. We find, instead, a correlation between the integrated sub-mm flux (a proxy for the disk mass) and the exponential cut-off radii (a proxy of the disk size) of the Lupus disks. Comparing these results with observations at similar angular resolution of Taurus-Auriga and Ophiuchus disks found in literature and scaling them to the same distance, we observe that the Lupus disks are generally fainter and larger at a high level of statistical significance. Considering the 1–2 Myr age difference between these regions, it is possible to tentatively explain the offset in the disk mass-size relation with viscous spreading, however with the current measurements other mechanisms cannot be ruled out.