Stellar multiplicity affects the correlation between protoplanetary disc masses and accretion rates: binaries explain high accretors in Upper Sco

Monthly Notices of the Royal Astronomical Society, vol. 512, pp. 3538–3550

Abstract

ABSTRACT In recent years, a correlation between mass accretion rates onto new-born stars and their protoplanetary disc masses was detected in nearby young star-forming regions. Although such a correlation can be interpreted as due to viscous-diffusion processes in the disc, highly accreting sources with low disc masses in more evolved regions remain puzzling. In this paper, we hypothesize that the presence of a stellar companion truncating the disc can explain these outliers. First, we searched the literature for information on stellar multiplicity in Lupus, Chamaeleon I, and Upper Sco, finding that roughly 20 per cent of the discs involved in the correlation are in binaries or higher order multiple stellar systems. We prove with high statistical significance that at any disc mass these sources have systematically higher accretion rates than those in single-stars, with the bulk of the binary population being clustered around $M_\mathrm{disc}/\dot{M}_\mathrm{acc}\approx 0.1\, \mathrm{Myr}$. We then run coupled gas and dust one-dimensional evolutionary models of tidally truncated discs to be compared with the data. We find that these models are able to reproduce well most of the population of observed discs in Lupus and Upper Sco, even though the unknown eccentricity of each binary prevents an object by object comparison. In the latter region, the agreement improves if the grain coagulation efficiency is reduced, as may be expected in discs around close binaries. Finally, we mention that thermal winds and sub-structures can be important in explaining few outlying sources.

Authors 4

1. Francesco Zagaria corresponding

   University of Cambridge

   Affiliation as printed

   Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK

2. Cathie J. Clarke

   University of Cambridge

   Affiliation as printed

   Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK

3. Giovanni P. Rosotti Aachen Leiden Observatory

   Leiden University · University of Leicester · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, PO Box 9513, NL-2300 RA Leiden, the Netherlands

   School of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK

4. Carlo Felice Manara

   European Southern Observatory

   Affiliation as printed

   European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching bei München, Germany