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

Abstract

In recent years a correlation between mass accretion rates onto new-born stars and their proto-planetary 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 hypothesise that the presence of a stellar companion truncating the disc can explain these outliers. Firstly, 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 disc / 𝑀 acc ≈ 0.1 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.

GIARPS High-resolution Observations of T Tauri stars (GHOsT)

“…This can be explained by the fact that disks in multiple stars are subject to tidal truncation which increase the grain radial drift and reduce the disk lifetime. In our sample we have found two distinct distributions in the Ṁacc − M dust,disk plane between single and multiple sources, an evidence that can be compatible with the scenario described in Zagaria et al (2022).…”

“…In conclusion, the large spread observed in the Ṁacc − M dust,disk plane can be partially due to source multiplicity, as found in Zagaria et al (2022). However, it might also be due to systematics in the computation of M dust,disk stemming from the adoption of the same dust opacity for the all three disk categories.…”

“…In addition, a recent work of Zagaria et al (2022) found that binaries or high-order multiple star systems present higher values of Ṁacc , compared with single stars at a given M disk , for the SFR populations of Lupus, Chamaeleon I and Upper Scorpius. This can be explained by the fact that disks in multiple stars are subject to tidal truncation which increase the grain radial drift and reduce the disk lifetime.…”

“…Lynden-Bell & Pringle 1974), the observed high dispersion suggests a more complex scenario for disk evolution, in which MHD winds, external photo-evaporation and local dust processing may play a crucial role (e.g., Manara et al 2022, and references therein). In addition, recent works have pointed out that stellar multiplicity can be another ingredient at the basis of the high accretion observed in some sources (Zagaria et al 2022).…”