Observational constraints on disc sizes in protoplanetary discs in multiple systems in the Taurus region. II. Gas disc sizes

TL;DR

This study uses high-resolution ALMA observations to analyze gas and dust disc sizes in multiple stellar systems in Taurus, revealing larger gas discs compared to dust discs and consistency with tidal truncation models.

Contribution

First uniform analysis of gas emission in protoplanetary discs around multiple systems, providing new insights into disc size ratios and truncation effects.

Findings

Gas discs are on average 4.2 times larger than dust discs in multiple systems.

No difference in flux ratio distribution when considering 68% flux radius.

Gas sizes align with tidal truncation models for typical binary eccentricities.

Abstract

The formation of multiple stellar systems is a natural by-product of the star-formation process, and its impact on the properties of protoplanetary discs and on the formation of planets is still to be fully understood. To date, no detailed uniform study of the gas emission from a sample of protoplanetary discs around multiple stellar systems has been performed. Here we analyse new ALMA observations at a $\sim$21 au resolution of the molecular CO gas emission targeting discs in eight multiple stellar systems in the Taurus star-forming regions. $^{12}$CO gas emission is detected around all primaries and in seven companions. With these data, we estimate the inclination and the position angle for all primary discs and for five secondary or tertiary discs, and measure the gas disc radii of these objects with a cumulative flux technique on the spatially resolved zeroth moment images. When considering the radius including 95\% of the flux as a metric, the estimated gas disc size in multiple stellar systems is found to be on average $\sim 4.2$ times larger than the dust disc size. This ratio is higher than what was recently found in a population of more isolated and single systems. On the contrary, when considering the radius including 68\% of the flux, no difference between multiple and single discs is found in the distribution of ratios. This discrepancy is due to the sharp truncation of the outer dusty disc observed in multiple stellar systems. The measured gas disc sizes are consistent with tidal truncation models in multiple stellar systems assuming eccentricities of $\sim0.15$-$0.5$, as expected in typical binary systems.