The frequency of accretion disks around single stars: Chamaeleon I

TL;DR

This study investigates the frequency of ongoing accretion disks around single stars in the Chamaeleon I region, finding a significantly higher accretor fraction compared to close binary systems, which impacts understanding of disk evolution and planet formation.

Contribution

It provides the first robust comparison of accretion disk presence between single stars and binaries in Chamaeleon I, accounting for undetected multiplicity and sensitivity biases.

Findings

39.5% of single stars show Brγ emission indicating accretion

Close binaries (<100 AU) have only 6.5% accretor fraction

Single stars have an inferred accretor fraction of about 48%

Abstract

It is well known that stellar companions can influence the evolution of a protoplanetary disk. Nevertheless, previous disk surveys did not - and could not - consistently exclude binaries from their samples. We present a study dedicated to investigating the frequency of ongoing disk accretion around single stars in a star-forming region. We obtained near-infrared spectroscopy of 54 low-mass stars selected from a high-angular resolution survey in the 2-3 Myr-old Chamaeleon I region to determine the presence of Brackett-$\gamma$ emission, taking the residual chance of undetected multiplicity into account, which we estimate to be on the order of 30%. The result is compared with previous surveys of the same feature in binary stars of the same region to provide a robust estimate of the difference between the accretor fractions of single stars and individual components of binary systems. We find Br$\gamma$ emission among $39.5^{+14.0}_{-9.9}$% of single stars, which is a significantly higher fraction than for binary stars in Chamaeleon I. In particular, close binary systems with separations <100 AU show emission in only $6.5^{+16.5}_{-3.0}$% of the cases according to the same analysis. The emitter frequency of wider binaries appears consistent with the single star value. Interpreting Br$\gamma$ emission as a sign of ongoing accretion and correcting for sensitivity bias, we infer an accretor fraction of single stars of F_acc=$47.8^{+14.0}_{-9.9}$%. This is slightly higher but consistent with previous estimates that do not clearly exclude binaries from their samples. Through our robust and consistent analysis, we confirm that the fraction of young single stars harboring accretion disks is much larger than that of close binaries at the same age. Our findings have important implications for the timescales of disk evolution and planet formation.