The frequency of accretion disks around single stars: Chamaeleon I

Abstract

Context. 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. Aims. We present a study dedicated to investigating the frequency of ongoing disk accretion around single stars in a star-forming region. Methods. We obtained near-infrared spectroscopy of 54 low-mass stars selected from a high-angular resolution survey in the 2-3 Myrold Chamaeleon I region to determine the presence of Brackett-γ 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. Results. We find Brγ 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 Brγ 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. Conclusions. 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.

Protoplanetary Disk Evolution: Singles vs. Binaries

“…The single star accretor fraction appears to be slightly larger but consistent with both wide binaries and the decay curve found by previous surveys without binary correction (e.g., Fedele et al 2010). In particular, our new measurement of the single star accretor fraction is less than 1σ larger than previous estimates of the accretion frequency in Chamaeleon I (∼41%, based on Damjanov et al 2007). The data disfavor a scenario where all stars retain their disks until 2-3 Myr (Alexander & Armitage 2009).…”

“…Disk frequency of single stars and components of binary stars in the Orion Nebula Cluster (1 Myr) and Chamaeleon I (2 Myr). Left: accretion inferred from Brackett-γ emission.Right: hot circumstellar dust as inferred from H-K and K-L ′ excess(Daemgen et al 2012(Daemgen et al , 2013(Daemgen et al , 2015. The blue continuous and dotted lines show exponential decay functions measured byFedele et al (2010, τaccr ∼ 2.3 Myr, τ dust ∼ 3 Myr), not corrected for undetected multiplicity.…”

Globules and pillars in Cygnus X

“…The high Class I-to-Class II ratio together with the absence of a significant Class III population suggests that the age of the cluster is much shorter than typical disk dispersal timescales. The latter are suspected to depend on the central object's mass, the stellar density of the environment (Luhman et al 2010) and binarity (Daemgen et al 2016), but disk lifetimes of 1-3 Myr appear to be typical, both on a theoretical and an observational basis (e.g., Li & Xiao 2016). The duration of the Class I phase has been traditionally estimated by comparing the relative number of Class I to Class II YSOs in star-forming regions under the assumption of a constant star-formation rate (Evans et al 2009), but recent work based on detailed observations and modelling of the accretion on the central object have challenged an evolutionary picture in which the circumstellar envelope steadily disperses until the Class I/II transition takes place, suggesting instead that Class I objects may reach ages comparable to those of T Tauri stars, up to 1 Myr and older (White et al 2007, and references therein).…”

Understanding discs in binary YSOs – detailed modelling of VV CrA

“…Furthermore, studying coeval systems could yield new constraints for models of planet formation. For example, stars in multiple systems are less likely to be observed to have a disc at any age when compared with single stars (Cieza et al 2009;Daemgen et al 2013Daemgen et al , 2015, yet planets have been detected in a variety of multiple systems (e.g. Doyle et al 2011;Roell et al 2012).…”