Primordial Circumstellar Disks in Binary Systems: Evidence for Reduced Lifetimes

Abstract

We combine the results from several multiplicity surveys of pre-main-sequence stars located in four nearby star-forming regions with Spitzer data from three different Legacy Projects. This allows us to construct a sample of 349 targets, including 125 binaries, which we use to to investigate the effect of companions on the evolution of circumstellar disks. We find that the distribution of projected separations of systems with Spitzer excesses is significantly different (P ∼ 2.4e-5, according to the KS test for binaries with separations < 400 AU) from that of systems lacking evidence for a disk. As expected, systems with projected separations < 40 AU are half as likely to retain at least one disk than are systems with projected separations in the 40-400 AU range. These results represent the first statistically significant evidence for a correlation between binary separation and the presence of an inner disk (r ∼ 1 AU). Several factors (e.g., the incompleteness of the census of close binaries, the use of unresolved disk indicators, and projection effects) have previously masked this correlation in smaller samples. We discuss the implications of our findings for circumstellar disk lifetimes and the formation of planets in multiple systems.

Searching for Spectroscopic Binaries Within Transition Disk Objects*

“…Cieza et al (2009), like Ratzka et al (2005, found no evidence for multiplicity. C10 identified the system as a TD and determined it to be a K7-type star, in agreement with our measurements above.…”

“…However, several studies (Ghez et al 1997;White & Ghez 2001;Cieza et al 2009;Duchêne 2010;Kraus et al 2012) have found protoplanetary disk fractions are lower for young ( 5 Myr) binary systems with a<50 au than for single stars or wider binaries. With the exception of Kraus et al (2012), these studies were not sensitive to the tight binary systems to which our study was especially sensitive.…”

Study of infrared excess from circumstellar disks in binaries with Spitzer/IRAC

“…Binaries with separations closer than ∼40 AU show a lower frequency of infrared excess compared with single or wide binary sources (e.g., Monin et al 2007;Cieza et al 2009;Kraus et al 2012). This suggests that these triples and quadruples should have a higher fraction of mixed pairs.…”

“…Because the close components should exhibit rapid disk clearing (Monin et 4 al. 2007;Cieza et al 2009;Kraus et al 2012), whether this parameter affects our discussion or not is explored in later sections. Binarity in these systems, especially those that are widely separated, has yet to be confirmed by multi-epoch astrometry; therefore, many of these systems are candidates of binaries.…”

“…Cieza et al (2009) showed that the lifetime of circumstellar disks in binary systems was significantly shorter at separations of 40 AU and below compared to disks of single stars. They investigated infrared excess from binaries in four nearby star-forming regions (∼1-3 Myr) using the [3.6] − [8.0] color obtained with Spitzer/IRAC without resolving the individual stellar components.…”