AAS 201st Meeting, January, 2003
Session 20. Star Formation I
Poster, Monday, January 6, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[20.05] Evidence for Disk Clearing in Young Triple Star Systems

R. J. White, L. Hillenbrand, S. Metchev, J. Patience ()

We present high spatial resolution near-infrared observations of the young star AS 353 obtained with the Palomar Adaptive Optics system (PALAO) on the Palomar 200-inch telescope. AS 353 is a well known T Tauri binary (separation 5".7) that is somewhat peculiar because the primary is accreting but the secondary is not; "mixed-pairs" such as this are uncommon among T Tauri binaries. The new observations reveal that the non-accreting secondary is itself a 0".25 binary of nearly equal brightness, making AS 353 a triple star system. Dynamical disruption of the disk(s) by a close companion is a possible explanation for the early termination of secondary's accretion. We investigate this possibility further by studying 11 other spatially resolved hierarchical triples, like AS 353, in which at least one component of the wide pair shows signs of accretion. Two-thirds of these systems (8/12) are mixed pairs, a fraction that is considerably higher than the fraction of mixed pairs found for T Tauri binaries. Furthermore, for the 8 mixed hierarchical triples, the close binary is always the non-accreting component. Although the effects of close companions on disk accretion have been previously investigated by comparing the fractions of accreting T Tauri singles versus accreting T Tauri binaries, these studies showed no convincing evidence for a companion's influence. The results here demonstrate that when the age and local environmental influences are held fixed by studying triple star systems, a close binary terminates its accretion before a more isolated star does.

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