  We present new results on how the presence of stellar companions affects disk
evolution based on a study of the 5-11 Myr old Upper Scorpius OB Association.
Of the 50 G0-M3 Upper Sco members with disks in our sample, only seven host a
stellar companion within 2" and brighter than K = 15, compared to 35 of 75
members without disks. This matches a trend seen in the 1-2 Myr old Taurus
region, where systems with a stellar companion within 40 au have a lower
fraction of infrared-identified disks than those without such companions,
indicating shorter disk lifetimes in close multiple systems. However, the
fractions of disk systems with a stellar companion within 40 au match in Upper
Sco and Taurus. Additionally, we see no difference in the millimeter
brightnesses of disks in Upper Sco systems with and without companions, in
contrast to Taurus where systems with a companion within 300 au are
significantly fainter than wider and single systems. These results suggest that
the effects of stellar companions on disk lifetimes occur within the first 1-2
Myr of disk evolution, after which companions play little further role. By
contrast, disks around single stars lose the millimeter-sized dust grains in
their outer regions between ages of 1-2 Myr and 5-11 Myr. The end result of
small dust disk sizes and faint millimeter luminosities is the same whether the
disk has been truncated by a companion or has evolved through internal
processes.
