The formation of planets is directly linked to the evolution of the
circumstellar (CS) disk from which they are born. The dissipation timescales of
CS disks are, therefore, of direct astrophysical importance in evaluating the
time available for planet formation. We employ Spitzer Space Telescope spectra
to complete the CS disk census for the late-type members of the ~8 Myr-old eta
Chamaeleontis star cluster. Of the 15 K- and M-type members, eight show excess
emission. We find that the presence of a CS disk is anti-correlated with
binarity, with all but one disk associated with single stars. With nine single
stars in total, about 80% retain a CS disk. Of the six known or suspected close
binaries the only CS disk is associated with the primary of RECX 9. No
circumbinary disks have been detected. We also find that stars with disks are
slow rotators with surface values of specific angular momentum j = 2-15 j_sun.
All high specific angular momentum systems with j = 20-30 j_sun are confined to
the primary stars of binaries. This provides novel empirical evidence for
rotational disk locking and again demonstrates the much shorter disk lifetimes
in close binary systems compared to single star systems. We estimate the
characteristic mean disk dissipation timescale to be ~5 Myr and ~9 Myr for the
binary and single star systems, respectively.Comment: Accepted by ApJ