Debris Disks in NGC 2547

Abstract

We have surveyed the 30Myr old cluster NGC 2547 for planetary debris disks using Spitzer.At 4.5Y8 mwe are sensitive to the photospheric level down to mid-M stars (0.2M), and at 24 mto earlyGstars (1.2M).We find only two to four stars with excesses at 8 mout of 400Y500 cluster members, resulting in an excess fractionP1%at this wavelength. By contrast, the excess fraction at 24 mis 40% (for BYF types). Out of four late-type stars with excesses at 8 mtwo marginal ones are consistent with asteroid-like debris disks. Among starswith strong 8 mex- cesses one is possibly from a transitional disk, while another one can be a result of a catastrophic collision. Our survey demonstrates that the inner 0.1Y1 AU parts of disks around solar-type stars clear out very thoroughly by 30 Myr of age.Comparingwith themuch slower decay of excesses at 24 and 70m, disks clear from the inside out, of order 10 Myr for the inner zones probed at 8 m, compared with 100 or more megayears for those probed with the two longer wavelengths.