<i>Spitzer</i>Observations of IC 348: The Disk Population at 2-3 Million Years

Abstract

We present near and mid-infrared photometry obtained with the Spitzer Space\nTelescope of 300 known members of the IC348 cluster. We merge this photometry\nwith existing ground-based optical and near-infrared photometry in order to\nconstruct optical-infrared spectral energy distributions (SEDs) for all the\ncluster members and present a complete atlas of these SEDs. We employ these\nobservations to both investigate the frequency and nature of the circumstellar\ndisk population in the cluster. The observations are sufficiently sensitive to\nenable the first detailed measurement of the disk frequency for very low mass\nstars at the peak of the stellar IMF. Using measurements of infrared excess\nbetween 3.6 and 8 microns we find the total frequency of disk-bearing stars in\nthe cluster to be 50 +/- 6%. However, only 30 +/- 4% of the member stars are\nsurrounded by optically thick, primordial disks, while the remaining\ndisk-bearing stars are surrounded by what appear to be optically thin,anemic\ndisks. The disk fraction appears to be a function of spectral type and stellar\nmass. The disk longevity and thus conditions for planet formation appear to be\nmost favorable for stars which are of comparable mass to the sun. The optically\nthick disks around later type (&gt; M4) stars appear to be less flared than the\ndisks around earlier type stars. This may indicate a greater degree of dust\nsettling and a more advanced evolutionary state for the late M disk population.\nFinally we find that the presence of an optically thick dust disk is correlated\nwith gaseous accretion as measured by the strength of Halpha emission. These\nresults suggest that it is more likely for dust disks to persist in the absence\nof active gaseous accretion than for active accretion to persist in the absence\nof dusty disks.\n