Observations of IC348: The Disk Population at 2-3 Million Years

摘要

We present near and mid-infrared photometry obtained with the Spitzer SpaceTelescope of 300 known members of the IC348 cluster. We merge this photometrywith existing ground-based optical and near-infrared photometry in order toconstruct optical-infrared spectral energy distributions (SEDs) for all thecluster members and present a complete atlas of these SEDs. We employ theseobservations to both investigate the frequency and nature of the circumstellardisk population in the cluster. The observations are sufficiently sensitive toenable the first detailed measurement of the disk frequency for very low massstars at the peak of the stellar IMF. Using measurements of infrared excessbetween 3.6 and 8 microns we find the total frequency of disk-bearing stars inthe cluster to be 50 +/- 6%. However, only 30 +/- 4% of the member stars aresurrounded by optically thick, primordial disks, while the remainingdisk-bearing stars are surrounded by what appear to be optically thin,anemicdisks. The disk fraction appears to be a function of spectral type and stellarmass. The disk longevity and thus conditions for planet formation appear to bemost favorable for stars which are of comparable mass to the sun. The opticallythick disks around later type (> M4) stars appear to be less flared than thedisks around earlier type stars. This may indicate a greater degree of dustsettling and a more advanced evolutionary state for the late M disk population.Finally we find that the presence of an optically thick dust disk is correlatedwith gaseous accretion as measured by the strength of Halpha emission. Theseresults suggest that it is more likely for dust disks to persist in the absenceof active gaseous accretion than for active accretion to persist in the absenceof dusty disks.