DISK EVOLUTION IN OB ASSOCIATIONS: DEEP<i>SPITZER</i>/IRAC OBSERVATIONS OF IC 1795

Abstract

We present a deep Spitzer/IRAC survey of the OB association IC 1795 carried\nout to investigate the evolution of protoplanetary disks in regions of massive\nstar formation. Combining Spitzer/IRAC data with Chandra/ACIS observations, we\nfind 289 cluster members. An additional 340 sources with an infrared excess,\nbut without X-ray counterpart, are classified as cluster member candidates.\nBoth surveys are complete down to stellar masses of about 1 Msun. We present\npre-main sequence isochrones computed for the first time in the Spitzer/IRAC\ncolors. The age of the cluster, determined via the location of the Class III\nsources in the [3.6]-[4.5]/[3.6] color-magnitude diagram, is in the range of 3\n- 5 Myr. As theoretically expected, we do not find any systematic variation in\nthe spatial distribution of disks within 0.6 pc of either O-type star in the\nassociation. However, the disk fraction in IC 1795 does depend on the stellar\nmass: sources with masses &gt;2 Msun have a disk fraction of ~20%, while lower\nmass objects (2-0.8 Msun) have a disk fraction of ~50%. This implies that disks\naround massive stars have a shorter dissipation timescale.\n