We present a deep Spitzer/Infrared Array Camera (IRAC) survey of the OB association IC 1795 carried out to investigate the evolution of protoplanetary disks in regions of massive star formation. Combining Spitzer/IRAC data with Chandra/Advanced CCD Imaging Spectrometer observations, we find 289 cluster members. An additional 340 sources with an infrared excess, but without X-ray counterpart, are classified as cluster member candidates. Both surveys are complete down to stellar masses of about 1M(circle dot). We present pre-main-sequence isochrones computed for the first time in the Spitzer/IRAC colors. The age of the cluster, determined via the location of the Class III sources in the [3.6]-[4.5]/[3.6] color-magnitude diagram, is in the range of 3-5 Myr. As theoretically expected, we do not find any systematic variation in the spatial distribution of disks within 0.6 pc of either O-type star in the association. However, the disk fraction in IC 1795 does depend on the stellar mass: sources with masses >2M(circle dot) have a disk fraction of similar to 20%, while lower mass objects (2-0.8M(circle dot)) have a disk fraction of similar to 50%. This implies that disks around massive stars have a shorter dissipation timescale.
- ISM: individual objects (W3) open clusters and associations: individual (W3 IC1795) protoplanetary disks stars: formation stars: pre-main sequence X-rays: stars ORION-NEBULA-CLUSTER STAR-FORMING REGION ETA-CHAMAELEONTIS CLUSTER INFRARED ARRAY CAMERA MAIN-SEQUENCE STARS YOUNG STELLAR CLUSTER INITIAL MASS FUNCTION SPACE-TELESCOPE CIRCUMSTELLAR DISKS PROTOPLANETARY DISK