Disk Evolution in OB Associations - Deep Spitzer/IRAC Observations of IC 1795

TL;DR

This study uses deep Spitzer and Chandra observations to analyze protoplanetary disk evolution in the OB association IC 1795, revealing mass-dependent disk dissipation timescales over a 3-5 million-year period.

Contribution

First to compute pre-main sequence isochrones in Spitzer/IRAC colors and analyze disk evolution in IC 1795 with combined infrared and X-ray data.

Findings

Disk fraction decreases with increasing stellar mass.

No spatial variation in disk presence near O-type stars.

Cluster age estimated at 3-5 million years.

Abstract

We present a deep Spitzer/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/ACIS 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 1 Msun. 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 >2 Msun have a disk fraction of ~20%, while lower mass objects (2-0.8 Msun) have a disk fraction of ~50%. This implies that disks around massive stars have a shorter dissipation timescale.