Invited review abstract

NGC 6823 is a young open cluster that lies at a distance of ~2 kpc in the Vulpecula OB1 association. Previous studies using CCD photometry and spectroscopy have identified a trapezium system of bright O- and B-type stars at its center, along with some 100 massive O- B- and A-type stars in the cluster. We present deep optical VRI and near-infrared JHK observations, complemented with Spitzer/IRAC observations, with an aim to identify the young low-mass population as well as the disk candidates in this region. The cluster shows variable extinction, with Av ranging between ~2 and 20 magnitude. After applying an extensive selection criteria in order to correct for field star contamination, our final candidate member sample consists of 177 young stellar objects (YSOs), with a mean Av~3 mag. A 62% fraction of these are Class II systems, 4% are Class I/Flat systems, while 34% are Class III/photospheric sources. Our survey reaches down to I~21 mag. We have constructed the initial mass function (IMF) of the cluster from ~1.5 Msun down to ~0.05 Msun. The IMF shows a rise towards lower masses, with a peak at masses between 0.08 and 0.1 Msun. The age distribution for NGC 6823 shows accelerated star formation activity in the last ~1 Myr, with a large ~87% fraction of candidate members lying at ages of ~0.1-1 Myr. This young population is also the less massive in the cluster (<0.6 Msun). We discuss the possibility that the formation of this new generation of young low-mass stars may have been triggered by the massive stars in the cluster.