SCYON Abstract

Received on October 13 2006

Correlation between the spatial distribution of the circumstellar disks and the massive stars in the open cluster NGC 6611

Authors	M.G. Guarcello, L. Prisinzano, G. Micela, F. Damiani, G. Peres, and S. Sciortino
Affiliation	Osservatorio Astronomico di Palermo
Accepted by	Astronomy & Astrophysics
Contact	mguarce@astropa.unipa.it
URL	http://astropa.unipa.it/~mguarce
Links	NGC 6611

Abstract

Context: the observations of young stars with circumstellar disks suggest that the disks are dissipated, starting from the inner region, by the radiation of the central star and eventually by the formation of rocky planetesimals, over a time scale of several million years. It was also shown that strong UV radiation emitted by nearby massive stars can heat a circumstellar disk up to some thousand degrees inducing the photoevaporation of the gas. This process strongly reduces the dissipation time scale. Aims: the aim of this work is to study if there exists a correlation between the spatial distribution of stars with circumstellar disks and the position of massive stars with spectral class earlier than B5, in the open cluster NGC 6611. Methods: for our purpose, we created a multiband catalog of the cluster, down to V∼23, using optical data from a WFI observation at 2.2m of ESO in the BVI bands, the 2MASS public point source catalog and an archival X-ray observation made with CHANDRA/ACIS. We selected the stars with infrared excess (due to the emission of a circumstellar disk) using suitable color indices independent from extinction, and studied their spatial distribution. Results: we found that the spatial distribution of the stars with K band excess (due to the presence of a circumstellar disk) is anti correlated with that of the massive stars: the disks are more frequent at large distances from these stars. We argue that this is in agreement with the hypothesis that the circumstellar disks are heated by the UV radiation from the massive stars and photoevaporated.