Specific Star Forming Regions -- Oral Presentation
The low-mass star and disk populations in NGC 6611
Joana Oliveira, Keele University, UK
The aim of our observational program is to find empirical
answers to two major questions. Do regions of high-mass star formation
also produce lots of solar- and low-mass stars, i.e. is the low-mass IMF
unaffected by high-mass siblings? Can low-mass stars in hostile environments
retain circumstellar disks? We present results of our survey of NGC
6611, a massive cluster with an age of approximately 2 Myr which is
currently ionizing the Eagle nebula. This cluster contains a dozen
O-stars that emit 10 times more ionizing radiation than the Trapezium,
providing a challenging environment for their lower-mass siblings. Our
dataset consists of wide field optical and near infrared imaging,
intermediate resolution spectroscopy (ESO-VLT) and deep L-band photometry.
We have photometrically selected solar- and low-mass stars, placed them
on the HR diagram and determined the IMF over an area sufficient to deal
with mass segregation. We show that the IMF in NGC6611 is similar to
that of the Orion Nebula Cluster down to 0.5Msun. Using K-L indices we
search for colour excesses that betray the presence of circumstellar
material and study what fraction of solar-mass stars still possess disks
as a function of age and proximity to the massive stars. By comparing
the disk frequency in NGC6611 with similarly aged but quieter regions,
we find no evidence that the harsher environment of NGC6611 significantly
hastens disk dissipation. Apparently the massive stars in NGC6611 have
no global effect on the probability of low-mass star formation or disk
retention. We have an approved HST program that will allows us to
investigate the very low-mass and brown dwarf populations in NGC6611.
And we complement our IR imaging with Spitzer/ORAC data, extending the
area of our ground-based survey.