Related papers: Clustered star formation towards Berkeley 87 / ON2…
We describe a first attempt to apply adaptive optics to the study of resolved stellar populations in galaxies. Advantages over traditional approaches are (i) improved spatial resolution and point-source sensitivity through adaptive optics,…
The most massive star clusters include several generations of stars with a different chemical composition (mainly revealed by an Na-O anti-correlation) while low-mass star clusters appear to be chemically homogeneous. We are investigating…
We present the results of a study of young unresolved stellar groupings (clusters, OB associations, and their complexes) associated with HII regions, based on the coupling of spectroscopic, photometric and H{\alpha} spectrophotometric…
The large majority of extragalactic star cluster studies done to date have essentially used two or three-passband aperture photometry, combined with theoretical stellar population synthesis models, to obtain age estimates. The accuracy to…
After leaving the main sequence, massive stars undergo complex evolution, still poorly understood. With a population of 100s OB stars, the starburst cluster Westerlund~1 offers an unparallelled environment to study their evolutionary…
The morphology and stellar content of the Cygnus OB2 association has been determined using 2MASS infrared observations in the J, H, and K bands. The analysis reveals a spherically symmetric association of 2 deg in diameter with a half light…
Studies of star formation rely heavily on observations in the near-infrared, but they typically need information from other wavelengths for interpretation. We show that we can infer distances and estimate the membership of young stellar…
Galaxy clusters identified with optical imaging tend to suffer from projection effects, which impact richness (the number of member galaxies in a cluster) and lensing coherently. Physically unassociated galaxies can be mistaken as cluster…
(ABRIDGED) We assess the systematic uncertainties in (young) cluster age, mass, and - to a lesser extent - extinction and metallicity determinations, based on broad-band imaging observations with the Hubble Space Telescope. Our aim here is…
We present adaptive optics (AO) near-infrared (JHKs) observations of the deeply embedded massive cluster RCW 38 using NACO on the VLT. Narrowband AO observations centered at wavelengths of 1.28, 2.12, and 2.17 micron were also obtained. The…
The details of bulge formation via collapse, mergers, secular processes or their interplay remain unresolved. To start answering this question and quantify the importance of distinct mechanisms, we mapped a sample of three galactic bulges…
The formation of stars in massive clusters is one of the main modes of the star formation process. However, the study of massive star forming regions is hampered by their typically large distances to the Sun. One exception to this is the…
The formation, properties, and evolution of massive stars remain subject to considerable uncertainty; impacting on fields as diverse as galactic feedback and the nature of the progenitors of both electromagnetic and gravitational wave…
The past two decades have seen dramatic progress in our knowledge of the population of young stars of age <200 Myr that lie within 150 pc of the Sun. These nearby, young stars, most of which are found in loose, comoving groups, provide the…
We present new results concerning the sub-stellar binary population in the Orion Nebula Cluster (ONC). Using the Karhunen-Lo\`{e}ve Image Projection (KLIP) algorithm, we have reprocessed images taken with the IR channel of the Wide Field…
The Orion OB1 Association, at a distance of roughly 400 pc and spanning over ~200 deg^2 on the sky, is one of the largest and nearest OB associations. With a wide range of ages and environmental conditions, Orion is an ideal laboratory for…
Traditional studies of stellar clusters in external galaxies use surface photometry and therefore focus on systems that are still bright and compact enough to be separated from the stellar background. Consequently, the latter stages of…
The integrated properties of young star clusters are subject to large cluster-to-cluster variations because they depend directly on small numbers of bright stars. At ages at which red supergiants are expected to exist, these luminous but…
The compact association Cygnus OB2 is known to contain a large population of massive stars, but its total mass is currently a matter of debate. While recent surveys have uncovered large numbers of OB stars in the area around Cyg OB2,…
We present the results of a high-resolution X-ray imaging study of the stellar population in the Galactic massive star-forming region RCW49 and its central OB association Westerlund 2. We obtained a 40 ks X-ray image of a 17'x17' field…