Research:
My main research interest is related to the studies of young massive clusters.
Young star clusters are numerously formed in interacting/merging galaxies and (more generally speaking) in starburst galaxies. Due to their properties (masses, radii, stellar content) at least a fraction of them is expected to be long-lived and to evolve into the counterparts of the genuinely old globular clusters. Therefore by determining the ages of star clusters one can study the star formation history (in particular the violently starforming episodes) of the clusters' host galaxy.
A star cluster forms by the collapse of a giant molecular gas cloud. Therefore all stars in a star cluster have essentially the same properties, except that their initial masses are distributed according to a well-constrained initial mass function (generally speaking,there are less high-mass stars as compared to low-mass stars). Models of star clusters are therefore significantly simpler than equivalent models of galaxies as a whole, making the interpretation of observations more straightforward and reliable.

My particular interests are:

• spectrophotometric modelling of star clusters, by maintaining and expanding the GALEV code (link: http://www.astro.physik.uni-goettingen.de/~galev ).
• techniques and caveats in star cluster modelling and in the analysis of star cluster observations
• the dynamical evolution of star clusters using N-body simulations, in particular to improve spectrophotometric models of star clusters
• the determination of physical cluster parameters from observations, to study the evolution of individual galaxies

Two galaxies for which I have studied their star cluster systems in detail so far are:
- NGC 1569, a nearby dwarf starburst galaxy, harbouring 2 very prominent young and massive star clusters plus a sample of fainter clusters (approx. 160 clusters in total). The majority of the clusters were formed in the past few tens Myrs, during the recent, now declining burst of star formation. Although the 2 prominent star clusters clearly stand out in terms of luminosity, other clusters are only little inferior in terms of mass (but older and/or more extincted and therefore less luminous). A picture of NGC1569.
- NGC 4038/39, the ``Antennae galaxies'', the nearest ongoing merger of two gas-rich spiral galaxies. This merger triggered a strong burst in star and star cluster formation. This burst started relatively recent (several tens - few hundreds Myrs), and the peak in star formation activity is still to come during the next close encounter of the galaxies' nuclei, according to dynamical simulations. We find the young star clusters in the Antennae galaxies to be different from the young star clusters in the Local Group, with properties already resembling those of old globular clusters rather than those of local young clusters. A picture of Antennae galaxies.

Relevant collaborations:

• Fritze -- v. Alvensleben (Goettingen & Hatfield)
• de Grijs (Sheffield)
• Portegies Zwart (Amsterdam)
• Baumgardt (Bonn)