• Stellar populations, massive star feedback, and triggered star formation in OB associations:

  I lead a long-term project to explore the full stellar population of the Upper Scorpius OB Association, the most nearby region of recent massive star formation. Following large multi-object spectroscopic surveys to identify a representative sample of low-mass members, our studies of the mass function and the age distribution of the members allowed a rather detailed reconstruction of the star formation process of this association. The results suggest that the star formation process in Upper Sco was triggered, most likely by the shock-wave of an expanding supernova- and wind-driven superbubble from the nearby Upper Centaurus Lupus association. I will soon start a new project (funded in the context of the DFG Priority Program 1573: Physics of the Interstellar Medium) in which we will study the interaction of the winds and ionizing radiation of the massive stars with the surrounding interstellar medium in detail.
  The largest current project is our multi-wavelength investigation of the Carina Nebula.

  Relevant publications: A5, A2, A1, B78, B77, B75, B74, B71, B70, B69, B29, B22, B16, B12, C29; several presentations are also available.

  

• X-ray studies of Young Stellar Objects:

  Young stars generally show very strong X-ray emission. A good knowledge of the X-ray properties of YSOs is of paramount importance not only for the understanding of the physical mechanisms that lead to the X-ray emission and their relation to the magnetic activity; the X-ray irradiation of protoplanetary disks has also far-reaching implications for the formation of planetary systems, and the evolution of protoplanetary atmospheres. Furthermore, since X-ray radiation is much less affected by extinction than optical light, X-ray observations can penetrate up to AV ~ 500 mag into dark clouds and allow a deep look at embedded YSOs. Since X-ray activity is particularly effective in discriminating YSOs from unrelated fore- and background field stars, X-ray studies are also a very important tool for the investigation of the stellar populations of star-forming regions.
  I have performed numerous X-ray observations of young stellar clusters (in particular IC 348, NGC 1333, and the Serpens dark cloud) and investigated the flares and X-ray spectra of YSOs. I have been deeply involved in the Chandra Orion Ultradeep Project (COUP), a unique 10-day long observation of the Orion Nebula Cluster, provided the most comprehensive dataset ever acquired on the X-ray emission of young stars. A recent large X-ray project where I am deeply involved is the Chandra Carina Complex Project.
  Together with Maria Massi I organized the conference "Coronae of Stars and Accretion Disks" that was held at the Bonn in December 2006.

  Relevant publications: A3, B80, B77, B76, B75, B74, B73, B72, B69, B63, B60, B59, B53, B51, B50, B49, B48, B47, B46, B42, B40, B36, B33, B32, B27, B24, B17, B15, B14, B13, B11, B10, B8, B7, B6, B3, B2; several presentations are also available.

  

• Infrared Interferometry of Young Stellar Objects:

  Speckle Interferometry allows to overcome the image blurring effect of the earth atmosphere and to obtain images with diffraction-limited resolution, which is much better (e.g. 0.04 arcsec at 1 micron with a 6-m telescope) than the typical seeing-limited resolution of about 1 arcsec of conventional images. Long-baseline Interferometry combines the light of several telescopes and can provide even higher spatial resolution. For example, at its longest baseline, the ESO VLTI reaches an angular resolution of 0.001 arcsec at 1 micron. This translates to linear dimensions of less than 0.2 AU at the distance of nearby YSOs. These observations allow, for the first time, to directly study the formation region of terrestrial planets in protoplanetary disks, the way in which protostellar jets and outflows are launched and collimated, and to resolve close multiple systems.
  Relevant publications: B81, B68, B66, B64, B62, B61, B58, B57, B56, B55, B54, B52, B45, B44, B43, B41, B39, B38, B37, B34, B31, B30, B28, B26, B25, B21, B20, B19; several presentations are also available.

Here is a (recently updated) collection of some of my X-ray images and infrared images of star forming regions.

A growing number of new X-ray, infrared, and sub-mm images of the Carina Nebula Complex is available since March 2011 on the webpage describing our Carina Multiwavelength Project.