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We perform, analyze, and interpret
observations of individual young stars and whole star forming
regions at optical, infrared, X-ray, and sub-mm wavelengths.
The main areas of research
are currently:
Stellar Populations and Triggered Star
Formation in OB Associations |
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We have performed a comprehensive investigation of the
Upper Scorpius OB Association.
Following large multi-object spectroscopic surveys to identify
a large and representative sample of low-mass members,
our studies of the
mass function and the age distribution of the members allowed
a detailed reconstruction of the
star formation history 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.
We will soon start a new project (funded in the context of the
DFG Priority Program 1573: Physics of the Interstellar Medium)
to investigate the effect of the
winds and ionizing radiation of the massive stars on the surrounding
interstellar medium.
Currently, the group is strongly involved in a large
multi-wavelength project to
study the young stellar populations in the Carina Nebula.
This site of very recent and ongoing massive star formation
allows a detailed look at the interaction of the winds and radiation
of the numerous very massive young stars with the surrounding
molecular clouds.
With near-infrared, X-ray, and sub-mm observations we will investigate
how the feedback from the massive stars disperses remnant clouds
at some locations and triggers new generations of stars in other
locations.
Relevant publications: A3, A1, B78, B77, B75, B74, B73, B72, B71, B70, B69,
B29, B22, B16, B12, C29; several presentations
are also available.
X-ray Studies of Young Stars |
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Young stars generally show very strong X-ray emission, hundreds
to thousands times stronger than our Sun.
A good knowledge of the X-ray properties of young stars
is not only of paramount importance 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 very
young stellar objects (protostars).
Since X-ray activity is particularly effective in discriminating
young (up to ~ 50 million years old) stars
from unrelated, much older fore- and background field stars,
X-ray studies are also a very important tool to reveal the
stellar populations of star-forming regions.
A few years ago, 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.
Currently, we are involved in the
Chandra Carina Complex Project that has used 1.5 Megaseconds (17.4 days)
Chandra observing time to perform a 1.4 square-degree X-ray survey of the
entire Carina complex.
A recent summary of the high-energy processes in stellar coronae
can be found in the proceedings of the conference
"Coronae of Stars and Accretion Disks".
Relevant publications: A2, 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.
Speckle-Interferometry allows to overcome the image blurring effect
of the earth atmosphere and provides
images of individual young stellar objects
with diffraction-limited angular resolution.
The technique of
Long-baseline Interferometry
combines the light of several telescopes; 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 star forming regions.
Such observations allow, for the first time, to directly study
the formation region of terrestrial planets in proto
planetary disks,
the way in which protostellar jets and outflows are launched
and collimated, and to resolve close multiple systems.
The analysis of the interferometric data often requires detailed modeling
with numerical radiative transfer simulations.
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.
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