ARI Institute Colloquium
Summer Term 2012
19.04.2012 11:15hSeminar room of the ARI
C. Chiosi Univ. Padova
The origin of the mass-radius relation of Galaxies
We investigate the mechanisms which concur to shape the mass-radius relation of early type galaxies, in order to cast light on the physical origin of its slope, tightness, and zero point. We suggest that the mass-radius relation is the result of two competing mechanisms: on the one hand, local physical processes which fix the mass and the radius of individual objects; on the other hand, cosmological, global, statistical principles, which shape the distribution of objects in the mass-radius plane. We reproduce the mass-radius relation with a simple numerical technique based on this view.
26.04.2012 11:15h
Seminar room of the ARI
S. Jordan ARI
Magnetic fields in subdwarfs, central stars of planetary nebulae and white dwarfs?
10-15 % of all white dwarfs possess magnetic fields up to 1 Gigagauss. While the strong magnetic fields in white dwarfs are easily detectable by Zeeman splitting and high degrees of polarisation, the detection of smaller fields (below about 30 kilogauss (kG)) is much more difficult. Only with 8m-class telescopes and through the measurement of extremely small amounts of polarisation (0.1 %) it became feasible to push the detection limit down to less than a kG. In order to clarify the question whether magnetic fields were already present in the direct precursors of white dwarfs, central stars of planetary nebulae and hot sub-dwarfs were observed with the FORS1 polarimeter of the ESO VLT. Of particular importance is the question whether magnetic fields in the central stars could explain the mostly non-spherical shape of planetary nebulae. From the polarimetric measurements magnetic fields up to 3 kG were deduced. However, a very careful data reduction and calibration of the spectro-polarimetric measurements are extremely crucial. In this talk I will discuss whether the detected magnetic fields are real or spurious.
03.05.2012 11:15h
Seminar room of the ARI
J. Vickers ARI
Statistical Photometry with Large Datasets
Modern sky surveys are rapidly growing larger and larger and new techniques are needed to properly exploit the abundance of information. Of particular interest, with respect to galactic structure finding, is the isolation of specific species of stars which may be used to characterize stellar streams, clouds and other associations. Specifically, I will talk about a new color based method to accurately select Blue Horizontal Branch stars (near-standard candles, and widely used Halo tracers) photometrically from Pan-STARRS data.
10.05.2012 11:15h
Seminar room of the ARI
A. Piskunov ARI/INASAN, Moscow
Global survey of star clusters in the Milky Way: results for quadrants 1-3
We report on the current status of the SFB project that aims at a global survey of star clusters in the Milky Way. Using the 2MASS and PPMXL catalogues, we have examined more than 2800 objects located in the first three Galactic quadrants, and confirmed 78% of them to be real star clusters. The remaining 22% were rated either to be non-existent, or objects wrongly identified in the literature, or being too faint to be visible in 2MASS. Based on kinematic and photometric criteria, we determine a set of cluster members which are used to derive astrophysical, spatial and kinematic parameters of the confirmed clusters. The comparison with literature data (e.g. ages, distances, radii) indicates that the derived parameters are compatible with optical scales, based on the UBV photoelectric observations. Kinematic parameters of the open cluster subsystem reproduce the local law of differential rotation up to 5 kpc from the Sun. Our sample is complete within about 2 kpc from the Sun. There is, however, a significant deficiency of clusters at Galactic latitudes |b| > 20 deg. We discuss preliminary results and their implications for studies of the structure and evolution of the Galactic disk populations.
24.05.2012 11:15h
Seminar room of the ARI
A. Bik MPIA
Reconstructing the complex formation history of high-mass
Massive stars are typically observed to form in clustered environments, with morphologies ranging from very dense, centrally concentrated starburst clusters to loose associations. These associations and clusters are morphologically and dynamically different. It is not clear if these differences arise from different initial conditions in the star formation process or environmental effects, like triggered star formation. We have started a large observational campaign to derive the star formation history of several massive star formation complexes in order to reconstruct the star formation mechanisms. I will demonstrate that near-infrared spectroscopy and photometry using LBT and VLT, combined with a large suite of multi-wavelength observations allow us to obtain a detailed picture of the stellar clusters and their stellar populations. Different stellar populations are found in many embedded clusters, suggesting that the star formation history is much more complex than a single star formation event. Based on LBT multi-object spectroscopy of the massive stellar content of W3 Main I will present strong evidence for an age spread where the oldest massive star formed 2-3 Myrs ago while some other massive stars are still in their formation process.
Seminar room of the ARI
A. Bik MPIA
Reconstructing the complex formation history of high-mass
Massive stars are typically observed to form in clustered environments, with morphologies ranging from very dense, centrally concentrated starburst clusters to loose associations. These associations and clusters are morphologically and dynamically different. It is not clear if these differences arise from different initial conditions in the star formation process or environmental effects, like triggered star formation. We have started a large observational campaign to derive the star formation history of several massive star formation complexes in order to reconstruct the star formation mechanisms. I will demonstrate that near-infrared spectroscopy and photometry using LBT and VLT, combined with a large suite of multi-wavelength observations allow us to obtain a detailed picture of the stellar clusters and their stellar populations. Different stellar populations are found in many embedded clusters, suggesting that the star formation history is much more complex than a single star formation event. Based on LBT multi-object spectroscopy of the massive stellar content of W3 Main I will present strong evidence for an age spread where the oldest massive star formed 2-3 Myrs ago while some other massive stars are still in their formation process.
31.05.2012 11:15h
Seminar room of the ARI
R. Haschke ARI
The variable stars of the Magellanic Clouds: Tracers for structure and abundances
14.06.2012 11:15h
Seminar room of the ARI
tbc
21.06.2012 11:15h
Seminar room of the ARI
M. Hauser ARI
tbc
28.06.2012 11:15h
Seminar room of the ARI
A. Just ARI
An evolutionary model of the extended solar neighbourhood
05.07.2012 11:15h
Seminar room of the ARI
tbc
12.07.2012 11:15h
Seminar room of the ARI
M. Demleitner ARI
tbc
19.07.2012 11:15h
Seminar room of the ARI
U. Bastian ARI
tbc
26.07.2012 11:15h
Seminar room of the ARI
Th. Lisker ARI
tbc
Previous Colloquia
- Winter Term 2011/2012
- Summer Term 2011
- Winter Term 2010/2011
- Summer Term 2010
- Winter Term 2009/2010
- Summer Term 2009
- Winter Term 2008/2009
- Summer Term 2008
- Winter Term 2007/2008
- Summer Term 2007
Contact: I. Seckel
