Seminars
Our seminars take place in the lecture room of the building at
Praha–Sporilov.
Next seminar:
27.05.2016 10:00
Simone Recchi
Astronomical Institute, Academy of Sciences, Prague
New ideas on the formation of globular clusters
Abstract
Simone Recchi
New ideas on the formation of globular clusters
Several ideas have been put forward in the recent past about the formation of globular clusters (GCs), but none of them seem to be fully satisfactory. In particular it is very challenging to explain the presence of multiple populations of stars and the anticorrelations between some light elements (in particular the Na/O and Mg/Al anticorrelations) within GC. For most of the proposed scenarios, in order to fit these anticorrelation the GC must lose a very large fraction of first generation stars, but it is unclear how to disperse such a huge fraction of stars. We propose here that first generation stars are formed in a supershell, swept up after the explosion of a very massive primordial star (the so-called popIII star). Since these supershell stars are born at some distance from the center of the GC, and since they inherit the outward-directed radial velocity of the supershell, it is likely that most of them will be unbound. On the other hand, a significant fraction of the ejecta of these supershell stars can propagate, almost unimpeded, towards the center of the GC. They pile up there, cool (because of the large densities reached in the center) and can form a new generation of stars. We will present in this seminar the details of this scenario and 1-D chemo-dynamical simulations corroborating it.
to be confirmed
Previous seminar:
28.04.2016 14:00
Johannes Andersen, Birgitta Nordström
Dark Cosmology Centre, University of Copenhagen, and Stellar Astrophysics Centre, University of Aarhus, Denmark
Chemical enrichment processing in the early galaxy
Abstract
Johannes Andersen, Birgitta Nordström
Chemical enrichment processing in the early galaxy
The most extreme metal-poor stars (EMP; [Fe/H] <= -2.5) are faint and their metal lines very weak. UVES@VLT revealed that they are chemically surprisingly homogeneous, but a few subgroups exhibit dramatic overabundances of notably carbon and neutron-capture elements. The standard, local, explanation is transfer and dilution of processed matter from a former, more evolved binary companion to the surface of the lower-mass EMP star we see today, and the binary frequency of stars enriched in C and s-process elements is indeed high. But accurate long-term radial-velocity monitoring has now proved that stars enriched in only C or r-process are generally single, so their anomalous abundances must have been implanted already in their natal ISM clouds by external sources at interstellar distances. This is not what current models of galaxy formation would predict.
If you would like to give a seminar in our group, please contact Vladimir Karas or Jaroslav Hamersky.
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