Archiv seminářů pro rok 2015
Solar spectropolarimetry from 0-D to 3-D geometry
Scattering line polarization and the Hanle effect are among the most important mechanisms for diagnostics of the solar and stellar atmospheres. The fact that real stellar atmospheres are horizontally inhomogeneous makes the spectral synthesis and interpretation very challenging because the effect of thermodynamic fluctuations on spectral line polarization is entangled with the action of magnetic fields. This applies to the spatially resolved as well as to the averaged spectra. The necessary step towards the interpretation of such spectra is to study the line formation in sufficiently realistic 3D MHD models and to compare the synthetic spectra with observations. I'll present a brief overview of the relevant mechanisms involved in polarized spectral line formation and the recent progress in the field of 3D NLTE synthesis of polarized spectral lines.
HI shells: why I find them interesting even after 20 years' acquaintance
I will give an introduction to HI shells: what they are, where we can find them and why many members of our working group study them. I will focus on the connection between HI shells and other gaseous environment in the Galaxy and will deal with the importance of HI shells in the evolution of galaxies and the Galaxy.
Exoplanets at Ondřejov
Since 1995, when the first exoplanet was detected, this scientific field is rapidly developing. Nowadays, we are not only detecting the new worlds but we try to understand how did they evolve and how they do look like. The most recent topic is characterization of exoplanetary atmospheres. Current situation, advances and plans for the future development of the exoplantary research in Ondřejov will be presented.
Bolide Žďár – First results of the recent precisely documented meteorite fall
Instrumental observations of fireballs, especially those that can produce meteorites, are of great scientific interest and importance because meteorites provide us with a surviving physical record of the formation of our solar system, and a direct link to their parent asteroids. Last such event occurred over Czech Republic on December 9, 2014 at late dusk. It was exceptionally well documented because cameras of the Czech part of the European Fireball Network provided us with 10 all-sky photographic images and 21 radiometric records. It enabled us to get very reliable and complex information about position, dynamics, photometry and absolute timing of this extraordinary event. The first results based on the analysis of the best available records and describing fireball trajectory, luminosity, dynamics, fragmentation, orbit, and impact position will be presented. Recovery of meteorites and their analysis will be also shortly mentioned.
Multi-Generation Star Clusters
Massive star clusters are essential components of galaxies. When they form and during their early times they influence the surrounding interstellar medium with radiation, winds and supernova ejecta. This stellar feedback removes the gas out of the parent molecular cloud, star cluster expands, and in many cases it dissolves completely. Remaining globular star clusters reside in galaxy haloes. The model of massive star cluster formation as the monolithic collapse of the parent molecular cloud needs to be revisited due to discovery of multiple stellar generations of long-lived stars in globular clusters. We propose a new "cooling winds model" explaning formation of the second stellar generation out of matter that is enriched by H-burning products of the first stellar generation. Above a critical mass of the star cluster, winds form thermally unstable clumps reducing locally the temperature and pressure of the hot 10^7 K cluster wind. The matter reinserted by stars, and mass loaded in interactions with pristine gas and with evaporating circumstellar disks, accumulates in clumps that are ionized with photons produced by massive stars. We shall discuss if they may become self-shielded when they reach the central part of the cluster, or even before it during their free fall to the cluster center. We shall explore the importance of early mass loading of the stellar winds, and we shall analyse the role of additional cooling by dust produced in supernova events.
Non-Maxwellian distributions in the solar corona
Observations of the solar wind show pervasive presence of the non-Maxwellian kappa-distributions of electron energies characterized by a power-law high-energy tail. Theory has shown that such distributions can arise in the solar corona during impulsive heating by magnetic reconnection and also wave-particle interactions. We explored the consequences of the presence of such kappa-distributions on the optically thin spectra of the solar corona emitted in the X-rays, UV, and visible wavelengths. In particular, several line combinations allow for diagnostics of the kappa-distributions. A diagnostic from the EUV line ratios observed by Hinode/EIS space-borne spectrometer is performed and it is shown that the electron distribution can be strongly non-Maxwellian.
High-Mass X-ray Binaries in the Small Magellanic Cloud
High-Mass X-ray Binaries (HMXBs) are a phase in the life of some binary stellar systems that consist of a compact object (black hole or neutron star) and a massive companion (an early OB-type star). Their X-ray emission is powered by the infall of matter, provided by the massive companion, into the strong gravitational field of the compact star. The Small Magellanic Cloud (SMC) is a powerhouse of HMXB production (almost 100 systems), and due to its proximity we are able to investigate individual sources. However, we haven't yet fully characterize its HMXB population. To address that we have initiated wide spectroscopic and Halpha imaging campaigns. I will discuss our results and how the SMC HMXB population compares with that of our Galaxy.
Subcatastrophic collisions between asteroids
Mutual collisions between asteroids affect their size distribution, spins and surface morphology. Subcatastrophic collisions may be responsible for an excited asteroid rotations. We created a numerical model to investigate this hypothesis and also other effects of small collisions between asteroids. Recently, we showed that erosion caused by collisions increases the elongation of asteroid shapes on a timescale much longer than their collisional lifetime.
Initial mass function and feedback in dwarf galaxies
The stellar initial mass function (IMF) is a crucial quantity for the evolution of galaxies. It determines the fraction of stars in various mass ranges; hence it affects various crucial feedback mechanisms (e.g. from supernovae and radiation by massive stars). In the last years, systematic IMF variations in galaxies, particularly in low-mass ones, have been reported. I will review in this seminar what is know about IMF variations in dwarf galaxies and I will show how these variations affect the chemical evolution of galaxies. I will describe in particular the so-called integrated galactic IMF (IGIMF) theory, according to which the IMF is steeper in dwarf galaxies and flatter in larger ones. I will show which evidences support this theory and which evidenced do not support it. However, the IMF does not only change the rate of metal production. It changes also the dynamics and thermodynamics of gas, which in turn affect star formation and metal circulation. I will then review our efforts to implemented IMF variations in chemo-dynamical simulations of dwarf-galaxy evolution and I will show the multiple ways in which IMF variations can affect the dynamical and chemical evolution of galaxies. I will finish my presentation with some new ideas and modelling of the induced star formation in supershells and its connection with the formation and evolution of globular clusters.
Recent meteor shower outbursts and storms - models and observations
A number of the meteor shower outbursts and storms occurred in recent years starting with several Leonid storms around 2000. The methods of the meteoroid streams modelling became better and more precise. An increasing number of the observing systems enabled better coverage of such events. The observers provide modellers with an important feedback on precision of their models. Here we present comparison of several observational results with the model predictions. As the main source of the data the video observations of our team are used.
Space Instrumentation Development at the Astronomical Institute
The Solar Physics Department studies is not only focused on the basic research and ground observations of the active phenomena from the solar atmosphere throughout the whole heliosphere but also participates in development of remote/in-situ space experiments on several future ESA missions. Currently the largest involvement inheres in the Solar Orbiter mission (namely the RPW, STIX, and METIS experiments) with a planned launch in 2018. Another two contributions are related to the ASPIICS sensor on mission Proba-3 and RPWI instrument on mission JUICE. Here the current status of all the space hardware activities will be presented.
Astroinformatics - The Key to New Astronomical Discoveries
The current astronomy is flooded by the data. Some instruments have been already producing petabyte-scaled data flows, the reduction and analysis of which require supercomputing clusters. Astronomy becomes the data-driven science where the major part of budget of big projects will not go into telescope and instrumentation but to the data processing infrastructure. Astronomy, as well as other science disciplines has begun to recognize informatics, advanced statistics and machine learning as a key part of its methodology and new astronomical discoveries are expected from knowledge extraction of federated astronomical databases and archives. The new ways of multi-dimensional data analysis are being tested using wider range of 3D visualization devices including the immersive Virtual reality and virtual worlds. The changing nature of next-decade astronomy also requires education of a new type of experts - the astronomical data scientist with deep knowledge of both astronomy and physics as well as modern computer science and software engineering, well prepared to analyze petabyte-scale data in multi-cloud environment. The need to address all such problems led to the emergence of a new astronomical discipline - Astroinformatics. We give a brief overview of its subjects and methodology and present some astroinformatics projects ongoing in the Astronomical Institute of CAS in collaboration with several faculties of information technology in CR.