Přednášky a semináře
Astronomický ústav AV ČR pořádá celoústavní semináře, kde se představuje každé vědecké oddělení - Stelární oddělení, Sluneční oddělení, Oddělení meziplanetární hmoty a Oddělení galaxií a planetárních systémů, a to jak organizačními novinkami z oddělení, tak jednou nominovanou přednáškou na vědecké téma. Semináře pořádáme se zhruba čtvrtletní periodou v půldenním bloku.
Cascade disruptions in asteroid clusters
We studied genetically associated asteroid clusters suggesting a possibility of at least two disruption events in their recent history (≤ 5 Myr). We searched for new members of known asteroid pairs and clusters and we verified their membership using backward orbital integrations. We found four asteroid clusters that show at least two separation events of small fragments that occurred at significantly different times. We considered a possible formation mechanism for these clusters, in which a parent asteroid is spun-up to its critical rotational frequency purely by the Yarkovsky–O’Keefe–Radzievskii–Paddack effect and we created a simple model to test this hypothesis. We obtained a good agreement between the model and the cluster properties for two clusters and we discussed the remaining two clusters that do not agree with our model.
Solar orbiter: Czech participation in an unprecedented high-tech ESA mission towards the Sun
In introduction a brief history, development and materialization of the project as well as the way which led to our participation in it will be given. In the following section a technical description of the satellite as well as a brief description of ten scientific instruments on its board will be given. Two institutes of our Academy took part in the development and materialization of three of the instruments and therefore more details of those could be presented. Substantial part of the talk will be presentation of science goals of the mission. To help to our colleagues who could maybe participate in some of future ESA projects, certain practical knowledge in financing and in communication with private firms will be passed on. Finally, a few impressions and photos from the launch (if successful) will be shown.
How Important is the Obscured Phase of Supermassive Black Hole Growth?
To answer some of the major open questions in the fields of supermassive black hole (SMBH) and galaxy evolution, an unambiguous and robust selection strategy of SMBH growth, i.e., active galactic nuclei (AGN), is required. However, most mass is accreted onto SMBHs behind thick columns of gas and dust, and identifying the most obscured systems is very challenging due to complex photon reprocessing in the obscurer with many geometric degrees of freedom. To address this, we present NuLANDS - a large multi-wavelength legacy Survey of AGN with the X-ray telescopes NuSTAR, XMM-Newton and Swift. The established far-infrared selection and sensitive X-ray observations circumvent line-of-sight X-ray obscuration biases even in the thickest obscurers. The initial results from the survey indicate that > 30% of all AGN in the local Universe are heavily obscured, and that high-energy X-ray selection alone preferentially selects less-obscured AGN. As such, NuLANDS marks a major step in completing the local census of SMBH growth, and provides vital boundary conditions for evolutionary studies into the co-evolution of AGN and obscuration across cosmic time.
Mass loss rates and NLTE wind models of massive stars
Determination of mass-loss rates of massive stars is an important output of massive star analysis. Stellar mass-loss rates are usually determined using wind models with a different level of sophistication. Commonly used models are based on an assumption of spherical symmetry and solve the NLTE radiative transfer consistently for a given density and velocity structure, which means that hydrodynamic structure is not solved. Usually, a simplified dependence of velocity on radius is being assumed (the so-called beta velocity law). Mass loss rates can be also predicted by hydrodynamic models, which do not solve the radiative transfer, but they describe the radiation force in a parametric way(using force multipliers). Our models do not use the simplifications of the beta velocity law and force multlipliers. Consistent NLTE wind models including both the wind dynamics and NLTE radiative transfer can be calculated.
Archiv minulých seminářů
Dále se konají menší tématické semináře jednotlivých oddělení:
Semináře slunečního oddělení
Vždy ve čtvrtek od 11:00 (září–červen) v zasedací místnosti slunečního oddělení pracoviště Ondřejov.
Magnetic properties of short-lived penumbral microjets
Studying the polarization properties of penumbral microjets that have the shortest durations requires spectropolarimetric observations with the fastest temporal cadence possible and is currently a challenging task. Here, we approach this task using fast-cadence spectropolarimetric measurements of the Ca II 8542 A line made with the CRISP instrument at the Swedish 1 m Solar Telescope. We exploited the diagnosis capabilities of this line to retrieve the magnetic field configuration and its evolution in the upper photosphere and low chromosphere by applying the weak field approximation to its wings and line core wavelengths respectively. We found that the short-lived microjets are associated with a transient perturbation in the photospheric magnetic field and sometimes they show clear but weaker changes in the chromospheric field as well. We will describe the different types of evolution that were identified.
Semináře oddělení GPS
Obvykle v pondělí od 14 hod v přednáškové místnosti pracoviště Praha–Spořilov.