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.
Outflows from evolved stars
In my PhD Thesis we study the origin of powerful stellar outbursts in the late phases of evolution of stars like the Sun. This is one of the most controversial topics in the field, as the extraordinary variety of shapes revealed by observations are not expected to be the result of the evolution of stars that are basically spherical all over their lives. The stellar explosions that we are studying (GK Persei, R Aquarii) occur and develop on time-scales of years, even months. This allows us to study their evolution in real-time, a very rare opportunity in Astrophysics. To this aim, we have gathered over the years a unique collection of high-resolution images, from which we produce "movies" that reveal the expansion of the nebulae as projected in the plane of the sky. Images are complemented by spectra that measure the line-of-sight velocities, also required to build 3D models of the dynamical evolution of the outflows, a privileged information for theoretical modelling.
Solar Flares and Eruptions in Three Dimensions
Solar flares and eruptions are the most energetic phenomena in the outer solar atmosphere. They are traditionally described by the Standard solar flare model in 2D, which however cannot account neither for the three-dimensional flare morphology nor some of the observed dynamics. Recent three-dimensional extensions to this model have proven highly successful, yielding a number of predictions that were subsequently verified by observations. We summarize these advancements and discuss the latest predictions of new types of three-dimensional magnetic reconnection.
Observations of binary asteroid Didymos in support of DART and Hera missions
The binary near-Earth asteroid (65803) Didymos is the target for the Asteroid Impact and Deflection Assessment (AIDA) mission, which is a concept with two spacecraft: NASA’s DART (Double Asteroid Redirection Test) impactor and ESA’s Hera orbiter. The DART spacecraft is designed to impact the secondary in the Didymos system, whose 160-meter size is typical of the size of asteroids that could pose a more common hazard to Earth, and modify its trajectory through momentum transfer. The Hera spacecraft would then visit Didymos to survey the diverted secondary, measure its mass and perform high-resolution mapping of the crater left by the DART impact. A key scientific goal of both AIDA missions is to measure and characterize the deflection caused by this impact. Prior to the DART impact in 2022, we must establish the pre-impact system properties. Lightcurve observations of Didymos taken in 2003, 2015, 2017, 2019 and those planned in near future are a key contribution to this task. I will present an up-to-date knowledge of the system parameters obtained using past observations.
Unification of accreting black holes across the mass scale
Astrophysical black holes exist with a wide range of masses, from a few to ten billion times the mass of the Sun. If “fed” by surrounding gas, they become the most efficient X-ray emitters in the Universe. The gas can be accreted from a nearby star (as in stellar-mass X-ray binaries, XRB), or from the material in the nucleus of external galaxies (as in the active galactic nuclei, AGN). The largely different mass between XRB and AGN implies the different size- and time-scales. While XRBs evolve rapidly and change their accretion mode, most AGNs remain in the same state over periods of decades. Study of AGN spectral states is still possible with a large sample of multi-wavelength observations. In this talk, I will review our knowledge about AGN spectral states and their comparison to XRBs. Investigation of what is inherently different between AGN and XRB and what can be scaled up (down) will allow us to use the knowledge of one black-hole class to the other. Vice versa, understanding the differences could help us to explain yet-open problems in AGN and XRB physics.
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.
Emergence of small-scale magnetic flux in the quiet Sun, observed from the photosphere to the corona
We study the emergence and evolution of new magnetic flux in the vicinity of a quiet Sun network. We employ high-resolution spectropolarimetric, spectroscopic and spectral imaging observations from ground-based (Dutch Open Telescope) and space-born instruments (TRACE, Hinode, SoHO), which provided a multi-wavelength, tomographic view of the region from the photosphere up to the corona. Throughout its evolution, the region exhibited many of the phenomena revealed by recent simulations. The event starts with a series of granular-scale events, which follow the photospheric flow field and merge to form a small-scale magnetic flux system of the order of 1018 Mx. Spectropolarimetric inversions reveal an evolving, complicated pattern of horizontal and vertical magnetic field patches at the region between the main polarities. As the magnetic flux accumulates and the region expands, Doppler-shifted H-alpha absorption features appear above and at the crests of the structure, indicating an immediate interaction with the pre-existing, overlying magnetic field. Roughly 60 min after the region first emerged at the photosphere, a jet-like feature appeared in the chromosphere and a small soft X-ray bright point formed in the corona. The coronal brightening exhibited intense spatial and temporal variations and had a lifetime that exceeded one hour. EUV spectroscopy and DEM analysis revealed temperatures up to 106 K and densities up to 1010 cm-3. Even in the absence of a strong ambient magnetic field, small-scale magnetic flux emergence affects dramatically the dynamics and shape of the quiet Sun.
Semináře oddělení GPS
Obvykle v pondělí od 14 hod v přednáškové místnosti pracoviště Praha–Spořilov.