Special Seminars


"Testing the CDM paradigm: the new era of high-resolution super simulations"

Wojciech Hellwing (Institute of Cosmology&Gravitation University of Portsmouth, UK)

The rapid growth of available computer power accompanied by constant developement of numerical techniques lead to opening new prospective windows of testing the Dark Matter paradigm with a galaxy-scale structure formation. I shall discuss tantalizing results that stem from a the newest state-of-the-art cosmological simulations of the EAGLE, APOSTOLE and COCO suites. I shall review and discuss our main results including: - properties Warm and Cold Dark Matter haloes; - spatial patterns in satellites of Milky-Way and Andromeda-like systems; - prospects of using strong-lensing of dark subhaloes for detecting the Cold Dark Matter; - Local Group satellite galaxies properties in "gastrophysical" APOSTOLE simulations; - importance and magnitude of galaxy physics effects in cosmic velocity and density fields.


"The Gravitational Wave Era : Peeling the onion layer by layer down to the event horizon"

Pau Amaro-Seoane (Max Planck Institute Gravitational Physics)

One of the most interesting sources of gravitational waves is the inspiral of compact objects on to a massive black hole (MBH), commonly referred to as an extreme-mass ratio inspiral. The small object, typically a stellar black hole, emits significant amounts of GW along each orbit in the detector bandwidth. On the other hand, recent observations of the Galactic center revealed a dearth of giant stars inside the inner parsec relative to the numbers theoretically expected for a fully relaxed stellar cusp. In this talk I will give a general overview on the relevance of astrophysics to general relativity in galactic nuclei and vice-versa.

Seminar will be held at 11:15 am, in the CAMK Lecture Theater


"First Statistical Tests for Clumpy-Torus Models: Constraints from RXTE monitoring of Seyfert AGN"

Alex Markowitz (University of California San Diego)

We present an analysis of multi-timescale variability in line of sight X-ray absorbing gas as a function of optical classification in AGN to derive the first statistical constraints for recent _clumpy_ absorbing torus models. Such models represent the paradigm shift away from a classical "solid donut" morphology. We use the vast archive of Rossi X-ray Timing Explorer multi-timescale monitoring of dozens of type I and Compton-thin type II Seyfert AGN to search for discrete absorption events due to clouds transiting the line of sight. Most of our detected clouds are Compton-thin and located in the outer BLR or inner dusty torus. We discuss the resulting implications for cloud distributions in the context of the clumpy-torus models. We present the density profiles of the highest-quality eclipse events. We discuss cloud sizes, stability, and radial distribution across a wide range of distances, and explore the exhibited range in density profiles for the highest-quality eclipse events, and we discuss possible connections to the mechanisms that form and launch clouds.

Lecture starts at 11:15 am, Copernicus Astronomical Center, Warsaw, Lecture Hall.


"A lack of classical Cepheids in the inner part of the Galactic disk"

Matsunaga Noriyuki 松永 典之 (まつなが のりゆき) (University of Tokyo )

Recent large-scale infrared surveys have been revealing stellar populations in the inner Galaxy seen through strong interstellar extinction in the disk. In particular, classical Cepheids with their period-luminosity and period-age relations are useful tracers of Galactic structure and evolution. Interesting groups of Cepheids reported recently include four Cepheids in the Nuclear Stellar Disk (NSD), about 200 pc around the Galactic Centre, found by Matsunaga et al. (2011, Nature, 477, 190) and those spread across the bulge region reported based on VVV data (Dekany et al. 2015, ApJ, 812, L29). In this talk, I'll talk our discovery of several classical Cepheids towards the bulge region and discuss the large impact of the reddening correction on distance estimates for these objects. Most of the other Cepheids discussed here are located signifficantly further than the Galactic Centre. This suggests a lack of Cepheids in the inner 3 kpc region of the Galactic disk except the NSD. I'll also present some results and plans of near-infrared spectroscopy of Cepheids.

Lecture at 11:15 am, Copernicus Center, Lecture Hall.


"The initial binary-star population distribution functions and dynamical population synthesis"

Pavel Kroupa (Helmholtz-Institut fuer Strahlen- und Kernphysik, Universitaet Bonn)

Most and probably all stars form in binary systems and some in higher-order systems. The distribution function of binaries at their birth is not observable because it evolves rapidly. Very young binaries evolve due to system-internal processes termed pre-main sequence eigenevolution, while older binaries evolve through tidal circularisation. Binary systems are also split apart into two single stars due to stellar-dynamical encounters in the birth embedded clusters, and some binaries merge as well. I will show how the initial distribution functions for periods, mass-ratios and eccentricities can be constrained for late-type stars by using observations of stars in the Galactic field and in star-forming regions. This leads to possibly universal distribution functions. Assuming all stars form as binaries in embedded star clusters we can then synthesize the population of binaries in a whole galaxy. The prediction of this dynamical population synthesis is that massive elliptical galaxies ought to have a low binary fraction (about 30 per cent) while star-forming dwarf galaxies ought to have a binary fraction of about 80 per cent, where the Galaxy has a binary fraction of about 55 per cent as is observed to be the case. This approach has much potential for further applications.

Lecture in the main lecture hall at NCAC will start at 11:15 am and will last 1,5 h.