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Seminarium środowe


"Discovering new hot Jupiters with the WASP transit survey and probing planetary atmospheres with occultation measurements"

Alexis Smith (NCAC, Warsaw)

I will talk about two aspects of my exoplanet research, firstly the SuperWASP (Wide Angle Search for Planets) project, which is the leading ground-based discoverer of transiting planets. I will give an overview of the project, and briefly mention some of our discoveries and discuss the future of WASP in the Kepler era. Secondly, I will discuss some of my characterisation work on hot Jupiter atmospheres, specifically occultation measurements made with Spitzer and with ground-based telescopes. These observations allow us to begin to probe the atmospheric structure and composition of worlds beyond our solar system.


"Modelling the Remnant and the Afterglow of Compact Binary Mergers "

Francesco Pannarale (Max Planck Institute for Gravitational Physics (Albert Einstein Institute))

In recent years, several approaches were developed to calculate the final spin of the remnant of binary black hole mergers. I present a new model, based on one of these approaches, which allows for predictions on the spin and mass of the black hole remnant of black hole-neutron star binary mergers. I validate the model and assess its accuracy by testing it against numerical-relativity simulation results. I then investigate the space of parameters consisting of the binary mass ratio, the initial black hole spin, and the neutron star mass and equation of state, providing indirect support to the cosmic censorship conjecture. I further show that the presence of a neutron star affects the quasi-normal mode frequency of the black hole remnant, thus suggesting that the ringdown epoch of the gravitational wave signal may virtually be used to (1) distinguish binary black hole from black hole-neutron star mergers and to (2) constrain the neutron star equation of state. In the second part of the talk, I report on new fully general-relativistic numerical simulations of magnetized binary neutron star mergers leading to the formation of a rapidly and differentially rotating hyper-massive neutron star. I examine the resulting electromagnetic radiation and compare it to other recent simulations.


"Accretion in supergiant High Mass X-ray Binaries"

Antonios Manousakis (NCAC, Warsaw)

Supergiant High Mass X-ray Binaries (sgHMXBs) consist of a neutron star accreting material from its early-type, massive, stellar companion. The interplay between the neutron star and the stellar companion can influence accretion significantly. Thanks to INTEGRAL, a hidden population of obscured sgHMXBs has been revealed. Subsequent XMM-Newton observations of the highly obscured eclipsing sgHMXBs IGR J17252-3616 has shown that the absorbing column density (nH) is highly variable. The variability of nH has been interpreted as the effect of a slow wind with an accretion wake formed around the neutron star. This hypothesis is now supported by the hydrodynamical simulations for this system. Such low stellar wind velocities are not expected in massive stars. In addition, the mass of the neutron star can be inferred. Besides the heavily obscured systems, classical sgHMXB Vela X-1 has also been studied in depth over the years. Recent results on hydrodynamical simulation combined with observed properties of this system are also discussed.


"Dark energy distribution from quasar monitoring: Reverberation strategy"

Ishita Maity

I enumerate the various methods of determining the distribution of dark energy in universe and subsequently choosing the cosmological model that agrees with the observed data. I then discuss how quasars can be used as standard candles based on the theoretical model developed by Czerny and Hryniewicz and hence to test the properties of the universe. The aforementioned model gives a simple relation between the BLR radius and the absolute luminosity of a quasar. The advantage of this method over using Supernovae as standard candles lies in the fact that unlike supernovae, due to high metallicity of quasars, the relation between BLR radius and absolute luminosity is unlikely to depend on time or redshift. Having assumed this, we perform Monte Carlo simulations to estimate in advance the accuracy of determination of the time delay between the continuum observed from the central region and the emission lines. I discuss the errors we get from using different numerical methods and also varying parameters like the quasar variability amplitude, distribution of measurements in time, etc. We try to determine the threshold for the systematic error we have the liberty of introducing for which we can still recover the delay artificially introduced. Finally we check how these values and errors translate when calculating the luminosity distance to the source.