Wednesday Colloquium


"Is dark energy just a mathematical difficulty?"

Boud Roukema (Centre for Astronomy, N. Copernicus University, Toruń)

The Concordance Model of the Universe is a good phenomenological model, fitting an interlocking web of many different extragalactic observations. However, it is incomplete, not only because the curvature and topology of comoving space have not yet been determined, but also because the observational estimate of the dark energy parameter (Omega_Lambda = 0.7) has a systematic uncertainty of order unity. This is because the standard phenomenological approach is based on solutions of the Einstein field equations that assume that the Universe is perfectly homogeneous, while the real Universe is inhomogeneous: the planet Earth exists. Two approaches to a more accurate cosmological model will be briefly introduced: the Tolman-Lemaitre-Bondi models and the averaging approach.


"Ultra high energy cosmic ray particles"

Pieter Bierman (Max-Planck-Institute fur Radioastronomie, Bonn)

Particles near 10^20 eV are the most energetic particles known to us in the universe, also called ultra high energy cosmic rays. Events have been detected of an energy up to 3x10^20 eV, which is a macroscopic energy. Independently, new spectral components of cosmic ray electrons, positrons and all nuclei have been detected, all of which are flatter. The now abundant observations are readily and quantitatively interpreted with the action in magnetic s tellar winds. This then may also explain the Auger data as due to the action of the relativistic jet in the radio galaxy Cen A on the starburst region full of cosmic rays. A further test will be the match to the Kaskade-Grande data covering the energy range from 10^14 eV to 10^{19} eV. With this we have proposed a theory for the origin of cosmic rays (1993), and tested the quantitative predictions (2009-2011); many more tests will be possible soon with neutrino data.


"Pi of the Sky telescopes in Spain and Chile . Photometric analysis of the Pi of the Sky data"

Małgorzata Siudek (Centre for Theoretical Physics, Warsaw)

Pi of the Sky is a system of robotic telescopes designed for observations of short timescale astrophysical phenomena, like prompt optical GRB emission. The apparatus is designed to monitor a large fraction of the sky with 12m to 13m range and time resolution of the order of 1 to 10 seconds. In October 2010 the first unit of the new Pi of the Sky detector system was successfully installed in the INTA El Arenosillo Test Centre in Spain. We have also successfully moved our prototype detector from Las Campanas Observatory to San Pedro de Atacama Observatory in March 2011. Database containing stars measurements from period 2006-2009 taken by the Pi of the Sky detector located in Las Campanas Observatory in Chile contains more than 2 billions measurements of almost 17 millions of objects. All measurements are available on the Pi of the Sky web site through a dedicated interface which also allows to download the selected data.Accurate analysis of Pi of the Sky data is a real challenge because of a number of factors that can influence measurements. Reading the chip with the shutter opened, strong and varying sky background, passing planets or planetoids, clouds and hot pixels are among possible sources of errors in our measurements. In order to facilitate analysis of variable stars we have developed a system of dedicated filters to remove bad measurements or frames. The spectral sensitivity of the detector is taken into account by appropriate corrections based on the spectral type of reference stars. This process is illustrated by the analysis of the BG Ind system where we have been able to reduce the systematic uncertainty to about 0.013 magnitudo.


"Transiting Extrasolar Planets: Detection, Analysis, Results"

Geza Kovacs (Konkoly Observatory, Budapest)

We summarize the available methodology used to detect and analyze transiting planets. Special attention will be paid on the detection, including detrending from systematics. We also review current ground- and space-based photometric projects, focusing on HATNet. Finally, we highlight some exceptional results, primarily those related to multi-planetary systems.