Nicolaus Copernicus Astronomical Center

Scientific research

Bartycka 18, 00-716 Warsaw, POLAND
+48 (22) 8410041 fax. +48 (22) 8410046
email: camk@camk.edu.pl
www: http://www.camk.edu.pl

VARIABLE AND DOUBLE STARS

Astronomers from Warsaw have traditionally been specialists in the field of variable and double stars. Their research exploits spectroscopy, photometry and astrometry using orbital telescopes and terrestrial instruments located at various points around the globe. The latest observational technique, simultaneous CCD photometry of large numbers of objects, is used to search for variable stars in clusters and nearby galaxies. The N. Copernicus Astronomical Centre (CAMK) also coordinates the Polish involvement in the construction of the 11m diameter telescope SALT in South Africa.

Involved in this research are Krzysztof Belczyński, Janusz Kałużny, Konrad Kulczycki, Beata Mazur, Joanna Mikołajewska, Arkadiusz Olech, Paweł Pietrukiewicz, Michał Różyczka, Marek J. Sarna, Aleksander Schwarzenberg-Czerny, Józef I. Smak, Grzegorz Stachowski and Janusz Ziółkowski.

STELLAR ATMOSPHERES

Research into stellar atmospheres, planetary nebulae and circumstellar matter is being carried out by Adam Frankowski, Sławomir Górny, Tomasz Plewa, Michał Różyczka, Mirosław Schmidt, Natasza Siódmak, Ryszard Szczerba and Romuald Tylenda.

STELLAR PULSATIONS (ASTROSEISMOLOGY)

The research is concentrated on the observation and interpretation of oscillations of white dwarfs, the analysis of the pulsations of classical Cepheids and main sequence stars and the theoretical applications of helio- and astroseisomological data. The CAMK staff participate in observations carried out by a specialist group of telescopes place on all continents except Antarctica (the Whole Earth Telescope, http://ceti.as.utexas.edu/wetpage.html). The group studying stellar pulsations includes Wojciech Dziembowski, Paweł Moskalik, Rafał Nowakowski, Alosza Pamiatnych and Ryszard Sienkiewicz.

NEUTRON STARS

This area of study covers problems in the internal structure of neutron stars and their atmospheres. Models of recently-formed neutron stars (proto-neutron stars). The results include theoretical spectra of their radial pulsations. Also studied is the effect of homogenous rotation of proto-neutron stars on the properties of isolated pulsars and the role of the direct URCA process on the gravitational radiation instability of neutron stars.

Neutron stars are the subject of research by Michał Bejger, Tomasz Bulik, Dorota Gondek-Rosińska, Paweł Haensel, Włodzimierz Kluźniak, Bronisław Rudak, Agnieszka Woźna i Julian Zdunik.

HIGH ENERGY ASTROPHYSICS

Most numerous in CAMK is the high anergy astrophysics group, whose members analyse high-energy spectra of active galaxies and galactic black hole candidates taken by the satellites ASCA, EXOSAT, GINGA and GRO. They study the interactions which lead to the emission of high-energy photons, develop models of gamma and X-ray emmitting regions, and investigate the sources of cosmic background radiation in the X-ray and gamma ranges. Together with a group from the Space Research Centre the participate in the INTEGRAL satellite mission (http://astro.estec.esa.nl/Integral). The group also studies gamma ray bursts.

The group includes Tomasz Bulik, Bożena Czerny, Agnieszka Janiuk, Włodzimierz Kluźniak, Zbigniew Loska, Rafał Moderski, Marek Nikołajuk, Tomasz Plewa, Michał Różyczka, Marek Sikora, Anna Szostek, Małgorzata Sobolewska, Andrzej Zdziarski and Piotr Życki.

COSMOLOGY

The cosmology group studies the statistical properties of the cosmic background radiation and the spatial distribution of distant objects (Lyman-alpha clouds, galaxies). The aim is a description of the formation processes of galaxies and large scale cosmic structures. The detailed list of research topics includes non-linear evolution of cosmic density and velocity fields (described through both analytical perturbation equations and numerical hydrodynamic and N-body simulations), the anisotropy of the CMB, and reduction software for data from the next generation cosmic background probes (Planck Explorer). Also analysed are the correlations between the distribution of soft X-ray background radiation and the number density of galaxies on the sky. Similar analysis is being carried out for data from the ROSAT (PSPC All--Sky Survey) and COBE satellites.

The group includes Stanisław Bajtlik, Michał Chodorowski, Michał Frąckowiak, Roman Juszkiewicz, Ewa Łokas, Tomasz Plewa, Michał Różyczka, Weronika Śliwa, Andrzej Sołtan.

NUMERICAL SIMULATIONS

Mirosław Giersz works on the construction of software based on the Monte Carlo method to simulate the evolution of globular clusters. The approach used by him allows the simulation of clusters containing millions of stars. Michał Różyczka and Artur Gawryszczak use hydrodynamical simulations to build models of protoplanetary disks. Kacper Kornet simulates accretion disks around cataclismic stars. Michał Błażejowski builds numerical codes to simulate active galactic nuclei. Andrzej Krasiński works on new versions of his own package for algebraic calculations in Relativity Theory.

THEORY OF GRAVITY

Work on the theory of gravity is concentrated on the construction of inhomogenous cosmological models and homogenous cosmological models with rotation. Work in this area is being carried out by Andrzej Krasiński.

FUNDAMENTAL PARTICLES

The research is concentrated on the structure of nucleons and the development of a chromodynamical description of inelastic collisions between hadrons. The research is being carried out by Stanisław Tatur i Lech Mankiewicz.

TERRESTRIAL MAGNETOSPHERE

Roman Schreiber studies radio emission from magnetospheric sources, and models the propagation of electromagnetic waves in the vicinity of auroral radiation sources, along with the nonlinear processes in the regions in which they form.

ACHIEVEMENTS

Wojciech Krzemiński (currently at the Carnegie Institution Observatories) is one of the observers who in the 1960s discovered the binary nature of cataclysmic variables. In a series of articles from the 60s and 70s he and Józef Smak suggested that accretion occurs in these objects and correctly interpreted their light curves as arising from an accretion disk hit by a narrow stream of matter flowing through the inner Lagrange point from the less-massive component of the system. At the beginning of the 1970s, Professor Józef Smak was the first to discover the variations in the size of the accretion disk in the U Gem system, thus providing observational data in support of the theory explaining dwarf novae as arising from disk instabilities. Professor Józef Smak is one of the researchers who at the beginning of the 1980s discovered the thermal instabilities of the disks in cataclysmic systems.

In 1986, Paweł Haensel and his co-workers obtained the first detailed models of strange stars (compact objects wholly or mostly built out of quark matter). That moment marked the beginning of the search for strange stars among the objects considered to be neutron stars. In 1989 Prof. Haensel and his co-workers obtained a simple and yet very accurate formula linking the rotational angular velocity of a neutron star to the maximum mass and its equivalent static radius. The simplicity and universal application of this formula make it an extremely useful tool for observational differentiation of different equations of state proposed for dense matter. In 1991, Prof. Haensel and his team showed that, in contrast to previous estimates, direct URCA processes also occur in very high density matter. This discovery prompted extensive changes in the proposed scenarios for the evolution of young neutron stars.

Wojciech Dziembowski is a world-class expert on stellar pulsations and helio- and astroseismology. At the beginning of the 1990s he and his co-workers used helioseismological data to obtain models of the Solar interior which unambiguously demonstrated the correctness of the standard model. He also showed that the discrepancy between the theoretical and observed Solar neutrino flux results from the theory of fundamental particles and not astrophysics. Professor Dziembowski also developed numerical methods which allowed the analysis of astroseismological data and the deduction from them of rotational velocity distributions and magnetic field strengths inside stars.

Andrzej Zdziarski and his co-workers are widely known for their work on gamma and X-ray radiation from active galactic nuclei (AGN). Professor Zdziarski was one of the first to establish the importance of Compton scattering of AGN radiation from the cold accretion disc. BAsed on Seyfert-type AGN he showed that the X-ray cosmic background radiation, the nature of which was not known at the time, can arise from the combination of photons from active galactic nuclei.

In 1995, Bożena Czerny presented a model explaining a range of types of X-ray emission observed in AGN. Its basic component is a relatively thin and cool accretion disc enclosed within a much thicker and hotter corona, which, like the disc, can accrete onto a central black hole. At low rates of accretion the corona is very weak (or, in extreme circumstances, entirely absent), as a result of which hard X-rays are not observed in the AGN spectrum. At higher rates of accretion the corona reaches thermal equilibrium, a hard component appears in the spectrum and, in addition to the normal disc accretion, stron coronal accretion is excited. Professor Czerny's model adds further arguments for the existence of black holes. It also explains the spectroscopic and photometric properties of binary X-ray sources, in which the major component is a neutron star rather than a black hole.

The most important problem of modern cosmology is the formation of galaxies, galactic clusters and large scale structure visible in the spatial distribution of galaxies and in their velocity field. Roman Juszkiewicz, Franois Bouchet and their co-workers and students from CAMK and the Institut d`Astrophysique in Paris have developed a mathematical formalism which enables them to follow the evolution of the density distribution of the velocity field in an expanding Universe. The results of their analytical perturbation equations are fully consistent with the results of n-body simulations. What is more, they also match with observational data from large-scale galactic surveys. The agreement of theory with observation is a strong argument in favour of the hypothesis that today's cosmological structures evolved from Gaussian density perturbations under the influence of gravitational instabilities in the early Universe (non-Gaussian models, based for example on strings or textures, give much less satisfactory interpretations of the same data). The perturbation methods of Prof. Juszkiewicz can be used to improve estimates of the cosmological density parameter "omega" and as a precision tool for probing and interpreting the structure of the Universe in the era of large-scale galactic redshift surveys (2dF and SDSS). At the beginning of the year 2000, Docent Juszkiewicz and his co-workers presented an analysis of the dynamics of pairs of galaxies, showing that the matter density in the Universe is only one third of the critical density, at which the Universe would be flat.

Andrzej Sołtan observed correlations between fluctuations in the cosmic X-ray background and the distribution of galactic clusters. This may mean that galactic clusters have halos of very low density hot plasma. If this is confirmed, it will have an important influence on our understanding of the amount and distribution of dark matter in the Universe. Similar correlations have been observed by Prof. Sołtan in the case of individual galaxies.