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Publications of the Astronomy Department of the Eötvös University

On Computer processing and use of satellite data in astronomy and astrophysics
and
3rd Workshop of Young Researchers in Astronomy & Astrophysics
Edited by E. Forgács-Dajka, K. Petrovay and R. Erdélyi

The N+N Young Researchers' Workshop scheme, initiated and funded by the British Council, aims to provide an opportunity for young researchers to exchange ideas, knowledge and information by coming together in the form of N$+$N workshops and meetings. Here the term N+N workshop refers to a workshop involving a number of researchers from the UK and an equal number of local researchers. The workshops are followed by real and virtual networking to sustain the contacts made with a view to produce a proposal for longer term externally funded collaboration or applications for further funding.
As at the Department of Astronomy of the Eötvös University we have had a tradition of national workshops of young researchers in astronomy and astrophysics with similar characteristics, the call for meeting proposals by the British Council seemed an ideal way to extend the geographical scope of our meeting, while still maintaining its general format and spirit. Thus, this year's Hungarian Young Researchers' Workshop in Astronomy and Astrophysics was held in tandem with the British-Hungarian N+N workshop, and the contributions are also presented together in this volume.
For the topic of this year's meeting we chose "Computer processing and use of satellite data in astronomy and astrophysics". The reason for this is that, thanks to a high number of space probes, in the past decades a vast amount data has been collected from the extraterrestrial world, from the magnetosphere to the most distant galaxies and beyond. We are now in a situation where the amount data grows much faster than the speed by which they can be processed and duly analyzed. The workshop was devoted to methods aimed at improving on this situation, as well as to scientific results born out of the use of space data.
Finally, the co-directors would like to express their thanks to The British Council for the initiation of the project and for its generous support. In particular, we are grateful to the staff of British Council Hungary, Éva Salamon, Paul Clementson and Jim McGrath for their enthusiastic moral support and for their helpfulness in the management of the event.

Kristóf Petrovay

 K. Petrovay: Past and future of scientific space missions: an overview

After briefly mentioning a few highlights of recent, current and future scientific space missions, an extensive list of all the most important such missions, together with web links, is given.

 S. Dalla: Spacecraft measurements of solar energetic particles

Solar energetic particles (SEPs) are accelerated in the solar atmosphere during flares and coronal mass ejections. They can escape from the Sun and propagate through interplanetary space, where they can be measured by particle detectors on board spacecraft. Key to understanding the acceleration and propagation of these particles are: 1) combined analysis of SEP data and solar flare/CME observations and 2) easy comparison of SEP data from different spacecraft/instruments. This paper will demonstrate the importance of the multi-spacecraft and multi-instrument approach by showing new results from the analysis of SEP data from Ulysses and Wind.

 G. Facskó: Low-Energy Particle Studies Near the Earth Using Data of Cluster RAPID Measurements

The Cluster mission has been designed to perform simultaneous 3D plasma, magnetic field and energetic particles measurements in the Earth's plasma environment. The advanced energetic charged particle spectrometer RAPID on board the four spacecraft provide a complete coverage of energy, mass, and angular distribution of ions and electrons, over the energy range from 30 keV to 1.5 MeV. By combining with other Cluster measurements, primarily FGM and CIS, small-scale features can be observed and examined with unprecedented detail in the magnetosphere of the Earth and near the bow shock. In this paper I present a data processing method together with the observations of a hot flow anomaly (HFA) event as an illustrative example.

 A. Opitz, et al.: STEREO mission: overview, the plasma instrument, calibrations and data

This is an overview of the next generation solar space mission called STEREO. We focus on the plasma instrument and its calibrations at the University of Bern. The management of the plasma data is also discussed briefly.

 Zs. Bebesi: The Plasma Environment of Jupiter as observed by the onboard Plasma Instruments of Cassini

The Cassini spacecraft - on its way to Saturn - explored the plasma environment of Jupiter during the millenium flyby near the ecliptic plane along the dusk side of the planet. In this paper I give a general overview of the Cassini-Huygens mission focusing on the plasma instruments onboard of Cassini, and summarize the main scientific concepts. The orbit of Cassini at Jupiter was oriented along the Jovian Bow Shock (BS), so there were several occasions for the spacecraft to intercept the BS and to detect other various types of plasma events too. Therefore I present some results concerning the BS crossings, and some of the events that are suggested to be the consequence of the interaction of the BS with the Solar Wind (SW) flow. The more precise analysis of these "unusual" events will be the subject of future studies.

 G. Facskó: A Study of Solar Energetic Particle Events and Coronal Mass Ejections Using SOHO Data

The relation of coronal mass ejections (CMEs) and solar energetic particle events (SEPs) is a field where our understanding of the underlying physical processes has been subject to rapid changes recently. Two paradigms are still competing: the earlier one is that solar energetic particle events (SEPs) are triggered by flares. The recently more popular viewpoint is that from the two classes of SEPs, gradual events and impulsive events, only the latter are caused by flares, large spectacular gradual events are related to CMEs, and entirely unrelated to flares. Most recent observations seem to indicate that many events do not fit into this simplified scheme, and many combinations termed as hybrid events may exist. Here I present two typical SEPs, and then two new hybrid'' class SEPs are reviewed.

 S. Frey: Very Long Baseline Interferometry from Space: Past, Present and Future

Space VLBI (SVLBI) is a relatively new radio astronomical technique used for high angular resolution imaging of bright, compact active galactic nuclei. SVLBI is an extension of ground-based VLBI networks by placing another interferometer element into Earth orbit. The first dedicated SVLBI satellite, the Japanese HALCA was launched in 1997. The technical background and highlights of HALCA scientific observations are reviewed, with special emphasis on the Hungarian contribution. The current perspectives for next-generation SVLBI satellites are outlined.

 L. Mosoni and S. Frey: A Close Look on Thousands of Faint Radio Sources: Pilot Results of the DEVOS Survey

We briefly demonstrate the pilot results of the Deep Extragalactic VLBI-Optical Survey (DEVOS). Our ultimate aim is to eventually construct a large sample of compact sources (~10^4 objects) up to two orders of magnitude fainter than studied in VLBI surveys until now. This would lead to an unprecedented data base for various astrophysical and cosmological studies. The first global VLBI observations were successfully conducted in May 2002. We selected sources from the VLA FIRST catalogue, detected with MERLIN in the areas expected to be surveyed by the Sloan Digital Sky Survey with spectroscopic redshift measured. By means of observations of mJy-level sources in this pilot project we want to estimate the outcome of and the resources needed for a full-scale DEVOS project and obtain results valuable in their own right.

 Cs. Kiss: The infrared sky structure and the ISO Data Archive

ISO observations opened a new window to the studies of the infrared sky background, providing measurements surpassing IRAS in wavelength coverage, spatial resolution, number of photometric bands and spectroscopic capabilities. These measurements - which will remain unique for decades - provide an excellent data base to investigate the physical parameters, dust composition and spatial structure of the astrophysical components of the infrared sky background. In this proceeding I review the ISO Data Archive-based results and future capabilities of Zodiacal Light, Galactic cirrus and extragalactic background studies.

 V. Könyves, Cs. Kiss and A. Moór: Infrared loops and the large scale structure of the diffuse interstellar matter in the Milky Way

We performed an all-sky survey searching for loop- and arc-like intensity enhancements in the diffuse far-infrared emission using IRAS data. We identified 477 of these objects, analysed their indivual FIR properties and their distribution. Our objects trace out the spiral arm structure of the Galaxy in the neighbourhood of the Sun and their distribution clearly suggests that there is an efficient process that can generate loop-like features at high Galactic latitudes. We derived distances for 80 loops with the help of associated objects. Deviations in the celestial distribution of far-infrared loops clearly indicate, that violent events frequently overwrite the structure of the interstellar matter in the inner Galaxy. We obtained observational estimates of f_{in}=6.8% and f_{out}=4.8% for the hot gas volume filling factor of the immediate inward and outward Galactic neighbourhood of the Solar System.

 Z.T. Kiss, Cs. Kiss, P. Ábrahám and L.V. Tóth: Determination of dust temperature and emissivity from IRAS and ISO observations

We examined the dust emissivity at far-infrared wavelengths, and proposed a method to reproduce ISOPHOT temperatures combining ISOPHOT and IRAS far-infrared data. Analysing a sample of 13 clouds we compared the temperature values obtained using our method to those determined from ISOPHOT data and verified the accuracy of our method. This method allows one to extend the sample of clouds appropriate for investigation of dust emissivity properties. We applied our method for 8 clouds, for which ISOPHOT data are available olny at one wavelength, to determine dust colour temperature, and the dust emissivity was also computed for 3 of these clouds.

 Á. Kóspál, et al.: The long-term evolution of 7 FU Orionis-type stars at infrared wavelengths

We investigate the brightness evolution of 7 FU Orionis systems in the 1-100mikrom wavelength range using data from the Infrared Space Observatory, 2MASS and MSX. The spectral energy distributions (SEDs) based on these data points are representative of the period 1996-2000. These SEDs were compared with earlier ones derived from the IRAS photometry and from ground-based observations carried out around 1983, in order to look for long-term evolution. Our data show that three objects have become fainter, while the others remained constant. We investigate the case of V1057 Cyg and discuss whether its observed fading could be understood in the framework of the existing models.

 Y. Taroyan and J.G. Doyle: Solar Oscillations and the Magnetic Atmosphere

With the launch of the SOHO and TRACE satellites two new branches of solar physics have emerged: time-distance helioseismology and coronal seismology. In time-distance helioseismology the travel time of the acoustic waves between different points on the solar surface is measured to infer the local structure and properties of the subsurface layers of the Sun. The travel time changes due to the atmospheric magnetic field are evaluated theoretically. Coronal seismology utilises MHD waves in solar coronal structures as a tool to diagnose the physical parameters of the coronal plasma. Theoretical modelling of recently observed slow standing mode oscillations in stratified loops is presented. It is shown that large-amplitude resonant standing waves can be driven by small-amplitude oscillations at the chromospheric footpoints of the loops. The periods and the behaviour of these waves are different from those predicted by the classical theory of isothermal loop oscillations. The possible relationsheep between the oscillations studied in time-distance helioseismology and in coronal seismology is addressed.

 R. Erdélyi and A. Kerekes: Influence of random magnetic field on solar global oscillations

The discrepancies between theoretically predicted and observed frequencies of solar global oscillations (e.g. p- and f-modes) have attracted major attention in the past two decades. In the following we wish to explore further whether the solar atmosphere may account for the apparent frequency paradox. Magnetic flux is continuously emerging at photospheric levels and expanding into the solar atmosphere. We investigate the possible effects of an atmospheric random magnetic field on the solar fundamental mode (f-mode).

 I. Ballai: Damping of coronal global waves

Observations with the Extreme Ultraviolet Imaging Telescope (EIT) onboard SOHO have revealed the existence of transient coronal wave-like phenomena which are generated by an impulsive event and propagate across the visible solar disk for very long distances. Since these waves are able to carry information about the plasma in which they propagate, they are a perfect tool for coronal plasma diagnostics. We propose to study these waves to obtain information about the average values of the magnetic field and mean transport coefficients in the quiet Sun. The present contribution answers some of the 'hottest' questions related to the nature and proprieties of EIT waves.

 T. Török and B. Kliem: The kink instability of a coronal magnetic loop as a trigger mechanism for solar eruptions

The kink instability of twisted magnetic flux tubes in the solar corona is regarded as a possible initiation process of solar eruptions. We study the stability properties and the dynamic evolution of such coronal magnetic loops using 3D numerical simulations within the framework of ideal MHD. The analytical force-free coronal loop model by Titov and Demoulin (1999) is used as initial condition in the simulations. The loop model is found to be kink-unstable if a critical twist is exceeded. The growing kink perturbation leads to the formation of current sheets, which steepen exponentially and define the locations of plasma heating. Due to the twist in the magnetic field, the heated structures are S shaped - in very good agreement with soft X-ray observations of solar eruptions. The model, however, does not yet show a successful eruption, rather the kink instability starts to saturate. We present an improvement of the model which is promising with regard to eruption: a modification of the equilibrium so that the magnetic field surrounding the loop decreases more rapidly with height above the photosphere. Furthermore, we briefly discuss how the simulation results can be related to observations of solar eruptive phenomena.

 E. Forgács-Dajka: Structure of the solar tachocline: confrontation of theoretical models with SOHO/MDI helioseismic constraints

Helioseismic measurements indicate that the solar tachocline is very thin, its full thickness not exceeding 4% of the solar radius. The mechanism that inhibits differential rotation to propagate from the convective zone to deeper into the radiative zone is not known, though several propositions have been made. We present detailed numerical calculations of the fast solar tachocline based on the assumption that the dynamo field dominates over the dynamics of the tachocline.

 B. Major: Fine structure of the butterfly diagram

Fine-structure of the butterfly diagram has been studied using the Greenwich Photoheliographic Results (GPR) between the years of 1874-1976. Two main activity zones have been found situated between 5^\circ-17^\circ and 17^\circ-35^\circ, respectively.

 Zs. Regály: General Purpose Hydrodynamic Code

The hydrodynamic code developed by the author is capable to model fluid convections described by conservative form hydrodynamic equations in multidimension and versatile orthogonal coordinate systems, such as Cartesian, cylindrical and spherical geometry. The conservative form of hydrodynamic equations can be rewritten in form of nonlinear time-dependent continuity equations. Multidimensional physical problems can be modeled by split step method in versatile orthogonal geometries. The applied numerical algorithms were three types of flux-corrected transport method capable to handle steep gradients of fluid properties generally appears in astrophysical phenomena.

 T. Borkovits: Short term tidal and third body perturbations in close hierarchical triple stellar systems

We introduce our first results with a new numerical integrator which was developed for studying the orbital and spin evolution of hierarchical triple stellar systems. (The code includes equilibrium tide approximations with arbitrary direction of rotational axes.) The variation of the orbital elements (e.g. the inclination of the close -eclipsing- binary) and its observational consequences according to the distorted models with different mass-distributions of the stars, as well as with and without dissipation is studied in the case of the well-known eclipsing triple system Algol. We found that in lack of the stellar dissipation, the presence of the third star may cause sudden fluctuations in the orbital elements and the stellar rotation of the binary members even in the previously synchronized case, too. The dissipation can eliminate these fluctuations, nevertheless some variations which would produce observable effects in the same order which have been measured in several eclipsing binaries are also present. We also studied the perturbations of a hypothetical third companion on the eccentric eclipsing binary AS Cam. We found that the complex influence of the variation of the orbital elements on the occurence of the minima events can make it impossible to obtain the real apsidal motion rate from an O--C curve which covers only a small fraction of the period of the rotation of the apsidal line.

 Zs. Kõvári and M. Weber: Differential rotation of LQ Hya and IL Hya from Doppler imaging

We introduce two techniques of detecting surface differential rotation on stars, cross-correlation of consecutive Doppler images and the sheared-image method. We test the methods using artificial and real data. As a result, for the rapidly rotating K2 dwarf LQ Hya we find an almost rigid rotation, with weak (\alpha=0.0056) equatorial acceleration. On the giant component of the RS CVn-type star IL Hya we detect solar-type differential rotation with \alpha=0.03.

 R. Szabó: Adventures in the World of Pulsating Variable Stars: Multisite Photometric Campaigns

Advantages of photometric multisite campaigns are discussed, then published or prospective results of four - preceding and ongoing - observing runs are presented. Prospects and limits of photometric observations carried out from Hungary with small (~ 1m) telescopes are also outlined.

 G.G. Barnaföldi P. Lévai and B. Lukács: Fermion Stars in 3+1 vs. 4+1 Dimensional Space-Time

We introduce the description of a fermion star in 3+1_c+1 dimensional space-time, where 1_c is a 1-dimensional compactified spatial dimension with size ~10^{-13} cm. This compactification size might be interpreted as the strangeness quantum number, but in a geometrical way. A neutron moving into the extra dimension would behave as a \Lambda_s or a barion with even higher strangeness content. We display the Einstein equations for a static, spherically symmetric fermion star and discuss a special solution, which leads to the standard Tolman-Oppenheimer-Volkov equation and an extra condition for the extra dimensional contribution.

 G. Marschalkó: Visual light variation of Mira Ceti

Omicron Ceti is the earliest discovered periodic variable star. We examined the variations of Mira based on all the available data, with special regard to regularities that may occur in the amplitude variations.

 Zs. Hetesi and Zs. Regály: Old questions reassessed by modern cosmology and astrobiology

We critically investigate some aspects of modern cosmology and astrobiology, which are a central place for contemporary research. Three important fields are investigated: the quantum cosmology, the concept of anthropic principle and the SETI (Search for Extraterrestrial Intelligence) within the context of the combined methods of physics and philosophy.

 I. Nagy: Protoplanets in the protoplanetary disc

This paper is an overview of the formation of planetary systems. We discuss the star formation with the X-mechanism. After that, we review the two main planet formation processes. At the end, we give a summary of planet-disc interaction with planet migration, which can cause the evolution of resonant orbits. These resonant orbits in the protoplanetary disc change when the disc disappears.

 Á. Süli: On the comparison of the different methodes to calculate the derivatives of the Laplace-coefficients

The determination of the secular variations of the orbital elements of objects in N-body systems is based on the literal development of the perturbing function. The development makes use of the Laplace coefficients and their derivatives. In this paper a new method is shortly described for the analytical computation of the derivatives of the Laplace coefficients. It is an explicit formula in the sense that it only contains the Laplace coefficients and the parameter \alpha on which the Laplace coefficients depend. The advantage of this method is that it directlly gives the desired numerical results. Easy coding is a further benefit of the method and it provides more accurate numerical results. The paper describes in detail the application of the method through an example and gives a detailed comparison with former methods.

 I. Nagy: Numerical investigation of the orbit of Interball-1

We investigated the orbit of the artificial satellite Interball-1 by using Zare's method. The satellite was perturbated the strongest by the Moon and it fell down as a result of this perturbation. The measured and computed orbital elements differ from each other within the measured error bound. We could predict the end of the lifetime of the satellite with large precision.

 A. Pál and Á. Süli: Distribution of Asteroids in the Solar System: The Trojans

Although there is no difference between the stability properties between the Lagrangian points L_4 and L_5 both in the circular and elliptical restricted three-body problem, the number of the observed Trojan asteroids around the two Lagrangian points of Jupiter is not the same. We summarize our first numerical results concerning the difference of the phase space structure around the two Lagrangian points, taking into account the effect of Saturn as a perturber. These results show us that the size of the stable region around the leading point is even larger also for highly inclined and eccentric orbits.

 T. Kovács: On the stability of exoplanets in binary systems

In this paper we examine the dynamical stability of exoplanets around binary stars depending on the inclination. To explore the structure of the phase space we have applied the method of the relative Lyapunov indicators. We have used the models of the elliptic restricted three- and four-body problem to study the stability of exoplanets in fictitious and real binary systems.

 P. Klagyivik and Sz. Csizmadia: Contact binary stars as standard candles

Rucinski (1996) suggested to use contact binary stars as standard candles. We investigated the properties of contact binary stars in order to search for possibility of their using as standard candles. For this purpose a catalogue of their light curve solution was compiled and on the basis of the catalogue data we calculated the rate of energy transfer between the two components. This allowed us to determine the mass-luminosity relation of the primary as well as secondary components in a contact binary and using Kepler's third law and the strict geometry a very reliable distance determination method was developed.