Cover figures: Map of interstellar extinction around the galactic plane near the Polaris and Orion regions with T Tauri-like objects based on 2MASS stellar colour indices. (Z.T. Kiss et al., PADEU, 17, 173)

It is a great pleasure for the Organizers to present the proceedings already the Fourth Workshop of Young Researchers in Astronomy & Astrophysics. Six years ago the Organizers of the first meeting of these conference series declared that their intention is to begin a long-lasting tradition of such biennial conference series where the young postgraduate scientists can meet each other as well as with senior scholars on the wide fields of astronomy & astrophysics, and they can present their results, getting important experiences in presentation oral lectures. And, of course, vice versa this is a great possibility for the senior astronomers and astrophysicists to know the new generation, and form new connections.
I am glad to say that the idea became successful. On the present, fourth meeting almost 50 lectures -- which covers many areas of astrophysics and related topics from solar physics to cosmology -- was presented by the young researchers affiliated to all those Hungarian scientific institutes, where astronomy and/or astrophysics are studied. It is a new and happily sequel, that a lot of hungarian young researchers who are working abroad came back to Hungary for a while to present their science. Like a bridge between the generation, a significant part of the lecturers are already not PhD students. They are mainly postdoctoral researchers who attended on the first conferences as young scientists, but feel theirself young in their hearts, and return back from meetings to meetings due to their nice memories. They are highly welcomed in the future, too. Furthermore, last, but not least I mention, that as a manifestation of the great honour of the senior generations to the young scientists several leading Hungarian experts of the different fields kindly accepted our invitation to present invited lectures on their research topics.
The above mentiond topics of the present conference were as follows:

• Solar physics
• Space Physics
• Celestial Mechanics
• Observational Stellar Physics
• Infrared and Radio Astronomy
• Galactic Astronomy
• Cosmology

Tamás Borkovits

K. Petrovay, P. Chaterjee, A. Choudhuri: Helical Magnetic Fields in Solar Active Regions: Theory vs. Observations - Invited Talk

The mean value of the normalized current helicity $\alpha_p=\vc B\cdot(\nabla\times\vc B)/B^2$ in solar active regions is on the order of $10^{-8}\,$m$^{-1}$, negative in the northern hemisphere, positive in the southern hemisphere. Observations indicate that this helicity has a subsurface origin. Possible mechanisms leading to a twist of this amplitude in magnetic flux tubes include the solar dynamo, convective buffeting of rising flux tubes, and the accretion of weak external poloidal flux by a rising toroidal flux tube. After briefly reviewing the observational and theoretical constraints on the origin of helicity, we present a recently developed detailed model for poloidal flux accretion.

G. Mező, T. Baranyi: East-West Asymmetry in the sunspot number distribution on the basis of different sunspots catalogues

The east-west asymmetry of the number of sunspots has been analyzed on the basis of the Debrecen Photoheliographic Data (DPD), the single spots of Greenwich Photoheliographic Results (GPHR), and the Sunspot Feature Catalogue (SFC). The DPD and SFC do not show E-W asymmetry in the number distribution of the spots for the spots with area of greater than 20 millionth of the solar hemisphere (MSH). The GPHR shows large E-W asymmetry. Its rate is increasing from center to limb while the area of the affected spots is also increasing from 10 to 50 MSH. The East-West asymmetry of the number of spots can be detected for small spots (<20 MSH) in all the three catalogues but its rate depends on the studied catalogue.

J. Muraközy, A. Ludmány: Connection of sunspot's distribution with the torsional wave

The torsional oscillation is a well-known observational fact, but its cause is unidentified yet. There were some theoretical assumptions for its reason, but no final solution has been accepted. Our work focuses on the study of correspondence between torsional waves and the distribution of several sunspot features which were based on the DPD (Debrecen Photoheliographic Data). Two of studied features show some spatial correlation with the shearing zones.

G. Facskó, K. Kecskeméty, M. Tátrallyay: Hybrid Simulations of Hot Flow Anomalies in the Light of Cluster Measurements

Known for about 20 years, the explanation of hot flow anomaly events is still far from being complete. Among the few hybrid simulations the results of Lin (2002) are cited frequently. We check some of its predictions using FGM and CIS measurements aboard Cluster. Several known geometrical features are verified and the average size of the affected determined. The results are confronted with the simulation.

A. Hirn, T. Pázmándi, S. Deme, I. Apáthy, A. Csőke, L. Bodnár: A New Method for Determining the Equivalent Dose of Astronauts

One of the many risks of long-duration space flights is the excessive exposure to cosmic radiation, which has great importance particularly during solar flares and higher solar activity. Since space radiation mainly consists of charged heavy particles, the equivalent dose differs significantly from the absorbed dose. The objectives of this project are to develop and manufacture a three-axis silicon detector telescope, and to develop software for data evaluation of the measured energy deposition spectra. Research and development began in the KFKI Atomic Energy Research Institute several years ago. Elements of the 3D telescope system, issues of the electronic block diagram, requirements for the mechanical construction and possibilities of data handling and data evaluation are analyzed in this paper.

Á. Süli: Motion indicators in the 2D standard map

In this article four motion (chaos) indicators were analyzed and compared using the framework of the 2D standard map. These indicators, namely the LCE, FLI, RLI and SALI may provide a global picture of the phase space. Until now a detailed comparison of these methods have not been performed. To supersede this imperfection is the aim of the present paper.

B. Mikóczi, Z. Keresztes: Generalized eccentric vs. true anomaly parametrizations in the perturbed Keplerian motion

The angular and the radial parts of the dynamics of the perturbed Kepler motion are separable in many important cases. In this paper we study the radial motion and its parametrizations. We develop in detail a generalized eccentric anomaly parametrization and a procedure of computing a generic class of integrals based on the residue theorem. We apply the formalism to determine various contributions to the luminosity of a compact binary.

I. Nagy, Á. Süli, B. Érdi: P-type orbits in the Pluto-Charon system

The dynamical structure of the phase space of the Pluto-Charon system is studied in the model of the spatial circular restricted three-body problem by using numerical methods. With the newly discovered two small satellites S/2005 P1 and S/2005 P2, the Pluto-Charon system can be considered as the first known binary system in which celestial bodies move in P-type orbits. It is shown that the two satellites are in the stable region of the phase space and their origin by capture is unlikely.

K. Oláh: Activity on single dwarf stars - Invited Talk

The importance of studies of late-type, low-mass active stars is discussed, with emphasis on the possible dynamo mechanisms that can be constrained through observing results.

K. Vida: Four-colour photometry of the spotted dMe-star EY Draconis

We present the first four-colour photometry and spot modelling of the fast-rotating active star EY Draconis. In the result of the modelling possible spot evolution can be seen. The observed light curve appeared to be stable through 118 rotational cycles.

R. Csorvási: Photometry of LO Pegasi in B, V, R colors

Variable magnetic activity manifested by starspot distribution is investigated on the single K5-K7 dwarf LO Peg, using one month long photometric observations. We supposed three circular spots for light curve solution. We find variable spot temperature, whose average is 3960 K. The sizes of spots were stable for two spots and one spot showed a significant decrease. Different migration periods on two spots indicate differential rotation, the magnitude of the migration is slow. During the measured 90 stellar rotations (38.5 days) the location of the activity remained on the same hemisphere of the star.

J. Bartus, Zs. Kővári, K. Oláh, T. Granzer, K.G. Strassmeier, M. Weber: STELLA Robotic Observatory for Stellar Activity Research

The STELLA Robotic Observatory (abbreviation for STELLar Activity) is a long-term project for observing and monitoring activity tracers on cool stars with two robotic telescopes: STELLA-I equipped with a high resolution echelle spectrograph, a large-format CCD imager and photometer, and STELLA-II also equipped with an optical CCD imager and photometer. After listing the most important technical details we focus on some of the scientific programs planned for routine observations of active stars by STELLA.

T. Borkovits, Sz. Csizmadia, J. Nuspl, I.B. Bíró: Indirect evidence for short period magnetic cycles in overcontact binary stars

Complex period variations of five W~UMa type binaries (AB~And, OO~Aql, DK~Cyg, V566~Oph, U~Peg) were investigated by the analysis of their O--C diagrams, and several common features were found. Four of the five systems show secular period variations at a constant rate in the order of $|\dot{P}_\mathrm{sec}/P|\sim10^{-7}$~y$^{-1}$. In the case of AB~And, OO~Aql and U~Peg a high-amplitude, nearly one-century long quasi-sinusoidal pattern was also found. It might be explained as light-time effect, or by some magnetic phenomena. The most interesting feature of the studied O--C diagrams is a low amplitude ($\sim2-4\times10^{-3}$ d) modulation with a period around 18--20 yr in four of the five cases. This phenomenon might be an indirect evidence of some magnetic cycle in late-type overcontact binaries as an analog to the observed activity cycles in RS~CVn systems.

Á. Sódor: The long term behaviour of RR Gem

The photometric observations of RR~Gem obtained at the Konkoly Observatory during the last 70 years have been analysed in search of the signs of Blazhko modulation. The analysis showed that RR~Gem was modulated nearly all the time with the same 7.21\,d period as nowadays. The amplitude of the modulation varied inversely with the variation of the pulsation period.

P. Klagyivik, L. Szabados: Metallicity dependence of some parameters of Cepheids

Dependence of phenomenological properties of Cepheids on the heavy element abundance is studied. It is found that the amplitude of the pulsation depends on the metallicity of the stellar atmosphere.

P. Székely, R. Jackson, L. L. Kiss, K. Szatmáry: A survey of variable stars in the globular cluster NGC 362

We present the first results of our survey in NGC 362 globular cluster. We found numerous variable stars in the field: 38 RR Lyr stars, 5 eclipsing binaries and 13 other pulsating stars. Five RR Lyrae stars can be member of the halo/SMC population.

Cs. Kiss, A. Pál, Th. Müller, P. Ábrahám: An asteroid model of the mid- and far-infrared sky

We developed a statistical model for the asteroid component of the far-infrared sky for wavelengths \lele{5\,$\mu$m}{$\lambda$}{1000\,$\mu$m} based on the Statistical Asteroid Model (Tedesco et al., 2005). Far-infrared fluxes of $\sim$1.9 million asteroids are used to calculate confusion noise values and expected asteroid counts for space IR instruments in operation or in the near future. Our results show that the confusion noise due to asteroids will not increase the detection threshold for most of the sky. However, there are specific areas near the ecliptic plane where the effect of asteroids can be comparable to the contribution of Galactic cirrus emission and of the extragalactic background.

Á. Kóspál, D. Apai, P. Ábrahám: Parsamian 21: a FUor surrounded by an edge-on disc

FU Orionis objects (FUors) are young stars that have recently undergone major outbursts, probably powered by enhanced accretion from the circumstellar disc to the star. Parsamian 21 is a unique FUor, as it is thought to be surrounded by an edge-on circumstellar disc, making it an ideal case for studying the geometry and structure of the circumstellar material. In this paper we report on new adaptive optics assisted near-infrared direct and polarimetric measurements of Parsamian 21 taken with the NaCO instrument on the VLT. With the help of these observations, we search for companions and study the innermost part of the circumstellar disc with an unprecedented resolution and contrast.

S. Frey, P. Veres, K. Vida: Celestial positions in radio and optical

We discuss the importance of the direct link between the most accurate radio and optical reference frames that will become possible with the next-generation space astrometry missions in about a decade. The positions of more than 500 active galactic nuclei that are common in the precise Very Long Baseline Interferometry (VLBI) catalogues and the Sloan Digital Sky Survey (SDSS) Data Release 4 (DR4) are compared. While obtaining an ``independent'' estimate for the SDSS coordinate accuracies, we find indications that the assumption of spatially coincident brightness peaks for the same objects in radio and optical does not hold for each object.

L. Mosoni: Interferometry in radio and infrared

In this paper I give three brief examples, two astrophysical applications and an image reconstruction study for a future instrument, of interferometric projects in which Hungarian groups are involved.

Z. Kovács: Test of the Infrared Wide-Field Camera OMEGA2000 and its Application for an Extragalactic Survey

The near-infrared wide-field camera OMEGA2000, mounted on the 3.5m telescope at Calar Alto is presented here. We give an overview on the first results of its scientific operation for the MANOS project. We discuss briefly the redshift and spectral energy distribution of the red bright galaxy sample detected in one of the COMBO-17 fields.

L.G. Balázs: Statistical phenomena in astronomy - Invited Talk

This paper represents the short version of the author's DSc theses. The whole text is available at the web site of http://www.konkoly.hu/staff/balazs/dissertation.pdf

Z. T. Kiss, L. V. Tóth, L. G. Balázs, V. Könyves: The distribution of photometrically selected T Tauri candidates in the outer Galaxy

We mapped the NIR extinction in the 2$^{nd}$ and 3$^{rd}$ galactic quadrant in the $\pm30\deg$ latitude range covering a $\approx$10300 square degree area based on the 2MASS Point Source Catalogue. We selected the sources with T~Tauri like NIR colours, and investigated their distribution. We describe the variation of the CTT candidate number density as function of galactic latitude and longitude. We searched for CTT candidate clustering and compiled a catalogue of associations found. We found that significant fraction of clusters found are situated in the shells of GIRLs.

G. Marschalkó: Superdiffusion in molecular clouds

The chemistry of molecular clouds is a complex system influenced by wide scale of different factors; amongst them one of the most important is the turbulent diffusion. Whilst the previous improved models laid emphasis on the chemistry, we wish to examine the turbulence with special regard to the superdiffusion.

D. Koronczay: Evolution of Luminous Red Galaxies based on SDSS data

We compared the broadband colors of different simulated galaxies with $\sim10^5$ luminous red galaxies from the Sloan Digital Sky Survey to obtain constraints for the possible star formation histories of this type of galaxies. The simulation was done using the GALAXEV evolutionary stellar population synthesis code. Our results are consistent with these objects having solar metallicities, having formed 11 Gyr before present and evolving passively, without significant star formation since then.

N. Sipos, J. Vinkó: Interstellar Reddening of Type Ia Supernovae

We re-investigate the Lira-Phillips relation of Type Ia supernovae and its use for determination of reddening of individual SNe Ia. We use a more recent, more extensive dataset of SNe Ia with negligible reddening, and attempt to refine the prediction of the intrinsic B-V color index. We find that the Lira-Phillips relation is valid, but the dispersion of the intrinsic B-V colors is substantial. The present data may suggest slightly redder intrinsic colors, thus, the previously calculated total extinctions (and the corresponding distance moduli) should be decreased by $\sim 0.19$ mag.

Z. Keresztes, I. Képíró: Irradiated closed Friedmann brane-worlds

We consider the evolution of a closed Friedmann brane irradiated by a bulk black hole. Both absorption on the brane and transmission across the brane are allowed, the latter representing a generalization over a previously studied model. Without transmission, a critical behaviour could be observed, when the acceleration due to radiation pressure and the deceleration introduced by the increasing self-gravity of the brane roughly compensate each other. We show here that increasing transmission leads to the disappearance of the critical behaviour.

László Á. Gergely, Barbara Darázs: Weak gravitational lensing in brane-worlds

We derive the deflection angle of light rays caused by a brane black hole with mass $m$ and tidal charge $q$ in the weak lensing approach, up to the second order in perturbation theory. We point out when the newly derived second order contributions become important.

B. Nagy, Z. Keresztes: On the luminosity-redshift relation in brane-worlds with cosmological constant

In this paper we calculate the luminosity distance - redshift relation for a special type of flat Friedmann branes with cosmological constant. This special case is singled out by its simplicity, the luminosity distance being given in terms of elementary functions. We compare our analytical result with the expresssion of the luminosity distance for the flat Friedmann-Lemaitre-Robertson-Walker (FLRW) universe and discuss the differences.

Zs. Horváth, Z. Kovács: Canonical theory of the Kantowski-Sachs cosmological models

We briefly discuss the Hamiltonian formalism of the Kantowski-Sachs space-times with vacuum, anisotropic fluid and two cross-streaming radiation field sources. For these models a cosmological time is introduced. New constraints are found in which the fluid momenta are separated from the rest of the variables. In consequence their Poisson brackets give an Abelian algebra.

J. Majár: Gravitational Waveforms from Compact Binary Systems

Here we present the basics of the method for determining the polarization states $h_+$ and $h_{\times}$ of the detectable gravitational waves emitted by a compact spinning binary system. The waveform and the dynamics of the binary are described with the use of the post-Newtonian (PN) approximation up to 1.5\,PN relative order, related to the leading order newtonian expressions. Beyond point mass effects we investigate the influence of the rotation of the bodies on the waveform to linear order, in the case of eccentric orbits.

Zs. Hetesi, L. Végh: On anthropic principles fine tuning and chaos

Anthropic principles were grown from the problem of fine tuning. Although anthropic principles have been discussed in cosmology for years there are no exact definitions for fine tuning. To define the fine tuning quantitatively we investigate how one can use Lyapunov indicator in the definition of fine tuning. Our result is an alternative Lyapunov indicator, which shows how fine tuned is a possible Universe with physical constants different from ours.