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The large-scale magnetic field of the Sun and solar-type stars is probably generated near the interface of the radiative core and the convection zone. One of the well-known difficulties of interface-type and other dynamo models is to explain the latitudinal distribution of magnetic fields as observed on the Sun. In this contribution new results of numerical MHD simulations of transport coefficients of magnetic fields in the rapid rotation regime, relevant for the base of the solar convection zone, are presented that may contribute to explaining the latitudinal distribution of magnetic fields observed on the Sun. A brief outlook on further numerical simulations of transport coefficients and their relevance for mean-field dynamo theory is given.
The recent on-line availability of large-scale, wide-field surveys of the Galaxy and Magellanic Clouds in several optical and near/mid-infrared passbands has provided unprecedented opportunities to refine selection techniques and eliminate contaminants in PN surveys. This has been coupled with new surveys offering improved detection rates via higher sensitivity and resolution. This will permit more extreme ends of the PN luminosity function to be explored and enable studies of under represented PN evolutionary states. Known PNe in our Galaxy and LMC have thus been significantly increased over the last few years due primarily to the advent of narrow-band imaging in important nebula lines such as H$\alpha$, [O iii] and [S iii]. These PNe are generally of lower surface brightness, larger angular extent, in more obscured regions and in later stages of evolution than those in most previous surveys. A more representative PN population for in-depth study is now available, particularly in the LMC where the known distance adds considerable utility for derived PN parameters. Future prospects for Galactic and LMC PNe research are briefly highlighted.
It is great privilege for me to welcome so many of you to Prague, or Praha as we call our capital in Czech.
We have been witnessing a very rapid development of observational techniques over the past few decades, leading to many exciting discoveries, quite often in the field of extragalactic research. I sometimes sense the tendency to consider the studies of binaries and stars in general as exhausted topics. However, we all know that the better our real and deep understanding of the principal sources of radiative energy in the Universe becomes, the safer will be the ground for studies of all higher hierarchical systems.
The warm neutral medium, warm ionized medium, and cool neutral medium all show strong evidence for turbulence as a process dominating their structure and motions on a wide range of scales. The spatial power spectra of density fluctuations in all three phases are consistent with a Kolmogorov slope. Turbulence in the magnetic field in the diffuse medium can also be measured through the structure function of the Faraday rotation measure. With new surveys, new analysis techniques, and new telescopes, in the next few years it will be possible to measure the structure function of the magnetic field over a similarly wide range of scales. This will give a complete picture of the turbulence as a magneto-acoustic process.
This talk describes a proposal to set up a series of international institutions in different parts of the world to serve as nodes in a network that links astronomers from the developing nations worldwide. This network, along with its nodes is visualized as an economic way of upgrading the facilities for teaching, research and development of astronomy in the Third World countries. By way of illustration, the modus-operandi of the Inter-University Centre for Astronomy and Astrophysics in Pune, India is described. A network of this kind is suggested as a cost-efficient way of sharing limited resources.
We review the status of current observations of the fundamental parameters of intermediate redshift (z ≤ 1.2) disk galaxies. Advances in instrumentation of 8-10m class telescopes have made possible detailed measurements of galaxy luminosity, morphology, kinematics and mass, in both the optical and the infrared passbands. By studying such well known star formation indicators as [OII]3727A (in the optical) and Hα (redshifted to the infrared), the internal velocity structure and star formation rates of galaxies can be traced through this entire redshift regime. The combination of throughput and optimum seeing conditions yields spectra which can be combined with high resolution multiband imaging to explore the evolution of galaxies of various morphologies, and to place constraints on current models of galaxy formation and star formation histories.
Out to redshifts of unity, these data form a high redshift Tully-Fisher relation that spans four magnitudes and extends to well below L*, with no obvious change in shape or slope with respect to the local relation. A comparison of disk surface brightness between local and high redshift samples yields an offset in accordance with distance-dependent surface brightness selection effects, as can the apparent change in disk size with redshift for disks of a given mass. These results support low Ω0 models of formation, and provide further evidence for modest increases in luminosity with lookback time for the bulk of the observed field spiral galaxy population.
Finally, a comparison of spatially resolved spectra versus integrated emission line widths for distant galaxies suggests that observational constraints bias each type of observational sample toward different sub-groups of galaxies, with different evolutionary histories. Like varying selection effects, this will lead to a wide range of projected evolutionary trends.
Some of the problems related to Near Earth Objects (NEOs), like orbit determination and ephemeris computation, are not new, and had to be dealt with since the beginning of NEO astronomy. The latter practically started with the discovery of Comet D/1770 L1 Lexell, that passed very close to the Earth in 1770; studies of the chaotic dynamics of this exceptional object continued well into the XIXth century. At the end of the XXth century there has been a renewal of interest in NEOs, as attested by IAU Symposium 236.
Welcome to Prague. Welcome to this Congress Centre built in a close neighbourhood of the ancient seat of the first Czech dukes (Fig. 1). Its name Vyšehrad means the Upper Town. According to the oldest Czech chronicles, it was here where the legendary princess Libuše ordered her people to found the city of Prague and where she envisaged its glory touching the stars (Fig. 2). It was also here where the canon of Vyšehrad recorded in the first half of the 12th century into his chronicle some observed astronomical and meteorological phenomena.
We briefly review some constraints for stellar models in various mass regimes and evolutionary stages as provided by observational data from spectroscopy to multi-wavelenghts photometry. The accuracy of present generation of stellar models can be significantly improved only through an extensive comparison between theory and observations.
If one strives for a reliable description of “Turbulent Mixing in Stars” one must account for a large variety of physical processes. These include non-locality, that is needed in unstably stratified regimes, overshooting, which occurs in a stably stratified regime, double-diffusion processes (semi-convection and salt-fingers), transport of angular momentum, the Li7 problem, compressibility, and magnetic fields. While phenomenological models are manifestly inadequate, LES are too computer intensive to tackle this large variety of processes. Since the requirement of completeness of the description of these processes must also result in models that are usable in stellar structure-evolution codes, we conclude that only the RSM (Reynolds Stress Model) can do so and a description of the state of the art in that field is presented in Part 2.
Radial velocity studies of X-ray binaries provide the most solid evidence for the existence of stellar-mass black holes. We currently have 20 confirmed cases, with dynamical masses in excess of 3 M⊙. Accurate masses have been obtained for a subset of systems which gives us a hint at the mass spectrum of the black hole population. This review summarizes the history of black hole discoveries and presents the latest results in the field.
The Tully-Fisher Relation (TFR) links two fundamental properties of disk galaxies: their luminosity and their rotation velocity (mass). The pioneering work of Vogt et al. in the 1990's showed that it is possible to study the TFR for spiral galaxies at considerable look-back-times, and use it as a powerful probe of their evolution. In recent years, several groups have studied the TFR for galaxies in different environments reaching redshifts beyond one. In this brief review I summarise the main results of some of these studies and their consequences for our understanding of the formation and evolution of disk galaxies. Particular emphasis is placed on the possible environment-driven differences in the behaviour of the TFR for field and cluster galaxies.
After a brief review of the observational evidences indicating how the populations of Be stars, red/blue supergiants, Wolf-Rayet stars vary as a function of metallicity, we discuss the implications of these observed trend for our understanding of the massive star evolution. We show how the inclusion of the effects of rotation in stellar models improves significantly the correspondence between theory and observation.
The observational record of turbulence within the molecular gas phase of the interstellar medium is summarized. We briefly review the analysis methods used to recover the velocity structure function from spectroscopic imaging and the application of these tools on sets of cloud data. These studies identify a near-invariant velocity structure function that is independent of the local environment and star formation activity. Such universality accounts for the cloud-to-cloud scaling law between the global line-width and size of molecular clouds found by Larson (1981) and constrains the degree to which supersonic turbulence can regulate star formation. In addition, the evidence for large scale driving sources necessary to sustain supersonic flows is summarized.
An overview is presented of the many new and exciting developments in binary and multiple star studies that were discussed at IAU Symposium 240. Impacts on binary and multiple star studies from new technologies, techniques, instruments, missions and theory are highlighted. It is crucial to study binary and multiple stars because the vast majority of stars (>60%) in our Galaxy and in other galaxies consist, not of single stars, but of double and multiple star systems. To understand galaxies we need to understand stars, but since most are members of binary and multiple star systems, we need to study and understand binary stars. The major advances in technology, instrumentation, computers, and theory have revolutionized what we know (and also don't know) about binary and multiple star systems. Data now available from interferometry (with milliarcsecond [mas] and sub-mas precisions), high-precision radial velocities (∼1-2 m/s) and high precision photometry (<1–2 milli-mag) as well as the wealth of new data that are pouring in from panoramic optical and infrared surveys (e.g., > 10,000 new binaries found since 1995), have led to a renaissance in binary star and multiple star studies. For example, advances have lead to the discovery of new classes of binary systems with planet and brown dwarf components (over 200 systems). Also, extremely valuable data about binary stars are available across the entire electromagnetic spectrum — from gamma-ray to IR space missions and from the ground using increasingly more powerful and plentiful optical and radio telescopes as well as robotic telescopes. In the immediate future, spectral coverage could even be extended beyond the radio to the first detection of gravity waves from interacting close binaries. Also, both the quality and quantity of data now available on binary and multiple stars are making it possible to gain unprecedented new insights into the structure, and formation and evolution of binary stars, as well as providing valuable astrophysical information (like precise stellar masses, radii, ages, luminosities and distances) to test and constrain current astrophysical theory. These major advances permit tests of current theories and ideas in stellar astrophysics and provide the foundations for the next steps in modeling and improvements in theory to be taken.
The exact solution of the evolution equation for the magnetic field in ideal MHD, Callebaut (2006), with an azimuthal velocity which is function of $r$ and $\vartheta$ only (spherical coordinates) is applied to a bipolar magnetic seed field and to a quadripolar field. Resistivity and $\alpha$-effect are not yet taken into account, but the extensions are possible. From the surface observations we had derived an approximate analytic expression for the differential rotation in order to work fully analytically in the application. Qualitatively the results for a quadripolar field are as for a bipolar seed field. The main features are the same: for some latitudes the field may increase by two orders of magnitude, the separation between sunspots and polar faculae is clearcut, there is, relatively speaking, a too strong amplification in the polar regions (the latter occurs in other models too). The hypothesis that the seed fields are situated at the tachocline is not required: the amplification is active throughout the whole convective zone, albeit with different strengths, and thus during the transit of the flux tubes from tachocline to the solar surface too.
We investigate the energy dependencies of X-ray quasi-periodic oscillations in black hole X-ray binaries. We analyze RXTE data on both the low- and high-frequency QPO. We construct the low-f QPO energy spectra, and demonstrate that they do not contain the thermal disk component, even though the latter is present in the time averaged spectra. The disk thus does not seem to participate in the oscillations. Moreover the QPO spectra are harder than the time averaged spectra when the latter are soft, which can be modeled as a result of modulations occurring in the hot plasma. The QPO spectra are softer than the time averaged spectra when the latter are hard. The absence of the disk component in the QPO spectra is true also for the high-frequency (hecto-Hz) QPO observed in black hole binaries. We compute the QPO spectra expected from the model of disk resonances.
George Wetherill and I worked together as scientific collaborators when I was a postdoctoral fellow in 1977-1978 at the Department of Terrestrial Magnetism (DTM) of the Carnegie Institution of Washington (CIW) in Washington, D.C. We worked on problems of meteoroids interacting in Earth's atmosphere along with Richard McCrosky at Harvard College Observatory and Zdeněk Ceplecha at the Ondřejov Observatory in Czechoslovakia and also with Sundar Rajan who had already arrived at DTM from the University of California at Berkeley before me.
The Local Group (LG) represents the best environment to study in detail the PN population in a large number of morphological types of galaxies. The closeness of the LG galaxies allows one to investigate the faintest side of the PN luminosity function and to detect PNe also in the less luminous galaxies, the dwarf galaxies, where a small number of them is expected.
A review of the results of the most recent imaging surveys in the LG is presented. Some applications of the surveys for PNe to the study of the star formation history of the host galaxies are analyzed. In addition, these new observational data are an invaluable resource for follow-up spectroscopy to derive the chemical properties of not only PNe, but also other important emission-line sources like HII regions. These are fundamental tools for the discussion of the chemical evolution of the host galaxies, mapping the history of their chemical enrichment at different epochs. The latest results on this subject are presented.
In this paper I report the results of a survey of the astronomical outputs of all 63 IAU member countries as well as several non-member countries, based on an analysis of the affiliations of the authors given for nearly 900 thousand astronomical papers appearing in ADS between the years 1976 and 2005. The results show a roughly three-fold increase in the number of published papers per year over this 30-year interval. This increase is seen both in developed and also in most developing countries. The number of publications per IAU member correlates strongly with gross domestic product. It is over 2 papers per IAU member per year in the countries with the strongest economies but less than 0.5 in the countries with low GDP per capita. Since 2001 there has been a dramatic increase in the number of multi-author multinational papers published. This increase is especially noticeable for authors in developing countries, indicating that astronomers in these countries are increasingly participating in international collaborations for their research activities.