ALBERT

Description:    A comprehensive review is given of the theory and properties of nonrelativistic shocks in hot collisionless plasmas—in view of their possible application in astrophysics. Understanding non-relativistic collisionless shocks is an indispensable step towards a general account of collisionless astrophysical shocks of high Mach number and of their effects in dissipating flow-energy, in heating matter, in accelerating particles to high—presumably cosmic-ray—energies, and in generating detectable radiation from radio to X-rays. Non-relativistic shocks have Alfvénic Mach numbers \fancyscript M A 〈〈 Ö   m i / m e   ( w pe / w ce ) , where m i / m e is the ion-to-electron mass ratio, and ω pe , ω ce are the electron plasma and cyclotron frequencies, respectively. Though high, the temperatures of such shocks are limited (in energy units) to T 〈 m e c 2 . This means that particle creation is inhibited, classical theory is applicable, and reaction of radiation on the dynamics of the shock can be neglected. The majority of such shocks are supercritical, meaning that non-relativistic shocks are unable to self-consistently produce sufficient dissipation and, thus, to sustain a stationary shock transition. As a consequence, supercritical shocks act as efficient particle reflectors. All these shocks are microscopically thin, with shock-transition width of the order of the ion inertial length λ i = c / ω pi (with ω pi the ion plasma frequency). The full theory of such shocks is developed, and the different possible types of shocks are defined. Since all collisionless shocks are magnetised, the most important distinction is between quasi-perpendicular and quasi-parallel shocks. The former propagate about perpendicularly, the latter roughly parallel to the upstream magnetic field. Their manifestly different behaviours are described in detail. In particular, although both types of shocks are non-stationary, they have completely different reformation cycles. From numerical full-particle simulations it becomes evident that, on ion-inertial scales close to the shock transition, all quasi-parallel collisionless supercritical shocks are locally quasi-perpendicular. This property is of vital importance for the particle dynamics near the quasi-parallel shock front. Considerable interest focusses on particle acceleration and the generation of radiation. Radiation from non-relativistic shocks results mainly in wave–wave interactions among various plasma waves. Non-thermal charged particles can be further accelerated to high energies by a Fermi-like mechanism. The important question is whether the shock can pre-accelerate shock-reflected particles to sufficiently high energies in order to create the seed-population of the non-thermal particles required by the Fermi mechanism. Based on preliminary full-particle numerical simulations, this question is answered affirmatively. Such simulations provide ample evidence that collisionless shocks with high-Mach numbers—even when non-relativistic—could probably by themselves produce the energetic seed-particle population for the Fermi-process. Content Type Journal Article Category Review Article Pages 409-535 DOI 10.1007/s00159-009-0024-2 Authors R. A. Treumann, Department of Geophysics and Environmental Sciences, Geophysics Section, Ludwig-Maximilians-University Munich, Theresienstr. 37-41, 80333 Munich, Germany Journal Astronomy and Astrophysics Review Online ISSN 1432-0754 Print ISSN 0935-4956 Journal Volume Volume 17 Journal Issue Volume 17, Number 4

Description:    Saturn’s satellite Titan is a particularly interesting body in our solar system. It is the only satellite with a dense atmosphere, which is primarily made of nitrogen and methane. It harbours an intricate photochemistry, that populates the atmosphere with aerosols, but that should deplete irreversibly the methane. The observation that methane is not depleted led to the study of Titan’s methane cycle, starting with its atmospheric part. The features that inhabit Titan’s atmosphere can last for timescales varying from year to day. For instance, the reversal of the north–south asymmetry is linked to the 16-year seasonal cycle. Diurnal phenomena have also been observed, like a stratospheric haze enhancement or a possible tropospheric drizzle. Furthermore, clouds have been reported on Titan since 1993. From these first detections and up to now, with the recent inputs from the Cassini–Huygens mission, clouds have displayed a large range of shapes, altitudes, and natures, from the flocky tropospheric clouds at the south pole to the stratiform ones in the northern stratosphere. It is still difficult to compose a clear picture of the physical processes governing these phenomena, even though of lot of different means of observation (spectroscopy, imaging) are available now. We propose here an overview of the phenomena reported between 1993 and 2008 in the low atmosphere of Titan, with indications on the location, altitude, and their characteristics in order to give a perspective of our up-to-date understanding of Titan’s meteorological manifestations. We shall focus mainly on direct imaging observations, from both space- and ground-based facilities. All of these observations, published in more than 30 different refereed papers to date, allow us to build a precise chronology of Titan’s atmospheric changes (including the north–south asymmetry, diurnal and seasonal effects, etc). Since the interpretation is at an early stage, we only briefly mention some of the current theories regarding the features’ nature. Content Type Journal Article Category Review Article Pages 105-147 DOI 10.1007/s00159-009-0018-0 Authors Mathieu Hirtzig, LATMOS, IPSL Verrières-le-Buisson France Tetsuya Tokano, Universität zu Köln Institut für Geophysik und Meteorologie Cologne Germany Sébastien Rodriguez, CNRS, UniversitéParis Diderot, IRFU/SAp Laboratoire AIM, CEA/DSM Gif-sur-Yvette France Stéphane le Mouélic, Laboratoire de Planétologie et Géodynamique Nantes France Christophe Sotin, Jet Propulsion Laboratory Pasadena CA USA Journal Astronomy and Astrophysics Review Online ISSN 1432-0754 Print ISSN 0935-4956 Journal Volume Volume 17 Journal Issue Volume 17, Number 2

Description:    We review the properties and nature of luminous high-redshift radio galaxies (HzRGs, z 〉 2) and the environments in which they are located. HzRGs have several distinct constituents which interact with each other—relativistic plasma, gas in various forms, dust, stars and an active galactic nucleus (AGN). These building blocks provide unique diagnostics about conditions in the early Universe. We discuss the properties of each constituent. Evidence is presented that HzRGs are massive forming galaxies and the progenitors of brightest cluster galaxies in the local Universe. HzRGs are located in overdense regions in the early Universe and are frequently surrounded by protoclusters. We review the properties and nature of these radio-selected protoclusters. Finally we consider the potential for future progress in the field during the next few decades. A compendium of known HzRGs is given in an appendix. Content Type Journal Article Category Review Article Pages 67-144 DOI 10.1007/s00159-007-0008-z Authors George Miley, Sterrewacht, Leiden University Postbus 9513 2300RA Leiden The Netherlands Carlos De Breuck, European Southern Observatory Karl-Schwarzschild-Strasse 2 85748 Garching Germany Journal Astronomy and Astrophysics Review Online ISSN 1432-0754 Print ISSN 0935-4956 Journal Volume Volume 15 Journal Issue Volume 15, Number 2

Description:    We review how the recent increase in X-ray and radio data from black hole and neutron star binaries can be merged together with theoretical advances to give a coherent picture of the physics of the accretion flow in strong gravity. Both long term X-ray light curves, X-ray spectra, the rapid X-ray variability and the radio jet behaviour are consistent with a model where a standard outer accretion disc is truncated at low luminosities, being replaced by a hot, inner flow which also acts as the launching site of the jet. Decreasing the disc truncation radius leads to softer spectra, as well as higher frequencies (including quasi periodic oscillations, QPOs) in the power spectra, and a faster jet. The collapse of the hot flow when the disc reaches the last stable orbit triggers the dramatic decrease in radio flux, as well as giving a qualitative (and often quantitative) explanation for the major hard–soft spectral transition seen in black holes. The neutron stars are also consistent with the same models, but with an additional component due to their surface, giving implicit evidence for the event horizon in black holes. We review claims of observational data which conflict with this picture, but show that these can also be consistent with the truncated disc model. We also review suggested alternative models for the accretion flow which do not involve a truncated disc. The most successful of these converge on a similar geometry, where there is a transition at some radius larger than the last stable orbit between a standard disc and an inner, jet dominated region, with the X-ray source associated with a mildly relativistic outflow, beamed away from the disc. However, the observed uniformity of properties between black holes at different inclinations suggests that even weak beaming of the X-ray emission may be constrained by the data. After collapse of the hot inner flow, the spectrum in black hole systems can be dominated by the disc emission. Its behaviour is consistent with the existence of a last stable orbit, and such data can be used to estimate the black hole spin. By contrast, these systems can also show very different spectra at these high luminosities, in which the disc spectrum (and probably structure) is strongly distorted by Comptonization. The structure of the accretion flow becomes increasingly uncertain as the luminosity approaches (and exceeds) the Eddington luminosity, though there is growing evidence that winds may play an important role. We stress that these high Eddington fraction flows are key to understanding many disparate and currently very active fields such as ULX, Narrow Line Seyfert 1’s, and the growth of the first black holes in the Early Universe. Content Type Journal Article Category Review Article Pages 1-66 DOI 10.1007/s00159-007-0006-1 Authors Chris Done, University of Durham Department of Physics South Road Durham DH1 3LE UK Marek Gierliński, University of Durham Department of Physics South Road Durham DH1 3LE UK Aya Kubota, Institute of Physical and Chemical Research (RIKEN) 2-1 Hirosawa, Wako Saitama 351-019 Japan Journal Astronomy and Astrophysics Review Online ISSN 1432-0754 Print ISSN 0935-4956 Journal Volume Volume 15 Journal Issue Volume 15, Number 1

Description:    Mass loss is a key process in the evolution of massive stars, and must be understood quantitatively if it is to be successfully included in broader astrophysical applications such as galactic and cosmic evolution and ionization. In this review, we discuss various aspects of radiation driven mass loss, both from the theoretical and the observational side. We focus on developments in the past decade, concentrating on the winds from OB-stars, with some excursions to the winds from Luminous Blue Variables (including super-Eddington, continuum-driven winds), winds from Wolf–Rayet stars, A-supergiants and Central Stars of Planetary Nebulae. After recapitulating the 1-D, stationary standard model of line-driven winds, extensions accounting for rotation and magnetic fields are discussed. Stationary wind models are presented that provide theoretical predictions for the mass-loss rates as a function of spectral type, metallicity, and the proximity to the Eddington limit. The relevance of the so-called bi-stability jump is outlined. We summarize diagnostical methods to infer wind properties from observations, and compare the results from corresponding campaigns (including the VLT- flames survey of massive stars) with theoretical predictions, featuring the mass loss-metallicity dependence. Subsequently, we concentrate on two urgent problems, weak winds and wind-clumping , that have been identified from various diagnostics and that challenge our present understanding of radiation driven winds. We discuss the problems of “measuring” mass-loss rates from weak winds and the potential of the NIR Br α -line as a tool to enable a more precise quantification, and comment on physical explanations for mass-loss rates that are much lower than predicted by the standard model. Wind-clumping, conventionally interpreted as the consequence of a strong instability inherent to radiative line-driving, has severe implications for the interpretation of observational diagnostics, since derived mass-loss rates are usually overestimated when clumping is present but ignored in the analyses. Depending on the specific diagnostics, such overestimates can amount to factors of 2 to 10, and we describe ongoing attempts to allow for more uniform results. We point out that independent arguments from stellar evolution favor a moderate reduction of present-day mass-loss rates. We also consider larger scale wind structure, interpreted in terms of co-rotating interacting regions, and complete this review with a discussion of recent progress on the X-ray line emission from massive stars. Such emission is thought to originate both from magnetically confined winds and from non-magnetic winds, in the latter case related to the line-driven instability and/or clump-clump collisions. We highlight as to how far the analysis of such X-ray line emission can give further clues regarding an adequate description of wind clumping. Content Type Journal Article Category Review Article Pages 209-325 DOI 10.1007/s00159-008-0015-8 Authors Joachim Puls, Universitätssternwarte München Scheinerstr. 1 81679 München Germany Jorick S. Vink, Armagh Observatory College Hill Armagh BT61 9DG Northern Ireland, UK Francisco Najarro, CSIC Instituto de Estructura de la Materia Serrano 121 28006 Madrid Spain Journal Astronomy and Astrophysics Review Online ISSN 1432-0754 Print ISSN 0935-4956 Journal Volume Volume 16 Journal Issue Volume 16, Numbers 3-4

Description:    Ions heavier than 4 He are treated as “minors” in the solar wind. This is justified for many applications since minor ions have no significant influence on the dynamics of the interplanetary plasma. However, minor ions carry information on many aspects of the formation, on the acceleration and on the transfer of solar plasma from the corona into the interplanetary space. This review concentrates on various aspects of minor ions as diagnostic tracers. The elemental abundance patterns of the solar wind are shaped in the chromosphere and in the lower transition region by processes, which are not fully understood at this moment. Despite this lack of detailed understanding, observed abundance patterns have been classified and are now commonly used to characterize the sources, and to trace back solar-wind flows to their origins in the solar atmosphere. Furthermore, the solar wind is the most important source of information for solar isotopic abundances and for solar abundances of volatile elements. In order to fully exploit this information, a comprehensive understanding of elemental and isotopic fractionation processes is required. We provide observational clues to distinguish different processes at work. Content Type Journal Article Category Paper Pages 1-40 DOI 10.1007/s00159-006-0002-x Authors Peter Bochsler, University of New Hampshire Institute for the Study of Earth, Oceans and Space, Morse Hall Durham NH 03824 USA Journal Astronomy and Astrophysics Review Online ISSN 1432-0754 Print ISSN 0935-4956 Journal Volume Volume 14 Journal Issue Volume 14, Number 1

Description:    This review surveys hard X-ray emissions of non-thermal electrons in the solar corona. These electrons originate in flares and flare-related processes. Hard X-ray emission is the most direct diagnostic of electron presence in the corona, and such observations provide quantitative determinations of the total energy in the non-thermal electrons. The most intense flare emissions are generally observed from the chromosphere at footpoints of magnetic loops. Over the years, however, many observations of hard X-ray and even γ-ray emission directly from the corona have also been reported. These coronal sources are of particular interest as they occur closest to where the electron acceleration is thought to occur. Prior to the actual direct imaging observations, disk occultation was usually required to study coronal sources, resulting in limited physical information. Now RHESSI has given us a systematic view of coronal sources that combines high spatial and spectral resolution with broad energy coverage and high sensitivity. Despite the low density and hence low bremsstrahlung efficiency of the corona, we now detect coronal hard X-ray emissions from sources in all phases of solar flares. Because the physical conditions in such sources may differ substantially from those of the usual “footpoint” emission regions, we take the opportunity to revisit the physics of hard X-radiation and relevant theories of particle acceleration. Content Type Journal Article Category Review Article Pages 155-208 DOI 10.1007/s00159-008-0014-9 Authors S. Krucker, University of California Space Sciences Laboratory Berkeley CA 94720-7450 USA M. Battaglia, ETH Zurich Institute of Astronomy 8093 Zurich Switzerland P. J. Cargill, Blackett Laboratory, Imperial College Space and Atmospheric Physics London SW7 2BW UK L. Fletcher, University of Glasgow Department of Physics and Astronomy Glasgow G12 8QQ UK H. S. Hudson, University of California Space Sciences Laboratory Berkeley CA 94720-7450 USA A. L. MacKinnon, University of Glasgow DACE/Department of Physics and Astronomy Glasgow G12 8QQ UK S. Masuda, Nagoya University Solar-Terrestrial Environment Laboratory Furo-cho, Chikusa-ku Nagoya 4648601 Japan L. Sui, Solar Physics Laboratory NASA Goddard Space Flight Center Code 671 Greenbelt MD 20771 USA M. Tomczak, University of Wroclaw Astronomical Institute ul. Kopernika 11 51-622 Wroclaw Poland A. L. Veronig, University of Graz Institute of Physics/IGAM Universitätsplatz 5 8010 Graz Austria L. Vlahos, University of Thessaloniki Department of Physics Thessaloniki 54124 Greece S. M. White, University of Maryland Astronomy Department College Park MD 20742 USA Journal Astronomy and Astrophysics Review Online ISSN 1432-0754 Print ISSN 0935-4956 Journal Volume Volume 16 Journal Issue Volume 16, Numbers 3-4

Description:    Asteroseismology provides us with a unique opportunity to improve our understanding of stellar structure and evolution. Recent developments, including the first systematic studies of solar-like pulsators, have boosted the impact of this field of research within astrophysics and have led to a significant increase in the size of the research community. In the present paper we start by reviewing the basic observational and theoretical properties of classical and solar-like pulsators and present results from some of the most recent and outstanding studies of these stars. We centre our review on those classes of pulsators for which interferometric studies are expected to provide a significant input. We discuss current limitations to asteroseismic studies, including difficulties in mode identification and in the accurate determination of global parameters of pulsating stars, and, after a brief review of those aspects of interferometry that are most relevant in this context, anticipate how interferometric observations may contribute to overcome these limitations. Moreover, we present results of recent pilot studies of pulsating stars involving both asteroseismic and interferometric constraints and look into the future, summarizing ongoing efforts concerning the development of future instruments and satellite missions which are expected to have an impact in this field of research. Content Type Journal Article Category Review Article Pages 217-360 DOI 10.1007/s00159-007-0007-0 Authors M. S. Cunha, Centro de Astrofísica da Universidade do Porto Rua das Estrelas 4150-762 Porto Portugal C. Aerts, Katholieke Universiteit Leuven Instituut voor Sterrenkunde Celestijnenlaan 200 D 3001 Leuven Belgium J. Christensen-Dalsgaard, Aarhus Universitet Institut for Fysik og Astronomi Aarhus Denmark A. Baglin, UMR CNRS 8109 LESIA Observatoire de Paris Paris France L. Bigot, UMR 6202 Observatoire de la Côte d’Azur BP 4229 06304 Nice Cedex 4 France T. M. Brown, Las Cumbres Observatory Inc. Goleta CA 93117 USA C. Catala, UMR CNRS 8109 LESIA Observatoire de Paris Paris France O. L. Creevey, National Center for Atmospheric Research High Altitude Observatory Boulder CO 80301 USA A. Domiciano de Souza, Max-Planck-Institut für Radioastronomie Auf dem Hügel 69 53121 Bonn Germany P. Eggenberger, Observatoire de Genève 51 chemin des Maillettes 1290 Sauverny Switzerland P. J. V. Garcia, Centro de Astrofísica da Universidade do Porto Rua das Estrelas 4150-762 Porto Portugal F. Grundahl, Aarhus Universitet Institut for Fysik og Astronomi Aarhus Denmark P. Kervella, UMR CNRS 8109 LESIA Observatoire de Paris Paris France D. W. Kurtz, University of Central Lancashire Centre for Astrophysics Preston PR1 2HE UK P. Mathias, UMR 6203 Observatoire de la Côte d’Azur BP 4229 06304 Nice Cedex 4 France A. Miglio, Institut d’Astrophysique et de Géophysique de l’Université de Liège Allée du 6 Août 17 4000 Liège Belgium M. J. P. F. G. Monteiro, Universidade do Porto Centro de Astrofísica e Departamento de Matemática Aplicada da Faculdade de Ciências Porto Portugal G. Perrin, UMR CNRS 8109 LESIA Observatoire de Paris Paris France F. P. Pijpers, Imperial College London Space and Atmospheric Physics Group Exhibition Road London SW7 2AZ UK D. Pourbaix, Université Libre de Bruxelles F.R.S-FNRS, Institut d’Astronomie et d’Astrophysique 1050 Brussels Belgium A. Quirrenbach, Zentrum für Astronomie der Universität Heidelberg Landessternwarte Königstuhl 69117 Heidelberg Germany K. Rousselet-Perraut, Laboratoire d’Astrophysique de l’Observatoire de Grenoble BP 53 38041 Grenoble Cedex 9 France T. C. Teixeira, Centro de Astrofísica da Universidade do Porto Rua das Estrelas 4150-762 Porto Portugal F. Thévenin, UMR 6203 Observatoire de la Côte d’Azur BP 4229 06304 Nice Cedex 4 France M. J. Thompson, University of Sheffield School of Mathematics and Statistics Hounsfield Road Sheffield S3 7RH UK Journal Astronomy and Astrophysics Review Online ISSN 1432-0754 Print ISSN 0935-4956 Journal Volume Volume 14 Journal Issue Volume 14, Numbers 3-4

Description:    Space debris—man-made non-functional objects of all sizes in near-Earth space—has been recognized as an increasing threat for current and future space operations. The debris population in near-Earth space has therefore been extensively studied during the last decade. Information on objects at altitudes higher than about 2,000 km is, however, still comparatively sparse. Debris in this region is best detected by surveys utilizing optical telescopes. Moreover, the instruments and the applied observation techniques, as well as the processing methods, have many similarities with those used in optical surveys for ‘astronomical’ objects like near-Earth objects (NEOs). The present article gives a general introduction to the problem of space debris, presents the used observation and processing techniques emphasizing the similarities and differences compared to optical surveys for NEOs, and reviews the results from optical surveys for space debris in high-altitude Earth orbits. Predictions on the influence of space debris on the future of space research and space astronomy in particular are reported as well. Content Type Journal Article Category Paper Pages 41-111 DOI 10.1007/s00159-006-0003-9 Authors Thomas Schildknecht, Astronomical Institute of the University of Bern 3012 Bern Switzerland Journal Astronomy and Astrophysics Review Online ISSN 1432-0754 Print ISSN 0935-4956 Journal Volume Volume 14 Journal Issue Volume 14, Number 1

Description:    Among the observed circumstellar dust envelopes a certain population, planetary debris disks, is ascribed to systems with optically thin dust disks and low gas content. These systems contain planetesimals and possibly planets and are believed to be systems that are most similar to our solar system in an early evolutionary stage. Planetary debris disks have been identified in large numbers by a brightness excess in the near-infrared, mid-infrared and/or submillimetre range of their stellar spectral energy distributions. In some cases, spatially resolved observations are possible and reveal complex spatial structures. Acting forces and physical processes are similar to those in the solar system dust cloud, but the observational approach is obviously quite different: overall spatial distributions for systems of different ages for the planetary debris disks, as opposed to detailed local information in the case of the solar system. Comparison with the processes of dust formation and evolution observed in the solar system therefore helps understand the planetary debris disks. In this paper, we review our present knowledge of observations, acting forces, and major physical interactions of the dust in the solar system and in similar extra-solar planetary systems. Content Type Journal Article Category Paper Pages 159-228 DOI 10.1007/s00159-006-0028-0 Authors Ingrid Mann, Westfälische Wilhelms-Universität Institut für Planetologie Wilhelm-Klemm-Str. 10 48149 Münster Germany Melanie Köhler, Westfälische Wilhelms-Universität Institut für Planetologie Wilhelm-Klemm-Str. 10 48149 Münster Germany Hiroshi Kimura, Hokkaido University Institute of Low Temperature Science Sapporo Japan Andrzej Cechowski, Polish Academy of Sciences Space Research Center Warsaw Poland Tetsunori Minato, Westfälische Wilhelms-Universität Institut für Planetologie Wilhelm-Klemm-Str. 10 48149 Münster Germany Journal Astronomy and Astrophysics Review Online ISSN 1432-0754 Print ISSN 0935-4956 Journal Volume Volume 13 Journal Issue Volume 13, Number 3