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Publisher: Springer-Verlag (Total: 2355 journals)

 Astronomy and Astrophysics Review   [SJR: 4.511]   [H-I: 44]   [22 followers]  Follow         Hybrid journal (It can contain Open Access articles)    ISSN (Print) 1432-0754 - ISSN (Online) 0935-4956    Published by Springer-Verlag  [2355 journals]
• Mass loss of stars on the asymptotic giant branch
• Authors: Susanne Höfner; Hans Olofsson
Abstract: Abstract As low- and intermediate-mass stars reach the asymptotic giant branch (AGB), they have developed into intriguing and complex objects that are major players in the cosmic gas/dust cycle. At this stage, their appearance and evolution are strongly affected by a range of dynamical processes. Large-scale convective flows bring newly-formed chemical elements to the stellar surface and, together with pulsations, they trigger shock waves in the extended stellar atmosphere. There, massive outflows of gas and dust have their origin, which enrich the interstellar medium and, eventually, lead to a transformation of the cool luminous giants into white dwarfs. Dust grains forming in the upper atmospheric layers play a critical role in the wind acceleration process, by scattering and absorbing stellar photons and transferring their outward-directed momentum to the surrounding gas through collisions. Recent progress in high-angular-resolution instrumentation, from the visual to the radio regime, is leading to valuable new insights into the complex dynamical atmospheres of AGB stars and their wind-forming regions. Observations are revealing asymmetries and inhomogeneities in the photospheric and dust-forming layers which vary on time-scales of months, as well as more long-lived large-scale structures in the circumstellar envelopes. High-angular-resolution observations indicate at what distances from the stars dust condensation occurs, and they give information on the chemical composition and sizes of dust grains in the close vicinity of cool giants. These are essential constraints for building realistic models of wind acceleration and developing a predictive theory of mass loss for AGB stars, which is a crucial ingredient of stellar and galactic chemical evolution models. At present, it is still not fully possible to model all these phenomena from first principles, and to predict the mass-loss rate based on fundamental stellar parameters only. However, much progress has been made in recent years, which is described in this review. We complement this by discussing how observations of emission from circumstellar molecules and dust can be used to estimate the characteristics of the mass loss along the AGB, and in different environments. We also briefly touch upon the issue of binarity.
PubDate: 2018-01-09
DOI: 10.1007/s00159-017-0106-5
Issue No: Vol. 26, No. 1 (2018)

• The Main Belt Comets and ice in the Solar System
• Authors: Colin Snodgrass; Jessica Agarwal; Michael Combi; Alan Fitzsimmons; Aurelie Guilbert-Lepoutre; Henry H. Hsieh; Man-To Hui; Emmanuel Jehin; Michael S. P. Kelley; Matthew M. Knight; Cyrielle Opitom; Roberto Orosei; Miguel de Val-Borro; Bin Yang
Abstract: Abstract We review the evidence for buried ice in the asteroid belt; specifically the questions around the so-called Main Belt Comets (MBCs). We summarise the evidence for water throughout the Solar System, and describe the various methods for detecting it, including remote sensing from ultraviolet to radio wavelengths. We review progress in the first decade of study of MBCs, including observations, modelling of ice survival, and discussion on their origins. We then look at which methods will likely be most effective for further progress, including the key challenge of direct detection of (escaping) water in these bodies.
PubDate: 2017-11-14
DOI: 10.1007/s00159-017-0104-7
Issue No: Vol. 25, No. 1 (2017)

• Radio observations of active galactic nuclei with mm-VLBI
• Authors: B. Boccardi; T. P. Krichbaum; E. Ros; J. A. Zensus
Abstract: Abstract Over the past few decades, our knowledge of jets produced by active galactic nuclei (AGN) has greatly progressed thanks to the development of very-long-baseline interferometry (VLBI). Nevertheless, the crucial mechanisms involved in the formation of the plasma flow, as well as those driving its exceptional radiative output up to TeV energies, remain to be clarified. Most likely, these physical processes take place at short separations from the supermassive black hole, on scales which are inaccessible to VLBI observations at centimeter wavelengths. Due to their high synchrotron opacity, the dense and highly magnetized regions in the vicinity of the central engine can only be penetrated when observing at shorter wavelengths, in the millimeter and sub-millimeter regimes. While this was recognized already in the early days of VLBI, it was not until the very recent years that sensitive VLBI imaging at high frequencies has become possible. Ongoing technical development and wide band observing now provide adequate imaging fidelity to carry out more detailed analyses. In this article, we overview some open questions concerning the physics of AGN jets, and we discuss the impact of mm-VLBI studies. Among the rich set of results produced so far in this frequency regime, we particularly focus on studies performed at 43 GHz (7 mm) and at 86 GHz (3 mm). Some of the first findings at 230 GHz (1 mm) obtained with the Event Horizon Telescope are also presented.
PubDate: 2017-11-06
DOI: 10.1007/s00159-017-0105-6
Issue No: Vol. 25, No. 1 (2017)

• Major achievements of the Rosetta mission in connection with the origin of
the solar system
• Authors: M. A. Barucci; M. Fulchignoni
Abstract: Abstract Comets have been studied from a long time and are believed to preserve pristine materials, so they are fundamental to understand the origin of the solar system and life. Starting in the early 1990s, ESA decided to have a more risky and fantastic mission to a comet. As Planetary Cornerstone mission of the ESA Horizon 2000 program, the Rosetta mission was selected with the aim of realizing two asteroid fly-bys, a rendezvous with a comet to deliver a surface science package and to hover around the comet from 4 AU inbound up to perihelion and outbound back to 3.7 AU. The mission was successfully launched on March 2, 2004 with Ariane V that started its 10-year journey toward comet 67P/Churyumov–Gerasimenko. After several planetary gravity assists, Rosetta flew by two asteroids—on September 5, 2008 (Steins) and on July 10, 2010 (Lutetia), respectively, and performed the comet orbit insertion maneuver on August 6, 2014. The onboard instruments characterized the nucleus orbiting the comet at altitudes down to few kilometers. On November 12, 2014, the lander Philae was delivered realizing the first landing ever on a comet surface. Although the exploration of the comet was planned up to the end of 2015, the mission duration was extended for nine more months than the nominal one, to follow the comet on its outbound orbit. To terminate the mission, following a series of very low orbits, a controlled impact of Rosetta spacecraft with the comet was realized on September 30, 2016. The scientific objectives of the mission have been largely achieved. The challenging mission provided the science community with an enormous quantity of data of extraordinary scientific value. In this paper, a detailed description of the mission and the highlights of the obtained scientific results on the exploration of an extraordinary world are presented. The paper also includes lessons learned and directions for the future.
PubDate: 2017-10-24
DOI: 10.1007/s00159-017-0103-8
Issue No: Vol. 25, No. 1 (2017)

• Active galactic nuclei: what’s in a name'
• Authors: P. Padovani; D. M. Alexander; R. J. Assef; B. De Marco; P. Giommi; R. C. Hickox; G. T. Richards; V. Smolčić; E. Hatziminaoglou; V. Mainieri; M. Salvato
Abstract: Abstract Active galactic nuclei (AGN) are energetic astrophysical sources powered by accretion onto supermassive black holes in galaxies, and present unique observational signatures that cover the full electromagnetic spectrum over more than twenty orders of magnitude in frequency. The rich phenomenology of AGN has resulted in a large number of different “flavours” in the literature that now comprise a complex and confusing AGN “zoo”. It is increasingly clear that these classifications are only partially related to intrinsic differences between AGN and primarily reflect variations in a relatively small number of astrophysical parameters as well the method by which each class of AGN is selected. Taken together, observations in different electromagnetic bands as well as variations over time provide complementary windows on the physics of different sub-structures in the AGN. In this review, we present an overview of AGN multi-wavelength properties with the aim of painting their “big picture” through observations in each electromagnetic band from radio to $$\gamma$$ -rays as well as AGN variability. We address what we can learn from each observational method, the impact of selection effects, the physics behind the emission at each wavelength, and the potential for future studies. To conclude, we use these observations to piece together the basic architecture of AGN, discuss our current understanding of unification models, and highlight some open questions that present opportunities for future observational and theoretical progress.
PubDate: 2017-08-23
DOI: 10.1007/s00159-017-0102-9
Issue No: Vol. 25, No. 1 (2017)

• Giant star seismology
• Authors: S. Hekker; J. Christensen-Dalsgaard
Abstract: Abstract The internal properties of stars in the red-giant phase undergo significant changes on relatively short timescales. Long near-uninterrupted high-precision photometric timeseries observations from dedicated space missions such as CoRoT and Kepler have provided seismic inferences of the global and internal properties of a large number of evolved stars, including red giants. These inferences are confronted with predictions from theoretical models to improve our understanding of stellar structure and evolution. Our knowledge and understanding of red giants have indeed increased tremendously using these seismic inferences, and we anticipate that more information is still hidden in the data. Unraveling this will further improve our understanding of stellar evolution. This will also have significant impact on our knowledge of the Milky Way Galaxy as well as on exo-planet host stars. The latter is important for our understanding of the formation and structure of planetary systems.
PubDate: 2017-06-15
DOI: 10.1007/s00159-017-0101-x
Issue No: Vol. 25, No. 1 (2017)

• The realm of the galaxy protoclusters
• Authors: Roderik A. Overzier
Abstract: Abstract The study of galaxy protoclusters is beginning to fill in unknown details of the important phase of the assembly of clusters and cluster galaxies. This review describes the current status of this field and highlights promising recent findings related to galaxy formation in the densest regions of the early universe. We discuss the main search techniques and the characteristic properties of protoclusters in observations and simulations, and show that protoclusters will have present-day masses similar to galaxy clusters when fully collapsed. We discuss the physical properties of galaxies in protoclusters, including (proto-)brightest cluster galaxies, and the forming red sequence. We highlight the fact that the most massive halos at high redshift are found in protoclusters, making these objects uniquely suited for testing important recent models of galaxy formation. We show that galaxies in protoclusters should be among the first galaxies at high redshift making the transition from a gas cooling regime dominated by cold streams to a regime dominated by hot intracluster gas, which could be tested observationally. We also discuss the possible connections between protoclusters and radio galaxies, quasars, and $$\hbox {Ly}\alpha$$ blobs. Because of their early formation, large spatial sizes and high total star-formation rates, protoclusters have also likely played a crucial role during the epoch of reionization, which can be tested with future experiments that will map the neutral and ionized cosmic web. Lastly, we review a number of promising observational projects that are expected to make significant impact in this growing, exciting field.
PubDate: 2016-11-11
DOI: 10.1007/s00159-016-0100-3
Issue No: Vol. 24, No. 1 (2016)

Abstract: Abstract Radio astronomy has changed. For years it studied relatively rare sources, which emit mostly non-thermal radiation across the entire electromagnetic spectrum, i.e. radio quasars and radio galaxies. Now, it is reaching such faint flux densities that it detects mainly star-forming galaxies and the more common radio-quiet active galactic nuclei. These sources make up the bulk of the extragalactic sky, which has been studied for decades in the infrared, optical, and X-ray bands. I follow the transformation of radio astronomy by reviewing the main components of the radio sky at the bright and faint ends, the issue of their proper classification, their number counts, luminosity functions, and evolution. The overall “big picture” astrophysical implications of these results, and their relevance for a number of hot topics in extragalactic astronomy, are also discussed. The future prospects of the faint radio sky are very bright, as we will soon be flooded with survey data. This review should be useful to all extragalactic astronomers, irrespective of their favourite electromagnetic band(s), and even stellar astronomers might find it somewhat gratifying.
PubDate: 2016-09-29
DOI: 10.1007/s00159-016-0098-6
Issue No: Vol. 24, No. 1 (2016)

• Erratum to: Radio AGN in the local universe: unification, triggering and
evolution
PubDate: 2016-07-22
DOI: 10.1007/s00159-016-0097-7
Issue No: Vol. 24, No. 1 (2016)

• Time delay cosmography
• Authors: Tommaso Treu; Philip J. Marshall
Abstract: Abstract Gravitational time delays, observed in strong lens systems where the variable background source is multiply imaged by a massive galaxy in the foreground, provide direct measurements of cosmological distance that are very complementary to other cosmographic probes. The success of the technique depends on the availability and size of a suitable sample of lensed quasars or supernovae, precise measurements of the time delays, accurate modeling of the gravitational potential of the main deflector, and our ability to characterize the distribution of mass along the line of sight to the source. We review the progress made during the last 15 years, during which the first competitive cosmological inferences with time delays were made, and look ahead to the potential of significantly larger lens samples in the near future.
PubDate: 2016-07-21
DOI: 10.1007/s00159-016-0096-8
Issue No: Vol. 24, No. 1 (2016)

• Radio AGN in the local universe: unification, triggering and evolution
Abstract: Abstract Associated with one of the most important forms of active galactic nucleus (AGN) feedback, and showing a strong preference for giant elliptical host galaxies, radio AGN ( $$L_{1.4\,\mathrm{GHz}} > 10^{24}$$  W $$\hbox {Hz}^{-1}$$ ) are a key sub-class of the overall AGN population. Recently their study has benefitted dramatically from the availability of high-quality data covering the X-ray to far-IR wavelength range obtained with the current generation of ground- and space-based telescope facilities. Reflecting this progress, here I review our current state of understanding of the population of radio AGN at low and intermediate redshifts ( $$z < 0.7$$ ), concentrating on their nuclear AGN and host galaxy properties, and covering three interlocking themes: the classification of radio AGN and its interpretation; the triggering and fuelling of the jet and AGN activity; and the evolution of the host galaxies. I show that much of the observed diversity in the AGN properties of radio AGN can be explained in terms of a combination of orientation/anisotropy, mass accretion rate, and variability effects. The detailed morphologies of the host galaxies are consistent with the triggering of strong-line radio galaxies (SLRG) in galaxy mergers. However, the star formation properties and cool ISM contents suggest that the triggering mergers are relatively minor in terms of their gas masses in most cases, and would not lead to major growth of the supermassive black holes and stellar bulges; therefore, apart from a minority (<20 %) that show evidence for higher star formation rates and more massive cool ISM reservoirs, the SLRG represent late-time re-triggering of activity in mature giant elliptical galaxies. In contrast, the host and environmental properties of weak-line radio galaxies (WLRG) with Fanaroff–Riley class I radio morphologies are consistent with more gradual fuelling of the activity via gas accretion at low rates onto the supermassive black holes.
PubDate: 2016-06-03
DOI: 10.1007/s00159-016-0094-x
Issue No: Vol. 24, No. 1 (2016)

• Accurate abundance analysis of late-type stars: advances in atomic physics
• Authors: Paul S. Barklem
Abstract: Abstract The measurement of stellar properties such as chemical compositions, masses and ages, through stellar spectra, is a fundamental problem in astrophysics. Progress in the understanding, calculation and measurement of atomic properties and processes relevant to the high-accuracy analysis of F-, G-, and K-type stellar spectra is reviewed, with particular emphasis on abundance analysis. This includes fundamental atomic data such as energy levels, wavelengths, and transition probabilities, as well as processes of photoionisation, collisional broadening and inelastic collisions. A recurring theme throughout the review is the interplay between theoretical atomic physics, laboratory measurements, and astrophysical modelling, all of which contribute to our understanding of atoms and atomic processes, as well as to modelling stellar spectra.
PubDate: 2016-05-31
DOI: 10.1007/s00159-016-0095-9
Issue No: Vol. 24, No. 1 (2016)

• Erratum to: Magnetic fields in spiral galaxies
• Authors: Rainer Beck
PubDate: 2016-02-29
DOI: 10.1007/s00159-016-0092-z
Issue No: Vol. 24, No. 1 (2016)

• Complex organics in space from Solar System to distant galaxies
• Authors: Sun Kwok
Abstract: Abstract Recent observational and experimental evidence for the presence of complex organics in space is reviewed. Remote astronomical observations have detected $$\sim$$ 200 gas-phased molecules through their rotational and vibrational transitions. Many classes of organic molecules are represented in this list, including some precursors to biological molecules. A number of unidentified spectral phenomena observed in the interstellar medium are likely to have originated from complex organics. The observations of these features in distant galaxies suggests that organic synthesis had already taken place during the early epochs of the Universe. In the Solar System, almost all biologically relevant molecules can be found in the soluble component of carbonaceous meteorites. Complex organics of mixed aromatic and aliphatic structures are present in the insoluble component of meteorites. Hydrocarbons cover much of the surface of the planetary satellite Titan and complex organics are found in comets and interplanetary dust particles. The possibility that the early Solar System, or even the early Earth, have been enriched by interstellar organics is discussed.
PubDate: 2016-02-29
DOI: 10.1007/s00159-016-0093-y
Issue No: Vol. 24, No. 1 (2016)

• Accretion disks in luminous young stellar objects
• Authors: M. T. Beltrán; W. J. de Wit
Abstract: Abstract An observational review is provided of the properties of accretion disks around young stars. It concerns the primordial disks of intermediate- and high-mass young stellar objects in embedded and optically revealed phases. The properties were derived from spatially resolved observations and, therefore, predominantly obtained with interferometric means, either in the radio/(sub)millimeter or in the optical/infrared wavelength regions. We make summaries and comparisons of the physical properties, kinematics, and dynamics of these circumstellar structures and delineate trends where possible. Amongst others, we report on a quadratic trend of mass accretion rates with mass from T Tauri stars to the highest mass young stellar objects and on the systematic difference in mass infall and accretion rates.
PubDate: 2016-01-11
DOI: 10.1007/s00159-015-0089-z
Issue No: Vol. 24, No. 1 (2016)

• GG Tau: the ringworld and beyond
• Authors: Anne Dutrey; Emmanuel Di Folco; Tracy Beck; Stéphane Guilloteau
Abstract: Abstract In binary stellar systems, exoplanet searches have revealed planetary mass companions orbiting both in circumstellar and in circumbinary orbits. Modelling studies suggest increased dynamical complexity around the young stars that form such systems. Circumstellar and circumbinary disks likely exhibit different physical conditions for planet formation, which also depends on the stellar separation. Although binaries and higher order multiple stars are relatively common in nearby star-forming regions, surprisingly few systems with circumbinary distributions of proto-planetary material have been found. With its spectacular ring of dust and gas encircling the central triple star, one such system, GG Tau A, has become a unique laboratory for investigating the physics of circumsystem gas and dust evolution. We review here its physical properties.
PubDate: 2016-01-11
DOI: 10.1007/s00159-015-0091-5
Issue No: Vol. 24, No. 1 (2016)

• Mars: a small terrestrial planet
• Abstract: Abstract Mars is characterized by geological landforms familiar to terrestrial geologists. It has a tenuous atmosphere that evolved differently from that of Earth and Venus and a differentiated inner structure. Our knowledge of the structure and evolution of Mars has strongly improved thanks to a huge amount of data of various types (visible and infrared imagery, altimetry, radar, chemistry, etc) acquired by a dozen of missions over the last two decades. In situ data have provided ground truth for remote-sensing data and have opened a new era in the study of Mars geology. While large sections of Mars science have made progress and new topics have emerged, a major question in Mars exploration—the possibility of past or present life—is still unsolved. Without entering into the debate around the presence of life traces, our review develops various topics of Mars science to help the search of life on Mars, building on the most recent discoveries, going from the exosphere to the interior structure, from the magmatic evolution to the currently active processes, including the fate of volatiles and especially liquid water.
PubDate: 2016-11-16
DOI: 10.1007/s00159-016-0099-5

• Magnetic fields in spiral galaxies
• Authors: Rainer Beck
Abstract: Abstract Radio synchrotron emission, its polarization and Faraday rotation of the polarization angle are powerful tools to study the strength and structure of magnetic fields in galaxies. Unpolarized synchrotron emission traces isotropic turbulent fields which are strongest in spiral arms and bars (20–30 $$\upmu$$ G) and in central starburst regions (50–100 $$\upmu$$ G). Such fields are dynamically important; they affect gas flows and drive gas inflows in central regions. Polarized emission traces ordered fields, which can be regular or anisotropic turbulent, where the latter originates from isotropic turbulent fields by the action of compression or shear. The strongest ordered fields (10–15 $$\upmu$$ G) are generally found in interarm regions. In galaxies with strong density waves, ordered fields are also observed at the inner edges of spiral arms. Ordered fields with spiral patterns exist in grand-design, barred and flocculent galaxies and in central regions. Ordered fields in interacting galaxies have asymmetric distributions and are a tracer of past interactions between galaxies or with the intergalactic medium.—Faraday rotation measures of the diffuse polarized radio emission from galaxy disks reveal large-scale spiral patterns that can be described by the superposition of azimuthal modes; these are signatures of regular fields generated by mean-field dynamos. “Magnetic arms” between gaseous spiral arms may also be products of dynamo action, but need a stable spiral pattern to develop. Helically twisted field loops winding around spiral arms were found in two galaxies so far. Large-scale field reversals, like the one found in the Milky Way, could not yet be detected in external galaxies. In radio halos around edge-on galaxies, ordered magnetic fields with X-shaped patterns are observed. The origin and evolution of cosmic magnetic fields, in particular their first occurrence in young galaxies and their dynamical importance during galaxy evolution, will be studied with forthcoming radio telescopes like the Square Kilometre Array.
PubDate: 2015-12-29
DOI: 10.1007/s00159-015-0084-4
Issue No: Vol. 24, No. 1 (2015)

• Authors: Anuschka Pauluhn; Martin C. E. Huber; Peter L. Smith; Luis Colina
Abstract: Abstract Radiometry, i.e. measuring the power of electromagnetic radiation—hitherto often referred to as “photometry”—is of fundamental importance in astronomy. We provide an overview of how to achieve a valid laboratory calibration of space telescopes and discuss ways to reliably extend this calibration to the spectroscopic telescope’s performance in space. A lot of effort has been, and still is going into radiometric “calibration” of telescopes once they are in space; these methods use celestial primary and transfer standards and are based in part on stellar models. The history of the calibration of the Hubble Space Telescope serves as a platform to review these methods. However, we insist that a true calibration of spectroscopic space telescopes must directly be based on and traceable to laboratory standards, and thus be independent of the observations. This has recently become a well-supported aim, following the discovery of the acceleration of the cosmic expansion by use of type-Ia supernovae, and has led to plans for launching calibration rockets for the visible and infrared spectral range. This is timely, too, because an adequate exploitation of data from present space missions, such as Gaia, and from many current astronomical projects like Euclid and WFIRST demands higher radiometric accuracy than is generally available today. A survey of the calibration of instruments observing from the X-ray to the infrared spectral domains that include instrument- or mission-specific estimates of radiometric accuracies rounds off this review.
PubDate: 2015-12-21
DOI: 10.1007/s00159-015-0086-2
Issue No: Vol. 24, No. 1 (2015)

• The extragalactic gamma-ray sky in the Fermi era
• Authors: Francesco Massaro; David J. Thompson; Elizabeth C. Ferrara
Abstract: Abstract The Universe is largely transparent to $$\gamma$$ -rays in the GeV energy range, making these high-energy photons valuable for exploring energetic processes in the cosmos. After 7 years of operation, the Fermi  Gamma-ray Space Telescope has produced a wealth of information about the high-energy sky. This review focuses on extragalactic $$\gamma$$ -ray sources: what has been learned about the sources themselves and about how they can be used as cosmological probes. Active galactic nuclei (blazars, radio galaxies, Seyfert galaxies) and star-forming galaxies populate the extragalactic high-energy sky. Fermi observations have demonstrated that these powerful non-thermal sources display substantial diversity in energy spectra and temporal behavior. Coupled with contemporaneous multifrequency observations, the Fermi results are enabling detailed, time-dependent modeling of the energetic particle acceleration and interaction processes that produce the $$\gamma$$ -rays, as well as providing indirect measurements of the extragalactic background light and intergalactic magnetic fields. Population studies of the $$\gamma$$ -ray source classes compared to the extragalactic $$\gamma$$ -ray background place constraints on some models of dark matter. Ongoing searches for the nature of the large number of $$\gamma$$ -ray sources without obvious counterparts at other wavelengths remain an important challenge.
PubDate: 2015-12-19
DOI: 10.1007/s00159-015-0090-6
Issue No: Vol. 24, No. 1 (2015)

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