bluuebunny/crossref_metadata_2025_split huggingface dataset:
Metal jumps across sloshing cold fronts: The case of A 496
Authors: Ghizzardi S. , De Grandi S. , Molendi S. 
Published: October 2014

AbstractCold‐fronts in cool‐core clusters are thought to be induced by minor mergers and to develop through a sloshing mechanism. While temperature and surface‐brightness jumps have been detected and measured in many systems, a detailed characterization of the metal abundance across the discontinuity is only available for a handful of objects. Within the sloshing scenario, we expect the central cool and metal rich gas to be displaced outwards into lower abundance regions, thus generating a metal discontinuity across the front. We analyzed a long (120 ks) XMM‐Newton observation of A496 to study the metal distribution and its correlation with the cold‐fronts. We find Fe discontinuities across the two main cold‐fronts located ∼ 60 kpc NNW and ∼ 160 kpc south of the peak and a metal excess in the south direction. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
X‐ray measurement of the elemental abundances at the outskirts of the Perseus cluster with Suzaku
Authors: Ueda S. , Hayashida K. , Nakajima H. , Tsunemi T. 
Published: October 2014

AbstractWe report on the abundance of metals (Mg and Fe) in the intracluster medium (ICM) at the outskirts (0.2 r200–0.8 r200) of the Perseus cluster. The X‐ray spectra were obtained in the Suzaku/XIS mapping observations of this region. We employ single temperature models to fit all the X‐ray spectra. The ICM temperature smoothly decreases toward the outer region from 6 keV to 4 keV. The Fe abundance is uniformly distributed at the outskirts (∼0.3 solar). The Mg abundance is ∼ 1 solar at the outskirts. The solar ratios of Mg/Fe of the outskirts region (Mg/Fe ∼ 4) are a factor of 4 larger than those of the central region. Various systematic effects, including the spatial fluctuations in the cosmic X‐ray background, are taken into account and evaluated. Our results have not changed significantly. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Progress in search for high‐redshift galaxies magnified by gravitational lensing
Authors: Zheng W. , Bradley L. , Zitrin A. , Moustakas J. , Postman M. , Ford H. , Shu X. , Coe D. , Moustakas L.A. , Koekemoer A. , Milino A. , Jouvel S. , Høst O. , Broadhurst T. , Kelson D.D. 
Published: October 2014

AbstractOur searches in the CLASH data have found many high‐redshift galaxy candidates. One object at z = 6.2 in MACS J0329‐02 is quadruply lensed. Another object in MACS J1149+22 is at redshift z = 9.6 and AB = 25.7, the first candidate at z > 9 that is bright enough for spectroscopic observations. The discovery of more than 80 galaxy candidates at z > 7 demonstrates the unique potential of galaxy cluster fields for finding highly magnified, intrinsically faint galaxies at the highest redshifts. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cluster science from ROSAT to eROSITA
Authors: Chon G. , Böhringer H. 
Published: October 2014

AbstractGalaxy clusters are one of the important cosmological probes to test the consistency of the observable structure and evolution of our Universe with the predictions of specific cosmological models. We use results from our analysis of the X‐ray flux‐limited REFLEX cluster sample from the ROSAT All‐Sky Survey to illustrate the constraints on cosmological parameters that can be achieved with this approach. The upcoming eROSITA project of the Spektrum‐Roentgen‐Gamma mission will increase these capabilities by two orders of magnitude and importantly also increase the redshift range of such studies. We use the projected instrument performance to make predictions on the scope of the eROSITA survey and the potential of its exploitation. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The 2200 Å bump and the interstellar extinction curve
Authors: Zagury F. 
Published: October 2014

AbstractThe 2200 Å bump is a major figure of interstellar extinction. However, extinction curves with no bump exist and are, with no exception, linear from the near‐infrared down to 2500 Å at least, often over all the visible‐UV spectrum. The duality linear versus bump‐like extinction curves can be used to re‐investigate the relationship between the bump and the continuum of interstellar extinction, and answer questions as why do we observe two different kinds of extinction (linear or with a bump) in interstellar clouds? How are they related? How does the existence of two different extinction laws fits with the requirement that extinction curves depend exclusively on the reddening E (B – V) and on a single additional parameter? What is this free parameter? It will be found that (1) interstellar dust models, which suppose the existence of three different types of particles, each contributing to the extinction in a specific wavelength range, fail to account for the observations; (2) the 2200 Å bump is very unlikely to be absorption by some yet unidentified molecule; (3) the true law of interstellar extinction must be linear from the visible to the far‐UV, and is the same for all directions including other galaxies (as the Magellanic Clouds). In extinction curves with a bump the excess of starlight (or the lack of extinction) observed at wavelengths less than λ = 4000 Å arises from a large contribution of light scattered by hydrogen on the line of sight. Although counter‐intuitive this contribution is predicted by theory. The free parameter of interstellar extinction is related to distances between the observer, the cloud on the line of sight, and the star behind it (the parameter is likely to be the ratio of the distances from the cloud to the star and to the observer). The continuum of the extinction curve and the bump contain no information on the chemical composition of interstellar clouds. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A simple way to classify supermassive black holes
Authors: Feoli A. 
Published: October 2014

AbstractWe propose a classification of supermassive black holes (SMBHs) based on their efficiency in the conversion of infalling mass in emitted radiation. We use a theoretical model that assumes a conservation of angular momentum between the gas falling inside the hole and the photons emitted outwards, and suggests the existence of the scaling relation M•‐Reσ3, where M• is the mass of the central SMBH, whereas Re and σ are the effective radius and velocity dispersion of the host galaxies (bulges), respectively. We apply our model on a data set of 57 galaxies of different morphological types and with M• measurements, obtained through the analysis of Spitzer /IRAC 3.6‐µ m images. In order to find the best fit of the corresponding scaling law, we use the FITEXY routine to perform a least‐squares regression of M• on Reσ3 for the considered sample of galaxies. Our analysis shows that the relation is tight and our theoretical model allows to easily estimate the efficiency of mass conversion into radiation of the central SMBHs. Finally we propose a new appealing way to classify the SMBHs in terms of this parameter. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Integer‐ambiguity resolution in astronomy and geodesy
Authors: Lannes A. , Prieur J.‐L. 
Published: October 2014

AbstractRecent theoretical developments in astronomical aperture synthesis have revealed the existence of integer‐ambiguity prob‐lems. Those problems, which appear in the self‐calibration procedures of radio imaging, have been shown to be similar to the nearest‐lattice point (NLP) problems encountered in high‐precision geodetic positioning and in global navigation satellite systems. In this paper we analyse the theoretical aspects of the matter and propose new methods for solving those NLP problems. The related optimization aspects concern both the preconditioning stage, and the discrete‐search stage in which the integer ambiguities are finally fixed. Our algorithms, which are described in an explicit manner, can easily be implemented. They lead to substantial gains in the processing time of both stages. Their efficiency was shown via intensive numerical tests. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growing evidence for a core formation threshold traced in Herschel Gould Belt survey clouds
Authors: Könyves V. , André Ph. , Schneider N. , Palmeirim P. , Arzoumanian D. , Men'shchikov A. 
Published: October 2014

AbstractIt has already been suggested that a threshold in column density – or in visual extinction – may need to be exceeded to form dense cores and then protostars. Based on Herschel Gould Belt survey results in the Aquila and Orion B molecular cloud complexes we observe clear connection between the locations of the detected prestellar cores and their background column density values. This finding appears to support a core formation scenario where such threshold corresponds to the extinction above which interstellar filaments become gravitationally unstable and fragment into cores. In these two actively star‐forming regions we find the vast majority of the gravitationally bound prestellar cores above a high column density of about (6–7) × 1021 cm–2 (AV ∼ 6–7). This limit similarly appears in the column density probability distribution function (PDF) of the regions as well. The spatial distribution of the protostars and young stellar objects (YSOs) also shows a tight connection with the densest sites of both clouds, as more than 70 % of them appear above the mentioned AV thresholds. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Relativistic model for cold spherical interstellar gas clouds
Authors: Barta D. 
Published: October 2014

AbstractWe investigate interstellar gas spheres by determining the metric functions, the material distribution, and the features of particle orbits in terms of stability and geodesics. An exact solution of the Einstein equations for interstellar gas clouds is derived. The solution determines the distribution of pressure and density, and it is suitable to describe the energy, speed, trajectory, and further relevant physical features of the cloud's particles. We describe the space‐time inside the nebula and give the density profile and the geodesics of particles. We find that circular orbits are stable and the cloud rotates rigidly at an angular velocity that is inversely proportional to the radius. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Paleoflood reconstruction in the Gale crater of Mars
Authors: Kereszturi A. 
Published: October 2014

AbstractAnalyzing a fluvial channel and related depositional fan at its termination in the Gale crater of Mars, the eroded and the deposited volume determined tobe close to each other around 0.47 and 0.32 km3 respectively. Using the Darcy‐Weisbach equation and a sediment transport capacity characteristic for high‐speed rivers, the duration to erode the channel and build up the sediment were found between 1.5 hours and 3.3 days. The short period might indicate that this ancient river was ephemeral and does not suggest a long duration of wetter and warmer climate, and also addresses a question regarding the general view of long‐period fluvial erosion on Mars. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Test of relativity: Determination of Mercury's apsidal motion excess using transit photographic data
Authors: Constantin D.R. 
Published: October 2014

AbstractIn this paper we determine the excess in Mercury's apsidal motion rate using, as a new approach, photographic observations of the planet transits on the solar disk during the period 1927–1973. Prior to compute the equations of condition in equatorial coordinates, we obtain the 616 small differences O –C (observed – calculated) in (α, δ), which are in the interval [–6″, 6″]. Using these results, via the Simon‐Bretagnon ephemeris and the least squares method (LSQ Method), we compute the variations corrections for the orbital elements λ, e, ϖ. As regards the relativistic theory, we obtain the perihelion longitude variation correction δϖ ′ = –1′′.7 cy–1 which is negative, this fact being consistent with a slightly diminished value for Mercury's relativistic excess. Since this correction is of arcseconds order, we conclude that Mercury's transits photographic observations in coordinates confirm the excess in Mercury's apsidal motion rate deduced in General Relativity. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stability of librational motion in the spatial circular restricted three‐body problem for high inclinations and mass ratios
Authors: Bazsó Á. , Schwarz R. , Érdi B. , Funk B. 
Published: October 2014

AbstractIn the spatial circular restricted three‐body problem librational motion around the Lagrangian points L4 and L5 exists up to high inclinations of the massless object. We report the results of numerical investigations on the stability of this librational motion for systematic variations in the inclination of the Trojan and the mass‐ratio μ of the two massive bodies. We show that stable motion prevails for inclinations below 60 degrees and mass‐ratios μ < 0.04 for typical integration times up to 106 revolution periods. At even higher mass‐ratios – beyond the critical mass‐ratio for the planar case – stable orbits were found to exist for up to 107 periods at moderate inclinations. We extracted the librational frequencies on a grid in the parameter space from the Fourier spectra and traced their variation. Several resonances between the short and long period librational frequency as well as the vertical frequency lie inside the investigated region. The application of the Lyapunov characteristic indicator and spectral number methods also reveals the chaotic regions. This simple model is equally applicable in the Solar system for low mass ratios for Trojans of the planets, as well as to Trojan‐type exoplanets in binary star systems at high mass‐ratios. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photo‐Met: A non‐parametric method for estimating stellar metallicity from photometric observations
Authors: Kerekes Gy. , Csabai I. , Dobos L. , Trencséni M. 
Published: October 2014

AbstractGetting spectra at good signal‐to‐noise ratios takes orders of magnitudes more time than photometric observations. Building on the technique developed for photometric redshift estimation of galaxies, we develop and demonstrate a nonparametric photometric method for estimating the chemical composition of Galactic stars. We investigate the efficiency of our method using spectroscopically determined stellar metallicities from SDSS DR7. The technique is generic in the sense that it is not restricted to certain stellar types or stellar parameter ranges and makes it possible to obtain metallicities and error estimates for a much larger sample than spectroscopic surveys would allow. We find that our method performs well, especially for brighter stars and higher metallicities and, in contrast to many other techniques, we are able to reliably estimate the error of the predicted metallicities. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of the connection between the intermediate gamma‐ray bursts and X‐ray flashes
Authors: Kóbori J. , Bagoly Zs. , Balázs L.G. , Horváth I. 
Published: October 2014

AbstractGamma‐ray bursts (GRBs) can be divided into three groups: short‐, intermediate‐ and long‐duration bursts. While the progenitors of the short and long ones are relatively known, the progenitors of the intermediate‐duration bursts (IBs) are generally unknown. However, recent statistical studies suggest that they can be related to the long‐duration bursts. Another types of GRBs are the so‐called X‐ray flashes (XRFs) and X‐ray rich GRBs (XRRs). The former ones radiate more intensively in the X‐ray bands than common GRBs, but in the cases of XRFs the main component of the emission is produced entirely at X‐ray wavelengths. Also, the XRFs and IBs show some similarities regarding their prompt‐ and afterglow properties. In this work we investigate whether there is a difference between the global parameters of the X‐ray flashes and intermediate‐duration group of gamma‐ray bursts. The statistical tests do not show any significant discrepancy regarding most of the parameters, except the BAT photon index, which is only a consequence of the definition of the XRFs. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Angular distribution of discontinuity normals of the interplanetary magnetic field
Authors: Lukács K. , Erdős G. 
Published: October 2014

AbstractHigh time resolved (6 s) magnetic field data from the Helios‐1 and Ulysses spacecrafts were used to investigate MHD discontinuities in the heliosphere. The identification of discontinuities was based on the rotation of the field vectors relative to the distance to the plasma in which the vectors were supposed to be frozen. In order to obtain the real thickness of the discontinuity transition region, the surface normal of discontinuities were calculated by both the minimum variance and cross‐product methods. We found an anisotropy in the angular distribution of the discontinuity surface normals in the heliosphere where the average interplanetary magnetic field is close to radial. It is an indirect evidence that most of the discontinuities are tangential rather than rotational ones. This result is also supported by the fact that the Minimum Variance and Cross‐Product methods gave similar results for the determination of the surface normals. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparison of chaos detection methods in the circular restricted three‐body problem
Authors: Racoveanu O. 
Published: October 2014

AbstractIn this study, a sample of orbits is considered in the framework of the planar circular restricted three‐body problem. In order to separate ordered from chaotic orbits three numerical methods are compared: the Largest Lyapunov Characteristic Exponent (LLCE) and the Smaller Alignment Index (SALI) provide a fairly good characterization of the chaotic motions, while the computational time required is of the same order; the Correlation Dimension (CD) has the advantage of correctly classifying sticky orbits, but at the expense of a longer computational time. In order to classify a given orbit, any pair of the three methods can be considered, but LLCE and SALI are recommended due to their speed. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Precovery of near‐Earth asteroids by a citizen‐science project of the Spanish Virtual Observatory
Authors: Solano E. , Rodrigo C. , Pulido R. , Carry B. 
Published: October 2014

AbstractThis article describes a citizen‐science project conducted by the Spanish Virtual Observatory (SVO) to improve the orbits of near‐Earth asteroids (NEAs) using data from astronomical archives. The list of NEAs maintained at the Minor Planet Center (MPC) is checked daily to identify new objects or changes in the orbital parameters of already catalogued objects. Using NEODyS we compute the position and magnitude of these objects at the observing epochs of the 938 046 images comprising the Eigth Data Release of the Sloan Digitised Sky Survey (SDSS). If the object lies within the image bound‐aries and the magnitude is brighter than the limiting magnitude, then the associated image is visually inspected by the project's collaborators (the citizens) to confirm or discard the presence of the NEA. If confirmed, accurate coordinates and, sometimes, magnitudes are submitted to the MPC. Using this methodology, 3226 registered users have made during the first fifteen months of the project more than 167 000 measurements which have improved the orbital elements of 551 NEAs (6% of the total number of this type of asteroids). Even more remarkable is the fact that these results have been obtained at zero cost to telescope time as NEAs were serendipitously observed while the survey was being carried out. This demonstrates the enormous scientific potential hidden in astronomical archives. The great reception of the project as well as the results obtained makes it a valuable and reliable tool for improving the orbital parameters of near‐Earth asteroids. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Composite spectra XIX: HD 208253, a long‐period binary whose hot secondary has enhanced strontium and barium
Authors: Griffin R.E.M. , Griffin R.F. 
Published: October 2014

AbstractWe separate and analyse the component spectra of the composite‐spectrum binary HD 208253. We find that the cool primary is an evolving star of spectral type G7 III, while its hot secondary is an early‐A dwarf. The giant is currently near the lowest point of the red‐giant branch and is slightly less luminous than its dwarf companion. We provide a set of precise radial‐velocity measurements for both stars. The double‐lined orbit which we derive from them shows that the component mass ratio is close to unity (q = 1.05 ± 0.01). We deduce the physical properties of both stars, determine their respective masses to be 2.75 ± 0.07 Me (giant) and 2.62 ± 0.07 Me (dwarf), and show that the orbit's inclination is within a degree or two of 68°. The spectrum of the A‐type component has quite component has quite narrow lines (we infer a rotational velocity of 18 km s–1), though since the period of the orbit is well over 1 year that component cannot be in synchronous rotation. An intriguing property of the dwarf is its enhanced Sr and Ba, though it does not exhibit the other spectral peculiarities that would signal a classical Am star. While by no means unique amongst the multitude of oddities exhibited by A and early‐F stars, this dwarf which we have uncovered in a long‐period binary offers valuable constraints and challenges to stellar‐evolution theory. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The LOFAR view of cosmic magnetism
Authors: Beck R. , Anderson J. , Heald G. , Horneffer A. , Iacobelli M. , Köhler J. , Mulcahy D. , Pizzo R. , Scaife A. , Wucknitz O. , the team of the LOFAR Magnetism Key Science Project  
Published: October 2014

AbstractThe origin of magnetic fields in the Universe is an open problem in astro‐physics and fundamental physics. Polarization observations with the forthcoming large radio telescopes will open a new era in the observation of magnetic fields and should help to understand their origin. At low frequencies, LOFAR (10–240 MHz) will allow us to map the structure of weak magnetic fields in the outer regions and halos of galaxies, in galaxy clusters and in the Milky Way via their synchrotron emission. Even weaker magnetic fields can be measured at low frequencies with help of Faraday rotation measures. A detailed view of the magnetic fields in the local Milky Way will be derived by Faraday rotation measures from pulsars. First promising images with LOFAR have been obtained for the Crab pulsar‐wind nebula, the spiral galaxy M 51, the radio galaxy M 87 and the galaxy clusters A 2255 and A 2256. With help of the polarimetric technique of “Rotation Measure Synthesis”, diffuse polarized emission has been detected from a magnetic bubble in the local Milky Way. Polarized emission and rotation measures were measured for more than 20 pulsars so far. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)