bluuebunny/crossref_metadata_2025 huggingface dataset:
Velocity and abundance precisions for future high‐resolution spectroscopic surveys: A study for 4MOST
Authors: Caffau E. , Koch A. , Sbordone L. , Sartoretti P. , Hansen C.J. , Royer F. , Leclerc N. , Bonifacio P. , Christlieb N. , Ludwig H.‐G. , Grebel E.K. , de Jong R.S. , Chiappini C. , Walcher J. , Mignot S. , Feltzing S. , Cohen M. , Minchev I. , Helmi A. , Piffl T. , Depagne E. , Schnurr O.
Published: October 2014

In preparation for future, large‐scale, multi‐object, high‐resolution spectroscopic surveys of the Galaxy, we present a series of tests of the precision in radial velocity and chemical abundances that any such project can achieve at a 4 m class telescope. We briefly discuss a number of science cases that aim at studying the chemo‐dynamical history of the major Galactic components (bulge, thin and thick disks, and halo) – either as a follow‐up to the Gaia mission or on their own merits. Based on a large grid of synthetic spectra that cover the full range in stellar parameters of typical survey targets, we devise an optimal wavelength range and argue for a moderately high‐resolution spectrograph. As a result, the kinematic precision is not limited by any of these factors, but will practically only suffer from systematic effects, easily reaching uncertainties <1km s–1. Under realistic survey conditions (namely, considering stars brighter than r = 16 mag with reasonable exposure times) we prefer an ideal resolving power of R ∼20 000 on average, for an overall wavelength range (with a common two‐arm spectrograph design) of [395;456.5] nm and [587;673] nm. We show for the first time on a general basis that it is possible to measure chemical abundance ratios to better than 0.1 dex for many species (Fe, Mg, Si, Ca, Ti, Na, Al, V, Cr, Mn, Co, Ni, Y, Ba, Nd, Eu) and to an accuracy of about 0.2 dex for other species such as Zr, La, and Sr. While our feasibility study was explicitly carried out for the 4MOST facility, the results can be readily applied to and used for any other conceptual design study for high‐resolution spectrographs. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Helioseismic analysis of active regions using HMI and AIA data
Authors: Tripathy S.C. , Jain K. , Howe R. , Bogart R.S. , Hill F.
Published: October 2014

We apply the ring‐diagram technique to analyze three active regions located near the central meridian. Using Doppler, continuum intensity, and line depth images from the Helioseismic Magnetic Imager (HMI), we investigate the variation in the high‐degree mode asymmetry, frequencies, and horizontal flows. We find that the sub‐surface zonal and meridional flows do not change significantly with the choice of different observables representing different heights in the solar photosphere, while the mode frequencies differ. We also examine the 2‐d acoustic power distribution using data from HMI and the Atmospheric Imaging Assembly (AIA) 1600 and 1700 Å bands (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
New pulsating variable stars in the Stock 14 open cluster and surrounding fields
Authors: Drobek D.
Published: October 2014

This paper presents the preliminary results of a multicolour photometric study of the young open cluster Stock 14 and adjacent ßelds. The reddening, distance and age of the cluster were determined from colour‐colour and colour‐magnitude diagrams by means of isochrone ßtting. Fourier analysis of the acquired time‐series data was performed, which resulted in the discovery of new pulsating variable stars and candidates for such objects (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Properties of extrasolar planets and their host stars: A case study of HAT‐P‐7
Authors: Van Eylen V. , Kjeldsen H. , Christensen‐Dalsgaard J. , Aerts C.
Published: October 2014

Data from the Kepler satellite (Q0‐Q11) are used to study HAT‐P‐7. The satellite's data are extremely valuable for asteroseismic studies of stars and for observing planetary transits; in this work we do both. An asteroseismic study of the host star improves the accuracy of the stellar parameters derived by Christensen‐Dalsgaard et al. (2010), who followed largely the same procedure but based the analysis on only one month of Kepler data. The stellar information is combined with transit observations, phase variations and occultations to derive planetary parameters. In particular, we confirm the presence of ellipsoidal variations as discovered by Welsh et al. (2010), but revise their magnitude, and we revise the occultation depth (Borucki et al. 2009), which leads to different planetary temperature estimates. All other stellar and planetary parameters are now more accurately determined (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photometric study in the young open cluster NGC 6823
Authors: Zahajkiewicz E.
Published: October 2014

The preliminary results of the variability survey in the Þeld of the very young open cluster NGC 6823 are reported. Several dozen variables were found, including the fourteen already known. The new variable stars comprise eight SPB candidates, a δ Sct star, three eclipsing binaries, and a large sample of stars with mostly irregular light variations. The latter group contains over thirty stars that are likely pre‐main sequence members of the cluster (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stellar model fits and inversions
Authors: Christensen‐Dalsgaard J.
Published: October 2014

The recent asteroseismic data from the CoRoT and Kepler missions have provided an entirely new basis for investigating stellar properties. This has led to a rapid development in techniques for analysing such data, although it is probably fair to say that we are still far from having the tools required for the full use of the potential of the observations. Here I provide a brief overview of some of the issues related to the interpretation of asteroseismic data (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A new orbit for comet C/1858 L1 (Donati)
Authors: Branham R.L.
Published: October 2014

A new orbit for comet C/1858 L1 (Donati), based on 1036 observations in α and 971 in σ made between 7 June 1858 and 5 March 1859, is calculated using iteratively reweighted least squares. Residuals were weighted by the Welsch weighting function. The orbit represents a high eccentricity ellipse, e = 0.996265, with large semi‐major axis, a = 154.8612 AU, and long period, P = 1927.22 yr. The residuals are relatively random, a 10.7% chance of being random, but with a slight indication of possible nongravitational forces influencing the motion. The comet will not return until the year 3759, when it will pass 0.8442 AU from the Earth. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hα emission objects in Circinus
Authors: Noroozi S. , Haas M. , Chen Z. , Chini R.
Published: October 2014

We present a new survey for Hα emission objects in the Circinus cloud complex and introduce an efficient photometric method for detecting Hα emission via observations in a narrow‐band filter. The observed flux is compared to a blackbody fit of the continuum. Our search strategy reveals 20 stars with strong Hα emission (EW > 10 Å), eight of them being new detections. All Hα stars display infrared excess corroborating their youth. On the other hand, the region contains a number of infrared excess objects that do not show Hα emission. Our results support the picture that accretion – as witnessed by Hα emission – is a highly variable phenomenon. Therefore, Hα surveys can only trace the temporarily active objects. In contrast, infrared excess is a more robust tracer that reveals most of the population of young stellar objects in a star forming region. Our analysis of the general stellar content of the region yields a reliable distance of 450 pc for the Circinus cloud. Moreover, we find a ratio of total‐to‐selective extinction of RV = 2.8 suggesting that smaller‐than‐normal dust grains may be present. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic fields of accretion disks and outflows in prograde and retrograde black holes
Authors: Gnedin Yu.N. , Piotrovich M.Yu. , Buliga S.D. , Natsvlishvili T.M.
Published: October 2014

We show that for the accretion disk with equipartition between magnetic and radiative pressures, prograde black holes generate outflowing energy in jets more efficiently than retrograde black holes do. Both viscous radiative and irradiative disks provide more efficient outflow jets in the case of a prograde black hole than in the case of a retrograde black hole. Our results confirm the conclusion of Tchekhovskoy & McKinney (2012) that, for the same absolute value of the spin, prograde black holes with geometrically thick accretion disks generate outflows several times more efficiently than retrograde black holes do. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A simple recipe for estimating masses of elliptical galaxies and clusters of galaxies
Authors: Lyskova L.
Published: October 2014

We discuss a simple and robust procedure to evaluate the mass/circular velocity of massive elliptical galaxies and clusters of galaxies. It relies only on the surface density and the projected velocity dispersion profiles of tracer particles and therefore can be applied even in case of poor or noisy observational data. Stars, globular clusters or planetary nebulae can be used as tracers for mass determination of elliptical galaxies. For clusters the galaxies themselves can be used as tracer particles. The key element of the proposed procedure is the selection of a “sweet” radius Rsweet, where the sensitivity to the unknown anisotropy of the tracers' orbits is minimal. At this radius the surface density of tracers declines approximately as I(R) α R–2, thus placing Rsweet not far from the half‐light radius of the tracers Reff. The procedure was tested on a sample of cosmological simulations of individual galaxies and galaxy clusters and then applied to real observational data. Independently the total mass profile was derived from the hydrostatic equilibrium equation for the gaseous atmosphere. Mismatch in mass profiles obtained from optical and X‐ray data is used to estimate the non‐thermal contribution to the gas pressure and/or to constrain the distribution of tracers' orbits. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Clustering algorithms: Sensitivity of mass determination using A 3581
Authors: Wilson S. , Oozeer N. , Loubser S.I.
Published: October 2014

In this paper we discuss various methods for clustering in order to determine estimates of the cluster mass, focusing on the cluster A3581. Using virtual observatory (VO) tools, possible galaxy cluster candidates are selected. Using the Kayes Mixture Model (KMM) algorithm and the Gaussian Mixing Model (GMM), we determine the most likely cluster member candidates. We then compare the results obtained to SIMBADs method of hierarchy. The mass of A 3581 was calculated and checked with literature values. We discuss the sensitivity of the mass determination and show that the GMM provides a very robust method to determine member candidates for cluster A 3581. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
AGN feedback in clusters: Shock and sound heating
Authors: Nulsen P.E.J. , McNamara PB.R.
Published: October 2014

Observations support the view that feedback, in the form of radio outbursts from active nuclei in central galaxies, prevents catastro‐phic cooling of gas and rapid star formation in many groups and clusters of galaxies. Variations in jet power drive a succession of weak shocks that can heat regions close to the active galactic nuclei (AGN). On larger scales, shocks fade into sound waves. The Braginskii viscosity determines a well‐defined sound damping rate in the weakly magnetised intracluster medium (ICM) that can provide sufficient heating on larger scales. It is argued that weak shocks and sound dissipation are the main means by which radio AGN heat the ICM, in which case, the power spectrum of AGN outbursts plays a central role in AGN feedback. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Solving the cooling flow problem through mechanical AGN feedback
Authors: Gaspari M. , Brighenti F. , Ruszkowski M.
Published: October 2014

Unopposed radiative cooling of plasma would lead to the cooling catastro‐phe, a massive inflow of condensing gas, manifest in the core of galaxies, groups and clusters. The last generation X‐ray telescopes, Chandra and XMM, have radically changed our view on baryons, indicating AGN heating as the balancing counterpart of cooling. This work reviews our extensive investigation on self‐regulated heating. We argue that the mechanical feedback, based on massive subrelativistic outflows, is the key to solving the cooling flow problem, i.e. dramatically quenching the cooling rates for several Gyr without destroying the cool‐core structure. Using a modified version of the 3D hydrocode FLASH, we show that bipolar AGN outflows can further reproduce fundamental observed features, such as buoyant bubbles, weak shocks, metals dredgeup, and turbulence. The latter is an essential ingredient to drive nonlinear thermal instabilities, which cause the formation of extended cold gas, a residual of the quenched cooling flow and, later, fuel for the feedback engine. Compared to clusters, groups and galaxies require a gentler mechanical feedback, in order to avoid catastro‐phic overheating. We highlight the essential characteristics for a realistic AGN feedback, with emphasis on observational consistency. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The influence of cooling and feedback on cluster pressure profiles
Authors: Pike S.R. , Kay S.T. , Newton R.D.A.
Published: October 2014

In this paper, a new set of 30 high resolution cosmological simulations of galaxy clusters, run with increasingly realistic physics, are presented and compared to observations of the Sunyaev‐Zel'dovich (SZ) effect. It is found that the best fit to the Y500‐M500 relation is from the model without gas cooling, and that supernova feedback is insufficient to counteract the effect of cooling on the gas pressure. Clearly another more powerful source of feedback is required, suggesting that including the effects of active galactic nuclei (AGN) is vital if we are to replicate the SZ properties of the clusters accurately. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The jet feedback mechanism (JFM): From supernovae to clusters of galaxies
Authors: Soker N. , Akashi M. , Gilkis A. , Hillel S. , Papish O. , Refaelovich M. , Tsebrenko D.
Published: October 2014

We study the similarities of jet‐medium interactions in several quite different astro‐physical systems using 2D and 3D hydrodynamical numerical simulations, and find many similarities. The systems include cooling flow (CF) clusters of galaxies, core collapse supernovae (CCSNe), planetary nebulae (PNe), and common envelope (CE) evolution. The similarities include hot bubbles inflated by jets in a bipolar structure, vortices on the sides of the jets, vortices inside the inflated bubbles, fragmentation of bubbles to two and more bubbles, and buoyancy of bubbles. The activity in many cases is regulated by a negative feedback mechanism. In CF clusters we find that heating of the intra‐cluster medium (ICM) is done by mixing hot shocked jet gas with the ICM, and not by shocks. Our results strengthen the jet feedback mechanism (JFM) as a common process in many astro‐physical objects. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Active and star‐forming galactic nuclei in WINGS: A preliminary report
Authors: Marziani P. , D' Onofrio M. , Bettoni D. , Fasano G. , Fritz J. , Poggianti B.M. , Cava A.
Published: October 2014

We analyzed the spectra collected under the wide‐field nearby galaxy clusters survey (WINGS) to reveal emission lines in cluster galaxies. After removing stellar emission with dedicated population synthesis models we found evidence of faint emission line activity in a sizable number of sources. Diagnostic diagrams were used to define or at least constrain the origin of the emission line activity. Cross‐correlation with radio surveys is also being used for the identification of “true” active nuclei. We report the discovery of a previously unknown Seyfert 1 nucleus, WINGS J230945.81+072431.0, and preliminary results on prevalence and basic properties of the active and star forming galaxies we identified. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Metal jumps across sloshing cold fronts: The case of A 496
Authors: Ghizzardi S. , De Grandi S. , Molendi S.
Published: October 2014

Cold‐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

We 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

Our 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

Galaxy 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

The 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

We 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

Recent 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

It 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

We 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

Analyzing 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

In 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

In 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

Getting 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

Gamma‐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

High 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

In 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

This 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

We 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

The 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)
First stars and reionization: Spinstars
Authors: Chiappini C.
Published: October 2014

Soon after the Big Bang, the appearance of the first stellar generations (hereafter, first stars) drastically changed the course of the history of the Universe by enriching the primordial gas with elements heavier than helium (referred to as metals) through both stellar winds and supernova explosions. High‐resolution hydrodynamical simulations of the formation of the first stars suggest these objects to have formed in dark matter mini‐halos, and to have played a key role in the formation of the first galaxies. Today these stars are (most likely) long dead, and even though next generation facilities will push the observational frontier to extremely high redshifts, with the aim of discovering the first galaxies, the first stars will still lie beyond reach. Thus, the only way to constrain our theoretical understanding of the formation of the first stars is to search for their imprints left in the oldest, still surviving, stars in our own backyard: the Milky Way and its satellites. Which imprints are we looking for, and where can we find them? We address these questions in the present review. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Abundance analysis of the γ Doradus–δ Scuti hybrid metallic line (Am) star HD 8801
Authors: Neuteufel R. , Weiss W. , Handler G.
Published: October 2014

Low frequency oscillation, typical for γ Doradus g‐mode type stellar core sensitive pulsation, as well as higher frequency δ Scuti type pulsation typical for p ‐modes, sensitive to the envelope, make HD 8801 a remarkable hybrid pulsator with the potential to probe a stellar structure over a wide range of radius. In addition HD 8801 is a rare pulsating metallic line (Am) star. We determined the astro‐physical fundamental parameters to locate HD 8801 in the H‐R diagram. We analyzed the element abundances, paying close attention to the errors involved, and confirm the nature of HD 8801 as a metallic line (Am) star. We also determined an upper limit on the magnetic field strength. Our abundance analysis is based on classical techniques, but uses for the final step a model atmosphere calculated with the abundances determined by us. We also discuss spectropolarimetric observations obtained for HD 8801. This object is remarkable in several respects. It is a nonmagnetic metallic line (Am) star, pulsating simultaneously in p‐ and g‐modes, but also shows oscillations with periods in between these two domains, whose excitation requires explanation. Overall, the pulsational incidence in unevolved classical Am stars is believed to be quite low; HD 8801 does not conform to this picture. Finally, about 75 % of Am stars are located in short‐period binaries, but there is no evidence that HD 8801 has a companion. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Kinematics of nearby OB3 stars with interstellar Ca II line distances
Authors: Bobylev V.V. , Bajkova A.T.
Published: October 2014

We tested distances derived from the equivalent widths of interstellar Ca II spectral lines by Megier et al. (2009). To this end, we used a sample of nearby 126 young OB3 stars (r < 1 kpc) with known proper motions and line‐of‐site velocities. We shown that these stars are closely associated with the Gould Belt structure. The bulk of the sample (about 100 stars) shows the same kinematics as the sample of distant OB3 stars. Their galactocentric radial velocities agree well with the following spiral density wave parameters: the amplitude of radial perturbations fR ≈ 12 km s–1, wavelength λ ≈ 2.3 kpc, and phase of the Sun in spiral wave χ⊙ ≈ –90°. However, we revealed 20 stars with absolutely unusual kinematical features. Their galactocentric radial velocities show a wave shifted by ≈180° with respect to the wave found from the entire sample. The superposition of two spiral patterns seems to be a likely explanation. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Gravitational stability and mass estimation of stellar disks
Authors: Saburova A.S. , Zasov A.V.
Published: October 2014

We estimate masses of galaxy disks using the marginal gravitational stability criterion and compare them with the photometric disk‐mass evaluations. The comparison reveals that stellar disks of most spiral galaxies we have considered cannot be substantially overheated (at least within several radial scale lengths) and are therefore unlikely to have experienced a significant merging event in their history. However, for a substantial part of S0‐type galaxies, their stellar velocity dispersion is well in excess of the gravitational stability threshold suggesting a major merger event in the past. For four low‐surface‐brightness galaxies, we find the disk masses corresponding to the marginal stability condition to be significantly higher than one may expect from their brightness. Either their disks are dynamically overheated, or they contain a large amount of non‐luminous matter. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stabilization of generalized polytropes
Authors: Polyachenko E.V. , Polyachenko V.L. , Shukhman I.G.
Published: October 2014

Stabilization of classical generalized polytropic models is studied. We discuss some contradictions found in the literature: on the one hand, calculations of the growth rates in the framework of linear stability theory and N‐body simulations show that these systems are stable if the velocity anisotropy parameter of the stellar distribution is lower than some finite positive value. On the other hand, instability is shown to persist up to the isotropic limit (zero anisotropy parameter). We demonstrate that stabilization of generalized polytropic models cannot be adequately described by approximate equations derived for nearly radial orbits. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On some fundamental concepts of galactic dynamics
Authors: Ossipkov L.P.
Published: October 2014

We discuss the following fundamental concepts of galactic dynamics: (a) regular (smoothed) and irregular (random) forces, (b) truncation of the impact parameter, (c) the invariance of the Maxwellian velocity distribution, and (d) the Jeans theorem. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Equilibrium figures with polar rings
Authors: Kondratyev B.P.
Published: October 2014

We study the dynamics of a spheroidal galaxy with a gravitating polar ring whose plane is perpendicular to the equator. We consider this problem in the tidal approximation and derive a closed set of equations, which we reduce to a seventh‐order differential equation. We solve the resulting equation to find that perturbations from the polar ring deform the spheroid into a non‐stationary rotating triaxial ellipsoid with linear internal velocity field. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cepheids and RR Lyrae type variables
Authors: Berdnikov L.N. , Dambis A.K. , Kniazev Vorname
Published: October 2014

Current status and development prospects of Cepheid and RR Lyrae‐type variable‐star studies (photometry, radial velocity measurements, galactic structure and kinematics, and distance‐scale refinement) at the Sternberg Astronomical Institute are reported. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The LYRA photometric system and the catalog of photometric reference standard stars
Authors: Zakharov A.I. , Mironov A.V. , Nikolaev F.N. , Prokhorov M.E. , Tuchin M.S.
Published: October 2014

The 10‐color photometric system for the Russian space photometric experiment LYRA is described. It is shown that the system is effective for the determination of interstellar extinction, separation of supergiants, and evaluation of metallicity. The creation of a large grid of high‐precision photometric standards is one of the most important tasks of the LYRA experiment. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Expected characteristics of data from the LYRA mission
Authors: Zakharov A.I. , Mironov A.V. , Prokhorov M.E. , Nikolaev F.N. , Tuchin M.S. , Biryukov A.V.
Published: October 2014

The purpose of the LYRA mission is a multi‐color all‐sky survey of objects from 3m to 16m from the International Space Station, to result in a high‐precision photometric catalog (Zakharov et al. 2013b). The expected error of the catalog will be 0.001–0.003m for stars brighter than 12m and 0.01m for the stars down to 16m. The estimated duration of the survey is about 5 years. This paper describes the characteristics of data to be received in the course of the LYRA experiment for future users. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Classification of stars with WBVR photometry
Authors: Sichevskiy S.G. , Mironov A.V. , Malkov O.Yu.
Published: October 2014

We present a method of obtaining the most reliable stellar spectral type based on multi‐color photometry. The method also allows us to estimate color excess EB—V and distance to the star. Approbation of the method using bright stars with known spectral classification and WBVR photometry permits to estimate its reliability. Stellar spectra models from Pickles (1998) library and Fluks et al. (1994) interstellar extinction law were used in the application of the method. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)