bluuebunny/crossref_metadata_2025_split huggingface dataset:
Starspot simulations for Kepler
Authors: Nielsen M.B. , Karoff C. 
Published: October 2014

AbstractThe NASA Kepler mission yields an unprecedented amount of data in the form of photometric light curves. Apart from valuable information on exoplanets and stellar pulsations, the light curves contain rotation signals from starspots crossing the stellar disk. These modulations of the light curves are modeled and 105 simulations are carried out to analyze and understand a similar analysis of the Kepler light curves. The periodogram is calculated for each light curve. Under the assumption that the main source of variability at periods >1 day is due to spots, the simulations show that the rotation period can be easily determined for spot lifetimes of 30–60 days, but becomes more unreliable for spots lifetimes of 10–20 days. The amplitude of the periodogram peaks appear to be only weakly dependent on changes in the size of the spots, while the width of the peaks shows no clear change with increasing spot lifetimes (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ground‐based multi‐color photometry of the γ Doradus–δ Scuti hybrid star KIC 6761539
Authors: Herzberg W. , Uytterhoeven K. , Roth M. 
Published: October 2014

AbstractWe present a preliminary analysis of the first three nights of multi‐color photometric data for a γ Doradus‐δ Scuti hybrid star (KIC 6761539) that is also being observed with the Kepler space telescope. We find that up to four (depending on the filter) of the highest amplitude modes, whose frequencies could be determined from Kepler data, are visible from the ground. Our goal is to use the multi‐color information for mode identification, but this will only be possible with a longer time series. A multi‐color photometric multi‐site campaign is currently ongoing for this purpose (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Identification of pulsational modes in rotating slowly pulsating B stars
Authors: Szewczuk W. , Daszyńska‐Daszkiewicz J. 
Published: October 2014

AbstractMode identification for several slowly pulsating B‐type stars (SPB) including effects of rotation is presented. The effects of the Coriolis force are incorporated via the traditional approximation. We show that even for slow rotators amongst the SPB stars, rotation cannot be ignored when the angular numbers of pulsational modes are determined. Moreover, some constraints on the rotational velocity and inclination angle are derived (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The Blazhko modulation of TV Boo in 2010
Authors: Hajdu G. , Jurcsik J. , Sódor Á. , Szeidl B. , Smitola P. , Belucz B. , Posztobányi K. , Vida K. , Kun E. 
Published: October 2014

AbstractWe present the analysis of the multicolour CCD observations in the 2010 season of the Blazhko RRc star TV Boo. TV Boo shows a complex Blazhko modulation dominated by two independent modulations with periods Pfm1 = 9.74 d and Pfm2 = 21.43 d. Both modulation components appear in the frequency spectra as multiplet structures around the harmonics of the pulsation. The positive value of the asymmetry parameter (Q = +0.51) of the primary modulation suggests that it is similar in its character to the Blazhko‐effect of most of the modulated RRab stars. Interestingly, the secondary, lower‐amplitude modulation exhibits a negative asymmetry parameter (Q = −0.22), which is an unusually low value when compared to the Blazhko‐modulated RRab stars. Apart from the two modulation frequencies, the spectra also show an additional frequency f’ and its linear combinations with the pulsation and the primary modulation f1 + f’ and f1 − f’ − fm1. We conclude that the additional frequency most probably belongs to a non‐radial mode (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Kappa‐effect and brightness oscillations of stars
Authors: Zhugzhda Y. D. , Roth M. , Herzberg W. 
Published: October 2014

AbstractIn this paper the theory of visibility and darkening functions for the brightness oscillations of stars is outlined. For this the non‐grey approximation is used and the effect of opacity disturbances on stellar brightness oscillations is explored for different types of stars. An explanation of the Procyon paradox is proposed. Special features of the brightness oscillations are discussed. The effect of opacity fluctuations on the damping of p‐mode oscillations is considered. Furthermore, the photospheric kappa‐mechanism is discussed (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Low‐frequency heliographic observations of the quiet Sun corona
Authors: Stanislavsky A.A. , Koval A.A. , Konovalenko A.A. 
Published: October 2014

AbstractWe present new results of heliographic observations of quiet‐Sun radio emission fulfilled by the UTR‐2 radio telescope. The solar corona investigations have been made close to the last solar minimum (Cycle 23) in the late August and early September of 2010 by means of the two‐dimensional heliograph within 16.5–33 MHz. Moreover, the UTR‐2 radio telescope was used also as an 1‐D heliograph for one‐dimensional scanning of the Sun at the beginning of September 2010 as well as in short‐time observational campaigns in April and August of 2012. The average values of integral flux density of the undisturbed Sun continuum emission at different frequencies have been found. Using the data, we have determined the spectral index of quiet‐Sun radio emission in the range 16.5–200 MHz. It is equal to –2.1±0.1. The brightness distribution maps of outer solar corona at frequencies 20.0 MHz and 26.0 MHz have been obtained. The angular sizes of radio Sun were estimated. It is found that the solar corona at these frequencies is stretched‐out along equatorial direction. The coefficient of corona ellipticity varies slightly during above period. Its mean magnitudes are equal to ≈ 0.75 and ≈ 0.73 at 20.0 MHz and 26.0 MHz, respectively. The presented results for continuum emission of solar corona conform with being ones at higher frequencies. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
X‐ray luminosity functions of different morphological and X‐ray type AGN populations
Authors: Pović M. , Pérez García A.M. , Sánchez‐Portal M. , Bongiovanni A. , Cepa J. , Fernández Lorenzo M. , Lara‐López M.A. , Gallego J. , Ederoclite A. , Márquez I. , Masegosa J. , Alfaro E. , Castañeda H. , González‐Serrano J.I. , González J.J. 
Published: October 2014

AbstractLuminosity functions are one of the most important observational clues when studying galaxy evolution over cosmic time. In this paper we present the X‐ray luminosity functions for X‐ray detected AGN in the SXDS and GWS fields. The limiting fluxes of our samples are 9.0 ×10–15 and 4.8 ×10–16 erg cm–2 s–1 in the 0.5–7.0 keV band in the two fields, respectively. We carried out analysis in three X‐ray bands and in two redshift intervals up to z ≤ 1.4. Moreover, we derive the luminosity functions for different optical morphologies and X‐ray types. We confirm strong luminosity evolution in all three bands, finding the most luminous objects at higher redshift. However, no signs of density evolution are found in any tested X‐ray band. We obtain similar results for compact and early‐type objects. Finally, we observe the “Steffen effect”, where X‐ray type‐1 sources are more numerous at higher luminosities in comparison with type‐2 sources. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Bulk motion measurements in clusters of galaxies with ATHENA‐like missions
Authors: Nevalainen J. 
Published: October 2014

AbstractThe hierarchical formation of clusters of galaxies by accretion of material releases gravitational energy which dissipates into the intracluster gas. The process heats the material and generates gas turbulence and bulk motions and thus kinetic pressure. Mapping the velocity fields of the moving subunits would enable a new diagnostics tool for cluster formation studies and unbiased X‐ray mass estimates. The required spatially resolved high resolution spectroscopy is not currently available. I demonstrate here the feasibility of detecting and mapping the velocities of the bulk motions using the Doppler shift of the Fe XXV Kα line with the proposed ATHENA satellite. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
X‐ray observations of the merging cluster CIZA J2242.8+5301
Authors: Ogrean G. , Brüggen M. , Simionescu A. , Röttgering H. , van Weeren R.J. , Croston J.H. , Hoeft M. 
Published: October 2014

AbstractMultiwavelength studies of radio relics at merger shocks set powerful constraints on the relics origin and formation mech‐anism. However, for X‐ray observations, a main difficulty is represented by the low X‐ray surface brightness far out in the cluster outskirts, where relics are typically found. Here, we present XMM‐Newton results from a 130‐ks observation of CIZA J2242.8+5301, a cluster at z = 0.19 that hosts a double radio relic. We focus on the well‐defined northern relic. There is a difference of ∼55% between the temperature we measure behind the relic, and the temperature measured with Suzaku. We analyse the reasons for this large discrepancy, and discuss the possibility of reliably measuring the temperature beyond the northern relic. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Merger shocks in Abell 3667 and the Cygnus A cluster
Authors: Sarazin C.L. , Finoguenov A. , Wik D.R. 
Published: October 2014

AbstractWe present new XMM‐Newton observations of the northwest (NW) radio relic region in the cluster Abell 3667. We detect a jump in the X‐ray surface brightness and X‐ray temperature at the sharp outer edge of the radio relic which indicate that this is the location of a merger shock with a Mach number of about 2. Comparing the radio emission to the shock properties implies that approximately 0.2% of the dissipated shock kinetic energy goes into accelerating relativistic electrons. This is an order of magnitude smaller than the efficiency of shock acceleration in many Galactic supernova remnants, which may be due to the lower Mach numbers of cluster merger shocks. The X‐ray and radio properties indicate that the magnetic field strength in the radio relic is ≳ 3 µG, which is a very large field at a projected distance of ∼ 2.2 Mpc from the center of a cluster. The radio spectrum is relatively flat at the shock, and steepens dramatically with distance behind the shock. This is consistent with radiative losses by the electrons and the post‐shock speed determined from the X‐ray properties. The Cygnus A radio source is located in a merging cluster of galaxies. This appears to be an early‐stage merger. Our recent Suzaku observation confirm the presence of a hot region between the two subclusters which agrees with the predicted shocked region. The high spectral resolution of the CCDs on Suzaku allowed us to measure the radial component of the merger velocity, Δvr ≈ 2650 km s–1. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cluster mass profiles from X‐ray observations: Present constraints and limitations
Authors: Ettori S. 
Published: October 2014

AbstractThe distribution of the gravitating and baryonic mass in galaxy clusters is the key ingredient to use these structures as astro‐physical laboratories and cosmological probes. I review the methods used to recover the gas and total mass profiles for galaxy clusters from X‐ray observations. I discuss some of the limitations affecting the X‐ray analysis. I illustrate how the estimates of the gas mass fraction and of the mass concentration can be used as robust cosmological tools. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
X‐ray emission from RX J1720.1+2638 and Abell 267: A comparison between a fossil and a non‐fossil system
Authors: Jiménez‐Bailón E. , Lozada‐Muñoz M. , Aguerri J.A.L. 
Published: October 2014

AbstractWe present the XMM‐Newton X‐ray analysis of RX J1720.1+2638 and Abell 267, a non‐fossil and a fossil system, respectively. The whole spectrum of both objects can be explained by thermal emission. The luminosities found for RX J1720.1+2638 and Abell 267 in the 2–10 keV band are 6.20+0.04 –0.02 × 1044 and 3.90+0.10 –0.11 ×1044 erg s–1, respectively. The radial profiles show a cool core nature for the non‐fossil system RX J1720.1+2638, while Abell 267 shows a constant behaviour of temperature with radius. Metallicity profiles have also been produced, but no evidence of any gradient was detected due to the large uncertainties in the determination of this parameter. Finally, density and mass profiles were also produced allowing to derive M500 for RX J1720.1+2638 and Abell 267. The masses obtained are high, in the range of (5–7)× 1014 M⊙. The X‐ray properties obtained for both systems are not always in good agreement with what is expected: cool cores are expected for fossil systems, as Abell 267, considering them as and relaxed systems. However, the decrement of the temperature in Abell 267 could start at lower radii. Also the presence of a recent merger in Abell 267, already suggested in the literature, could have increased the central temperature. The non‐fossil system RX J1720.1+2638 actually exhibits a cool core profile, but also evidence of a recent merger has been reported. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
X‐ray properties and scaling relations for Planck ESZ clusters
Authors: Jones C. , Forman W. , Fogarty K. , Murray S. , Vikhlinin A. 
Published: October 2014

AbstractClusters of galaxies were first recognized through overdensities of galaxies. With the advent of X‐ray telescopes, large numbers of clusters were by found by the spatially extended nature of their X‐ray emission. Today with the availability of millimeter wave telescopes capable of finding clusters through the Sunyaev‐Zeldovich effect, it is possible to compare the overall characteristics of clusters detected by different methods and the specific properties of individual clusters measured in different ways. Here we compare the X‐ray properties of relatively low redshift clusters measured with the Chandra Observatory with their SZ signal measured in the Planck mission. Based on a sample of 114 Planck detected clusters of galaxies, we show the SZ signal strengths are strongly correlated with X‐ray measured mass proxies, in particular those measured through the cluster X‐ray luminosities, so long as the cluster core is excluded, and those measured from YX, the product of the gas temperature and gas mass, which is an X‐ray analog of the SZ signal YSZ. A comparison of the hundred brightest X‐ray clusters and the hundred Planck clusters with the highest SZ signals shows that the Planck ESZ cluster sample is more X‐ray luminous and more massive than X‐ray cluster sample, due in part to the larger volume that Planck clusters are detected over, due to the nearly redshift independence of the SZ strength. As previously found, on average the SZ cluster samples show a larger fraction of clusters undergoing mergers than do X‐ray selected samples. For the Planck ESZ cluster PLCKESZ G189.84–37.24, we report the detection of extended X‐ray emission associated with an overdensity of distant galaxies located 6′.5 from the Planck ESZ position. Future X‐ray observations of the Planck low redshift (z < 0.35) cluster sample will better define the low redshift cluster mass function for comparison to high redshift SZ selected cluster samples to better constrain cosmological parameters, particularly the equation of state for dark energy. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On mass and shape of galaxy clusters by comparison of X‐ray, Sunyaev‐Zel'dovich effect, and gravitational lensing observations
Authors: Sereno M. , Umetsu K. , Ettori S. , Baldi A. 
Published: October 2014

AbstractThe accurate determination of the mass of galaxy clusters is crucial to precision astronomy. We have often to deal with either biased measurements or precise determinations of peculiar quantities. A better understanding of intrinsic shapes plays a major role. We consider how the shape of the intracluster medium (ICM) can be inferred by combining X‐ray photometry and spectroscopy with the measurement of the Sunyaev‐Zel'dovich effect (SZe). Together with gravitational lensing (GL), we can get unbiased estimates of mass and concentration and probe the hydrodynamical properties of the cluster. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Search for galaxy‐ICM interaction in rich clusters of galaxies
Authors: Gu L. , Gandhi P. , Inada N. , Kawaharada M. , Kodama T. , Konami S. , Nakazawa K. , Shimasaku K. , Xu Haiguang , Makishima K. 
Published: October 2014

AbstractBased on optical and X‐ray data for a sample of 34 relaxed rich clusters with redshift of 0.1–0.9, we studied the relative spatial distribution of the two major baryon contents, the cluster galaxies and the hot plasmas. Using photometric data taken with the UH88 telescope, we determined the integrated radial light profiles of member galaxies in each cluster using two independent approaches, i.e., the field background subtraction and the color‐magnitude filtering. The ICM mass profile of each cluster in our sample was derived from a spatially‐resolved spectral analysis using XMM‐Newton and Chandra data. When the sample is divided into three subsamples with redshift intervals of z = 0.11–0.22, 0.22–0.45, and 0.45– 0.89, the galaxy light vs. ICM mass ratio profiles for the central 0.65R500 regions were found to steepen from the higher‐ to lower‐ redshift subsamples, meaning that the galaxies become more concentrated in the ICM sphere towards lower redshifts. Besides, the galaxy light vs. total mass ratio profiles also exhibit gradual concentration towards lower redshift. We interpret that the galaxies, the ICM, and the dark matter components followed a similar spatial distribution in the early phase (z > 0.5), while the galaxies have fallen towards the center relative to the ICM and dark matter. Such galaxy infall is likely tobe caused by ICM drag when galaxies move through the ICM, even though the dynamical friction can enhance the infall of the most massive galaxies. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Galaxy And Mass Assembly (GAMA): The M‐Z relation for galaxy groups
Authors: Lara‐López M.A. , Hopkins A.M. , Robotham A. , Owers M.S. , Colless M. , Brough S. , Norberg P. , Steele O. , Taylor E.N. , Thomas D. 
Published: October 2014

AbstractThe stellar mass and metallicity are among the fundamental parameters of galaxies. An understanding of the interplay between those properties as well as their environmental dependence will give us a general picture of the physics and feedback processes ongoing in groups of galaxies. We study the relationships and environmental dependencies between the stellar mass, and gas metallicity for more than 1900 galaxies in groups up to redshift 0.35 using the Galaxy And Mass Assembly (GAMA) survey. Using a control sample of more than 28000 star‐forming field galaxies, we find evidence for a decrement of the gas metallicity for galaxies in groups. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A spectral differential approach to characterizing low‐mass companions to late‐type stars
Authors: Kostogryz N.M. , Kürster M. , Yakobchuk T.M. , Lyubchik Y. , Kuznetsov M.K. 
Published: October 2014

AbstractIn this paper, we develop a spectral differential technique with which the dynamical mass of low‐mass companions can be found. This method aims at discovering close companions to late‐type stars by removing the stellar spectrum through a subtraction of spectra obtained at different orbital phases and discovering the companion spectrum in the difference spectrum in which the companion lines appear twice (positive and negative signal). The resulting radial velocity difference of these two signals provides the true mass of the companion, if the orbital solution for the radial velocities of the primary is known. We select the CO line region in the K band for our study, because it provides a favourable star‐to‐companion brightness ratio for our test case GJ 1046, an M2V dwarf with a low‐mass companion that most likely is a brown dwarf. Furthermore, these lines remain largely unblended in the difference spectrum so that the radial velocity amplitude of the companion can be measured directly. Only if the companion rotates rapidly and has a small radial velocity due to a high mass, does blending occur for all lines so that our approach fails. We also consider activity of the host star, and show that the companion difference flux can be expected to have larger amplitude than the residual signal from the active star so that stellar activity does not inhibit the determination of the companion mass. In addition to determining the companion mass, we restore the single companion spectrum from the difference spectrum using singular value decomposition. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic fields during high redshift structure formation
Authors: Schleicher D.R.G. , Latif M. , Schober J. , Schmidt W. , Bovino S. , Federrath C. , Niemeyer J. , Banerjee R. , Klessen R.S. 
Published: October 2014

AbstractWe explore the amplification of magnetic fields in the high‐redshift Universe. For this purpose, we perform high‐resolution cosmological simulations following the formation of primordial halos with ∼ ⊙ 107 M, revealing the presence of turbulent structures and complex morphologies at resolutions of at least 32 cells per Jeans length. Employing a turbulence subgrid‐scale model, we quantify the amount of unresolved turbulence and show that the resulting turbulent viscosity has a significant impact on the gas morphology, suppressing the formation of low‐mass clumps. We further demonstrate that such turbulence implies the efficient amplification of magnetic fields via the small‐scale dynamo. We discuss the properties of the dynamo in the kinematic and non‐linear regime, and explore the resulting magnetic field amplification during primordial star formation. We show that field strengths of ∼ 10–5 G can be expected at number densities of ∼ 5 cm–3. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Brightness fluctuations of the Sun and p‐mode oscillations: The inverse problem and nonadiabatic waves in the photosphere
Authors: Prokhorov A. , Zhugzhda Y.D. , Berdyugina S. 
Published: October 2014

AbstractUsing photometric observations of the Sun as a star (DIFOS, SoHO) we were able to solve the inverse heloiseismic problem and determine the global time‐dependent relative temperature fluctuations as functions of the geometric height. This was done under the adiabatic assumption. A mathematical tool was developed to solve the inverse problem, which is ill‐posed. The calculations were done using the numerical software Matlab 7. The adiabatic solution shows signs of temperature waves in the lower photosphere, which agrees with calculations done by Rodríguez Hidalgo et al. (2001) and Stodilka (2011). (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Probing the temporal and spatial variations of dust emission in the protoplanetary disk of DG Tau with VLTI/MIDI: Preliminary results
Authors: Gabányi K. É. , Mosoni L. , Juhász A. , Ábrahám P. , Ratzka Th. , Sipos N. , van Boekel R. , Jaffe W. 
Published: October 2014

AbstractThe signatures of dust processing and grain growth – related to the formation of rocky planets – are easily seen in midinfrared spectral features. One important diagnostic tool in this context is the silicate feature in the spectra of young stellar objects (YSO). The low‐mass YSO, DG Tau shows unique temporal variations in its silicate feature. We conducted multi‐epoch observations of DG Tau with the MID‐Infrared Interferometric instrument of the Very Large Telescope Interferometer to obtain the spectra of the inner and outer disk regions in order to investigate where the previously reported variations of the silicate feature originate from. Here we present the preliminary results of the first two epochs of observations. We found that on a time‐scale of two months, the source showed significant brightening. At the same time the mid‐infrared emitting region expanded. While the identification of the silicate feature is difficult, our results qualitatively agree with the scenario explaining the varying silicate feature with dust lifted up above the disk. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)