bluuebunny/crossref_metadata_2025 huggingface dataset:
Full-surface emission of graphene-based vertical-type organic light-emitting transistors with high on/off contrast ratios and enhanced efficiencies
Authors: Park Byoungchoo , Lee Won Seok , Na Seo Yeong , Huh Jun Nyeong , Bae In-Gon
Published: April 2019

Surface-emitting organic light-emitting transistors (OLETs) could well be a core element in the next generation of active-matrix (AM) displays. We report some of the key characteristics of graphene-based vertical-type organic light-emitting transistors (Gr-VOLETs) composed of a single-layer graphene source and an emissive channel layer. It is shown that FeCl3 doping of the graphene source results in a significant improvement in the device performance of Gr-VOLETs. Using the FeCl3-doped graphene source, it is demonstrated that the full-surface electroluminescent emission of the Gr-VOLET can be effectively modulated by gate voltages with high luminance on/off ratios (~104). Current efficiencies are also observed to be much higher than those of control organic light-emitting diodes (OLEDs), even at high luminance levels exceeding 500 cd/m2. Moreover, we propose an operating mechanism to explain the improvements in the device performance i.e., the effective gate-bias-induced modulation of the hole tunnelling injection at the doped graphene source electrode. Despite its inherently simple structure, our study highlights the significant improvement in the device performance of OLETs offered by the FeCl3-doped graphene source electrode.
The critical Barkhausen avalanches in thin random-field ferromagnets with an open boundary
Authors: Tadić Bosiljka , Mijatović Svetislav , Janićević Sanja , Spasojević Djordje , Rodgers Geoff J.
Published: April 2019

The interplay between the critical fluctuations and the sample geometry is investigated numerically using thin random-field ferromagnets exhibiting the field-driven magnetisation reversal on the hysteresis loop. The system is studied along the theoretical critical line in the plane of random-field disorder and thickness. The thickness is varied to consider samples of various geometry between a two-dimensional plane and a complete three-dimensional lattice with an open boundary in the direction of the growing thickness. We perform a multi-fractal analysis of the Barkhausen noise signals and scaling of the critical avalanches of the domain wall motion. Our results reveal that, for sufficiently small thickness, the sample geometry profoundly affects the dynamics by modifying the spectral segments that represent small fluctuations and promoting the time-scale dependent multi-fractality. Meanwhile, the avalanche distributions display two distinct power-law regions, in contrast to those in the two-dimensional limit, and the average avalanche shapes are asymmetric. With increasing thickness, the scaling characteristics and the multi-fractal spectrum in thicker samples gradually approach the hysteresis loop criticality in three-dimensional systems. Thin ferromagnetic films are growing in importance technologically, and our results illustrate some new features of the domain wall dynamics induced by magnetisation reversal in these systems.
Serum GM3(d18:1-16:0) and GM3(d18:1-24:1) levels may be associated with lymphoma: An exploratory study with haematological diseases
Authors: Nishikawa Masako , Kurano Makoto , Nitta Takahiro , Kanoh Hirotaka , Inokuchi Jin-ichi , Yatomi Yutaka
Published: April 2019

GM3 (monosialodihexosylganglioside) is a type of ganglioside, which is a molecule composed of ceramide and oligosaccharide containing one or more sialic acids. Since GM3 is abundantly expressed in blood cells, we investigated the association between GM3 molecular species and haematological diseases. We measured the serum levels of seven GM3 molecular species in subjects with various haematological diseases (n = 52) and healthy subjects (n = 24) using a liquid chromatography tandem-mass spectrometry technique as an exploratory study. In all the subjects with haematological diseases, GM3(d18:1-16:0) were inversely correlated with the erythrocytes counts. Regarding the difference in serum GM3 molecular species levels among each haematological diseases and healthy subjects, the levels of GM3(d18:1-16:0) and GM3(d18:1-24:1) were higher in the lymphoid neoplasm group than healthy subjects. Principal component analyses also revealed that the GM3(d18:1-16:0) and GM3(d18:1-24:1) levels were significant contributing factors for discriminating the lymphoid neoplasm group. Moreover, in the lymphoid neoplasm group, the GM3(d18:1-16:0) levels were significantly and positively correlated with the levels of C-reactive protein, soluble interleukin-2 receptor, and lactate dehydrogenase. In conclusion, in our exploratory study with haematological diseases, GM3 molecular species showed different distribution among disease groups, and serum GM3(d18:1-16:0) and GM3(d18:1-24:1) might be associated with lymphoma.
Alkali metal and stoichiometric effects in intermolecular hydroamination catalysed by lithium, sodium and potassium magnesiates
Authors: Davin Laia , Hernán-Gómez Alberto , McLaughlin Calum , Kennedy Alan R. , McLellan Ross , Hevia Eva
Published: April 2019

Cooperative catalytic hydroamination of diphenylacetylene and styrene is accomplished by magnesiates with efficiency dependent on the alkali metal and monoanionic or dianionic nature of the ate with dianionic [(PMDETA)2K2Mg(CH2SiMe3)4] performing best.
C8N12O10: a promising energetic compound with excellent detonation performance and desirable sensitivity
Authors: Xiong Hualin , Cheng Guangbin , Zhang Zaichao , Yang Hongwei
Published: April 2019

A promising energetic molecule bis(4-nitro-1,2,5-oxadiazole-2-oxid-3-yl)-azo-1,2,4-oxadiazole was synthesized and characterized. It has high density, acceptable thermal stability, high heat of formation, outstanding detonation properties and desirable mechanical properties.
Catalyst-free regioselective hydroxyfluorination and aminofluorination of α,β-unsaturated ketones
Authors: Zhou Jiadi , Fang Ye , Wang Fang , Li Jianjun
Published: April 2019

Catalyst-free direct regioselective α-fluoro-β-hydroxylation and α-fluoro-β-amidation of various α,β-unsaturated ketones via a radical based pathway has been developed.
Inverted energy gap law for the nonradiative decay in fluorescent floppy molecules: larger fluorescence quantum yields for smaller energy gaps
Authors: Shi Junqing , Izquierdo Maria A. , Oh Sangyoon , Park Soo Young , Milián-Medina Begoña , Roca-Sanjuán Daniel , Gierschner Johannes
Published: April 2019

The non-radiative decay of substituted dicyano-distyrylbenzenes in solution increase with the Franck–Condon energy, being opposite to the conventional energy gap law.
Copper-catalyzed direct couplings of terminal alkynes with primary and secondary benzyl bromides
Authors: Zhang Huiru , Sun Nan , Hu Baoxiang , Shen Zhenlu , Hu Xinquan , Jin Liqun
Published: April 2019

We have developed a facile Cu-catalyzed benzylation of terminal alkynes from easily available benzyl bromides.
Transition of the exchange bias effect from in-plane to out-of-plane in La0.7Sr0.3MnO3:NiO nanocomposite thin films
Authors: Wu Ying Jie , Wang Zhan Jie , Bai Yu , Liang Yong Mei , Ning Xing Kun , Wang Qiang , Liu Wei , Zhang Zhi Dong
Published: April 2019

The exchange bias effect of LSMO:NiO composite films transforms from in-plane to out-of-plane with the control of the microstructure.
miR-26a prevents neural stem cells from apoptosis via β-catenin signaling pathway in cardiac arrest-induced brain damage
Authors: Li Fang , Wei Hongyan , Li Hengjie , Li Xin , Hu Chunlin , Zhang Jie , Deng Yubin , Liao Xiaoxing
Published: April 2019

Neural stem cells (NSCs) transplantation is one of the most promising strategies for the treatment of CA-induced brain damage. The transplanted NSCs could differentiate into new neuron and replace the damaged one. However, the poor survival of NSCs in severe hypoxic condition is the limiting step to make the best use of this kind of therapy. In the present study, we investigated whether the overexpression of miR-26a improves the survival of NSCs in hypoxic environment in vitro and in vivo. In vitro hypoxia injury model is established in NSCs by CoCl2 treatment, and in vivo cardiac arrest (CA) model is established in Sprague-Dawley (SD) rats. Quantitative real-time polymerase chain reaction is used to detect the mRNA level and Western blot is used to examine the protein level of indicated genes. TUNEL staining and flow cytometry are applied to evaluate apoptosis. Dual-luciferase reporter assay is utilized to analyze the target gene of miR-26a. The expression of miR-26a is reduced in both in vitro and in vivo hypoxic model. MiR-26a directly targets 3′-UTR of glycogen synthase kinase 3β (GSK-3β), resulting in increased β-catenin expression and decreased apoptosis of NSCs. Overexpression of miR-26a in transplanted NSCs improves the survival of NSCs and neurological function in CA rats. MiR-26a prevents NSCs from apoptosis by activating β-catenin signaling pathway in CA-induced brain damage model. Modulating miR-26a expression could be a potential strategy to attenuate brain damage induced by CA.
Murchison Widefield Array and XMM-Newton observations of the Galactic supernova remnant G5.9+3.1
Authors: Onić D. , Filipović M. D. , Bojičić I. , Hurley-Walker N. , Arbutina B. , Pannuti T. G. , Maitra C. , Urošević D. , Haberl F. , Maxted N. , Wong G. F. , Rowell G. , Bell M. E. , Callingham J. R. , Dwarakanath K. S. , For B.-Q. , Hancock P. J. , Hindson L. , Johnston-Hollitt M. , Kapińska A. D. , Lenc E. , McKinley B. , Morgan J. , Offringa A. R. , Porter L. E. , Procopio P. , Staveley-Smith L. , Wayth R. B. , Wu C. , Zheng Q.
Published: April 2019

Aims. In this paper we discuss the radio continuum and X-ray properties of the so-far poorly studied Galactic supernova remnant (SNR) G5.9 + 3.1.

Methods. We present the radio spectral energy distribution (SED) of the Galactic SNR G5.9 + 3.1 obtained with the Murchison Widefield Array (MWA). Combining these new observations with the surveys at other radio continuum frequencies, we discuss the integrated radio continuum spectrum of this particular remnant. We have also analyzed an archival XMM-Newton observation, which represents the first detection of X-ray emission from this remnant.

Results. The SNR SED is very well explained by a simple power-law relation. The synchrotron radio spectral index of G5.9 + 3.1 is estimated to be 0.42 ± 0.03 and the integrated flux density at 1 GHz to be around 2.7 Jy. Furthermore, we propose that the identified point radio source, located centrally inside the SNR shell, is most probably a compact remnant of the supernova explosion. The shell-like X-ray morphology of G5.9 + 3.1 as revealed by XMM-Newton broadly matches the spatial distribution of the radio emission, where the radio-bright eastern and western rims are also readily detected in the X-ray while the radio-weak northern and southern rims are weak or absent in the X-ray. Extracted MOS1+MOS2+PN spectra from the whole SNR as well as the north, east, and west rims of the SNR are fit successfully with an optically thin thermal plasma model in collisional ionization equilibrium with a column density NH ~ 0.80 × 1022 cm−2 and fitted temperatures spanning the range kT ~ 0.14–0.23 keV for all of the regions. The derived electron number densities ne for the whole SNR and the rims are also roughly comparable (ranging from ~0.20f−1∕2 to ~0.40f−1∕2 cm−3, where f is the volume filling factor). We also estimate the swept-up mass of the X-ray emitting plasma associated with G5.9+3.1 to be ~46f−1∕2 M⊙.
Representation learning for automated spectroscopic redshift estimation
Authors: Frontera-Pons J. , Sureau F. , Moraes B. , Bobin J. , Abdalla F. B.
Published: April 2019

Context. Determining the radial positions of galaxies up to a high accuracy depends on the correct identification of salient features in their spectra. Classical techniques for spectroscopic redshift estimation make use of template matching with cross-correlation. These templates are usually constructed from empirical spectra or simulations based on the modeling of local galaxies.

Aims. We propose two new spectroscopic redshift estimation schemes based on new learning techniques for galaxy spectra representation, using either a dictionary learning technique for sparse representation or denoising autoencoders. We investigate how these representations impact redshift estimation.

Methods. We first explored dictionary learning to obtain a sparse representation of the rest-frame galaxy spectra modeling both the continuum and line emissions. As an alternative, denoising autoencoders were considered to learn non-linear representations from rest-frame emission lines extracted from the data. In both cases, the redshift was then determined by redshifting the learnt representation and selecting the redshift that gave the lowest approximation error among the tested values.

Results. These methods have been tested on realistic simulated galaxy spectra, with photometry modeled after the Large Synoptic Survey Telescope (LSST) and spectroscopy reproducing properties of the Sloan Digital Sky Survey (SDSS). They were compared to Darth Fader, a robust technique extracting line features and estimating redshift through eigentemplates cross-correlations. We show that both dictionary learning and denoising autoencoders provide improved accuracy and reliability across all signal-to-noise (S/N) regimes and galaxy types. Furthermore, the former is more robust at high noise levels; the latter is more accurate on high S/N regimes. Combining both estimators improves results at low S/N.

Conclusions. The representation learning framework for spectroscopic redshift analysis introduced in this work offers high performance in feature extraction and redshift estimation, improving on a classical eigentemplates approach. This is a necessity for next-generation galaxy surveys, and we demonstrate a successful application in realistic simulated survey data.
Constraining the orbit of the planet-hosting binary τ Boötis
Authors: Justesen A. B. , Albrecht S.
Published: April 2019

Context. The formation of planets in compact or highly eccentric binaries and the migration of hot Jupiters are two outstanding problems in planet formation. Detailed characterisation of known systems is important for informing and testing models. The hot Jupiter τ Boo Ab orbits the primary star in the long-period (P ≳ 1000 yr), highly eccentric (e ~ 0.9) double star system τ Boötis. Due to the long orbital period, the orbit of the stellar binary is poorly constrained.

Aims. Here we aim to constrain the orbit of the stellar binary τ Boo AB in order to investigate the formation and migration history of the system. The mutual orbital inclination of the stellar companion and the hot Jupiter has important implications for planet migration. The binary eccentricity and periastron distance are important for understanding the conditions under which τ Boo Ab formed.

Methods. We combine more than 150 yr of astrometric data with twenty-five years of high-precision radial velocities. The combination of sky-projected and line-of-sight measurements places tight constraints on the orbital inclination, eccentricity, and periastron distance of τ Boo AB.

Results. We determine the orbit of τ Boo B and find an orbital inclination of 47.2−3.7+2.7°, a periastron distance of 28.3−3.0+2.3 au, and an eccentricity of 0.87−0.03+0.04. We find that the orbital inclinations of τ Boo Ab and τ Boo B, as well as the stellar spin-axis of τ Boo A coincide at ~45°, a result consistent with the assumption of a well-aligned, coplanar system.

Conclusions. The likely aligned, coplanar configuration suggests planetary migration within a well-aligned protoplanetary disc. Due to the high eccentricity and small periastron distance of τ Boo B, the protoplanetary disc was tidally truncated at ≈6 au. We suggest that τ Boo Ab formed near the edge of the truncated disc and migrated inwards with high eccentricity due to spiral waves generated by the stellar companion.
Advanced aspects of Galactic habitability
Authors: Đošović Vladimir , Vukotić Branislav , Ćirković Milan M.
Published: April 2019

Context. Astrobiological evolution of the Milky Way (or the shape of its “astrobiological landscape”) has emerged as a key research topic in recent years. In order to build precise, quantitative models of the Galactic habitability, we need to account for two opposing tendencies of life and intelligence in the most general context: the tendency to spread to all available ecological niches (conventionally dubbed “colonization”) and the tendency to succumb to various types of existential catastrophes (“catastrophism”). These evolutionary tendencies have become objects of study in fields such as ecology, macroevolution, risk analysis, and futures studies, though a serious astrobiological treatment has so far been lacking.

Aims. Our aim is to numerically investigate the dynamics of opposed processes of expansion (panspermia, colonization) and extinction (catastrophic mechanisms) of life in the Galaxy.

Methods. We employed a new type of numerical simulation based on 1D probabilistic cellular automaton with very high temporal resolution, in order to study astrobiological dynamics.

Results. While the largest part of the examined parameter space shows very low habitability values, as expected, the remaining part has some observationally appealing features that imply, among other things, a reduction in the amount of fine-tuning necessary for resolving the Fermi paradox.

Conclusions. Advanced aspects of Galactic habitability are amenable to precision studies using massive parallel computer simulations. There are regions of the parameter space that correspond to a quasi-stationary state satisfying observable constraints and possessing viable SETI targets.
Hard and bright gamma-ray emission at the base of the Fermi bubbles
Authors: Herold L. , Malyshev D.
Published: April 2019

Context. The Fermi bubbles (FBs) are large gamma-ray emitting lobes extending up to 55° in latitude above and below the Galactic center (GC). Although the FBs were discovered eight years ago, their origin and the nature of the gamma-ray emission are still unresolved. Understanding the properties of the FBs near the Galactic plane may provide a clue to their origin. Previous analyses of the gamma-ray emission at the base of the FBs, what remains after subtraction of Galactic foregrounds, have shown an increased intensity compared to the FBs at high latitudes, a hard power-law spectrum without evidence of a cutoff up to approximately 1 TeV, and a displacement of the emission to negative longitudes relative to the GC.

Aims. We analyze nine years of Fermi Large Area Telescope data in order to study in more detail than the previous analyses the gamma-ray emission at the base of the FBs, especially at energies above 10 GeV.

Methods. We used a template analysis method to model the observed gamma-ray data and calculate the residual emission after subtraction of the expected foreground and background emission components. Since there are large uncertainties in the determination of the Galactic gamma-ray emission toward the GC, we used several methods to derive Galactic gamma-ray diffuse emission and the contribution from point sources to estimate the uncertainties in the emission at the base of the FBs.

Results. We confirm that the gamma-ray emission at the base of the FBs is well described by a simple power law up to 1 TeV energies. The 95% confidence lower limit on the cutoff energy is about 500 GeV. It has larger intensity than the FBs emission at high latitudes and is shifted to the west (negative longitudes) from the GC. If the emission at the base of the FBs is indeed connected to the high-latitude FBs, then the shift of the emission to negative longitudes disfavors models in which the FBs are created by the supermassive black hole at the GC. We find that the gamma-ray spectrum can be explained either by gamma rays produced in hadronic interactions or by leptonic inverse Compton scattering. In the hadronic scenario, the emission at the base of the FBs can be explained either by several hundred supernova remnants (SNRs) near the GC or by about ten SNRs at a distance of ~1 kpc. In the leptonic scenario, the necessary number of SNRs that can produce the required density of CR electrons is a factor of a few larger than in the hadronic scenario.
The effects of numerical resolution, heating timescales and background heating on thermal non-equilibrium in coronal loops
Authors: Johnston C. D. , Cargill P. J. , Antolin P. , Hood A. W. , De Moortel I. , Bradshaw S. J.
Published: April 2019

Thermal non-equilibrium (TNE) is believed to be a potentially important process in understanding some properties of the magnetically closed solar corona. Through one-dimensional hydrodynamic models, this paper addresses the importance of the numerical spatial resolution, footpoint heating timescales and background heating on TNE. Inadequate transition region (TR) resolution can lead to significant discrepancies in TNE cycle behaviour, with TNE being suppressed in under-resolved loops. A convergence on the periodicity and plasma properties associated with TNE required spatial resolutions of less than 2 km for a loop of length 180 Mm. These numerical problems can be resolved using an approximate method that models the TR as a discontinuity using a jump condition, as proposed by Johnston et al. (2017a, A&A, 597, A81; 2017b, A&A, 605, A8). The resolution requirements (and so computational cost) are greatly reduced while retaining good agreement with fully resolved results. Using this approximate method we (i) identify different regimes for the response of coronal loops to time-dependent footpoint heating including one where TNE does not arise and (ii) demonstrate that TNE in a loop with footpoint heating is suppressed unless the background heating is sufficiently small. The implications for the generality of TNE are discussed.
Automating Ellerman bomb detection in ultraviolet continua
Authors: Vissers Gregal J. M. , Rouppe van der Voort Luc H. M. , Rutten Robert J.
Published: April 2019

Ellerman bombs are transient brightenings in the wings of Hα 6563 Å that pinpoint photospheric sites of magnetic reconnection in solar active regions. Their partial visibility in the 1600 Å and 1700 Å continua registered routinely by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) offers a unique opportunity to inventory such magnetic-field disruptions throughout the AIA database if a reliable recipe for their detection can be formulated. This is done here. We have improved and applied an Hα Ellerman bomb detection code to ten data sets spanning viewing angles from solar disc centre to the limb. They combine high-quality Hα imaging spectroscopy from the Swedish 1 m Solar Telescope with simultaneous AIA imaging around 1600 Å and 1700 Å. A trial grid of brightness, lifetime and area constraints is imposed on the AIA images to define optimal recovery of the 1735 Ellerman bombs detected in Hα. The best results when optimising simultaneously for recovery fraction and reliability are obtained from 1700 Å images by requiring 5σ brightening above the average 1700 Å nearby quiet-Sun intensity, lifetime above one minute, area of 1–18 AIA pixels. With this recipe 27% of the AIA detections are Hα-detected Ellerman bombs while it recovers 19% of these (of which many are smaller than the AIA resolution). Better yet, among the top 10% AIA 1700 Å detections selected with combined brightness, lifetime and area thresholds as many as 80% are Hα Ellerman bombs. Automated selection of the best 1700 Å candidates therefore opens the entire AIA database for detecting most of the more significant photospheric reconnection events. This proxy is applicable as a flux-dynamics tell-tale in studying any Earth-side solar active region since early 2010 up to the present.
Purveyors of fine halos: Re-assessing globular cluster contributions to the Milky Way halo buildup with SDSS-IV
Authors: Koch Andreas , Grebel Eva K. , Martell Sarah L.
Published: April 2019

There is ample evidence in the Milky Way for globular cluster (GC) disruption. It may therefore be expected that part of the Galactic halo field star population may also once have formed in GCs. We seek to quantify the fraction of halo stars donated by GCs by searching for stars that bear the unique chemical fingerprints typical for a subset of GC stars often dubbed “second-generation stars”. These are stars showing light-element abundance anomalies such as a pronounced CN-band strength accompanied by weak CH-bands. Based on this indicator, past studies have placed the fraction of halo stars with a GC origin between a few to up to 50%. Using low-resolution spectra from the most recent data release (DR14) of the latest extension of the Sloan Digital Sky Survey (SDSS-IV), we were able to identify 118 metal-poor (−1.8 ≤ [Fe/H] ≤ −1.3) CN-strong stars in a sample of 4470 halo giant stars out to ∼50 kpc. This increases the number of known halo stars with GC-like light-element abundances by a factor of two and results in an observed fraction of these stars of 2.6 ± 0.2%. Using an updated formalism to account for the fraction of stars lost early on in the GC evolution, we thus estimate the fraction of the Galactic halo that stems from disrupted clusters to be very low, at 11 ± 1%. This number would represent the case that stars lost from GCs were entirely from the first generation and is thus merely an upper limit. Our conclusions are sensitive to our assumptions of the mass lost early on from the first generation formed in the GCs, the ratio of first-to-second generation stars, and other GC parameters. We carefully tested the influence of varying these parameters on the final result and find that under realistic scenarios, this fraction depends on the main assumptions at less than 10 percentage points. We further recover a flat trend in this fraction with Galactocentric radius, with a marginal indication of a rise beyond 30 kpc that could reflect the ex situ origin of the outer halo as is also seen in other stellar tracers.
The Galactic WN stars revisited
Authors: Hamann W.-R. , Gräfener G. , Liermann A. , Hainich R. , Sander A. A. C. , Shenar T. , Ramachandran V. , Todt H. , Oskinova L. M.
Published: April 2019

Comprehensive spectral analyses of the Galactic Wolf-Rayet stars of the nitrogen sequence (i.e. the WN subclass) have been performed in a previous paper. However, the distances of these objects were poorly known. Distances have a direct impact on the “absolute” parameters, such as luminosities and mass-loss rates. The recent Gaia Data Release (DR2) of trigonometric parallaxes includes nearly all WN stars of our Galactic sample. In the present paper, we apply the new distances to the previously analyzed Galactic WN stars and rescale the results accordingly. On this basis, we present a revised catalog of 55 Galactic WN stars with their stellar and wind parameters. The correlations between mass-loss rate and luminosity show a large scatter, for the hydrogen-free WN stars as well as for those with detectable hydrogen. The slopes of the log L − log Ṁ correlations are shallower than found previously. The empirical Hertzsprung–Russell diagram (HRD) still shows the previously established dichotomy between the hydrogen-free early WN subtypes that are located on the hot side of the zero-age main sequence (ZAMS), and the late WN subtypes, which show hydrogen and reside mostly at cooler temperatures than the ZAMS (with few exceptions). However, with the new distances, the distribution of stellar luminosities became more continuous than obtained previously. The hydrogen-showing stars of late WN subtype are still found to be typically more luminous than the hydrogen-free early subtypes, but there is a range of luminosities where both subclasses overlap. The empirical HRD of the Galactic single WN stars is compared with recent evolutionary tracks. Neither these single-star evolutionary models nor binary scenarios can provide a fully satisfactory explanation for the parameters of these objects and their location in the HRD.
Background modelling for γ-ray spectroscopy with INTEGRAL/SPI
Authors: Siegert Thomas , Diehl Roland , Weinberger Christoph , Pleintinger Moritz M. M. , Greiner Jochen , Zhang Xiaoling
Published: April 2019

Context. The coded-mask spectrometer-telescope SPI on board the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) records photons in the energy range between 20 and 8000 keV. A robust and versatile method for modelling the dominating instrumental background radiation is difficult to establish for such a telescope in the rapidly changing space environment.

Aims. In a previous paper we presented our spectral parameter database, developed from long-term monitoring of the SPI germanium detectors, that characterises the instrument response and background behaviour. Our aim is to build a self-consistent and broadly applicable background model for typical science cases of INTEGRAL/SPI based on this database.

Methods. The general analysis method for SPI relies on distinguishing between illumination patterns on the 19-element germanium detector array from background and sky in a maximum-likelihood framework. We illustrate how the complete set of measurements, even including the exposures of the sources of interest, can be used to define a background model. The observation strategy of INTEGRAL makes it possible to determine individual background components, originating from continuum and γ-ray line emission. We apply our method to different science cases, including point-like, diffuse, continuum, and line emission, and evaluate the adequacy in each case.

Results. From likelihood values and the number of fitted parameters, we determine how strong the impact of the unknown background variability is. We find that the number of fitted parameters, i.e. how often the background has to be re-normalised, depends on the emission type (diffuse with many observations over a large sky region, or point-like with concentrated exposure around one source), the spectral energy range, and bandwidth. A unique timescale, valid for all analysis issues, is not applicable for INTEGRAL/SPI, but must and can be inferred from the chosen data set.

Conclusions. We conclude that our background modelling method can be used in a wide variety of INTEGRAL/SPI science cases, and provides nearly systematics-free and robust results.
Correlation of the rate of Type Ia supernovae with the parent galaxy properties: Light and shadows
Authors: Greggio L. , Cappellaro E.
Published: April 2019

Context. The identification of the progenitors of Type Ia supernovae (SNIa) is extremely important in several astrophysical contexts, ranging from stellar evolution in close binary systems to evaluating cosmological parameters. Determining the distribution of the delay times (DTD) of SNIa progenitors can shed light on their nature. The DTD can be constrained by analysing the correlation between the SNIa rate and those properties of the parent galaxy which trace the average age of their stellar populations.

Aims. We investigate the diagnostic capabilities of this correlation by examining its systematics with the various parameters at play: simple stellar population models, the adopted description for the star formation history (SFH) in galaxies, and the way in which the masses of the galaxies are evaluated.

Methods. We computed models for the diagnostic correlations for a variety of input ingredients and for a few astrophysically motivated DTD laws appropriate for a wide range of possibilities for the SNIa progenitors. The models are compared to the results of three independent observational surveys.

Results. The scaling of the SNIa rate with the properties of the parent galaxy is sensitive to all input ingredients mentioned above. This is a severe limitation on the possibility to discriminate alternative DTDs. In addition, current surveys show some discrepancies for the reddest and bluest galaxies, likely because of limited statistics and the inhomogeneity of the observations. For galaxies with intermediate colours the rates are in agreement, leading to a robust determination of the productivity of SNIa from stellar populations of ≃0.8 events per 1000 M⊙.

Conclusions. Large stastistics of SNIa events along with accurate measurements of the SFH in the galaxies are required to derive firm constraints on the DTD. The LSST will achieve these results by providing a homogeneous, unbiased, and vast database on both SNIa and galaxies.
ComPRASS: a Combined Planck-RASS catalogue of X-ray-SZ clusters
Authors: Tarrío P. , Melin J.-B. , Arnaud M.
Published: April 2019

We present the first all-sky catalogue of galaxy clusters and cluster candidates obtained from joint X-ray-SZ detections using observations from the Planck satellite and the ROSAT all-sky survey (RASS). The catalogue contains 2323 objects and has been validated by careful cross-identification with previously known clusters. This validation shows that 1597 candidates correspond to already known clusters, 212 coincide with other cluster candidates still to be confirmed, and the remaining 514 are completely new detections. With respect to Planck catalogues, the ComPRASS catalogue is simultaneously more pure and more complete. Based on the validation results in the SPT and SDSS footprints, the expected purity of the catalogue is at least 84.5%, meaning that more than 365 clusters are expected to be found among the new or still-to-be-confirmed candidates with future validation efforts or specific follow-ups.
Influence of general-relativity effects, dynamical tides, and collisions on planet–planet scattering close to the star
Authors: Marzari F. , Nagasawa M.
Published: April 2019

Context.Planet–planet (P–P) scattering is an efficient and robust dynamical mechanism for producing eccentric exoplanets. Coupled to tidal interactions with the central star, this phenomenon can also explain close-in giant planets on circularized and potentially misaligned orbits.

Aims.We explore scattering events occurring close to the star and test if they can reproduce the main features of the observed orbital distribution of giant exoplanets on tight orbits.

Methods.In our modeling we exploited a numerical integration code based on the Hermite algorithm and including the effects of general relativity, dynamical tides, and two-body collisions.

Results.We find that P–P scattering events occurring in systems with three giant planets initially moving on circular orbits close to their star produce a population of planets similar to that presently observed, including eccentric and misaligned close-in planets. The contribution of tides and general relativity is relevant in determining the final outcome of the chaotic phase.

Conclusions.Even if two-body collisions dominate the chaotic evolution of three planets in crossing orbits close to their star, the final distribution shows a significant number of planets on eccentric orbits. The highly misaligned close-in giant planets are instead produced by systems where the initial semimajor axis of the inner planet was around 0.2 au or beyond.
Small iron meteoroids
Authors: Čapek David , Koten Pavel , Borovička Jiří , Vojáček Vlastimil , Spurný Pavel , Štork Rostislav
Published: April 2019

Context.A significant fraction of small meteors are produced by iron meteoroids. Their origin and the interaction with the atmosphere have not been well explained up to now.

Aims.The goals of the study are to observe faint, slow, low altitude meteors, to identify candidates for iron meteoroids among them, to model their ablation and light curves, and to determine their properties.

Methods.Double station video observations were used for the determination of atmospheric trajectories, heliocentric orbits, light curves, and spectra of meteors. Meteors with iron spectra or of suspected iron composition based on beginning heights and light curves were modeled. The immediate removal of liquid iron from the surface as a cloud of droplets with Nukiyama–Tanasawa size distribution and their subsequent vaporization was assumed as the main ablation process on the basis of our previous work. The numerical model has only five parameters: meteoroid initial velocityv∞, zenith distancez, initial massm∞, mean drop sizeDdr, and luminous efficiencyτ. The theoretical light curves were compared with the observed ones.

Results.The model is able to explain the majority of the selected light curves, and meteoroid parameters that are not directly observable –m∞,Ddr, andτ– are determined. Unlike in most meteor studies, the mass and luminous efficiency are determined independently. Luminous efficiency ranges from 0.08 to 5.8%; it weakly decreases with increasing initial meteoroid mass. No simple dependency on initial velocity was found. The mean size of iron drops depends on the meteoroid velocity. Slower meteoroids can produce drops with a wide range of mean sizes, whereas faster ones are better matched with larger drops with a smaller dispersion of sizes.
Hot exozodiacal dust: an exocometary origin?
Authors: Sezestre É. , Augereau J.-C. , Thébault P.
Published: April 2019

Context. Near- and mid-infrared interferometric observations have revealed populations of hot and warm dust grains populating the inner regions of extrasolar planetary systems. These are known as exozodiacal dust clouds, or exozodis, reflecting the similarity with the solar system’s zodiacal cloud. Radiative transfer models have constrained the dust to be dominated by tiny submicron-sized, carbon-rich grains that are accumulated very close to the sublimation radius. The origin of this dust is an unsolved issue.

Aims. We explore two exozodiacal dust production mechanisms, first re-investigating the Poynting-Robertson drag pile-up scenario, and then elaborating on the less explored but promising exocometary dust delivery scenario.

Methods. We developed a new, versatile numerical model that calculates the dust dynamics, with non-orbit-averaged equations for the grains close to the star. The model includes dust sublimation and incorporates a radiative transfer code for direct comparison to the observations. We consider in this study four stellar types, three dust compositions, and we assume a parent belt at 50 au.

Results. In the case of the Poynting-Robertson drag pile-up scenario, we find that it is impossible to produce long-lived submicron-sized grains close to the star. The inward drifting grains fill in the region between the parent belt and the sublimation distance, producing an unrealistically strong mid-infrared excess compared to the near-infrared excess. The dust pile-up at the sublimation radius is by far insufficient to boost the near-IR flux of the exozodi to the point where it dominates over the mid-infrared excess. In the case of the exocometary dust delivery scenario, we find that a narrow ring can form close to the sublimation zone, populated with large grains from several tens to several hundreds of micrometers in radius. Although not perfect, this scenario provides a better match to the observations, especially if the grains are carbon-rich. We also find that the number of active exocomets required to sustain the observed dust level is reasonable.

Conclusions. We conclude that the hot exozodiacal dust detected by near-infrared interferometry is unlikely to result from inward grain migration by Poynting-Robertson drag from a distant parent belt, but could instead have an exocometary origin.
Constraining non-linear dynamo models using quasi-biennial oscillations from sunspot area data
Authors: Inceoglu F. , Simoniello R. , Arlt R. , Rempel M.
Published: April 2019

Context. Solar magnetic activity exhibits variations with periods between 1.5 and 4 years, the so-called quasi-biennial oscillations (QBOs), in addition to the well-known 11-year Schwabe cycles. Solar dynamo is thought to be the mechanism responsible for the generation of QBOs.

Aims. In this work, we analyse sunspot areas to investigate the spatial and temporal behaviour of the QBO signal and study the physical mechanisms responsible using simulations from fully non-linear mean-field flux-transport dynamos.

Methods. We investigated the behaviour of the QBOs in the sunspot area data for the full disk, and the northern and southern hemispheres, using wavelet and Fourier analyses. We also ran solar dynamos with two different approaches to generating a poloidal field from an existing toroidal field, namely Babcock–Leighton and turbulent α mechanisms. We then studied the simulated magnetic field strengths as well as meridional circulation and differential rotation rates using the same methods.

Results. The results from the sunspot areas show that the QBOs are present in the full disk and hemispheric sunspot areas. These QBOs show slightly different spatial and temporal behaviours, indicating slightly decoupled solar hemispheres. The QBO signal is generally intermittent and in-phase with the sunspot area data, surfacing when the solar activity is at its maximum. The results from the BL-dynamos show that they are neither capable of generating the slightly decoupled behaviour of solar hemispheres nor can they generate QBO-like signals. The turbulent α-dynamos on the other hand generated decoupled hemispheres and some QBO-like shorter cycles.

Conclusions. In conclusion, our simulations show that the turbulent α-dynamos with the Lorentz force seem more efficient in generating the observed temporal and spatial behaviour of the QBO signal compared with the BL-dynamos.
The CORALIE survey for southern extrasolar planets
Authors: Rickman E. L. , Ségransan D. , Marmier M. , Udry S. , Bouchy F. , Lovis C. , Mayor M. , Pepe F. , Queloz D. , Santos N. C. , Allart R. , Bonvin V. , Bratschi P. , Cersullo F. , Chazelas B. , Choplin A. , Conod U. , Deline A. , Delisle J.-B. , Dos Santos L. A. , Figueira P. , Giles H. A. C. , Girard M. , Lavie B. , Martin D. , Motalebi F. , Nielsen L. D. , Osborn H. , Ottoni G. , Raimbault M. , Rey J. , Roger T. , Seidel J. V. , Stalport M. , Suárez Mascareño A. , Triaud A. , Turner O. , Weber L. , Wyttenbach A.
Published: April 2019

Context. Since 1998, a planet-search around main sequence stars within 50 pc in the southern hemisphere has been underway with the CORALIE spectrograph at La Silla Observatory.

Aims. With an observing time span of more than 20 yr, the CORALIE survey is able to detect long-term trends in data with masses and separations large enough to select ideal targets for direct imaging. Detecting these giant companion candidates will allow us to start bridging the gap between radial-velocity-detected exoplanets and directly imaged planets and brown dwarfs.

Methods. Long-term precise Doppler measurements with the CORALIE spectrograph reveal radial-velocity signatures of massive planetary companions and brown dwarfs on long-period orbits.

Results. In this paper, we report the discovery of new companions orbiting HD 181234, HD 13724, HD 25015, HD 92987 and HD 50499. We also report updated orbital parameters for HD 50499b, HD 92788b and HD 98649b. In addition, we confirm the recent detection of HD 92788c. The newly reported companions span a period range of 15.6–40.4 yr and a mass domain of 2.93–26.77 MJup, the latter of which straddles the nominal boundary between planets and brown dwarfs.

Conclusions. We report the detection of five new companions and updated parameters of four known extrasolar planets. We identify at least some of these companions to be promising candidates for imaging and further characterisation.
CIELO-RGS: a catalog of soft X-ray ionized emission lines
Authors: Mao Junjie , Kaastra Jelle S. , Guainazzi Matteo , González-Riestra Rosario , Santos-Lleó Maria , Kretschmar Peter , Grinberg Victoria , Kalfountzou Eleni , Ibarra Aitor , Matzeu Gabi , Parker Michael , Rodríguez-Pascual Pedro
Published: April 2019

Context.High-resolution X-ray spectroscopy has advanced our understanding of the hot Universe by revealing physical properties like kinematics, temperature, and abundances of the astrophysical plasmas. Despite technical and scientific achievements, the lack of scientific products at a level higher than count spectra is hampering complete scientific exploitation of high-quality data. This paper introduces the Catalog of Ionized Emission Lines Observed by the Reflection Grating Spectrometer (CIELO-RGS) onboard theXMM-Newtonspace observatory.

Aims.The CIELO-RGS catalog aims to facilitate the exploitation of emission features in the public RGS spectra archive. In particular, we aim to analyze the relationship between X-ray spectral diagnostics parameters and measurements at other wavelengths. This paper focuses on the methodology of catalog generation, describing the automated line-detection algorithm.

Methods.A moderate sample (∼2400 observations) of high-quality RGS spectra available atXMM-NewtonScience Archive is used as our starting point. A list of potential emission lines is selected based on a multi-scale peak-detection algorithm in a uniform and automated way without prior assumption on the underlying astrophysical model. The candidate line list is validated via spectral fitting with simple continuum and line profile models. We also compare the catalog content with published literature results on a small number of exemplary sources.

Results.We generate a catalog of emission lines (1.2 × 104) detected in ∼1600 observations toward stars, X-ray binaries, supernovae remnants, active galactic nuclei, and groups and clusters of galaxies. For each line, we report the observed wavelength, broadening, energy and photon flux, equivalent width, and so on.
Long X-ray flares from the central source in RCW 103
Authors: Esposito P. , De Luca A. , Turolla R. , Coti Zelati F. , Hummel W. , Tiengo A. , Israel G. L. , Rea N. , Mignani R. P. , Borghese A.
Published: April 2019

We observed the slowly revolving pulsar 1E 161348–5055 (1E 1613, spin period of 6.67 h) in the supernova remnant RCW 103 twice with XMM-Newton and once with the Very Large Telescope (VLT). The VLT observation was performed on 2016 June 30, about a week after the detection of a large outburst from 1E 1613. At the position of 1E 1613, we found a near-infrared source with Ks = 20.68 ± 0.12 mag that was not detected (Ks >  21.2 mag) in data collected with the same instruments in 2006, during X-ray quiescence. Its position and behavior are consistent with a counterpart in the literature that was discovered with the Hubble Space Telescope in the following weeks in adjacent near-IR bands. The XMM-Newton pointings were carried out on 2016 August 19 and on 2018 February 14. While the collected spectra are similar in shape between each other and to what is observed in quiescence (a blackbody with kT ∼ 0.5 keV plus a second, harder component, either another hotter blackbody with kT ∼ 1.2 keV or a power law with photon index Γ ∼ 3), the two pointings caught 1E 1613 at different luminosity throughout its decay pattern: about 4.8 × 1034 erg s−1 in 2016 and 1.2 × 1034 erg s−1 in 2018 (0.5–10 keV, for the double-blackbody model and for 3.3 kpc), which is still almost about ten times brighter than the quiescent level. The pulse profile displayed dramatic changes, apparently evolving from the complex multi-peak morphology observed in high-luminosity states to the more sinusoidal form characteristic of latency. The inspection of the X-ray light curves revealed two flares with unusual properties in the 2016 observation: they are long (∼1 ks to be compared with 0.1–1 s of typical magnetar bursts) and faint (≈1034 erg s−1, with respect to 1038 erg s−1 or more in magnetars). Their spectra are comparatively soft and resemble the hotter thermal component of the persistent emission. If the flares and the latter component have a common origin, this may be a spot on the star surface that is heated by back-flowing currents that are induced by a magnetospheric twist. In this hypothesis, since the increase in luminosity of 1E 1613 during the flare is only ∼20%, an irregular variation of the same order in the twist angle could account for it.