bluuebunny/crossref_metadata_2025 huggingface dataset:
A new oxygen-free cobalt-based compound SmCoAsF with multiple magnetic transitions
Authors: Lin Dan , Luo Qinxin , Zheng Hui , Tang Lulu , Zhan Wenqi , Tang Kaibin
Published: June 2020

A new quaternary oxygen-free cobalt-based compound SmCoAsF, which crystallizes with the tetragonal ZrCuSiAs-type structure, is synthesized via a solid state metathesis reaction.
Pushing the limits of the electrochemical window with pulse radiolysis in chloroform
Authors: Bird Matthew J. , Cook Andrew R. , Zamadar Matibur , Asaoka Sadayuki , Miller John R.
Published: June 2020

We show that pulse radiolysis in chloroform enables the creation and study of radical cations beyond traditional electrochemical windows.
Spectroscopic evidence for intact carbonic acid stabilized by halide anions in the gas phase
Authors: Zhang Hanhui , Cao Wenjin , Yuan Qinqin , Wang Lei , Zhou Xiaoguo , Liu Shilin , Wang Xue-Bin
Published: June 2020

The whole series of halide anions can stabilize elusive carbonic acid in the gas phase through dual hydrogen bonds.
Dielectric function modelling and sensitivity forecast for Au–Ag alloy nanostructures
Authors: Wang Xiu , Kan Caixia , Xu Juan , Zhu Xingzhong , Jiang Mingming , Ni Yuan
Published: June 2020

Based on theoretical calculations, FDTD simulations and experimental results, the refractive index sensitivity of Au–Ag alloy nanostructures were investigated, indicating the credibility and feasibility of the modelled dielectric data of alloy.
High thermoelectric performance of rapidly microwave-synthesized Sn1−δS
Authors: Prado-Gonjal Jesús , Gainza Javier , Aguayo Isabel , Durá Óscar Juan , Rodríguez-Pérez Sara , Serrano-Sánchez Federico , Nemes Norbert M. , Fernández-Díaz María Teresa , Alonso José Antonio , Morán Emilio
Published: June 2020

Promising thermoelectric properties were found for polycrystalline Sn1−δS synthesized by a microwave-hydrothermal route (ZT= 0.76 at 523 K).
Terbium metal–organic frameworks as capable electrodes for supercapacitors
Authors: Jafari Hossein , Mohammadnezhad Parizad , Khalaj Zahra , Naderi Hamid Reza , Kohan Elmira , Milani Hosseini Mohammad-Reza , Shiralizadeh Dezfuli Amin
Published: June 2020

Tb-MOF as electrode material for supercapacitors with high specific capacitance and excellent capacitance retention.
In silico and in vitro metabolism of ribociclib: a mass spectrometric approach to bioactivation pathway elucidation and metabolite profiling
Authors: Alsubi Thamer A. , Attwa Mohamed W. , Bakheit Ahmed H. , Darwish Hany W. , Abuelizz Hatem A. , Kadi Adnan A.
Published: June 2020

Nine phase I metabolites and one product of KCN trapping of RBC were characterized. Aryl piperazine is considered a structural alert for toxicity as proposed by the DEREK report. Methyl-RBC exhibited less toxicity and more binding affinity to CDK6.
Ionic liquids as potentially new antifungal agents against Alternaria species
Authors: Karaman Maja , Vraneš Milan , Tot Aleksandar , Papović Snežana , Miljaković Dragana , Gadžurić Slobodan , Ignjatov Maja
Published: June 2020

The objective of this study was to examine the in vitro antifungal activities of 18 newly synthesized ionic liquids (ILs) against three Alternaria strains: A. padwickii, A. dauci and A. linicola.
S-doped porous carbon anode with superior capacity for high-performance sodium storage
Authors: Liang Yaru , Liu Rutie , Xiong Xiang
Published: June 2020

A novel S-doped porous carbon material with superior sodium storage performance was obtained through spray-drying and subsequent sulfur doping treatment.
The development of novel bioactive porous titanium as a bone reconstruction material
Authors: Doi Kazuya , Kobatake Reiko , Makihara Yusuke , Oki Yoshifumi , Umehara Hanako , Kubo Takayasu , Tsuga Kazuhiro
Published: June 2020

Porous titanium fabricated by the resin-impregnated titanium substitute technique has good mechanical strength and osteoconduction.
Hierarchical Co(OH)2@NiMoS4 nanocomposite on carbon cloth as electrode for high-performance asymmetric supercapacitors
Authors: Li Junxian , Zhao Jianwei , Qin Lirong , Zhang Qitao , Tang Xiaolan , Xu Yingying
Published: June 2020

A hierarchical Co(OH)2@NiMoS4 nanocomposite was prepared on the surface of carbon cloth, which exhibited good electrochemical performance as a supercapacitor electrode.
Absorption induced ordered ring and inner network structures on a nanoporous substrate
Authors: Li Weibin , Ji Wenjie , Lan Ding , Wu Ke , Wang Yuren
Published: June 2020

Liquid absorption induced the formation of a novel pattern of an ordered ring with inner networks on the nanoporous substrate.
Highly spin-polarized electronic structure and magnetic properties of Mn2.25Co0.75Al1−xGex Heusler alloys: first-principles calculations
Authors: Wang Yue , Wang Liying , Mi Wenbo
Published: June 2020

The complete spin polarizations of Mn2.25Co0.75Al1−xGex are proved to be robust against stoichiometric defect and lattice deformation, whose easy magnetization direction can be manipulated from in-plane direction to out-of-plane one under uniaxial strain.
Single-molecular phosphorus phthalocyanine-based near-infrared-II nanoagent for photothermal antitumor therapy
Authors: Zhou Li-Na , Pan Houhe , Kan Jing-Lan , Guan Qun , Zhou Yang , Dong Yu-Bin
Published: June 2020

A molecular phosphorus phthalocyanine (P-Pc)-based nanoagentP-Pc-HSA, which can be a highly efficient NIR-II antitumor agent, is reported.
Development of sulfide, nitrogen co-doping hollow carbon with wideband electromagnetic absorption capability
Authors: Bao Wenli , Chen Cong , Si Zhenjun
Published: June 2020

Exploration of an economic, easy-producing method to develop high-performance electromagnetic absorber has been a global research interest, owing to the increasingly electromagnetic pollution and interference.
Hybrid capacitor with anthraquinone-grafted carbon as a battery-type electrode operating in a low pH aqueous salt solution
Authors: Pameté Emmanuel , Gorska Barbara , Ratajczak Paula , Béguin François
Published: June 2020

The aqueous hybrid capacitor made of a positive EDL carbon electrode and its battery-type counterpart obtained by grafting of anthraquinone moieties competes advantageously in terms of energy, safety and cost with traditional symmetric EDLCs in organic electrolyte.
Highly selective filler–polymer gaps in situ fabricated in mixed matrix membranes for gas separation
Authors: Jia Xuemeng , Qiao Zhihua , He Benqiao , Zhong Chongli
Published: June 2020

We report an interface self-assembly strategy to build high speed gas transport channels throughout mixed matrix membranes in situ using the gaps between hydrophilic polymers and hydrophobic fillers (normally considered as defects that lower the gas separation performance).
Activating the lattice oxygen in (Bi0.5Co0.5)2O3 by vacancy modulation for efficient electrochemical water oxidation
Authors: Liu Huan , Li Xiaoning , Peng Cailing , Zhu Liuyang , Zhang Yuanxi , Cheng Huiru , Cui Jiameng , Wu Qingmei , Zhang Yingying , Chen Zezhi , Zou Wei , Gu Wen , Huang Haoliang , Wang Jianlin , Ye Bangjiao , Fu Zhengping , Lu Yalin
Published: June 2020

Lattice-oxygen-active (Bi0.5Co0.5)2O3 was successfully prepared through vacancy modulation and demonstrated great OER activity and performance.
Tunable LiCl@UiO-66 composites for water sorption-based heat transformation applications
Authors: Sun Yangyang , Spieß Alex , Jansen Christian , Nuhnen Alexander , Gökpinar Serkan , Wiedey Raphael , Ernst Sebastian-Johannes , Janiak Christoph
Published: June 2020

No deliquescence, cycle stability, increased water uptake over a neat MOF and LiCl at low humidity, and high coefficient of performance.
Superfast and efficient hydrogen gas sensor using PdAualloy@ZnO core–shell nanoparticles
Authors: Le Hu-Jun , Van Dao Dung , Yu Yeon-Tae
Published: June 2020

PdAualloy@ZnO CSNPs are prepared and evaluated for hydrogen detection with superior behavior with respect to pure ZnO. Improvement is attributed to .synergistically catalytic effects between Pd, Au and ZnO in PdAualloy@ZnO core–shell sensory system
Real and virtual polymorphism of titanium selenide with robust interatomic potentials
Authors: Mora-Fonz David , Schön J. Christian , Prehl Janett , Woodley Scott M. , Catlow C. Richard A. , Shluger Alexander L. , Sokol Alexey A.
Published: June 2020

The first successful pairwise potential for a layered material, TiSe2, has been parameterised to fit the experimental data, using a genetic algorithm as the optimisation tool for the parameters of the interatomic potential.
Elucidating the optical, electronic, and photoelectrochemical properties of p-type copper vanadate (p-Cu5V2O10) photocathodes
Authors: Song Angang , Berglund Sean P. , Chemseddine Abdelkrim , Friedrich Dennis , Abdi Fatwa F. , van de Krol Roel
Published: June 2020

Compact spray-pyrolysed Cu5V2O10 photocathodes with 1.9 eV bandgap show positive photocurrent onset voltage and promising photoresponse.
Volatilizable and cost-effective quinone-based solid additives for improving photovoltaic performance and morphological stability in non-fullerene polymer solar cells
Authors: Zhang Youdi , Cho Yongjoon , Lee Jungho , Oh Jiyeon , Kang So-Huei , Lee Sang Myeon , Lee Byongkyu , Zhong Lian , Huang Bin , Lee Seungjin , Lee Jin-Woo , Kim Bumjoon J. , Li Yongfang , Yang Changduk
Published: June 2020

Two solid additives, BDT-1 and BDT-2, in non-fullerene polymer solar cells enhance photovoltaic efficiencies up to 16.26% with improved thermal and photoinduced stabilities.
Progress in the therapeutic applications of polymer-decorated black phosphorus and black phosphorus analog nanomaterials in biomedicine
Authors: An Dong , Fu Jianye , Xie Zhongjian , Xing Chenyang , Zhang Bin , Wang Bing , Qiu Meng
Published: June 2020

Owing to fascinating properties and biodegradability, opportunities and challenges of emerging black phosphorus (BP) and BP analogs (BPAs) in biomedical applications have been coexisted to study.
Zn(ii)/Cd(ii)-based metal–organic frameworks: crystal structures, Ln(iii)-functionalized luminescence and chemical sensing of dichloroaniline as a pesticide biomarker
Authors: Qu Xianglong , Yan Bing
Published: June 2020

Four new MOFs containing transition metals and mixed ligands were synthesized. Then Ln(iii)@4 hybrids are successfully fabricated by cation-exchange. Significantly, Tb(iii)@4 can be first regarded as an efficient sensor for biomarker dichloroanilines.
Joint source‐pair and relay selection for relay‐assisted network
Authors: Ozduran Volkan
Published: June 2020

This study investigates the opportunistic joint source‐pair and relay selection policy for cooperative networks. The investigation considers multi‐user pair and multiple bi‐directional amplify‐and‐forward based relays in the system model. The strategy selects an appropriate user‐pair and relay among N candidate user‐pairs and R available relays based on the maximum achievable sum‐rate of each user pair and related relay terminal. Analytical, asymptotic, and Monte Carlo based computer simulation results reveal that the joint‐selection strategy achieves multi‐user and cooperative diversity order in high signal‐to‐noise ratios. The results also show that the opportunistic joint source‐pair and relay selection strategy outperforms the max–min based selection policy. Moreover, the system contains a single relay, the joint‐selection strategy achieves only a multi‐user diversity and performs worse than the system that contains multiple relays. The results also show that the total achievable diversity order equals to the total number of possible paths between user‐pairs and relays, which is , while in the multi‐user and a single relay model, the diversity order only equals to N. Results also reveal that the proposed selection strategy provides an equal transmission opportunity for each of the user‐pairs.
Misalignment tolerance wireless power transfer system combining inductive and capacitive coupling
Authors: Luo Bo , Zhou Xingyu , Long Tao , Mai Ruikun , He Zhengyou
Published: June 2020

To resonate with the capacitive power transfer (CPT) system, inductors are usually needed, while additional capacitors are required for the inductive power transfer (IPT) system. To take advantage of the inductance of the IPT system, this study proposes a misalignment tolerance wireless power transfer system that employs the IPT coupler to compensate part of CPT's capacitance for railway applications. In the proposed system, two power transfer paths are formed by the IPT and CPT couplers. Additionally, the system merits a good anti‐misalignment ability by carefully designing the parameters of the proposed system. In a well‐alignment case, only the CPT coupler is utilised to transfer power. While in misalignment case, the IPT coupler is activated to transfer power to improve the misalignment tolerance. Besides, the transfer capability of the combined system can be improved when the misalignment happens. The system coupler, connection method and output power characteristics are presented in detail. Then, the general design procedure is provided with an example system at 1 kW. Experimental results show that the maximum variation of the output is 5.6% when misalignment is up to 250 mm (50%). While the power variation of the system involving single CPT can be as large as 52%.
Second‐order matrix pencil‐based phasor measurement algorithm for P‐class PMUs
Authors: Li Jiaxian , Liu Hao , Bi Tianshu , Zhao Junbo
Published: June 2020

Phasor measurement units (PMUs) have made real‐time monitoring and control of power systems possible, thanks to their time synchronisation and fast reporting rate. It is critical that the PMUs can track the dynamics of complex power systems accurately. In this study, a measurement bandwidth extraction method based on signal reconstruction is proposed to filter the out‐of‐band signals without extra response time. The synthetic phasor is modelled by the second‐order Taylor's series expansion. A matrix pencil‐based fast phasor measurement algorithm is proposed for P‐class PMUs. Simulation and experiment results show that the accuracy and the response time of the proposed algorithm meet the requirements of the IEEE standard. Field data test shows that out‐of‐band signals have been reduced and the dynamic change of power system can be accurately reflected by phasor estimations. All results demonstrate that the proposed algorithm is suitable for P‐class PMUs in complex power systems.
Real‐time identification of electromechanical oscillations through dynamic mode decomposition
Authors: Berizzi Alberto , Bosisio Alessandro , Simone Riccardo , Vicario Andrea , Giannuzzi Giorgio , Pisani Cosimo , Zaottini Roberto
Published: June 2020

The increasing penetration of inverter‐based resources is affecting the overall power system security, so that effective tools are needed to provide system awareness and identify the most suited countermeasures. To tackle this problem, real‐time monitoring and assessment of transmission grids based on synchrophasor measurements have drawn the attention of many researchers over the last decade, thanks to the high temporal resolution of data provided by phasor measurement units. In this study, a new version of the dynamic mode decomposition (DMD) is proposed as a tool for the real‐time identification of electromechanical oscillations. This approach is able to provide information on the dynamic characteristics (frequency and damping) and the spatial correlation (mode shape) of the modes identified. Besides, an improved criterion is used to track and discern the dominant modes. The effectiveness of the DMD method has been tested on the two‐area Kundur system and validated using data from a real event on the European synchronous grid, giving promising results. Thanks to its reliability and robustness, the DMD is now implemented in the Terna (the Italian transmission system operator) Wide Area Measurement System in use in the control room.
Estimating black hole masses: Accretion disk fitting versus reverberation mapping and single epoch
Authors: Campitiello Samuele , Celotti Annalisa , Ghisellini Gabriele , Sbarrato Tullia
Published: June 2020

We selected a sample of 28 Type 1 active galactic nuclei for which a black hole mass has been inferred using the reverberation mapping technique and single epoch scaling relations. All 28 sources show clear evidence of the “Big Blue Bump” in the optical-UV band whose emission is produced by an accretion disk (AD) around a supermassive black hole. We fitted the spectrum of these sources with the relativistic thin AD model KERRBB in order to infer the black hole masses and compared them with those from Reverberation mapping and Single epoch methods, discussing the possible uncertainties linked to such a model by quantifying their weight on our results. We find that for the majority of the sources, KERRBB is a good description of the AD emission for a wide wavelength range. The overall uncertainty on the black hole mass estimated through the disk fitting procedure is ∼0.45 dex (which includes the uncertainty on fitting parameters such as e.g., spin and viewing angle), comparable to the systematic uncertainty of reverberation mapping and single epoch methods; however, such an uncertainty can be ≲0.3 dex if one of the parameters of the fit is well constrained. Although all of the estimates are affected by large uncertainties, the masses inferred using the three methods are compatible if the dimensionless scale factorf(linked to the unknown kinematics and geometry of the Broad Line Region) is assumed to be larger than one. For the majority of the sources, the comparison between the results coming from the three methods favors small spin values. To check the goodness of the KERRBB results, we compared them with those inferred with other models, such as AGNSED, a model that also accounts for the emission originating from an X-ray corona: using two sources with a good data coverage in theXband, we find that the masses estimated with the two models differ at most by a factor of ∼0.2 dex.
The chemical evolution of the dwarf spheroidal galaxy Sextans
Authors: Theler R. , Jablonka P. , Lucchesi R. , Lardo C. , North P. , Irwin M. , Battaglia G. , Hill V. , Tolstoy E. , Venn K. , Helmi A. , Kaufer A. , Primas F. , Shetrone M.
Published: June 2020

We present our analysis of the FLAMES dataset targeting the central 25′ region of the Sextans dwarf spheroidal galaxy (dSph). This dataset is the third major part of the high-resolution spectroscopic section of the ESO large program 171.B-0588(A) obtained by the Dwarf galaxy Abundances and Radial-velocities Team. Our sample is composed of red giant branch stars down to V ∼ 20.5 mag, the level of the horizontal branch in Sextans, and allows users to address questions related to both stellar nucleosynthesis and galaxy evolution. We provide metallicities for 81 stars, which cover the wide [Fe/H] = −3.2 to −1.5 dex range. The abundances of ten other elements are derived: Mg, Ca, Ti, Sc, Cr, Mn, Co, Ni, Ba, and Eu. Despite its small mass, Sextans is a chemically evolved system, showing evidence of a contribution from core-collapse and Type Ia supernovae as well as low-metallicity asymptotic giant branch stars (AGBs). This new FLAMES sample offers a sufficiently large number of stars with chemical abundances derived with high accuracy to firmly establish the existence of a plateau in [α/Fe] at ∼0.4 dex followed by a decrease above [Fe/H] ∼ −2 dex. These features reveal a close similarity with the Fornax and Sculptor dSphs despite their very different masses and star formation histories, suggesting that these three galaxies had very similar star formation efficiencies in their early formation phases, probably driven by the early accretion of smaller galactic fragments, until the UV-background heating impacted them in different ways. The parallel between the Sculptor and Sextans dSph is also striking when considering Ba and Eu. The same chemical trends can be seen in the metallicity region common to both galaxies, implying similar fractions of SNeIa and low-metallicity AGBs. Finally, as to the iron-peak elements, the decline of [Co/Fe] and [Ni/Fe] above [Fe/H] ∼ −2 implies that the production yields of Ni and Co in SNeIa are lower than that of Fe. The decrease in [Ni/Fe] favours models of SNeIa based on the explosion of double-degenerate sub-Chandrasekhar mass white dwarfs.
Numerical simulations of the lower solar atmosphere heating by two-fluid nonlinear Alfvén waves
Authors: Kuźma B. , Wójcik D. , Murawski K. , Yuan D. , Poedts S.
Published: June 2020

Context. We present new insight into the long-standing problem of plasma heating in the lower solar atmosphere in terms of collisional dissipation caused by two-fluid Alfvén waves.

Aims. Using numerical simulations, we study Alfvén wave propagation and dissipation in a magnetic flux tube and their heating effect.

Methods. We set up 2.5-dimensional numerical simulations with a semi-empirical model of a stratified solar atmosphere and a force-free magnetic field mimicking a magnetic flux tube. We consider a partially ionized plasma consisting of ion + electron and neutral fluids, which are coupled by ion-neutral collisions.

Results. We find that Alfvén waves, which are directly generated by a monochromatic driver at the bottom of the photosphere, experience strong damping. Low-amplitude waves do not thermalize sufficient wave energy to heat the solar atmospheric plasma. However, Alfvén waves with amplitudes greater than 0.1 km s−1 drive through ponderomotive force magneto-acoustic waves in higher atmospheric layers. These waves are damped by ion-neutral collisions, and the thermal energy released in this process leads to heating of the upper photosphere and the chromosphere.

Conclusions. We infer that, as a result of ion-neutral collisions, the energy carried initially by Alfvén waves is thermalized in the upper photosphere and the chromosphere, and the corresponding heating rate is large enough to compensate radiative and thermal-conduction energy losses therein.
Turnaround density as a probe of the cosmological constant
Authors: Pavlidou Vasiliki , Korkidis Giorgos , Tomaras Theodore N. , Tanoglidis Dimitrios
Published: June 2020

Spherical collapse predicts that a single value of the turnaround density, meaning the average matter density within the scale on which a structure detaches from the Hubble flow, characterizes all cosmic structures at the same redshift. It was recently shown by Korkidis et al. that this feature persists in complex non-spherical galaxy clusters that have been identified in N-body simulations. Here we show that the low-redshift evolution of the turnaround density constrains the cosmological parameters and it can be used to derive a local constraint on ΩΛ, 0 alone, independent of Ωm, 0. The turnaround density thus offers a promising new method for exploiting upcoming large cosmological datasets.
The NIBLES bivariate luminosity–H I mass distribution function revised using Arecibo follow-up observations
Authors: Butcher Z. , van Driel W. , Schneider S.
Published: June 2020

We present a modified optical luminosity–H I mass bivariate luminosity function based on H I line observations from the Nançay Interstellar Baryons Legacy Extragalactic Survey (NIBLES), including data from our new, four times more sensitive follow-up H I line observations obtained with the Arecibo radio telescope. The follow-up observations were designed to probe the underlying H I mass distribution of the NIBLES galaxies that were undetected or marginally detected in H I at the Nançay Radio Telescope. Our total follow-up sample consists of 234 galaxies, and it spans the entire luminosity and color range of the parent NIBLES sample of 2600 nearby (900 <  cz <  12 000 km s−1) SDSS galaxies. We incorporated the follow-up data into the bivariate analysis by scaling the NIBLES undetected fraction by an Arecibo-only distribution. We find the resulting increase in low H I mass-to-light ratio densities to be about 10% for the bins −1.0 ≤ log(MHI/M⊙/Lr/L⊙) ≤ −0.5, which produces an increased H I mass function (HIMF) low mass slope of α = −1.14 ± 0.07, being slightly shallower than the values of −1.35 ± 0.05 obtained by recent blind H I surveys. Applying the same correction to the optically corrected bivariate luminosity function from our previous paper produces a larger density increase of about 0.5 to 1 dex in the lowest H I mass-to-light ratio bins for a given luminosity while having a minimal effect on the resulting HIMF low mass slope, which still agrees with blind survey HIMFs. This indicates that while low H I-mass-to-light ratio galaxies do not contribute much to the one-dimensional HIMF, their inclusion has a significant impact on the densities in the two-dimensional distribution.
Pebble-driven planet formation around very low-mass stars and brown dwarfs
Authors: Liu Beibei , Lambrechts Michiel , Johansen Anders , Pascucci Ilaria , Henning Thomas
Published: June 2020

We conduct a pebble-driven planet population synthesis study to investigate the formation of planets around very low-mass stars and brown dwarfs in the (sub)stellar mass range between 0.01 M⊙ and 0.1 M⊙. Based on the extrapolation of numerical simulations of planetesimal formation by the streaming instability, we obtain the characteristic mass of the planetesimals and the initial mass of the protoplanet (largest body from the planetesimal populations), in either the early self-gravitating phase or the later non-self-gravitating phase of the protoplanetary disk evolution. We find that the initial protoplanets form with masses that increase with host mass and orbital distance, and decrease with age. Around late M-dwarfs of 0.1 M⊙, these protoplanets can grow up to Earth-mass planets by pebble accretion. However, around brown dwarfs of 0.01 M⊙, planets do not grow to the masses that are greater than Mars when the initial protoplanets are born early in self-gravitating disks, and their growth stalls at around 0.01 Earth-mass when they are born late in non-self-gravitating disks. Around these low-mass stars and brown dwarfs we find no channel for gas giant planet formation because the solid cores remain too small. When the initial protoplanets form only at the water-ice line, the final planets typically have ≳15% water mass fraction. Alternatively, when the initial protoplanets form log-uniformly distributed over the entire protoplanetary disk, the final planets are either very water rich (water mass fraction ≳15%) or entirely rocky (water mass fraction ≲5%).
Interferometric imaging with LOFAR remote baselines of the fine structures of a solar type-IIIb radio burst
Authors: Zhang PeiJin , Zucca Pietro , Sridhar Sarrvesh Seethapuram , Wang ChuanBing , Bisi Mario M. , Dabrowski Bartosz , Krankowski Andrzej , Mann Gottfried , Magdalenic Jasmina , Morosan Diana E. , Vocks Christian
Published: June 2020

Context. Solar radio bursts originate mainly from high energy electrons accelerated in solar eruptions like solar flares, jets, and coronal mass ejections. A sub-category of solar radio bursts with short time duration may be used as a proxy to understand wave generation and propagation within the corona.

Aims. Complete case studies of the source size, position, and kinematics of short term bursts are very rare due to instrumental limitations. A comprehensive multi-frequency spectroscopic and imaging study was carried out of a clear example of a solar type IIIb-III pair.

Methods. In this work, the source of the radio burst was imaged with the interferometric mode, using the remote baselines of the LOw Frequency ARray (LOFAR). A detailed analysis of the fine structures in the spectrum and of the radio source motion with imaging was conducted.

Results. The study shows how the fundamental and harmonic components have a significantly different source motion. The apparent source of the fundamental emission at 26.56 MHz displaces away from the solar disk center at about four times the speed of light, while the apparent source of the harmonic emission at the same frequency shows a speed of < 0.02 c. The source size of the harmonic emission observed in this case is smaller than that in previous studies, indicating the importance of the use of remote baselines.
Kinematics of coronal mass ejections in the LASCO field of view
Authors: Ravishankar Anitha , Michałek Grzegorz , Yashiro Seiji
Published: June 2020

In this paper we present a statistical study of the kinematics of 28894 coronal mass ejections (CMEs) recorded by the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory spacecraft from 1996 until mid-2017. The initial acceleration phase is characterized by a rapid increase in CME velocity just after eruption in the inner corona. This phase is followed by a non-significant residual acceleration (deceleration) characterized by an almost constant speed of CMEs. We demonstrate that the initial acceleration is in the range 0.24–2616 m s−2 with median (average) value of 57 m s−2 (34 m s−2) and it takes place up to a distance of about 28 RSUN with median (average) value of 7.8 RSUN (6 RSUN). Additionally, the initial acceleration is significant in the case of fast CMEs (V >  900 km s−1), where the median (average) values are about 295 m s−2 (251 m s−2), respectively, and much weaker in the case of slow CMEs (V <  250 km s−1), where the median (average) values are about 18 m s−2 (17 m s−2), respectively. We note that the significant driving force (Lorentz force) can operate up to a distance of 6 RSUN from the Sun during the first 2 hours of propagation. We found a significant anti-correlation between the initial acceleration magnitude and the acceleration duration, whereas the residual acceleration covers a range from −1224 to 0 m s−2 with a median (average) value of −34 m s−2 (−17 m s−2). One intriguing finding is that the residual acceleration is much smaller during the 24th cycle in comparison to the 23rd cycle of solar activity. Our study has also revealed that the considered parameters, initial acceleration (ACCINI), residual acceleration (ACCRES), maximum velocity (VMAX), and time at maximum velocity (TimeMAX) mostly follow solar cycles and the intensities of the individual cycle.
Statistics of solar wind electron breakpoint energies using machine learning techniques
Authors: Bakrania M. R. , Rae I. J. , Walsh A. P. , Verscharen D. , Smith A. W. , Bloch T. , Watt C. E. J.
Published: June 2020

Solar wind electron velocity distributions at 1 au consist of a thermal “core” population and two suprathermal populations: “halo” and “strahl”. The core and halo are quasi-isotropic, whereas the strahl typically travels radially outwards along the parallel or anti-parallel direction with respect to the interplanetary magnetic field. Using Cluster-PEACE data, we analyse energy and pitch angle distributions and use machine learning techniques to provide robust classifications of these solar wind populations. Initially, we used unsupervised algorithms to classify halo and strahl differential energy flux distributions to allow us to calculate relative number densities, which are of the same order as previous results. Subsequently, we applied unsupervised algorithms to phase space density distributions over ten years to study the variation of halo and strahl breakpoint energies with solar wind parameters. In our statistical study, we find both halo and strahl suprathermal breakpoint energies display a significant increase with core temperature, with the halo exhibiting a more positive correlation than the strahl. We conclude low energy strahl electrons are scattering into the core at perpendicular pitch angles. This increases the number of Coulomb collisions and extends the perpendicular core population to higher energies, resulting in a larger difference between halo and strahl breakpoint energies at higher core temperatures. Statistically, the locations of both suprathermal breakpoint energies decrease with increasing solar wind speed. In the case of halo breakpoint energy, we observe two distinct profiles above and below 500 km s−1. We relate this to the difference in origin of fast and slow solar wind.
Axisymmetric equilibrium models for magnetised neutron stars in scalar-tensor theories
Authors: Soldateschi J. , Bucciantini N. , Del Zanna L.
Published: June 2020

Among the possible extensions of general relativity that have been put forward to address some long-standing issues in our understanding of the Universe, scalar-tensor theories have received a lot of attention for their simplicity. Interestingly, some of these predict a potentially observable non-linear phenomenon, known as spontaneous scalarisation, in the presence of highly compact matter distributions, as in the case of neutron stars. Neutron stars are ideal laboratories for investigating the properties of matter under extreme conditions and, in particular, they are known to harbour the strongest magnetic fields in the Universe. Here, for the first time, we present a detailed study of magnetised neutron stars in scalar-tensor theories. First, we showed that the formalism developed for the study of magnetised neutron stars in general relativity, based on the “extended conformally flat condition”, can easily be extended in the presence of a non-minimally coupled scalar field, retaining many of its numerical advantages. We then carried out a study of the parameter space considering the two extreme geometries of purely toroidal and purely poloidal magnetic fields, varying both the strength of the magnetic field and the intensity of scalarisation. We compared our results with magnetised general-relativistic solutions and un-magnetised scalarised solutions, showing how the mutual interplay between magnetic and scalar fields affect the magnetic and the scalarisation properties of neutron stars. In particular, we focus our discussion on magnetic deformability, maximum mass, and range of scalarisation.
New constraints on the location of P9 obtained with the INPOP19a planetary ephemeris
Authors: Fienga A. , Di Ruscio A. , Bernus L. , Deram P. , Durante D. , Laskar J. , Iess L.
Published: June 2020

Context.We used the new released INPOP19a planetary ephemerides benefiting from Jupiter-updated positions by theJunomission and reanalyzedCassiniobservations.

Aims.We test possible locations of the unknown planet P9. To do this, we used the perturbations it produces on the orbits of the outer planets, more specifically, on the orbit of Saturn.

Methods.Two statistical criteria were used to identify possible acceptable locations of P9 according to (i) the difference in planetary positions when P9 is included compared with the propagated covariance matrix, and (ii) theχ2likelihood of postfit residuals for ephemerides when P9 is included.

Results.No significant improvement of the residuals was found for any of the simulated locations, but we provide zones that induce a significant degradation of the ephemerides.

Conclusions.Based on the INPOP19a planetary ephemerides, we demonstrate that if P9 exists, it cannot be closer than 500 AU with a 5M⊕and no closer than 650 AU with a 10M⊕. We also show that there is no clear zone that would indicate the positive existence of planet P9, but there are zones for which the existence of P9 is compatible with the 3σaccuracy of the INPOP planetary ephemerides.
Three short-period Jupiters from TESS
Authors: Nielsen L. D. , Brahm R. , Bouchy F. , Espinoza N. , Turner O. , Rappaport S. , Pearce L. , Ricker G. , Vanderspek R. , Latham D. W. , Seager S. , Winn J. N. , Jenkins J. M. , Acton J. S. , Bakos G. , Barclay T. , Barkaoui K. , Bhatti W. , Briceño C. , Bryant E. M. , Burleigh M. R. , Ciardi D. R. , Collins K. A. , Collins K. I. , Cooke B. F. , Csubry Z. , dos Santos L. A. , Eigmüller Ph. , Fausnaugh M. M. , Gan T. , Gillon M. , Goad M. R. , Guerrero N. , Hagelberg J. , Hart R. , Henning T. , Huang C. X. , Jehin E. , Jenkins J. S. , Jordán A. , Kielkopf J. F. , Kossakowski D. , Lavie B. , Law N. , Lendl M. , de Leon J. P. , Lovis C. , Mann A. W. , Marmier M. , McCormac J. , Mori M. , Moyano M. , Narita N. , Osip D. , Otegi J. F. , Pepe F. , Pozuelos F. J. , Raynard L. , Relles H. M. , Sarkis P. , Ségransan D. , Seidel J. V. , Shporer A. , Stalport M. , Stockdale C. , Suc V. , Tamura M. , Tan T. G. , Tilbrook R. H. , Ting E. B. , Trifonov T. , Udry S. , Vanderburg A. , Wheatley P. J. , Wingham G. , Zhan Z. , Ziegler C.
Published: June 2020

We report the confirmation and mass determination of three hot Jupiters discovered by the Transiting Exoplanet Survey Satellite (TESS) mission: HIP 65Ab (TOI-129, TIC-201248411) is an ultra-short-period Jupiter orbiting a bright (V = 11.1 mag) K4-dwarf every 0.98 days. It is a massive 3.213 ± 0.078 MJ planet in a grazing transit configuration with an impact parameter of b = 1.17−0.08+0.10. As a result the radius is poorly constrained, 2.03−0.49+0.61RJ. The planet’s distance to its host star is less than twice the separation at which it would be destroyed by Roche lobe overflow. It is expected to spiral into HIP 65A on a timescale ranging from 80 Myr to a few gigayears, assuming a reduced tidal dissipation quality factor of Qs′ = 107 − 109. We performed a full phase-curve analysis of the TESS data and detected both illumination- and ellipsoidal variations as well as Doppler boosting. HIP 65A is part of a binary stellar system, with HIP 65B separated by 269 AU (3.95 arcsec on sky). TOI-157b (TIC 140691463) is a typical hot Jupiter with a mass of 1.18 ± 0.13 MJ and a radius of 1.29 ± 0.02 RJ. It has a period of 2.08 days, which corresponds to a separation of just 0.03 AU. This makes TOI-157 an interesting system, as the host star is an evolved G9 sub-giant star (V = 12.7). TOI-169b (TIC 183120439) is a bloated Jupiter orbiting a V = 12.4 G-type star. It has a mass of 0.79 ±0.06 MJ and a radius of 1.09−0.05+0.08RJ. Despite having the longest orbital period (P = 2.26 days) of the three planets, TOI-169b receives the most irradiation and is situated on the edge of the Neptune desert. All three host stars are metal rich with [Fe / H] ranging from 0.18 to0.24.
Self-scattering of non-spherical dust grains
Authors: Kirchschlager Florian , Bertrang Gesa H.-M.
Published: June 2020

Context. The understanding of (sub-)millimetre polarisation has made a leap forward since high-resolution imaging with the Atacama Large (sub-)Mm Array (ALMA) became available. Amongst other effects, self-scattering (i.e. the scattering of thermal dust emission on other grains) is thought to be the origin of millimetre polarisation. This opens the first window to a direct measurement of dust grain sizes in regions of optically thick continuum emission as it can be found in protoplanetary discs and star-forming regions. However, the newly derived values of grain sizes are usually around ~100 μm and thus one order of magnitude smaller than those obtained from more indirect measurements, as well as those expected from theory (~1 mm).

Aims. We see the origin of this contradiction in the applied dust model of current self-scattering simulations: a perfect compact sphere. The aim of this study is to test our hypothesis by investigating the impact of non-spherical grain shapes on the self-scattering signal.

Methods. We applied discrete dipole approximation simulations to investigate the influence of the grain shape on self-scattering polarisation in three scenarios: an unpolarised and polarised incoming wave under a fixed and a varying incident polarisation angle.

Results. We find significant deviations of the resulting self-scattering polarisation when comparing non-spherical to spherical grains. In particular, tremendous deviations are found for the polarisation signal of grains when observed outside the Rayleigh regime, that is for >100 μm sized grains observed at the 870 μm wavelength. Self-scattering by oblate grains produces higher polarisation degrees compared to spheres, which challenges the interpretation of the origin of observed millimetre polarisation. A (nearly) perfect alignment of the non-spherical grains is required to account for the observed millimetre polarisation in protoplanetary discs. Furthermore, we find conditions under which the emerging scattering polarisation of non-spherical grains is flipped in orientation by 90°.

Conclusions. These results show clearly that the perfect compact sphere is an oversimplified model, which has reached its limit. Our findings point towards a necessary re-evaluation of the dust grain sizes derived from (sub-)millimetre polarisation.
VLT/SPHERE survey for exoplanets around young early-type stars, including systems with multi-belt architectures
Authors: Lombart M. , Chauvin G. , Rojo P. , Lagadec E. , Delorme P. , Beust H. , Bonnefoy M. , Galicher R. , Gratton R. , Mesa D. , Bonavita M. , Allard F. , Bayo A. , Boccaletti A. , Desidera S. , Girard J. , Jenkins J. S. , Klahr H. , Laibe G. , Lagrange A.-M. , Lazzoni C. , Marleau G-D. , Minniti D. , Mordasini C.
Published: June 2020

Context. Dusty debris disks around pre- and main-sequence stars are potential signposts for the existence of planetesimals and exoplanets. Giant planet formation is therefore expected to play a key role in the evolution of the disk. This is indirectly confirmed by extant submillimeter near-infrared images of young protoplanetary and cool dusty debris disks around main-sequence stars that usually show substantial spatial structures. With two decades of direct imaging of exoplanets already studied, it is striking to note that a majority of recent discoveries of imaged giant planets have been obtained around young early-type stars hosting a circumstellar disk.

Aims. Our aim was to create a direct imaging program designed to maximize our chances of giant planet discovery and target 22 young early-type stars. About half of them show indications of multi-belt architectures.

Methods. Using the IRDIS dual-band imager and the IFS integral field spectrograph of SPHERE to acquire high-constrast coronagraphic differential near-infrared images, we conducted a systematic search in the close environment of these young, dusty, and early-type stars. We used a combination of angular and spectral differential imaging to reach the best detection performances down to the planetary mass regime.

Results. We confirm that companions detected around HIP 34276, HIP 101800, and HIP 117452 are stationary background sources and binary companions. The companion candidates around HIP 8832, HIP 16095, and HIP 95619 are determined as background contaminations. Regarding the stars for which we infer the presence of debris belts, a theoretical minimum mass for planets required to clear the debris gaps can be calculated. The dynamical mass limit is at least 0.1 MJ and can exceed 1 MJ. Direct imaging data is typically sensitive to planets down to ~3.6 MJ at 1′′, and 1.7 MJ in the best case. These two limits tightly constrain the possible planetary systems present around each target. These systems will be probably detectable with the next generation of planet imagers.
Radio and high-energy emission of pulsars revealed by general relativity
Authors: Giraud Q. , Pétri J.
Published: June 2020

Context. According to current pulsar emission models, photons are produced within their magnetosphere and current sheet, along their separatrix, which is located inside and outside the light cylinder. Radio emission is favoured in the vicinity of the polar caps, whereas the high-energy counterpart is presumably enhanced in regions around the light cylinder, whether this is the magnetosphere and/or the wind. However, the gravitational effect on their light curves and spectral properties has only been sparsely researched.

Aims. We present a method for simulating the influence that the gravitational field of the neutron star has on its emission properties according to the solution of a rotating dipole evolving in a slowly rotating neutron star metric described by general relativity.

Methods. We numerically computed photon trajectories assuming a background Schwarzschild metric, applying our method to neutron star radiation mechanisms such as thermal emission from hot spots and non-thermal magnetospheric emission by curvature radiation. We detail the general-relativistic effects onto observations made by a distant observer.

Results. Sky maps are computed using the vacuum electromagnetic field of a general-relativistic rotating dipole, extending previous works obtained for the Deutsch solution. We compare Newtonian results to their general-relativistic counterpart. For magnetospheric emission, we show that aberration and curvature of photon trajectories as well as Shapiro time delay significantly affect the phase delay between radio and high-energy light curves, although the characteristic pulse profile that defines pulsar emission is kept.
Precise calibration of the dependence of surface brightness–colour relations on colour and class for late-type stars
Authors: Salsi A. , Nardetto N. , Mourard D. , Creevey O. , Huber D. , White T. R. , Hocdé V. , Morand F. , Tallon-Bosc I. , Farrington C. D. , Chelli A. , Duvert G.
Published: June 2020

Context. Surface brightness–colour relations (SBCRs) are used to derive the stellar angular diameters from photometric observations. They have various astrophysical applications, such as the distance determination of eclipsing binaries or the determination of exoplanet parameters. However, strong discrepancies between the SBCRs still exist in the literature, in particular for early and late-type stars.

Aims. We aim to calibrate new SBCRs as a function of the spectral type and the luminosity class of the stars. Our goal is also to apply homogeneous criteria to the selection of the reference stars and in view of compiling an exhaustive and up-to-date list of interferometric late-type targets.

Methods. We implemented criteria to select measurements in the JMMC Measured Diameters Catalog. We then applied additional criteria on the photometric measurements used to build the SBCRs, together with stellar characteristics diagnostics.

Results. We built SBCRs for F5/K7–II/III, F5/K7–IV/V, M–II/III and M–V stars, with respective rms of σFV = 0.0022 mag, σFV = 0.0044 mag, σFV = 0.0046 mag, and σFV = 0.0038 mag. This results in a precision on the angular diameter of 1.0%, 2.0%, 2.1%, and 1.7%, respectively. These relations cover a large V − K colour range of magnitude, from 1 to 7.5. Our work demonstrates that SBCRs are significantly dependent on the spectral type and the luminosity class of the star. Through a new set of interferometric measurements, we demonstrate the critical importance of the selection criteria proposed for the calibration of SBCR. Finally, using the Gaia photometry for our samples, we obtained (G − K) SBCRs with a precision on the angular diameter between 1.1% and 2.4%.

Conclusions. By adopting a refined and homogeneous methodology, we show that the spectral type and the class of the star should be considered when applying an SBCR. This is particularly important in the context of PLATO.
Bipolar molecular outflow of the very low-mass star Par-Lup3-4
Authors: Santamaría-Miranda A. , de Gregorio-Monsalvo I. , Huélamo N. , Plunkett A. L. , Ribas Á. , Comerón F. , Schreiber M. R. , López C. , Mužić K. , Testi L.
Published: June 2020

Context. Very low-mass stars are known to have jets and outflows, which is indicative of a scaled-down version of low-mass star formation. However, only very few outflows in very low-mass sources are well characterized.

Aims. We characterize the bipolar molecular outflow of the very low-mass star Par-Lup3-4, a 0.12 M⊙ object known to power an optical jet.

Methods. We observed Par-Lup3-4 with ALMA in Bands 6 and 7, detecting both the continuum and CO molecular gas. In particular, we studied three main emission lines: CO(2–1), CO(3–2), and 13CO(3–2).

Results. Our observations reveal for the first time the base of a bipolar molecular outflow in a very low-mass star, as well as a stream of material moving perpendicular to the primary outflow of this source. The primary outflow morphology is consistent with the previously determined jet orientation and disk inclination. The outflow mass is 9.5 × 10−7 M⊙, with an outflow rate of 4.3 × 10−9 M⊙ yr−1. A new fitting to the spectral energy distribution suggests that Par-Lup3-4 may be a binary system.

Conclusions. We have characterized Par-Lup3-4 in detail, and its properties are consistent with those reported in other very low-mass sources. This source provides further evidence that very low-mass sources form as a scaled-down version of low-mass stars.