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Slipping motions of magnetic field lines are a distinct signature of three-dimensional magnetic reconnection, a fundamental process driving solar and stellar flares. While being a key prediction of numerical experiments, the rapid super-Alfvénic field line slippage driven by the 'slip-running' reconnection has remained elusive in previous observations. New frontiers into exploring transient flare phenomena were introduced by recently designed high cadence observing programs of the Interface Region Imaging Spectrograph (IRIS). By exploiting high temporal resolution imagery (~2 s) of IRIS, here we reveal slipping motions of flare kernels at speeds reaching thousands of kilometres per second. The fast kernel motions are direct evidence of slip-running reconnection in quasi-separatrix layers, regions where magnetic field strongly changes its connectivity. Our results provide observational proof of theoretical predictions unaddressed for nearly two decades and extend the range of magnetic field configurations where reconnection-related phenomena can occur., Competing Interests: Competing interestsThe authors declare no competing interests., (© The Author(s) 2024.)

Galaxy clusters are the most massive gravitationally bound structures in the Universe. They grow by accreting smaller structures in a merging process that produces shocks and turbulence in the intracluster gas. We observed a ridge of radio emission connecting the merging galaxy clusters Abell 0399 and Abell 0401 with the Low-Frequency Array (LOFAR) telescope network at 140 megahertz. This emission requires a population of relativistic electrons and a magnetic field located in a filament between the two galaxy clusters. We performed simulations to show that a volume-filling distribution of weak shocks may reaccelerate a preexisting population of relativistic particles, producing emission at radio wavelengths that illuminates the magnetic ridge. [ABSTRACT FROM AUTHOR]

We present simulations of isolated disc galaxies in a realistic environment performed with the Tree-SPMHD-Code Gadget-3. Our simulations include a spherical circumgalactic medium (CGM) surrounding the galactic disc, motivated by observations and the results of cosmological simulations. We present three galactic models with different halo masses between |$10^{10}$| and |$10^{12} \, \mathrm{M}_\odot$|⁠, and for each we use two different approaches to seed the magnetic field as well as a control simulation without a magnetic field. We find that the amplification of the magnetic field in the centre of the disc leads to a biconical magnetic outflow of gas that magnetizes the CGM. This biconical magnetic outflow reduces the star formation rate (SFR) of the galaxy by roughly |$40 {{\ \rm per\ cent}}$| compared to the simulations without magnetic fields. As the key aspect of our simulations, we find that small-scale turbulent motion of the gas in the disc leads to the amplification of the magnetic field up to tens of |$\mu {\rm G}$|⁠, as long as the magnetic field strength is low. For stronger magnetic fields, turbulent motion does not lead to significant amplification but is replaced by an α–ω dynamo. The occurrence of a small-scale turbulent dynamo becomes apparent through the magnetic power spectrum and analysis of the field lines' curvature. In accordance with recent observations, we find an anticorrelation between the spiral structure in the gas density and in the magnetic field due to a diffusion term added to the induction equation. [ABSTRACT FROM AUTHOR]

Following previous investigations of quasiperiodic plasma density structures in the solar wind at 1 AU, we show using the Helios1 and Helios2 data their first identification in situ in the inner heliosphere at 0.3, 0.4, and 0.6 AU. We present five events of quasiperiodic density structures with time scales ranging from a few minutes to a couple of hours in slow solar wind streams. Where possible, we locate the solar source region of these events using photospheric field maps from the Mount Wilson Observatory as input for the Wang‐Sheeley‐Arge model. The detailed study of the plasma properties of these structures is fundamental to understanding the physical processes occurring at the origin of the release of solar wind plasma. Temperature changes associated with the density structures are consistent with these periodic structures developing in the solar atmosphere as the solar wind is formed. One event contains a flux rope, suggesting that the solar wind was formed as magnetic reconnection opened up a previously closed flux tube at the Sun. This study highlights the types of structures that Parker Solar Probe and the upcoming Solar Orbiter mission will observe, and the types of data analyses these missions will enable. The data from these spacecrafts will provide additional in situ measurements of the solar wind properties in the inner heliosphere allowing, together with the information of the other interplanetary probes, a more comprehensive study of solar wind formation. Key Points: Quasiperiodic solar wind density structures observed closer to the Sun than ever before by in situ dataConcomitant density/temperature enhancements suggest the release of coronal plasma from closed‐field regions by magnetic reconnectionOne occurrence of quasiperiodic structures maps to a region far from the heliospheric current sheet, supporting the S‐web model of the slow solar wind [ABSTRACT FROM AUTHOR]

The origin of cosmic magnetic fields is an unsolved problem and magnetogenesis could have occurred in the early Universe. We study the evolution of such primordial magnetic fields across the cosmological recombination epoch via 3D magnetohydrodynamic numerical simulations. We compute the effective or net heating rate of baryons due to decaying magnetic fields and its dependence on the magnetic field strength and spectral index. In the drag-dominated regime (⁠|$z$| ≳ 1500), prior to recombination, we find no real heating is produced. Our simulations allow us to smoothly trace a new transition regime (600 ≲ |$z$| ≲ 1500), where magnetic energy decays, at first, into the kinetic energy of baryons. A turbulent velocity field is built up until it saturates, as the net heating rate rises from a low value at recombination to its peak towards the end of the transition regime. This is followed by a turbulent decay regime (⁠|$z$| ≲ 600) where magnetic energy dissipates via turbulent decay of both magnetic and velocity fields while net heating remains appreciable and declines slowly. Both the peak of the net heating rate and the onset of turbulent decay are delayed significantly beyond recombination, by up to 0.5 Myr (until |$z$| ≃ 600–700), for scale-invariant magnetic fields. We concentrate on low magnetic field strength to avoid confusion with magnetic field-generated density fluctuations. Analytic approximations are provided and we present numerical results for a range of field strengths (≃10−3− 2 × 10−2nG) and spectral indices, illustrating the redshift-dependence of dissipation and net heating rates. These can be used to study cosmic microwave background constraints on primordial magnetic fields. [ABSTRACT FROM AUTHOR]

HD 149277 is a rare SB2 system with a slowly rotating magnetic He-rich primary with P rot = 25.4 d. The CFHT/ESPaDOnS archive spectra revealed P orb = 11.5192 ± 0.0005 d indicating strong subsynchronous rotation of the primary component. Such a strong subsynchronous rotation was not detected in any other SB2 system with a magnetic chemically peculiar component. Our inspection of the spectra revealed the presence of resolved Zeeman split spectral lines allowing us to determine the variability of the mean magnetic field modulus over the rotation period. The maximum of the magnetic field modulus coincides roughly with the positive extremum of the longitudinal field, whereas the minimum of the modulus with the negative extremum of the longitudinal field. No evidence for a longitudinal magnetic field was seen in the circularly polarized spectra of the secondary component. Using archival data from the ASAS3 survey, we find in the frequency spectrum only one significant peak, corresponding to the period P phot = 25.390 ± 0.014 d. This value is in good agreements with the previous determination of the rotation period, P rot = 25.380 ± 0.007 d, which was based on longitudinal magnetic field measurements. [ABSTRACT FROM AUTHOR]

The coupling of equatorial and low‐latitude ionosphere has been an active area of research for many years. At low latitude, the occurrences of E and valley region irregularities during postsunset hours are obviously different from those around the magnetic equator. In this work, we statistically investigated the occurrences of postsunset ionospheric E, valley, and F region irregularities, the postsunset rise of F layer, and their correlations by using the Sanya (18.4°N, 109.6°E, dip latitude 12.8°N) very high frequency radar and ionosonde observations during equinoctial months of 2012–2016. A statistically significant correlation between the presence of valley region irregularities and that of equatorial spread F (ESF) was found over Sanya. For the days without ESF, valley region irregularity was rarely observed. The Doppler velocities of valley region irregularities were mainly upward which resemble those of simultaneous ESF irregularities. On the other hand, an occurrence peak of E region irregularities was detected around sunset. After sunset, E region irregularity echo was frequently disrupted. The disruption can appear on both ESF and non‐ESF days, when the amplitudes of F layer postsunset rise were significantly different. The effects of polarization electric field associated with ESF and of equatorial ionospheric background condition on the E and valley region irregularities over Sanya are discussed. Key Points: Occurrences of low‐latitude E, valley, and F region irregularities are statistically investigated with a large data setClose link between low‐latitude E, valley region irregularities, and ESF after sunsetMappings of electric fields from equatorial to low‐latitude ionosphere modify the evolution of E and valley region irregularities over Sanya [ABSTRACT FROM AUTHOR]

Due to its polar orbit Cluster spacecraft crossed plasmaspheric plumes out of the magnetic equatorial plane. We study the occurrence of broadband, narrowband, and rising tone emissions in the plume vicinity, below the local proton gyrofrequency. Based on a database of 935 Cluster plumes crossings, reduced to 189 unique plumes, we find that broadband activity is the most common case. We confirm result from a previous study showing that plume vicinity is not a preferred place for observing narrowband emissions. Rising tones are the less frequently observed of these three kinds of emissions. Nevertheless, ElectroMagnetic Ion Cyclotron (EMIC) rising tone occurrence rate is high compared to the narrowband one: Tones are seen in six of 30 plume events (20%) when narrowband emissions are observed. Rising tones are observed at absolute magnetic latitudes larger than 17° and up to 35° . We detail the 16 August 2005 plume crossing when a rising tone is observed. Results of a ray tracing analysis agree with a tone triggering process taking place above 15° of magnetic latitude. Key Points: Coherent rising tones are found in 20% (6/30) of the plume (and vicinity) events with EMIC emissionsEMIC rising tones are observed at magnetic latitudes larger than 17 degrees and up to 35 degreesEmissions below H+ gyrofrequency in the vicinity of plasmaspheric plumes are mainly broadband [ABSTRACT FROM AUTHOR]

Radiation belt behavior is often analyzed in terms of adiabatic invariants, of which the third roughly characterizes the radial distance of particle drift shells. The outermost, or last closed drift shell, can be an important boundary for numerical modeling, especially for drift‐averaged treatments such as three‐dimensional diffusion codes. Here we discuss calculation of the last closed drift shell, using the widely used International Radiation Belt Environment Modeling (IRBEM) Library, the LanlGeoMag code, and a guiding center code named AFRL‐Shell, in conjunction with a variety of current magnetic field models. We present results for the four events in 2013, comprising the radiation belt challenge organized by the Quantitative Assessment of Radiation Belt Modeling focus group of the Geospace Environment Modeling (GEM) program. Key Points: Several codes to calculate L* in realistic magnetic field models are presentedMethods for finding last closed drift shells with these codes are discussedResults for four GEM radiation belt challenge events, using a variety of magnetic field models, are compared [ABSTRACT FROM AUTHOR]

Understanding the effects of coronal mass ejections (CMEs) requires knowing if and when they will impact and their properties upon impact. Of particular importance is the strength of a CME's southward magnetic field component (Bz). Kay et al. (2013, https://doi:10.1088/0004-637X/775/1/5, 2015, https://doi:10.1088/948 0004-637X/805/2/168) have shown that the simplified analytic model Forecasting a CME's Altered Trajectory (ForeCAT) can reproduce the deflection and rotation of CMEs. Kay, Gopalswamy, Reinard, and Opher (2017, https://doi.org/10.3847/1538-4357/835/2/117) introduced ForeCAT In situ Data Observer, which uses ForeCAT results to simulate magnetic field profiles. ForeCAT In situ Data Observer reproduces the in situ observations on roughly hourly time scales, suggesting that these models could be extremely useful for predictions of Bz. However, as with all models, both models are sensitive to their input parameters, which may not be precisely known for predictions. We explore this sensitivity using ensembles having small changes in the initial latitude, longitude, and orientation of the erupting CME. We explore the effects of different background magnetic field models and find that the changes in deflection and rotation resulting from the uncertainty in the initial parameters tend to exceed the changes from different magnetic backgrounds. The range in the in situ profiles tends to scale with the range in the deflection and rotation. We also consider a simple arrival time model using ForeCAT results and find an average absolute error of only 3 hr. We show that an uncertainty in the CME position of 8.1° ± 6.9° leads to variations of 6 hr in the arrival time. This measure depends strongly on the location of impact within the CME with the arrival time changing less for impacts near the nose. Key Points: Ensembles show that a CME's coronal motion is sensitive to small changes in its initial positionThe results are more sensitive to different magnetograms than different magnetic field modelsCoronal ensembles can be used to generate the range of in situ magnetic field and arrival times [ABSTRACT FROM AUTHOR]

This paper presents storm time total electron content (TEC) modeling results based on artificial neural networks, for both low‐latitude and midlatitude African regions. The developed storm time TEC models were based on Global Positioning System (GPS) observations from GPS receiver stations selected in low latitude, Northern and Southern hemisphere midlatitude regions of the African sector. GPS data selection was based on a storm criterion of Dst≤ −50 nT and storm data sets used to develop the models were within the periods 2001–2015, 2000–2015, and 1998–2015, for African low latitude, Northern and Southern Hemisphere midlatitude regions, respectively. For the first time in storm time TEC modeling, the meridional wind velocity was introduced as an additional input to the well‐known TEC modeling inputs (diurnal variation, seasonal variation, solar activity, and geomagnetic activity representations) to take into account the effect of neutral winds in moving ionization within the ionosphere along the magnetic field lines. Results showed that the use of meridional wind as an additional input leads to overall percentage improvements of about 5%, 10%, and 5% for the low‐latitude, Northern and Southern Hemisphere midlatitude regions, respectively. High‐latitude storm‐induced winds and the interhemispheric blows of the meridional winds from summer to winter hemisphere may be associated with these improvements. Key Points: Evaluation of the performance of artificial neural networks in estimating storm time TEC over African low‐latitude and midlatitude regionsInvestigation of the role of meridional winds in storm time TEC modeling.Inclusion of meridional wind leads to overall percentage improvements of about 5%, 10%, and 5%, for the low‐latitude, Northern and Southern Hemisphere midlatitude regions, respectively [ABSTRACT FROM AUTHOR]

An electromagnetic particle‐in‐cell code is used to investigate self‐consistent evolution of the fast magnetosonic mode in a one‐dimensional configuration along the radial direction in a dipole background magnetic field. A previous observation of this wave mode is used to select the simulation parameters. A partial shell velocity distribution of energetic protons with a moderate pitch angle anisotropy is used to excite the waves self‐consistently. Consistent with local linear theory analysis, wave growth occurs only at exact harmonics of the local proton cyclotron frequency, Ωp. However, radial propagation quickly removes the waves from the region where they can grow, leading to a time scale of wave amplification much longer than that predicted by linear theory. In addition, radial propagation from multiple wave sources makes the frequency spectrum measured at a single point much broader. The warm background plasma plays an important role in two ways. First, it increases the phase speed of the fast magnetosonic mode; and second, it causes the breakup of the extraordinary mode dispersion relation in the vicinity of the harmonics, where the broken dispersion curves are connected with multiple ion Bernstein modes. In this case, the waves propagating radially are absorbed at locations where their frequency reaches integer multiples of Ωp and background protons experience perpendicular heating at those locations. Key Points: An electromagnetic particle‐in‐cell code is developed for dipole geometryThis code is used to investigate self‐consistent evolution of fast magnetosonic waves in the radial directionThe warm plasma effect on wave propagation is examined [ABSTRACT FROM AUTHOR]

The Grad‐Shafranov (GS) reconstruction may recover the steady two‐dimensional magnetohydrodynamic equilibrium structure from single spacecraft data. In this study we report first results on magnetopause structure from a newly developed GS solver that includes the effects of temperature anisotropy and field‐aligned flow. Double‐polytropic laws are used as energy closure to describe various thermodynamic states for anisotropic plasmas including double‐adiabatic and isothermal conditions as special cases. The new GS solver is benchmarked and applied to a Time History of Events and Macroscale Interactions during Substorms magnetopause crossing event with field‐aligned flow and p⊥ > p∥, where p⊥ and p∥ are the pressure components perpendicular and parallel to the local magnetic field, respectively. The recovered magnetic field maps for various thermodynamic conditions show qualitatively similar features with magnetic islands imbedded within the magnetopause current. The mirror‐type anisotropy with p⊥ > p∥ may lead to relatively inflated magnetic islands as compared to the isotropic case, consistent with earlier theoretical prediction. Plain Language Summary: The magnetopause separates Earth's magnetosphere from the solar wind. Through in situ measurements of plasma and magnetic field by single spacecraft traversing the magnetopause along with the plasma magnetohydrodynamic theory, it is possible to reconstruct its two‐dimensional internal structures via the so‐called Grad‐Shafranov (GS) reconstruction method. Past studies based on GS solver have revealed that the magnetopause is usually imbedded with single or multiple magnetic islands, a result of magnetic reconnection between the solar wind and Earth's magnetic fields. One important physics not considered in previous studies is the effects of temperature or pressure anisotropy that is an intrinsic characteristics of space plasmas due to the lack of sufficient collisions. Based on newly developed GS reconstruction method, the effects of temperature anisotropy and thermodynamic conditions on magnetopause structures are first revealed by a Time History of Events and Macroscale Interactions during Substorms spacecraft event. Our results confirm for the first time with the theoretical prediction that magnetic reconnection with relatively inflated magnetic islands occurs as a result of temperature anisotropy. Key Points: First results on two‐dimensional reconstruction of Earth's magnetopause with temperature anisotropyThe major features of magnetic field and plasma distributions are retained for various thermodynamic conditionsThe result that temperature anisotropy may lead to inflated magnetic island is consistent with theoretical prediction [ABSTRACT FROM AUTHOR]

Self-diffusion in a two-dimensional simple fluid is investigated by both analytical and numerical means. We investigate the anomalous aspects of self-diffusion in two-dimensional fluids with regards to the mean square displacement, the time-dependent diffusion coefficient, and the velocity autocorrelation function (VACF) using a consistency equation relating these quantities. We numerically confirm the consistency equation by extensive molecular dynamics simulations for finite systems, corroborate earlier results indicating that the kinematic viscosity approaches a finite, non-vanishing value in the thermodynamic limit, and establish the finite size behavior of the diffusion coefficient. We obtain the exact solution of the consistency equation in the thermodynamic limit and use this solution to determine the large time asymptotics of the mean square displacement, the diffusion coefficient, and the VACF. An asymptotic decay law of the VACF resembles the previously known self-consistent form,1/(t√ln t) , however with a rescaled time. [ABSTRACT FROM AUTHOR]

The M dwarf GJ 436 hosts a transiting warm Neptune known to experience atmospheric escape. Previous observations revealed the presence of a giant hydrogen exosphere transiting the star for more than 5 h, and absorbing up to 56% of the flux in the blue wing of the stellar Lyman-α line of neutral hydrogen (H i Lyα). The unexpected size of this comet-like exosphere prevented observing the full transit of its tail. In this Letter, we present new Lyα observations of GJ 436 obtained with the Space Telescope Imaging Spectrograph (STIS) instrument onboard the Hubble Space Telescope. The stability of the Lyα line over six years allowed us to combine these new observations with archival data sets, substantially expanding the coverage of the exospheric transit. Hydrogen atoms in the tail of the exospheric cloud keep occulting the star for 10-25 h after the transit of the planet, remarkably confirming a previous prediction based on 3D numerical simulations with the EVaporating Exoplanet code (EVE). This result strengthens the interpretation that the exosphere of GJ 436b is shaped by both radiative braking and charge exchanges with the stellar wind. We further report flux decreases of 15 ± 2% and 47 ± 10% in the red wing of the Lyα line and in the line of ionised silicon (Si iii). Despite some temporal variability possibly linked with stellar activity, these two signals occur during the exospheric transit and could be of planetary origin. Follow-up observations will be required to assess the possibility that the redshifted Lyα and Si iii absorption signatures arise from interactions between the exospheric flow and the magnetic field of the star. [ABSTRACT FROM AUTHOR]

Context. Stellar dynamos are affected by boundary conditions imposed by stellar coronae. Under some approximations, it is possible to find analytical solutions. Interior dynamo models often consider a current-free corona without taking into account the constraints imposed by the presence of currents in the corona. Aims. We aim to analytically evaluate the effect of coronal currents and of an outer boundary condition on the efficiency of an α2 dynamo. We intend to estimate the change in geometry and dynamo excitation numbers with respect to the current-free case. Methods. We analytically solved the turbulent dynamo induction equation for a homogeneous, non-mirror symmetric turbulence in a spherical domain surrounded by a linear force-free corona with the mean magnetic field B satisfying ∇ × B = βB. Results. The dynamo number is a decreasing function of β. Moreover, if the current is parallel to the field (β > 0), the dynamo number is smaller than in the force-free case. In contrast, for (β < 0), the dynamo number is greater than in the force-free case. Conclusions. Currents in the corona need to be taken into account because they affect the condition for excitation of a dynamo. [ABSTRACT FROM AUTHOR]

Context. The young, rapidly rotating Bp star HR5624 (HD 133880) shows an unusually strong non-sinusoidal variability of its longitudinal magnetic field. This behaviour was previously interpreted as the signature of an exceptionally strong, quadrupole-dominated surface magnetic field geometry. Aims. We studied the magnetic field structure and chemical abundance distributions of HR5624 with the aim to verify the unusual quadrupolar nature of its magnetic field and to investigate correlations between the field topology and chemical spots. Methods.We analysed high-resolution, time series Stokes parameter spectra of HR5624 with the help of a magnetic Doppler imaging inversion code based on detailed polarised radiative transfer modelling of the line profiles. Results. We refined the stellar parameters, revised the rotational period, and obtained new longitudinal magnetic field measurements. Our magnetic Doppler inversions reveal that the field structure of HR5624 is considerably simpler and the field strength is much lower than proposed by previous studies.We find a maximum local field strength of 12 kG and a mean field strength of 4 kG, which is about a factor of three weaker than predicted by quadrupolar field models. Our model implies that overall large-scale field topology of HR5624 is better described as a distorted, asymmetric dipole rather than an axisymmetric quadrupole. The chemical abundance maps of Mg, Si, Ti, Cr, Fe, and Nd obtained in our study are characterised by large-scale, high-contrast abundance patterns. These structures correlate weakly with the magnetic field geometry and, in particular, show no distinct element concentrations in the horizontal field regions predicted by theoretical atomic diffusion calculations. Conclusions. We conclude that the surface magnetic field topology of HR5624 is not as unusual as previously proposed. Considering these results together with other recent magnetic mapping analyses of early-type stars suggests that predominantly quadrupolar magnetic field topologies, invoked to be present in a significant number of stars, probably do not exist in real stars. This finding agrees with an outcome of the MHD simulations of fossil field evolution in stably stratified stellar interiors. [ABSTRACT FROM AUTHOR]

Large-scale magnetic fields at the surface of massive stars do not only influence the outer-most layers of the star, but also have consequences for the deep interior, only observationally accessible through asteroseismology. We performed a detailed characterization of the dipolar magnetic field at the surface of the B3.5V star HD43317, a SPB/β Cep hybrid pulsator, by studying the rotationally modulated magnetic field of archival and new Narval spectropolarimetry. Additionally, we employed a grid-based approach to compare the Zeeman signatures with model profiles. By studying the rotational modulation of the He lines in both the Narval and HARPS spectroscopy caused by co-rotating surface abundance inhomogeneities, we updated the rotation period to 0.897673 ±0.000004 d. The inclination angle between the rotation axis and the observer's line of sight remains ill-defined, because of the low level of variability in Stokes V and deformations in the intensity profiles by stellar pulsation modes. The obliquity angle between the rotation and magnetic axes is constrained to β ∈ [67; 90]°, and the strength of the dipolar magnetic field is of the order of 1 kG to 1.5 kG. This magnetic field at the stellar surface is su°ciently strong to warrant a uniformly rotating radiative envelope, causing less convective core overshooting, which should be visible in future forward seismic modeling. [ABSTRACT FROM AUTHOR]

Context. Magnetic fields play a fundamental role in star formation processes and the best method to evaluate their intensity is to measure the Zeeman effect of atomic and molecular lines. However, a direct measurement of the Zeeman spectral pattern from interstellar molecular species is challenging due to the high sensitivity and high spectral resolution required. So far, the Zeeman effect has been detected unambiguously in star forming regions for very few non-masing species, such as OH and CN. Aims. We decided to investigate the suitability of sulfur monoxide (SO), which is one of the most abundant species in star forming regions, for probing the intensity of magnetic fields via the Zeeman effect. Methods. We investigated the Zeeman effect for several rotational transitions of SO in the (sub-)mm spectral regions by using a frequency-modulated, computer-controlled spectrometer, and by applying a magnetic field parallel to the radiation propagation (i.e., perpendicular to the oscillating magnetic field of the radiation). To support the experimental determination of the g factors of SO, a systematic quantum-chemical investigation of these parameters for both SO and O2 has been carried out. Results. An effective experimental-computational strategy for providing accurate g factors as well as for identifying the rotational transitions showing the strongest Zeeman effect has been presented. Revised g factors have been obtained from a large number of SO rotational transitions between 86 and 389 GHz. In particular, the rotational transitions showing the largest Zeeman shifts are: N,J = 2, 2 ← 1, 1 (86.1 GHz), N,J = 4, 3 ← 3, 2 (159.0 GHz), N,J = 1, 1 ← 0, 1 (286.3 GHz), N,J = 2, 2 ← 1, 2 (309.5 GHz), and N,J = 2, 1 ← 1, 0 (329.4 GHz). Our investigation supports SO as a good candidate for probing magnetic fields in high-density star forming regions. [ABSTRACT FROM AUTHOR]

Context. Solar ultraviolet (UV) bursts are small-scale features that exhibit intermittent brightenings that are thought to be due to magnetic reconnection. They are observed abundantly in the chromosphere and transition region, in particular in active regions. Aims. We investigate in detail a UV burst related to a magnetic feature that is advected by the moat flow from a sunspot towards a pore. The moving feature is parasitic in that its magnetic polarity is opposite to that of the spot and the pore. This comparably simple photospheric magnetic field distribution allows for an unambiguous interpretation of the magnetic geometry leading to the onset of the observed UV burst. Methods. We used UV spectroscopic and slit-jaw observations from the Interface Region Imaging Spectrograph (IRIS) to identify and study chromospheric and transition region spectral signatures of said UV burst. To investigate the magnetic topology surrounding the UV burst, we used a two-hour-long time sequence of simultaneous line-of-sight magnetograms from the Helioseismic and Magnetic Imager (HMI) and performed data-driven 3D magnetic field extrapolations by means of a magnetofrictional relaxation technique. We can connect UV burst signatures to the overlying extreme UV (EUV) coronal loops observed by the Atmospheric Imaging Assembly (AIA). Results. The UV burst shows a variety of extremely broad line profiles indicating plasma flows in excess of ±200 km s-1 at times. The whole structure is divided into two spatially distinct zones of predominantly up- and downflows. The magnetic field extrapolations show a persistent fan-spine magnetic topology at the UV burst. The associated 3D magnetic null point exists at a height of about 500 km above the photosphere and evolves co-spatially with the observed UV burst. The EUV emission at the footpoints of coronal loops is correlated with the evolution of the underlying UV burst. Conclusions. The magnetic field around the null point is sheared by photospheric motions, triggering magnetic reconnection that ultimately powers the observed UV burst and energises the overlying coronal loops. The location of the null point suggests that the burst is triggered low in the solar chromosphere. [ABSTRACT FROM AUTHOR]

Context. The Kepler space mission has made it possible to measure the rotational splittings of mixed modes in red giants, thereby providing an unprecedented opportunity to probe the internal rotation of these stars. Aims. Asymmetries have been detected in the rotational multiplets of several red giants. This is unexpected since all the red giants whose rotation profiles have been measured thus far are found to rotate slowly, and low rotation, in principle, produces symmetrical multiplets. Our aim here is to explain these asymmetries and find a way of exploiting them to probe the internal rotation of red giants. Methods. We show that in the cases where asymmetrical multiplets were detected, near-degeneracy effects are expected to occur, because of the combined effects of rotation and mode mixing. Such effects have not been taken into account so far. By using both perturbative and non-perturbative approaches, we show that near-degeneracy effects produce multiplet asymmetries that are very similar to the observations. We then propose and validate a method based on the perturbative approach to probe the internal rotation of red giants using multiplet asymmetries. Results. We successfully apply our method to the asymmetrical l = 2 multiplets of the Kepler young red giant KIC 7341231 and obtain precise estimates of its mean rotation in the core and the envelope. The observed asymmetries are reproduced with a good statistical agreement, which confirms that near-degeneracy effects are very likely the cause of the detected multiplet asymmetries. Conclusions. We expect near-degeneracy effects to be important for l = 2 mixed modes all along the red giant branch (RGB). For l = 1 modes, these effects can be neglected only at the base of the RGB. They must therefore be taken into account when interpreting rotational splittings and as shown here, they can bring valuable information about the internal rotation of red giants. [ABSTRACT FROM AUTHOR]

The universe is permeated by magnetic fields, with strengths ranging from a femtogauss in the voids between the filaments of galaxy clusters to several teragauss in black holes and neutron stars. The standard model behind cosmological magnetic fields is the nonlinear amplification of seed fields via turbulent dynamo to the values observed. We have conceived experiments that aim to demonstrate and study the turbulent dynamo mechanism in the laboratory. Here, we describe the design of these experiments through simulation campaigns using FLASH, a highly capable radiation magnetohydrodynamics code that we have developed, and large-scale three-dimensional simulations on the Mira supercomputer at the Argonne National Laboratory. The simulation results indicate that the experimental platform may be capable of reaching a turbulent plasma state and determining the dynamo amplification. We validate and compare our numerical results with a small subset of experimental data using synthetic diagnostics. [ABSTRACT FROM AUTHOR]

We developed a numerical model of the interstellar dust distribution in the global heliosphere including the heliospheric interface, where the solar wind plasma interacts with the local interstellar plasma. The model is based on the plasma distributions obtained by the 3D kinetic-MHD model of the heliospheric interface developed by Izmodenov & Alexashov (2015). This paper explores how the dust particles with different initial charge-to-mass ratios (q∞/m) are filtered and deflected in the outer heliosheath. It is shown that the Lorentz force caused by the interstellar magnetic field leads to formation of specific features of the distribution of dust especially in the case of intermediate gyroradius (~several AU). We also study the characteristics of the dust flow at the entrance to the heliosphere. We show that more than 70% of particles with q∞/m ≤ 2 C/kg-1 penetrate to the heliosphere. At the nose part of the heliopause these dust particles are decelerated up to 15% and deflected from the interstellar wind direction by up to 35°. This deflection depends on polarity of the interstellar magnetic field. Distribution of particles with q∞/m > 0.5 C/kg-1 upstream of the heliopause is not uniform and even not axisymmetric due to the assumed inclination of the interstellar magnetic field with respect to the interstellar wind direction. [ABSTRACT FROM AUTHOR]

In the derivation of synchrotron radiation formulae, it has been assumed that the pitch angle of a charge remains constant during the radiation process. However, from the radiation reaction formula, while the component of the velocity vector perpendicular to the magnetic field reduces in magnitude due to radiative losses, the parallel component does not undergo any change during radiation. Therefore, there is a change in the ratio of the two components, implying a change in the pitch angle. We derive the exact formula for the change in energy of radiating electrons by taking into account the change of the pitch angle due to radiative losses. From this, we derive the characteristic decay time of synchrotron electrons over which they turn from highly relativistic into mildly relativistic ones. [ABSTRACT FROM AUTHOR]

The spallation neutron source at the Los Alamos Neutron Science Center Weapons Neutron Research facility was used to populate excited states in 186Re via (n,2nγ) reactions on an enriched 187Re target. Gamma rays were detected with the GErmanium Array for Neutron Induced Excitations spectrometer, a Compton-suppressed array of 18 HPGe detectors. Incident neutron energies were determined by the time-of-flight technique and used to obtain y-ray excitation functions for the purpose of identifying γ rays by reaction channel. Analysis of the singles γ-ray spectrum gated on the neutron energy range 10 ≤ En ≤ 25 MeV resulted in five transitions and one level added to the 186Re level scheme. The additions include the placement of three y rays at 266.7, 381.2, and 647.7 keV which have been identified as feeding the 2.0 x 105 yr, Jπ = (8+) isomer and yield an improved value of 148.2(5) keV for the isomer energy. These transitions may have astrophysical implications related to the use of the Re-Os cosmochronometer. [ABSTRACT FROM AUTHOR]

The paper is devoted to mathematical modeling of the nonlinear vacuum electrodynamics effect: the action of the strong magnetic field of a pulsar on the propagation of electromagnetic waves. It is shown that, due to the birefringence of the vacuum, for one normal wave, it takes more time to travel from a pulsar to a detector installed on astrophysical satellites than for the other normal wave. The delay of the pulse carried by the second normal wave relative to pulse carried by the first normal wave from the common point of origin to the satellite is calculated. [ABSTRACT FROM AUTHOR]

We have studied current-voltage (I-V) characteristics of α-Fe1.64Ga0.36O3, a typical canted ferromagnetic semiconductor. The sample showed a transformation of the I-V curves from linear to non-linear character with the increase of bias voltage. The I-V curves showed irreversible features with hysteresis loop and bi-stable electronic states for up and down modes of voltage sweep. We report positive magnetoresistance and magnetic field induced negative differential resistance as the first time observed phenomena in metal doped hematite system. The magnitudes of critical voltage at which I-V curve showed peak and corresponding peak current are affected by magnetic field cycling. The shift of the peak voltage with magnetic field showed a step-wise jump between two discrete voltage levels with least gap (ΔVP) 0.345(± 0.001) V. The magnetic spin dependent electronic charge transport in this new class of magnetic semiconductor opens a wide scope for tuning large electroresistance (~500-700%), magnetoresistance (70-135%) and charge-spin dependent conductivity under suitable control of electric and magnetic fields. The electric and magnetic field controlled charge-spin transport is interesting for applications of the magnetic materials in spintronics, e.g., magnetic sensor, memory devices and digital switching. [ABSTRACT FROM AUTHOR]

Observations of low-mass stars reveal a variety of magnetic field topologies ranging from large-scale, axial dipoles to more complex magnetic fields. At the same time, three-dimensional spherical simulations of convectively driven dynamos reproduce a similar diversity, which is commonly obtained either with Boussinesq models or with more realistic models based on the anelastic approximation, which take into account the variation of the density with depth throughout the convection zone. Nevertheless, a conclusion from different anelastic studies is that dipolar solutions seem more difficult to obtain as soon as substantial stratifications are considered. In this paper, we aim at clarifying this point by investigating in more detail the influence of the density stratification on dipolar dynamos. To that end, we rely on a systematic parameter study that allows us to clearly follow the evolution of the stability domain of the dipolar branch as the density stratification is increased. The impact of the density stratification both on the dynamo onset and the dipole collapse is discussed and compared to previous Boussinesq results. Furthermore, our study indicates that the loss of the dipolar branch does not ensue from a specific modification of the dynamo mechanisms related to the background stratification, but could instead result from a bias as our observations naturally favour a certain domain in the parameter space characterized by moderate values of the Ekman number, owing to current computational limitations. Moreover, we also show that the critical magnetic Reynolds number of the dipolar branch is scarcely modified by the increase of the density stratification, which provides an important insight into the global understanding of the impact of the density stratification on the stability domain of the dipolar dynamo branch. [ABSTRACT FROM AUTHOR]

We study the linear stability of weakly magnetized differentially rotating plasmas in both collisionless kinetic theory and Braginskii's theory of collisional, magnetized plasmas. We focus on the very weakly magnetized limit in which β ≳ ωc/Ω, where β is the ratio of thermal to magnetic energy and ωc/Ω is the ratio of the cyclotron frequency to rotation frequency. This regime is important for understanding how astrophysical magnetic fields originate and are amplified at high redshift. We show that the single instability of fluid theory – the magnetorotational instability mediated by magnetic tension – is replaced by two distinct instabilities, one associated with ions and one with electrons. Each of these has a different way of tapping into the free energy of differential rotation. The ion instability is driven by viscous transport of momentum across magnetic field lines due to a finite ion cyclotron frequency (gyroviscosity); the fastest growing modes have wavelengths significantly longer than magnetohydrodynamic (MHD) and Hall MHD predictions. The electron instability is a whistler mode driven unstable by the temperature anisotropy generated by differential rotation; the growth time can be orders of magnitude shorter than the rotation period. The electron instability is an example of a broader class of instabilities that tap into the free energy of differential rotation or shear via the temperature anisotropy they generate. We briefly discuss the application of our results to the stability of planar shear flows and show that such flows are linearly overstable in the presence of fluid gyroviscosity. We also briefly describe the implications of our results for magnetic field amplification in the virialized haloes of high-redshift galaxies. [ABSTRACT FROM AUTHOR]

Aims. The magnetic field in the chromosphere of the quiet sun is too weak to be diagnosed via the general Zeeman effect. To obtain the hidden magnetic field vector, a complete comprehension of the linear polarization produced by scattering and modified by magnetic field is needed. We report a systematic and quantitative investigation of the sensitivity of the fractional linear polarization of the magnesium triplet to a weak magnetic field in the chromosphere, which can be a guide for the diagnostics of a weak magnetic field in the solar chromosphere. Methods. We focus on the fractional linear polarization of the magnesium triplet induced by scattering. We use the quantum theory under the flat-spectrum approximation developed by Landi Degl'Innocenti for the investigation. A seven-level atomic model of magnesium is adopted, while we do not take the radiative transfer or partial frequency redistribution (PRD) into account. Results. Polarization is directly related to the anisotropy factor, and modified by the continuum, collision, and magnetic field as well as dichroism effect. In our calculation, the elastic collision rates found are not large enough to destroy the population imbalances of the lower levels of the b2 and b1 lines. This is the prerequisite for the lower level Hanle effect and dichroism effect. When considering the dichroism effect, the magnetic field can influence the polarization not only in the line cores but also in the line wings. However, the magnetic field cannot obviously influence the polarization degree in the line wings once the continuum becomes significant. The polarization of the triplet is sensitive to the magnetic field between 0.001 and 0.1 Gauss due to the lower level Hanle effect and between 1 and 10 Gauss due to the upper level Hanle effect. In the lower level Hanle effect dominated region, the Q/I amplitude of the b4 line increases with magnetic field strength because of the coupling among atomic alignments of the involved levels as described in the statistical equilibrium equations, while the amplitudes of the b2 and b1 lines decrease. In the upper level Hanle effect dominated region, the most sensitive line is the b4. Conclusions. The polarized lower levels and the contribution of dichroism have to be considered to fit the observed profiles of Mg I b triplet in the line cores. Therefore the b2 and b1 lines can be potential candidates for probing sub-Gauss range magnetic field, because their Q/I amplitudes are sensitive to the magnetic field strength between 0.001 and 0.1 Gauss due to the lower level Hanle effect. The b4 line is suitable for diagnostics of magnetic field between 1 Gauss and 10 Gauss. [ABSTRACT FROM AUTHOR]

We report results from a search for stable particles with charge ≳10-5e in bulk matter using levitated dielectric microspheres in high vacuum. No evidence for such particles was found in a total sample of 1.4 ng, providing an upper limit on the abundance per nucleon of 2.5 × 10-14 at the 95% confidence level for the material tested. These results provide the first direct search for single particles with charge ≲0.1 e bound in macroscopic quantities of matter and demonstrate the ability to perform sensitive force measurements using optically levitated microspheres in vacuum. [ABSTRACT FROM AUTHOR]

Magnetic fields are proposed to have played a critical role in some of the most enigmat processes of planetary formation by mediating the rapid accretion of disk material onto the central star and the formation of the first solids. However, there have been no experimental constraints on the intensity of these fields. Here we show that dusty olivine-bearing chondrules from the Semarkona meteorite were magnetized in a nebular field of 54 21 microteslas. This intensity supports chondrule formation by nebular shocks or planetesimal collisions rather than by electric currents, the x-wind, or other mechanisms near the Sun. This implies that background magnetic fields in the terrestri planet-forming region were likely 5 to 54 microteslas, which is sufficient to account for measured rates of mass and angular momentum transport in protoplanetary disks.

The astrophysical parameters of seven OH maser condensations are estimated based on magnetic fields obtained from polarization observations carried out on the Nan cay Radio Telescope (France) in the 1665 and 1667 MHz lines in four Stokes parameters. Regions in the studied sources containing the observed clusters of maser condensations, as well as clusters of Class I and II methanol masers, have been identified. The associations of the masers are real; i.e., the magnetic field in the clusters can also extend to groups of methanol masers. The linear dimensions of these associations have been found. The ratio of the mass to the magnetic flux, ratio of the thermal to the magnetic pressure, and virial relationships between energies (kinetic, magnetic, and gravitational) in the regions containing the OH andmethanol masers have been obtained. In sources whose magnetic fields have been determined fairly reliably, the ratio of the mass to the magnetic flux exceeds a critical value, and the energies of chaotic motions and of the magnetic field are considerably smaller than the gravitational binding energy. On the other hand, in all cases, the ratio of the thermal to the magnetic pressure is <1, suggesting that the clouds may be in amagnetically dominated regime. This inconsistency is related to probable uncertainties in the the magnetic field values and the estimated distances to the sources, which may lead to overestimation of the sizes of the regions studied. [ABSTRACT FROM AUTHOR]

Recent observations of astrophysical magnetic fields have shown the presence of fluctuations being wavelike (propagating in the plasma frame) and those described as being structure-like (advected by the plasma bulk velocity). Typically with single-spacecraft missions it is impossible to differentiate between these two fluctuations, due to the inherent spatio-temporal ambiguity associated with a single point measurement. However missions such as Cluster which contain multiple spacecraft have allowed for temporal and spatial changes to be resolved, using techniques such as k filtering. While this technique does not assume Taylor's hypothesis it requires both weak stationarity of the time series and that the fluctuations can be described by a superposition of plane waves with random phases. In this paper we test whether the method can cope with a synthetic signal which is composed of a combination of non-random-phase coherent structures with a mean radius d and a mean separation λ, as well as plane waves with random phase. [ABSTRACT FROM AUTHOR]

We study the impact of primordial magnetic fields on the H I absorption from the epoch of reionization. The presence of these fields results in two distinct effects: (1) the heating of the halos from the decay of the magnetic fields owing to ambipolar diffusion, and (2) an increase in the number of halos owing to additional matter fluctuations induced by magnetic fields. We analyze both of these effects and show that the latter is potentially observable because the number of halos along of line of sight can increase by many orders of magnitude. While this effect is not strongly dependent on the magnetic field strength in the range 0.3-0.6 nG, it is extremely sensitive to the magnetic field power spectral index for the near scale-free models. Therefore, the detection of such absorption features could be a sensitive probe of the primordial magnetic field and its power spectrum. We discuss the detectability of these features with the ongoing and future radio interferometers. In particular, we show that LOFAR might be able to detect these absorption features at z ≃ 10 in less than 10 hr of integration if the flux of the background source is 400 mJy. [ABSTRACT FROM AUTHOR]

The nature of the mechanisms apparently driving X-rays from intermediate mass stars lacking strong convection zones or massive winds remains poorly understood, and the possible role of hidden, lower mass close companions is still unclear. A 20 ks Chandra HRC-I observation of HR 4796A, an 8 Myr old main sequence A0 star devoid of close stellar companions, has been used to search for a signature or remnant of magnetic activity from the Herbig Ae phase. X-rays were not detected and the X-ray luminosity upper limit was LX ⩽ 1.3 × 1027 erg s–1. The result is discussed in the context of various scenarios for generating magnetic activity, including rotational shear and subsurface convection. A dynamo driven by natal differential rotation is unlikely to produce observable X rays, chiefly because of the difficulty in getting the dissipated energy up to the surface of the star. A subsurface convection layer produced by the ionization of helium could host a dynamo that should be effective throughout the main sequence but can only produce X-ray luminosities of the order 1025 erg s–1. This luminosity lies only moderately below the current detection limit for Vega. Our study supports the idea that X-ray production in Herbig Ae/Be stars is linked largely to the accretion process rather than the properties of the underlying star, and that early A stars generally decline in X-ray luminosity at least 100,000 fold in only a few million years. [ABSTRACT FROM AUTHOR]