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Magnetic fields are thought to influence the formation and evolution of circumstellar envelopes around evolved stars. Thermal dust polarization from aligned grains is a promising tool for probing magnetic fields and dust properties in these environments; however, a quantitative study on the dependence of thermal dust polarization on the physical properties of dust and magnetic fields for these circumstellar environments is still lacking. In this paper, we first perform the numerical modelling of thermal dust polarization in the IK Tau envelope using the magnetically enhanced radiative torque (MRAT) alignment mechanism implemented in our updated POLARIS code, accounting for the effect of grain drift relative to the gas. Despite experiencing grain drift and high gas density |$n_{\rm gas} \gt 10^6\, \rm cm^{-3}$|⁠ , the minimum grain size required for efficient MRAT alignment of silicate grains is |$\sim 0.007\!-\!0.05\, \rm \mu m$| due to strong stellar radiation fields. Ordinary paramagnetic grains can achieve perfect alignment by MRAT in the inner envelope of |$r \lt 500\, \rm au$| due to stronger magnetic fields of |$B\sim 10$|  mG–1G, producing the polarization degree of |$\sim 10~{{\rm per\ cent}}$|⁠. The polarization degree can be enhanced to |$\sim 20\!-\!40~{{\rm per\ cent}}$| for superparamagnetic grains with embedded iron inclusions. The magnetic field geometry affects the resulting polarization degree due to the projection effect. We investigate the effect of rotational disruption by RATs (RAT-D) and find that the RAT-D effect decreases the dust polarization degree due to the decrease in the maximum grain size. Our modelling results motivate further observational studies at far-infrared/sub-millimeter to constrain the properties of magnetic fields and dust in evolved star's envelopes. [ABSTRACT FROM AUTHOR]

The relationship between B-field orientation and density structure in molecular clouds is often assessed using the histogram of relative orientations (HRO). We perform a plane-of-the-sky geometrical analysis of projected B-fields, by interpreting HROs in dense, spheroidal, pre-stellar, and protostellar cores. We use James Clerk Maxwell Telescope POL-2 850 |$\mu$| m polarization maps and Herschel column density maps to study dense cores in the Ophiuchus molecular cloud complex. We construct two-dimensional core models, assuming Plummer column density profiles and modelling both linear and hourglass B-fields. We find that high-aspect ratio ellipsoidal cores produce strong HRO signals, as measured using the shape parameter |$\xi$|⁠. Cores with linear fields oriented |$<\!\! 45 ^{\circ }$| from their minor axis produce constant HROs with |$-1 \lt \xi \lt 0$|⁠ , indicating that fields are preferentially parallel to column density gradients. Fields parallel to the core minor axis produce the most negative value of |$\xi$|⁠. For low-aspect ratio cores, |$\xi \approx 0$| for linear fields. Hourglass fields produce a minimum in |$\xi$| at intermediate densities in all cases, converging to the minor-axis-parallel linear field value at high and low column densities. We create HROs for six dense cores in Ophiuchus. |$\rho$| Oph A and IRAS 16293 have high aspect ratios and preferentially negative HROs, consistent with moderately strong field behaviour. |$\rho$| Oph C, L1689A, and L1689B have low aspect ratios, and |$\xi \approx 0$|⁠. |$\rho$| Oph B is too complex to be modelled using a simple spheroidal field geometry. We see no signature of hourglass fields, agreeing with previous findings that dense cores generally exhibit linear fields on these size scales. [ABSTRACT FROM AUTHOR]

In this paper, we provide a detailed investigation of the energization processes in two-dimensional, two and a half-dimensional, and three-dimensional collapsing magnetic trap models. Using kinematic magnetohydrodynamic models of collapsing magnetic traps, we examine the importance of Fermi acceleration in comparison with betatron acceleration in these models. We extend previous work by investigating particle orbits in two-dimensional models without and with a guide field component and from full three-dimensional models. We compare the outcomes for the different models and how they depend on the chosen initial conditions. While in the literature betatron acceleration has been emphasized as the major mechanism for particle energization in collapsing magnetic traps, we find that Fermi acceleration can play a significant role as well for particle orbits with suitable initial conditions. [ABSTRACT FROM AUTHOR]

VY Scl binaries are a sub-class of cataclysmic variable (CV) which show extended low states, but do not show outbursts which are seen in other classes of CV. To better determine how often these systems spend in low states and to resolve the state transitions we have analysed Zwicky Transient Facility (ZTF) data on eight systems and Transiting Exoplanet Survey Satellite (TESS) data on six systems. Half of the sample spent most of the time in a high state; three show a broad range and one spends roughly half the time transitioning between high and low states. Using the ZTF data, we explore the colour variation as a function of brightness. In KR Aur, we identify a series of repeating outburst events whose brightness appears to increase over time. Using TESS data, we searched for periods other than the orbital. In LN UMa, we find evidence for a peak whose period varies between 3 and 6 d. We outline the current models which aim to explain the observed properties of VY Scl systems which includes disc irradiation and a white dwarf having a significant magnetic field. [ABSTRACT FROM AUTHOR]

This study investigates the extinction properties, dust distribution, and magnetic field characteristics of the CB26 cloud. Extinction mapping, derived from near-infrared photometry, reveals a good correlation with the dust distribution, as traced by Herschel 1 SPIRE 500 |$\mu\mathrm{ m}$| data, indicating a close link between dust and extinction. The derived column density estimates align with previous Herschel studies. Our optical polarization observations of CB26 reveal a well-aligned magnetic field in the cloud's low-density envelope, closely following the Galactic plane. In contrast, our reanalysis of archival submillimetre polarization data of CB26 suggests a distinct magnetic field orientation within the cloud core. The offset angle between the core and Galactic magnetic fields is approximately 90 |$^\circ$|⁠ , suggesting a decoupling of the core's magnetic field from the large-scale Galactic field. A relationship is found between polarization rate and distance for 24 field stars in CB26, suggesting that most of the polarization is contributed by dust within 600 pc along the line of sight. [ABSTRACT FROM AUTHOR]

We find that the observed pressure-mode rotational splittings of slowly/moderately rotating |$\delta$| Scuti stars and |$\beta$| Cephei stars mostly have a positive asymmetry. That is, the left frequency spacing is larger than the right spacing in the dipole mode splitting triplets and the |$l=2$| mode splitting multiplets (considering |$m=1, 0, -1$| modes only). This is in agreement with the second-order perturbative effect of the rotational non-spherical distortion: both the prograde and retrograde modes have their frequencies shifted towards lower values relative to the |$m=0$| modes. We thus study the rotational perturbation both in the first and second order, as well as the near-degeneracy mode coupling effect in MESA models representing |$\delta$| Scuti stars. For faster rotators, the near-degeneracy mode coupling between the nearest radial and quadrupole modes can significantly shift the |$m=0$| modes, reduce the splitting asymmetry, and even change its sign. We find the theoretical splitting asymmetry from the second-order non-spherical distortion can explain the observed asymmetry quantitatively. To facilitate future detections, we predict correlations between splitting asymmetry, splitting amplitude, and pulsation frequency. We also discuss additional factors that can influence splitting asymmetry, including embedded magnetic fields, resonant mode coupling, and binarity. [ABSTRACT FROM AUTHOR]

Measurement of a jet geometry transition region is an important instrument of assessing the jet ambient medium properties, plasma bulk motion acceleration, parameters of a black hole, and location of a jet-launching radius. In this work, we explore the possibility of a presence of a core shift break, associated with the geometry and jet physical properties transition. We obtain the relations on the core shift offset jump due to a change in a core shift exponent. The condition of a proper frame magnetic field continuity and the core shift break can be used as an instrument to refine the magnetic field estimates upstream the break. This method is applied to the jet in NGC 315. We also argue that a local change in the plasma properties in the jet, for example due to the occurrence of a standing shock or a magnetic field reconnection, will also affect the dependence of the core shift on frequency. The properties of such a jump will be different than in the previous case. We propose to use the multifrequency core shift measurements to increase the number of sources with a detected jet shape break and to boost the accuracy of assessing the properties of a jet geometry transition region. [ABSTRACT FROM AUTHOR]

We report the results of a comprehensive study of the spectroscopic binary (SB2) system HD 34736 hosting two chemically peculiar (CP) late B-type stars. Using new and archival observational data, we characterize the system and its components, including their rotation and magnetic fields. Fitting of the radial velocities yields |$P_\mathrm{orb}=83\rm{.\!\!^{ {\rm{d}}}}219(3)$| and |$e=0.8103(3)$|⁠. The primary component is a CP He-wk star with |$T_{{\rm eff}A}$| |$\,\,=13000\pm 500$|  K and |$\upsilon _{\rm e}\sin i\,$| |$\,\,=75\pm 3$|  km s |$^{-1}\,$|⁠ , while the secondary exhibits variability of Mg and Si lines, and has |$T_{{\rm eff}B}$| |$\,\,=11500\pm 1000$|  K and |$\upsilon _{\rm e}\sin i\,$| |$\,\,=110$| –180 km s |$^{-1}\,$|⁠. Transiting Exoplanet Survey Satellite and Kilodegree Extremely Little Telescope photometry reveal clear variability of the primary component with a rotational period |$P_{\mathrm{rot}A}=1\rm{.\!\!^{ {\rm{d}}}}279\, 988\, 5(11)$|⁠ , which is lengthening at a rate of 1.26(6) s yr |$^{-1}$|⁠. For the secondary, |$P_{\mathrm{rot}B}=0\rm{.\!\!^{ {\rm{d}}}}522\, 693\, 8(5)$|⁠ , reducing at a rate of |$-0.14(3)$| s yr |$^{-1}$|⁠. The longitudinal component |$\langle B_{\rm z}\rangle$| of the primary's strongly asymmetric global magnetic field varies from |$-6$| to +5 kG. Weak spectropolarimetric evidence of a magnetic field is found for the secondary star. The observed X-ray and radio emission of HD 34736 may equally be linked to a suspected T Tau-like companion or magnetospheric emission from the principal components. Given the presence of a possible third magnetically active body, one can propose that the magnetic characteristics of the protostellar environment may be connected to the formation of such systems. [ABSTRACT FROM AUTHOR]

We present the first model aimed at understanding how the Meissner effect in a young neutron star affects its macroscopic magnetic field. In this model, field expulsion occurs on a dynamical time-scale, and is realized through two processes that occur at the onset of superconductivity: fluid motions causing the dragging of field lines, followed by magnetic reconnection. Focusing on magnetic fields weaker than the superconducting critical field, we show that complete Meissner expulsion is but one of four possible generic scenarios for the magnetic-field geometry, and can never expel magnetic flux from the centre of the star. Reconnection causes the release of up to |$\sim 5\times 10^{46}\, \mathrm{erg}$| of energy at the onset of superconductivity, and is only possible for certain favourable early-phase dynamics and for pre-condensation fields |$10^{12}\, \mathrm{G}\lesssim B\lesssim 5\times 10^{14}\, \mathrm{G}$|⁠. Fields weaker or stronger than this are predicted to thread the whole star. [ABSTRACT FROM AUTHOR]

We introduce the construction of polarized intensity cubes |$\mathbb{P}$| (RA, Dec, |$\Phi$|⁠) and their visualization as movies, as a powerful technique for interpreting Faraday structure. |$\mathbb{P}$| is constructed from maps of peak polarized intensity P(RA, Dec) with their corresponding Faraday depth maps |$\Phi$| (RA, Dec). We illustrate the extensive scientific potential of such visualizations with a variety of science use cases from ASKAP and MeerKAT, presenting models that are consistent with the data but not necessarily unique. We demonstrate how one can, in principle, distinguish between cube structures that originate from unrelated foreground screens from those due to magnetized plasmas local to the emitting source. Other science use cases illustrate how variations in the local |$n_{\rm e}$| B , and line-of-sight distance to the synchrotron emitting regions can be distinguished using Faraday rotation. We show, for the first time, how the line-of-sight orientation of active galactic nuclei (AGN) jets can be determined. We also examine the case of M87 to show how internal jet magnetic field configurations can be identified, and extend earlier results. We recommend using this technique to re-evaluate all previous analyses of polarized sources that are well-resolved both spatially and in Faraday depth. Recognizing the subjective nature of interpretations at this early stage, we also highlight the need and utility for further scientific and technical developments. [ABSTRACT FROM AUTHOR]

Studying the Magellanic System can help us understand the role that magnetic fields play in the evolution and structure of interacting low-mass galaxies. We have measured the Faraday rotation measure (RM) of 185 extra-galactic radio sources behind the Large Magellanic Cloud (LMC) to determine the structure of the magnetic field of the LMC. These observations were conducted with the CSIRO Australia Telescope Compact Array (ATCA) with a frequency range of 1.6–3.0 GHz. Our observations double the density of the grid of RMs for the LMC. With these new RM observations in conjunction with previous measurements, we find that the |RM| on the east side of the LMC is greater than the west. Using dispersion measure information from known LMC pulsars, we find that the magnitude of the coherent line-of-sight (LOS) magnetic field, |$B_{||}$|⁠ , is weakest to the north-west of the LMC, and the random LOS magnetic field is stronger in the east side. We find that |$B_{||}$| traces neutral hydrogen arm-like structures within the LMC. Overall, the LMC does not appear to have a magnetic field like that of the Small Magellanic Cloud and Magellanic Bridge, indicating that the LMC is not directly part of the 'pan-Magellanic' magnetic field. [ABSTRACT FROM AUTHOR]

We present 850 |$\mu$| m polarized observations of the molecular cloud G34.26 + 0.15 taken using the POL-2 polarimeter mounted on the James Clerk Maxwell Telescope (JCMT). G34.26 + 0.15 is a hub–filament system with ongoing high-mass star formation, containing multiple H  ii regions. We extend the histogram of relative orientations technique with an alternative application that considers the alignment of the magnetic field to the filaments and a H  ii region boundary, denoted as the filament alignment factor (⁠|$\xi _{F}$|⁠) and the ellipse alignment factor (⁠|$\xi _{E}$|⁠), respectively. Using these metrics, we find that, although in general the magnetic field aligns parallel to the filamentary structure within the system in the north-west, the magnetic field structure of G34.26 + 0.15 has been radically reshaped by the expansion of an evolved H  ii region in the south-east, which itself may have triggered further high-mass star formation in the cloud. Thus, we suggest high-mass star formation is occurring through both mass accretion as per the hub–filament model from one side and compression of gas under stellar feedback from the other. We also use HARP (Heterodyne Array Receiver Program) observations of C |$^{18}$| O from the CHIMPS survey to estimate the magnetic field strength across the cloud, finding strengths of |$\sim$| 0.5–1.4 mG. [ABSTRACT FROM AUTHOR]

The Early Data Release (EDR) of the Dark Energy Spectroscopic Instrument (DESI) comprises spectroscopy obtained from 2020 December 14 to 2021 June 10. White dwarfs were targeted by DESI both as calibration sources and as science targets and were selected based on Gaia photometry and astrometry. Here, we present the DESI EDR white dwarf catalogue, which includes 2706 spectroscopically confirmed white dwarfs of which approximately 60 per cent have been spectroscopically observed for the first time, as well as 66 white dwarf binary systems. We provide spectral classifications for all white dwarfs, and discuss their distribution within the Gaia Hertzsprung–Russell diagram. We provide atmospheric parameters derived from spectroscopic and photometric fits for white dwarfs with pure hydrogen or helium photospheres, a mixture of those two, and white dwarfs displaying carbon features in their spectra. We also discuss the less abundant systems in the sample, such as those with magnetic fields, and cataclysmic variables. The DESI EDR white dwarf sample is significantly less biased than the sample observed by the Sloan Digital Sky Survey, which is skewed to bluer and therefore hotter white dwarfs, making DESI more complete and suitable for performing statistical studies of white dwarfs. [ABSTRACT FROM AUTHOR]

In this paper, we studied the X-ray polarization of the jet in the Vela Pulsar Wind Nebula. After the background subtraction, we found a high degree of polarization in the helical jet region, close to the upper limit allowed by the synchrotron radiation mechanism. This result indicates the magnetic field is highly ordered, even though the jet's morphology is curved and varies rapidly, which suggests that the magnetic collimation process for the jet does not introduce significant turbulence. The polarization angle is perpendicular to the symmetry axis of the nebula, consistent with the results from the magnetohydrodynamic numerical simulations. This finding sheds light on the underlying mechanisms related to the dynamics and evolution of the jet structures. [ABSTRACT FROM AUTHOR]

The high-precision measurements of exoplanet transit light curves that are now available contain information about the planet properties, their orbital parameters, and stellar limb darkening (LD). Recent 3D magnetohydrodynamical (MHD) simulations of stellar atmospheres have shown that LD depends on the photospheric magnetic field, and hence its precise determination can be used to estimate the field strength. Among existing LD laws, the uses of the simplest ones may lead to biased inferences, whereas the uses of complex laws typically lead to a large degeneracy among the LD parameters. We have developed a novel approach in which we use a complex LD model but with second derivative regularization during the fitting process. Regularization controls the complexity of the model appropriately and reduces the degeneracy among LD parameters, thus resulting in precise inferences. The tests on simulated data suggest that our inferences are not only precise but also accurate. This technique is used to re-analyse 43 transit light curves measured by the NASA Kepler and Transiting Exoplanet Survey Satellite missions. Comparisons of our LD inferences with the corresponding literature values show good agreement, while the precisions of our measurements are better by up to a factor of 2. We find that 1D non-magnetic model atmospheres fail to reproduce the observations while 3D MHD simulations are qualitatively consistent. The LD measurements, together with MHD simulations, confirm that Kepler-17, WASP-18, and KELT-24 have relatively high magnetic fields (⁠|$\gt 200$| G). This study paves the way for estimating the stellar surface magnetic field using the LD measurements. [ABSTRACT FROM AUTHOR]

Hot Jupiters might reside inside the Alfvén surface of their host star wind, where the stellar wind is dominated by magnetic energy. The implications of such a sub-Alfvénic environment for atmospheric escape are not fully understood. Here, we employ 3D radiation-magnetohydrodynamic simulations and Ly- |$\alpha$| transit calculations to investigate atmospheric escape properties of magnetized hot Jupiters. By varying the planetary magnetic field strength (⁠|$B_\mathrm{p}$|⁠) and obliquity, we find that the structure of the outflowing atmosphere transitions from a magnetically unconfined regime, where a tail of material streams from the nightside of the planet, to a magnetically confined regime, where material escapes through the polar regions. Notably, we find an increase in the planet escape rate with |$B_\mathrm{p}$| in both regimes, with a local decrease when the planet transitions from the unconfined to the confined regime. Contrary to super-Alfvénic interactions, which predicted two polar outflows from the planet, our sub-Alfvénic models show only one significant polar outflow. In the opposing pole, the planetary field lines connect to the star. Finally, our synthetic Ly- |$\alpha$| transits show that both the red-wing and blue-wing absorptions increase with |$B_\mathrm{p}$|⁠. Furthermore, there is a degeneracy between |$B_\mathrm{p}$| and the stellar wind mass-loss rate when considering absorption of individual Ly- |$\alpha$| wings. This degeneracy can be broken by considering the ratio between the blue-wing and the red-wing absorptions, as stronger stellar winds result in higher blue-to-red absorption ratios. We show that, by using the absorption ratios, Ly- |$\alpha$| transits can probe stellar wind properties and exoplanetary magnetic fields. [ABSTRACT FROM AUTHOR]

Magnetic reconnection before flux cancellation in the solar photosphere when two opposite-polarity photospheric magnetic fragments are approaching one another is usually modelled by assuming that a small so-called 'floating current sheet' forms about a null point or separator that is situated in the overlying atmosphere. Here, instead we consider the reconnection that is initiated as soon as the fragments become close enough that their magnetic fields interact. The resulting current sheet, which we term a 'fin sheet' extends up from the null point or separator that is initially located in the solar surface. We develop here non-linear analyses for finite-length models of both fin and floating current sheets that extend the previous models that were limited to short floating current sheets. These enable the length of the current sheet and the rate of heating to be calculated in both cases as functions of the separation distance of the sources and the reconnection rate. Usually, the fin current sheet liberates more energy than a floating current sheet. [ABSTRACT FROM AUTHOR]

Almost all accreting black hole and neutron star (NS) X-ray binary systems (XRBs) exhibit prominent brightness variations on a few characteristic time-scales and their harmonics. These quasi-periodic oscillations (QPOs) are thought to be associated with the precession of a warped accretion disc, but the physical mechanism that generates the precessing warp remains uncertain. Relativistic frame dragging (Lense–Thirring precession) is one promising candidate, but a misaligned magnetic field is an alternative, especially for NS XRBs. Here, we report the discovery of five accreting white dwarf systems (AWDs) that display strong optical QPOs with characteristic frequencies and harmonic structures that suggest they are the counterpart of the QPOs seen in XRBs. Since AWDs are firmly in the classical (non-relativistic) regime, Lense–Thirring precession cannot account for these QPOs. By contrast, a weak magnetic field associated with the white dwarf can drive disc warping and precession in these systems, similar to what has been proposed for NS XRBs. Our observations confirm that magnetically driven warping is a viable mechanism for generating QPOs in disc-accreting astrophysical systems, certainly in AWDs and possibly also in NS XRBs. Additionally, they establish a new way to estimate magnetic field strengths, even in relatively weak-field systems where other methods are not available. [ABSTRACT FROM AUTHOR]

GRB 190829A has been widely studied due to its nature and the high-energy emission presented. Due to the detection of a very high energy component by the High Energy Stereoscopic System and the event's atypically middling luminosity, it has been categorized in a select, limited group of bursts bordering classic gamma-ray bursts (GRBs) and nearby sub-energetic events. Given the range of models utilized to adequately characterize the afterglow of this burst, it has proven challenging to identify the most probable explanation. Nevertheless, the detection of polarization data provided by the MASTER (Mobile Astronomical System of TElescope Robots) collaboration has added a new aspect to GRB 190829A that permits us to attempt to explore this degeneracy. In this paper, we present a polarization model coupled with a thin-shell synchrotron forward-shock model – a component in all models used to describe GRB 190829A's afterglow – in order to fit the polarization's temporal evolution with the existing upper limits (⁠|$\Pi < 6{{\ \rm per\, cent}}$|⁠). We find that the polarization generated from an on-axis emission is favoured for strongly anisotropic magnetic field ratios, while an off-axis scenario cannot be fully ruled out when a more isotropic framework is taken into account. [ABSTRACT FROM AUTHOR]

Coronal mass ejections (CMEs) are solar eruptions that involve large-scale changes to the magnetic topology of an active region. There exists a range of models for CME onset which are based on twisted or sheared magnetic field above a polarity inversion line (PIL). We present observational evidence that topological changes at PILs, in the photosphere, form a key part of CME onset, as implied by many models. In particular, we study the onset of 30 CMEs and investigate topological changes in the photosphere by calculating the magnetic winding flux, using the artop code. By matching the times and locations of winding signatures with CME observations produced by the almanac code, we confirm that these signatures are indeed associated with CMEs. Therefore, as well as presenting evidence that changes in magnetic topology at the photosphere are a common signature of CME onset, our approach also allows for the finding of the source location of a CME within an active region. [ABSTRACT FROM AUTHOR]

We present in this paper an analysis of near-infrared observations of the 0.3- |${\rm M}_{\odot }$| protostar V347 Aurigae (V347 Aur) collected with the SPIRou high-resolution spectropolarimeter and velocimeter at the 3.6-m Canada-France-Hawaii Telescope from 2019 October to 2023 April. From a set of 79 unpolarized and circularly polarized spectra of V347 Aur to which we applied Least-Squares Deconvolution (LSD), we derived radial velocities and longitudinal fields, along with their temporal variations over our monitoring campaign of 1258 d. Our data show that V347 Aur is an eccentric binary system with an orbital period of |$154.6\pm 0.7$| d, experiencing strong-to-extreme accretion events near periastron. The companion is a |$29.0\pm 1.6$| |${\rm M}_{{2\!\!_{\mathbf +}}}$| brown dwarf, a rare member of the brown dwarf desert of close companions around M dwarfs. We detect weak longitudinal fields (⁠|$\lt $| 100 G) at the surface of V347 Aur, significantly weaker than those of more evolved prototypical T Tauri stars. These fields show small-amplitude rotational modulation, indicating a mainly axisymmetric parent large-scale magnetic topology, and larger fluctuations at half the orbital period, suggesting that what we dub a 'pulsed dynamo' triggered by orbital motion and pulsed accretion operates in V347 Aur. Applying Zeeman–Doppler imaging to our circularly polarized LSD profiles, we find that the large-scale field of V347 Aur is mainly toroidal for most of our observations, with the toroidal component switching sign near periastron and apoastron. The weak large-scale dipole (⁠|$\simeq 30$| G) is not able to disrupt the disc beyond 1.3 |$R_{\star }$| even at the lowest accretion rates, implying longitudinally distributed (rather than localized) accretion at the surface of the protostar. [ABSTRACT FROM AUTHOR]

It has been suggested that the line width of ions in molecular clouds is narrower than that of the co-existing neutral particles, which has been interpreted as an indication of the decoupling of neutral turbulence from magnetic fields within a partially ionized environment. We calculate the principal component analysis (PCA) correlation coefficients of CCH versus H |$^{13}$| CO |$^{+}$| and H |$^{13}$| CN versus H |$^{13}$| CO |$^{+}$|⁠. We find aside from H |$^{13}$| CN, CCH could also be strongly spatial correlated with H |$^{13}$| CO |$^{+}$| in high-mass star-forming regions. CCH and H |$^{13}$| CO |$^{+}$| line emissions are strongly spatial correlated with each other in 48 per cent sources with a PCA correlation coefficient over 0.7. So, we investigate the ambipolar diffusion (AD) effect using CCH and H |$^{13}$| CO |$^{+}$| lines as a neutral/ion pair in a sample of 129 high-mass star-forming clumps. We conduct a careful analysis of line widths of the CCH–H |$^{13}$| CO |$^{+}$| pair pixel-by-pixel in 12 sources, which show a strong correlation in CCH–H |$^{13}$| CO |$^+$| emission and no obvious outflows or multiple velocity components. The mean velocity dispersion of CCH is about the same as H |$^{13}$| CO |$^{+}$| in 12 sources. In low-density regions of most sources, CCH shows a broader velocity dispersion than H |$^{13}$| CO |$^{+}$|⁠. However, the AD effect is not significant from a statistical point of view. [ABSTRACT FROM AUTHOR]

We present initial results from the Polarization Sky Survey of the Universe's Magnetism (POSSUM), analysing 22 817 Faraday rotation measures (RMs) with median uncertainties of 1.2 rad m |$^{-2}$| across 1520 deg2 to study magnetized gas associated with 55 nearby galaxy groups (⁠|$z\lesssim 0.025$|⁠) with halo masses between |$10^{12.5}$| and |$10^{14.0}$| M |$_\odot$|⁠. We identify two distinct gas phases: the intragroup medium (IGrM) within 0–2 splashback radii and the warm-hot intergalactic medium (WHIM) extending from 2 to 7 splashback radii. These phases enhance the standard deviation of residual (i.e. Galactic foreground RM-subtracted) RMs by |$6.9\pm 1.8$| rad m |$^{-2}$| and |$4.2 \pm 1.2$| rad m |$^{-2}$|⁠ , respectively. Estimated magnetic field strengths are several μ G within the IGrM and 0.1–1 μ G in the WHIM. We estimate the plasma |$\beta$| in both phases, and show that magnetic pressure might be more dynamically important than in the ICM of more massive clusters or sparse cosmic web filaments. Our findings indicate that 'missing baryons' in the WHIM likely extend beyond the gravitational radii of group-mass haloes to Mpc scales, consistent with large-scale, outflow-driven 'magnetized bubbles' seen in cosmological simulations. We demonstrate that RM grids are an effective method for detecting magnetized thermal gas at galaxy group interfaces and within the cosmic web. This approach complements X-ray and Sunyaev-Zel'dovich effect methods, and when combined with fast radio burst dispersion measures, data from the full POSSUM survey – comprising approximately a million RMs – will allow direct magnetic field measurements to further our understanding of baryon circulation in these environments and the magnetized universe. [ABSTRACT FROM AUTHOR]

Magnetic sounding using data collected from the Juno mission can be used to provide constraints on Jupiter's interior. However, inwards continuation of reconstructions assuming zero electrical conductivity and a representation in spherical harmonics are limited by the enhancement of noise at small scales. Here we describe new time-independent reconstructions of Jupiter's internal magnetic field based on physics-informed neural networks and either the first 33 (PINN33) or the first 50 (PINN50) of Juno's orbits. The method can resolve local structures, and allows for weak ambient electrical currents. Our models are not hampered by noise amplification at depth, and provide a smooth picture of the interior structure without explicit regularization. We estimate that the dynamo boundary is at a fractional radius of 0.8. At this depth, the magnetic field is arranged into longitudinal bands, and strong local features such as the great blue spot appear to be rooted in neighbouring structures of oppositely signed flux. [ABSTRACT FROM AUTHOR]

We investigate vortex dynamics in three magnetic regions, viz. Quiet Sun, Weak Plage, and Strong Plage, using realistic three-dimensional simulations from a comprehensive radiation-magnetohydrodynamics (MHD) code, MURaM. We find that the spatial extents and spatial distribution of vortices vary for different set-ups even though the photospheric turbulence responsible for generating vortices has similar profiles for all three regions. We investigate kinetic and magnetic swirling strength and find them consistent with the Alfvén wave propagation. Using a flux tube expansion model and linear MHD wave theory, we find that the deviation in kinetic swirling strength from the theoretically expected value is the highest for the Strong Plage, least for the Weak Plage, and intermediate for the Quiet Sun at chromospheric heights. It suggests that Weak Plage is the most favoured region for chromospheric swirls, though they are of smaller spatial extents than in Quiet Sun. We also conjecture that vortex interactions within a single flux tube in Strong Plage lead to an energy cascade from larger to smaller vortices that further result in much lower values of kinetic swirling strength than other regions. Fourier spectra of horizontal magnetic fields at 1 Mm height also show the steep cascade from large to smaller scales for Strong Plage. These findings indicate the potential of vortex-induced torsional Alfvén waves to travel higher in the atmosphere without damping for weaker magnetic regions such as the Quiet Sun, whereas vortices would result in dissipation and heating due to the vortex interactions in narrow flux tubes for the strongly magnetized regions such as Strong Plage. [ABSTRACT FROM AUTHOR]

Magnetic fields are an energetically important component of star formation galaxies, but it is often difficult to measure their properties from observations. One of the complexities stems from the fact that the magnetic fields, especially in spiral galaxies, have a two-scale nature: a large-scale field, coherent over kpc scales, and a small-scale random field, with a scale of |${\lesssim} 100 \, {\rm pc}$|⁠. Moreover, it is known that the strength of small- and large-scale fields is comparable and this makes it even harder to find their imprints in radio polarization observations such as the Faraday rotation measure (RM), which is the integral over the path-length of the product of the thermal electron density and the parallel component of the magnetic field to the line of sight. Here, we propose and demonstrate the use of second-order structure functions of RM computed with multiple higher-order stencils as a powerful analysis to separate the small- and large-scale magnetic field components. In particular, we provide new methods and calibrations to compute the scale and the strength of the large-scale magnetic field in the presence of small-scale magnetic fluctuations. We then apply the method to find the scale of large-scale magnetic fields in the nearby galaxies M51 and NGC 6946, using archival data, and further discuss the need for computing the RM structure functions with higher-order stencils. With multiple modern radio polarization observatories and eventually the Square Kilometre Array, RM observations will significantly improve in quantity and quality, and the higher-order stencil structure function techniques developed here can be used to extract information about multiscale magnetic fields in galaxies. [ABSTRACT FROM AUTHOR]

Magnetic fields play an important role in shaping and regulating star formation in molecular clouds. Here, we present one of the first studies examining the relative orientations between magnetic (B) fields and the dust emission, gas column density, and velocity centroid gradients on the 0.02 pc (core) scales, using the BISTRO and VLA+GBT observations of the NGC 1333 star-forming clump. We quantified these relative orientations using the Project Rayleigh Statistic (PRS) and found preferential global parallel alignment between the B field and dust emission gradients, consistent with large-scale studies with Planck. No preferential global alignments, however, are found between the B field and velocity gradients. Local PRS calculated for subregions defined by either dust emission or velocity coherence further revealed that the B field does not preferentially align with dust emission gradients in most emission-defined subregions, except in the warmest ones. The velocity-coherent structures, on the other hand, also showed no preferred B field alignments with velocity gradients, except for one potentially bubble-compressed region. Interestingly, the velocity gradient magnitude in NGC 1333 ubiquitously features prominent ripple-like structures that are indicative of magnetohydrodynamic (MHD) waves. Finally, we found B field alignments with the emission gradients to correlate with dust temperature and anticorrelate with column density, velocity dispersion, and velocity gradient magnitude. The latter two anticorrelations suggest that alignments between gas structures and B fields can be perturbed by physical processes that elevate velocity dispersion and velocity gradients, such as infall, accretions, and MHD waves. [ABSTRACT FROM AUTHOR]

We present a finite-volume, genuinely fourth-order accurate numerical method for solving the equations of resistive relativistic magnetohydrodynamics in Cartesian coordinates. In our formulation, the magnetic field is evolved in time in terms of face-average values via the constrained-transport method, while the remaining variables (density, momentum, energy, and electric fields) are advanced as cell volume averages. Spatial accuracy employs fifth-order accurate WENO-Z reconstruction from point values (as described in a companion paper) to obtain left and right states at zone interfaces. Explicit flux evaluation is carried out by solving a Riemann problem at cell interfaces, using the Maxwell–Harten–Lax–van Leer with contact wave resolution. Time-stepping is based on the implicit–explicit Runge–Kutta (RK) methods, of which we consider both the third-order strong stability preserving SSP3(4,3,3) and a recent fourth-order additive RK scheme, to cope with the stiffness introduced by the source term in Ampere's law. Numerical benchmarks are presented in order to assess the accuracy and robustness of our implementation. [ABSTRACT FROM AUTHOR]

AB Dor is a young solar-type star with a surface large-scale magnetic field |$10^2$| to |$10^3$| times stronger than the that of the Sun. Although strong magnetic fields are thought to inhibit coronal mass ejections (CMEs), dimming signatures typically associated with an eruptive CME were recently observed in AB Dor. The uninterrupted, long-duration dimming signal suggests that a CME took place at a high latitude, where it remained in view as the star rotates. A high-latitude CME is also consistent with observations that indicate that AB Dor hosts polar active regions. To investigate magnetic confinement in AB Dor, we conduct a parametric modelling study of 21 CMEs at latitudes |${\sim} 60^\circ$|⁠ , varying the location, mass, and magnetic field strength of an injected flux rope. 12 models had the flux rope located in an open magnetic field region, while the remaining nine were in a closed region. Results show that CMEs in open-field regions are in general more likely to erupt. The four eruptive CMEs from closed regions had high free magnetic energies |${\gtrsim} 3\times 10^{35}$|  erg, and 10 CMEs predominantly from the closed-field regions (8/10) were confined. CMEs in closed-field regions exhibited lower kinetic energies, since part of the CME energy was expended to overcome magnetic tension and break open the overlying field. In conclusion our work suggests that eruptive CMEs in AB Dor may occur in high-latitude regions of open magnetic field, as the magnetic tension in such regions does not significantly inhibit the eruption. [ABSTRACT FROM AUTHOR]

4U 1954 |$+$| 31 is a high-mass X-ray binary (HMXB) that contains a neutron star (NS) and an M supergiant companion. The NS has a spin period of |$\sim 5.4$| h. The traditional wind-accreting model requires an ultra-strong magnetic field for the NS to explain its extremely long spin period, which seems problematic for the NS with age of a few |$10^7$| yr. In this work, we take into account the unsteady feature of wind accretion, which results in alternation of the direction of the wind matter's angular momentum. Accordingly, the torque exerted by the accreted wind matter varies between positive and negative from time to time, and largely cancels out over long time. In such a scenario, NSs can naturally attain long spin periods without the requirement of a very strong magnetic field. This may also provide a reasonable explanation for the spin period distribution of long-period NSs in HMXBs. [ABSTRACT FROM AUTHOR]

The thermal evolution of isolated neutron stars is a key element in unravelling their internal structure and composition and establishing evolutionary connections among different observational subclasses. Previous studies have predominantly focused on one-dimensional or axisymmetric two-dimensional models. In this study, we present the thermal evolution component of the novel three-dimensional magnetothermal code MATINS (MAgneto-Thermal evolution of Isolated Neutron Star). MATINS employs a finite volume scheme and integrates a realistic background structure, along with state-of-the-art microphysical calculations for the conductivities, neutrino emissivities, heat capacity, and superfluid gap models. This paper outlines the methodology employed to solve the thermal evolution equations in MATINS , along with the microphysical implementation that is essential for the thermal component. We test the accuracy of the code and present simulations with non-evolving magnetic fields of different configurations (all with electrical currents confined to the crust and a magnetic field that does not thread the core), to produce temperature maps of the neutron star surface. Additionally, for a specific magnetic field configuration, we show one fully coupled evolution of magnetic field and temperature. Subsequently, we use a ray-tracing code to link the neutron star surface temperature maps obtained by MATINS with the phase-resolved spectra and pulsed profiles that would be detected by distant observers. This study, together with our previous article focused on the magnetic formalism, presents in detail the most advanced evolutionary code for isolated neutron stars, with the aim of comparison with their timing properties, thermal luminosities and the associated X-ray light curves. [ABSTRACT FROM AUTHOR]

Utilizing four archival X-ray data sets taken with the Hard X-ray Detector onboard Suzaku , timing studies were performed on three magnetars, 1E 1841−045 (observed in 2006), SGR 0501+4516 (2008), and 1RXS J170849.0−400910 (2009 and 2010). Their pulsations were reconfirmed, typically in an energy range of 12–50 keV. The 11.783 s pulses of 1E 1841−045 and those of SGR 0501+4516 at 5.762 s were periodically phase modulated, with a long period of |$\approx 23.4$| and |$\approx 16.4$|  ks, respectively. The pulse-phase modulation was also observed, at |$\approx 46.5$|  ks, from two data sets of 1RXS J170849.0−400910. In all these cases, the modulation amplitude was 6 per cent to 16 per cent of the pulse cycle. Including previously confirmed four objects, this characteristic timing behaviour is now detected from seven magnetars in total, and interpreted as a result of free precession of neutron stars that are deformed to an asphericity of |$\sim 10^{-4}$|⁠. Assuming that the deformation is due to magnetic stress, these magnetars are inferred to harbour toroidal magnetic fields of |$B_{\rm t}\sim 10^{16}$|  G. By comparing the estimated |$B_{\rm t}$| of these objects with their poloidal dipole field |$B_{\rm d}$|⁠ , the |$B_{\rm t}/B_{\rm d}$| ratio is found to increase with their characteristic age. Therefore, the toroidal fields of magnetars are likely to last longer than their poloidal fields. This explains the presence of some classes of neutron stars that have relatively weak |$B_{\rm d}$| but are suspected to hide strong |$B_{\rm t}$| inside them. [ABSTRACT FROM AUTHOR]

A tight correlation between the radio and X-ray emission in the hard state of black hole X-ray binaries (BHXRBs) indicates an intrinsic disc–jet connection in stellar black hole (BH) accretion systems, though the detailed physics processes at work are still quite unclear. A hot accretion flow is suggested to match the outer cold thin disc at a certain radius in the hard state, which may vary with the accretion rate. In this work, we assume that the magnetic field generated in the outer thin disc is advected inwards by the inner hot accretion flow, which is substantially enhanced near the BH. Such a strong field threading the horizon of a spinning BH is responsible for launching relativistic jets in BHXRBs via the Blandford–Znajek mechanism. Thus, both the jet power and the X-ray emission increase with the mass accretion rate, and we find that our model calculations are able to reproduce the observed radio/X-ray correlation quantitatively. For some individual BHXRBs, the slopes of the radio/X-ray correlations become steeper when the sources are brighter. Our model calculations show that this feature is due to the transition of the outer disc from gas pressure dominated to radiation pressure dominated, which leads to different accretion rate dependence of the field strength in the outer disc. [ABSTRACT FROM AUTHOR]

The eclipses seen in the radio emission of some pulsars can be invaluable to study the properties of the material from the companion stripped away by the pulsar. We present a study of six consecutive eclipses of PSR J0024–7204O in the globular cluster 47 Tucanae as seen by the MeerKAT radio telescope in the UHF (544–1088 MHz) band. A high scintillation state boosted the signal during one of the orbits and allowed a detailed study of the eclipse properties. We measure significant dispersion measure (DM) variations and detect strong scattering that seems to be the dominating mechanism of the eclipses at these frequencies. A complete drop in the linear polarization together with a small increase in the rotation measure suggests the presence of a magnetic field of |$\sim 2$|  mG. The study of multiple eclipses allowed us to measure difference in the lengths of the eclipses and DM differences of |$\sim 0.01$|  pc cm |$^{-3}$| in consecutive orbits. One orbit, in particular, shows a delay in recovery of the linear polarization and a visible delay in the arrival of the pulses caused by a stronger scattering event. We suggest that these are caused by a higher variance of density fluctuations during the event. [ABSTRACT FROM AUTHOR]

The non-thermal particles escaping from collision-less shocks into the surrounding medium can trigger a non-resonant streaming instability that converts parts of their drift kinetic energy into large amplitude magnetic field perturbations, and promote the confinement and acceleration of high energy cosmic rays. We present simulations of the instability using an hybrid-Particle-in-Cell approach including Monte Carlo collisions, and demonstrate that the development of the non-resonant mode is associated with important ion pressure anisotropies in the background plasma. Depending on the initial conditions, the anisotropies may act on the instability by lowering its growth and trigger secondary micro-instabilities. Introducing collisions with neutrals yield a strong reduction of the magnetic field amplification as predicted by linear fluid theory. In contrast, Coulomb collisions in fully ionized plasmas are found to mitigate the self-generated pressure anisotropies and promote the growth of the magnetic field. [ABSTRACT FROM AUTHOR]

Lyα emission is an exceptionally informative tracer of the life cycle of evolving galaxies and the escape of ionizing photons. However, theoretical studies of Lyα emission are often limited by insufficient numerical resolution, incomplete sets of physical models, and poor line-of-sight (LOS) statistics. To overcome such limitations, we utilize here the novel pandora suite of high-resolution dwarf galaxy simulations that include a comprehensive set of state-of-the-art physical models for ionizing radiation, magnetic fields, supernova feedback, and cosmic rays. We post-process the simulations with the radiative transfer code rascas to generate synthetic observations and compare to the observed properties of Lyα emitters. Our simulated Lyα haloes are more extended than the spatial region from which the intrinsic emission emanates, and our spatially resolved maps of spectral parameters of the Lyα emission are very sensitive to the underlying spatial distribution and kinematics of neutral hydrogen. Lyα and LyC emissions display strongly varying signatures along different LOS depending on how each LOS intersects low-density channels generated by stellar feedback. Comparing galaxies simulated with different physics, we find the Lyα signatures to exhibit systematic offsets determined by the different levels of feedback strength and the clumpiness of the neutral gas. Despite this variance, and regardless of the different physics included in each model, we find universal correlations between Lyα observables and LyC escape fraction, demonstrating a robust connection between Lyα and LyC emission. Lyα observations from a large sample of dwarf galaxies should thus give strong constraints on their stellar feedback-regulated LyC escape and confirm their important role for the re-ionization of the Universe. [ABSTRACT FROM AUTHOR]

Alfvén-wave turbulence is known as a plasma heating mechanism associated with the acceleration of fast solar wind, found emanating from open magnetic fields adjacent to coronal holes. In this study, we expand the scope of this mechanism to investigate the thermodynamics of Alfvénic slow solar wind, a phenomenon originating from open fields near a streamer, as observed in recent inner heliospheric missions. We demonstrate a one-dimensional two-fluid model that incorporates three components: (1) low-frequency Alfvén-wave turbulence, serving as the primary dissipation mechanism, (2) a curved magnetic field that reproduces the streamer's boundary, and (3) the kinetic instabilities to address proton temperature anisotropy. Our findings suggest that this dissipation mechanism can be applied in common to both fast and Alfvénic slow solar winds. We identify the proton-cyclotron instability near the Sun and the oblique and parallel firehose instabilities occurring close to 1 au as crucial factors governing temperature anisotropy. This study contributes to our understanding of the complex thermodynamics of solar winds and provides valuable insights for future space missions. [ABSTRACT FROM AUTHOR]

We analyse, using new analytical models and numerical general relativistic magnetohydrodynamic simulations, the three-dimensional properties of accretion flows inside the plunging region of black hole spacetimes (i.e. at radii smaller than the innermost stable circular orbit). These simulations are of thick discs, with aspect ratios of order unity |$h/r \sim 1$|⁠ , and with a magnetic field geometry given by the standard low-magnetization 'SANE' configuration. This work represents the first step in a wider analysis of this highly relativistic region. We show that analytical expressions derived in the 'thin disc' limit describe the numerical results remarkably well, despite the large aspect ratio of the flow. We further demonstrate that accretion within this region is typically mediated via spiral arms, and that the geometric properties of these spiral structures can be understood with a simple analytical model. These results highlight how accretion within the plunging region is fundamentally two-dimensional in character, which may have a number of observational implications. We derive a modified theoretical description of the pressure within the plunging region which accounts for turbulent heating and may be of use to black hole image modelling. [ABSTRACT FROM AUTHOR]

The majority of stars are in binary/multiple systems. How such systems form in turbulent, magnetized cores of molecular clouds in the presence of non-ideal magnetohydrodynamic (MHD) effects remains relatively underexplored. Through athena ++-based non-ideal MHD adaptive mesh refinement simulations with ambipolar diffusion, we show that the collapsing protostellar envelope is dominated by dense gravo-magneto-sheetlets, a turbulence-warped version of the classic pseudodisc produced by anisotropic magnetic resistance to the gravitational collapse, in agreement with previous simulations of turbulent, magnetized single-star formation. The sheetlets feed mass, magnetic fields, and angular momentum to a Dense ROtation-Dominated (DROD) structure, which fragments into binary/multiple systems. This DROD fragmentation scenario is a more dynamic variant of the traditional disc fragmentation scenario for binary/multiple formation, with dense spiral filaments created by inhomogeneous feeding from the highly structured larger-scale sheetlets rather than the need for angular momentum transport, which is dominated by magnetic braking. Provided that the local material is sufficiently demagnetized, with a plasma- |$\beta$| of 10 or more, collisions between the dense spiralling filaments play a key role in facilitating gravitational collapse and stellar companion formation by pushing the local magnetic Toomre parameter |$Q_\mathrm{m}$| below unity. This mechanism can naturally produce in situ misaligned systems on the 100-au scale, often detected with high-resolution Atacama Large Millimeter Array (ALMA) observations. Our simulations also highlight the importance of non-ideal MHD effects, which affect whether fragmentation occurs and, if so, the masses and orbital parameters of the stellar companions formed. [ABSTRACT FROM AUTHOR]

This paper reports on computational results of continuum spectra of atomic lithium in white-dwarf-strength magnetic fields. The adiabatic-basis-expansion method with R -matrix propagation has been used to study photoionization of magnetized alkali metal atoms. The R -matrix propagation technique and the two-dimensional matching scheme were utilized to obtain wavefunctions of the continuum states. Cross-sections of photoionization are calculated for lithium atoms in magnetic fields. Continuum spectra for its various bound-free transitions in magnetic white dwarf stars are presented as a function of field strengths ranging from 11.75 to 117.50 MG. Comparison is made between continuum spectra of diamagnetic hydrogen and lithium atoms. The comparison shows good agreement or remarkable difference for final continuum states with different symmetries in the photoionization processes concerned. A detailed analysis has been performed to understand the obtained results. The good agreement displayed manifests the reliability of the extended adiabatic-basis-expansion method. This method is suited to produce a large number of photoionization cross-section data for alkali metal atoms in a strong magnetic field, and therefore can serve as a tool to simulate continuum spectra observed in the atmospheres of magnetic white dwarfs with alkali metal atoms. [ABSTRACT FROM AUTHOR]

We explore the dynamical behaviour of dust particles that populate the surface of inner optically thick protoplanetary discs. This is a disc region with the hottest dust and is of a great importance for planet formation and dust evolution, but we still struggle to understand all the forces that shape this environment. In our approach, we combine results from two separate numerical studies, one is the wind velocity and density distributions obtained from magnetohydrodynamical simulations of accretion discs, and the other is a high-resolution multigrain dust radiation transfer. In our previous paper in the series, we described the methodology for utilizing these results as an environmental input for the integration of dust trajectories driven by gravity, gas drag, and radiation pressure. Now we have two improvements, we incorporate time changes in the wind density and velocity, and we implement the non-radial radiation pressure force. We applied our analysis on the Herbig Ae and T Tau stars. We confirm that the radiation pressure force can lead to dust outflow, especially in the case of more luminous stars. Additionally, it opposes dust accretion at the inner disc edge and reduces dust settling. These effects are enhanced by the disc wind, especially in the zone where the stellar and the disc magnetic fields meet. Our results suggest that dust grains can stay in the hottest disc region for an extended period and then end up ejected into the outer disc regions. [ABSTRACT FROM AUTHOR]

This work focuses on the analysis of the mean longitudinal magnetic field as a stellar activity tracer in the context of small exoplanet detection and characterization in radial-velocity (RV) surveys. We use Solar Dynamics Observatory/Helioseismic and Magnetic Imager filtergrams to derive Sun-as-a-star magnetic field measurements, and show that the mean longitudinal magnetic field is an excellent rotational period detector and a useful tracer of the solar magnetic cycle. To put these results into context, we compare the mean longitudinal magnetic field to three common activity proxies derived from HARPS-N Sun-as-a-star data: the full width at half-maximum, the bisector span, and the S-index. The mean longitudinal magnetic field does not correlate with the RVs and therefore cannot be used as a one-to-one proxy. However, with high cadence and a long baseline, the mean longitudinal magnetic field outperforms all other considered proxies as a solar rotational period detector, and can be used to inform our understanding of the physical processes happening on the surface of the Sun. We also test the mean longitudinal magnetic field as a 'stellar proxy' on a reduced solar data set to simulate stellar-like observational sampling. With a Gaussian Process regression analysis, we confirm that the solar mean longitudinal magnetic field is the most effective of the considered indicators, and is the most efficient rotational period indicator over different levels of stellar activity. This work highlights the need for polarimetric time series observations of stars. [ABSTRACT FROM AUTHOR]

We study the wide-binary eccentricity (e) distribution in young star clusters and the role of turbulence in setting the form of the e distribution using magnetohydrodynamical simulations of star cluster formation. The simulations incorporate gravity, turbulence, magnetic fields, protostellar heating, and jets/outflows. We find that (1) simulations that employ purely compressive turbulence driving produce binaries with a superthermal e distribution [ |$\alpha \gt 1$| in |$p(e) \propto e^\alpha$| ], while simulations with purely solenoidal driving or natural mixture of driving modes produce subthermal/thermal distributions (⁠|$\alpha \le$| 1), (2) the e distribution over the full range of binary separations in our simulations is set at the early stages of the star cluster formation process, (3) while binaries (separation of |$r_{\mathrm{pair}} \le 1000\, \mathrm{AU}$|⁠) have subthermal to thermal e distributions (⁠|$\alpha \sim 0.8$|⁠), wide binaries (⁠|$r_{\mathrm{pair}} \gt 1000\, \mathrm{AU}$|⁠) have a superthermal distribution (⁠|$\alpha \sim 1.8$|⁠), and (4) low-mass binary systems (system masses of |$M_{\mathrm{sys}} \le 0.8\, \mathrm{M_\odot }$|⁠) have a highly superthermal distribution (⁠|$\alpha \sim 2.4$|⁠), whereas high-mass systems (⁠|$M_{\mathrm{sys}} \gt 0.8\, \mathrm{M_\odot }$|⁠) exhibit a subthermal/thermal distribution (⁠|$\alpha \sim 0.8$|⁠). The binary eccentricity distribution is often modelled as a thermal distribution. However, our results suggest that the e distribution depends on the range of separation of the sampled binaries, which agrees with the findings from recent Gaia observations. We conclude that the dependence of the e distribution on the binary separation and mass is linked to the binary formation mechanism governed by the turbulent properties of the parent cloud. [ABSTRACT FROM AUTHOR]

Jetted astrophysical phenomena with black hole engines, including binary mergers, jetted tidal disruption events, and X-ray binaries, require a large-scale vertical magnetic field for efficient jet formation. However, a dynamo mechanism that could generate these crucial large-scale magnetic fields has not been identified and characterized. We have employed three-dimensional global general relativistic magnetohydrodynamical simulations of accretion discs to quantify, for the first time, a dynamo mechanism that generates large-scale magnetic fields. This dynamo mechanism primarily arises from the non-linear evolution of the magnetorotational instability (MRI). In this mechanism, large non-axisymmetric MRI-amplified shearing wave modes, mediated by the axisymmetric azimuthal magnetic field, generate and sustain the large-scale vertical magnetic field through their non-linear interactions. We identify the advection of magnetic loops as a crucial feature, transporting the large-scale vertical magnetic field from the outer regions to the inner regions of the accretion disc. This leads to a larger characteristic size of the, now advected, magnetic field when compared to the local disc height. We characterize the complete dynamo mechanism with two time-scales: one for the local magnetic field generation, |$t_{\rm gen}$|⁠ , and one for the large-scale scale advection, |$t_{\rm adv}$|⁠. Whereas the dynamo we describe is non-linear, we explore the potential of linear mean field models to replicate its core features. Our findings indicate that traditional |$\alpha$| -dynamo models, often computed in stratified shearing box simulations, are inadequate and that the effective large-scale dynamics is better described by the shear current effects or stochastic |$\alpha$| -dynamos. [ABSTRACT FROM AUTHOR]

We investigate star formation from subpc to kpc scales with magnetohydrodynamic models of a cloud structure and a section of galactic spiral arm. We aim to understand how magnetic fields affect star formation and cloud formation, and how feedback couples with magnetic fields on scales of clouds and clumps. We find that magnetic fields overall suppress star formation by |${\sim}$| 10 per cent with a weak field (5 |$\mu$| G) and |${\sim} 50$|  per cent with a stronger field (50 |$\mu$| G). Cluster masses are reduced by about 40 per cent with a strong field but show little change with a weak field. We find that clouds tend to be aligned parallel to the field with a weak field and become perpendicularly aligned with a stronger field, whereas on clump scales the alignment is more random. The magnetic fields and densities of clouds and clumps in our models agree with the Zeeman measurements of the Crutcher relation |$B\!-\!\rho$| in the weaker field models, while the strongest field models show a relation that is too flat compared to the observations. In all our models, we find that both subcritical and supercritical clouds and clumps are present. We also find that if using a line-of-sight (1D) measure of the magnetic field to determine the critical parameter, the magnetic field, and thereby also criticality, can vary by a factor of 3–4 depending on whether the direction the field is measured along corresponds to the direction of the ordered component of the magnetic field. [ABSTRACT FROM AUTHOR]

We have mapped the magnetic field (B -field) for a region of about 30 pc around the centre of our Galaxy, which encompasses the circumnuclear disc (CND), the minispiral, and the 20 and 50 km s−1 molecular clouds, using thermal dust polarization observations obtained from SOFIA/HAWC+ and JCMT/SCUPOL. We decompose the spectra of 12CO (J = 3 → 2) transition from this region into individual cloud components and find the polarization observed at different wavelengths might be tracing completely different layers of dust along the line of sight. We use modified Davis–Chandrasekhar–Fermi methods to measure the strength of B -field projected in the plane of the sky (⁠|$B_{{}_{\mathrm{POS}}}$|⁠). The mean |$B_{{}_{\mathrm{POS}}}$| of the CND and the minispiral, probed at 53 μ m is of the order of ∼2 mG. |$B_{{}_{\mathrm{POS}}}\!\!\!\lt \!1$| mG close to the Galactic Centre, in the region of the ionized mini-cavity within the CND, and increases outwards. However, the longer wavelength polarization at 216 μ m appears to come from a dust layer that is cooler and behind the CND and has a stronger B -field of about 7 mG. The B -field strength is lowest along the Eastern Arm of the minispiral, which is also the only region with Alfvén Mach number, |$\mathcal {M}_{\mathrm{A}}\gt 1$| and mass-to-flux ratio, λ ≳ 1. Such an observed weak B -field could be a result of the low resolution of the observation, where the tangled B -fields due to the strong turbulence in the high density clumps of the CND are lost within the beam size of the observation. [ABSTRACT FROM AUTHOR]

In this paper, we report near-infrared observations of the classical T Tauri star TW Hya with the SPIRou high-resolution spectropolarimeter and velocimeter at the 3.6-m Canada–France–Hawaii Telescope in 2019, 2020, 2021, and 2022. By applying Least-Squares Deconvolution (LSD) to our circularly polarized spectra, we derived longitudinal fields that vary from year to year from –200 to +100 G, and exhibit low-level modulation on the 3.6 d rotation period of TW Hya, despite the star being viewed almost pole-on. We then used Zeeman–Doppler Imaging to invert our sets of unpolarized and circularly polarized LSD profiles into brightness and magnetic maps of TW Hya in all four seasons, and obtain that the large-scale field of this T Tauri star mainly consists of a 1.0–1.2 kG dipole tilted at about 20° to the rotation axis, whereas the small-scale field reaches strengths of up to 3–4 kG. We find that the large-scale field is strong enough to allow TW Hya to accrete material from the disc on the polar regions at the stellar surface in a more or less geometrically stable accretion pattern, but not to succeed in spinning down the star. We also report the discovery of a radial velocity signal of semi-amplitude |$11.1^{+3.3}_{-2.6}$| m s−1 (detected at 4.3σ) at a period of 8.3 d in the spectrum of TW Hya, whose origin may be attributed to either a non-axisymmetric density structure in the inner accretion disc, or to a |$0.55^{+0.17}_{-0.13}$| MꝜ candidate close-in planet (if orbiting in the disc plane), at an orbital distance of 0.075 ± 0.001 au. [ABSTRACT FROM AUTHOR]

The merger of two magnetized compact objects, such as neutron stars, forms a compact object which may launch a relativistic and collimated jet. Numerical simulations of the process show that a dense and highly magnetized medium surrounds the system. This study presents a semi-analytical model that models the effects that a static magnetized medium with a tangled field produces in relativistic, collimated, and non-magnetized jets. The model is a first approximation that addresses the magnetic field present in the medium and is based on pressure equilibrium principles between the jet, cocoon, and external medium. A fraction of the ambient medium field is allowed to be entrained in the cocoon. We find that the jet and cocoon properties may be affected by high magnetic fields (≳ 1015 G) and mixing. The evolution of the system may vary up to |$\sim 10{{\ \rm per\ cent}}$| (compared to the non-magnetized case). Low-mixing may produce a slower broader jet with a broader and more energetic cocoon would be produced. On the other hand, high-mixing could produce a faster narrower jet with a narrow and less-energetic cocoon. Two-dimensional hydrodynamical simulations are used to validate the model and to constrain the mixing parameter. Although the magnetic field and mixing have a limited effect, our semi-analytic model captures the general trend consistent with numerical results. For high magnetization, the results were found to be more consistent with the low mixing case in our semi-analytic model. [ABSTRACT FROM AUTHOR]

Highly magnetized neutron stars exhibit the vacuum non-linear electrodynamics effects, which can be well-described using the one-loop effective action for quantum electrodynamics. In this context, we study the propagation and polarization of pulsar radiation, based on the post-Maxwellian Lagrangian from the Heisenberg–Euler–Schwinger action. Given the refractive index obtained from this Lagrangian, we determine the leading-order corrections to both the propagation and polarization vectors due to quantum refraction via perturbation analysis. In addition, the effects on the orthogonality between the propagation and polarization vectors and the Faraday rotation angle, all due to quantum refraction are investigated. Furthermore, from the dual refractive index and the associated polarization modes, we discuss quantum birefringence, with the optical phenomenology analogous to its classical counterpart. [ABSTRACT FROM AUTHOR]

There has been a growing interest within the astrophysics community in highly magnetized and fast-spinning white dwarfs (WDs), commonly referred to as HMWDs. WDs with these characteristics are quite uncommon and possess magnetic fields ≥106 G, along with short rotation periods ranging from seconds to just a few minutes. Based on our previous work, we analyse the emission of Gravitational Waves (GWs) in HMWDs through two mechanisms: matter accretion and magnetic deformation, which arise due to the asymmetry surrounding the star's rotational axis. Here, we perform a thorough self-consistent analysis, accounting for rotation and employing a realistic equation of state to investigate the stability of stars. Our investigation focuses on the emission of gravitational radiation from six rapidly spinning WDs: five of them are situated within binary systems, while one is an AXP, proposed as a magnetic accreting WD. Furthermore, we apply the matter accretion mechanism alongside the magnetic deformation mechanism to assess the influence of one process on the other. Our discoveries indicate that these WDs could potentially act as GW sources for BBO and DECIGO, depending on specific parameters, such as their mass, the angle (α) between the magnetic and rotational axes, and the accumulated mass (δ m) at their magnetic poles, which is influenced by the effect of matter accretion. However, detecting this particular class of stars using the LISA and TianQin space detectors seems unlikely due to the challenging combination of parameters such as a large δ m , a large α angle and a small WD mass value. [ABSTRACT FROM AUTHOR]