Sazuna/UAT_keywords huggingface dataset:
Alpha Core─Beam Origin in Low-β Solar Wind Plasma: Insights from Fully Kinetic Simulations. In situ observations of the fast solar wind in the inner heliosphere show that minor ions and ion subpopulations often exhibit distinct drift velocities. Both alpha particles and proton beams stream at speeds that rarely exceed the local Alfvén speed relative to the core protons, suggesting the presence of instabilities that constrain their maximum drift. We aim to propose a mechanism that generates an alpha-particle beam through nonlinear Landau damping, primarily driven by the relative super-Alfvénic drift between protons and alpha particles. To investigate this process, we perform one-dimensional, fully kinetic particle-in-cell simulations of a nonequilibrium multispecies plasma complemented by its linear theory to validate the model during the linear phase. Our results provide clear evidence that the system evolves by producing an alpha-particle beam, thereby suggesting a local mechanism for alpha-beam generation via nonlinear Landau damping.

Keywords: Space plasmas, Plasma physics, Solar wind, Plasma astrophysics, Alfven waves
Simulations of Coronal Mass Ejection Injection into the Inner Heliosphere with Displacement of the Heliospheric Magnetic Field. Magnetohydrodynamic (MHD) simulations are a useful tool for understanding the propagation of coronal mass ejections (CMEs) in the inner heliosphere and their interaction with the background solar wind. This understanding is important for improving our ability to predict CME properties at Earth. A common approach in models of the inner heliosphere starting from ≍0.1 astronomical unit (au) is to inject CMEs with analytically prescribed magnetic structures—such as magnetic spheromaks—by superimposing the CME's magnetic field onto the heliospheric magnetic field. However, the superposition method leads to the heliospheric magnetic field penetrating the CME, immediately distorting the CME's magnetic structure during the injection. In this work, we introduce a new, more physically accurate displacement method for the CME injection into the inner heliosphere by dynamically bending the heliospheric magnetic field around the incoming CME. Using the GAMERA-Helio MHD model of the inner heliosphere (0.1─1 au) and a Gibson─Low model of a CME with an internal magnetic field, we demonstrate that the displacement method preserves the CME's internal structure, unlike superposition. Moreover, the displacement method produces a current distribution around the CME that is consistent with results from previous coronal MHD simulations with a self-consistent description of CME initiation and evolution. The displacement approach represents a step forward in modeling magnetized CMEs in the inner heliosphere to study their evolution and impacts at Earth.

Keywords: Magnetic fields, Solar coronal mass ejections, Heliosphere, Magnetohydrodynamical simulations
Outward Migration of a Gas Accreting Planet: A Semianalytical Formula. Type II orbital migration is a key process to regulate the mass and semimajor axis distribution of exoplanetary giant planets. The conventional formula of Type II migration generally predicts too rapid inward migration to reconcile with the observed pileup of gas giants beyond 1 au. Analyzing the recent high-resolution hydrodynamical simulations by Y.-P. Li et al. and J.-P. Pan et al. that show robust outward migration of a gas accreting planet, we here clarify the condition for the outward migration to occur and derive a general semianalytical formula that can be applied for a broad range of planet mass and disk conditions. The striking outward migration is caused by azimuthal asymmetry in corotation torque exerted from circumplanetary disk regions (connecting to horseshoe flows) that is produced by the planetary gas accretion, while the conventional inward migration model is based on radial asymmetry in the torques from the circumstellar protoplanetary disk. We found that the azimuthal asymmetry dominates and the migration is outward when the gap depth defined by the surface density reduction factor of  1/(1+K')  is in the range of  0.03≲K'≲50 . Using simple models with the new formula, we demonstrate that the outward migration plays an important role in shaping the mass and semimajor axis distribution of gas giants. The concurrent dependence of planets' accretion rate and migration direction on their masses and disk properties potentially reproduces the observed pileup of exoplanetary gas giants beyond 1 au, although more detailed planet population synthesis calculations are needed in the future.

Keywords: Exoplanet dynamics, Exoplanet migration, Planetary migration
Concurrent Accretion and Migration of Giant Planets in their Natal Disks with Consistent Accretion Torque. II. Parameter Survey and Condition for Outward Migration. Migration typically occurs during the formation of planets and is closely linked to the planetary formation process. In classical theories of nonaccreting planetary migration, both type I and type II migration typically result in inward migration, which is hard to align with the architecture of planetary systems. In this work, we conduct systematic, high-resolution 3D/2D numerical hydrodynamic simulations to investigate the migration of an accreting planet. Under different disk conditions, we compared the dynamical evolution of planets with different planet-to-star mass ratios. We find that accretion of planets can significantly diminish the inward migration tendency of planets, or even change the direction of migration. The migration of low-/high-mass planets is classified as type I/II inward migration, respectively, while intermediate-mass planets, which have the strongest accretion, show an outward migration trend. We confirm that the outward migration is mainly attributed to the positive torque from the azimuthal asymmetric structures around the accreting planet, similar to Y.-P. Li et al. The termination of planetary mass growth is thus synonymous with the transition from outward to inward migration. For the cases of high viscosity α = 0.04 and disk aspect ratio h0 = 0.05, the range of mass ratio for planetary outward migration is 1 × 10−4 ≲ q ≲ 4 × 10−3. For the case of low viscosity with α = 0.001 and/or low disk aspect ratio h0 = 0.03, the range of mass ratio for outward migration will shift toward the lower end. Our parameter survey reveals that a simple gap-opening parameter determines the condition for outward migration; details of the analytical interpretation are presented by S. Ida et al.

Keywords: Accretion, Hydrodynamical simulations, Black holes, Protoplanetary disks, Tidal interaction, Extrasolar gaseous giant planets
Irradiation-driven Formation of Supersoft X-Ray Sources following Classical Novae. Supersoft X-ray sources (SSSs) are characterized by persistent thermonuclear burning on the surfaces of white dwarfs (WDs). The standard model requires high mass-transfer rates of ∼10−7 M⊙ yr−1 from massive companions, presenting a theoretical impediment to the observed short-period SSSs, whose orbital periods imply low-mass donors theoretically incapable of sustaining such accretion. To resolve this paradox, we propose and demonstrate through detailed simulations that irradiative feedback following a classical nova eruption provides a natural formation channel. Through detailed binary evolution simulations with MESA, we reveal that sustained WD irradiation—initially from the outburst and subsequently from accretion luminosity—triggers significant and stable expansion of the low-mass companion. This, in turn, drives mass-transfer rates into the stable hydrogen-burning regime and sustains it beyond 104 yr after the initiation of hydrogen burning. This mechanism robustly explains the observed population of short-period SSSs. Moreover, when the irradiation-driven mass-transfer rate drops below the stable accretion rate, it may lead to the rapid accumulation of sufficient material on shorter timescales to trigger a recurrent nova outburst instead of SSS, thereby also offering an explanation for the origin of short-period recurrent novae.

Keywords: Close binary stars, Cataclysmic variable stars, X-ray binary stars, Type Ia supernovae
X-Ray Binaries: A Potential Dominant Contributor to the Cosmic-Ray Spectral Knee Structure. "PeVatrons" refer to astrophysical sources capable of accelerating particles to energies of ∼PeV and higher, potentially contributing to the cosmic-ray spectrum in the knee region. Recently, the High-Altitude Water Cherenkov Observatory (HAWC) and the Large High Altitude Air Shower Observatory (LHAASO) have discovered a new type of PeVatron─X-ray binary, allowing us to investigate in greater depth the contributions of these sources to cosmic rays around the knee region. There are hundreds of X-ray binaries observed in our Galaxy that are potential PeVatrons. In this work, we derive the radial distribution of X-ray binaries in the Galaxy. Then we use the DRAGON package to calculate energy spectrum, anisotropy of cosmic rays, and the resulting diffuse gamma-ray emissions, after considering them as factories of cosmic rays in the knee energy bands. Our findings show that the contributions from X-ray binary PeVatrons may be dominant. More X-ray binary PeVatrons can be observed by LHAASO and HAWC in the future and will confirm the contribution of X-ray binaries to high-energy cosmic rays.

Keywords: X-ray binary stars, Cosmic ray sources, Ultra-high-energy cosmic radiation
The ONs and OFFs of Pulsar Radio Emission: Characterizing the Nulling Phenomenon. Radio emission from pulsars is known to exhibit a diverse range of emission phenomena, among which nulling, where the emission becomes temporarily undetectable, is an intriguing example. Observations suggest nulling is prevalent in many long-period pulsars and thus must be understood to obtain a more comprehensive picture of pulsar emission and its evolution. However, one of the limitations in the observational characterization of nulling is the limited signal-to-noise ratio, which often makes individual pulses difficult to distinguish from noise or from any putative faint emission. Although some of the approaches in the published literature attempt to address this, they lose efficacy when individual pulses appear indistinguishable from noise, and as a result can lead to less accurate measurements. Here, we develop a new method (the  N sum algorithm) that uses sums of pulses to improve distinguishability from noise, thus measuring the nulling fraction more robustly. The algorithm can be employed to measure nulling fractions in weaker pulsars and can be applied to observations with a limited number of pulses. We compare our method with the recently developed Gaussian mixture modeling approach, using both simulated and real data, and find that our approach yields consistent results for generic and weaker pulsars. We also explore quasiperiodicity in nulling and measure the related parameters for five pulsars, including PSRs J1453−6413, J0950+0755, and J0026−1955, for which these are also the first such measurements. We compare and contrast our analysis of quasiperiodic nulling with previously published work, and explore the use of spin-down energy loss ( Ė ) to distinguish between different types of modulation behaviour.

Keywords: High energy astrophysics, Time domain astronomy, Pulsars, Radio pulsars
Ultraviolet Radiation and Neutrinos: Two Messengers from CCSNe in the CSM Scenario. Massive stars (&gt;8 M⊙) often undergo intense mass loss through winds or eruptive events in the final stages of their evolution, leading to the formation of a dense circumstellar medium (CSM). This material, expelled months to years before core collapse, shapes the pre-explosion environment and influences the early supernova (SN) emission. In particular, the interaction of the SN ejecta with the dense CSM can power an extended emission into the ultraviolet(UV)/optical bands, as seen in a growing fraction of type II SN. Recent events such as SN 2023ixf and SN 2024ggi confirm the relevance of dense environments and highlight the value of UV observations. Moreover, fast blue optical transients may represent extreme cases of this interaction, possibly linked to more compact/massive CSM. In this work, we model the SN─CSM shock interaction in order to (i) estimate the maximum detection horizons and expected rates for future UV missions like ULTRASAT, and (ii) to estimate the intensity and expected rate of potential neutrino signals detectable by IceCube and KM3NeT. We then discuss the prospects for multi-messenger observations of such events in the near future.

Keywords: Type II supernovae, Neutrino astronomy, Ultraviolet transient sources
Broadband X-Ray Observations of the Periodic Optical Source ZTF J185139.81+171430.3 and Its Identification as a Massive Intermediate Polar. We present X-ray observations of the periodic optical source ZTF J185139.81+171430.3 (hereafter ZTF J1851) by the XMM-Newton, NICER, and NuSTAR telescopes. The source was initially speculated to be a white dwarf (WD) pulsar system, due to its short period (P ∼ 12 minutes) and highly modulated optical lightcurves. Our observations revealed a variable X-ray counterpart extending up to 40 keV with an X-ray luminosity of LX ∼ 3 × 1033 erg s−1 (0.3─40 keV). Utilizing timing data from XMM-Newton and NICER, we detected a periodic signal at Pspin = 12.2640(7) ± 0.0583 minutes with &gt;6σ significance. The pulsed profile displays ∼25% and ∼10% modulation in the 0.3─2 and 2─10 keV bands, respectively. Broadband X-ray spectra are best characterized by an absorbed optically thin thermal plasma model with kT ≍ 25 keV and a Fe K-α fluorescent line at 6.4 keV. The bright and hard X-ray emission rules out the possibility of a WD pulsar or ultra-compact X-ray binary. The high plasma temperature and Fe emission lines suggest that ZTF J1851 is an intermediate polar spinning at 12.264 minutes. We employed an X-ray spectral model composed of the accretion column emission and X-ray reflection to fit the broadband X-ray spectra. Assuming spin equilibrium between the WD and the inner accretion disk, we derived a WD mass range of MWD = (1.07─1.32)M⊙, exceeding the mean WD mass of IPs (&lt;MWD&gt; = 0.8M⊙). Our findings illustrate that follow-up broadband X-ray observations could provide unique diagnostics to elucidate the nature of periodic optical sources anticipated to be detected in the upcoming Rubin all-sky optical surveys.

Keywords: Accretion, X-ray astronomy, DQ Herculis stars, Compact objects, Cataclysmic variable stars
On the Importance of Geometry in Exoplanet Irradiation: Implications for the Day─Night Contrast. The irradiance received by a spherical body or a planet close to a spherically symmetric source does not follow the point-source approximation and the inverse-square variation of irradiation if spherical symmetry is broken. In the penumbral zones of the planet, spherical symmetry of the star reduces to an axial symmetry. Our work aims to put forward a fundamental explanation, using energy conservation, to determine the variation of irradiance in the penumbral zone on a close-in planet where the point-source approximation fails. Consequently, we propose a numerical model that accurately predicts the irradiance within the boundaries of the penumbral zone and the fully illuminated zone. Our analysis also corrects a previous study on exoplanet irradiation that violates energy conservation. We find that night-side illumination partially explains the observed night-side temperatures on the planets considered; this reduces reliance on heat transport models to explain the night-side temperature for the few exemplar rocky close-in planets, namely K2-141 b, 55 Cancri e, TOI-561 b, TOI-431 b, and Kepler-10 b, that are discussed in this work. We provide improved day─night contrast temperatures, considering an airless scenario, and highlight the need for revisiting the heat transport models associated with atmospheric modelling of planets where the night-side illumination is significant.

Keywords: Computational methods, Planetary climates, Radiative transfer, Exoplanets
A 7 Day Multiwavelength Flare Campaign on AU Mic. IV. Quiescent Gyrosynchrotron and Gyroresonance Radiation from 12 to 25 GHz. We present an analysis of the radio quiescent data from a multiwavelength campaign of the active M dwarf flare star AU Mic (dM1e) that occurred in 2018 October. Using Ku-band data (12─18 GHz) from the Karl G. Jansky Very Large Array and K-band data (17─25 GHz) from the Australia Telescope Compact Array, we find that the quiescent spectrum can be decomposed into two components: one falling with frequency and one that remains flat. The flat component has a relatively steady flux density of 0.64 ± 0.14 mJy. The falling component varies in strength, but exhibits a spectral index of α = −0.88 ± 0.10. The falling component is thus consistent with nonthermal, optically thin gyrosynchrotron radiation with a corresponding power-law index similar to flares from AU Mic. While a flat component may arise from thermal, optically thin free─free emission, the observed flux density and inferred mass-loss rate are both too large compared to previous stellar wind and X-ray emission theory and models, necessitating an alternative explanation. This flat component instead matches well with an optically thick gyroresonance component integrated over multiple source regions such that the composite spectra are reasonably flat. The persistence of these components across the rotational period suggests multiple source regions, which may help explain changes in flux density and persistent high-energy electrons.

Keywords: M dwarf stars, Red dwarf flare stars, Stellar activity, Flare stars, Radio continuum emission, Time domain astronomy, Variable stars, Discrete radio sources, Radio astronomy
Constraining the Occurrence of ZLK-induced White Dwarf Pollution with Dissipative Precession. Von Zeipel─Lidov−Kozai (ZLK) oscillations, induced by bound, perturbative companions to white dwarfs (WDs), have been suggested as a dynamical mechanism that may contribute to WD pollution. To trigger ZLK oscillations, however, a three-body system must reach a sufficiently large mutual inclination between orbits. The occurrence of these high-mutual-inclination configurations can be curtailed by dissipative precession at the protoplanetary disk stage, which pushes exoplanet-hosting close binary systems toward preferential orbit─orbit alignment. In this work, we constrain the fraction of WDs with binary companions that can undergo ZLK-driven pollution given the effects of dissipative precession. To accrete pollution via ZLK oscillations, a WD binary system must be sufficiently inclined and the characteristic timescale of the oscillations must be sufficiently short to perturb material within the WD's cooling age. Considering a sample of 4400 known WD/main-sequence binaries, we find that 50%─70% have favorable parameters for ZLK pollution, depending on the orbital separation of the polluting body. While the conditions for oscillations are favorable, the tendency for ZLK to result in massive but more infrequent polluters likely restricts the rates of ZLK-induced pollution among the observed population. In general, dissipative precession is a limiting factor in pollution rates for more closely separated binaries (initial separations &lt;500−800 au), while ZLK timescale constraints are most limiting for wider binaries.

Keywords: Exoplanet dynamics, White dwarf stars, Binary stars
Spatial and Dynamical Relations between Spicules and Network Bright Points. Spicules are among the most ubiquitous small-scale, jet-like features in the solar chromosphere and are widely believed to play a significant role in transporting mass and energy into the solar corona, with their mechanisms not fully understood. We utilize high-resolution Hα images acquired from the 1.6 m Goode Solar Telescope at Big Bear Solar Observatory to investigate spatial and dynamical properties of both spicules and network bright points (NBPs), and for the first time, incorporated NBP motions in the analyses of spicules. Our main results are as follows: (1) The speed distributions of blueshifted spicules and NBPs both exhibit distinct peaks, whereas that of redshifted spicules is monotonically decreasing. (2) Torsional motions of spicules inferred from alternating signs of Doppler shifts are faster than the NBPs' transversal motions by a factor of 10─102, which may imply the mass density ratio in two different heights as 102─104. (3) Blueshifted spicules are found to be more abundant than redshifted spicules in general, but their relative population difference reduces to ∼10% at Doppler speeds above ∼35 km s−1. (4) Redshifted spicules lying at higher heights share morphological and dynamical similarity with the blueshifted spicules, which implies the same driving mechanism operating in both directions. (5) These two populations appear above NBPs concentrated under the AIA 193 Å bright region. We interpret these results in favor of a scenario that Alfvén waves generated by NBPs' motions impart their energies to spicules in both torsional and field-aligned motions, and also contribute to the coronal heating and possibly the acceleration of the solar wind.

Keywords: Solar activity, Solar chromosphere, Solar magnetic bright points, Solar spicules
The 2023 Australian Total Solar Eclipse: Line Emission of Fe XIV, Fe X, and Fe XI out to 6 Solar Radii. We present narrowband observations of the Fe XIV (530.3 nm), Fe X (637.4 nm), and Fe XI (789.2 nm) coronal emission lines from the 2023 April 20 Total Solar Eclipse in Australia. We deployed pairs of telescopes for each emission line that were equipped with narrowband filters centered on, and several nanometers away from, the center wavelengths of the lines. The secondary continuum telescopes were used to measure and remove the combined continuum K- (electron) and F- (dust) corona, which dominate coronal emission at optical and infrared wavelengths. Significant emission was detected from all three lines from 1.03 solar radii (R⊙) continuously outward to at least 6 R⊙. The brightness of the lines and continuum are absolutely calibrated to the solar disk, and are validated by a comparison with LASCO-C2 observations made at the same time. Using these observations, we inferred the line emission ratios resolved throughout the middle-corona (defined as 1.5─6 R⊙) for the first time. These line ratios are a probe of the electron temperature, which have important implications for constraining models of coronal heating and the characterization of solar wind formation, yet these emission lines have scarcely been quantified beyond 3 R⊙ in the corona. This study demonstrates the enduring potential of eclipse observations for coronal physics and suggests that future spacecraft missions could observe these lines farther out than has been attempted previously.

Keywords: Solar cycle, Solar eclipses, Solar physics, Solar optical telescopes, Solar corona, Solar coronal streamers