adsabs/SciX_UAT_keywords huggingface dataset:
Extragalactic Magnetism with SOFIA (Legacy Program). I. The Magnetic Field in the Multiphase Interstellar Medium of M51

The recent availability of high-resolution far-infrared (FIR) polarization observations of galaxies using HAWC+/SOFIA has facilitated studies of extragalactic magnetic fields in the cold and dense molecular disks. We investigate whether any significant structural differences are detectable in the kiloparsec-scale magnetic field of the grand design face-on spiral galaxy M51 when traced within the diffuse (radio) and the dense and cold (FIR) interstellar medium (ISM). Our analysis reveals a complex scenario where radio and FIR polarization observations do not necessarily trace the same magnetic field structure. We find that the magnetic field in the arms is wrapped tighter at 154 μm than at 3 and 6 cm; statistically significant lower values for the magnetic pitch angle are measured at FIR in the outskirts (R ≥ 7 kpc) of the galaxy. This difference is not detected in the interarm region. We find strong correlations of the polarization fraction and total intensity at FIR and radio with the gas column density and 12CO(1-0) velocity dispersion. We conclude that the arms show a relative increase of small-scale turbulent B-fields at regions with increasing column density and dispersion velocities of the molecular gas. No correlations are found with H I neutral gas. The star formation rate shows a clear correlation with the radio polarized intensity, which is not found in FIR, pointing to a small-scale dynamo-driven B-field amplification scenario. This work shows that multiwavelength polarization observations are key to disentangling the interlocked relation between star formation, magnetic fields, and gas kinematics in the multiphase ISM. * The SOFIA Legacy Group for Magnetic Fields in Galaxies software repository is available at https://github.com/galmagfields/hawc via the official project website, http://galmagfields.com/, and Zenodo/GitHub, https://doi.org/10.5281/zenodo.5116134.

Keywords: spiral galaxies; extragalactic magnetic fields; magnetic fields; star formation; molecular clouds; far infrared astronomy; radio astronomy; polarimetry
Analysis of Solar Diameter Measurements Made at the Basilica of San Petronio during and after the Maunder Minimum

A series of measurements of the solar diameter taken in the meridian line of the Basilica of San Petronio (Bologna, Italy) between 1655 and 1736 has been analyzed. This series is of interest because the measurement period includes the Maunder Minimum (1645-1715; hereafter MM) when solar activity was abnormally low. Some authors have suggested an increase of the solar diameter during the MM. Trying to detect these changes, statistical analyses comparing measurements taken in San Petronio during the MM (1655-1715) and other ones taken in a subsequent period (1716-1736) have been performed. Mann-Whitney U tests and Student's t-tests indicate that there is no statistically significant difference in the medians and averages of the solar diameter in both periods. In fact, we have found differences around 0"6 in the medians and the averages, which are below the mean accuracy of the instrument. Therefore, we conclude that there is no difference between the solar diameter value measured during the MM (1655-1715) and that for the subsequent period 1716-1736. This implies that there has not been an increase in the solar diameter of several arcseconds during the MM as has been speculated by some authors.

Keywords: astronomy databases; solar radius; maunder minimum
Modeling Radio Recombination in MWC 349A. I. Saturation Properties

Strong nonlocal thermodynamic equilibrium recombination line emission from the envelope of MWC 349A has been studied observationally and theoretically and has been used to derive information about the physical and kinematic properties of the circumstellar environment around this object. In this paper, we construct a detailed model of radiative transfer of the commonly observed maser lines H26α and H30α in MWC 349A, specifically taking into account the effect of maser saturation. The envelope is modeled as a combination of an ionized Keplerian rotating disk and a disk wind expanding at a velocity of 60 km s-1. Our modeling results show that millimeter-line H26α is significantly affected by the saturation effect. The line intensity is predicted to be greatly reduced in comparison with previous models which ignore the saturation effect. The H30α maser is predicted to be unsaturated. Our model shows that the predicted intensity and line shape are in agreement with observations. The predicted position-velocity diagrams are also consistent with observations and the interpretation that the H26α maser appears at smaller radii in comparison to the H30α maser. We also emphasize that the wind component is important in shaping the line profiles of the recombination masers.

Keywords: astrophysical masers
Migration Traps as the Root Cause of the Kepler Dichotomy

It is often assumed that the "Kepler dichotomy"-the apparent excess of planetary systems with a single detected transiting planet in the Kepler catalog-reflects an intrinsic bimodality in the mutual inclinations of planetary orbits. After conducting 600 simulations of planet formation followed by simulated Kepler observations, we instead propose that the apparent dichotomy reflects a divergence in the amount of migration and the separation of planetary semimajor axes into distinct "clusters." We find that our simulated high-mass systems migrate rapidly, bringing more planets into orbital periods of less than 200 days. The outer planets are often caught in a migration trap-a range of planet masses and locations in which a dominant corotation torque prevents inward migration-which splits the system into two clusters. If clusters are sufficiently separated, the inner cluster remains dynamically cold, leading to low mutual inclinations and a higher probability of detecting multiple transiting planets. Conversely, our simulated low-mass systems typically bring fewer planets within 200 days, forming a single cluster that quickly becomes dynamically unstable, leading to collisions and high mutual inclinations. We propose an alternative explanation for the apparent Kepler dichotomy in which migration traps during formation lead to fewer planets within the Kepler detection window, and where mutual inclinations play only a secondary role. If our scenario is correct, then Kepler's Systems with Tightly packed Inner Planets are a sample of planets that escaped capture by corotation traps, and their sizes may be a valuable probe into the structure of protoplanetary disks.

Keywords: planet formation; planetary system formation; protoplanetary disks; dynamical evolution; exoplanet migration
HaloSat Observation of the Virgo Intracluster Medium

Contained within a galaxy cluster, the Intracluster Medium is comprised of hot, X-ray emitting material between member galaxies. The nearest (~16.1 Mpc) large galaxy cluster is Virgo. Virgo covers an approximately 12° diameter field, making it challenging to observe in its entirety. The HaloSat satellite utilized a 7° radius field of view to obtain the first full cluster observations since 1994. We then fit the cluster spectra with a plasma emission model of fixed metallicity. Our best fit temperature is kT = 1.39 ± 0.11 keV. We report a cluster luminosity of 5.8 ± 0.7 × 1043 erg s-1 and an emission measure of 5.8 ± 0.6 × 1066 cm-3.

Keywords: virgo cluster; galaxy clusters; intracluster medium; x-ray astronomy; x-ray sources
Deep XMM-Newton Observations Reveal the Origin of Recombining Plasma in the Supernova Remnant W44

Recent X-ray studies have revealed overionized recombining plasmas in a dozen mixed-morphology (MM) supernova remnants (SNRs). However, the physical process of the overionization has not yet been fully understood. Here we report on spatially resolved spectroscopy of X-ray emission from W44, one of the overionized MM SNRs, using XMM-Newton data from deep observations, with the aim of clarifying the physical origin of the overionization. We find that combination of low electron temperature and low recombination timescale is achieved in the region interacting with dense molecular clouds. Moreover, a clear anticorrelation between the electron temperature and the recombination timescale is obtained from each of the regions with and without the molecular clouds. The results are well explained if the plasma was overionized by rapid cooling through thermal conduction with the dense clouds hit by the blast wave of W44. Given that a few other overionized SNRs show evidence for adiabatic expansion as the major driver of the rapid cooling, our new result indicates that both processes can contribute to overionization in SNRs, with the dominant channel depending on the evolutionary stage.

Keywords: supernova remnants; molecular clouds; x-ray astronomy; plasma astrophysics
Network of Star Formation: Fragmentation Controlled by Scale-dependent Turbulent Pressure and Accretion onto the Massive Cores Revealed in the Cygnus-X GMC Complex

Molecular clouds have complex density structures produced by processes including turbulence and gravity. We propose a triangulation-based method to dissect the density structure of a molecular cloud and study the interactions between dense cores and their environments. In our approach, a Delaunay triangulation is constructed, which consists of edges connecting these cores. Starting from this construction, we study the physical connections between neighboring dense cores and the ambient environment in a systematic fashion. We apply our method to the Cygnus-X massive GMC complex and find that the core separation is related to the mean surface density by ${{\rm{\Sigma }}}_{\mathrm{edge}}\propto {l}_{\mathrm{core}}^{-0.28}$ , which can be explained by fragmentation controlled by a scale-dependent turbulent pressure (where the pressure is a function of scale, e.g., p ~ l2/3). We also find that the masses of low-mass cores ( ${M}_{\mathrm{core}}\lt 10\,{M}_{\odot }$ ) are determined by fragmentation, whereas massive cores ( ${M}_{\mathrm{core}}\gt 10\,{M}_{\odot }$ ) grow mostly through accretion. The transition from fragmentation to accretion coincides with the transition from a log-normal core mass function (CMF) to a power-law CMF. By constructing surface density profiles measured along edges that connect neighboring cores, we find evidence that the massive cores have accreted a significant fraction of gas from their surroundings and thus depleted the gas reservoir. Our analysis reveals a picture where cores form through fragmentation controlled by scale-dependent turbulent pressure support, followed by accretion onto the massive cores, and the method can be applied to different regions to achieve deeper understandings in the future.

Keywords: star formation; computational methods; gravitational collapse; stellar accretion
Curvature of Magnetic Field and Its Role on Plasma in Turbulent Magnetosheath

This study presents statistical features of magnetic field curvature in the magnetosheath region. Two sets of high-quality field and plasma data measured by the Magnetospheric Multiscale mission are analyzed by the multiple-point analysis method. The results include the following: (a) The probability distribution function (PDF) of the curvature exhibits two different power laws consistent with previous studies; the PDF of small curvatures depends on the plasma condition and the PDF of large curvatures shows better agreement. (b) The data validate the derived relation between the current density and the guiding center current as well as the diamagnetic current. (c) The acceleration due to curvature drifts in the perpendicular direction occurs when κ/κ rms is larger than 1, which is a potential mechanism for anisotropic distribution of plasma pressure at large curvatures.

Keywords: space plasmas
The Gravitational Imprint of an Interior-Orbital Resonance in Jupiter-Io

At mid-mission perijove 17, NASA's Juno mission has revealed a 7σ discrepancy between Jupiter's observed high-degree tidal response and the theoretical equilibrium tidal response, namely, the Love number k 42. Here we propose an interpretation for this puzzling disagreement based on an interior-orbital resonance between internal gravity waves trapped in Jupiter's dilute core and the orbital motion of Io. We use simple Jupiter models to calculate a fractional correction Δk 42 to the equilibrium tidal response that comes from the dynamical tidal response of a g-mode trapped in Jupiter's dilute core. Our results suggest that an extended dilute core (r ≳ 0.7 R J) produces an interior-orbital resonance with Io that modifies Jupiter's tidal response in Δk 42 ~ -11%, allowing us to fit Juno's k 42. In our proposed self-consistent scenario, Jupiter's dilute core evolves in resonant locking with Io's orbital migration, which allows the interior-orbital resonance to persist over geological timescales. This scenario requires a dilute core that becomes smoother or shrinks over time, together with a ${}_{4}^{2}{g}_{1}$ mode (ℓ, m, n = 4, 2, 1) with resonant tidal dissipation reaching Q 4 ~ 1000. Jupiter's dilute core evolution path and the dissipation mechanism for the resonant ${}_{4}^{2}{g}_{1}$ mode are uncertain and motivate future analysis. No other alternative exists so far to explain the 7σ discrepancy in Juno k 42. Our proposed interior-orbital resonance can be tested by Juno observations of k 42 tides raised on Jupiter by Europa, as obtained at the end of the extended mission (mid-2025), and by future seismological observations of Jupiter's ${}_{4}^{2}{g}_{1}$ mode oscillation frequency.

Keywords: solar system gas giant planets; planetary cores; planetary interior
A Modeling Investigation for Solar Flare X-Ray Stereoscopy with Solar Orbiter/STIX and Earth-orbiting Missions

The Spectrometer/Telescope for Imaging X-rays (STIX) on board Solar Orbiter (SolO) provides a unique opportunity to systematically perform stereoscopic X-ray observations of solar flares with current and upcoming X-ray missions at Earth. These observations will produce the first reliable measurements of hard X-ray (HXR) directivity in decades, providing a new diagnostic of the flare-accelerated electron angular distribution and helping to constrain the processes that accelerate electrons in flares. However, such observations must be compared to modeling, taking into account electron and X-ray transport effects and realistic plasma conditions, all of which can change the properties of the measured HXR directivity. Here, we show how HXR directivity, defined as the ratio of X-ray spectra at different spacecraft viewing angles, varies with different electron and flare properties (e.g., electron angular distribution, highest-energy electrons, and magnetic configuration), and how modeling can be used to extract these typically unknown properties from the data. Finally, we present a preliminary HXR directivity analysis of two flares, observed by the Fermi Gamma-ray Burst Monitor and SolO/STIX, demonstrating the feasibility and challenges associated with such observations, and how HXR directivity can be extracted by comparison with the modeling presented here.

Keywords: the sun; solar flares; solar x-ray flares; solar energetic particles; solar atmosphere; active solar corona; active solar chromosphere
Deep-learning Reconstruction of Sunspot Vector Magnetic Fields for Forecasting Solar Storms

Solar magnetic activity produces extreme solar flares and coronal mass ejections, which pose grave threats to electronic infrastructure and can significantly disrupt economic activity. It is therefore important to appreciate the triggers of explosive solar activity and develop reliable space weather forecasting. Photospheric vector magnetic field data capture sunspot magnetic field complexity and can therefore improve the quality of space weather prediction. However, state-of-the-art vector field observations are consistently only available from Solar Dynamics Observatory/Helioseismic and Magnetic Imager (HMI) since 2010, with most other current and past missions and observational facilities, such as Global Oscillations Network Group (GONG), only recording line-of-sight (LOS) fields. Here, using an inception-based convolutional neural network (CNN), we reconstruct HMI sunspot vector field features from LOS magnetograms of HMI and GONG with high fidelity (~90% correlation) and sustained flare forecasting accuracy. We rebuild vector field features during the 2003 Halloween storms, for which only LOS field observations are available, and the CNN-estimated electric current helicity accurately captures the observed rotation of the associated sunspot prior to the extreme flares, showing a striking increase. Our study thus paves the way for reconstructing three solar cycles worth of vector field data from past LOS measurements, which are of great utility in improving space weather forecasting models and gaining new insights about solar activity.

Keywords: solar activity; solar active region magnetic fields
The Featureless Transmission Spectra of Two Super-puff Planets

The Kepler mission revealed a class of planets known as "super-puffs," with masses only a few times larger than Earth's but radii larger than Neptune, giving them very low mean densities. All three of the known planets orbiting the young solar-type star Kepler 51 are super-puffs. The Kepler 51 system thereby provides an opportunity for a comparative study of the structures and atmospheres of this mysterious class of planets, which may provide clues about their formation and evolution. We observed two transits each of Kepler 51b and 51d with the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope. Combining new WFC3 transit times with reanalyzed Kepler data and updated stellar parameters, we confirmed that all three planets have densities lower than 0.1 g cm-3. We measured the WFC3 transmission spectra to be featureless between 1.15 and 1.63 μm, ruling out any variations greater than 0.6 scale heights (assuming a H/He-dominated atmosphere), thus showing no significant water absorption features. We interpreted the flat spectra as the result of a high-altitude aerosol layer (pressure <3 mbar) on each planet. Adding this new result to the collection of flat spectra that have been observed for other sub-Neptune planets, we find support for one of the two hypotheses introduced by Crossfield & Kreidberg, that planets with cooler equilibrium temperatures have more high-altitude aerosols. We strongly disfavor their other hypothesis that the H/He mass fraction drives the appearance of large-amplitude transmission features.

Keywords: atmospheric composition; exoplanet atmospheres; exoplanet structure; exoplanet evolution; transit timing variation method; transits; hubble space telescope; exoplanets
High-altitude Magnetospheric Emissions from Two Pulsars

We discover three new weak pulse components in two known pulsars, one in PSR J0304+1932 and two in PSR J1518+4904. These components are emitted about halfway between the main emission beam and the interpulse beam (beam from the opposite pole). They are separated from their main pulse peak by 99° ± 3° for J0304+1932 and 123.°6 ± 0.°7 (leading) and 93° ± 0.°4 (trailing) for J1518+4904. Their peak-intensity ratios to main pulses are ~ 0.06% for J0304+1932 and ~0.17% and ~0.83% for J1518+4904. We also analyzed the flux fluctuations and profile variations of the emissions for the two pulsars. The results show correlations between the weak pulses and their main pulses, indicating that these emissions come from the same pole. We estimated the emission altitude of these weak pulses and derived a height of about half of the pulsar's light-cylinder radius. These pulse components are a unique sample of high-altitude emissions from pulsars, and challenge the current pulsar emission models.

Keywords: radio pulsars
A New Population of Mid-infrared-selected Tidal Disruption Events: Implications for Tidal Disruption Event Rates and Host Galaxy Properties

Most tidal disruption events (TDEs) are currently found in time-domain optical and soft X-ray surveys, both of which are prone to significant obscuration. The infrared (IR), however, is a powerful probe of dust-enshrouded environments; hence, we recently performed a systematic search of NEOWISE mid-IR data for nearby, obscured TDEs within roughly 200 Mpc. We identified 18 TDE candidates in galactic nuclei, using difference imaging to uncover nuclear variability among significant host galaxy emission. These candidates were selected based on the following IR light-curve properties: (1) L W2 ≳ 1042 erg s‑1 at peak; (2) fast rise, followed by a slow, monotonic decline; (3) no significant prior variability; and (4) no evidence for active galactic nucleus (AGN) activity in Wide-field Infrared Survey Explorer (WISE) colors. The majority of these sources showed no variable optical counterpart, suggesting that optical surveys indeed miss numerous obscured TDEs. Using narrow-line ionization levels and variability arguments, we identified six sources as possible underlying AGN, yielding a total of 12 TDEs in our gold sample. This gold sample yields a lower limit on the IR-selected TDE rate of (2.0 ± 0.3) × 10‑5 galaxy‑1 yr‑1 ((1.3 ± 0.2) × 10‑7 Mpc‑3 yr‑1), which is comparable to optical and X-ray TDE rates. The IR-selected TDE host galaxies do not show a green valley overdensity nor as a preference for quiescent, Balmer strong galaxies, which are both overrepresented in optical and X-ray TDE samples. This IR-selected sample represents a new population of dusty TDEs that have historically been missed by optical and X-ray surveys and helps alleviate tensions between observed and theoretical TDE rates and the so-called missing energy problem.

Keywords: supermassive black holes; accretion; transient sources; time domain astronomy; tidal disruption
Core-collapse Supernovae: From Neutrino-driven 1D Explosions to Light Curves and Spectra

We present bolometric and broadband light curves and spectra for a suite of core-collapse supernova models exploded self-consistently in spherical symmetry within the PUSH framework. We analyze broad trends in these light curves and categorize them based on morphology. We find that these morphological categories relate simply to the progenitor radius and mass of the hydrogen envelope. We present a proof-of-concept sensitive-variable analysis, indicating that an important determining factor in the properties of a light curve within a given category is 56Ni mass. We follow spectra from the photospheric to the nebular phase. These spectra show characteristic iron-line blanketing at short wavelengths and Doppler-shifted Fe II and Ti II absorption lines. To enable this analysis, we develop a first-of-its-kind pipeline from a massive progenitor model, through a self-consistent explosion in spherical symmetry, to electromagnetic counterparts. This opens the door to more detailed analyses of the collective properties of these observables. We provide a machine-readable database of our light curves and spectra online at go.ncsu.edu/astrodata.

Keywords: core-collapse supernovae; type ii supernovae; type ib supernovae; type ic supernovae; light curves; light curve classification; transient sources; time domain astronomy; high energy astrophysics; radiative transfer; radiative transfer simulations