Sazuna/UAT_keywords huggingface dataset:
Modeling the Solar Wind during Different Phases of the Last Solar Cycle. We describe our first attempt to systematically simulate the solar wind during different phases of the last solar cycle with the Alfvén Wave Solar atmosphere Model (AWSoM) developed at the University of Michigan. Key to this study is the determination of the optimal values of one of the most important input parameters of the model, the Poynting flux parameter, which prescribes the energy flux passing through the chromospheric boundary of the model in the form of Alfvén wave turbulence. It is found that the optimal value of the Poynting flux parameter is correlated with the area of the open magnetic field regions with the Spearman's correlation coefficient of 0.96 and anticorrelated with the average unsigned radial component of the magnetic field with the Spearman's correlation coefficient of ‑0.91. Moreover, the Poynting flux in the open field regions is approximately constant in the last solar cycle, which needs to be validated with observations and can shed light on how Alfvén wave turbulence accelerates the solar wind during different phases of the solar cycle. Our results can also be used to set the Poynting flux parameter for real-time solar wind simulations with AWSoM.

Keywords: Solar cycle, Magnetohydrodynamics, Solar wind
Detection of Dust in High-velocity Cloud Complex C-Enriched Gas Accreting onto the Milky Way. We present the detection of dust depletion in Complex C, a massive, infalling, low-metallicity high-velocity cloud in the northern Galactic hemisphere that traces the ongoing accretion of gas onto the Milky Way. We analyze a very high signal-to-noise Hubble Space Telescope Cosmic Origins Spectrograph spectrum of active galactic nucleus (AGN) Mrk 817 formed by coadding 165 individual exposures taken under the AGN STORM 2 program, allowing us to determine dust-depletion patterns in Complex C at unprecedented precision. By fitting Voigt components to the O I, S II, N I, Si II, Fe II, and Al II absorption and applying ionization corrections from customized CLOUDY photoionization models, we find subsolar elemental abundance ratios of [Fe/S] = -0.42 ± 0.08, [Si/S] = -0.29 ± 0.05, and [Al/S] = -0.53 ± 0.08. These ratios indicate the depletion of Fe, Si, and Al into dust grains, since S is mostly undepleted. The detection of dust provides an important constraint on the origin of Complex C, as dust grains indicate the gas has been processed through galaxies, rather than being purely extragalactic. We also derive a low metallicity of Complex C of [S/H] = -0.51 ± 0.16 (≈31% solar), confirming earlier results from this sight line. We discuss origin models that could explain the presence of dust in Complex C, including Galactic fountain models, tidal stripping from the Magellanic Clouds or other satellite galaxies, and precipitation of coronal gas onto dust-bearing "seed" clouds. * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated with program 16196.

Keywords: Interstellar dust, High-velocity clouds, Chemical abundances, Ultraviolet astronomy, Circumgalactic medium
A Candidate Runaway Supermassive Black Hole Identified by Shocks and Star Formation in its Wake. The interaction of a runaway supermassive black hole (SMBH) with the circumgalactic medium (CGM) can lead to the formation of a wake of shocked gas and young stars behind it. Here we report the serendipitous discovery of an extremely narrow linear feature in Hubble Space Telescope (HST) Advanced Camera for Surveys images that may be an example of such a wake. The feature extends 62 kpc from the nucleus of a compact star-forming galaxy at z = 0.964. Keck Low-resolution Imaging Spectrometer spectra show that the [O III]/Hβ ratio varies from ~1 to ~10 along the feature, indicating a mixture of star formation and fast shocks. The feature terminates in a bright [O III] knot with a luminosity of ≈1.9 × 1041 erg s-1. The stellar continuum colors vary along the feature and are well fit by a simple model that has a monotonically increasing age with the distance from the tip. The line ratios, colors, and overall morphology are consistent with an ejected SMBH moving through the CGM at a high speed while triggering star formation. The best-fit time since ejection is ~39 Myr, and the implied velocity is v BH ~ 1600 km s-1. The feature is not perfectly straight in the HST images, and we show that the amplitude of the observed spatial variations is consistent with the runaway SMBH interpretation. Opposite the primary wake is a fainter and shorter feature, marginally detected only in [O III] and the rest-frame far-ultraviolet. This feature may be shocked gas behind a binary SMBH that was ejected at the same time as the SMBH that produced the primary wake.

Keywords: Supermassive black holes
Ultrafast Variability in AGN Jets: Intermittency and Lighthouse Effect. Gamma-ray flares from active galactic nuclei (AGNs) show substantial variability on ultrafast timescales (i.e., shorter than the light-crossing time of the AGN's supermassive black hole). We propose that ultrafast variability is a by-product of the turbulent dissipation of the jet Poynting flux. Due to the intermittency of the turbulent cascade, the dissipation is concentrated in a set of reconnecting current sheets. Electrons energized by reconnection have a strong pitch-angle anisotropy, i.e., their velocity is nearly aligned with the guide magnetic field. Then each current sheet produces a narrow radiation beam, which dominates the emission from the whole jet when it is directed toward the observer. The ultrafast variability is set by the light-crossing time of a single current sheet, which is much shorter than the light-crossing time of the whole emission region. The predictions of our model are (i) the bolometric luminosity of ultrafast AGN flares is dominated by the inverse Compton (IC) emission as the lower-energy synchrotron emission is suppressed due to the pitch-angle anisotropy; (ii) if the observed luminosity includes a nonflaring component, the variations of the synchrotron luminosity have a small amplitude; and (iii) the synchrotron and IC emission are less variable at lower frequencies, as the cooling time of the radiating particles exceeds the light-crossing time of the current sheet. Simultaneous multiwavelength observations of ultrafast AGN flares can test these predictions.

Keywords: Blazars, Galaxy jets, Gamma-rays
Axion-mediated Transport of Fast Radio Bursts Originating in Inner Magnetospheres of Magnetars. Among magnetar models of fast radio bursts (FRBs), there is ongoing debate about whether the site of coherent radio emission lies within or beyond the light cylinder. We propose a mechanism by which FRBs produced near the magnetar surface are transported out of the magnetosphere by axions, which are hypothetical particles that couple to photons. If the emission site hosts strong accelerating electric fields, a considerable fraction of the FRB energy budget is converted to an axion burst. Once produced, the axion burst free streams out of the magnetosphere due to the rapidly decreasing magnetic field. The burst may escape through either the open or closed magnetosphere while retaining the temporal signature of the original FRB. In the wind region, axions resonantly excite ordinary (O) modes that escape as the plasma density decreases. The radio efficiency of this mechanism satisfies energetics constraints from FRB 121102 for axion-photon coupling strengths that have not been excluded by other astrophysical probes.

Keywords: Rotation powered pulsars, Cold dark matter, Plasma astrophysics, Radio transient sources, Magnetars, Particle astrophysics, Radio pulsars
A Comprehensive Model of Morphologically Realistic Cosmic Dust Particles: An Application to Mimic the Unusual Polarization Properties of the Interstellar Comet 2I/Borisov. The cosmic dust particles found in space are mainly porous aggregates of smaller grains. Theoretically, these aggregates are replicated using fractal geometry, assuming a cluster of spheres. Although the light scattering response of cosmic dust aggregates has been thoroughly studied using clusters of spherical grains in the past few decades, the effect of irregularities on the surface of each grain in an entire aggregate has mostly been neglected. We introduce, for the first time, a visually realistic cosmic dust model that incorporates a mixture of rough fractal aggregates (RFA) and agglomerated debris (Solids) to replicate the unusual polarization-phase curve observed in the case of the interstellar comet 2I/Borisov at multiple wavelengths. The authenticity of the RFA structures has been verified by replicating light scattering results of circumstellar dust analogs from the Granada Amsterdam Light Scattering Database. We demonstrate that the light scattering response from the RFA structures has a very close resemblance to the experimental values. Finally, we model the observed polarization-phase curve of the interstellar comet 2I/Borisov using a mixture of RFA and solid particles. The best-fit data indicate the presence of a higher percentage of porous RFA structures (80%) owing to the fact that the comet carries a higher percentage of small and highly porous pristine cosmic dust particles. Further, the model indicates that the unusually steep polarimetric slope and the high dust-to-gas ratio in newer comets are mainly due to a higher porous-to-compact ratio.

Keywords: Interstellar objects, Radiative transfer simulations, Comets, Polarimetry, Coma dust
AGN STORM 2. III. A NICER View of the Variable X-Ray Obscurer in Mrk 817. The AGN STORM 2 Collaboration targeted the Seyfert 1 galaxy Mrk 817 for a year-long multiwavelength, coordinated reverberation mapping campaign including Hubble Space Telescope, Swift, XMM-Newton, NICER, and ground-based observatories. Early observations with NICER and XMM revealed an X-ray state 10 times fainter than historical observations, consistent with the presence of a new dust-free, ionized obscurer. The following analysis of NICER spectra attributes variability in the observed X-ray flux to changes in both the column density of the obscurer by at least one order of magnitude (N H ranges from ${2.85}_{-0.33}^{+0.48}\times {10}^{22}\,{\mathrm{cm}}^{-2}$ to ${25.6}_{-3.5}^{+3.0}\times {10}^{22}\,{\mathrm{cm}}^{-2}$ ) and the intrinsic continuum brightness (the unobscured flux ranges from 10-11.8 to 10-10.5 erg s-1 cm-2). While the X-ray flux generally remains in a faint state, there is one large flare during which Mrk 817 returns to its historical mean flux. The obscuring gas is still present at lower column density during the flare, but it also becomes highly ionized, increasing its transparency. Correlation between the column density of the X-ray obscurer and the strength of UV broad absorption lines suggests that the X-ray and UV continua are both affected by the same obscuration, consistent with a clumpy disk wind launched from the inner broad-line region.

Keywords: Accretion, Black hole physics, Active galactic nuclei, X-ray active galactic nuclei
Detection and Seismic Study of Gravity and Rossby Mode Pulsations in Four Contact Binaries. We report the detection of gravity (g) and Rossby (r) mode pulsations of four short-period eclipsing binaries, KIC 5439790, KIC 7501230, KIC 9350889, and KIC 9453192 based on the 4 yr Kepler high-precision photometry. Light-curve modeling reveals that the four binaries are all contact systems with small mass ratios. We study the short-term variability of the light-curve residuals after the removal of the binary model and attribute them to the g- and r-mode pulsations that stem from the primary stars. By introducing a new criterion, we attempt to identify period-spacing patterns in the Fourier spectra, which refers to the determination of the rotation rates of stellar interior and envelope as well as the asymptotic period spacings of the pulsating stars. It is interesting to find that the rotation rates of the stellar envelopes are all nearly equal to the orbits. The near-core rotations, however, are significantly slower by about 10%. Based on the derived asymptotic period spacings, stellar parameters were constrained from asteroseismology models. The pulsators are revealed to be evolved main-sequence stars with high metallicities.

Keywords: Asteroseismology, Contact binary stars
New Aspects of Energy Conversion in Magnetic Island Dynamics: Particle-in-cell Simulation of Multiple Island Coalescence and MMS Observations. Coalescence of multiple magnetic islands is recognized as an effective process to energize particles during magnetic reconnection, while its energy conversion process still remains unclear. Here, a two-dimensional fully kinetic simulation of multiple island coalescence with a small reconnection guide field is studied. In the analysis of energy conversion within a magnetic island, the dot product of ${{\boldsymbol{V}}}_{e}\cdot \left({\boldsymbol{j}}\times {\boldsymbol{B}}\right)={w}_{1}$ is a useful quantity to compare with j · E = w 2, since the average work done by the Lorentz force on the circulating particles is negligible in the island and ${w}_{2}-{w}_{1}={\boldsymbol{j}}\cdot \left({\boldsymbol{E}}+{{\boldsymbol{V}}}_{e}\times {\boldsymbol{B}}\right)={\boldsymbol{j}}\cdot {{\boldsymbol{E}}}^{{\prime} }={w}_{3}$ . A bipolar pattern of w 1 is found at a secondary island when the electrons are in circular motion inside the island. Significant energy dynamo (w 3 &lt; 0) resulting from j ∥ E ∥ is found at the secondary island, which has not been reported before, where the parallel electric field E ∥ is highly correlated with w 3. Moreover, significant energy dissipation (w 3 &gt; 0) due to ${{\boldsymbol{j}}}_{\perp }\cdot {{\boldsymbol{E}}}_{\perp }^{{\prime} }$ is seen in the merging region between two coalescing islands. Both types of energy conversions are accompanied by enhancements in j ∥ and the parallel electron temperature T  e∥. Three ion-scale magnetic islands (FR1, FR2, and FR3) observed by the Magnetospheric Multiscale spacecraft are compared favorably with the simulated signatures of energy dynamo and dissipation of an evolving secondary island. In particular, FR1 displayed a similar energy dynamo signature as that simulated in an early stage of the secondary island. FR2 and FR3 showed a dominant ${{\boldsymbol{j}}}_{\perp }\cdot {{\boldsymbol{E}}}_{\perp }^{{\prime} }$ energy conversion similar to that obtained in a later stage of the secondary island.

Keywords: Interplanetary physics
Validation and Testing of the CROBAR 3D Coronal Reconstruction Method with a MURaM Simulation. I report on validation and testing of a novel 3D reconstruction method than can obtain coronal plasma properties from a single snapshot perspective. I first reported on the method in 2021, and I have since named it the Coronal Reconstruction Onto B-Aligned Regions (CROBAR) method. The testing and validation are carried out with a cube from a MURaM 3D MHD simulation, which affords a coronal-like "ground truth" against which the reconstruction method can be applied and compared. I find that the method does quite well, recovering the "coronal veil"-like features recently reported from the MURaM simulations and allaying concerns that these features would thwart recovery of valid 3D coronal structure from a limited number of perspectives. I also find that a second perspective between ~45° and 90° does significantly improve the reconstructions. Two distinct channels with soft-X-ray-like temperature response (peaking above 5 MK) would suffice for CROBAR's optically thin observables A suite of AIA-like EUV passbads, with good coverage in the 3-8 MK range, is also well suited to CROBAR.

Keywords: Astronomy data modeling, Solar extreme ultraviolet emission, Solar coronal loops, Astronomy data analysis, Solar x-ray emission, Computational methods, Solar corona, Solar magnetic fields, Active solar corona
Toward Robust Atmospheric Retrieval on Cloudy L Dwarfs: the Impact of Thermal and Abundance Profile Assumptions. Constraining L dwarf properties from their spectra is challenging. Near-infrared (NIR) spectra probe a limited range of pressures, while many species condense within their photospheres. Condensation creates two complexities: gas-phase species "rain out" (decreasing in abundances by many orders of magnitude) and clouds form. We designed tests using synthetic data to determine the best approach for retrieving L dwarf spectra, isolating the challenges in the absence of cloud opacity. We conducted atmospheric retrievals on synthetic cloud-free L dwarf spectra derived from the Sonora Bobcat models at SpeX resolution using a variety of thermal and chemical abundance profile parameterizations. For objects hotter than L5 (T eff ~ 1700 K), the limited pressure layers probed in the NIR are mostly convective; parameterized pressure-temperature (PT) profiles bias results and free, unsmoothed profiles should be used. Only when many layers both above and below the radiative-convective boundary are probed can parameterized profiles provide accurate results. Furthermore, a nonuniform abundance profile for FeH is needed to accurately retrieve bulk properties of early-to-mid L dwarfs. Nonuniform prescriptions for other gases in NIR retrievals may also be warranted near the L/T transition (CH4) and early Y dwarfs (Na and K). We demonstrate the utility of using realistic, self-consistent models to benchmark retrievals and suggest how they can be used in the future.

Keywords: Brown dwarfs, Atmospheric structure, L dwarfs, Planetary atmospheres, Atmospheric composition, Stellar atmospheres
Chemical Modeling of Orion Nebula Cluster Disks: Evidence for Massive, Compact Gas Disks with Interstellar Gas-to-dust Ratios. The stellar cluster environment is expected to play a central role in the evolution of circumstellar disks. We use thermochemical modeling to constrain the dust and gas masses, disk sizes, UV and X-ray radiation fields, viewing geometries, and central stellar masses of 20 class II disks in the Orion Nebula Cluster (ONC). We fit a large grid of disk models to 350 GHz continuum, CO J = 3 - 2, and HCO+ J = 4 - 3 Atacama Large Millimeter/submillimeter Array observations of each target, and we introduce a procedure for modeling interferometric observations of gas disks detected in absorption against a bright molecular cloud background. We find that the ONC disks are massive and compact, with typical radii &lt;100 au, gas masses ≥10-3 M ⊙, and gas-to-dust ratios ≥100. The interstellar‑medium‑like gas-to-dust ratios derived from our modeling suggest that compact, externally irradiated disks in the ONC are less prone to gas-phase CO depletion than the massive and extended gas disks that are commonly found in nearby low-mass star-forming regions. The presence of massive gas disks indicates that external photoevaporation may have only recently begun operating in the ONC; though it remains unclear whether other cluster members are older and more evaporated than the ones in our sample. Finally, we compare our dynamically derived stellar masses with the stellar masses predicted from evolutionary models and find excellent agreement. Our study has significantly increased the number of dynamical mass measurements in the mass range ≤0.5 M ⊙, demonstrating that the ONC is an ideal region for obtaining large samples of dynamical mass measurements toward low-mass M-dwarfs.

Keywords: Proplyds, Young star clusters, Young stellar objects, Pre-main sequence stars, Protoplanetary disks, Circumstellar disks, Submillimeter astronomy, Radio astronomy, Planet formation
Transient Stellar Collisions as Multimessenger Probes: Nonthermal, Gravitational-wave Emission and the Cosmic Ladder Argument. In dense stellar clusters like galactic nuclei and globular clusters, stellar densities are so high that stars might physically collide with each other. In galactic nuclei the energy and power output can be close to, and even exceed, those from supernovae events. We address the event rate and the electromagnetic characteristics of collisions of main-sequence stars (MS) and red giants (RGs). We also investigate the case in which the cores form a binary and emit gravitational waves. In the case of RGs, this is particularly interesting because the cores are degenerate. We find that MS event rate can be as high as tens per year, and that of RGs 1 order of magnitude larger. The collisions are powerful enough to mimic supernovae or tidal disruptions events. We find Zwicky Transient Facility observational data that seem to exhibit the features we describe. The cores embedded in the gaseous debris experience a friction force that has an impact on the chirping mass of the gravitational wave. As a consequence, the two small cores in principle mimic two supermassive black holes merging. However, their evolution in frequency along with the precedent electromagnetic burst and the ulterior afterglow are efficient tools to reveal the impostors. In the particular case of RGs, we derive the properties of the degenerate He cores and their H-burning shells to analyze the formation of the binaries. The merger is such that it can be misclassified with SN Ia events. Because the masses and densities of the cores are so dissimilar in values depending on their evolutionary stage, the argument about standard candles and cosmic ladder should be reevaluated.

Keywords: Gravitational wave sources, High energy astrophysics
Follow-up Survey for the Binary Black Hole Merger GW200224_222234 Using Subaru/HSC and GTC/OSIRIS. The LIGO/Virgo detected a gravitational wave (GW) event, named GW200224_222234 (also known as S200224ca) and classified as a binary-black hole coalescence, on 2020 February 24. Given its relatively small localization skymap (71 deg2 for a 90% credible region; revised to 50 deg2 in GWTC-3), we performed target-of-opportunity observations using the Subaru/Hyper Suprime-Cam (HSC) in the r2 and z bands. Observations were conducted on 2020 February 25 and 28 and March 23, with the first epoch beginning 12.3 hr after the GW detection. The survey covered the highest-probability sky area of 56.6 deg2, corresponding to a 91% probability. This was the first deep follow-up (m  r  ≳ 24, m  z  ≳ 23) for a binary-black hole merger covering &gt;90% of the localization. By performing image subtraction and candidate screening including light-curve fitting with transient templates and examples, we found 22 off-nucleus transients that were not ruled out as the counterparts of GW200224_222234 with our Subaru/HSC data alone. We also performed GTC/OSIRIS spectroscopy of the probable host galaxies for five candidates; two are likely to be located within the 3D skymap, whereas the others are not. In conclusion, 19 transients remain as possible optical counterparts of GW200224_222234; but we could not identify a unique promising counterpart. If there are no counterparts in the remaining candidates, the upper limits of the optical luminosity are $\nu {L}_{\nu }\lt {5.2}_{-1.9}^{+2.4}\times {10}^{41}$ erg s-1 and $\nu {L}_{\nu }\lt {1.8}_{-0.6}^{+0.8}\times {10}^{42}$ erg s-1 in the r2 and z bands, respectively, at ~12 hr after GW detection. We also discuss improvements in the strategies of optical follow-ups for future GW events.

Keywords: Surveys, Gravitational waves, Black holes