Sazuna/UAT_keywords huggingface dataset:
Explosive Ejections Generated by Gravitational Interactions. During the fragmentation and collapse of a molecular cloud, it is expected that it will have close encounters with (proto)stellar objects that can lead to the ejection of a fraction of them as runaway objects. However, the duration and consequences of such encounters are perhaps small enough for there to be no direct evidence of their occurrence. As a first approximation, herein we analytically study the interaction of a massive object that moves at high velocity into a cluster of negligible-mass particles with an initial number density distribution ∝ R-α. We have found that the runaway conditions of the distribution after the encounter are related to the mass and the velocity of the star and the impact parameter of each particle to the stellar object. Then, the cluster particles are gravitationally accelerated by the external approaching star, destroying the cluster, and the dispersion and velocities of the particles have explosive characteristics. We compare this analytical model with several numerical simulations and, finally, apply our results to the Orion fingers in the Orion BN/KL region, which show an explosive outflow that could be triggered by the gravitational interaction of several (proto)stellar objects.

Keywords: Star forming regions, Interstellar dynamics, Interstellar medium
Boundary Conditions at the Heliospheric Termination Shock with Pickup Ions. In a collisionless shock the directed flow energy is converted mainly in thermal energy of the plasma species. At the termination shock (TS) a substantial portion of energy goes into heating of pickup ions (PUIs), while heating of the solar wind protons (SW) is weaker than it would be without PUI. Heating of both species is nonadiabatic. Downstream pressure of the mixture is determined by conservation laws for the whole mixture. SW heating is sensitive to the details of the shock front, while heating of PUI is not. The profile is an analytical approximation of the observed TS. Here the downstream temperature and pressure of PUIs are obtained for the first time using test particle analysis in a model shock profile for various magnetic compression ratios and shock angles. The profile is an analytical approximation of the observed TS. The results of the analysis are used in the pressure balance equation and the corresponding SW heating is estimated. The analysis is supported by full particle simulations, except for the SW heating that was not studied using test particle data due to its apparent dependence on fine structure of the shock front.

Keywords: Shocks, Interplanetary shocks, Heliosphere, Termination shock
The Masses of Supernova Remnant Progenitors in NGC 6946. We constrained the progenitor masses for 169 supernova remnants (SNRs), eight historically observed supernovae (SNe), and the black hole formation candidate in NGC 6946, finding that they are consistent with originating from a standard initial mass function. Additionally, there were 16 remnants that showed no sign of nearby star formation consistent with a core-collapse SN, making them good Type Ia candidates. Using Hubble Space Telescope broadband imaging, we measured the stellar photometry of ACS/WFC fields in the F435W, F555W, F606W, and F814W filters, as well as WFC3/UVIS fields in F438W, F606W, and F814W. We then fitted this photometry with stellar evolutionary models to determine the ages of the young populations present at the positions of the SNRs and SNe. We then inferred a progenitor mass probability distribution from the fitted age distribution. For 37 SNRs, we tested how different filter combinations affected the inferred masses. We find that filters sensitive to Hα, [N II], and [S II] gas emission can bias mass estimates for remnants that rely on our technique. Using a Kolmogorov-Smirnov test analysis on our most reliable measurements, we find that the progenitor mass distribution is well matched by a power-law index of $-{2.6}_{-0.6}^{+0.5}$, which is consistent with a standard initial mass function.

Keywords: Stellar populations, Massive stars, Supernovae, Stellar evolution
On the Impulsive Heating of Quiet Solar Corona. The solar corona consists of a million degree Kelvin plasma. A complete understanding of this phenomenon demands the study of quiet Sun (QS) regions. In this work, we study QS regions in the 171 Å, 193 Å, and 211 Å passbands of the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory, by combining the empirical impulsive heating forward model of Pauluhn &amp; Solanki with a machine-learning inversion model that allows uncertainty quantification. We find that there are &amp;approx;2-3 impulsive events per minute, with a lifetime of about 10-20 minutes. Moreover, for all the three passbands, the distribution of power-law slope α peaks above 2. Our exploration of correlations among the frequency of impulsive events and their timescales and peak energy suggests that conduction losses dominate over radiative cooling losses. All these findings suggest that impulsive heating is a viable heating mechanism in QS corona.

Keywords: Quiet sun, Convolutional neural networks, Quiet solar corona
Dynamical Surface Imaging of λ Andromedae. We present temperature maps of RS CVn star λ Andromedae, reconstructed from interferometric data acquired in 2010 and 2011 by the Michigan Infra-Red Combiner instrument at the Center for High Angular Resolution Astronomy Array. To constrain the stellar parameters required for this imaging task, we first modeled the star using our GPU-accelerated code SImulation and Modeling Tool for Optical Interferometry. The stellar surface was then imaged using our open source interferometric imaging code ROTational Image Reconstruction, in the process further refining the estimation of stellar parameters. We report that the measured angular diameter is 2.742 ± 0.010 mas with a limb-darkening coefficient of 0.231 ± 0.024. While our images are consistent with those of prior works, we provide updated physical parameters for λ Andromedae (R⋆ = 7.78 ± 0.05 R⊙, M⋆ = 1.24 ± 0.72 M⊙, and log L/L⊙ = 1.46 ± 0.04).

Keywords: Observational astronomy, Starspots, Optical interferometry, Late-type stars, Astronomy data analysis, Long baseline interferometry, Stellar rotation, Interferometry
A Magnetic Disk-outflow Model for Changing Look Active Galactic Nuclei. The timescales of the variabilities in changing look (CL) active galactic nuclei (AGNs) are usually on the order of years to tens of years (some of them are even shorter than one year), which is much shorter than the viscous timescale of a standard thin accretion disk. This implies that the variabilities of CL AGNs cannot be reproduced by varying the mass accretion rate of the thin disk. In this work, we employ a magnetic accretion disk-outflow model to calculate the inflow time of the disk predominantly driven by magnetic outflows. In this model, most angular momentum of the gas in the disk is carried away by the outflows, and therefore its radial velocity can be substantially higher than that of a conventional viscous disk. Our calculations show that the inflow time of such a disk with outflows can be around several years to tens of years. The calculated spectra of the disk with outflows can fit the observed spectra of a CL AGN Mrk 1018 quite well both in the low and high states. The derived inflow time of such a disk with outflows is around 5 yr in the high state, while it becomes ~20 yr in the low state, which is roughly consistent with the observations of the variabilities in Mrk 1018.

Keywords: Accretion, Black hole physics, Quasars, Interstellar medium, Stellar accretion disks, Magnetic fields
A Simulation of Radius-frequency Mapping for PSR J1848-0123 with an Inverse Compton Scattering Model. The radio radiation mechanism is one of the open questions for pulsars. Multiband observations are very helpful to constrain pulsar radiation models. We observed PSR J1848-0123 at the 5 GHz band with the Shanghai Tianma 65 m radio telescope (TMRT). The 5 GHz observation together with the European Pulsar Network (EPN) and CSIRO ATNF Data Archives databases provides a broadband evolution property of the pulse profiles for this pulsar. We reprocessed these data sets to obtain the multiband pulse profiles. It was found that the pulse profile of PSR J1848-0123 narrows with increasing emission frequency. We separated the emission components of each pulse profile with a multi-Gaussian fitting method, and then calculated the beaming angle and emission radius of each component with the basic radiation geometry of pulsar. With the calculated beam angles and radiation radii, we simulated the radius-frequency mapping of this pulsar with an inverse Compton scatting model (ICS). It was found that the observed radio radiation could be generated in the core gap region above the polar cap of the pulsar. The beaming angle and emission radius versus frequency for PSR J1848-0123 can be explained well with the ICS model.

Keywords: Rotation powered pulsars, Pulsars
An Observational Signature of Sub-equipartition Magnetic Fields in the Spectra of Black Hole Binaries. A common assumption used in the study of accretion disks is that the magnetic energy density and the kinetic energy density should be in equipartition. This assumption relies on the faster growth rate of the magnetic field strength against the kinetic energy of the particles in the flow, for decreasing radius, combined with a dissipation mechanism that tends toward equipartition. In this paper, we examine this assumption by modeling the radio, millimeter, and optical spectra of several black hole binaries in their quiescent state. We use a standard two-component disk model, consisting of an inner geometrically thick and optically thin disk, emitting thermal synchrotron radiation, along with an outer, thin disk, which radiates as a multicolor blackbody. We find that at the low accretion rates typical of the quiescent state, the spectral shape is qualitatively reproduced using magnetic fields that are between 0.1% and 1% of the equipartition value, considerably smaller than previously thought. We discuss our findings in view of (1) the launching of jets in these objects, which is commonly believed to rely on the presence of a strong magnetic field in the central region of the disk, and (2) the role of magnetic dissipation in the structure of the inflow.

Keywords: X-ray binary stars, Jets, Stellar mass black holes, Magnetic fields
Alfvénicity-related Long Recovery Phases of Geomagnetic Storms: A Space Weather Perspective. This paper reports, for the first time on a statistical basis, on the key role played by the Alfvénic fluctuations in modulating the recovery phase of the geomagnetic storms, slowing down the restoration of the magnetosphere toward its pre-storm equilibrium state. Using interplanetary and geomagnetic measurements collected over more than one solar cycle, a high correlation between the durations of Alfvénic streams and concurrent recovery phases is found, pointing to a clear coupling between Alfvénic turbulence and magnetospheric ring current dynamics. By exploiting current solar wind models, these observations also provide space weather opportunities of predicting the total duration of any geomagnetic storm induced by any solar driver provided that it is followed by an Alfvénic stream, a crucial piece of information for ground technologies and infrastructures that are affected by time-integrated effects throughout the duration of the storm.

Keywords: Interplanetary medium, Space plasmas, Magnetohydrodynamics, Heliosphere, Interplanetary turbulence, Space weather, Solar wind, Alfven waves, Solar-terrestrial interactions, Solar storm, Time series analysis
Characteristics of Interplanetary Discontinuities in the Inner Heliosphere Revealed by Parker Solar Probe. We present a statistical analysis for the characteristics and spatial evolution of the interplanetary discontinuities (IDs) in the solar wind, from 0.13-0.9 au, by using the Parker Solar Probe measurements on Orbits 4 and 5. We collected 3948 IDs, including 2511 rotational discontinuities (RDs) and 557 tangential discontinuities (TDs), with the remnant unidentified. The statistical results show that (1) the ID occurrence rate decreases from 200 events per day at 0.13 au to 1 event per day at 0.9 au, following a spatial scaling of r-2.00, (2) the RD to TD ratio decreases quickly with the heliocentric distance, from 8 at r &lt; 0.3 au to 1 at r &gt; 0.4 au, (3) the magnetic field tends to rotate across the IDs, 45° for TDs and 30° for RDs, in the pristine solar wind within 0.3 au, (4) a special subgroup of RDs exists within 0.3 au, characterized by small field rotation angles and parallel or antiparallel propagations to the background magnetic fields, (5) the TD thicknesses normalized by local ion inertial lengths (di) show no clear spatial scaling and generally range from 5-35 di and the normalized RD thicknesses follow an r-1.09 spatial scaling, and (6) the outward (antisunward) propagating RDs predominate in all RDs, with the propagation speeds in the plasma rest frame proportional to r-1.03. This work could improve our understanding of the ID characteristics and evolution and shed light on the study of the turbulent environment in the pristine solar wind.

Keywords: Interplanetary discontinuities, Magnetohydrodynamics, Solar wind, Interplanetary magnetic fields
Brightness Fluctuation Spectra of Sun-like Stars. I. The Mid-frequency Continuum. We analyze space-based time-series photometry of Sun-like stars, mostly in the Pleiades, but also field stars and the Sun itself. We focus on timescales between roughly 1 hr and 1 day. In the corresponding frequency band these stars display brightness fluctuations with a decreasing power-law continuous spectrum. K2 and Kepler observations show that the rms flicker due to this mid-frequency continuum (MFC) can reach almost 1%, approaching the modulation amplitude from active regions. The MFC amplitude varies by a factor up to 40 among Pleiades members with similar Teff, depending mainly on the stellar Rossby number Ro. For Ro ≤ 0.04, the mean amplitude is roughly constant at about 0.4%; at larger Ro the amplitude decreases rapidly, shrinking by about two orders of magnitude for Ro ≃ 1. Among stars, the MFC amplitude correlates poorly with that of modulation from rotating active regions. Among field stars observed for 3 yr by Kepler, the quarterly average modulation amplitudes from active regions are much more time variable than the quarterly MFC amplitudes. We argue that the process causing the MFC is largely magnetic in nature and that its power-law spectrum comes from magnetic processes distinct from the star's global dynamo, with shorter timescales. By analogy with solar phenomena, we hypothesize that the MFC arises from a (sometimes energetic) variant of the solar magnetic network, perhaps combined with rotation-related changes in the morphology of supergranules.

Keywords: Stellar rotation, Supergranulation, Solar dynamo, Stellar activity
Three-dimensional Reconstruction of Weak-lensing Mass Maps with a Sparsity Prior. I. Cluster Detection. We propose a novel method to reconstruct high-resolution three-dimensional mass maps using data from photometric weak-lensing surveys. We apply an adaptive LASSO algorithm to perform a sparsity-based reconstruction on the assumption that the underlying cosmic density field is represented by a sum of Navarro-Frenk-White halos. We generate realistic mock galaxy shear catalogs by considering the shear distortions from isolated halos for the configurations matched to the Subaru Hyper Suprime-Cam Survey with its photometric redshift estimates. We show that the adaptive method significantly reduces line-of-sight smearing that is caused by the correlation between the lensing kernels at different redshifts. Lensing clusters with lower mass limits of 1014.0 h-1 M⊙, 1014.7 h-1 M⊙, 1015.0 h-1 M⊙ can be detected with 1.5σ confidence at the low (z &lt; 0.3), median (0.3 ≤ z &lt; 0.6), and high (0.6 ≤ z &lt; 0.85) redshifts, respectively, with an average false detection rate of 0.022 deg-2. The estimated redshifts of the detected clusters are systematically lower than the true values by Δz ~ 0.03 for halos at z ≤ 0.4, but the relative redshift bias is below 0.5% for clusters at 0.4 &lt; z ≤ 0.85. The standard deviation of the redshift estimation is 0.092. Our method enables direct three-dimensional cluster detection with accurate redshift estimates.

Keywords: Cosmology, Galaxy dark matter halos, Galaxy clusters, Weak gravitational lensing
Accretion Flow Properties of GRS 1915+105 During Its θ Class Using AstroSat Data. The Galactic microquasar GRS 1915+105 shows rich variability that is categorized into different classes. In this paper, we report the temporal and spectral analysis of GRS 1915+105 to study the properties of the accretion flow when the light curve shows θ class variability. For this purpose, we use the Large Area X-ray Proportional Counter data from the Target of Opportunity observations of India's first multiwavelength astronomy satellite AstroSat. The θ class is marked by the recurrent appearance of U-shaped regions in the light curve, where the photon count rate first decreases rapidly and then increases slowly. For our analysis, we use U-shaped regions of the first two orbits (02345 and 02346) on 2016 March 4. In both cases, the dynamic power-density spectra (PDS) showed significant power at around 4-5 Hz, suggesting the presence of a low-frequency quasi-periodic oscillation (QPO) around that frequency interval. The QPO frequency is found to increase with time when the energy flux is also enhanced. From the evolution of the spectra, we determine the evolution of the accretion flow parameters in these two observations. Fitting the spectra with the transonic flow solution-based two-component advective flow (TCAF) model in the 4-25 keV energy band shows that the Keplerian disk accretion rate increases with the increase in radiation intensity, while the location of the centrifugal pressure-driven shock front decreases. In both these data, a gradual increment of power-law photon index with intensity is observed, suggesting the progressive softening of the source.

Keywords: Accretion, X-ray binary stars, Jets, Black holes
Revealing the Physical Conditions around Sgr A* Using Bayesian Inference. I. Observations and Radiative Transfer. We report subarcsecond Atacama Large Millimeter/submillimeter Array (ALMA) observations between 272 and 375 GHz toward Sgr A*'s circumnuclear disk (CND). Our data comprise eight individual pointings, with significant SiO (87-76) and SO (7-6) emission detected toward 98 positions within these pointings. Additionally, we identify H2CS (91,9-81,8), OCS (25-24), and CH3OH (21,1-20,2) toward a smaller subset of positions. By using the observed peak line flux density, together with a Bayesian inference technique informed by radiative transfer models, we systematically recover the physical gas conditions toward each of these positions. We estimate that the bulk of the surveyed gas has temperature Tkin &lt; 500 K and density nH ⪅ 106 cm-3, consistent with previous studies of similar positions as traced by HCN clumps. However, we identify an uncharacteristically hot (Tkin ≈ 600 K) and dense (nH ≈ 106 cm-3) source in the Northeastern Arm. This position is found to be approximately consistent with a gravitationally bound region dominated by turbulence. We also identify a nearby cold (Tkin ≈ 60 K) and extremely dense (nH ≈ 107 cm-3) position that is again potentially bound and dominated by turbulence. We also determine that the total gas mass contained within the CND is MCND ≲ 4 × 104 M⊙. Furthermore, we qualitatively note that the observed chemical enrichment across large scales within the CND is consistent with bulk grain processing, though multiple desorption mechanisms are plausibly responsible. Further chemical modeling is required to identify the physical origin of the grain processing, as well as the localized H2CS and OCS emission.

Keywords: Observational astronomy, Bayesian statistics, Spectral line identification, Molecular clouds, Astrochemistry, Star formation, Radiative transfer, Interstellar medium
Model-independent Estimation of H<SUB>0</SUB> and Ω<SUB>K</SUB> from Strongly Lensed Fast Radio Bursts. Model-independent estimation of H0 and ΩK can provide clues about the origin of the intractable Hubble constant tension and the current cosmic-curvature crisis. Strongly lensed fast radio bursts (FRBs) have been proposed as precision probes of the universe since the time delay ~ ${ \mathcal O }$ (10 days) between images could be precisely measured due to short durations ~ ${ \mathcal O }({ms})$ of this kind of bright radio pulses. Here, on the basis of the distance sum rule, we investigate the capacity of model-independently estimating these two parameters from time-delay distances of strongly lensed FRBs and luminosity distances of the upcoming Wide Field InfraRed Survey Telescope (WFIRST) type Ia supernovae observations. Considering the expected FRB detection rate of upcoming facilities, we find that H0 could be determined to a ~1% precision and ΩK could be constrained to ~0.1 simultaneously from 10 lensed FRBs. These estimations, which are independent of the energy contents of the universe and validity of Einstein's equation on cosmological scales, will be complementary to popular probes and of great importance for clarifying the current crises of cosmology.

Keywords: Strong gravitational lensing, Radio bursts, Cosmological parameters
Energy Injection Driven by Precessing Jets in Gamma-Ray Burst Afterglows. Jet precession is considered to universally exist in different-scale astronomical phenomena, including gamma-ray bursts (GRBs). For the long-lived GRB central engine, the relativistic precessing jets will periodically inject kinetic energy into the external shocks, then significantly modulate the shapes of the light curves (LCs) in GRB afterglows. In this paper, we adopt the standard external shock model to investigate the effects of jet precession on GRB X-ray afterglows in cases with different parameters, i.e., the steady or time-dependent jet powers, precession periods, precession angles, and viewing angles. In the case where the jet powers are in steady or slow decay and the jet can sweep across the line of sight, shallow decay (or plateau) segments should appear; otherwise, a giant bump will emerge in the GRB afterglow LCs. We show that jet precession is a new plausible mechanism of the energy injection in GRBs. Moreover, some observed X-ray transients without GRB associations might be powered by the precessing jets.

Keywords: Shocks, Gamma-ray bursts, Relativistic jets
Evolution of the Water Snow Line in Magnetically Accreting Protoplanetary Disks. The low water content of the terrestrial planets in the solar system suggests that the protoplanets formed within the water snow line. Accurate prediction of the snow line location moving with time provides a clue to constraining the formation process of the planets. In this paper, we investigate the migration of the snow line in protoplanetary disks whose accretion is controlled by laminar magnetic fields, which have been proposed by various nonideal magnetohydrodynamic (MHD) simulations. We propose an empirical model of the disk temperature based on our nonideal MHD simulations, which show that the accretion heating is significantly less efficient than that in turbulent disks, and calculate the snow line location over time. We find that the snow line in magnetically accreting laminar disks moves inside the current Earth's orbit within 1 Myr after star formation, whereas the time for the conventional turbulent disk is much longer than 1 Myr. This result suggests that either the rocky protoplanets formed in such an early phase of the disk evolution, or the protoplanets moved outward to the current orbits after they formed close to the protosun.

Keywords: Magnetohydrodynamics, Solar system terrestrial planets, Protoplanetary disks, Planet formation