Sazuna/UAT_keywords huggingface dataset:
Gaussian Decomposition of λ21 cm H I profiles, the Critical Ionization Velocity, and the Interstellar Helium Abundance. Following an established protocol of science-that results must be reproducible-we examine the Gaussian fits to Galactic λ21 cm (H I) emission profiles obtained by two seemingly complementary methods using data from the Leiden-Argentine-Bonn all-sky survey. One is based on the method used by Verschuur, the other by Nidever et al. (2008). The comparisons led to the identification of four problems that might arise when an algorithm is applied to huge databases without close monitoring: (1) different methods of calculating ${\tilde{\chi }}^{2}$ measuring the goodness of fit; (2) an ultra-broad component found to imperfectly bridge the gap between low- and intermediate-velocity gas; (3) the lack of an imposed spatial coherence allowing different components to appear and disappear in profiles separated by a fraction of a beamwidth; and (4) multiple, fundamentally different solutions for profiles at both the north and south Galactic poles. Confirming evidence emerges from this study of an underlying component with a line width of an order 34 km s-1. If this feature is the result of the critical ionization velocity effect acting on interstellar helium, it can be used to calculate its interstellar abundance. Analysis of H I profiles in an area in the southern Galactic hemisphere using multitelescope data gives a helium abundance of 0.094 ± 0.035, in excellent agreement with the accepted cosmic abundance of 0.085.

Keywords: Interstellar line emission
Synchrotron Self-Compton Afterglow Closure Relations and Fermi-LAT-detected Gamma-Ray Bursts. The Fermi Large Area Telescope (Fermi-LAT) Collaboration reported the Second Gamma-ray Burst Catalog (2FLGC), which comprises a subset of 29 bursts with photon energies above 10 GeV. Although the standard synchrotron forward-shock model has successfully explained the gamma-ray burst (GRB) afterglow observations, energetic photons higher than 10 GeV from these transient events can hardly be described in this scenario. We present the closure relations (CRs) of the synchrotron self-Compton (SSC) afterglow model in the adiabatic and radiative scenario, and when the central engine injects continuous energy into the blast wave to study the evolution of the spectral and temporal indexes of those bursts reported in 2FLGC. We consider the SSC afterglow model evolving in stellar-wind and the interstellar medium (ISM), and the CRs as a function of the radiative parameter, the energy injection index, and the electron spectral index for 1 &lt; p &lt; 2 and 2 ≤ p. We select all GRBs that have been modeled with both a simple or a broken power law in the 2FLGC. We found that the CRs of the SSC model can satisfy a significant fraction of the burst that cannot be interpreted in the synchrotron scenario, even though those that require an intermediate density profile (e.g., GRB 130427A) or an atypical fraction of total energy given to amplify the magnetic field (ɛ  B ). The value of this parameter in the SSC model ranges (ɛ  B  ≈ 10-5 - 10-4) when the cooling spectral break corresponds to the Fermi-LAT band for typical values of GRB afterglow. The analysis shows that the ISM is preferred for the scenario without energy injection and the stellar-wind medium for an energy injection scenario.

Keywords: Gamma-ray bursts, Radiative processes
Space-weather-driven Variations in Lyα Absorption Signatures of Exoplanet Atmospheric Escape: MHD Simulations and the Case of AU Mic b. We simulate the space environment around AU Microscopii b and the interaction between the magnetized stellar wind and a planetary atmospheric outflow for ambient stellar wind conditions and coronal mass ejection (CME) conditions. We also calculate synthetic Lyα absorption due to neutral hydrogen in the ambient and the escaping planetary atmosphere affected by this interaction. We find that the Lyα absorption is highly variable owing to the highly varying stellar wind conditions. A strong Doppler blueshift component is observed in the Lyα profile, in contradiction to the actual escape velocity observed in the simulations themselves. This result suggests that the strong Doppler blueshift is likely attributed to the stellar wind, not the escaping neutral atmosphere, either through its advection of neutral planetary gas or through the creation of a fast neutral flow via charge exchange between the stellar wind ions and the planetary neutrals. Indeed, our CME simulations indicate a strong stripping of magnetospheric material from the planet, including some of the neutral escaping atmosphere. Our simulations show that the pressure around close-in exoplanets is not much lower, and may be even higher, than the pressure at the top of the planetary atmosphere. Thus, the neutral atmosphere is hydrodynamically escaping with a very small velocity (&lt;15 km s-1). Moreover, our simulations show that an MHD treatment is essential in order to properly capture the coupled magnetized stellar wind and the escaping atmosphere, despite the atmosphere being neutral. This coupling should be considered when interpreting Lyα observations in the context of exoplanets' atmospheric escape.

Keywords: Magnetohydrodynamics, Stellar winds, Star-planet interactions, Magnetic fields, Exoplanet atmospheres
Observations of Instability-driven Nanojets in Coronal Loops. The recent discovery of nanojets by Antolin et al. represents magnetic reconnection in a braided field, thus clearly identifying reconnection-driven nanoflares. Due to their small scale (500 km in width, 1500 km in length) and short timescales (&lt;15 s), it is unclear how pervasive nanojets are in the solar corona. In this paper, we present Interface Region Imaging Spectrograph and Solar Dynamics Observatory observations of nanojets found in multiple coronal structures, namely, in a coronal loop powered by a blowout jet, and in two other coronal loops with coronal rain. In agreement with previous findings, we observe that nanojets are accompanied by small nanoflare-like intensity bursts in the (E)UV, have velocities of 150-250 km s-1 and occur transversely to the field line of origin, which is sometimes observed to split. However, we find a variety of nanojet directions in the plane transverse to the loop axis. These nanojets are found to have kinetic and thermal energies within the nanoflare range, and often occur in clusters. In the blowout jet case study, the Kelvin-Helmholtz instability (KHI) is directly identified as the reconnection driver. For the other two loops, we find that both, KHI and Rayleigh-Taylor instability (RTI) are likely to be the drivers. However, we find that KHI and RTI are each more likely in one of the other two cases. These observations of nanojets in a variety of structures and environments support nanojets being a general result of reconnection that are driven here by dynamic instabilities.

Keywords: Magnetohydrodynamics, Solar prominences, The Sun, Solar magnetic fields, Solar corona
Formation of Low-mass Black Holes and Single Millisecond Pulsars in Globular Clusters. Close encounters between neutron stars and main-sequence stars occur in globular clusters and may lead to various outcomes. Here we study encounters resulting in the tidal disruption of the star. Using N-body models, we predict the typical stellar masses in these disruptions and the dependence of the event rate on the host cluster properties. We find that tidal disruption events occur most frequently in core-collapsed globular clusters and that roughly 25% of the disrupted stars are merger products (i.e., blue straggler stars). Using hydrodynamic simulations, we model the tidal disruptions themselves (over timescales of days) to determine the mass bound to the neutron star and the properties of the accretion disks formed. In general, we find roughly 80%-90% of the initial stellar mass becomes bound to the neutron star following disruption. Additionally, we find that neutron stars receive impulsive kicks of up to about 20 km s-1 as a result of the asymmetry of unbound ejecta; these kicks place these neutron stars on elongated orbits within their host cluster, with apocenter distances well outside the cluster core. Finally, we model the evolution of the (hypercritical) accretion disks on longer timescales (days to years after disruption) to estimate the accretion rate onto the neutron stars and accompanying spin-up. As long as ≳1% of the bound mass accretes onto the neutron star, millisecond spin periods can be attained. We argue the growing numbers of isolated millisecond pulsars observed in globular clusters may have formed, at least in part, through this mechanism. In the case of significant mass growth, some of these neutron stars may collapse to form low-mass (≲3 M ⊙) black holes.

Keywords: Globular star clusters, Hydrodynamical simulations, Neutron stars, Millisecond pulsars, Stellar mass black holes, N-body simulations
Observational Evidence for a Spin-up Line in the P- \dot{P} Diagram of Millisecond Pulsars. It is believed that millisecond pulsars attain their fast spins by accreting matter and angular momentum from companion stars. Theoretical modeling of the accretion process suggests a spin-up line in the period-period derivative (P- $\dot{P}$ ) diagram of millisecond pulsars, which plays an important role in population studies of radio millisecond pulsars and accreting neutron stars in X-ray binaries. Here we present observational evidence for such a spin-up line using a sample of 143 radio pulsars with P &lt; 30 ms. We also find that PSRs J1823-3021A and J1824-2452A, located near the classic spin-up line, are consistent with the broad population of millisecond pulsars. Finally, we show that our approach of Bayesian inference can probe accretion physics, allowing constraints to be placed on the accretion rate and the disk-magnetosphere interaction.

Keywords: Neutron stars, Stellar accretion, Millisecond pulsars
Reconciling Power-law Slopes in Solar Flare and Nanoflare Size Distributions. We unify the power laws of size distributions of solar flare and nanoflare energies. We present three models that predict the power-law slopes α  E  of flare energies defined in terms of the 2D and 3D fractal dimensions (D  A , D  V ): (i) the spatiotemporal standard self-organized criticality model, defined by the power-law slope α  E1 =1 + 2/(D  V  + 2) = (13/9) ≈ 1.44; (ii) the 2D thermal energy model, α  E2 = 1 + 2/D  A  = (7/3) ≈ 2.33; and (iii) the 3D thermal energy model, α  E3 = 1 + 2/D  V  = (9/5) ≈ 1.80. The theoretical predictions of energies are consistent with the observational values of these three groups, i.e., α  E1 = 1.47 ± 0.07, α  E2 = 2.38 ± 0.09, and α  E3 = 1.80 ± 0.18. These results corroborate that the energy of nanoflares does not diverge at small energies, since (α  E1 &lt; 2) and (α  E3 &lt; 2), except for the 2D model (α  E2 &gt; 2). Thus, while this conclusion does not support nanoflare scenarios of coronal heating from a dimensionality point of view, magnetic reconnection processes with quasi-1D or quasi-2D current sheets cannot be ruled out.

Keywords: Active solar corona, Solar flares, Solar x-ray flares
Identification of Inertial Modes in the Solar Convection Zone. The observation of global acoustic waves (p modes) in the Sun has been key to unveiling its internal structure and dynamics. A different kind of wave, known as sectoral Rossby modes, has been observed and identified, which potentially opens the door to probing internal processes that are inaccessible through p-mode helioseismology. Yet another set of waves, appearing as retrograde-propagating, equatorially antisymmetric vorticity waves, has also been observed but their identification remained elusive. Here, through a numerical model implemented as an eigenvalue problem, we provide evidence supporting the identification of those waves as a class of inertial eigenmodes, distinct from the Rossby-mode class, with radial velocities comparable to the horizontal ones deep in the convective zone but still small compared to the horizontal velocities toward the surface. We also suggest that the signature of tesseral-like Rossby modes might be present in recent observational data.

Keywords: Solar oscillations, Solar rotation, Astrophysical fluid dynamics
Radio Constraints on r-process Nucleosynthesis by Collapsars. The heaviest elements in the universe are synthesized through rapid neutron capture (r-process) in extremely neutron-rich outflows. Neutron star mergers were established as an important r-process source through the multimessenger observation of GW170817. Collapsars were also proposed as a potentially major source of heavy elements; however, this is difficult to probe through optical observations due to contamination by other emission mechanisms. Here we present observational constraints on r-process nucleosynthesis by collapsars based on radio follow-up observations of nearby long gamma-ray bursts (GRBs). We make the hypothesis that late-time radio emission arises from the collapsar wind ejecta responsible for forging r-process elements, and consider the constraints that can be set on this scenario using radio observations of a sample of Swift/Burst Alert Telescope GRBs located within 2 Gpc. No radio counterpart was identified in excess of the radio afterglow of the GRBs in our sample. This gives the strictest limit to the collapsar r-process contribution of ≲0.2 M ⊙ for GRB 060505 and GRB 05826, under the models we considered. Our results additionally constrain energy injection by a long-lived neutron star remnant in some of the considered GRBs. While our results are in tension with collapsars being the majority of r-process production sites, the ejecta mass and velocity profile of collapsar winds, and the emission parameters, are not yet well modeled. As such, our results are currently subject to large uncertainties, but further theoretical work could greatly improve them.

Keywords: R-process, Gamma-ray bursts
On the Probability of the Extremely Lensed z = 6.2 Earendel Source Being a Population III Star. The recent discovery of the extremely lensed Earendel object at z = 6.2 is remarkable in that it is likely a single star or stellar multiple, observed within the first billion years of cosmic history. Depending on its mass, which is still uncertain but will soon be more tightly constrained with the James Webb Space Telescope, the Earendel star might even be a member of the first generation of stars, the so-called Population III (Pop III). By combining results from detailed cosmological simulations of the assembly of the first galaxies, including the enrichment of the pristine gas with heavy chemical elements, with assumptions on key stellar parameters, we quantify the probability that Earendel indeed has a Pop III origin. We find that this probability is nonnegligible throughout the mass range inferred for Earendel, specifically ranging from a few percent at the lower-mass end to near unity for some Pop III initial mass function (IMF) models toward the high-mass end of the allowed range. For models that extend the metal-enriched IMF to 500 M ⊙, the likelihood of Earendel being a Pop III star stays at the few to 10% level. We discuss the implications of such a discovery for the overall endeavor to probe the hitherto so elusive first stars in the universe.

Keywords: Early universe, Population III stars, Gravitational lensing, Population II stars, Reionization
A Comprehensive Measurement of the Local Value of the Hubble Constant with 1 km s<SUP>-1</SUP> Mpc<SUP>-1</SUP> Uncertainty from the Hubble Space Telescope and the SH0ES Team. We report observations from the Hubble Space Telescope (HST) of Cepheid variables in the host galaxies of 42 Type Ia supernovae (SNe Ia) used to calibrate the Hubble constant (H 0). These include the complete sample of all suitable SNe Ia discovered in the last four decades at redshift z ≤ 0.01, collected and calibrated from ≥1000 HST orbits, more than doubling the sample whose size limits the precision of the direct determination of H 0. The Cepheids are calibrated geometrically from Gaia EDR3 parallaxes, masers in NGC 4258 (here tripling that sample of Cepheids), and detached eclipsing binaries in the Large Magellanic Cloud. All Cepheids in these anchors and SN Ia hosts were measured with the same instrument (WFC3) and filters (F555W, F814W, F160W) to negate zero-point errors. We present multiple verifications of Cepheid photometry and six tests of background determinations that show Cepheid measurements are accurate in the presence of crowded backgrounds. The SNe Ia in these hosts calibrate the magnitude-redshift relation from the revised Pantheon+ compilation, accounting here for covariance between all SN data and with host properties and SN surveys matched throughout to negate systematics. We decrease the uncertainty in the local determination of H 0 to 1 km s-1 Mpc-1 including systematics. We present results for a comprehensive set of nearly 70 analysis variants to explore the sensitivity of H 0 to selections of anchors, SN surveys, redshift ranges, the treatment of Cepheid dust, metallicity, form of the period-luminosity relation, SN color, peculiar-velocity corrections, sample bifurcations, and simultaneous measurement of the expansion history. Our baseline result from the Cepheid-SN Ia sample is H 0 = 73.04 ± 1.04 km s-1 Mpc-1, which includes systematic uncertainties and lies near the median of all analysis variants. We demonstrate consistency with measures from HST of the TRGB between SN Ia hosts and NGC 4258, and include them simultaneously to yield 72.53 ± 0.99 km s-1 Mpc-1. The inclusion of high-redshift SNe Ia yields H 0 = 73.30 ± 1.04 km s-1 Mpc-1 and q 0 = -0.51 ± 0.024. We find a 5σ difference with the prediction of H 0 from Planck cosmic microwave background observations under ΛCDM, with no indication that the discrepancy arises from measurement uncertainties or analysis variations considered to date. The source of this now long-standing discrepancy between direct and cosmological routes to determining H 0 remains unknown.

Keywords: Hubble constant
Theoretically Modeling Photoionized Regions with Fractal Geometry in Three Dimensions. We create a photoionization model embedded in the turbulent interstellar medium (ISM) by using the state-of-the-art Messenger Monte Carlo MAPPINGS V code (M3) in conjunction with the CMFGEN stellar atmosphere model. We show that the turbulent ISM causes the inhomogeneity of electron temperature and density within the nebula. The fluctuation in the turbulent ISM creates complex ionization structures seen in nearby nebulae. The inhomogeneous density distribution within the nebula creates a significant scatter on the spatially resolved standard optical diagnostic diagrams, which cannot be represented by the spherical constant-density photoionization model. We analyze the dependence of different optical emission lines on the complexity of nebular geometry, finding that the emission lines residing on the nebular boundary are highly sensitive to the complexity of nebular geometry, while the emission lines produced throughout the nebula are sensitive to the density distribution of the ISM within the nebula. Our fractal photoionization model demonstrates that a complex nebular geometry is required for the accurate modeling of H II regions and emission-line galaxies, especially for the high-redshift galaxies, where the ISM is highly turbulent based on increasing observational evidence.

Keywords: Emission nebulae, High-redshift galaxies
Formation of Quiescent Prominence Magnetic Fields by Supergranulations. To understand the formation of quiescent solar prominences, the origin of their magnetic field structures, i.e., magnetic flux ropes (MFRs), must be revealed. We use three-dimensional magnetofriction simulations in a spherical subdomain to investigate the role of typical supergranular motions in the long-term formation of a prominence magnetic field. Time-dependent horizontal supergranular motions with and without the effect of Coriolis force are simulated on the solar surface via Voronoi tessellation. The vortical motions by the Coriolis effect at boundaries of supergranules inject magnetic helicity into the corona. The helicity is transferred and accumulated along the polarity inversion line (PIL) as a strongly sheared magnetic field via helicity condensation. The diverging motions of supergranules converge opposite magnetic polarities at the PIL and drive the magnetic reconnection between footpoints of the sheared magnetic arcades to form an MFR. The magnetic network, negative-helicity MFR in the northern hemisphere, and fragmented-to-continuous formation process of magnetic dip regions are in agreement with observations. Although diverging supergranulations, differential rotation, and meridional flows are included, the simulation without the Coriolis effect cannot produce an MFR or sheared arcades to host a prominence. Therefore, Coriolis force is a key factor for helicity injection and the formation of magnetic structures of quiescent solar prominences.

Keywords: Solar magnetic fields, Supergranulation, Solar prominences, Magnetohydrodynamical simulations
Inefficient Growth of SiOx Grains: Implications for Circumstellar Outflows. To explain observations of abundant circumstellar dust and high stellar wind velocity, most models simply postulate the efficient nucleation and growth of silicate dust particles. Here, we report measurement of the SiO-(SiOx)n grain sticking coefficient in a microgravity sounding rocket experiment, indicating very inefficient (0.005-0.016) grain formation from the vapor. Application of this measurement to radiative-driven winds in oxygen-rich asymptotic giant branch stars indicates that the initial grain condensate population should consist of very tiny dust particles in very large numbers. Aggregation of this dust population will produce low-dimension fractal aggregates that should couple well to the stellar radiation field and efficiently drive stellar mass loss.

Keywords: Circumstellar dust
Kinematic Evidence for an Embedded Planet in the IM Lupi Disk. We test the hypothesis that an embedded giant planet in the IM Lupi protostellar disk can produce velocity kinks seen in CO line observations as well as the spiral arms seen in scattered light and continuum emission. We inject planets into 3D hydrodynamics simulations of IM Lupi, generating synthetic observations using Monte Carlo radiative transfer. We find that an embedded planet of 2-3 M Jup can reproduce non-Keplerian velocity perturbations, or "kinks", in the 12CO J = 2-1 channel maps. Such a planet can also explain the spiral arms seen in 1.25 mm dust continuum emission and 1.6 μm scattered-light images. We show that the wake of the planet can be traced in the observed peak velocity map, which appears to closely follow the morphology expected from our simulations and from analytic models of planet-disk interaction.

Keywords: Hydrodynamical simulations, Exoplanet migration, Planetary-disk interactions, Protoplanetary disks, Circumstellar disks, Exoplanet formation, Planet formation