Sazuna/UAT_keywords huggingface dataset:
Radial Diffusion of Planetary Radiation Belts' Particles by Fluctuations with Finite Correlation Time. Radial diffusion in planetary radiation belts is a dominant transport mechanism resulting in the energization and losses of charged particles by large-scale electromagnetic fluctuations. In this study, we revisit the radial diffusion formalism by relaxing the assumption of zero correlation time in the spectrum of fluctuations responsible for the transport of charged particles. We derive a diffusion coefficient by assuming fluctuations that (1) are time homogeneous, (2) too small to trap the particles, and (3) can decorrelate on timescales comparable to the transit time of the particles. We demonstrate through self-similar solutions of the Fokker-Planck equation that autocorrelation time τc much larger than the linear transit time/particle drift period ${\tau }_{L}={{\rm{\Omega }}}_{D}^{-1}$ results in characteristic time for transport independent of the drift frequency and faster than for short correlation time. In both instances, that is for short (τL ≫ τc) and long (τL ≪ τc) autocorrelation time, the diffusion of particles is subdiffusive since the variance of increments along the magnetic drift shells L*, scales as &lt;ΔL*2&gt; ∼ ts, with s &lt; 1. However, in the absence of sources and sinks, particle transport for both short and long autocorrelation times result in equilibrium distribution along L* with differences of less than 10% across lower magnetic drift shells. The main consequence of incorporating finite correlation time appears in intermediate times much longer than the drift period but before the distribution function reaches equilibrium and indicates the importance of quantifying observationally the spectral properties of fluctuations for the modeling of planetary radiation belts.

Keywords: Space plasmas, Plasma physics, Van Allen radiation belts, Plasma astrophysics, Alfven waves
Investigating X-Ray Sources during the Epoch of Reionization with the 21 cm Signal. Heating of neutral gas by energetic sources is crucial for the prediction of the 21 cm signal during the epoch of reionization. To investigate differences induced on the statistics of the 21 cm signal by various source types, we use five radiative transfer simulations that have the same stellar UV emission model and varying combinations of more energetic sources, such as X-ray binaries (XRBs), accreting nuclear black holes (BHs), and hot interstellar medium emission (ISM). We find that the efficient heating from the ISM increases the average global 21 cm signal while reducing its fluctuations and thus power spectrum. A clear impact is also observed in the bispectrum in terms of scale and timing of the transition between a positive and a negative value. The impact of XRBs is similar to that of the ISM, although it is delayed in time and reduced in intensity because of the less efficient heating. Due to the paucity of nuclear BHs, the behavior of the 21 cm statistics in their presence is very similar to that of a case when only stars are considered, with the exception of the latest stages of reionization, when the effect of BHs is clearly visible. We find that differences between the source scenarios investigated here are larger than the instrumental noise of SKA1-low at z ≳ 7-8, suggesting that in the future it might be possible to constrain the spectral energy distribution of the sources contributing to the reionization process.

Keywords: Early universe, H I line emission, X-ray sources, Radiative transfer simulations, Reionization
Metallicity of Galactic RR Lyrae from Optical and Infrared Light Curves. I. Period-Fourier-Metallicity Relations for Fundamental-mode RR Lyrae. We present newly calibrated period-φ31-[Fe/H] relations for fundamental-mode RR Lyrae stars in the optical and, for the first time, mid-infrared. This work's calibration data set provides the largest and most comprehensive span of parameter space to date, with homogeneous metallicities from -3 ≲ [Fe/H] ≲ 0.4 and accurate Fourier parameters derived from 1980 ASAS-SN (V band) and 1083 WISE (NEOWISE extension, W1 and W2 bands) RR Lyrae stars with well-sampled light curves. We compare our optical period-φ31-[Fe/H] relation with those available in the literature and demonstrate that our relation minimizes systematic trends in the lower and higher metallicity range. Moreover, a direct comparison shows that our optical photometric metallicities are consistent with both those from high-resolution spectroscopy and globular clusters, supporting the good performance of our relation. We found an intrinsic scatter in the photometric metallicities (0.41 dex in the V band and 0.50 dex in the infrared) by utilizing large calibration data sets covering a broad metallicity range. This scatter becomes smaller when optical and infrared bands are used together (0.37 dex). Overall, the relations derived in this work have many potential applications, including large-area photometric surveys with James Webb Space Telescope in the infrared and LSST in the optical.

Keywords: Globular star clusters, Pulsating variable stars, RR Lyrae variable stars, RRab variable stars, Metallicity
Measuring Stellar Masses of Emission-line Galaxies at 1.2 &lt; z &lt; 1.9. The accurate measurement of stellar masses over a wide range of galaxy properties is essential for better constraining models of galaxy evolution. Emission-line galaxies (ELGs) tend to have better redshift estimates than continuum-selected objects, and have been shown to span a large range of physical properties, including stellar mass. Using data from the 3D-HST Treasury program, in this work, we construct a carefully vetted sample of 4350 ELGs at redshifts of 1.16 &lt; z &lt; 1.90. We combine the 3D-HST emission-line fluxes with far-UV through near-IR photometry, and use the MCSED spectral energy distribution fitting code to constrain the galaxies' physical parameters, such as their star-formation rate and stellar masses. Our sample is consistent with the z ∼ 2 mass-metallicity relation. More importantly, we show that there is a simple, but tight correlation between stellar mass and absolute magnitude in a near-IR filter, which should prove particularly useful in terms of the rapid calculation of accurate stellar masses for millions of galaxies in upcoming missions such as Euclid, and the Nancy Grace Roman Space Telescope.

Keywords: High-redshift galaxies, Spectral energy distribution, Galaxy evolution, Stellar masses
On the Possibility of Stellar Lenses in the Black Hole Candidate Microlensing Events MACHO-96-BLG-5 and MACHO-98-BLG-6. Although stellar-mass black holes (BHs) are likely to be abundant in the Milky Way (N = 108-109), only 20 have been detected to date, all in accreting binary systems. Gravitational microlensing is a proposed technique to search for isolated BHs, which have not yet been detected. Two specific microlensing events, MACHO-1996-BLG-5 (M96-B5) and MACHO-1998-BLG-6 (M98-B6), initially observed near the lens-source minimum angular separation in 1996 and 1998, respectively, have long Einstein crossing times (&gt;300 days), identifying the lenses as candidate black holes. Twenty years have elapsed since the time of lens-source closest approach for each of these events, indicating that if the lens and source are both luminous, and if their relative proper motion is sufficiently large, the two components should be spatially resolvable. In this work, we attempt to eliminate the possibility of a stellar lens for these events by: (1) using Keck near-infrared adaptive optics images to search for a potentially now-resolved, luminous lens, and (2) examining multi-band photometry of the source to search for flux contributions from a potentially unresolved, luminous lens. We combine detection limits from NIRC2 images with light-curve data to eliminate all non-BH lenses for relative lens-source proper motions above 0.81 mas yr-1 for M96-B5, and 2.48 mas yr-1 for M98-B6. Furthermore, we use WFPC2 broad-band images to eliminate the possibility of stellar lenses at any proper motion. We present the narrow range of non-BH possibilities permitted by our varied analyses. Finally, we suggest future observations to constrain the remaining parameter space via the methods developed in this work.

Keywords: Black holes, Light curves, High-resolution microlensing event imaging, Stellar mass black holes, Compact objects, Gravitational microlensing
The Photometric Metallicity and Carbon Distributions of the Milky Way's Halo and Solar Neighborhood from S-PLUS Observations of SDSS Stripe 82. We report photometric estimates of effective temperature, Teff, metallicity, [Fe/H], carbonicity, [C/Fe], and absolute carbon abundances, A(C), for over 700,000 stars from the Southern Photometric Local Universe Survey (S-PLUS) Data Release 2, covering a substantial fraction of the equatorial Sloan Digital Sky Survey Stripe 82. We present an analysis for two stellar populations: (1) halo main-sequence turnoff stars and (2) K-dwarf stars of mass 0.58 &lt; M/M⊙ &lt; 0.75 in the Solar Neighborhood. Application of the Stellar Photometric Index Network Explorer (SPHINX) to the mixed-bandwidth (narrow- plus wide-band) filter photometry from S-PLUS produces robust estimates of the metallicities and carbon abundances in stellar atmospheres over a wide range of temperatures, 4250 &lt; Teff(K) &lt; 7000. The use of multiple narrow-band S-PLUS filters enables SPHINX to achieve substantially lower levels of "catastrophic failures" (i.e., large offsets in metallicity estimates relative to spectroscopic determinations) than previous efforts using a single metallicity-sensitive narrow-band filter. We constrain the exponential slope of the Milky Way's K-dwarf halo metallicity distribution function (MDF), λ10,[Fe/H] = 0.85 ± 0.21, over the metallicity range -2.5 &lt; [Fe/H] &lt; -1.0; the MDF of our local-volume K-dwarf sample is well-represented by a gamma distribution with parameters α = 2.8 and β = 4.2. S-PLUS photometry obtains absolute carbon abundances with a precision of ∼0.35 dex for stars with Teff &lt; 6500 K. We identify 364 candidate carbon-enhanced metal-poor stars, obtain assignments of these stars into the Yoon-Beers morphological groups in the A(C)-[Fe/H] space, and we derive the CEMP frequencies.

Keywords: Sky surveys, Stellar abundances, Solar neighborhood, Medium band photometry, Milky Way stellar halo, Milky Way disk, Narrow band photometry
A Search for Cloud Cores Affected by Shocked Carbon Chain Chemistry in L1251. We searched for shocked carbon chain chemistry (SCCC) sources with C3S abundances surpassing those of HC5N toward the dark cloud L1251, using the Effelsberg telescope at the K band (18-26 GHz). L1251-1 and L1251-3 are identified as the most promising SCCC sources. The two sources harbor young stellar objects. We conducted mapping observations toward L1251-A, the western tail of L1251, at λ ∼ 3 mm with the Purple Mountain Observatory 13.7 m and the Nobeyama Radio Observatory 45 m telescopes in lines of C2H, N2H+, CS, HCO+, SO, HC3N, and C18O as well as in CO 3-2 using the James Clerk Maxwell Telescope (JCMT). The spectral data were combined with archival data including Spitzer and Herschel continuum maps for further analysis. Filamentary substructures labeled as F1-F6 were extracted in L1251, with F1 being associated with L1251-A hosting L1251-1. The peak positions of dense gas traced by HCO+ are misaligned relative to those of the dust clumps. Episodic outflows are common in this region. The twisted morphology of F1 and velocity distribution along L1251-A may originate from stellar feedback. SCCC in L1251-1 may have been caused by outflow activities originated from the infrared source IRS1. The signposts of ongoing SCCC and the broadened line widths of C3S and C4H in L1251-1 as well as the distribution of HC3N are also related to outflow activities in this region. L1251-1 (IRS1) together with the previously identified SCCC source IRS3 demonstrate that L1251-A is an excellent region to study SCCC.

Keywords: Stellar-interstellar interactions, Infrared dark clouds, Star forming regions, Stellar jets, Molecular clouds, Chemical abundances, Astrochemistry
Brought to Light. II. Revealing the Origins of Cloaked Spiral Features in Cluster Passive Dwarf Galaxies. In our companion paper (Brought to Light I: Michea et al.), we reveal spectacular spiral-galaxy-like features in deep optical imaging of nine Virgo early-type dwarf galaxies, hidden beneath a dominating smooth stellar disk. Using a new combination of approaches, we find that bar- and spiral-like features contribute 2.2%-6.4% of the total flux within 2 Reff. In this study, we conduct high-resolution simulations of cluster harassment of passive dwarf galaxies. Following close pericenter passages of the cluster core, tidal triggering generates features in our model disks that bear a striking resemblance to the observed features. However, we find the disks must be highly rotationally supported (Vpeak/σ0 ∼ 3), much higher than typically observed. We propose that some early-type dwarfs may contain a few percent of their mass in a cold, thin disk that is buried in the light of a hot, diffuse disk and only revealed when they undergo tidal triggering. The red optical colors of our sample do not indicate any recent significant star formation, and our simulations show that very plunging pericenter passages (rperi &lt; 0.25rvir) are required for tidal triggering. Thus, many cluster early-type dwarfs with less-plunging orbits may host a yet-undetected cold stellar disk component. We discuss possible origin scenarios and consider why similar-mass star-forming galaxies in the field are significantly more thin-disk dominated than in our cluster sample.

Keywords: Galaxy clusters, Galaxy dark matter halos, Galaxy stellar disks, Galaxy environments, Galaxy dynamics, Dwarf galaxies, Galaxy disks, N-body simulations, Galaxy encounters
On the Hubble Constant Tension in the SNe Ia Pantheon Sample. The Hubble constant (H0) tension between Type Ia supernovae (SNe Ia) and Planck measurements ranges from 4 to 6σ. To investigate this tension, we estimate H0 in the ΛCDM and ${w}_{0}{w}_{a}$ CDM (cold dark matter) models by dividing the Pantheon sample, the largest compilation of SNe Ia, into 3, 4, 20, and 40 bins. We fit the extracted H0 values with a function mimicking the redshift evolution: $g{(z)={H}_{0}(z)={\tilde{H}}_{0}/(1+z)}^{\alpha }$ , where α indicates an evolutionary parameter and ${\tilde{H}}_{0}={H}_{0}$ at z = 0. We set the absolute magnitude of SNe Ia so that ${H}_{0}\,=73.5\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$ , and we fix fiducial values for ${{\rm{\Omega }}}_{0m}^{{\rm{\Lambda }}\mathrm{CDM}}=0.298$ and ${{\rm{\Omega }}}_{0m}^{{w}_{0}{w}_{a}\mathrm{CDM}}=0.308$ . We find that H0 evolves with redshift, showing a slowly decreasing trend, with α coefficients consistent with zero only from 1.2 to 2.0σ. Although the α coefficients are compatible with zero in 3σ, this however may affect cosmological results. We measure locally a variation of ${H}_{0}(z=0)-{H}_{0}(z=1)=0.4\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$ in three and four bins. Extrapolating ${H}_{0}(z)$ to z = 1100, the redshift of the last scattering surface, we obtain values of H0 compatible in 1σ with Planck measurements independent of the cosmological models and number of bins we investigated. Thus, we have reduced the H0 tension in the range from 54% to 72% for both cosmological models. If the decreasing trend of ${H}_{0}(z)$ is real, it could be due to astrophysical selection effects or to modified gravity.

Keywords: Type Ia supernovae
Rapid Accretion State Transitions following the Tidal Disruption Event AT2018fyk. Following a tidal disruption event (TDE), the accretion rate can evolve from quiescent to near-Eddington levels and back over timescales of months to years. This provides a unique opportunity to study the formation and evolution of the accretion flow around supermassive black holes (SMBHs). We present 2 yr of multiwavelength monitoring observations of the TDE AT2018fyk at X-ray, UV, optical, and radio wavelengths. We identify three distinct accretion states and two state transitions between them. These appear remarkably similar to the behavior of stellar-mass black holes in outburst. The X-ray spectral properties show a transition from a soft (thermal-dominated) to a hard (power-law-dominated) spectral state around Lbol ∼ few × 10-2 LEdd and the strengthening of the corona over time ∼100-200 days after the UV/optical peak. Contemporaneously, the spectral energy distribution (in particular, the UV to X-ray spectral slope αox) shows a pronounced softening as the outburst progresses. The X-ray timing properties also show a marked change, initially dominated by variability at long (&gt;day) timescales, while a high-frequency (∼10-3 Hz) component emerges after the transition into the hard state. At late times (∼500 days after peak), a second accretion state transition occurs, from the hard into the quiescent state, as identified by the sudden collapse of the bolometric (X-ray+UV) emission to levels below 10-3.4 LEdd. Our findings illustrate that TDEs can be used to study the scale (in)variance of accretion processes in individual SMBHs. Consequently, they provide a new avenue to study accretion states over seven orders of magnitude in black hole mass, removing limitations inherent to commonly used ensemble studies.

Keywords: Accretion, High energy astrophysics, Transient sources, Active galactic nuclei, Time domain astronomy, Low-mass x-ray binary stars
The Effect of Thermal Pressure on Collisionless Magnetic Reconnection Rate. Modeling collisionless magnetic reconnection rate is an outstanding challenge in basic plasma physics research. While the seemingly universal rate of an order ${ \mathcal O }(0.1)$ is often reported in the low-β regime, it is not clear how reconnection rate scales with a higher plasma β. Due to the complexity of the pressure tensor, the available reconnection rate model is limited to the low plasma-β regime, where the thermal pressure is arguably negligible. However, the thermal pressure effect becomes important when $\beta \gtrsim { \mathcal O }(1)$ . Using first-principle kinetic simulations, we show that both the reconnection rate and outflow speed drop as β gets larger. A simple analytical framework is derived to take account of the self-generated pressure anisotropy and pressure gradient in the force balance around the diffusion region, explaining the varying trend of key quantities and reconnection rates in these simulations with different β. The predicted scaling of the normalized reconnection rate is $\simeq { \mathcal O }(0.1/\sqrt{{\beta }_{i0}})$ in the high-β limit, where βi0 is the ion β of the inflow plasma.

Keywords: Galactic center, Heliosphere, Plasma physics, Plasma astrophysics, Intergalactic medium
He I 10830 Å Dimming during Solar Flares. I. The Crucial Role of Nonthermal Collisional Ionizations. While solar flares are predominantly characterized by an intense broadband enhancement to the solar radiative output, certain spectral lines and continua will, in theory, exhibit flare-induced dimmings. Observations of transitions of orthohelium He I λλ 10830 Å and the He I D3 lines have shown evidence of such dimming, usually followed by enhanced emission. It has been suggested that nonthermal collisional ionization of helium by an electron beam, followed by recombinations to orthohelium, is responsible for overpopulating those levels, leading to stronger absorption. However, it has not been possible observationally to preclude the possibility of overpopulating orthohelium via enhanced photoionization of He I by EUV irradiance from the flaring corona followed by recombinations. Here we present radiation hydrodynamics simulations of nonthermal electron-beam-driven flares where (1) both nonthermal collisional ionization of helium and coronal irradiance are included, and (2) only coronal irradiance is included. A grid of simulations covering a range of total energies deposited by the electron beam and a range of nonthermal electron-beam low-energy cutoff values were simulated. In order to obtain flare-induced dimming of the He I 10830 Å line, it was necessary for nonthermal collisional ionization to be present. The effect was more prominent in flares with larger low-energy cutoff values and longer lived in weaker flares and flares with a more gradual energy deposition timescale. These results demonstrate the usefulness of orthohelium line emission as a diagnostic of flare energy transport.

Keywords: Hydrodynamical simulations, Solar flares, Solar flare spectra, Solar physics, Spectroscopy, Solar radiation, Radiative transfer simulations, Solar chromosphere, Active solar chromosphere
Kinetic Features for the Identification of Kelvin-Helmholtz Vortices in In Situ Observations. The boundaries identification of Kelvin-Helmholtz vortices in observational data has been addressed by searching for single-spacecraft small-scale signatures. A recent hybrid Vlasov-Maxwell simulation of Kelvin-Helmholtz instability has pointed out clear kinetic features that uniquely characterize the vortex during both the nonlinear and turbulent stage of the instability. We compare the simulation results with in situ observations of Kelvin-Helmholtz vortices by the Magnetospheric Multiscale satellites. We find good agreement between simulation and observations. In particular, the edges of the vortex are associated with strong current sheets, while the center is characterized by a low value for the magnitude of the total current density and strong deviation of the ion distribution function from a Maxwellian distribution. We also find a significant temperature anisotropy parallel to the magnetic field inside the vortex region and strong agyrotropies near the edges. We suggest that these kinetic features can be useful for the identification of Kelvin-Helmholtz vortices in in situ data.

Keywords: Space plasmas, Space probes, Planetary magnetospheres, Interplanetary discontinuities
The Source of Leaking Ionizing Photons from Haro11: Clues from HST/COS Spectroscopy of Knots A, B, and C. Understanding the escape of ionizing (Lyman continuum) photons from galaxies is vital for determining how galaxies contributed to reionization in the early universe. While directly detecting the Lyman continuum from high-redshift galaxies is impossible due to the intergalactic medium, low-redshift galaxies in principle offer this possibility but require observations from space. The first local galaxy for which Lyman continuum escape was found is Haro 11, a luminous blue compact galaxy at z = 0.02, where observations with the FUSE satellite revealed an escape fraction of 3.3%. However, the FUSE aperture covers the entire galaxy, and it is not clear from where the Lyman continuum is leaking out. Here we utilize Hubble Space Telescope/Cosmic Origins Spectrograph spectroscopy in the wavelength range 1100-1700 Å of the three knots (A, B, and C) of Haro 11 to study the presence of Lyα emission and the properties of intervening gas. We find that all knots have bright Lyα emission. UV absorption lines, originating in the neutral interstellar medium, as well as lines probing the ionized medium, are seen extending to blueshifted velocities of 500 km s-1 in all three knots, demonstrating the presence of an outflowing multiphase medium. We find that knots A and B have large covering fractions of neutral gas, making LyC escape along these sightlines improbable, while knot C has a much lower covering fraction (≲50%). Knot C also has the the highest Lyα escape fraction, and we conclude that it is the most likely source of the escaping Lyman continuum detected in Haro 11. * Based of observations with the NASA/ESA Hubble Space Telescope.

Keywords: Starburst galaxies, Blue compact dwarf galaxies, Photoionization, Interstellar line absorption, Lyman-alpha galaxies