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<jats:title>Abstract</jats:title> <jats:p>Coronal condensation and rain are a crucial part of the mass cycle between the corona and chromosphere. In some cases, condensation and subsequent rain originate in the magnetic dips formed during magnetic reconnection. This provides a new and alternative formation mechanism for coronal rain. Until now, only off-limb, rather than on-disk, condensation events during reconnection have been reported. In this paper, employing extreme-ultraviolet (EUV) images of the Solar Terrestrial Relations Observatory (STEREO) and Solar Dynamics Observatory (SDO), we investigate the condensations facilitated by reconnection from 2011 July 14–15, when STEREO was in quadrature with respect to the Sun–Earth line. Above the limb, in STEREO/EUV Imager (EUVI) 171 Å images, higher-lying open structures move downward, reconnect with the lower-lying closed loops, and form dips. Two sets of newly reconnected structures then form. In the dips, bright condensations occur in the EUVI 304 Å images repeatedly, which then flow downward to the surface. In the on-disk observations by SDO/Atmospheric Imaging Assembly (AIA) in the 171 Å channel, these magnetic structures are difficult to identify. Dark condensations appear in the AIA 304 Å images, and then move to the surface as on-disk coronal rain. The cooling and condensation of coronal plasma is revealed by the EUV light curves. If only the on-disk observations were be available, the relation between the condensations and reconnection, shown clearly by the off-limb observations, could not be identified. Thus, we suggest that some on-disk condensation events seen in transition region and chromospheric lines may be facilitated by reconnection.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The choice of the optimal value of the softening length (<jats:italic>ϵ</jats:italic> <jats:sub> <jats:italic>i</jats:italic> </jats:sub>) of each particle dealing with <jats:italic>N</jats:italic>-body simulations has a profound impact on error values in the gravitational force calculation. A slight deviation from its exact optimal value may result in a large error in the calculation. In this paper we augment the accuracy of the existing gravitational force calculation methods by providing a new technique to calculate the individual optimal values of <jats:italic>ϵ</jats:italic> <jats:sub> <jats:italic>i</jats:italic> </jats:sub> for various configurations of the Plummer density model. We have proposed an expression <jats:inline-formula> <jats:tex-math> <?CDATA ${\epsilon }_{\lambda ,i}={\lambda }_{i}{\left(\tfrac{{m}_{i}}{{\rho }_{i}}\right)}^{\tfrac{1}{3}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabe94dieqn1.gif" xlink:type="simple" /> </jats:inline-formula> that relates each particle by considering the average characteristic length (<jats:italic>λ</jats:italic> <jats:sub> <jats:italic>i</jats:italic> </jats:sub>) and density (<jats:italic>ρ</jats:italic> <jats:sub> <jats:italic>i</jats:italic> </jats:sub>), unlike previous studies that considered <jats:italic>ϵ</jats:italic> <jats:sub> <jats:italic>i</jats:italic> </jats:sub> as an exclusive function of <jats:italic>ρ</jats:italic> <jats:sub> <jats:italic>i</jats:italic> </jats:sub>. We have performed gravitational force calculations for each and every particle from the Plummer density model using compact as well as noncompact gravitational force methods based on smoothed particle hydrodynamics. We have tested our new equation for the entire range of numerical simulations performed during the study. It is found that the errors in our force calculations are not only lower than those estimated from previous studies but also remain flat for various considerations of nearest neighboring particles (<jats:italic>N</jats:italic> <jats:sub>neigh</jats:sub>). The adjusted expression of <jats:italic>ϵ</jats:italic> <jats:sub> <jats:italic>λ</jats:italic>,<jats:italic>i</jats:italic> </jats:sub> in our study has less dependence on <jats:italic>N</jats:italic> <jats:sub>neigh</jats:sub> in the Plummer sphere. Finally, based on the results obtained using the method proposed in this study, we find that it remarkably improves both the accuracy as well as the stability of the gravitational force calculation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In November 2020, the Swift team announced an update to the UltraViolet and Optical Telescope calibration to correct for the loss of sensitivity over time. This correction affects observations in the three near-ultraviolet (UV) filters, by up to 0.3 mag in some cases. As UV photometry is critical to characterizing tidal disruption events (TDEs) and other peculiar nuclear outbursts, we recomputed published Swift data for TDEs and other singular nuclear outbursts with Swift photometry in 2015 or later as a service to the community. Using archival UV, optical, and infrared photometry, we ran host SED fits for each host galaxy. From these, we computed synthetic host magnitudes and host-galaxy properties. We calculated host-subtracted magnitudes for each transient and computed blackbody fits. In addition to the nuclear outbursts, we include the ambiguous transient ATLAS18qqn (AT2018cow), which has been classified as a potential TDE on an intermediate-mass black hole. Finally, with updated bolometric light curves, we recover the relationship of Hinkle et al., where more-luminous TDEs decay more slowly than less-luminous TDEs, with decreased scatter compared to the original relationship.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present analytic estimates of the fractional uncertainties on the mass, radius, surface gravity, and density of a transiting planet, using only empirical or semi-empirical measurements. We first express these parameters in terms of transit photometry and radial velocity (RV) observables, as well as the stellar radius <jats:italic>R</jats:italic> <jats:sub>⋆</jats:sub>, if required. In agreement with previous results, we find that, assuming a circular orbit, the surface gravity of the planet (<jats:italic>g</jats:italic> <jats:sub> <jats:italic>p</jats:italic> </jats:sub>) depends only on empirical transit and RV parameters, namely the planet period <jats:italic>P</jats:italic>, the transit depth <jats:italic>δ</jats:italic>, the RV semi-amplitude <jats:italic>K</jats:italic> <jats:sub>⋆</jats:sub>, the transit duration <jats:italic>T</jats:italic>, and the ingress/egress duration <jats:italic>τ</jats:italic>. However, the planet mass and density depend on all these quantities, plus <jats:italic>R</jats:italic> <jats:sub>⋆</jats:sub>. Thus, an inference about the planet mass, radius, and density must rely upon an external constraint such as the stellar radius. For bright stars, stellar radii can now be measured nearly empirically by using measurements of the stellar bolometric flux, the effective temperature, and the distance to the star via its parallax, with the extinction <jats:italic>A</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub> being the only free parameter. For any given system, there is a hierarchy of achievable precisions on the planetary parameters, such that the planetary surface gravity is more accurately measured than the density, which in turn is more accurately measured than the mass. We find that surface gravity provides a strong constraint on the core mass fraction of terrestrial planets. This is useful, given that the surface gravity may be one of the best measured properties of a terrestrial planet.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Parker first proposed (1972) that coronal heating was the necessary outcome of an energy flux caused by the tangling of coronal magnetic field lines by photospheric flows. In this paper we discuss how this model has been modified by subsequent numerical simulations outlining in particular the substantial differences between the “nanoflares” introduced by Parker and “elementary events,” defined here as small-scale spatially and temporally isolated heating events resulting from the continuous formation and dissipation of field-aligned current sheets within a coronal loop. We present numerical simulations of the compressible 3D MHD equations using the HYPERION code. We use two clustering algorithms to investigate the properties of the simulated elementary events: an IDL implementation of a density-based spatial clustering of applications with noise technique, and our own physical distance clustering algorithm. We identify and track elementary heating events in time, both in temperature and in Joule heating space. For every event we characterize properties such as density, temperature, volume, aspect ratio, length, thickness, duration, and energy. The energies of the events are in the range of 10<jats:sup>18</jats:sup>–10<jats:sup>21</jats:sup> erg, with durations shorter than 100 s. A few events last up to 200 s and release energies up to 10<jats:sup>23</jats:sup> erg. While high temperatures are typically located at the flux tube apex, the currents extend all the way to the footpoints. Hence, a single elementary event cannot at present be detected. The observed emission is due to the superposition of many elementary events distributed randomly in space and time within the loop.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this work, we present simulations of thin accretion disks around black holes, in order to investigate a mean-field disk dynamo, using our resistive GRMHD code, which is able to produce a large-scale magnetic flux. We consider a weak seed field in an initially thin disk, a background (turbulent) magnetic diffusivity, and the dynamo action itself. A standard quenching mechanism is applied to mitigate an otherwise exponential increase in the magnetic field. Comparison simulations of an initial Fishbone–Moncrief torus suggest that reconnection may provide another quenching mechanism. The dynamo-generated magnetic flux expands from the disk interior into the disk corona, becomes advected by disk accretion, and fills the axial region of the domain. The dynamo leads to an initially rapid increase in magnetic energy and flux, while for later evolutionary stages the growth stabilizes. Accretion toward the black hole depends strongly on the type of magnetic-field structure that develops. The radial field component supports extraction of angular momentum, and thus accretion. It also sets the conditions for launching a disk wind, initially from the inner disk area. When a strong field engulfs the disk, strong winds are launched, predominantly driven by the pressure gradient of the toroidal field. For rotating black holes, we identify a Poynting flux-dominated jet, driven by the Blandford–Znajek mechanism. This axial Poynting flux is advected from the disk, and therefore accumulates at the expense of the flux carried by the disk wind, which is itself regenerated by the disk dynamo.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>It has been proposed that spin-polarized cosmic radiation can induce asymmetric changes in helical biopolymers that may account for the emergence of biological homochirality. The parity violation in the weak interaction has direct consequences on the transport of polarization in cosmic ray showers. In this paper, we show that muons retain their polarization down to energies at which they can initiate enantioselective mutagenesis. Therefore, muons are most likely to succeed in establishing the connection between broken symmetries in the standard model of particle physics and that found in living organisms. We calculate the radiation doses deposited by primary and secondary cosmic rays at various prime targets for the searches of life in the solar system: Mars, Venus, Titan, icy moons and planetesimals, and discuss the implications for the enantioselective mutagenesis proposed as to be the driver of homochiralization. Earth is unusual in that spin-polarized muons dominate the cosmic radiation at its surface.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We analyze the coronal elemental abundances during a small flare using Hinode/EIS observations. Compared to the preflare elemental abundances, we observed a strong increase in coronal abundance of Ca <jats:sc>xiv</jats:sc> 193.84 Å, an emission line with low first ionization potential (FIP &lt; 10 eV), as quantified by the ratio Ca/Ar during the flare. This is in contrast to the unchanged abundance ratio observed using Si <jats:sc>x</jats:sc> 258.38 Å/S <jats:sc>x</jats:sc> 264.23 Å. We propose two different mechanisms to explain the different composition results. First, the small flare-induced heating could have ionized S, but not the noble gas Ar, so that the flare-driven Alfvén waves brought up Si, S, and Ca in tandem via the ponderomotive force which acts on ions. Second, the location of the flare in strong magnetic fields between two sunspots may suggest fractionation occurred in the low chromosphere, where the background gas is neutral H. In this region, high-FIP S could behave more like a low-FIP than a high-FIP element. The physical interpretations proposed generate new insights into the evolution of plasma abundances in the solar atmosphere during flaring, and suggests that current models must be updated to reflect dynamic rather than just static scenarios.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The past decade has seen impressive progress in the detection of <jats:italic>z</jats:italic> &gt; 7 galaxies with the Hubble Space Telescope; however, little is known about their properties. The James Webb Space Telescope will revolutionize the high-<jats:italic>z</jats:italic> field by providing near-IR (i.e., rest-frame optical) data of unprecedented depth and spatial resolution. Measuring galaxy quantities such as resolved stellar ages or gas metallicity gradients traditionally requires spectroscopy, as broadband imaging filters are generally too coarse to fully isolate diagnostics such as the 4000 Å (rest-frame) break, continuum emission from aged stars, and key emission lines (e.g., [O <jats:sc>ii</jats:sc>], [O <jats:sc>iii</jats:sc>], H<jats:italic>β</jats:italic>). However, in this paper, we show that adding NIRCam images through a strategically chosen medium-band filter to common wide-band filter sets adopted by ERS and GTO programs delivers tighter constraints on these galactic properties. To constrain the choice of filter, we perform a systematic investigation of which combinations of wide-band filters from ERS and GTO programs and single medium-band filters offer the tightest constraints on several galaxy properties at redshifts <jats:italic>z</jats:italic> ∼ 7–11. We employ the JAGUAR extragalactic catalogs to construct statistical samples of physically motivated mock photometry and conduct SED-fitting procedures to evaluate the accuracy of galaxy property (and photo-<jats:italic>z</jats:italic>) recovery with a simple star formation history model. We find that adding &gt;4.1 <jats:italic>μ</jats:italic>m medium filters at comparable depth to the broadband filters can significantly improve photo-<jats:italic>z</jats:italic>s and yield close to order-of-magnitude improvements in the determination of quantities such as stellar ages, metallicities, SF-related quantities, and emission-line fluxes at <jats:italic>z</jats:italic> ∼ 8. For resolved sources, the proposed approach enables the spatially resolved determination of these quantities that would be prohibitive with slit spectroscopy.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Compact binary mergers that involve at least one neutron star, either binary neutron star or black hole–neutron star coalescences, are thought to be the potential sources of electromagnetic emission due to the material ejected during the merger or those left outside the central object after the merger. Since the intensity of these electromagnetic transients decays rapidly with time, one should pay more attention to early emissions from such events, which are useful in revealing the nature of these mergers. In this work, we study the early emission of kilonovae, short gamma-ray bursts (GRBs), and cocoons that could be produced in those mergers. We estimate their luminosities and timescales as functions of the chirp mass, which is the most readily constrained parameter from the gravitational wave detections of these events. We focus on the range of chirp mass as 1.3–2.7 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, which is compatible with one of the merging components being a so-called “mass gap” black hole. We show that the electromagnetic observation of these transients could be used to distinguish the types of the mergers when the detected chirp mass falls in the range of 1.5–1.7<jats:italic> M</jats:italic> <jats:sub>⊙</jats:sub>. Applying our analysis to the subthreshold GRB GBM-190816, we found that for this particular event the effective spin should be larger than 0.6 and the mass of the heavier object might be larger than 5.5<jats:italic> M</jats:italic> <jats:sub>⊙</jats:sub> for the phenomenological Steiner–Fischer–Hempel equation of state.</jats:p>