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<jats:title>Abstract</jats:title> <jats:p>We examine the cradle-to-grave magnetic evolution of 10 bipolar ephemeral active regions (BEARs) in solar coronal holes, especially aspects of the magnetic evolution leading to each of 43 obvious microflare events. The data are from the Solar Dynamics Observatory: 211 Å coronal EUV images and line-of-sight photospheric magnetograms. We find evidence that (1) each microflare event is a magnetic explosion that results in a miniature flare arcade astride the polarity inversion line (PIL) of the explosive lobe of the BEAR’s anemone magnetic field; (2) relative to the BEAR’s emerged flux-rope Ω loop, the anemone’s explosive lobe can be an inside lobe, an outside lobe, or an inside-and-outside lobe; (3) 5 events are confined explosions, 20 events are mostly confined explosions, and 18 events are blowout explosions, which are miniatures of the magnetic explosions that make coronal mass ejections (CMEs); (4) contrary to the expectation of Moore et al., none of the 18 blowout events explode from inside the BEAR’s Ω loop during the Ω loop’s emergence; and (5) before and during each of the 43 microflare events, there is magnetic flux cancellation at the PIL of the anemone’s explosive lobe. From finding evident flux cancellation at the underlying PIL before and during all 43 microflare events—together with BEARs evidently being miniatures of all larger solar bipolar active regions—we expect that in essentially the same way, flux cancellation in sunspot active regions prepares and triggers the magnetic explosions for many major flares and CMEs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Using idealized models of the accretion disk, we investigate the effects induced by the modified theories of gravity on the annihilation of the neutrino pair annihilation into electron–positron pairs (<jats:inline-formula> <jats:tex-math> <?CDATA $\nu \bar{\nu }\to {e}^{-}{e}^{+}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>ν</mml:mi> <mml:mover accent="true"> <mml:mrow> <mml:mi>ν</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>¯</mml:mo> </mml:mrow> </mml:mover> <mml:mo>→</mml:mo> <mml:msup> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> </mml:mrow> </mml:msup> <mml:msup> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac7140ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>), occurring near the rotational axis. For the accretion disk, we have considered the models with temperature <jats:italic>T</jats:italic> = constant and <jats:italic>T</jats:italic> ∝ <jats:italic>r</jats:italic> <jats:sup>−1</jats:sup>. In both cases, we find that the modified theories of gravity lead to an enhancement, up to more than 1 order of magnitude with respect to general relativity, of the neutrino pair annihilation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Disk Detective citizen science project recently released a new catalog of disk candidates found by visual inspection of images from NASA’s Wide-field Infrared Survey Explorer mission and other surveys. We applied this new catalog of well-vetted disk candidates to search for new members of nearby young stellar associations (YSAs) using a novel technique based on Gaia data and virtual reality (VR). We examined AB Doradus, Argus, <jats:italic>β</jats:italic> Pictoris, Carina, Columba, Octans-Near, Tucana–Horologium, and TW Hya by displaying them in VR together with other nearby stars, color coded to show infrared excesses found via Disk Detective. Using this method allows us to find new association members in mass regimes where isochrones are degenerate. We propose 10 new YSA members with infrared excesses: three of AB Doradus (HD 44775, HD 40540 and HD 44510), one of <jats:italic>β</jats:italic> Pictoris (HD 198472), two of Octans-Near (HD 157165 and BD+35 2953), and four disk-hosting members of a combined population of Carina, Columba, and Tucana–Horologium: CPD-57 937, HD 274311, HD 41992, and WISEA J092521.90-673224.8. This last object (J0925) appears to be an extreme debris disk with a fractional infrared luminosity of 3.7 × 10<jats:sup>−2</jats:sup>. We also propose two new members of AB Doradus that do not show infrared excesses: TYC 6518-1857-1 and CPD-25 1292. We find HD 15115 appears to be a member of Tucana–Horologium rather than <jats:italic>β</jats:italic> Pictoris. We advocate for membership in Columba–Carina of HD 30447, CPD-35 525, and HD 35841. Finally, we propose that three M dwarfs, previously considered members of Tucana–Horologium are better considered a separate association, tentatively called “Smethells 165”.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigate the formation of the large-scale structures in the present accelerated era in the <jats:italic>f</jats:italic>(<jats:italic>R</jats:italic>) gravity background. This is done by considering the linear growth of matter perturbations at low redshift <jats:italic>z</jats:italic> &lt; 1. The effect of <jats:italic>f</jats:italic>(<jats:italic>R</jats:italic>) alters the behavior of the matter density perturbations from the matter-dominated universe to the late-time accelerated universe, which is encoded in the Newtonian gravitational constant as <jats:italic>G</jats:italic> → <jats:italic>G</jats:italic> <jats:sub>eff</jats:sub>. The modified gravitational constant (<jats:italic>G</jats:italic> <jats:sub>eff</jats:sub>) depends on the form of <jats:italic>f</jats:italic>(<jats:italic>R</jats:italic>). The late-time accelerated expansion affects the formation of large-scale structures by slowing down the growth of matter density. On the other hand, <jats:italic>f</jats:italic>(<jats:italic>R</jats:italic>) increases the growth rate of the matter density perturbations. We have found that the source term in the <jats:italic>f</jats:italic>(<jats:italic>R</jats:italic>) background, <jats:italic>G</jats:italic> <jats:sub>eff</jats:sub>Ω<jats:sub> <jats:italic>m</jats:italic> </jats:sub>, overcomes the accelerated expansion and the effect of accelerated expansion suppresses the formation of the large-scale structures in the asymptotic future.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Recent work has revealed that the light curves of hydrogen-poor (Type I) superluminous supernovae (SLSNe), thought to be powered by magnetar central engines, do not always follow the smooth decline predicted by a simple magnetar spin-down model. Here we present the first systematic study of the prevalence and properties of “bumps” in the post-peak light curves of 34 SLSNe. We find that the majority (44%–76%) of events cannot be explained by a smooth magnetar model alone. We do not find any difference in supernova properties between events with and without bumps. By fitting a simple Gaussian model to the light-curve residuals, we characterize each bump with an amplitude, temperature, phase, and duration. We find that most bumps correspond with an increase in the photospheric temperature of the ejecta, although we do not see drastic changes in spectroscopic features during the bump. We also find a moderate correlation (<jats:italic>ρ</jats:italic> ≈ 0.5; <jats:italic>p</jats:italic> ≈ 0.01) between the phase of the bumps and the rise time, implying that such bumps tend to happen at a certain “evolutionary phase,” (3.7 ± 1.4)<jats:italic>t</jats:italic> <jats:sub>rise</jats:sub>. Most bumps are consistent with having diffused from a central source of variable luminosity, although sources further out in the ejecta are not excluded. With this evidence, we explore whether the cause of these bumps is intrinsic to the supernova (e.g., a variable central engine) or extrinsic (e.g., circumstellar interaction). Both cases are plausible, requiring low-level variability in the magnetar input luminosity, small decreases in the ejecta opacity, or a thin circumstellar shell or disk.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Recent observations of the stellar halo have uncovered the debris of an ancient merger, Gaia–Sausage–Enceladus (GSE), estimated to have occurred ≳8 Gyr ago. Follow-up studies have associated GSE with a large-scale tilt in the stellar halo that links two well-known stellar overdensities in diagonally opposing octants of the Galaxy (the Hercules–Aquila Cloud and Virgo Overdensity; HAC and VOD). In this paper, we study the plausibility of such unmixed merger debris persisting over several gigayears in the Galactic halo. We employ the simulated stellar halo from Naidu et al., which reproduces several key properties of the merger remnant, including the large-scale tilt. By integrating the orbits of these simulated stellar halo particles, we show that adoption of a spherical halo potential results in rapid phase mixing of the asymmetry. However, adopting a tilted halo potential preserves the initial asymmetry in the stellar halo for many gigayears. The asymmetry is preserved even when a realistic growing disk is added to the potential. These results suggest that HAC and VOD are long-lived structures that are associated with GSE and that the dark matter halo of the Galaxy is tilted with respect to the disk and aligned in the direction of HAC–VOD. Such halo–disk misalignment is common in modern cosmological simulations. Lastly, we study the relationship between the local and global stellar halo in light of a tilted global halo comprised of highly radial orbits. We find that the local halo offers a dynamically biased view of the global halo due to its displacement from the Galactic center.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We have developed a tracking algorithm to determine the speeds of supra-arcade downflows (SADs) and set up a system to automatically track SADs and measure some interesting parameters. By conducting an analysis of six flares observed by the Atmospheric Imaging Assembly on the Solar Dynamics Observatory, we detect more smaller and slower SADs than prior work, due to the higher spatial resolution of our observational data. The inclusion of these events with smaller and slower SADs directly results in lower median velocities and widths than in prior work, but the fitted distributions and evolutions of the parameters still show good consistency with prior work. The observed distributions of the widths, speeds, and lifetimes of SADs are consistent with log-normal distributions, indicating that random and unstable processes are responsible for generating SADs during solar eruptions. Also, we find that the fastest SADs occur at approximately the middle of the height ranges. The number of SADs in each image versus time shows that there are “rest phases” of SADs, when few SADs are seen. These findings support the idea that SADs originate from a fluid instability. We compare our results with a numerical simulation that generates SADs using a mixture of the Rayleigh–Taylor instability and the Richtmyer–Meshkov instability, and find that the simulation generates quantities that are consistent with our observational results.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Neutrinos are guaranteed to be observable from the next Galactic supernova (SN). Optical light and gravitational waves are also observable, but may be difficult to observe if the location of the SN in the Galaxy or the details of the explosion are unsuitable. The key to observing the next SN is to first use neutrinos to understand various physical quantities and then link them to other signals. In this paper, we present Monte Carlo sampling calculations of neutrino events from Galactic SN explosions observed with Super-Kamiokande. The analytical solution of neutrino emission, which represents the long-term evolution of the neutrino light curve from SNe, is used as a theoretical template. It gives the event rate and event spectrum through inverse beta decay interactions with explicit model parameter dependence. Parameter estimation is performed on these simulated sample data by fitting least squares using the analytical solution. The results show that the mass, radius, and total energy of a remnant neutron star produced by an SN can be determined with an accuracy of ∼ 0.1 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, ∼1 km, and ∼ 10<jats:sup>51</jats:sup> erg, respectively, for a Galactic SN at 8 kpc.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We model long-term variations in the scintillation of binary pulsar PSR J1603−7202, observed by the 64 m Parkes radio telescope (Murriyang) between 2004 and 2016. We find that the time variation in the scintillation arc curvature is well-modeled by scattering from an anisotropic thin screen of plasma between the Earth and the pulsar. Using our scintillation model, we measure the inclination angle and longitude of ascending node of the orbit, yielding a significant improvement over the constraints from pulsar timing. From our measurement of the inclination angle, we place a lower bound on the mass of J1603−7202's companion of ≳0.5 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> assuming a pulsar mass of ≳1.2 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. We find that the scintillation arcs are most pronounced when the electron column density along the line of sight is increased, and that arcs are present during a known extreme scattering event. We measure the distance to the interstellar plasma and its velocity, and we discuss some structures seen in individual scintillation arcs within the context of our model.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We analyzed multiline observations of a quiescent prominence from the slit spectrograph located at the Ondřejov Observatory. Dopplergrams and integrated intensity maps of the whole prominence were obtained from observations in six spectral lines: Ca <jats:sc>ii</jats:sc> H, H<jats:italic>ϵ</jats:italic>, H<jats:italic>β</jats:italic>, He <jats:sc>i</jats:sc> D3, H<jats:italic>α</jats:italic>, and Ca <jats:sc>ii</jats:sc> IR. By combining integrated intensity maps with non-LTE radiative-transfer modeling, we carefully identified areas in an optically thin regime. The comparison of the Doppler-velocity maps and scatterplots from different lines shows the existence of differences in the velocity of ions and neutrals called velocity drift. The drift is of a local nature, present mostly at prominence edges in the area with a large velocity gradient, as can be tentatively expected based on multifluid MHD models. We could not explore the time evolution of the drift, since our data set consists of a single scan only. Our paper brings another contribution to a rather controversial problem of the detection of multifluid effects in solar prominences.</jats:p>