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<jats:title>Abstract</jats:title> <jats:p>High-resolution observations from the Interface Region Imaging Spectrometer reveal the existence of a particular type of small solar jet, which arose singly or in clusters from a tornado-like prominence suspended in the corona. In this study, we perform a detailed statistical analysis of 43 selected mini-jets in the tornado event. Our results show that the mini-jets typically have (1) a projected length of 1.0–6.0 Mm, (2) a width of 0.2–1.0 Mm, (3) a lifetime of 10–50 s, (4) a velocity of 100–350 km s<jats:sup>−1</jats:sup>, and (5) an acceleration of 3–20 km s<jats:sup>−2</jats:sup>. Based on spectral diagnostics and EM-Loci analysis, these jets seem to be multithermal small-scale plasma ejections with an estimated average electron density of ∼2.4 × 10<jats:sup>10</jats:sup> cm<jats:sup>−3</jats:sup> and an approximate mean temperature of ∼2.6 × 10<jats:sup>5</jats:sup> K. Their mean kinetic energy density, thermal energy density, and dissipated magnetic field strength are roughly estimated to be ∼9 erg cm<jats:sup>−3</jats:sup>, 3 erg cm<jats:sup>−3</jats:sup>, and 16 G, respectively. The accelerations of the mini-jets, the UV and EUV brightenings at the footpoints of some mini-jets, and the activation of the host prominence suggest that the tornado mini-jets are probably created by fine-scale external or internal magnetic reconnections (a) between the prominence field and the enveloping or background field or (b) between twisted or braided flux tubes within the prominence. The observations provide insight into the geometry of such reconnection events in the corona and have implications for the structure of the prominence magnetic field and the instability that is responsible for the eruption of prominences and coronal mass ejections.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The recent discovery of diffuse dwarf galaxies that are deficient in dark matter appears to challenge the current paradigm of structure formation in our universe. We describe numerical experiments to determine if so-called dark matter deficient galaxies (DMDGs) could be produced when two gas-rich, dwarf-sized galaxies collide with a high relative velocity of ∼300 km s<jats:sup>−1</jats:sup>. Using idealized high-resolution simulations with both mesh-based and particle-based gravito-hydrodynamics codes, we find that DMDGs can form as high-velocity galaxy collisions and separate dark matter from the warm disk gas, which subsequently is compressed by shock and tidal interaction to form stars. Then using the large simulated universe Il<jats:sc>lustris</jats:sc>TNG, we discover a number of high-velocity galaxy collision events in which DMDGs are expected to form. However, we did not find evidence that these types of collisions actually produced DMDGs in the TNG100-1 run. We argue that the resolution of the numerical experiment is critical to realizing the “collision-induced” DMDG formation scenario. Our results demonstrate one of many routes in which galaxies could form with unconventional dark matter fractions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The astrophysical origin of gravitational-wave (GW) events is one of the most timely problems in the wake of the LIGO/Virgo discoveries. In active galactic nuclei (AGNs), binaries form and evolve efficiently by dynamical interactions and gaseous dissipation. Previous studies have suggested that binary black hole (BBH) mergers in AGN disks can contribute significantly to BBH mergers observed by GW interferometers. Here we examine the distribution of the effective spin parameter <jats:italic>χ</jats:italic> <jats:sub>eff</jats:sub> of this GW source population. We extend our semi-analytical model of binary formation and evolution in AGN disks by following the evolution of the binary orbital angular momenta and black hole (BH) spins. BH spins change due to gas accretion and BH mergers, while the binary orbital angular momenta evolve due to gas accretion and binary–single interactions. We find that the distribution of <jats:italic>χ</jats:italic> <jats:sub>eff</jats:sub> predicted by our AGN model is similar to the distribution observed during LIGO/Virgo O1 and O2. On the other hand, if radial migration of BHs is inefficient, <jats:italic>χ</jats:italic> <jats:sub>eff</jats:sub> is skewed toward higher values than the observed distribution, because of the paucity of scattering events that would randomize spin directions relative to the orbital plane. We suggest that high binary masses and the positive correlation between binary mass and the standard deviation of <jats:italic>χ</jats:italic> <jats:sub>eff</jats:sub> for chirp masses up to <jats:inline-formula> <jats:tex-math> <?CDATA $\approx 20\,{M}_{\odot }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaba2ccieqn1.gif" xlink:type="simple" /> </jats:inline-formula> can be possible signatures for mergers originating in AGN disks. Finally, hierarchical mergers in AGN disks naturally produce properties of the recent GW event GW190412, including a low mass ratio, a high primary BH spin, and a significant spin component in the orbital plane.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present new observations of the active star formation region NGC 1333 in the Perseus molecular cloud complex from the James Clerk Maxwell Telescope <jats:italic>B</jats:italic>-Fields In Star-forming Region Observations (BISTRO) survey with the POL-2 instrument. The BISTRO data cover the entire NGC 1333 complex (∼1.5 pc × 2 pc) at 0.02 pc resolution and spatially resolve the polarized emission from individual filamentary structures for the first time. The inferred magnetic field structure is complex as a whole, with each individual filament aligned at different position angles relative to the local field orientation. We combine the BISTRO data with low- and high- resolution data derived from Planck and interferometers to study the multiscale magnetic field structure in this region. The magnetic field morphology drastically changes below a scale of ∼1 pc and remains continuous from the scales of filaments (∼0.1 pc) to that of protostellar envelopes (∼0.005 pc or ∼1000 au). Finally, we construct simple models in which we assume that the magnetic field is always perpendicular to the long axis of the filaments. We demonstrate that the observed variation of the relative orientation between the filament axes and the magnetic field angles are well reproduced by this model, taking into account the projection effects of the magnetic field and filaments relative to the plane of the sky. These projection effects may explain the apparent complexity of the magnetic field structure observed at the resolution of BISTRO data toward the filament network.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Asteroseismology is a powerful tool for probing the inner structure and determining the evolutionary status and the fundamental parameters of stars. The oscillation spectra of slowly pulsating B (SPB) stars show almost uniform period spans, whose pattern is sensitive to the structure of the <jats:italic>μ</jats:italic>-gradient shell beyond the central convective core and hence can be used to efficiently describe their shapes and constrain the convective core. The SPB star KIC 8324482 was observed by Kepler for over 1470 days with a long-cadence pattern. Nearly equidistant period spacing patterns are found for the 14 connective dipolar modes that are extracted from the oscillation spectrum by Zhang et al. In the present work, we analyze them in depth with the <jats:italic>χ</jats:italic> <jats:sup>2</jats:sup>-matching method and determine their <jats:italic>χ</jats:italic> <jats:sup>2</jats:sup>-minimization models (CMMs). Based on those calculated CMMs, we find that KIC 8324482 is a young (<jats:inline-formula> <jats:tex-math> <?CDATA ${t}_{\mathrm{age}}={20.96}_{-1.28}^{+3.85}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaba430ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> Myr), metal-poor (<jats:inline-formula> <jats:tex-math> <?CDATA $[\mathrm{Fe}/{\rm{H}}]=-0.6.{9}_{-0.115}^{+0.176}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaba430ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> dex), and intermediate-mass (<jats:inline-formula> <jats:tex-math> <?CDATA $M={6.075}_{-0.2500}^{+0.1375}\,{M}_{\odot }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaba430ieqn3.gif" xlink:type="simple" /> </jats:inline-formula>) star with a convective core of <jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{\mathrm{CC}}={1.338}_{-0.091}^{+0.057}\,{M}_{\odot }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaba430ieqn4.gif" xlink:type="simple" /> </jats:inline-formula> in mass and <jats:inline-formula> <jats:tex-math> <?CDATA ${R}_{\mathrm{CC}}={0.5175}_{-0.0103}^{+0.0048}\,{R}_{\odot }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaba430ieqn5.gif" xlink:type="simple" /> </jats:inline-formula> in radius and with a surface rotation velocity <jats:inline-formula> <jats:tex-math> <?CDATA ${V}_{\mathrm{eq}}={2.61}_{-0.11}^{+0.13}\,\mathrm{km}\,{{\rm{s}}}^{-1}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaba430ieqn6.gif" xlink:type="simple" /> </jats:inline-formula>. The central hydrogen abundance is of <jats:inline-formula> <jats:tex-math> <?CDATA ${X}_{{\rm{C}}}={0.5046}_{-0.0074}^{+0.0018}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaba430ieqn7.gif" xlink:type="simple" /> </jats:inline-formula>. Asteroseismic analyses indicate that the “propagation time” of <jats:italic>g</jats:italic>-mode in KIC 8324482 is of <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{\Lambda }}}_{0}\,={276.85}_{-0.47}^{+1.26}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaba430ieqn8.gif" xlink:type="simple" /> </jats:inline-formula> <jats:italic>μ</jats:italic>Hz. To well match with the observed period spacing pattern, an extra diffusion mixing (<jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}{D}_{\mathrm{mix}}={3.125}_{-0.250}^{+0.125}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaba430ieqn9.gif" xlink:type="simple" /> </jats:inline-formula>) should be considered, but the normal core overshooting <jats:italic>f</jats:italic> <jats:sub>ov</jats:sub> must be fixed as zero in the best-fitting model. Such ultraweak mixing beyond the convective core corresponds to a fast rotation that is about 20–30 times the asteroseismic suggested rotation Ω<jats:sub>rot</jats:sub> ≃ 0.2 <jats:italic>μ</jats:italic>Hz, if it is thought of as shear mixing induced completely by differential rotation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A near-infrared, color-selected subset of carbon-rich asymptotic giant branch (C-AGB) stars is found to have tightly constrained luminosities in the near-infrared <jats:italic>J</jats:italic> band. Based on <jats:italic>JK</jats:italic> photometry of some 3300 C-AGB stars in the bar of the Large Magellanic Cloud (LMC) we find that these stars have a constant absolute magnitude of <jats:inline-formula> <jats:tex-math> <?CDATA $\langle {M}_{J}\rangle =-6.22$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaba045ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> mag, adopting the detached eclipsing binary (DEB) distance to the LMC of 18.477 ± 0.004 (stat) ± 0.026 (sys). Undertaking a second, independent calibration in the Small Magellanic Cloud, which also has a DEB geometric distance, we find <jats:inline-formula> <jats:tex-math> <?CDATA $\langle {M}_{J}\rangle =-6.18\pm $?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaba045ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> 0.01 (stat) ± 0.05 (sys) mag. For the LMC the scatter is ± 0.27 mag for single-epoch observations, (falling to ± 0.15 mag for multiple observations averaged over a window of more than one year). We provisionally adopt <jats:inline-formula> <jats:tex-math> <?CDATA $\langle {M}_{J}\rangle =-6.20$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaba045ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> mag ± 0.01 (stat) ± 0.04 (sys) mag for the mean absolute magnitude of these stars. Applying this calibration to stars recently observed in the galaxy NGC 253, we determine a distance modulus of 27.66 ± 0.01(stat) ± 0.04 mag (syst), corresponding to a distance of 3.40 ± 0.06 Mpc (stat). This is in excellent agreement with the average tip of the red giant branch (TRGB) distance modulus of 27.68 ± 0.05 mag, assuming <jats:italic>M</jats:italic> <jats:sub> <jats:italic>I</jats:italic> </jats:sub> = −4.05 mag for the TRGB zero-point.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We apply the near-infrared J-region asymptotic giant branch (JAGB) method, recently introduced by Madore &amp; Freedman, to measure the distances to 14 nearby galaxies out to 4 Mpc. We use the geometric detached eclipsing binary (DEB) distances to the LMC and SMC as independent zero-point calibrators. We find excellent agreement with previously published distances based on the tip of the red giant branch (TRGB): the JAGB distance determinations (including the LMC and SMC) agree in the mean to within <jats:inline-formula> <jats:tex-math> <?CDATA ${\rm{\Delta }}(\mathrm{JAGB}-\mathrm{TRGB})\,=+0.025\pm 0.013$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaba9d8ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> mag, just over 1%, where the TRGB <jats:italic>I</jats:italic>-band zero-point is <jats:italic>M</jats:italic> <jats:sub> <jats:italic>I</jats:italic> </jats:sub> = −4.05 mag. With further development and testing, the JAGB method has the potential to provide an independent calibration of Type Ia supernovae, especially with the James Webb Space Telescope. The JAGB stars (with <jats:italic>M</jats:italic> <jats:sub> <jats:italic>J</jats:italic> </jats:sub> = −6.20 mag) can be detected farther than the fainter TRGB stars, allowing greater numbers of calibrating galaxies for the determination of <jats:italic>H</jats:italic> <jats:sub>0</jats:sub>. Along with the TRGB and Cepheids, JAGB stars are amenable to theoretical understanding and further refined empirical calibration. A preliminary test shows little dependence, if any, of the JAGB magnitude on metallicity of the parent galaxy. These early results suggest that the JAGB method has considerable promise for providing high-precision distances to galaxies in the local universe that are independent of distances derived from the Leavitt Law and/or the TRGB method, and it has numerous and demonstrable advantages over the possible use of Mira variables.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We use a large <jats:italic>N</jats:italic>-body simulation to study the relation of the structural properties of dark matter halos to their assembly history and environment. The complexity of individual halo assembly histories can be well described by a small number of principal components (PCs), which, compared to formation times, provide a more complete description of halo assembly histories and have a stronger correlation with halo structural properties. Using decision trees built with the random ensemble method, we find that about 60%, 10%, and 20% of the variances in halo concentration, axis ratio, and spin, respectively, can be explained by combining four dominating predictors: the first PC of the assembly history, halo mass, and two environment parameters. Halo concentration is dominated by halo assembly. The local environment is found to be important for the axis ratio and spin but is degenerate with halo assembly. The small percentages of the variance in the axis ratio and spin that are explained by known assembly and environmental factors suggest that the variance is produced by many nuanced factors and should be modeled as such. The relations between halo intrinsic properties and environment are weak compared to their variances, with the anisotropy of the local tidal field having the strongest correlation with halo properties. Our method of dimension reduction and regression can help simplify the characterization of the halo population and clarify the degeneracy among halo properties.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Drift-pair bursts are an unusual type of solar low-frequency radio emission, which appear in the dynamic spectra as two parallel drifting bright stripes separated in time. Recent imaging spectroscopy observations allowed for the quantitative characterization of the drifting pairs in terms of source size, position, and evolution. Here, the drift-pair parameters are qualitatively analyzed and compared with the newly developed Monte Carlo ray-tracing technique simulating radio-wave propagation in the inhomogeneous anisotropic turbulent solar corona. The results suggest that drift-pair bursts can be formed due to a combination of refraction and scattering processes, with the trailing component being the result of turbulent reflection (turbulent radio echo). The formation of drift-pair bursts requires an anisotropic scattering with the level of plasma density fluctuations comparable to that in type III bursts, but with a stronger anisotropy at the inner turbulence scale. The anisotropic radio-wave scattering model can quantitatively reproduce the key properties of drift-pair bursts: the apparent source size and its increase with time at a given frequency, the parallel motion of the source centroid positions, and the delay between the burst components. The trailing component is found to be virtually cospatial and following the main component. The simulations suggest that drift-pair bursts are likely to be observed closer to the disk center and below 100 MHz due to the effects of free–free absorption and scattering. The exciter of drift pairs is consistent with propagating packets of whistlers, allowing for a fascinating way to diagnose the plasma turbulence and the radio emission mechanism.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Using the multi-instrument observations, we make the first simultaneous imaging and spectral study on the null point of a fan-spine magnetic topology during a solar flare. When magnetic reconnection occurs at the null point, the fan-spine configuration brightens in the (extreme-)ultraviolet channels. In the H<jats:italic>α</jats:italic> images, the fan-spine structure is partly filled and outlined by the bidirectional material flows ejected from the reconnection site. The extrapolated coronal magnetic field confirms the existence of the fan-spine topology. Before and after the flare peak, the total velocity of the outflows is estimated to be about 60 km s<jats:sup>−1</jats:sup>. During the flare, the Si <jats:sc>iv</jats:sc> line profile at the reconnection region is enhanced both in the blue-wing and red-wing. At the flare peak time, the total velocity of the outflows is found to be 144 km s<jats:sup>−1</jats:sup>. Superposed on the Si <jats:sc>iv</jats:sc> profile, there are several deep absorption lines with the blueshift of several tens of km s<jats:sup>−1</jats:sup>. The reason is inferred to be that the bright reconnection region observed in Si <jats:sc>iv</jats:sc> channel is located under the cooler material appearing as dark features in the H<jats:italic>α</jats:italic> line. The blueshifted absorption lines indicate the movement of the cooler material toward the observer. The depth of the absorption lines also depends on the amount of cooler material. These results imply that these kinds of spectral profiles can be used as a tool to diagnose the properties of cooler material above the reconnection site.</jats:p>