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<jats:title>Abstract</jats:title> <jats:p>We report results of <jats:inline-formula> <jats:tex-math> <?CDATA $0\buildrel{\prime\prime}\over{.} 05$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabadfcieqn1.gif" xlink:type="simple" /> </jats:inline-formula>-resolution observations toward the O-type proto-binary system IRAS 16547–4247 with the Atacama Large Millimeter/submillimeter Array. We present dynamical and chemical structures of the circumbinary disk, circumstellar disks, outflows, and jets, illustrated by multi-wavelength continuum and various molecular lines. In particular, we detect sodium chloride, silicon compounds, and vibrationally excited water lines as probes of the individual protostellar disks at a scale of 100 au. These are complementary to typical hot-core molecules tracing the circumbinary structures on a 1000 au scale. The H<jats:sub>2</jats:sub>O line tracing inner disks has an upper-state energy of <jats:inline-formula> <jats:tex-math> <?CDATA ${E}_{u}/k\gt 3000\,{\rm{K}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabadfcieqn2.gif" xlink:type="simple" /> </jats:inline-formula>, indicating a high temperature of the disks. On the other hand, despite the detected transitions of NaCl, SiO, and SiS not necessarily having high upper-state energies, they are enhanced only in the vicinity of the protostars. We posit that these molecules are the products of dust destruction, which only happens in the inner disks. This is the second detection of alkali metal halide in protostellar systems after the case of the disk of Orion Source I, and also one of few massive protostellar disks associated with high-energy transition water and silicon compounds. These new results suggest that these “hot-disk” lines may be common in innermost disks around massive protostars, and have great potential for future research of massive star formation. We also tentatively find that the twin disks are counter-rotating, which might give a hint of the origin of the massive proto-binary system IRAS 16547–4247.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Magnetosheath jets and plasmoids are very common phenomena downstream of Earth’s quasi-parallel bow shock. As the increase of the dynamic pressure is one of the principal characteristics of magnetosheath jets, the embedded paramagnetic plasmoids have been considered as an special case of the former. Although the properties of both types of structures have been widely studied during the last 20 years, their formation mechanisms have not been examined thoroughly. In this work we perform a 2D local hybrid simulation (kinetic ions – fluid electrons) of a quasi-parallel (<jats:italic>θ</jats:italic> <jats:sub> <jats:italic>Bn</jats:italic> </jats:sub> = 15°), supercritical (<jats:italic>M</jats:italic> <jats:sub> <jats:italic>A</jats:italic> </jats:sub> = 7) collisionless shock in order to study these mechanisms. Specifically, we analyze the formation of one jet and one plasmoid, showing for the first time that they can be produced by different mechanisms related to the same shock. In our simulation, the magnetosheath jet is formed according to the mechanism proposed by Hietala, where at the shock ripples the upstream solar wind suffers locally less deceleration and the flow is focused in the downstream side, producing a compressed and high-velocity region that leads to an increase of dynamic pressure downstream of the shock. The formation of the plasmoid, however, follows a completely new scenario being generated by magnetic reconnection between two plasma layers with opposite <jats:italic>B</jats:italic>-field orientation in the region just behind the shock.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In the Sun, the flows of hot plasma drive a dynamo that generates a global magnetic field as well as smaller-scale local fields. The existence of a magnetic field in turn affects the motion of plasma so that complex dynamic characteristics can be observed. In this Letter, we give an analysis on the localized amplification of magnetic fields in front of a moving pore. Moving with the pore, the formation of semicircular penumbra-like structures and enhancement of horizontal fields can be observed simultaneously. The increasing horizontal magnetic fields in a penumbra-like area probably did not come from the pore, since the penumbra-like structures were not connected to the pore and a magnetic gap existed. The possibility of flux emergence can also be safely excluded. We further report that horizontal magnetic fields in the front of a moving pore are amplified in accordance with the MHD induction equation after necessary yet reasonable simplification. All characteristics show that the flows driven by the moving pore can lead to the amplification of the magnetic fields around its front. The observations are from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present nebular spectra of the Type Ia supernova (SN Ia) SN 2019yvq, which had a bright flash of blue and ultraviolet light after exploding, followed by a rise similar to other SNe Ia. Although SN 2019yvq displayed several other rare characteristics, such as persistent high ejecta velocity near peak brightness, it was not especially peculiar, and if the early “excess” emission were not observed, it would likely be included in cosmological samples. The excess flux can be explained by several different physical models linked to the details of the progenitor system and explosion mechanism. Each has unique predictions for the optically thin emission at late times. In our nebular spectra, we detect strong [Ca <jats:sc>ii</jats:sc>] <jats:italic>λλ</jats:italic>7291, 7324 and Ca near-IR triplet emission, consistent with a double-detonation explosion. We do not detect H, He, or [O <jats:sc>i</jats:sc>] emission, predictions for some single-degenerate progenitor systems and violent white dwarf mergers. The amount of swept-up H or He is &lt;2.8 × 10<jats:sup>−4</jats:sup> and 2.4 × 10<jats:sup>−4</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, respectively. Aside from strong Ca emission, the SN 2019yvq nebular spectrum is similar to those of typical SNe Ia with the same light-curve shape. Comparing to double-detonation models, we find that the Ca emission is consistent with a model with a total progenitor mass of 1.15 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. However, we note that a lower progenitor mass better explains the early light-curve and peak luminosity. The unique properties of SN 2019yvq suggest that thick He-shell double detonations only account for <jats:inline-formula> <jats:tex-math> <?CDATA ${1.1}_{-1.1}^{+2.1} \% $?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabae6eieqn1.gif" xlink:type="simple" /> </jats:inline-formula> of the total “normal” SN Ia rate. The SN 2019yvq is one of the best examples yet that multiple progenitor channels appear necessary to reproduce the full diversity of “normal” SNe Ia.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The destruction of a star by the tides of a supermassive black hole (SMBH) powers a bright accretion flare, and the theoretical modeling of such tidal disruption events (TDEs) can provide a direct means of inferring SMBH properties from observations. Previously it has been shown that TDEs with <jats:italic>β</jats:italic> = <jats:italic>r</jats:italic> <jats:sub>t</jats:sub>/<jats:italic>r</jats:italic> <jats:sub>p</jats:sub> = 1, where <jats:italic>r</jats:italic> <jats:sub>t</jats:sub> is the tidal disruption radius and <jats:italic>r</jats:italic> <jats:sub>p</jats:sub> is the pericenter distance of the star, form an in-plane caustic, or “pancake,” where the tidally disrupted debris is compressed into a one-dimensional line within the orbital plane of the star. Here we show that this result applies generally to all TDEs for which the star is fully disrupted, i.e., that satisfy <jats:italic>β</jats:italic> ≳ 1. We show that the location of this caustic is always outside of the tidal disruption radius of the star and the compression of the gas near the caustic is at most mildly supersonic, which results in an adiabatic increase in the gas density above the tidal density of the black hole. As such, this in-plane pancake revitalizes the influence of self-gravity even for large <jats:italic>β</jats:italic>, in agreement with recent simulations. This finding suggests that for all TDEs in which the star is fully disrupted, self-gravity is revived post-pericenter, keeps the stream of debris narrowly confined in its transverse directions, and renders the debris prone to gravitational instability.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Star clusters appear to be the ideal environment for the assembly of neutron star–neutron star (NS–NS) and black hole–neutron star (BH–NS) binaries. These binaries are among the most interesting astrophysical objects, being potential sources of gravitational waves (GWs) and gamma-ray bursts. We use for the first time high-precision <jats:italic>N</jats:italic>-body simulations of young massive and open clusters to study the origin and dynamical evolution of NSs, within clusters with different initial masses, metallicities, primordial binary fractions, and prescriptions for the compact object natal kicks at birth. We find that the radial profile of NSs is shaped by the BH content of the cluster, which partially quenches the NS segregation due to the BH-burning process. This leaves most of the NSs out of the densest cluster regions, where NS–NS and BH–NS binaries could potentially form. Due to a large velocity kick that they receive at birth, most of the NSs escape the host clusters, with the bulk of their retained population made up of NSs of ∼1.3 <jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{\odot }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabb671ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> coming from the electron-capture supernova process. The details of the primordial binary fraction and pairing can smear out this trend. Finally, we find that a subset of our models produce NS–NS mergers, leading to a rate of ∼0.01–0.1 <jats:inline-formula> <jats:tex-math> <?CDATA ${\mathrm{Gpc}}^{-3}\,{\mathrm{yr}}^{-1}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabb671ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> in the local universe, and compute an upper limit of ∼3 × 10<jats:sup>−2</jats:sup>–3 × 10<jats:sup>−3</jats:sup> <jats:inline-formula> <jats:tex-math> <?CDATA ${\mathrm{Gpc}}^{-3}\,{\mathrm{yr}}^{-1}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabb671ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> for the BH–NS merger rate. Our estimates are several orders of magnitude smaller than the current empirical merger rate from LIGO/Virgo, in agreement with the recent rate estimates for old globular clusters.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Using the PHANGS–ALMA CO(2–1) survey, we characterize molecular gas properties on ∼100 pc scales across 102,778 independent sightlines in 70 nearby galaxies. This yields the best synthetic view of molecular gas properties on cloud scales across the local star-forming galaxy population obtained to date. Consistent with previous studies, we observe a wide range of molecular gas surface densities (3.4 dex), velocity dispersions (1.7 dex), and turbulent pressures (6.5 dex) across the galaxies in our sample. Under simplifying assumptions about subresolution gas structure, the inferred virial parameters suggest that the kinetic energy of the molecular gas typically exceeds its self-gravitational binding energy at ∼100 pc scales by a modest factor (1.3 on average). We find that the cloud-scale surface density, velocity dispersion, and turbulent pressure (1) increase toward the inner parts of galaxies, (2) are exceptionally high in the centers of barred galaxies (where the gas also appears less gravitationally bound), and (3) are moderately higher in spiral arms than in inter-arm regions. The galaxy-wide averages of these gas properties also correlate with the integrated stellar mass, star formation rate, and offset from the star-forming main sequence of the host galaxies. These correlations persist even when we exclude regions with extraordinary gas properties in galaxy centers, which contribute significantly to the inter-galaxy variations. Our results provide key empirical constraints on the physical link between molecular cloud populations and their galactic environment.</jats:p>