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<jats:title>Abstract</jats:title> <jats:p>The matter in an accretion disk must lose angular momentum when moving radially inwards but how this works has long been a mystery. By calculating the trajectories of individual colliding neutrals, ions, and electrons in a weakly ionized 2D plasma containing gravitational and magnetic fields, we numerically simulate accretion disk dynamics at the particle level. As predicted by Lagrangian mechanics, the fundamental conserved global quantity is the total canonical angular momentum, not the ordinary angular momentum. When the Kepler angular velocity and the magnetic field have opposite polarity, collisions between neutrals and charged particles cause: (i) ions to move radially inwards, (ii) electrons to move radially outwards, (iii) neutrals to lose ordinary angular momentum, and (iv) charged particles to gain canonical angular momentum. Neutrals thus spiral inward due to their decrease of ordinary angular momentum while the accumulation of ions at small radius and accumulation of electrons at large radius produces a radially outward electric field. In 3D, this radial electric field would drive an out-of-plane poloidal current that produces the magnetic forces that drive bidirectional astrophysical jets. Because this neutral angular momentum loss depends only on neutrals colliding with charged particles, it should be ubiquitous. Quantitative scaling of the model using plausible disk density, temperature, and magnetic field strength gives an accretion rate of 3 × 10<jats:sup>−8</jats:sup> solar mass per year, which is in good agreement with observed accretion rates.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A significant fraction of supernovae show signatures of dense circumstellar material (CSM). While multiple scenarios for creating a dense CSM exist, mass eruption due to injection of energy at the base of the outer envelope is a likely possibility. We carry out radiation hydrodynamical simulations of eruptive mass loss from a typical red supergiant progenitor with an initial mass of 15 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, for the first time focusing on the timescale of the injection as well as energy. We find that not only sufficient injection energy but also sufficient rate of energy injection per unit time, <jats:italic>L</jats:italic> <jats:sub>min</jats:sub> ∼ 8 × 10<jats:sup>40</jats:sup> erg s<jats:sup>−1</jats:sup> in this particular model, is required for eruption of unbound CSM. This result suggests that the energy injection rate needs to be greater than the binding energy of the envelope divided by the dynamical timescale for the eruption. The density profile of the resulting CSM, whose shape was analytically and numerically predicted in the limit of instantaneous energy injection, similarly holds for a finite injection timescale. We discuss our findings in the framework of proposed mass outburst scenarios, specifically wave-driven outbursts and common-envelope ejection.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study multiwavelength and multiscale data to investigate the kinematics of molecular gas associated with the star-forming complexes G045.49+00.04 (G45E) and G045.14+00.14 (G45W) in the Aquila constellation. An analysis of the FUGIN <jats:sup>13</jats:sup>CO(1–0) line data unveils the presence of a giant molecular filament (GMF G45.3+0.1; length ∼75 pc, mass ∼1.1 × 10<jats:sup>6</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) having a coherent velocity structure at [53, 63] km s<jats:sup>−1</jats:sup>. The GMF G45.3+0.1 hosts G45E and G45W complexes at its opposite ends. We find large-scale velocity oscillations along GMF G45.3+0.1, which also reveals the linear velocity gradients of −0.064 and +0.032 km s<jats:sup>−1</jats:sup> pc<jats:sup>−1</jats:sup> at its edges. The photometric analysis of point-like sources shows the clustering of young stellar object (YSO) candidate sources at the filament’s edges where the presence of dense gas and H <jats:sc>ii</jats:sc> regions are also spatially observed. The Herschel continuum maps along with the CHIMPS <jats:sup>13</jats:sup>CO(3–2) line data unravel the presence of parsec scale hub-filament systems (HFSs) in both sites, G45E and G45W. Our study suggests that the global collapse of GMF G45.3+0.1 is end dominated, with the addition to the signature of global nonisotropic collapse at the edges. Overall, GMF G45.3+0.1 is the first observational sample of filament where the edge-collapse and the hub-filament configurations are simultaneously investigated. These observations open the new possibility of massive star formation, including the formation of HFSs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Observations of <jats:sup>12</jats:sup>CO <jats:italic>J</jats:italic> = 1 – 0 and HCN <jats:italic>J</jats:italic> = 1 – 0 emission from NGC 5194 (M51) made with the 50 m Large Millimeter Telescope and the SEQUOIA focal plane array are presented. Using the HCN-to-CO ratio, we examine the dense gas mass fraction over a range of environmental conditions within the galaxy. Within the disk, the dense gas mass fraction varies along the spiral arms but the average value over all spiral arms is comparable to the mean value of interarm regions. We suggest that the near-constant dense gas mass fraction throughout the disk arises from a population of density-stratified, self-gravitating molecular clouds and the required density threshold to detect each spectral line. The measured dense gas fraction significantly increases in the central bulge in response to the effective pressure, <jats:italic>P</jats:italic> <jats:sub> <jats:italic>e</jats:italic> </jats:sub>, from the weight of the stellar and gas components. This pressure modifies the dynamical state of the molecular cloud population and, possibly, the HCN-emitting regions in the central bulge from self-gravitating to diffuse configurations in which <jats:italic>P</jats:italic> <jats:sub> <jats:italic>e</jats:italic> </jats:sub> is greater than the gravitational energy density of individual clouds. Diffuse molecular clouds comprise a significant fraction of the molecular gas mass in the central bulge, which may account for the measured sublinear relationships between the surface densities of the star formation rate and molecular and dense gas.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>While protoplanetary disks are often treated as isolated systems in planet formation models, observations increasingly suggest that vigorous interactions between Class II disks and their environments are not rare. DO Tau is a T Tauri star that has previously been hypothesized to have undergone a close encounter with the HV Tau system. As part of the DESTINYS ESO Large Programme, we present new Very Large Telescope (VLT)/SPHERE polarimetric observations of DO Tau and combine them with archival Hubble Space Telescope (HST) scattered-light images and Atacama Large Millimeter/submillimeter Array (ALMA) observations of CO isotopologues and CS to map a network of complex structures. The SPHERE and ALMA observations show that the circumstellar disk is connected to arms extending out to several hundred astronomical units. HST and ALMA also reveal stream-like structures northeast of DO Tau, some of which are at least several thousand astronomical units long. These streams appear not to be gravitationally bound to DO Tau, and comparisons with previous Herschel far-IR observations suggest that the streams are part of a bridge-like structure connecting DO Tau and HV Tau. We also detect a fainter redshifted counterpart to a previously known blueshifted CO outflow. While some of DO Tau’s complex structures could be attributed to a recent disk–disk encounter, they might be explained alternatively by interactions with remnant material from the star formation process. These panchromatic observations of DO Tau highlight the need to contextualize the evolution of Class II disks by examining processes occurring over a wide range of size scales.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>FRB 180301 is one of the most actively repeating fast radio bursts (FRBs) that has shown polarization angle changes in its radio burst emission, an indication for their likely origin in the magnetosphere of a highly magnetized neutron star. We carried out a multiwavelength campaign with the FAST radio telescope and NICER X-ray observatory to investigate any possible X-ray emission temporally coincident with the bright radio bursts. The observations took place on 2021 March 4, 9 and 19. We detected five bright radio bursts with FAST, four of which were strictly simultaneous with the NICER observations. The peak flux density of the radio bursts ranged between 28 and 105 mJy, the burst fluence between 27 and 170 mJy ms, and the burst durations between 1.7 and 12.3 ms. The radio bursts from FRB 180301 exhibited a complex time domain structure, and subpulses were detected in individual bursts, with no significant circular polarization. The linear degree of polarization in the L band reduced significantly compared to the 2019 observations. We do not detect any X-ray emission in excess of the background during the 5, 10, 100 ms, 1 and 100 s time intervals at/around the radio-burst barycenter-corrected arrival times, at a &gt; 5<jats:italic>σ</jats:italic> confidence level. The 5<jats:italic>σ</jats:italic> upper limits on the X-ray (a) persistent flux is &lt;7.64 × 10<jats:sup>−12</jats:sup> erg cm<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup>, equivalent to <jats:italic>L</jats:italic> <jats:sub>X</jats:sub> &lt; 2.50 × 10<jats:sup>45</jats:sup> erg s<jats:sup>−1</jats:sup> and (b) 5 ms fluence is &lt;2 × 10<jats:sup>−11</jats:sup> erg cm<jats:sup>−2</jats:sup>, at the radio burst regions. Using the 5 ms X-ray fluence upper limit, we can estimate the radio efficiency <jats:italic>η</jats:italic> <jats:sub> <jats:italic>R</jats:italic>/<jats:italic>X</jats:italic> </jats:sub> ≡ <jats:italic>L</jats:italic> <jats:sub>radio</jats:sub>/<jats:italic>L</jats:italic> <jats:sub>X−ray</jats:sub> ≳ 10<jats:sup>−8</jats:sup>. The derived lower limit on <jats:italic>η</jats:italic> <jats:sub> <jats:italic>R</jats:italic>/<jats:italic>X</jats:italic> </jats:sub> is consistent with both magnetospheric models and synchrotron maser models involving relativistic shocks.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Gamma-ray bursts (GRBs) are classified into long and short events. Long GRBs (LGRBs) are associated with the end states of very massive stars, while short GRBs (SGRBs) are linked to the merger of compact objects. GRB 200826A was a peculiar event, because by definition it was an SGRB, with a rest-frame duration of ∼0.5 s. However, this event was energetic and soft, which is consistent with LGRBs. The relatively low redshift (<jats:italic>z</jats:italic> = 0.7486) motivated a comprehensive, multiwavelength follow-up campaign to characterize its host, search for a possible associated supernova (SN), and thus understand the origin of this burst. To this aim we obtained a combination of deep near-infrared (NIR) and optical imaging together with spectroscopy. Our analysis reveals an optical and NIR bump in the light curve whose luminosity and evolution are in agreement with several SNe associated to LGRBs. Analysis of the prompt GRB shows that this event follows the <jats:italic>E</jats:italic> <jats:sub>p,i</jats:sub>–<jats:italic>E</jats:italic> <jats:sub>iso</jats:sub> relation found for LGRBs. The host galaxy is a low-mass star-forming galaxy, typical of LGRBs, but with one of the highest star formation rates, especially with respect to its mass (<jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}{M}_{* }/{M}_{\odot }=8.6$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>8.6</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac60a2ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, SFR ∼ 4.0 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup>). We conclude that GRB 200826A is a typical collapsar event in the low tail of the duration distribution of LGRBs. These findings support theoretical predictions that events produced by collapsars can be as short as 0.5 s in the host frame and further confirm that duration alone is not an efficient discriminator for the progenitor class of a GRB.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The effects of a total solar eclipse that occurred on 2021 December 4 on ionospheric total electron content (TEC) over Antarctic stations were studied. The study was based on GPS data obtained over Antarctica on the day of the eclipse and the days before and after the eclipse over six GPS stations. The findings of this study show that a total solar eclipse lowers the amount of ionization reaching the Earth’s surface with TEC values dropping across the stations. Finally, the enhancement of ΔTEC is quite different from one station to another station. This may also be due to the effect of solar heating conditions and the density of the Sun as exerted over the stations with the Sun side over one station and the clouded part over the others.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We continued our investigation of the plasma characteristics of a quiescent prominence that occurred on 2017 March 30. The prominence was observed simultaneously by several instruments, including the Interface Region Imaging Spectrograph (IRIS) and the Multichannel Subtractive Double Pass (MSDP) spectrograph operating at the Meudon solar tower. We focused on IRIS Mg <jats:sc>ii</jats:sc> h&amp;k and MSDP H<jats:italic>α</jats:italic> spectra, selecting 55 well-coaligned points within the prominence. We computed an extensive grid of 63,000 isothermal and isobaric 1D-slab prominence models with a non-LTE (i.e., departures from the local thermodynamic equilibrium) radiative transfer code. We then performed a 1.5D spectral inversion searching for an optimal model that best fits five parameters of the observed profiles (observables), namely, the integrated intensity of the H<jats:italic>α</jats:italic> and Mg <jats:sc>ii</jats:sc> k lines, the FWHM of both lines, and the ratio of intensities of the Mg <jats:sc>ii</jats:sc> k and Mg <jats:sc>ii</jats:sc> h lines. The latter is sensitive to temperature. Our results show that the prominence is a low-temperature structure, mostly below 10,000 K, with some excursions to higher values (up to 18,000 K) but also rather low temperatures (around 5000 K). The microturbulent velocity is typically low, peaking around 8 km s<jats:sup>−1</jats:sup>, and electron density values are of the order of 10<jats:sup>10</jats:sup> cm<jats:sup>−3</jats:sup>. The peak effective thickness is 500 km, although the values range up to 5000 km. The studied prominence is rather optically thin in the H<jats:italic>α</jats:italic> line and optically thick in the Mg <jats:sc>ii</jats:sc> h&amp;k lines.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Molecular hydrogen normally has only weak, quadrupole transitions between its rovibrational states, but in a static electric field it acquires a dipole moment and a set of allowed transitions. Here we use published ab initio calculations of the static electrical response tensors of the H<jats:sub>2</jats:sub> molecule to construct the perturbed rovibrational eigensystem and its ground state absorptions. We restrict attention to two simple field configurations that are relevant to condensed hydrogen molecules in the interstellar medium (ISM): a uniform electric field and the field of a pointlike charge. The energy eigenstates are mixtures of vibrational and angular momentum eigenstates so there are many transitions that satisfy the dipole selection rules. We find that mixing is strongest among the states with high vibrational excitation, leading to hundreds of absorption lines across the optical and near-infrared. These spectra are very different from that of the field-free molecule, so if they appeared in astronomical data they would be difficult to assign. Furthermore, in a condensed environment the excited states likely have short lifetimes to internal conversion, giving the absorption lines a diffuse appearance. We therefore suggest electrified H<jats:sub>2</jats:sub> as a possible carrier of the diffuse interstellar bands (DIBs). We further argue that in principle it may be possible to account for all of the DIBs with this one carrier. However, despite electrification, the transitions are not very strong and a large column of condensed H<jats:sub>2</jats:sub> would be required, making it difficult to reconcile this possibility with our current understanding of the ISM.</jats:p>