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<jats:title>Abstract</jats:title> <jats:p>We present a new high-sensitivity H <jats:sc>i</jats:sc> observation toward nearby spiral galaxy M101 and its adjacent 2° × 2° region using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). From the observation, we detect a more extended and asymmetric H <jats:sc>i</jats:sc> disk around M101. While the H <jats:sc>i</jats:sc> velocity field within the M101's optical disk region is regular, indicating that the relatively strong disturbance occurs in its outer disk. Moreover, we identify three new H <jats:sc>i</jats:sc> clouds located on the southern edge of the M101's H <jats:sc>i</jats:sc> disk. The masses of the three H <jats:sc>i</jats:sc> clouds are 1.3 × 10<jats:sup>7</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, 2.4 × 10<jats:sup>7</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, and 2.0 × 10<jats:sup>7</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, respectively. The H <jats:sc>i</jats:sc> clouds similar to dwarf companion NGC 5477 rotate with the H <jats:sc>i</jats:sc> disk of M101. Unlike NGC 5477, they have no optical counterparts. Furthermore, we detect a new H <jats:sc>i</jats:sc> tail in the extended H <jats:sc>i</jats:sc> disk of M101. The H <jats:sc>i</jats:sc> tail detected gives reliable evidence for M101 interaction with the dwarf companion NGC 5474. We argue that the extraplanar gas (three H <jats:sc>i</jats:sc> clouds) and the H <jats:sc>i</jats:sc> tail detected in the M101's disk may originate from a minor interaction with NGC 5474.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In the standard model of magnetic reconnection, both ions and electrons couple to the newly reconnected magnetic field lines and are ejected away from the reconnection diffusion region in the form of bidirectional burst ion/electron jets. Recent observations propose a new model: electron-only magnetic reconnection without ion coupling in an electron-scale current sheet. Based on the data from the Magnetospheric Multiscale (MMS) mission, we observe a long-extension inner electron diffusion region (EDR) at least 40 <jats:italic>d</jats:italic> <jats:sub>i</jats:sub> away from the <jats:italic>X</jats:italic>-line at the Earth’s magnetopause, implying that the extension of EDR is much longer than the prediction of the theory and simulations. This inner EDR is embedded in an ion-scale current sheet (the width of ∼4 <jats:italic>d</jats:italic> <jats:sub>i</jats:sub>, <jats:italic>d</jats:italic> <jats:sub>i</jats:sub> is ion inertial length). However, such ongoing magnetic reconnection was not accompanied with burst ion outflow, implying the presence of electron-only reconnection in an ion-scale current sheet. Our observations present a new challenge for understanding the model of standard magnetic reconnection and the electron-only reconnection model in an electron-scale current sheet.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Accurate mass-loss rates are essential for meaningful stellar evolutionary models. For massive single stars with initial masses between 8 and 30<jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>the implementation of cool supergiant mass loss in stellar models strongly affects the resulting evolution, and the most commonly used prescription for these cool-star phases is that of de Jager. Recently, we published a new <jats:inline-formula> <jats:tex-math> <?CDATA $\dot{M}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>̇</mml:mo> </mml:mrow> </mml:mover> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac2574ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> prescription calibrated to RSGs with initial masses between 10 and 25 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, which unlike previous prescriptions does not overestimate <jats:inline-formula> <jats:tex-math> <?CDATA $\dot{M}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>̇</mml:mo> </mml:mrow> </mml:mover> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac2574ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> for the most massive stars. Here, we carry out a comparative study to the MESA-MIST models, in which we test the effect of altering mass loss by recomputing the evolution of stars with masses 12–27 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> with the new <jats:inline-formula> <jats:tex-math> <?CDATA $\dot{M}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>̇</mml:mo> </mml:mrow> </mml:mover> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac2574ieqn3.gif" xlink:type="simple" /> </jats:inline-formula>-prescription implemented. We show that while the evolutionary tracks in the HR diagram of the stars do not change appreciably, the mass of the H-rich envelope at core collapse is drastically increased compared to models using the de Jager prescription. This increased envelope mass would have a strong impact on the Type II-P SN lightcurve, and would not allow stars under 30 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> to evolve back to the blue and explode as H-poor SN. We also predict that the amount of H-envelope around single stars at explosion should be correlated with initial mass, and we discuss the prospects of using this as a method of determining progenitor masses from supernova light curves.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Electron heating/acceleration in the foreshock, by which electrons may be energized beyond thermal energies prior to encountering the bow shock, is very important for the bow shock dynamics. And then these electrons would be more easily injected into a process like diffusive shock acceleration. Many mechanisms have been proposed to explain electrons heating/acceleration in the foreshock. Magnetic reconnection is one possible candidate. Taking advantage of the Magnetospheric Multiscale mission, we present two magnetic reconnection events in the dawnside and duskside ion foreshock region, respectively. Super-Alfvénic electron outflow, demagnetization of the electrons and the ions, and crescent electron distributions in the plane perpendicular to the magnetic field are observed in the sub-ion-scale current sheets. Moreover, strong energy conversion from the fields to the plasmas and significant electron temperature enhancement are observed. Our observations provide direct evidence that magnetic reconnection could occur in the foreshock region and heat/accelerate the electrons therein.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The evaluation of the electron–ion bremsstrahlung cross section—exact to all orders in the Coulomb potential—is computationally expensive due to the appearance of hypergeometric functions. Therefore, tabulations are widely used. Here, we provide an approximate formula for the nonrelativistic dipole process valid for all applicable relative velocities and photon energies. Its validity spans from the Born to the classical regime and from soft-photon emission to the kinematic endpoint. The error remains below 3% (and widely below 1%) except at an isolated region of hard-photon emission at the quantum-to-classical crossover. We use the formula to obtain the thermally averaged emission spectrum and cooling function in a Maxwellian plasma and demonstrate that they are accurate to better than 2%.</jats:p>