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<jats:title>Abstract</jats:title> <jats:p>The slow solar wind is generally believed to result from the interaction of open and closed coronal magnetic flux at streamers and pseudostreamers. We use three-dimensional magnetohydrodynamic simulations to determine the detailed structure and dynamics of open-closed interactions that are driven by photospheric convective flows. The photospheric magnetic field model includes a global dipole giving rise to a streamer together with a large parasitic polarity region giving rise to a pseudostreamer that separates a satellite coronal hole from the main polar hole. Our numerical domain extends out to 30<jats:italic>R</jats:italic> <jats:sub>⊙</jats:sub> and includes an isothermal solar wind, so that the coupling between the corona and heliosphere can be calculated rigorously. This system is driven by imposing a large set of quasi-random surface flows that capture the driving of coronal flux in the vicinity of streamer and pseudostreamer boundaries by the supergranular motions. We describe the resulting structures and dynamics. Interchange reconnection dominates the evolution at both streamer and pseudostreamer boundaries, but the details of the resulting structures are clearly different from one another. Additionally, we calculate in situ signatures of the reconnection and determine the dynamic mapping from the inner heliosphere back to the Sun for a test spacecraft orbit. We discuss the implications of our results for interpreting observations from inner heliospheric missions, such as Parker Solar Probe and Solar Orbiter, and for space weather modeling of the slow solar wind.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a study of the variation timescales of the chromospheric activity indicator H<jats:italic>α </jats:italic>on a sample of 13 fully convective, active mid-to-late M stars with masses between 0.1 and 0.3 solar masses. Our goal was to determine the dominant variability timescale and, by inference, a possible mechanism responsible for the variation. We gathered 10 or more high-resolution spectra each of 10 stars using the TRES spectrograph at times chosen to span all phases of stellar rotation, as determined from photometric data from the MEarth Observatories. All stars varied in their H<jats:italic>α</jats:italic> emission. For nine of these stars, we found no correlation between H<jats:italic>α </jats:italic>and rotational phase, indicating that constant emission from fixed magnetic structures, such as star spots and plage, are unlikely to be the dominant source of H<jats:italic>α</jats:italic> emission variability. In contrast, one star, G 7–34, shows a clear relationship between H<jats:italic>α </jats:italic>and stellar rotational phase. Intriguingly, we found that this star is a member of the AB Doradus moving group and hence has the young age of 149 Myr. High-cadence spectroscopic observations of three additional stars revealed that they are variable on timescales ranging from 20 to 45 minutes, which we posit may be due to flaring behavior. For one star, GJ 1111, simultaneous TESS photometry and spectroscopic monitoring show an increase in H<jats:italic>α</jats:italic> emission with increased photometric brightness. We conclude that low-energy flares are able to produce variation in H<jats:italic>α </jats:italic>on the timescales we observe and thus may be the dominant source of H<jats:italic>α </jats:italic>variability on active fully convective M dwarfs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present an investigation of the internal kinematic properties of M79 (NGC 1904). Our study is based on radial velocity measurements obtained from the ESO-VLT Multi-Instrument Kinematic Survey (MIKiS) of Galactic globular clusters for more than 1700 individual stars distributed between ∼0.″3 and 770″ (∼14 three-dimensional half-mass radii) from the center. Our analysis reveals the presence of ordered line-of-sight rotation with a rotation axis almost aligned along the east–west direction and a velocity peak of 1.5 km s<jats:sup>−1</jats:sup> at ∼70″ from the rotation axis. The velocity dispersion profile is well described by the same King model that best fits the projected density distribution, with a constant central plateau at <jats:italic>σ</jats:italic> <jats:sub>0</jats:sub> ∼ 6 km s<jats:sup>−1</jats:sup>. To investigate the cluster rotation in the plane of the sky, we have analyzed the proper motions provided by the Gaia EDR3, finding a signature of rotation with a maximum amplitude of ∼2.0 km s<jats:sup>−1</jats:sup> at ∼80″ from the cluster center. Analyzing the three-dimensional velocity distribution for a subsample of 130 stars, we confirm the presence of systemic rotation and find a rotation axis inclination angle of 37° with respect to the line of sight. As a final result, the comparison of the observed rotation curves with the results of a representative <jats:italic>N</jats:italic>-body simulation of a rotating star cluster shows that the present-day kinematic properties of NGC 1904 are consistent with those of a dynamically old system that has lost a significant fraction of its initial angular momentum.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We search for gravitational-wave signals associated with gamma-ray bursts (GRBs) detected by the Fermi and Swift satellites during the second half of the third observing run of Advanced LIGO and Advanced Virgo (2019 November 1 15:00 UTC–2020 March 27 17:00 UTC). We conduct two independent searches: a generic gravitational-wave transients search to analyze 86 GRBs and an analysis to target binary mergers with at least one neutron star as short GRB progenitors for 17 events. We find no significant evidence for gravitational-wave signals associated with any of these GRBs. A weighted binomial test of the combined results finds no evidence for subthreshold gravitational-wave signals associated with this GRB ensemble either. We use several source types and signal morphologies during the searches, resulting in lower bounds on the estimated distance to each GRB. Finally, we constrain the population of low-luminosity short GRBs using results from the first to the third observing runs of Advanced LIGO and Advanced Virgo. The resulting population is in accordance with the local binary neutron star merger rate.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Exoplanet detection in the past decade by efforts including NASA’s Kepler and TESS missions has revealed many worlds that differ substantially from planets in our own solar system, including more than 150 exoplanets orbiting binary or multi-star systems. This not only broadens our understanding of the diversity of exoplanets, but also promotes our study of exoplanets in the complex binary systems and provides motivation to explore their habitability. In this study, we investigate the habitable zones of circumbinary planets (P-type) based on planetary trajectory and dynamically informed habitable zones. Our results indicate that the mass ratio and orbital eccentricity of binary stars are important factors affecting the orbital stability and habitability of planetary systems. Moreover, planetary trajectory and dynamically informed habitable zones divide planetary habitability into three categories: habitable, periodic habitable, and non-habitable. Therefore, we successfully train a machine-learning model to quickly and efficiently classify these planetary systems, which provides more useful constraints.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We perform a full 3D general relativistic magnetohydrodynamical (GRMHD) simulation of an equal-mass, spinning, binary black hole approaching merger, surrounded by a circumbinary disk and with a minidisk around each black hole. For this purpose, we evolve the ideal GRMHD equations on top of an approximated spacetime for the binary that is valid in every position of space, including the black hole horizons, during the inspiral regime. We use relaxed initial data for the circumbinary disk from a previous long-term simulation, where the accretion is dominated by a <jats:italic>m</jats:italic> = 1 overdensity called the lump. We compare our new spinning simulation with a previous non-spinning run, studying how spin influences the minidisk properties. We analyze the accretion from the inner edge of the lump to the black hole, focusing on the angular momentum budget of the fluid around the minidisks. We find that minidisks in the spinning case have more mass over a cycle than the non-spinning case. However, in both cases we find that most of the mass received by the black holes is delivered by the direct plunging of material from the lump. We also analyze the morphology and variability of the electromagnetic fluxes, and we find they share the same periodicities of the accretion rate. In the spinning case, we find that the outflows are stronger than the non-spinning case. Our results will be useful to understand and produce realistic synthetic light curves and spectra, which can be used in future observations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Asteroseismology is used to infer the interior physics of stars. The Kepler and TESS space missions have provided a vast data set of red-giant lightcurves, which may be used for asteroseismic analysis. These data sets are expected to significantly grow with future missions such as PLATO, and efficient methods are therefore required to analyze these data rapidly. Here, we describe a machine-learning algorithm that identifies red giants from the raw oscillation spectra and captures <jats:italic>p-</jats:italic> and mixed-mode parameters from the red-giant power spectra. We report algorithmic inferences for large frequency separation (Δ<jats:italic>ν</jats:italic>), frequency at maximum amplitude (<jats:inline-formula> <jats:tex-math> <?CDATA ${\nu }_{\max }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>ν</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>max</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac5247ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>), and period separation (ΔΠ) for an ensemble of stars. In addition, we have discovered ∼25 new probable red giants among 151,000 Kepler long-cadence stellar-oscillation spectra analyzed by this method, among which four are binary candidates that appear to possess red-giant counterparts. To validate the results of this method, we selected ∼3000 Kepler stars, at various evolutionary stages ranging from subgiants to red clumps, and compare inferences of Δ<jats:italic>ν</jats:italic>, ΔΠ, and <jats:inline-formula> <jats:tex-math> <?CDATA ${\nu }_{\max }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>ν</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>max</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac5247ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> with estimates obtained using other techniques. The power of the machine-learning algorithm lies in its speed: It is able to accurately extract seismic parameters from 1000 spectra in ∼5 s on a modern computer (a single core of the Intel<jats:sup>®</jats:sup> Xeon<jats:sup>®</jats:sup> Platinum 8280 CPU).</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present 2007–2020 SpeX VISNIR spectral monitoring of the highly variable RW Aur A CTTS. We find direct evidence for a highly excited, IR-bright, asymmetric, and time-variable system. Comparison of the spectral and temporal trends found determines five different components: (1) a stable continuum from 0.7 to 1.3 <jats:italic>μ</jats:italic>m, with color temperature ∼4000 K, produced by the CTTS photospheric surface; (2) variable hydrogen emission lines emitted from hot excited hydrogen in the CTTS’s protostellar atmosphere/accretion envelope; (3) hot CO gas in the CTTS’s protostellar atmosphere/accretion envelope; (4) highly variable 1.8–5.0 <jats:italic>μ</jats:italic>m thermal continuum emission with color temperature ranging from 1130 to 1650 K, due to a surrounding accretion disk that is spatially variable and has an inner wall at <jats:italic>r</jats:italic> ∼ 0.04 au and <jats:italic>T</jats:italic> ∼ 1650 K and outer edges at ∼1200 K; and (5) transient, bifurcated signatures of abundant Fe <jats:sc>ii</jats:sc> + associated S <jats:sc>i</jats:sc>, Si <jats:sc>i</jats:sc>, and Sr <jats:sc>i</jats:sc> in the system’s jet structures. The bifurcated signatures first appeared in 2015, but these collapsed and disappeared into a small single-peaked protostellar atmosphere feature by late 2020. The temporal evolution of RW Aur A’s spectral signatures is consistent with a dynamically excited CTTS system forming differentiated Vesta-sized planetesimals in an asymmetric accretion disk and migrating them inward to be destructively accreted. By contrast, nearby coeval binary companion RW Aur B evinces only a stable WTTS photospheric continuum from 0.7 to 1.3 <jats:italic>μ</jats:italic>m + cold CO gas in absorption + stable 1.8–5.0 <jats:italic>μ</jats:italic>m thermal disk continuum emission with color temperature ∼1650 K.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Redshifted components of chromospheric emission lines in the hard X-ray impulsive phase of solar flares have recently been studied through their 30 s evolution with the high resolution of the Interface Region Imaging Spectrograph. Radiative-hydrodynamic flare models show that these redshifts are generally reproduced by electron-beam-generated chromospheric condensations. The models produce large ambient electron densities, and the pressure broadening of the hydrogen Balmer series should be readily detected in observations. To accurately interpret the upcoming spectral data of flares with the DKIST, we incorporate nonideal, nonadiabatic line-broadening profiles of hydrogen into the RADYN code. These improvements allow time-dependent predictions for the extreme Balmer line wing enhancements in solar flares. We study two chromospheric condensation models, which cover a range of electron-beam fluxes (1 − 5 × 10<jats:sup>11</jats:sup> erg s<jats:sup>−1</jats:sup> cm<jats:sup>−2</jats:sup>) and ambient electron densities (1 − 60 × 10<jats:sup>13</jats:sup> cm<jats:sup>−3</jats:sup>) in the flare chromosphere. Both models produce broadening and redshift variations within 10 s of the onset of beam heating. In the chromospheric condensations, there is enhanced spectral broadening due to large optical depths at H<jats:italic>α</jats:italic>, H<jats:italic>β</jats:italic>, and H<jats:italic>γ</jats:italic>, while the much lower optical depth of the Balmer series H12−H16 provides a translucent window into the smaller electron densities in the beam-heated layers below the condensation. The wavelength ranges of typical DKIST/ViSP spectra of solar flares will be sufficient to test the predictions of extreme hydrogen wing broadening and accurately constrain large densities in chromospheric condensations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present new two-fluid models of accretion disks in active galactic nuclei (AGNs) that aim to address the long-standing problem of Toomre instability in AGN outskirts. In the spirit of earlier works by Sirko &amp; Goodman and others, we argue that Toomre instability is eventually self-regulated via feedback produced by fragmentation and its aftermath. Unlike past semianalytic models, which (i) adopt local prescriptions to connect star formation rates to heat feedback, and (ii) assume that AGN disks self-regulate to a star-forming steady state (with Toomre parameter <jats:italic>Q</jats:italic> <jats:sub>T</jats:sub> = 1), we find that feedback processes are both temporally and spatially nonlocal. The accumulation of many stellar-mass black holes embedded in AGN gas eventually displaces radiation, winds, and supernovae from massive stars as the dominant feedback source. The nonlocality of feedback heating, in combination with the need for heat to efficiently mix throughout the gas, gives rise to steady-state AGN solutions that can have <jats:italic>Q</jats:italic> <jats:sub>T</jats:sub> ≫ 1 and no ongoing star formation. We find self-consistent steady-state solutions in much of the parameter space of AGN mass and accretion rate. These solutions harbor large populations of embedded compact objects that may grow in mass by factors of a few over the AGN lifetime, including into the lower and upper mass gaps. These feedback-dominated AGN disks differ significantly in structure from commonly used 1D disk models, which has broad implications for gravitational-wave-source formation inside AGNs.</jats:p>