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<jats:title>Abstract</jats:title> <jats:p>Over the past decade, the number of known wide-binary systems has expanded exponentially, thanks to the release of data from the Gaia Mission. Some of these wide-binary systems are actually higher-order multiples, where one of the components is an unresolved binary itself. One way to search for these systems is by identifying the overluminous components in the systems. In this study, we examine 4947 K+K wide-binary pairs from the SUPERWIDE catalog, and quantify the relative colors and luminosities of the components to find evidence for additional unresolved companions. The method is best illustrated in a graph that we call the “Lobster” diagram. To confirm that the identified overluminous components are close binary systems, we cross-match our wide binaries with the TESS, K2, and Kepler archives, and search for signs of eclipses and fast stellar rotation modulation in the light curves. We find that 78.9% ± 20.7% of the wide binaries that contain an eclipsing system are identified as overluminous in the “Lobster” diagram, and that 73.5% ± 12.4% of the wide binaries that contain a component showing fast rotation (<jats:italic>P</jats:italic> &lt; 5 days) also show an overluminous component. From these results, we calculate a revised lower limit on the higher-order multiplicity fraction for K+K wide binaries of 40.0% ± 1.6%. We also examine the higher-order multiplicity fraction as a function of projected physical separation and metallicity. The fraction is unusually constant as a function of projected physical separation, while we see no statistically significant evidence that the fraction varies with metallicity.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Interchange reconnection is thought to play an important role in determining the dynamics and material composition of the slow solar wind that originates from near coronal-hole boundaries. To explore the implications of this process we simulate the dynamic evolution of a solar wind stream along a newly-opened magnetic flux tube. The initial condition is composed of a piecewise continuous dynamic equilibrium in which the regions above and below the reconnection site are extracted from steady-state solutions along open and closed field lines. The initial discontinuity at the reconnection site is highly unstable and evolves as a Riemann problem, decomposing into an outward-propagating shock and inward-propagating rarefaction that eventually develop into a classic N-wave configuration. This configuration ultimately propagates into the heliosphere as a coherent structure and the entire system eventually settles to a quasi-steady wind solution. In addition to simulating the fluid evolution we also calculate the time-dependent non-equilibrium ionization of oxygen in real time in order to construct in situ diagnostics of the conditions near the reconnection site. This idealized description of the plasma dynamics along a newly-opened magnetic field line provides a baseline for predicting and interpreting the implications of interchange reconnection for the slow solar wind. Notably, the density and velocity within the expanding N-wave are generally enhanced over the ambient wind, as is the O<jats:sup>7+</jats:sup>/O<jats:sup>6+</jats:sup> ionization ratio, which exhibits a discontinuity across the reconnection site that is transported by the flow and arrives later than the propagating N-wave.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Ultracool dwarfs (UCDs) represent a significant proportion of stars in the Milky Way, and deep samples of these sources have the potential to constrain the formation history and evolution of low-mass objects in the Galaxy. Until recently, spectral samples have been limited to the local volume (<jats:italic>d</jats:italic> &lt; 100 pc). Here, we analyze a sample of 164 spectroscopically characterized UCDs identified by Aganze et al. in the Hubble Space Telescope (HST) WFC3 Infrared Spectroscopic Parallel Survey (WISPS) and 3D-HST. We model the observed luminosity function using population simulations to place constraints on scaleheights, vertical velocity dispersions, and population ages as a function of spectral type. Our star counts are consistent with a power-law mass function and constant star formation history for UCDs, with vertical scaleheights of 249<jats:inline-formula> <jats:tex-math> <?CDATA ${}_{-61}^{+48}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow /> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>61</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>48</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac7053ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> pc for late-M dwarfs, 153<jats:inline-formula> <jats:tex-math> <?CDATA ${}_{-30}^{+56}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow /> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>30</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>56</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac7053ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> pc for L dwarfs, and 175<jats:inline-formula> <jats:tex-math> <?CDATA ${}_{-56}^{+149}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow /> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>56</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>149</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac7053ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> pc for T dwarfs. Using spatial and velocity dispersion relations, these scaleheights correspond to disk population ages of 3.6<jats:inline-formula> <jats:tex-math> <?CDATA ${}_{-1.0}^{+0.8}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow /> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.0</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.8</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac7053ieqn4.gif" xlink:type="simple" /> </jats:inline-formula> Gyr for late-M dwarfs, 2.1<jats:inline-formula> <jats:tex-math> <?CDATA ${}_{-0.5}^{+0.9}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow /> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.5</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.9</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac7053ieqn5.gif" xlink:type="simple" /> </jats:inline-formula> Gyr for L dwarfs, and 2.4<jats:inline-formula> <jats:tex-math> <?CDATA ${}_{-0.8}^{+2.4}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow /> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.8</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>2.4</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac7053ieqn6.gif" xlink:type="simple" /> </jats:inline-formula> Gyr for T dwarfs, which are consistent with prior simulations that predict that L-type dwarfs are on average a younger and less dispersed population. There is an additional 1–2 Gyr systematic uncertainty on these ages due to variances in age-velocity relations. We use our population simulations to predict the UCD yield in the James Webb Space Telescope PASSAGES survey, a similar and deeper survey to WISPS and 3D-HST, and find that it will produce a comparably sized UCD sample, albeit dominated by thick disk and halo sources.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Particle acceleration during magnetic reconnection is a long-standing topic in space, solar, and astrophysical plasmas. Recent 3D particle-in-cell simulations of magnetic reconnection show that particles can leave flux ropes due to 3D field-line chaos, allowing particles to access additional acceleration sites, gain more energy through Fermi acceleration, and develop a power-law energy distribution. This 3D effect does not exist in traditional 2D simulations, where particles are artificially confined to magnetic islands due to their restricted motions across field lines. Full 3D simulations, however, are prohibitively expensive for most studies. Here, we attempt to reproduce 3D results in 2D simulations by introducing ad hoc pitch-angle scattering to a small fraction of the particles. We show that scattered particles are able to transport out of 2D islands and achieve more efficient Fermi acceleration, leading to a significant increase of energetic particle flux. We also study how the scattering frequency influences the nonthermal particle spectra. This study helps achieve a complete picture of particle acceleration in magnetic reconnection.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Constraining planet formation based on the atmospheric composition of exoplanets is a fundamental goal of the exoplanet community. Existing studies commonly try to constrain atmospheric abundances, or to analyze what abundance patterns a given description of planet formation predicts. However, there is also a pressing need to develop methodologies that investigate how to transform atmospheric compositions into planetary formation inferences. In this study we summarize the complexities and uncertainties of state-of-the-art planet formation models and how they influence planetary atmospheric compositions. We introduce a methodology that explores the effect of different formation model assumptions when interpreting atmospheric compositions. We apply this framework to the directly imaged planet HR 8799e. Based on its atmospheric composition, this planet may have migrated significantly during its formation. We show that including the chemical evolution of the protoplanetary disk leads to a reduced need for migration. Moreover, we find that pebble accretion can reproduce the planet’s composition, but some of our tested setups lead to too low atmospheric metallicities, even when considering that evaporating pebbles may enrich the disk gas. We conclude that the definitive inversion from atmospheric abundances to planet formation for a given planet may be challenging, but a qualitative understanding of the effects of different formation models is possible, opening up pathways for new investigations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We perform particle-in-cell simulations to elucidate the microphysics of relativistic weakly magnetized shocks loaded with electron-positron pairs. Various external magnetizations <jats:italic>σ</jats:italic> ≲ 10<jats:sup>−4</jats:sup> and pair-loading factors <jats:italic>Z</jats:italic> <jats:sub>±</jats:sub> ≲ 10 are studied, where <jats:italic>Z</jats:italic> <jats:sub>±</jats:sub> is the number of loaded electrons and positrons per ion. We find the following: (1) The shock becomes mediated by the ion Larmor gyration in the mean field when <jats:italic>σ</jats:italic> exceeds a critical value <jats:italic>σ</jats:italic> <jats:sub>L</jats:sub> that decreases with <jats:italic>Z</jats:italic> <jats:sub>±</jats:sub>. At <jats:italic>σ</jats:italic> ≲ <jats:italic>σ</jats:italic> <jats:sub>L</jats:sub> the shock is mediated by particle scattering in the self-generated microturbulent fields, the strength and scale of which decrease with <jats:italic>Z</jats:italic> <jats:sub>±</jats:sub>, leading to lower <jats:italic>σ</jats:italic> <jats:sub>L</jats:sub>. (2) The energy fraction carried by the post-shock pairs is robustly in the range between 20% and 50% of the upstream ion energy. The mean energy per post-shock electron scales as <jats:inline-formula> <jats:tex-math> <?CDATA ${\overline{E}}_{{\rm{e}}}\propto {\left({Z}_{\pm }+1\right)}^{-1}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mover accent="true"> <mml:mrow> <mml:mi>E</mml:mi> </mml:mrow> <mml:mrow> <mml:mo stretchy="true">¯</mml:mo> </mml:mrow> </mml:mover> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">e</mml:mi> </mml:mrow> </mml:msub> <mml:mo>∝</mml:mo> <mml:msup> <mml:mrow> <mml:mfenced close=")" open="("> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>Z</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>±</mml:mo> </mml:mrow> </mml:msub> <mml:mo>+</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:mfenced> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac713eieqn1.gif" xlink:type="simple" /> </jats:inline-formula>. (3) Pair loading suppresses nonthermal ion acceleration at magnetizations as low as <jats:italic>σ</jats:italic> ≈ 5 × 10<jats:sup>−6</jats:sup>. The ions then become essentially thermal with mean energy <jats:inline-formula> <jats:tex-math> <?CDATA ${\overline{E}}_{{\rm{i}}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mover accent="true"> <mml:mrow> <mml:mi>E</mml:mi> </mml:mrow> <mml:mrow> <mml:mo stretchy="true">¯</mml:mo> </mml:mrow> </mml:mover> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">i</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac713eieqn2.gif" xlink:type="simple" /> </jats:inline-formula>, while electrons form a nonthermal tail, extending from <jats:inline-formula> <jats:tex-math> <?CDATA $E\sim {\left({Z}_{\pm }+1\right)}^{-1}{\overline{E}}_{{\rm{i}}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>E</mml:mi> <mml:mo>∼</mml:mo> <mml:msup> <mml:mrow> <mml:mfenced close=")" open="("> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>Z</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>±</mml:mo> </mml:mrow> </mml:msub> <mml:mo>+</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:mfenced> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> <mml:msub> <mml:mrow> <mml:mover accent="true"> <mml:mrow> <mml:mi>E</mml:mi> </mml:mrow> <mml:mrow> <mml:mo stretchy="true">¯</mml:mo> </mml:mrow> </mml:mover> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">i</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac713eieqn3.gif" xlink:type="simple" /> </jats:inline-formula> to <jats:inline-formula> <jats:tex-math> <?CDATA ${\overline{E}}_{{\rm{i}}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mover accent="true"> <mml:mrow> <mml:mi>E</mml:mi> </mml:mrow> <mml:mrow> <mml:mo stretchy="true">¯</mml:mo> </mml:mrow> </mml:mover> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">i</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac713eieqn4.gif" xlink:type="simple" /> </jats:inline-formula>. When <jats:italic>σ</jats:italic> = 0, particle acceleration is enhanced by the formation of intense magnetic cavities that populate the precursor during the late stages of shock evolution. Here, the maximum energy of the nonthermal ions and electrons keeps growing over the duration of the simulation. Alongside the simulations, we develop theoretical estimates consistent with the numerical results. Our findings have important implications for models of early gamma-ray burst afterglows.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>By applying first principles quantum chemical calculations, we present a complete catalog of the theoretically expected mid-infrared signatures of cationic forms of fullerene with the general formula of <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{C}}}_{60}^{q+}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi mathvariant="normal">C</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>60</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>q</mml:mi> <mml:mo>+</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac75d5ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> (<jats:italic>q</jats:italic> = 1–26). The structural stability and bonding of these exotic species have been reported by us elsewhere. It is found that not only can some of these cations contribute significantly to the flux of the 17.4 and 18.9 <jats:italic>μ</jats:italic>m bands of fullerene that are observed in some planetary nebulae but they also show strong bands that match the position of key astronomical unidentified infrared emission at 11.21, 16.40 and 20–21 <jats:italic>μ</jats:italic>m, which makes them key species for identification. It is also found that the IR signatures of the group of these cations with <jats:italic>q</jats:italic> = 1–6 are well separated from the 6.2 <jats:italic>μ</jats:italic>m band that is associated with free/isolated aromatic hydrocarbon molecules. This is particularly important in the discrimination and exploration of the coexistence of complex hydrocarbon organics and fullerenes in astronomical sources. To provide insight into the effect of ionization on the IR spectrum of fullerene, particularly at the long-wavelength range, the quantitative analysis of the origin of key bands of these cations is presented. Finally, the potential target(s) among these species, specifically aromatic <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{C}}}_{60}^{10+}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi mathvariant="normal">C</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>60</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> <mml:mo>+</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac75d5ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>, are discussed for further astrochemical observations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study time-dependent relativistic jets under the influence of the radiation field of the accretion disk. The accretion disk consists of an inner compact corona and an outer sub-Keplerian disk. The thermodynamics of the fluid is governed by a relativistic equation of state (EOS) for multispecies fluid that enables us to study the effect of composition on jet dynamics. Jets originate from the vicinity of the central black hole, where the effect of gravity is significant and traverses large distances where only special relativistic treatment is sufficient. So we have modified the flat metric to include the effect of gravity. In this modified relativistic framework we have developed a new total variation diminishing routine along with a multispecies EOS for the purpose. We show that the acceleration of jets crucially depends on flow composition. All the results presented are transonic in nature; starting from very low injection velocities, the jets can achieve high Lorentz factors. For sub-Eddington luminosities, lepton-dominated jets can be accelerated to Lorentz factors &gt;50. The change in radiation field due to variation in the accretion disk dynamics will be propagated to the jet in a finite amount of time. Hence, any change in radiation field due to a change in disk configuration will affect the lower part of the jet before it affects the outer part. This can drive shock transition in the jet flow. Depending on the disk oscillation frequency, amplitude, and jet parameters, these shocks can collide with each other and may trigger shock cascades.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We measure the spatially resolved recent star formation history (SFH) of M33 using optical images taken with the Hubble Space Telescope as part of the Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region (PHATTER) survey. The area covered by the observations used in this analysis covers a de-projected area of ∼38 kpc<jats:sup>2</jats:sup> and extends to ∼3.5 and ∼2 kpc from the center of M33 along the major and semimajor axes, respectively. We divide the PHATTER optical survey into 2005 regions that measure 24 arcsec, ∼100 pc, on a side and fit color–magnitude diagrams for each region individually to measure the spatially resolved SFH of M33 within the PHATTER footprint. There are significant fluctuations in the SFH on small spatial scales and also galaxy-wide scales that we measure back to about 630 Myr ago. We observe a more flocculent spiral structure in stellar populations younger than about 80 Myr, while the structure of the older stellar populations is dominated by two spiral arms. We also observe a bar in the center of M33, which dominates at ages older than about 80 Myr. Finally, we find that the mean star formation rate (SFR) over the last 100 Myr within the PHATTER footprint is 0.32 ± 0.02 M<jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup>. We measure a current SFR (over the last 10 Myr) of 0.20 ± 0.03 M<jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup>. This SFR is slightly higher than previous measurements from broadband estimates, when scaled to account for the fraction of the D25 area covered by the PHATTER survey footprint.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present <jats:sc>GaiaHub</jats:sc>, a publicly available tool that combines Gaia measurements with Hubble Space Telescope (HST) archival images to derive proper motions (PMs). It increases the scientific impact of both observatories beyond their individual capabilities. Gaia provides PMs across the whole sky, but the limited mirror size and time baseline restrict the best PM performance to relatively bright stars. HST can measure accurate PMs for much fainter stars over a small field, but this requires two epochs of observation, which are not always available. <jats:sc>GaiaHub</jats:sc> yields considerably improved PM accuracy compared to Gaia-only measurements, especially for faint sources (<jats:italic>G</jats:italic> ≳ 18), requiring only a single epoch of HST data observed more than ∼7 yr ago (before 2012). This provides considerable scientific value, especially for dynamical studies of stellar systems or structures in and beyond the Milky Way (MW) halo, for which the member stars are generally faint. To illustrate the capabilities and demonstrate the accuracy of <jats:sc>GaiaHub</jats:sc>, we apply it to samples of MW globular clusters (GCs) and classical dwarf spheroidal (dSph) satellite galaxies. This allows us, e.g., to measure the velocity dispersions in the plane of the sky for objects out to and beyond ∼100 kpc. We find, on average, mild radial velocity anisotropy in GCs, consistent with existing results for more nearby samples. We observe a correlation between the internal kinematics of the clusters and their ellipticity, with more isotropic clusters being, on average, more round. Our results also support previous findings that Draco and Sculptor dSph galaxies appear to be radially anisotropic systems.</jats:p>