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<jats:title>Abstract</jats:title> <jats:p>The absolute electron capture cross sections for single and double charge exchanges (CEs) between the highly charged ion O<jats:sup>6+</jats:sup> and CO<jats:sub>2</jats:sub>, CH<jats:sub>4</jats:sub>, H<jats:sub>2</jats:sub>, and N<jats:sub>2</jats:sub>, the dominant collision processes in the solar wind, have been measured in the energies from 7 keV · q (2.63 keV u<jats:sup>−1</jats:sup>) to 52 keV · q (19.5 keV u<jats:sup>−1</jats:sup>). These measurements were carried out in the new experimental instrument setup at Fudan University, and the errors of the cross sections for single and double CEs at the 1<jats:italic>σ</jats:italic> confidence level were about 11% and 16%, respectively. Limited agreement is achieved with single electron capture results calculated by the classical overbarrier model. These cross section data are useful for the simulation of ion–neutral processes in astrophysical environments and to improve the present theoretical model of fundamental atomic processes.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present final Spitzer trigonometric parallaxes for 361 L, T, and Y dwarfs. We combine these with prior studies to build a list of 525 known L, T, and Y dwarfs within 20 pc of the Sun, 38 of which are presented here for the first time. Using published photometry and spectroscopy as well as our own follow-up, we present an array of color–magnitude and color–color diagrams to further characterize census members, and we provide polynomial fits to the bulk trends. Using these characterizations, we assign each object a <jats:italic>T</jats:italic> <jats:sub>eff</jats:sub> value and judge sample completeness over bins of <jats:italic>T</jats:italic> <jats:sub>eff</jats:sub> and spectral type. Except for types ≥T8 and <jats:italic>T</jats:italic> <jats:sub>eff</jats:sub> &lt; 600 K, our census is statistically complete to the 20 pc limit. We compare our measured space densities to simulated density distributions and find that the best fit is a power law (<jats:inline-formula> <jats:tex-math> <?CDATA ${dN}/{dM}\propto {M}^{-\alpha }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjsabd107ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) with <jats:italic>α</jats:italic> = 0.6 ± 0.1. We find that the evolutionary models of Saumon &amp; Marley correctly predict the observed magnitude of the space density spike seen at 1200 K &lt; <jats:italic>T</jats:italic> <jats:sub>eff</jats:sub> &lt; 1350 K, believed to be caused by an increase in the cooling timescale across the L/T transition. Defining the low-mass terminus using this sample requires a more statistically robust and complete sample of dwarfs ≥Y0.5 and with <jats:italic>T</jats:italic> <jats:sub>eff</jats:sub> &lt; 400 K. We conclude that such frigid objects must exist in substantial numbers, despite the fact that few have so far been identified, and we discuss possible reasons why they have largely eluded detection.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The CatWISE2020 Catalog consists of 1,890,715,640 sources over the entire sky selected from Wide-field Infrared Survey Explorer (WISE) and NEOWISE survey data at 3.4 and 4.6 <jats:italic>μ</jats:italic>m (W1 and W2) collected from 2010 January 7 to 2018 December 13. This data set adds two years to that used for the CatWISE Preliminary Catalog, bringing the total to six times as many exposures spanning over 16 times as large a time baseline as the AllWISE catalog. The other major change from the CatWISE Preliminary Catalog is that the detection list for the CatWISE2020 Catalog was generated using <jats:italic>crowdsource</jats:italic> from Schlafly et al., while the CatWISE Preliminary Catalog used the detection software used for AllWISE. These two factors result in roughly twice as many sources in the CatWISE2020 Catalog. The scatter with respect to Spitzer photometry at faint magnitudes in the COSMOS field, which is out of the Galactic Plane and at low ecliptic latitude (corresponding to lower WISE coverage depth) is similar to that for the CatWISE Preliminary Catalog. The 90% completeness depth for the CatWISE2020 Catalog is at W1 = 17.7 mag and W2 = 17.5 mag, 1.7 mag deeper than in the CatWISE Preliminary Catalog. In comparison to Gaia, CatWISE2020 motions are accurate at the 20 mas yr<jats:sup>−1</jats:sup> level for W1∼15 mag sources and at the ∼100 mas yr<jats:sup>−1</jats:sup> level for W1∼17 mag sources. This level of accuracy represents a 12× improvement over AllWISE. The CatWISE catalogs are available in the WISE/NEOWISE Enhanced and Contributed Products area of the NASA/IPAC Infrared Science Archive.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a three-dimensional (3D) numerical solver of the linearized compressible Euler equations (Global Acoustic Linearized Euler), used to model acoustic oscillations throughout the solar interior. The governing equations are solved in conservation form on a fully global spherical mesh (0 ≤ <jats:italic>ϕ</jats:italic> ≤ 2<jats:italic>π</jats:italic>, 0 ≤ <jats:italic>θ</jats:italic> ≤ <jats:italic>π</jats:italic>, 0 ≤ <jats:italic>r</jats:italic> ≤ <jats:italic>R</jats:italic> <jats:sub>⊙</jats:sub>) over a background state generated by the standard solar model S. We implement an efficient pseudospectral computational method to calculate the contribution of the compressible material derivative dyad to internal velocity perturbations, computing oscillations over arbitrary 3D background velocity fields. This model offers a foundation for a “forward-modeling” approach, using helioseismology techniques to explore various regimes of internal mass flows. We demonstrate the efficacy of the numerical method presented in this paper by reproducing observed solar power spectra, showing rotational splitting due to differential rotation, and applying local helioseismology techniques to measure travel times created by a simple model of single-cell meridional circulation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this work, we present 8523 pairs of <jats:italic>R</jats:italic>-band optical photometry observations for the quasar 3C 454.3 made during the period of 2006 October–2018 February on the 70 cm meniscus telescope at Abastumani Observatory, Georgia, to study its intraday variabilities (IDVs) and long-term variations, and we have come to the following results. (1) We detected 10 outbursts, a Δ<jats:italic>R</jats:italic> = 3.825 mag variation, and some IDVs. The IDV timescales are from 4.1 to 285 minutes, with the corresponding variability amplitude being <jats:italic>A</jats:italic> = 2.9%–43.67%. The amplitude increases with IDV timescale. (2) The largest variation over a 1 day timescale is Δ<jats:italic>R</jats:italic> = 1.38 mag. (3) The IDV timescales suggest that the emission sizes are from 8.9 × 10<jats:sup>13</jats:sup> cm to 6.20 × 10<jats:sup>15</jats:sup> cm, and the magnetic field strengths are <jats:italic>B</jats:italic> = 0.18–0.79 G. (4) Period analysis results show three possible long-term periods, <jats:italic>p</jats:italic> = 3.04 ± 0.02 yr, <jats:italic>p</jats:italic> = 1.66 ± 0.06 yr, and <jats:italic>p</jats:italic> = 1.20 ± 0.03 yr in the optical light curve. We adopted the accretion disk models and the lighthouse models to period <jats:italic>p</jats:italic> = 3.04 ± 0.02 yr: in the accretion disk models, the binary black holes have masses <jats:italic>M</jats:italic> = 1.17 × 10<jats:sup>9</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>; in the lighthouse models, we used two boosted jet flux densities to fit the observational light curve. (5) WWZ analysis gives some short-period (high-frequency) signals associated with strong bursts (JD 2,454,302 and JD 2,454,521) with variable frequencies and lasting for the entire observation time span (11.3 yr).</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the first analysis of Cepheid stars observed by the TESS space mission in Sectors 1–5. Our sample consists of 25 pulsators: ten fundamental mode, three overtone and two double-mode classical Cepheids, plus three type II and seven anomalous Cepheids. The targets were chosen from fields with different stellar densities, both from the Galactic field and from the Magellanic System. Three targets have 2 minutes cadence light curves available by the TESS Science Processing Operations Center: for the rest, we prepared custom light curves from the full-frame images with our own differential photometric FITSH pipeline. Our main goal was to explore the potential and the limitations of TESS concerning the various subtypes of Cepheids. We detected many low-amplitude features: weak modulation, period jitter, and timing variations due to light-time effect. We also report signs of nonradial modes and the first discovery of such a mode in an anomalous Cepheid, the overtone star XZ Cet, which we then confirmed with ground-based multicolor photometric measurements. We prepared a custom photometric solution to minimize saturation effects in the bright fundamental-mode classical Cepheid, <jats:italic>β</jats:italic> Dor with the <jats:monospace>lightkurve</jats:monospace> software, and we revealed strong evidence of cycle-to-cycle variations in the star. In several cases, however, fluctuations in the pulsation could not be distinguished from instrumental effects, such as contamination from nearby sources, which also varies between sectors. Finally, we discuss how precise light-curve shapes will be crucial not only for classification purposes but also to determine physical properties of these stars.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Coronal mass ejections (CMEs) are the major drivers of space weather, and an accurate modeling of their initialization and propagation up to 1 au and beyond is an important issue for space weather research and forecasts. In this research, we use the newly developed three-dimensional (3D) flux-rope CME initialization model and 3D IN (interplanetary)-TVD MHD model to study the effect of different CME initial parameters on simulation outputs. The initial CME flux model is established based on the graduated cylindrical shell model. In order to test the influence of the CME initial parameters on the simulation results, we try to run several simulations with different CME initial parameters, then investigate the outputs in interplanetary space. Here, we focus only on cases in which observers are located in the same initial direction of propagation of the CME. Our analysis shows that the parameters specifying the CME initialization in the model, including the initial density, the thickness of CME flux tube, initial mass, and initial magnetic field, have different effects on the simulation results for observers near the Earth and Mars, and on the process of propagation of the CME in interplanetary space. This confirms the important role played by details of the initial implementation of geometric and physical parameters on space weather research and forecasts.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Charge exchange between highly charged ions and neutral atoms and molecules has been considered as one of the important mechanisms controlling soft X-ray emissions in many astrophysical objects and environments. However, for modeling charge exchange soft X-ray emission, the data of <jats:italic>n-</jats:italic> and <jats:italic>l</jats:italic>-resolved state-selective capture cross sections are often obtained by empirical and semiclassical theory calculations. With a newly built cold target recoil-ion momentum spectroscopy (COLTRIMS) apparatus, we perform a series of measurements of the charge exchange of Ne<jats:sup>(8,9)+</jats:sup> ions with He and H<jats:sub>2</jats:sub> for collision energy ranging from 1 to 24.75 keV/u. <jats:italic>n</jats:italic>-resolved state-selective capture cross sections are reported. By comparing the measured state-selective capture cross sections to those calculated by the multichannel Landau–Zener method (MCLZ), it is found that MCLZ calculations are in good agreement with the measurement for the dominant <jats:italic>n</jats:italic> capture for He target. Furthermore, by using <jats:italic>nl</jats:italic>-resolved cross sections calculated by MCLZ and applying <jats:italic>l</jats:italic> distributions commonly used in the astrophysical literature to experimentally derived <jats:italic>n</jats:italic>-resolved cross sections, we calculate the soft X-ray emissions in the charge exchange between 4 keV/u Ne<jats:sup>8+</jats:sup> and He by considering the radiative cascade from the excited Ne<jats:sup>7+</jats:sup> ions. Reasonable agreement is found in comparison to the measurement for even and separable models, and MCLZ calculations give results in a better agreement.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a comprehensive investigation of main-sequence binaries in the DRAGON simulations, which are the first one-million-particle direct <jats:italic>N</jats:italic>-body simulations of globular clusters. We analyze the orbital parameters of the binary samples in two of the DRAGON simulations, D1-R7-IMF93 and D2-R7-IMF01, focusing on their secular evolution and correlations up to 12 Gyr. These two models have different initial stellar mass functions: Kroupa 1993 (D1-R7-IMF93) and Kroupa 2001 (D2-R7-IMF01); and different initial mass-ratio distributions: random paring (D1-R7-IMF93) and a power law (D1-R7-IMF93). In general, the mass ratio of a population of binaries increases over time due to stellar evolution, which is less significant in D2-R7-IMF01. In D1-R7-IMF93, primordial binaries with a mass ratio <jats:italic>q</jats:italic> ≈ 0.2 are most common, and the frequency linearly declines with increasing <jats:italic>q</jats:italic> at all times. Dynamical binaries of both models have higher eccentricities and larger semimajor axes than primordial binaries. They are preferentially located in the inner part of the star cluster. Secular evolution of binary orbital parameters does not depend on the initial mass-ratio distribution, but is sensitive to the initial binary distribution of the system. At <jats:italic>t</jats:italic> = 12 Gyr, the binary fraction decreases radially outwards, and mass segregation is present. A color difference of 0.1 mag in F330W − F814W and 0.2 mag in <jats:italic>NUV</jats:italic> − <jats:italic>y</jats:italic> between the core and the outskirts of both clusters is seen, which is a reflection of the binary radial distribution and the mass segregation in the cluster. The complete set of data for primordial and dynamical binary systems at all snapshot intervals is made publicly available.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a study of molecular outflows using six molecular lines (including <jats:sup>12</jats:sup>CO/<jats:sup>13</jats:sup>CO/C<jats:sup>18</jats:sup>O/HCO<jats:sup>+</jats:sup> (<jats:italic>J</jats:italic> = 1−0) and CS/SiO (<jats:italic>J</jats:italic> = 2−1)) toward nine nearby high-mass star-forming regions with accurate known distances. This work is based on the high-sensitivity observations obtained with the 14 m millimeter telescope of the Purple Mountain Observatory in Delingha. The detection rate of outflows (including <jats:sup>12</jats:sup>CO, <jats:sup>13</jats:sup>CO, HCO<jats:sup>+</jats:sup>, and CS) is 100%. However, the emission of SiO was not detected for all sources. The full line widths (Δ<jats:italic>V</jats:italic>) at 3<jats:italic>σ</jats:italic> above the baseline of these molecular lines have the relationship <jats:inline-formula> <jats:tex-math> <?CDATA ${\rm{\Delta }}{V}_{{}^{12}\mathrm{CO}}\gt {\rm{\Delta }}{V}_{{\mathrm{HCO}}^{+}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjsabceceieqn1.gif" xlink:type="simple" /> </jats:inline-formula> &gt; <jats:inline-formula> <jats:tex-math> <?CDATA ${\rm{\Delta }}{V}_{\mathrm{CS}}\,\approx {\rm{\Delta }}{V}_{{}^{13}\mathrm{CO}}\gt {\rm{\Delta }}{V}_{{}^{18}\mathrm{CO}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjsabceceieqn2.gif" xlink:type="simple" /> </jats:inline-formula>. <jats:sup>12</jats:sup>CO and HCO<jats:sup>+</jats:sup> can be used to trace relatively high-velocity outflows, while <jats:sup>13</jats:sup>CO and CS can be employed to trace relatively low-velocity outflows. The dynamical timescales of the <jats:sup>13</jats:sup>CO and CS outflows are longer than those of the <jats:sup>12</jats:sup>CO and HCO<jats:sup>+</jats:sup> outflows. The mechanical luminosities, masses, mass-loss rates and forces of all outflows (including <jats:sup>12</jats:sup>CO, <jats:sup>13</jats:sup>CO, HCO<jats:sup>+</jats:sup>, and CS) are correlated with the bolometric luminosities of their central IRAS sources.</jats:p>