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<jats:title>Abstract</jats:title> <jats:p>The color–magnitude diagrams (CMDs) of intermediate-age star clusters (≲2 Gyr) are much more complex than those predicted by coeval, nonrotating stellar evolution models. Their observed extended main-sequence turnoffs (eMSTOs) could result from variations in stellar age, stellar rotation, or both. The physical interpretation of eMSTOs is largely based on the complex mapping between stellar models—themselves functions of mass, rotation, orientation, and binarity—and the CMD. In this paper, we compute continuous probability densities in three-dimensional color, magnitude, and <jats:inline-formula> <jats:tex-math> <?CDATA ${v}_{{\rm{e}}}\sin i$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>v</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">e</mml:mi> </mml:mrow> </mml:msub> <mml:mi>sin</mml:mi> <mml:mi>i</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac78e1ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> space for individual stars in a cluster’s eMSTO, based on a rotating stellar evolution model. These densities enable the rigorous inference of cluster properties from a stellar model, or, alternatively, constraints on the stellar model from the cluster’s CMD. We use the <jats:monospace>MIST</jats:monospace> stellar evolution models to jointly infer the age dispersion, the rotational distribution, and the binary fraction of the Large Magellanic Cloud cluster NGC 1846. We derive an age dispersion of ∼70–80 Myr, approximately half the earlier estimates due to nonrotating models. This finding agrees with the conjecture that rotational variation is largely responsible for eMSTOs. However, <jats:monospace>MIST</jats:monospace> models do not provide a satisfactory fit to all stars in the cluster and achieve their best agreement at an unrealistically high binary fraction. The lack of agreement near the main-sequence turnoff suggests specific physical changes to the stellar evolution models, including a lower mass for the Kraft break and potentially enhanced main-sequence lifespans for rapidly rotating stars.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The evolution of the metal content of the universe can be tracked through rest-frame UV spectroscopy of damped Ly<jats:italic>α</jats:italic> systems (DLAs). Gas-phase abundances in DLAs must be corrected for dust depletion effects, which can be accomplished by calibrating the relation between abundance ratios such as [Zn/Fe] and depletions (the fraction of metals in gas, as opposed to dust). Using samples of gas-phase abundances and depletions in the Milky Way (MW), LMC, and SMC, we demonstrate that the relation between [Zn/Fe] and other abundance ratios does not change significantly between these local galaxies and DLAs, indicating that [Zn/Fe] should trace depletions of heavy elements in those systems. The availability of photospheric abundances in young massive stars, a proxy for the total (gas+dust) metallicity of neutral gas, in the MW, LMC, and SMC allows us to calibrate the relation between [Zn/Fe] and depletions in these nearby galaxies. We apply the local calibrations of depletions to DLAs. We find that the fraction of metals in dust, the dust-to-gas ratio, and total abundances are 2–5 times lower than inferred from previous depletion calibrations based on MW measurements and a different formalism. However, the trend of dust abundance versus metallicity remains only slightly sublinear for all existing depletion calibrations, contrary to what is inferred from far-IR (FIR), 21 cm, and CO emission in nearby galaxies and predicted by chemical evolution models. Observational constraints on the FIR dust opacity and depletions at metallicities lower than 20% solar will be needed to resolve this tension.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Gravitational lensing of gamma-ray bursts (GRBs) can provide an opportunity to probe the massive compact objects in the universe at different redshifts. We have discovered two consecutive pulses in the light curve of GRB 090717034, with the same temporal profile and different count rate, separated by a time interval, which is identified as a gravitationally lensed candidate in the Fermi-GBM GRB catalog. Here, we use the <jats:italic>χ</jats:italic> <jats:sup>2</jats:sup> minimization method to investigate the similarity of the temporal profile variability of the two pulses as a gravitationally lensed GRB candidate. We find the magnification factor and the time delay between two pulses to minimize the <jats:italic>χ</jats:italic> <jats:sup>2</jats:sup> function. Then, we perform a Monte Carlo simulation on a sample of mock lensed GRBs and compare the <jats:italic>χ</jats:italic> <jats:sup>2</jats:sup> of the lensed GRB candidate with the simulation, which confirms this candidate with 1<jats:italic>σ</jats:italic> confidence level. Assuming that GRB 090717034 is lensed by a pointlike object, the redshifted lens mass is about <jats:italic>M</jats:italic> <jats:sub> <jats:italic>L</jats:italic> </jats:sub>(1 + <jats:italic>z</jats:italic>) = (4.839 ± 1.148) × 10<jats:sup>6 </jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. The lens of this GRB is a candidate for a supermassive black hole along the line of sight to the GRB.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigate a relationship between a decaying spectrum of magnetic field perturbations and kinetic instabilities in a slowly expanding magnetosheath plasma using two-dimensional hybrid expanding simulations in (<jats:italic>X</jats:italic>, <jats:italic>Y</jats:italic>) space. We impose an initial ambient magnetic field <jats:bold> <jats:italic>B</jats:italic> </jats:bold> <jats:sub>0</jats:sub>/<jats:italic>B</jats:italic> <jats:sub>0</jats:sub> = (1, 0, 0), and superimpose a flat spectrum of Alfvénic fluctuations with average amplitudes equal to <jats:italic>δ</jats:italic> <jats:italic>B</jats:italic> = ∣<jats:italic>B</jats:italic> − <jats:italic>B</jats:italic> <jats:sub>0</jats:sub>∣ ∼ 0.2<jats:italic>B</jats:italic> <jats:sub>0</jats:sub>. The expansion leads to the development of temperature anisotropy <jats:italic>A</jats:italic> <jats:sub> <jats:italic>p</jats:italic> </jats:sub> = <jats:italic>T</jats:italic> <jats:sub> <jats:italic>p</jats:italic>⊥</jats:sub>/<jats:italic>T</jats:italic> <jats:sub> <jats:italic>p</jats:italic>∥</jats:sub> &gt; 1 (<jats:italic>T</jats:italic> <jats:sub> <jats:italic>p</jats:italic>⊥</jats:sub>, <jats:italic>T</jats:italic> <jats:sub> <jats:italic>p</jats:italic>∥</jats:sub> are plasma temperatures perpendicular and parallel with respect to <jats:bold> <jats:italic>B</jats:italic> </jats:bold> <jats:sub>0</jats:sub>, respectively) and the system becomes unstable with respect to the ion cyclotron and mirror instabilities. The onset of mirror instability in the early stage of the simulation leads to the development of filaments that fill the simulation volume. The filaments represent pressure-balanced structures as they develop in the form of magnetic field (<jats:italic>δ</jats:italic> <jats:italic>B</jats:italic>) perturbations balanced with corresponding density perturbations. Further expansion of the system leads to the thinning of these filaments, which gradually become extremely narrow. The filamentation maintains the power spectral density in <jats:italic>δ</jats:italic> <jats:italic>B</jats:italic> <jats:sub>⊥</jats:sub> at <jats:inline-formula> <jats:tex-math> <?CDATA ${P}_{{{\boldsymbol{B}}}_{\perp }}\sim {10}^{-3}{B}_{0}^{2}{d}_{p0}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>P</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi mathvariant="bold-italic">B</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊥</mml:mo> </mml:mrow> </mml:msub> </mml:mrow> </mml:msub> <mml:mo>∼</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> <mml:msubsup> <mml:mrow> <mml:mi>B</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msubsup> <mml:msub> <mml:mrow> <mml:mi>d</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>p</mml:mi> <mml:mn>0</mml:mn> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac75c0ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> (here <jats:italic>d</jats:italic> <jats:sub> <jats:italic>p</jats:italic>0</jats:sub> is the proton inertial length) over the range 0.2 &lt; k<jats:italic>d</jats:italic> <jats:sub> <jats:italic>p</jats:italic>0</jats:sub> &lt; 1.1. The filaments remain well developed in the form of density, magnetic field, and temperature anisotropy perturbations at <jats:italic>t</jats:italic> ∼ 10,000/Ω<jats:sub> <jats:italic>p</jats:italic>0</jats:sub> (here Ω<jats:sub> <jats:italic>p</jats:italic>0</jats:sub> is the initial proton gyrofrequency) and slowly dissipate when the expansion continues further.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigate Chandra X-ray observations of the radio-loud quasars J1405+0415 and J1610+1811 at redshifts <jats:italic>z</jats:italic> = 3.215 and <jats:italic>z</jats:italic> = 3.122, respectively, for evidence of extended X-ray emission. Observations totalling 95 ks per target are combined, and X-ray jets that are spatially coincident with known radio features are detected at a greater than 4<jats:italic>σ</jats:italic> significance. Hardness ratios and emission spectra are determined for all X-ray features, and X-ray fluxes and luminosities are measured. Jet-to-core X-ray flux ratios are estimated for each system, and the ratios are consistent with those observed for nearby and more distant jet systems, although the spread in the parameter is large. These results suggest that to first order the X-ray jet emission mechanisms are redshift invariant. In addition to the extended emission analysis, incorporating also archival data from Swift, we examined the properties of a decline in the Chandra flux from the active galactic nucleus (AGN) of J1610+1811 observed between 2018 and 2021. We conclude that the variability is most likely due to a flaring event that occurred between the years 2017 and 2018 and originated from either the AGN or the inner jet region.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>GJ 229B was the first T dwarf to be discovered in 1995, and its spectrum has been more thoroughly observed than that of most other brown dwarfs. Yet a full spectroscopic analysis of its atmosphere has not been done with modern techniques. This spectrum has several peculiar features, and recent dynamical estimates of GJ 229B’s mass and orbit have disagreed widely, both of which warrant closer investigation. With a separation of tens of astronomical units from its host star, GJ 229B falls near the border of the planet and stellar population formation regimes, so its atmosphere could provide clues to formation processes for intermediate objects of this type. In an effort to resolve these questions, we performed retrievals on published spectra of GJ 229B over a wide range of wavelengths (0.5–5.1 <jats:italic>μ</jats:italic>m) using the open-source APOLLO code. Based on these retrievals, we present a more precise mass estimate of 41.6 ± 3.3 <jats:italic>M</jats:italic> <jats:sub> <jats:italic>J</jats:italic> </jats:sub> and an effective temperature estimate of <jats:inline-formula> <jats:tex-math> <?CDATA ${869}_{-7}^{+5}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>869</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>7</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>5</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac5590ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> K, which are more consistent with evolutionary models for brown dwarfs and suggest an older age for the system of &gt;1.0 Gyr. We also present retrieved molecular abundances for the atmosphere, including replicating the previously observed high CO abundance, and discuss their implications for the formation and evolution of this object. This retrieval effort will give us insight into how to study other brown dwarfs and directly imaged planets, including those observed with JWST and other next-generation telescopes.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In recent years, a crisis in the standard cosmology has been caused by inconsistencies in the measurements of some key cosmological parameters, the Hubble constant <jats:italic>H</jats:italic> <jats:sub>0</jats:sub> and cosmic curvature parameter Ω<jats:sub> <jats:italic>K</jats:italic> </jats:sub>, for example. It is necessary to remeasure them with the cosmological model-independent methods. In this paper, based on the distance sum rule, we present such a way to constrain <jats:italic>H</jats:italic> <jats:sub>0</jats:sub> and Ω<jats:sub> <jats:italic>K</jats:italic> </jats:sub> simultaneously in the late universe from strong gravitational lensing time-delay (SGLTD) data and gravitational wave (GW) standard siren data simulated from the future observation of the Einstein Telescope (ET). Based on the data for six currently observed SGLTDs, we find that the constraint precision of <jats:italic>H</jats:italic> <jats:sub>0</jats:sub> from the combined 100 GW events can be comparable with the measurement from the SH0ES collaboration. As the number of GW events increases to 700, the constraint precision of <jats:italic>H</jats:italic> <jats:sub>0</jats:sub> will exceed that of the Planck 2018 results. Considering 1000 GW events as the conservative estimation of ET in the 10 yr observation, we obtain <jats:italic>H</jats:italic> <jats:sub>0</jats:sub> = 73.69 ± 0.36 km s<jats:sup>−1</jats:sup> Mpc<jats:sup>−1</jats:sup> with a 0.5% uncertainty and <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{\Omega }}}_{K}={0.076}_{-0.087}^{+0.068}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">Ω</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>K</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>0.076</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.087</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.068</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac7ce4ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>. In addition, we simulate 55 strong gravitational lensing (SGL) systems with a 6.6% uncertainty for the measurement of time-delay distance. By combining with 1000 GWs, we infer that <jats:italic>H</jats:italic> <jats:sub>0</jats:sub> = 73.65 ± 0.35 km s<jats:sup>−1</jats:sup> Mpc<jats:sup>−1</jats:sup> and Ω<jats:sub> <jats:italic>K</jats:italic> </jats:sub> = 0.008 ± 0.048. Our results suggest that this approach can play an important role in exploring cosmological tensions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>I examine recent fittings of luminous supernovae (LSNe) with extra energy sources of magnetar and helium burning and find that in about half of these LSNe the fitting parameters have some problems. In some LSNe the total energy of these two energy sources is larger than the kinetic energy of the ejecta that the fitting yields. In some other LSNe the total energy of the delayed neutrino explosion mechanism and these two extra sources combined is smaller than the kinetic energy that the fitting yields. These difficulties suggest that, like earlier claims that jets power superluminous supernovae (SLSNe), jets also power the less luminous LSNe. A magnetar might also supply energy. However, in most cases jets supply more energy than the magnetar, during the explosion and possibly at late times. I strengthen an earlier claim that jets launched at magnetar birth cannot be ignored. I explain the trend of maximum rise time for a given luminosity of hydrogen deficient core collapse supernovae, in particular LSNe and SLSNe, with a toy model of jets that are active for a long time after explosion.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>An observation simulator is established, on an event-by-event basis, for the Polarimetry Focusing telescope Array (PFA) on board the planned enhanced X-ray Timing and Polarimetry observatory (eXTP). An event generator, based on XIMPOL, is used to sample the parameters of the X-rays reaching the aperture of the telescope. The trajectories and interactions of X-rays through the telescope and the corresponding secondaries are calculated using the optics and detector simulation model built in GEANT4, before being translated into signals in the pixelated readout electronics. It is shown that mirror deformation is required for the optics simulation model, and transportation of ionization electrons is required for the detector simulation model to reproduce the overall performance of the telescope. The developed tool is useful in different mission phases, such as payload optimization in the design phase, discrimination of new phenomena against known physics models in the calibration phases, and sensitivity studies of potential polarized X-ray sources in observation planning. The sensitivity of PFA to the Crab Nebula and Crab pulsar is investigated to demonstrate the application of the tool. Even with the dilution effect, space-resolved and phase-resolved polarimetry can reveal important aspects of the Crab Nebula and Crab pulsar and help break the degeneracy between different models.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We combine spectroscopic, photometric, and astrometric information from APOGEE data release 17 and Gaia early data release 3 to perform a self-consistent characterization of Gaia-Sausage/Enceladus (GSE), the remnant of the last major merger experienced by the Milky Way, considering stars and globular clusters (GCs) altogether. Our novel set of chemodynamical criteria to select genuine stars of GSE yields a metallicity distribution function with a median [Fe/H] of −1.22 and 0.23 dex dispersion. Stars from GSE present an excess of [Al/Fe] and [Mg/Mn] (also [Mg/Fe]) in comparison to surviving Milky Way dwarf satellites, which can be explained by differences in star formation efficiencies and timescales between these systems. However, stars from Sequoia, another proposed accreted halo substructure, essentially overlap the GSE footprint in all analyzed chemical-abundance spaces, but present lower metallicities. Among the probable GCs of GSE with APOGEE observations available, we find no evidence for atypical [Fe/H] spreads with the exception of <jats:italic>ω</jats:italic> Centauri (<jats:italic>ω</jats:italic>Cen). Under the assumption that <jats:italic>ω</jats:italic>Cen is a stripped nuclear star cluster, we estimate the stellar mass of its progenitor to be <jats:italic>M</jats:italic> <jats:sub>⋆</jats:sub> ≈ 1.3 × 10<jats:sup>9</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, well within literature expectations for GSE. This leads us to envision GSE as the best available candidate for the original host galaxy of <jats:italic>ω</jats:italic>Cen. We also take advantage of Gaia's photometry and APOGEE metallicities as priors to determine fundamental parameters for eight high-probability (&gt;70%) GC members of GSE via statistical isochrone fitting. Finally, the newly determined ages and APOGEE [Fe/H] values are utilized to model the age–metallicity relation of GSE.</jats:p>