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<jats:title>Abstract</jats:title> <jats:p>We determine the distance to the Sculptor Dwarf Spheroidal via three Population II stellar distance indicators: (a) the Tip of the Red Giant Branch (TRGB), (b) RR Lyrae variables (RRLs), and (c) the ridgeline of the blue horizontal branch (HB). High signal-to-noise, wide-field <jats:italic>VI</jats:italic> imaging that covers an area <jats:inline-formula> <jats:tex-math> <?CDATA $48^{\prime} \,\times \,48^{\prime} $?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>48</mml:mn> <mml:mo accent="false">′</mml:mo> <mml:mspace width="0.25em" /> <mml:mo>×</mml:mo> <mml:mspace width="0.25em" /> <mml:mn>48</mml:mn> <mml:mo accent="false">′</mml:mo> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6fe0ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> and reaches a photometric depth approximately 2 mag fainter than the HB was acquired with the Magellan-Baade 6.5 m telescope. The true modulus derived from Sculptor’s TRGB is found to be <jats:inline-formula> <jats:tex-math> <?CDATA ${\mu }_{o}^{\mathrm{TRGB}}=19.59\,\pm \,{0.07}_{\mathrm{stat}}\,\pm \,{0.05}_{\mathrm{sys}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>μ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>o</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>TRGB</mml:mi> </mml:mrow> </mml:msubsup> <mml:mo>=</mml:mo> <mml:mn>19.59</mml:mn> <mml:mspace width="0.25em" /> <mml:mo>±</mml:mo> <mml:mspace width="0.25em" /> <mml:msub> <mml:mrow> <mml:mn>0.07</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>stat</mml:mi> </mml:mrow> </mml:msub> <mml:mspace width="0.25em" /> <mml:mo>±</mml:mo> <mml:mspace width="0.25em" /> <mml:msub> <mml:mrow> <mml:mn>0.05</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>sys</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6fe0ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> mag. Along with periods adopted from the literature, newly acquired RRL phase points are fit with template light curves to determine <jats:inline-formula> <jats:tex-math> <?CDATA ${\mu }_{{W}_{I,V-I}}^{\mathrm{RRL}}=19.60\pm {0.01}_{\mathrm{stat}}\pm {0.05}_{\mathrm{sys}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>μ</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>W</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>I</mml:mi> <mml:mo>,</mml:mo> <mml:mi>V</mml:mi> <mml:mo>−</mml:mo> <mml:mi>I</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> <mml:mrow> <mml:mi>RRL</mml:mi> </mml:mrow> </mml:msubsup> <mml:mo>=</mml:mo> <mml:mn>19.60</mml:mn> <mml:mo>±</mml:mo> <mml:msub> <mml:mrow> <mml:mn>0.01</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>stat</mml:mi> </mml:mrow> </mml:msub> <mml:mo>±</mml:mo> <mml:msub> <mml:mrow> <mml:mn>0.05</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>sys</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6fe0ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> mag. Finally, the HB distance is found to be <jats:inline-formula> <jats:tex-math> <?CDATA ${\mu }_{o}^{\mathrm{HB}}\,=19.54\pm {0.03}_{\mathrm{stat}}\pm {0.09}_{\mathrm{sys}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>μ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>o</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>HB</mml:mi> </mml:mrow> </mml:msubsup> <mml:mspace width="0.25em" /> <mml:mo>=</mml:mo> <mml:mn>19.54</mml:mn> <mml:mo>±</mml:mo> <mml:msub> <mml:mrow> <mml:mn>0.03</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>stat</mml:mi> </mml:mrow> </mml:msub> <mml:mo>±</mml:mo> <mml:msub> <mml:mrow> <mml:mn>0.09</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>sys</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6fe0ieqn4.gif" xlink:type="simple" /> </jats:inline-formula> mag. Absolute calibrations of each method are anchored by independent geometric zero-points, utilize a different class of stars, and are determined from the same photometric calibration.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Many processes during the evolution of protoplanetary disks and during planet formation are highly sensitive to the sizes of dust particles that are present in the disk: the efficiency of dust accretion in the disk and volatile transport on dust particles, gravoturbulent instabilities leading to the formation of planetesimals, or the accretion of pebbles onto large planetary embryos to form giant planets are typical examples of processes that depend on the sizes of the dust particles involved. Furthermore, radiative properties like absorption or scattering opacities depend on the particle sizes. To interpret observations of dust in protoplanetary disks, a proper estimate of the dust particle sizes is needed. We present <jats:monospace>DustPy: </jats:monospace>a <jats:monospace>Python</jats:monospace> package to simulate dust evolution in protoplanetary disks. <jats:monospace>DustPy</jats:monospace> solves gas and dust transport including viscous advection and diffusion as well as collisional growth of dust particles. <jats:monospace>DustPy</jats:monospace> is written with a modular concept, such that every aspect of the model can be easily modified or extended to allow for a multitude of research opportunities.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the discovery and multiwavelength characterization of SRGA J181414.6-225604, a Galactic hard X-ray transient discovered during the ongoing SRG/ART-XC sky survey. Using data from the Palomar Gattini-IR survey, we identify a spatially and temporally coincident variable infrared (IR) source, IRAS 18111-2257, and classify it as a very-late-type (M7–M8), long-period (1502 ± 24 days), and luminous (<jats:italic>M</jats:italic> <jats:sub> <jats:italic>K</jats:italic> </jats:sub> ≈ −9.9 ± 0.2) O-rich Mira donor star located at a distance of ≈14.6<jats:sup>+2.9</jats:sup> <jats:sub>−2.3</jats:sub> kpc. Combining multicolor photometric data over the last ≈25 yr, we show that the IR counterpart underwent a recent (starting ≈800 days before the X-ray flare) enhanced mass-loss (reaching ≈2.1 × 10<jats:sup>−5</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup>) episode, resulting in an expanding dust shell obscuring the underlying star. Multi-epoch follow-up observations from Swift, NICER, and NuSTAR reveal a ≈200 day long X-ray outburst reaching a peak luminosity of <jats:italic>L</jats:italic> <jats:sub>X</jats:sub> ≈ 2.5 × 10<jats:sup>36</jats:sup> erg s<jats:sup>−1</jats:sup>, characterized by a heavily absorbed (<jats:italic>N</jats:italic> <jats:sub>H</jats:sub> ≈ 6 × 10<jats:sup>22</jats:sup> cm<jats:sup>−2</jats:sup>) X-ray spectrum consistent with an optically thick Comptonized plasma. The X-ray spectral and timing behavior suggest the presence of clumpy wind accretion, together with a dense ionized nebula overabundant in silicate material surrounding the compact object. Together, we show that SRGA J181414.6-225604 is a new symbiotic X-ray binary in outburst, triggered by an intense dust-formation episode of a highly evolved donor. Our results offer the first direct confirmation for the speculated connection between enhanced late-stage donor mass loss and the active lifetimes of symbiotic X-ray binaries.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In the two-phase scenario of galaxy formation, a galaxy’s stellar mass growth is first dominated by in-situ star formation, and subsequently by accretion. We analyze the radial distribution of the accreted stellar mass in ∼500 galaxies from the (48 Mpc/<jats:italic>h</jats:italic>)<jats:sup>3</jats:sup> box volume of the hydrodynamical cosmological simulation Magneticum, in a stellar-mass range of 10<jats:sup>10</jats:sup> to 10<jats:sup>12</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. We find that higher-mass galaxies have larger accreted fractions, as found in previous works, but predict generally higher accretion fractions for low-mass galaxies. Based on the 3D radial distribution of the accreted and in-situ components, we define six galaxy classes, from completely accretion to completely in-situ dominated, and measure the transition radii between in-situ and accretion-dominated regions for galaxies that reveal a transition. About 70% of our galaxies have one transition radius. However, about 10% of the galaxies are accretion dominated everywhere, and about 13% have two transition radii, with the center and the outskirts both being accretion dominated. We show that these classes are strongly correlated with the galaxy merger histories, especially with the cold gas fraction at the time of merging. We find high total in-situ (low accretion) fractions to be associated with smaller, lower-mass galaxies, lower central dark-matter fractions, and larger transition radii. Finally, we show that the dips in observed surface brightness profiles seen in many early-type galaxies do not correspond to the transition from in-situ to accretion-dominated regions, and that any inferred mass fractions are not indicative of the true accreted mass but contain information about the galaxies’ dry-merger history.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The bubble nebula surrounding NGC 1313 X-2 is believed to be powered by high velocity winds from the central ultraluminous X-ray source (ULX) as a result of supercritical accretion. With the Multi-Unit Spectroscopic Explorer (MUSE) observation of the nebula, we find enhanced [O <jats:sc>iii</jats:sc>] emission at locations spatially coincident with clusters of stars and the central X-ray source, suggesting that photoionization in addition to shock ionization plays an important role in powering the nebula. The X-ray luminosity of the ULX and the number of massive stars in the nebula region can account for the required ionizing luminosity derived with <jats:italic>MAPPINGS V</jats:italic>, which also confirms that pure shocks cannot explain the observed emission line ratios.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a statistical study of the in situ acceleration of solar wind suprathermal electrons at the Earth’s bow shock, utilizing the Wind measurements in ambient solar wind and MMS1 measurements around the bow shock from 2015 September to 2017 December. All the selected 74 cases show significant suprathermal electron acceleration at the bow shock. The observed power-law indexes of accelerated electron energy spectra are significantly larger than the first-order Fermi acceleration prediction and the flux enhancement ratio peaks near a 90° pitch angle, suggesting that the shock drift acceleration (SDA) process plays a crucial role in accelerating suprathermal electrons at the bow shock. According to the observed electron spectral characteristics, the 74 cases can be classified into Types 1, 2, 3 and 4. The electron acceleration efficiency roughly increases from Type 1 to Type 4. For the Type 4 cases with strong electron acceleration, the shocked suprathermal electrons show a double-power-law energy spectrum bending downwards at a break near ∼65 keV with a low-energy spectral index of ∼3.1 and high-energy index of ∼7.6. The observed break energy is comparable to a critical electron energy <jats:inline-formula> <jats:tex-math> <?CDATA ${\varepsilon }_{\mathrm{ramp}}^{{dn}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>ε</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>ramp</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="italic">dn</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac8157ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> with its cross-shock gyrodiameter equal to the shock’s ramp thickness <jats:italic>D</jats:italic> <jats:sub>ramp</jats:sub>. At energies below (above) <jats:inline-formula> <jats:tex-math> <?CDATA ${\varepsilon }_{\mathrm{ramp}}^{{dn}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>ε</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>ramp</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="italic">dn</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac8157ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>, the accelerated electrons can be effectively confined into (can easily escape from) the SDA process with a roughly energy-independent (energy-decreasing) drift time and a probably conserved (nonadiabatically reduced) magnetic moment, since their gyrodiameter is less (greater) than <jats:italic>D</jats:italic> <jats:sub>ramp</jats:sub>. Therefore, such an SDA process could produce the observed double-power-law spectrum bending downwards at a break energy that is associated with <jats:italic>D</jats:italic> <jats:sub>ramp</jats:sub>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In 2020, the Super-Kamiokande (SK) experiment moved to a new stage (SK-Gd) in which gadolinium (Gd) sulfate octahydrate was added to the water in the detector, enhancing the efficiency to detect thermal neutrons and consequently improving the sensitivity to low energy electron anti-neutrinos from inverse beta decay (IBD) interactions. SK-Gd has the potential to provide early alerts of incipient core-collapse supernovae through detection of electron anti-neutrinos from thermal and nuclear processes responsible for the cooling of massive stars before the gravitational collapse of their cores. These pre-supernova neutrinos emitted during the silicon burning phase can exceed the energy threshold for IBD reactions. We present the sensitivity of SK-Gd to pre-supernova stars and the techniques used for the development of a pre-supernova alarm based on the detection of these neutrinos in SK, as well as prospects for future SK-Gd phases with higher concentrations of Gd. For the current SK-Gd phase, high-confidence alerts for Betelgeuse could be issued up to 9 hr in advance of the core collapse itself.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Magnetohydrodynamic waves are ubiquitously detected in the finely structured solar atmosphere. At the same time, our Sun is a highly dynamic plasma environment, giving rise to flows of various magnitudes, which can lead to the instability of waveguides. Recent studies have employed the method of introducing waveguide asymmetry to generalize “classical” symmetric descriptions of the fine structuring within the solar atmosphere, with some of them introducing steady flows as well. Building on these recent studies, here we investigate the magnetoacoustic waves guided by a magnetic slab within an asymmetric magnetic environment, in which the slab is under the effect of a steady flow. We provide an analytical investigation of how the phase speeds of the guided waves are changed, and where possible, determine the limiting flow speeds required for the onset of the Kelvin–Helmholtz instability. Furthermore, we complement the study with initial numerical results, which allows us to demonstrate the validity of our approximations and extend the investigation to a wider parameter regime. This configuration is part of a series of studies aimed to generalize, step-by-step, well-known symmetric waveguide models and understand the additional physics stemming from introducing further sources of asymmetry.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Active galactic nuclei (AGN) show a range of morphologies and dynamical properties, which are determined not only by parameters intrinsic to the central engine but also their interaction with the surrounding environment. We investigate the connection of kiloparsec scale AGN jet properties to their intrinsic parameters and surroundings. This is done using a suite of 40 relativistic hydrodynamic simulations spanning a wide range of engine luminosities and opening angles. We explore AGN jet propagation with different ambient density profiles, including <jats:italic>r</jats:italic> <jats:sup>−2</jats:sup> (self-similar solution) and <jats:italic>r</jats:italic> <jats:sup>−1</jats:sup>, which is more relevant for AGN host environments. While confirmation awaits future 3D studies, the Fanaroff–Riley (FR) morphological dichotomy arises naturally in our 2D models. Jets with low energy density compared to the ambient medium produce a center-brightened emissivity distribution, while emissivity from relatively higher energy density jets is dominated by the jet head. We observe recollimation shocks in our simulations that can generate bright spots along the spine of the jet, providing a possible explanation for “knots” observed in AGN jets. We additionally find a scaling relation between the number of knots and the jet-head-to-surroundings energy density ratio. This scaling relation is generally consistent with the observations of the jets in M87 and Cygnus A. Our model also correctly predicts M87 as FRI and Cygnus A as FRII. Our model can be used to relate jet dynamical parameters such as jet head velocity, jet opening angle, and external pressure to jet power, and ambient density estimates.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Measuring the evolution of X-ray emission from pre-main-sequence (PMS) stars gives insight into two issues: the response of magnetic dynamo processes to changes in the interior structure, and the effects of high-energy radiation on protoplanetary disks and primordial planetary atmospheres. We present a sample of 6003 stars with ages 7–25 Myr in 10 nearby open clusters from Chandra X-ray and Gaia-EDR3 surveys. Combined with previous results in large samples of younger (≲5 Myr) stars in MYStIX and SFiNCs star-forming regions, mass-stratified activity-age relations are derived for the early phases of stellar evolution. X-ray luminosity (<jats:italic>L</jats:italic> <jats:sub> <jats:italic>X</jats:italic> </jats:sub>) is constant during the first few Myr, possibly due to the presence of extended X-ray coronas insensitive to temporal changes in stellar size. <jats:italic>L</jats:italic> <jats:sub> <jats:italic>X</jats:italic> </jats:sub> then decays during the 7–25 Myr period, more rapidly as stellar mass increases. This decay is interpreted as decreasing efficiency of the <jats:italic>α</jats:italic> <jats:sup>2</jats:sup> dynamo as radiative cores grow and a solar-type <jats:italic>α</jats:italic>Ω dynamo emerges. For more massive 3.5–7 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> fully radiative stars, the X-ray emission plummets—indicating the lack of an effective magnetic dynamo. The findings provide improved measurements of high-energy radiation effects on circumstellar material, first for the protoplanetary disk and then for the atmospheres of young planets. The observed X-ray luminosities can be so high that an inner Earth-mass rocky, unmagnetized planet around a solar-mass PMS star might lose its primary and secondary atmospheres within a few (several) million years. PMS X-ray emission may thus have a significant impact on the evolution of early-planetary atmospheres and the conditions promoting the rise of habitability.</jats:p>