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<jats:title>Abstract</jats:title> <jats:p>We present the results of high-resolution spectropolarimetric observations of the optically dominant component in the rare hydrogen-deficient binary system <jats:italic>υ</jats:italic> Sgr. Only a small number of such systems in a very late phase of helium shell burning are currently known. The mass transfer from the donor star in binary systems usually leads to the stripping of its hydrogen envelope. Consequently, since the mass of the secondary increases, it appears rejuvenated. Using a few ESO FORS 1 low-resolution spectropolarimetric observations of this system, Hubrig et al. announced in 2009 the presence of a magnetic field of the order of −70 to −80 G. Here we report on more recent high-resolution ESO HARPS spectropolarimetric observations showing that the primary in <jats:italic>υ</jats:italic> Sgr is a spectrum variable star and possesses a weak magnetic field of the order of a few tens of Gauss. The detection of a magnetic field in this rare hydrogen-deficient binary is of particular interest, as such systems are frequently discussed as probable progenitors of core-collapse supernovae and gravitational-wave sources. Future magnetic studies of such systems would be worthwhile to gain deeper insights into the role of magnetic fields in the evolution of massive stars in binary systems.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the results of a stacking analysis performed on Spitzer/Infrared Spectrograph high-resolution mid-infrared (mid-IR) spectra of luminous infrared galaxies (LIRGs) in the Great Observatories All-Sky LIRG Survey. By binning in relation to mid-IR active galactic nucleus (AGN) fraction and stacking spectra, we detect bright emission lines [Ne <jats:sc>ii</jats:sc>] and [Ne <jats:sc>iii</jats:sc>], which trace star formation, and fainter emission lines [Ne <jats:sc>v</jats:sc>] and [O <jats:sc>iv</jats:sc>], which trace AGN activity, throughout the sample. We find that the [Ne <jats:sc>ii</jats:sc>] luminosity is fairly constant across all AGN fraction bins, while the [O <jats:sc>iv</jats:sc>] and [Ne <jats:sc>v</jats:sc>] luminosities increase by over an order of magnitude. Our measured average line ratios, [Ne <jats:sc>v</jats:sc>]/[Ne <jats:sc>ii</jats:sc>] and [O <jats:sc>iv</jats:sc>]/[Ne <jats:sc>ii</jats:sc>], at low AGN fraction are similar to H II galaxies, while the line ratios at high AGN fraction are similar to LINERs and Seyferts. We decompose the [O <jats:sc>iv</jats:sc>] luminosity into star formation and AGN components by fitting the [O <jats:sc>iv</jats:sc>] luminosity as a function of the [Ne <jats:sc>ii</jats:sc>] luminosity and the mid-IR AGN fraction. The [O <jats:sc>iv</jats:sc>] luminosity in LIRGs is dominated by star formation for mid-IR AGN fractions ≲0.3. With the corrected [O <jats:sc>iv</jats:sc>] luminosity, we calculate black hole accretion rates (BHARs) ranging from 10<jats:sup>−5</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup> at low AGN fractions to 0.2 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup> at the highest AGN fractions. We find that using the [O <jats:sc>iv</jats:sc>] luminosity, without correcting for star formation, can lead to overestimation of the BHAR by up to a factor of 30 in starburst-dominated LIRGs. Finally, we show that the BHAR/star formation rate ratio increases by more than three orders of magnitude as a function of mid-IR AGN fraction in LIRGs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Gaia used a large sample of photometrically selected active galactic nuclei (AGNs) and quasars to remove the residual spin of its global proper motion system in order to achieve a maximally inertial reference frame. A small fraction of these reference objects have statistically significant astrometric proper motions in Gaia EDR3. We compile a source sample of 105,593 high-fidelity AGNs with accurate spectroscopically determined redshifts above 0.5 from the SDSS and normalized proper motions below 4. The rate of genuinely perturbed proper motions is at least 0.17%. A smaller high completeness sample of 152 quasars with excess proper motions at a confidence level of 0.9995 is examined in detail. Pan-STARRS images and Gaia-resolved pairs reveal that 29% of the sample are either double sources or gravitationally lensed quasars. An Anderson–Darling test on parameters of a smaller high-reliability sample and their statistical controls reveals 17 significant factors that favor multiplicity and multi-source structure as the main cause of perturbed astrometry. Using a nearest-neighbor distance statistical analysis and counts of close companions in Gaia on a much larger initial sample of AGNs, an excess of closely separated sources in Gaia is detected. At least 0.33% of all optical quasars are genuinely double or multiply imaged. We provide a list of 44 candidate double or multiple AGNs and four previously known gravitational lenses. Many proper motion quasars may be more closely separated, unresolved doubles exhibiting the variability imposed motion effect, and a smaller fraction may be chance alignments with foreground stars causing weak gravitational lensing.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Using the high-resolution Milky Way–like model from Auriga simulation we study the chemical properties of the Galactic bulge, focusing on the metallicity difference between stars on the near side (in front of the Galactic center) and the far side (behind the Galactic center). In general, along certain sight lines the near side is more metal-rich than the far side, consistent with the negative vertical metallicity gradient of the disk, since the far side is located higher above the disk plane than the near side. However, at the region <jats:italic>l</jats:italic> &lt; 0° and ∣<jats:italic>b</jats:italic>∣ ≤ 6°, the near side is even more metal-poor than the far side, and their difference changes with the Galactic longitude. This is mainly due to the fact that stars near the minor axis of the bar are more metal-poor than that around the major axis. Since the bar is tilted, in the negative longitude region, the near side is mainly populated by stars close to the minor-axis region rather than the far side resulting in such a metallicity difference. We extract stars in the X-shape structure by identifying the overdensities in the near and far sides. Their metallicity properties are consistent with the results of the whole Galactic bulge. The boxy/peanut-shaped bulge can naturally explain the metallicity difference of the double red clump stars in the observation. There is no need to involve a classical bulge component with different stellar populations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a series of numerical solutions of spherically symmetric stationary flows with nuclear burning accreted by a neutron star (or black hole). We consider the accretion of matter composed of carbon and oxygen, which mimics the flow after a neutron star is engulfed by a CO star or the CO core of a massive star. It is found that there are two types of transonic solutions depending on the accretion rate. The flow with a low accretion rate reaches the center (or the surface of the central object) at supersonic speeds. The other type with a high accretion rate has another sonic point inside the transonic point and the flow truncates at the sonic point. The critical accretion rate dividing these two types is derived as a function of the mass of the central object and the specific enthalpy in the ambient matter. We discuss implications from the solutions for a new mechanism of super-Chandrasekhar Type Ia supernovae and Type Icn supernovae.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The revolutionary power of future Rubin-LSST observations will allow us to significantly improve the physics of pulsating stars, including RR Lyrae. In this context, an updated theoretical scenario predicting all the relevant pulsation observables in the corresponding photometric filters is mandatory. The bolometric light curves are based on a recently computed extensive set of nonlinear convective pulsation models for RR Lyrae stars, covering a broad range of metal content, and have been transformed into the Vera C. Rubin Observatory Legacy Survey of Space and Time (Rubin-LSST) photometric system. Predicted Rubin-LSST mean magnitudes and pulsation amplitudes have been adopted to build the Bailey diagrams (luminosity amplitude versus period) and the color–color diagrams in these bands. The current findings indicate that the <jats:italic>g</jats:italic> <jats:sub>LSST</jats:sub>–<jats:italic>r</jats:italic> <jats:sub>LSST</jats:sub> and <jats:italic>r</jats:italic> <jats:sub>LSST</jats:sub>–<jats:italic>i</jats:italic> <jats:sub>LSST</jats:sub> colors obey to a well-defined linear relation with the metal content. Moreover, the period–luminosity relations display in the reddest filters (<jats:italic>r</jats:italic> <jats:sub>LSST</jats:sub>, <jats:italic>i</jats:italic> <jats:sub>LSST</jats:sub>, <jats:italic>z</jats:italic> <jats:sub>LSST</jats:sub>, <jats:italic>y</jats:italic> <jats:sub>LSST</jats:sub>) a significant dependence on the assumed metal abundance. In particular, more metal-rich RR Lyrae are predicted to be fainter at a fixed period. Metal-dependent period–Wesenheit relations for different combinations of optical and near-infrared filters are also provided. These represent powerful tools to infer individual distances independently of reddening uncertainties, once the metal abundance is known and no relevant deviations from the adopted extinction law occur. Finally, we also derived new linear and quadratic absolute magnitude metallicity relations (<jats:italic>g</jats:italic> <jats:sub>LSST</jats:sub> versus [Fe/H]) and the metallicity coefficient is consistent with previous findings concerning the <jats:italic>B</jats:italic> and the <jats:italic>V</jats:italic> band.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>One of the challenges in understanding the quenching processes for galaxies is connecting progenitor star-forming populations to their descendant quiescent populations over cosmic time. Here we attempt a novel approach to this challenge by assuming that the underlying stellar mass distribution of galaxies is not significantly altered during environmental-quenching processes that solely affect the gas content of cluster galaxies, such as strangulation and ram pressure stripping. Using the deep, high-resolution photometry of the Hubble Frontier Fields, we create resolved stellar mass maps for both cluster and field galaxies, from which we determine 2D Sérsic profiles, and obtain Sérsic indices and half-mass radii. We classify the quiescent cluster galaxies into disk-like and bulge-like populations based on their Sérsic indices, and find that bulge-like quiescent galaxies dominate the quiescent population at higher masses (<jats:italic>M</jats:italic> <jats:sub>⋆</jats:sub> &gt; 10<jats:sup>9.5</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>), whereas disk-like quiescent galaxies dominate at lower masses (10<jats:sup>8.5</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> &lt; <jats:italic>M</jats:italic> <jats:sub>⋆</jats:sub> &lt; 10<jats:sup>9.5</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>). Using both the Sérsic indices and half-mass radii, we identify a population of quiescent galaxies in clusters that are <jats:italic>morphological analogs</jats:italic> of field star-forming galaxies. These analogs are interpreted to be star-forming galaxies that had been environmentally quenched. We use these morphological analogs to compute the environmental-quenching efficiency, and we find that the efficiency decreases with increasing stellar mass. This demonstrates that environmental quenching is more effective on less massive galaxies and that the effect of environment on quenching galaxies is not completely separable from the effect of mass on quenching galaxies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Fermi Large Area Telescope receives ≪1 photon per rotation from any <jats:italic>γ</jats:italic>-ray pulsar. However, out of the billions of monitored rotations of the bright pulsars Vela (PSR J0835−4510) and Geminga (PSR J0633+1746), a few thousand have ≥2 pulsed photons. These rare pairs encode information about the variability of pulse amplitude and shape. We have cataloged such pairs and find the observed number to be in good agreement with simple Poisson statistics, limiting any amplitude variations to &lt;19% (Vela) and &lt;22% (Geminga) at 2<jats:italic>σ</jats:italic> confidence. Using an array of basis functions to model pulse-shape variability, the observed pulse phase distribution of the pairs limits the scale of pulse-shape variations of Vela to &lt;13%, while for Geminga we find a hint of ∼20% single-pulse-shape variability most associated with the pulse peaks. If variations last longer than a single rotation, more pairs can be collected, and we have calculated upper limits on amplitude and shape variations for assumed coherence times up to 100 rotations, finding limits of ∼1% (amplitude) and ∼3% (shape) for both pulsars. Because a large volume of the pulsar magnetosphere contributes to <jats:italic>γ</jats:italic>-ray pulse production, we conclude that the magnetospheres of these two energetic pulsars are stable over one rotation and very stable on longer timescales. All other <jats:italic>γ</jats:italic>-ray pulsars are too faint for similar analyses. These results provide useful constraints on rapidly improving simulations of pulsar magnetospheres, which have revealed a variety of large-scale instabilities in the thin equatorial current sheets where the bulk of GeV <jats:italic>γ</jats:italic>-ray emission is thought to originate.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a tabulated version of our slim-disk model for fitting tidal disruption events (TDEs). We create a synthetic X-ray spectral library by ray-tracing stationary general relativistic slim disks and including gravitational redshift, Doppler, and lensing effects self-consistently. We introduce the library to reduce computational expense and increase access for fitting future events. Fitting requires interpolation between the library spectra; the interpolation error in the synthetic flux is generally &lt;10% (it can rise to 40% when the disk is nearly edge-on). We fit the X-ray spectra of the TDEs ASASSN-14li and ASASSN-15oi, successfully reproducing our earlier constraints on black hole mass <jats:italic>M</jats:italic> <jats:sub>•</jats:sub> and spin <jats:italic>a</jats:italic> <jats:sub>•</jats:sub> from full on-the-fly ray-tracing. We use the library to fit mock observational data to explore the degeneracies among parameters, finding that (1) spectra from a hotter thermal disk and edge-on inclination angle offer tighter constraints on <jats:italic>M</jats:italic> <jats:sub>•</jats:sub> and <jats:italic>a</jats:italic> <jats:sub>•</jats:sub>; (2) the constraining power of spectra on <jats:italic>M</jats:italic> <jats:sub>•</jats:sub> and <jats:italic>a</jats:italic> <jats:sub>•</jats:sub> increases as a power law with the number of X-ray counts, and the index of the power law is higher for hotter thermal disk spectra; (3) multiepoch X-ray spectra partially break the degeneracy between <jats:italic>M</jats:italic> <jats:sub>•</jats:sub> and <jats:italic>a</jats:italic> <jats:sub>•</jats:sub>; (4) the time-dependent level of X-ray absorption can be constrained from spectral fitting. The tabulated model and slim-disk model are available at <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" xlink:href="https://doi.org/10.25739/hfhz-xn60" xlink:type="simple">https://doi.org/10.25739/hfhz-xn60</jats:ext-link>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The construction and implementation of atmospheric model grids is a popular tool in exoplanet characterization. These typically vary a number of parameters linearly, containing one model for every combination of parameter values. Here we investigate alternative methods of sampling parameters, including random sampling and Latin hypercube (LH) sampling, and how these compare to linearly sampled grids. We use a random forest to analyze the performance of these grids for two different models, as well as investigate the information content of the particular model grid from Goyal et al. (2019). We also use nested sampling to implement mock atmospheric retrievals on simulated James Webb Space Telescope transmission spectra by interpolating on linearly sampled model grids. Our results show that random or LH sampling outperforms linear sampling in parameter predictability for our higher-dimensional models, requiring fewer models in the grid, and thus allowing for more computationally intensive forward models to be used. We also found that using a traditional retrieval with interpolation on a linear grid can produce biased posterior distributions, especially for parameters with nonlinear effects on the spectrum. In particular, we advise caution when performing linear interpolation on the C/O ratio, cloud properties, and metallicity. Finally, we found that the information content analysis of the grid from Goyal et al. (2019) was able to highlight key areas of the spectra where the presence or absence of certain molecules can be detected, providing good indicators for parameters such as temperature and C/O ratio.</jats:p>