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<jats:title>Abstract</jats:title> <jats:p>We report on a long-term optical monitoring of the neutron star X-ray binary Centaurus X-4 performed during the last 13.5 yr. This source has been in quiescence since its outburst in 1979. Our monitoring reveals the overall evolution of the accretion disk; we detect short-duration flares, likely originating also in the disk, superimposed with a small-amplitude (&lt;0.1 mag) ellipsoidal modulation from the companion star due to geometrical effects. A long-term (∼2300 days) downward trend, followed by a shorter (∼1000 days) upward one, is observed in the disk light curve. Such a rise in the optical has been observed for other X-ray binaries preceding outbursts, as predicted by the disk instability model. For Cen X-4, the rise of the optical flux proceeded for ∼3 yr, and culminated in a flux increase at all wavelengths (optical–UV–X-rays) at the end of 2020. This increase faded after ∼2 weeks, without giving rise to a full outburst. We suggest that the propagation of an inside-out heating front was ignited due to a partial ionization of hydrogen in the inner disk. The propagation might have stalled soon after the ignition due to the increasing surface density in the disk that the front encountered while propagating outward. The stall was likely eased by the low-level irradiation of the outer regions of the large accretion disk, as shown by the slope of the optical/X-ray correlation, suggesting that irradiation does not play a strong role in the optical, compared to other sources of emission.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The origin of Uranus and Neptune is still unknown. In particular, it has been challenging for planet formation models to form the planets in their current radial distances within the expected lifetime of the solar nebula. In this paper, we simulate the in situ formation of Uranus and Neptune via pebble accretion and show that both planets can form within ∼3 Myr at their current locations, and have final compositions that are consistent with the heavy element to H–He ratios predicted by structure models. We find that Uranus and Neptune could have been formed at their current locations. In several cases a few earth masses (<jats:italic>M</jats:italic> <jats:sub>⊕</jats:sub> <jats:italic>) </jats:italic>of heavy elements are missing, suggesting that Uranus and/or Neptune may have accreted ∼1–3 <jats:italic>M<jats:sub>⊕</jats:sub> </jats:italic> of heavy elements after their formation via planetesimal accretion and/or giant impacts.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Solar wind charge exchange (SWCX) is the primary contamination of soft X-ray emission lines from the Milky Way (MW) hot gas. We report a solar cycle (≈10 yr) temporal variation of observed O <jats:sc>vii</jats:sc> and O <jats:sc>viii</jats:sc> emission line measurements in the XMM-Newton archive, which is tightly correlated with the solar cycle traced by the sunspot number (SSN). This temporal variation is expected to be associated with the heliospheric SWCX. Another observed correlation is that higher solar wind (SW) fluxes lead to higher O <jats:sc>vii</jats:sc> or O <jats:sc>viii</jats:sc> fluxes, which is due to the magnetospheric SWCX. We construct an empirical model to reproduce the observed correlation between the line measurements and the solar activity (i.e., the SW flux and the SSN). With this model we discovered a lag of <jats:inline-formula> <jats:tex-math> <?CDATA ${0.91}_{-0.22}^{+0.20}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>0.91</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.22</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.20</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6349ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> yr between the O <jats:sc>vii</jats:sc> flux and the SSN. This time lag is a combination of the SW transit time within the heliosphere, the lag of the neutral gas distribution responding to solar activity, and the intrinsic lag between the SSN and the launch of a high-energy SW (i.e., O<jats:sup>7+</jats:sup> and O<jats:sup>8+</jats:sup>). MW O <jats:sc>vii</jats:sc> and O <jats:sc>viii</jats:sc> fluxes have mean values of 5.4 L.U. and 1.7 L.U., which are reduced by 50% and 30%, compared to studies where the SWCX contamination is not removed. This correction also changes the determination of the density distribution and the temperature profile of the MW hot gas.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Ground-based gravitational-wave detectors like Cosmic Explorer (CE) can be tuned to improve their sensitivity at high or low frequencies by tuning the response of the signal extraction cavity. Enhanced sensitivity above 2 kHz enables measurements of the post-merger gravitational-wave spectrum from binary neutron star mergers, which depends critically on the unknown equation of state of hot, ultra-dense matter. Improved sensitivity below 500 Hz favors precision tests of extreme gravity with black hole ringdown signals and improves the detection prospects while facilitating an improved measurement of source properties for compact binary inspirals at cosmological distances. At intermediate frequencies, a more sensitive detector can better measure the tidal properties of neutron stars. We present and characterize the performance of tuned CE configurations that are designed to optimize detections across different astrophysical source populations. These tuning options give CE the flexibility to target a diverse set of science goals with the same detector infrastructure. We find that a 40 km CE detector outperforms a 20 km in all key science goals other than access to post-merger physics. This suggests that CE should include at least one 40 km facility.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>This paper aims to examine the effects of pressure anisotropy on the geometry of magnetic flux rope using the newly developed two-dimensional magnetohydrostatic reconstruction associated with pressure anisotropy. A small-scale magnetic flux rope observed by the Magnetospheric Multiscale mission, in the magnetosheath reconnection outflow during an outbound magnetopause crossing, is demonstrated. At the center of the flux rope, the magnetic field strength was enhanced with decreasing plasma pressure. The entire flux rope was mostly occupied by the pressure anisotropy of <jats:italic>p</jats:italic> <jats:sub>⊥</jats:sub> &gt; <jats:italic>p</jats:italic> <jats:sub>∥</jats:sub>, where the subscripts ∥ and ⊥ denote the components parallel and perpendicular to the local magnetic field, respectively. The estimated aspect ratio of the width to the length of the flux rope from reconstruction was ∼0.326 for <jats:italic>p</jats:italic> <jats:sub>⊥</jats:sub> &gt; <jats:italic>p</jats:italic> <jats:sub>∥</jats:sub> and ∼0.389 for isotropic pressure. By comparing the magnetic field map from the isotropic Grad–Shafranov reconstruction, the results show for <jats:italic>p</jats:italic> <jats:sub>⊥</jats:sub> &gt; <jats:italic>p</jats:italic> <jats:sub>∥</jats:sub> that (1) the width of the flux rope is reduced, leading to a small aspect ratio of the flux rope, and (2) the circular field line of the flux rope is contracted. Moreover, an experiment is conducted for <jats:italic>p</jats:italic> <jats:sub>∥</jats:sub> &gt; <jats:italic>p</jats:italic> <jats:sub>⊥</jats:sub> by exchanging <jats:italic>p</jats:italic> <jats:sub>⊥</jats:sub> and <jats:italic>p</jats:italic> <jats:sub>∥</jats:sub> of the flux rope, for which the isotropic pressure is less affected. The experimental results indicate that the effects of <jats:italic>p</jats:italic> <jats:sub>∥</jats:sub> &gt; <jats:italic>p</jats:italic> <jats:sub>⊥</jats:sub> on the geometry of the flux rope are opposite to that of <jats:italic>p</jats:italic> <jats:sub>⊥</jats:sub> &gt; <jats:italic>p</jats:italic> <jats:sub>∥</jats:sub>. The overall finding may provide new insight into charged particle acceleration within magnetic flux ropes/islands in anisotropic plasmas.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigate the [X/Mg] abundances of 16 elements for 82,910 Galactic disk stars from GALAH+ DR3. We fit the median trends of low-Ia and high-Ia populations with a two-process model, which describes stellar abundances in terms of a prompt core-collapse and delayed Type-Ia supernova component. For each sample star, we fit the amplitudes of these two components and compute the residual Δ[X/H] abundances from this two-parameter fit. We find rms residuals ≲0.07 dex for well-measured elements and correlated residuals among some elements (such as Ba, Y, and Zn) that indicate common enrichment sources. From a detailed investigation of stars with large residuals, we infer that roughly 40% of the large deviations are physical and 60% are caused by problematic data such as unflagged binarity, poor wavelength solutions, and poor telluric subtraction. As one example of a population with distinctive abundance patterns, we identify 15 stars that have 0.3–0.6 dex enhancements of Na but normal abundances of other elements from O to Ni and positive average residuals of Cu, Zn, Y, and Ba. We measure the median elemental residuals of 14 open clusters, finding systematic ∼0.1–0.4 dex enhancements of O, Ca, K, Y, and Ba and ∼0.2 dex depletion of Cu in young clusters. Finally, we present a restricted three-process model where we add an asymptotic giant branch star (AGB) component to better fit Ba and Y. With the addition of the third process, we identify a population of stars, preferentially young, that have much higher AGB enrichment than expected from their SNIa enrichment.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Whiting 1 is a faint and young globular cluster in the halo of the Milky Way, and was suggested to have originated in the Sagittarius spherical dwarf galaxy (Sgr dSph). In this paper, we use the deep DESI Legacy Imaging Surveys to explore tentative spatial connection between Whiting 1 and the Sgr dSph. We redetermine the fundamental parameters of Whiting 1 and use the best-fitting isochrone (age <jats:italic>τ</jats:italic> = 6.5 Gyr, metallicity <jats:italic>Z</jats:italic> = 0.005 and <jats:italic>d</jats:italic> <jats:sub>⊙</jats:sub> = 26.9 kpc) to construct a theoretical matched filter for the extra-tidal features searching. Without any smooth technique to the matched filter density map, we detect a round-shape feature with possible leading and trailing tails on either side of the cluster. This raw image is not totally new compared to old discoveries, but confirms that no more large-scale features can be detected under a depth of <jats:italic>r</jats:italic> &lt; =22.5 mag. In our results, the whole feature stretches 0°.1–0°.2 along the orbit of Whiting 1, which gives a much larger area than the cluster core. The tails on both sides of the cluster align along the orbital direction of the Sgr dSph as well as the cluster itself, which implies that these debris are probably stripped remnants of Whiting 1 by the Milky Way.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Forbidden atomic oxygen lines in emission are ubiquitous for cometary spectra in the visible region, and the oxygen atoms in metastable states causing the forbidden emission lines are considered as a proxy of H<jats:sub>2</jats:sub>O in coma. However, the photodissociation rate and related quantities for the dissociation reaction producing O(<jats:sup>1</jats:sup>S) from H<jats:sub>2</jats:sub>O have never been estimated based on experimental studies. Based on the recent laboratory study of the photodissociation reaction of H<jats:sub>2</jats:sub>O producing O(<jats:sup>1</jats:sup>S) by Chang et al., we derived the photodissociation rates of the reactions for both the O(<jats:sup>1</jats:sup>S) and O(<jats:sup>1</jats:sup>D) channels, consistent with the green-to-red line ratios observed in comets so far. Furthermore, the total kinetic energies released for the photodissociation products are also consistent with the intrinsic line widths of forbidden atomic oxygen emission lines observed in comets. The photodissociation rates of H<jats:sub>2</jats:sub>O leading to O(<jats:sup>1</jats:sup>S) and O(<jats:sup>1</jats:sup>D) calculated here do not significantly change the previous estimates of CO<jats:sub>2</jats:sub>/H<jats:sub>2</jats:sub>O in comets based on the green-to-red line ratios of the comets if we use the photodissociation rates of CO<jats:sub>2</jats:sub> (calculated elsewhere) with a correction for the difference of solar UV spectra used for calculating photodissociation rates of H<jats:sub>2</jats:sub>O and CO<jats:sub>2</jats:sub>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Brown dwarfs can serve as both clocks and chemical tracers of the evolutionary history of the Milky Way due to their continuous cooling and high sensitivity of spectra to composition. We focus on brown dwarfs in globular clusters that host some of the oldest coeval populations in the galaxy. Currently, no brown dwarfs in globular clusters have been confirmed, but they are expected to be uncovered with advanced observational facilities such as the James Webb Space Telescope (JWST). In this paper we present a new set of stellar models specifically designed to investigate low-mass stars and brown dwarfs in <jats:italic>ω</jats:italic> Centauri—the largest known globular cluster. The parameters of our models were derived from iterative fits to Hubble Space Telescope photometry of the main-sequence members of the cluster. Despite the complex distribution of abundances and the presence of multiple main sequences in <jats:italic>ω</jats:italic> Centauri, we find that the modal color–magnitude distribution can be represented by a single stellar population with parameters determined in this study. The observed luminosity function is well represented by two distinct stellar populations having solar and enhanced helium mass fractions and a common initial mass function, in agreement with previous studies. Our analysis confirms that the abundances of individual chemical elements play a key role in determining the physical properties of low-mass cluster members. We use our models to draw predictions of brown dwarf colors and magnitudes in anticipated JWST NIRCam data, confirming that the beginning of the substellar sequence should be detected in <jats:italic>ω</jats:italic> Centauri in forthcoming observations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>For testing different electron temperature (<jats:italic>T</jats:italic> <jats:sub>e</jats:sub>) prescriptions in general relativistic magnetohydrodynamics (GRMHD) simulations through observations, we propose to utilize linear polarization (LP) and circular polarization (CP) images. We calculate the polarization images based on a semi-magnetically arrested disk GRMHD model for various <jats:italic>T</jats:italic> <jats:sub>e</jats:sub> parameters, bearing M87 in mind. We find an LP–CP separation in the images of the low-<jats:italic>T</jats:italic> <jats:sub>e</jats:sub> disk cases at 230GHz; namely, the LP flux mainly originates from downstream of the jet, and the CP flux comes from the counter-side jet, while the total intensity is maximum at the jet base. This can be understood as follows: although the LP flux is generated through synchrotron emission widely around the black hole, most of the LP flux from the jet base does not reach the observer, since it undergoes Faraday rotation (<jats:inline-formula> <jats:tex-math> <?CDATA $\propto {T}_{{\rm{e}}}^{-2}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>∝</mml:mo> <mml:msubsup> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">e</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac66ddieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) when passing through the outer cold disk and is thus depolarized. Hence, only the LP flux from the downstream (not passing the cold dense plasmas) can survive. Meanwhile, the CP flux is generated from the LP flux by Faraday conversion ( ∝ <jats:italic>T</jats:italic> <jats:sub>e</jats:sub>) in the inner hot region. Stronger CP flux is thus observed from the counter-side jet. Moreover, the LP–CP separation is more enhanced at a lower frequency, such as 86 GHz, but is rather weak at 43 GHz, since the media in the latter case is optically thick for synchrotron self-absorption so that all of the fluxes should come from the photosphere. The same is true for cases with higher mass accretion rates and/or larger inclination angles.</jats:p>