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<jats:title>Abstract</jats:title> <jats:p>The high cosmic abundance of carbon monoxide (CO) and the ubiquitous nature of aluminum-coated dust grains sets the stage for the production of weakly bound triatomic molecules AlCO (X <jats:sup>2</jats:sup>Π) and AlOC (X <jats:sup>2</jats:sup>Π) in circumstellar envelopes of evolved stars. Following desorption of cold AlCO and AlOC from the dust grain surface, incoming stellar radiation in the 2–9 eV wavelength range (visible to vacuum ultraviolet) will drive various photochemical processes. Ionization to the singlet cation state will cause an immediate Al–X (X = C, O) bond dissociation to form Al<jats:sup>+</jats:sup> (<jats:sup>1</jats:sup>S) and CO (X <jats:sup>1</jats:sup>Σ<jats:sup>+</jats:sup>) coproducts, whereas ionization to the higher-lying triplet states will lead to stabilization of AlCO<jats:sup>+</jats:sup> (X <jats:sup>3</jats:sup>Π) and AlOC<jats:sup>+</jats:sup>(X <jats:sup>3</jats:sup>Π) in deep potential wells. In competition with ionization is electronic excitation. Excitation to the spectroscopically bright 1 <jats:sup>2</jats:sup>Π and 2 <jats:sup>2</jats:sup>Σ<jats:sup>+</jats:sup> states will lead to either highly Stokes-shifted fluorescence, or photodissociation to yield Al (<jats:sup>2</jats:sup>D) + CO (X <jats:sup>1</jats:sup>Σ<jats:sup>+</jats:sup>) products via nonadiabatic pathways, making AlCO and AlOC good candidates for electronic experimental studies. These many photoinduced pathways spanning orders of magnitude of the electromagnetic spectrum will lead to the depletion of AlCO and AlOC in astronomical environments, potentially explaining the lack of observational detection of these molecules. Furthermore, these results indicate new catalytic pathways to the freeing of aluminum atoms trapped in solid aluminum dust grains. Additionally, the results herein implicate an ion–neutral reaction as a possible important pathway in [Al, C, O] cation formation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present LAMOST J041920.07+072545.4 (hereafter J0419), a close binary consisting of a bloated, extremely low mass pre-white dwarf (pre-ELM WD) and a compact object with an orbital period of 0.607189 days. The large-amplitude ellipsoidal variations and the evident Balmer and He <jats:sc>i</jats:sc> emission lines suggest a filled Roche lobe and ongoing mass transfer. No outburst events were detected in the 15 years of monitoring of J0419, indicating a very low mass transfer rate. The temperature of the pre-ELM, <jats:inline-formula> <jats:tex-math> <?CDATA ${T}_{\mathrm{eff}}={5793}_{-133}^{+124}\,{\rm{K}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>eff</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>5793</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>133</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>124</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.25em" /> <mml:mi mathvariant="normal">K</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac75b6ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, makes it cooler than the known ELMs, but hotter than most cataclysmic variable donors. Combining the mean density within the Roche lobe and the radius constrained from our spectral energy distribution fitting, we obtain the mass of the pre-ELM, <jats:italic>M</jats:italic> <jats:sub>1</jats:sub> = 0.176 ± 0.014 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. The joint fitting of light and radial velocity curves yields an inclination angle of <jats:inline-formula> <jats:tex-math> <?CDATA $i={66.5}_{-1.7}^{+1.4}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>i</mml:mi> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>66.5</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.7</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>1.4</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac75b6ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> degrees, corresponding to a mass of the compact object of <jats:italic>M</jats:italic> <jats:sub>2</jats:sub> = 1.09 ± 0.05 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. The very bloated pre-ELM has a smaller surface gravity (<jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}g=3.9\pm 0.01$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mi>g</mml:mi> <mml:mo>=</mml:mo> <mml:mn>3.9</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.01</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac75b6ieqn3.gif" xlink:type="simple" /> </jats:inline-formula>, <jats:italic>R</jats:italic> <jats:sub>1</jats:sub> = 0.78 ± 0.02 <jats:italic>R</jats:italic> <jats:sub>⊙</jats:sub>) than the known ELMs or pre-ELMs. The temperature and the luminosity (<jats:inline-formula> <jats:tex-math> <?CDATA ${L}_{\mathrm{bol}}={0.62}_{-0.10}^{+0.11}\,{L}_{\odot }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>bol</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>0.62</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.10</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.11</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.25em" /> <mml:msub> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac75b6ieqn4.gif" xlink:type="simple" /> </jats:inline-formula>) of J0419 are close to those of the main sequence, which makes the selection of such systems through the H-R diagram inefficient. Based on the evolutionary model, the relatively long period and small <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}g$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mi>g</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac75b6ieqn5.gif" xlink:type="simple" /> </jats:inline-formula> indicate that J0419 could be close to the “bifurcation period” in the orbital evolution, which makes J0419 a unique source to connect ELM/pre-ELM WD systems, wide binaries, and cataclysmic variables.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Red supergiant stars lose a lot of mass in slow winds that forms a circumstellar medium (CSM) around the star. When the star retains a substantial hydrogen envelope at the time of explosion, it displays characteristic light curves and spectra of a Type II plateau supernova (SN), e.g., the nearby SN 2013ej. When the shock wave launched deep inside the star exits the surface, it probes the CSM and scripts the history of mass loss from the star. We simulate with the STELLA code the SN radiative display resulting from shock breakout (SBO) for a set of progenitor stars. We evolved these stars with the MESA code from their main-sequence to core-collapse phase using diverse evolutionary inputs. We explore the SN display for different internal convective overshoot and compositional mixing inside the progenitor stars and two sets of mass-loss schemes, one the standard “Dutch” scheme and the other an enhanced, episodic and late mass loss. The SBO from the star shows closely time-separated double-peaked bolometric light curves for the Dutch case, as well as high-velocity ejecta with minuscule mass accelerated during SBO. The earlier of the peaks, which we call the precursor peaks, are compared with analytical expressions for SBO of stars. We also contrast the breakout flash from an optically thick CSM with that of the rarefied medium established by Dutch wind. We describe how the multigroup photon spectra of the breakout flashes differ between these cases.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigate the relation between rotation periods <jats:italic>P</jats:italic> <jats:sub>rot</jats:sub> and photometric modulation amplitudes <jats:italic>R</jats:italic> <jats:sub>per</jats:sub> for ≈4000 Sun-like main-sequence stars observed by Kepler, using <jats:italic>P</jats:italic> <jats:sub>rot</jats:sub> and <jats:italic>R</jats:italic> <jats:sub>per</jats:sub> from McQuillan et al., effective temperature <jats:italic>T</jats:italic> <jats:sub>eff</jats:sub> from LAMOST DR6, and parallax data from Gaia EDR3. As has been suggested in previous works, we find that <jats:italic>P</jats:italic> <jats:sub>rot</jats:sub> scaled by the convective turnover time <jats:italic>τ</jats:italic> <jats:sub>c</jats:sub>, or the Rossby number Ro, serves as a good predictor of <jats:italic>R</jats:italic> <jats:sub>per</jats:sub>: <jats:italic>R</jats:italic> <jats:sub>per</jats:sub> plateaus at around 1% in relative flux for 0.2 ≲ Ro/Ro<jats:sub>⊙</jats:sub> ≲ 0.4, and decays steeply with increasing Ro for 0.4 ≲ Ro/Ro<jats:sub>⊙</jats:sub> ≲ 0.8, where Ro<jats:sub>⊙</jats:sub> denotes Ro of the Sun. In the latter regime we find <jats:inline-formula> <jats:tex-math> <?CDATA ${\rm{d}}\,\mathrm{ln}\,{R}_{\mathrm{per}}/{\rm{d}}\,\mathrm{ln}\,\mathrm{Ro}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">d</mml:mi> <mml:mspace width="0.25em" /> <mml:mi>ln</mml:mi> <mml:mspace width="0.25em" /> <mml:msub> <mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>per</mml:mi> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mi mathvariant="normal">d</mml:mi> <mml:mspace width="0.25em" /> <mml:mi>ln</mml:mi> <mml:mspace width="0.25em" /> <mml:mi>Ro</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac7527ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> ∼ −4.5 to −2.5, although the value is sensitive to detection bias against weak modulation and may depend on other parameters including <jats:italic>T</jats:italic> <jats:sub>eff</jats:sub> and surface metallicity. The existing X-ray and Ca <jats:sc>ii</jats:sc> H and K flux data also show transitions at Ro/Ro<jats:sub>⊙</jats:sub> ∼ 0.4, suggesting that all these transitions share the same physical origin. We also find that the rapid decrease of <jats:italic>R</jats:italic> <jats:sub>per</jats:sub> with increasing Ro causes rotational modulation of fainter Kepler stars with Ro/Ro<jats:sub>⊙</jats:sub> ≳ 0.6 to be buried under the photometric noise. This effect sets the longest <jats:italic>P</jats:italic> <jats:sub>rot</jats:sub> detected in the McQuillan et al. sample as a function of <jats:italic>T</jats:italic> <jats:sub>eff</jats:sub> and obscures the signature of stalled spin down that has been proposed to set in around Ro/Ro<jats:sub>⊙</jats:sub> ∼ 1.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present observations of the extremely luminous but ambiguous nuclear transient (ANT) ASASSN-17jz, spanning roughly 1200 days of the object’s evolution. ASASSN-17jz was discovered by the All-Sky Automated Survey for Supernovae (ASAS-SN) in the galaxy SDSS J171955.84+414049.4 on UT 2017 July 27 at a redshift of <jats:italic>z</jats:italic> = 0.1641. The transient peaked at an absolute <jats:italic>B</jats:italic>-band magnitude of <jats:italic>M</jats:italic> <jats:sub> <jats:italic>B</jats:italic>,peak</jats:sub> = −22.81, corresponding to a bolometric luminosity of <jats:italic>L</jats:italic> <jats:sub>bol,peak</jats:sub> = 8.3 × 10<jats:sup>44</jats:sup> erg s<jats:sup>−1</jats:sup>, and exhibited late-time ultraviolet emission that was still ongoing in our latest observations. Integrating the full light curve gives a total emitted energy of <jats:italic>E</jats:italic> <jats:sub>tot</jats:sub> = (1.36 ±0.08) × 10<jats:sup>52</jats:sup> erg, with (0.80 ± 0.02) × 10<jats:sup>52</jats:sup> erg of this emitted within 200 days of peak light. This late-time ultraviolet emission is accompanied by increasing X-ray emission that becomes softer as it brightens. ASASSN-17jz exhibited a large number of spectral emission lines most commonly seen in active galactic nuclei (AGNs) with little evidence of evolution. It also showed transient Balmer features, which became fainter and broader over time, and are still being detected &gt;1000 days after peak brightness. We consider various physical scenarios for the origin of the transient, including supernovae (SNe), tidal disruption events, AGN outbursts, and ANTs. We find that the most likely explanation is that ASASSN-17jz was a SN IIn occurring in or near the disk of an existing AGN, and that the late-time emission is caused by the AGN transitioning to a more active state.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present accurate and deep multiband (<jats:italic>g</jats:italic>, <jats:italic>r</jats:italic>, <jats:italic>i</jats:italic>) photometry of the Local Group dwarf irregular galaxy NGC 6822. The images were collected with wide-field cameras at 2 m/4 m (INT, CTIO, CFHT) and 8 m class telescopes (Subaru) covering a 2 deg<jats:sup>2</jats:sup> field of view across the center of the galaxy. We performed point-spread function photometry of ≈7000 CCD images, and the final catalog includes more than 1 million objects. We developed a new approach to identify candidate field and galaxy stars and performed a new estimate of the galaxy center by using old stellar tracers, finding that it differs by 1.′15 (R.A.) and 1.′53 (decl.) from previous estimates. We also found that young (main sequence, red supergiants), intermediate (red clump, asymptotic giant branch (AGB)), and old (red giant branch) stars display different radial distributions. The old stellar population is spherically distributed and extends to radial distances larger than previously estimated (∼1°). The young population shows a well-defined bar and a disk-like distribution, as suggested by radio measurements, that is off-center compared with the old population. We discuss pros and cons of the different diagnostics adopted to identify AGB stars and develop new ones based on optical–near-IR–mid-IR color–color diagrams to characterize oxygen- and carbon-rich stars. We found a mean population ratio between carbon and M-type (C/M) stars of 0.67 ± 0.08 (optical/near-IR/mid-IR), and we used the observed C/M ratio with empirical C/M–metallicity relations to estimate a mean iron abundance of [Fe/H] ∼ −1.25 (<jats:italic>σ</jats:italic> = 0.04 dex), which agrees quite well with literature estimates.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Mesoscale periodic structures observed in solar wind plasma serve as an important diagnostic tool for constraining the processes that govern the formation of the solar wind. These structures have been observed in situ and in remote data as fluctuations in proton and electron density. However, only two events of this type have been reported regarding the elemental and ionic composition. Composition measurements are especially important in gaining an understanding of the origin of the solar wind as the composition is frozen into the plasma at the Sun and does not evolve as it advects through the heliosphere. Here, we present the analysis of four events containing mesoscale periodic solar wind structure during which the Iron and Magnesium number density data, measured by the Solar Wind Ion Composition Spectrometer (SWICS) on board the Advanced Composition Explorer spacecraft, are validated at statistically significant count levels. We use a spectral analysis method specifically designed to extract periodic signals from astrophysical time series and apply it to the SWICS 12 minute native resolution data set. We find variations in the relative abundance of elements with low first ionization potential, mass dependencies, and charge state during time intervals in which mesoscale periodic structures are observed. These variations are linked to temporal or spatial variations in solar source regions and put constraints on the solar wind formation mechanisms that produce them. Techniques presented here are relevant for future, higher-resolution studies of data from new instruments such as Solar Orbiter’s Heavy Ion Sensor.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We analyze the simulation result shown in Hotta &amp; Kusano (2021) in which the solar-like differential rotation is reproduced. The Sun is rotating differentially with the fast equator and the slow pole. It is widely thought that the thermal convection maintains the differential rotation, but recent high-resolution simulations tend to fail to reproduce the fast equator. This fact is an aspect of one of the biggest problems in solar physics called the convective conundrum. Hotta &amp; Kusano succeed in reproducing the solar-like differential rotation without using any manipulation with an unprecedentedly high-resolution simulation. In this study, we analyze the simulation data to understand the maintenance mechanism of the fast equator. Our analyses lead to conclusions that are summarized as follows. (1) The superequipatition magnetic field is generated by the compression, which can indirectly convert the massive internal energy to magnetic energy. (2) The efficient small-scale energy transport suppresses large-scale convection energy. (3) Non-Taylor–Proudman differential rotation is maintained by the entropy gradient caused by the anisotropic latitudinal energy transport enhanced by the magnetic field. (4) The fast equator is maintained by the meridional flow mainly caused by the Maxwell stress. The Maxwell stress itself also has a role in the angular momentum transport for the fast near-surface equator (we call it the <jats:italic>P</jats:italic> <jats:italic>unching ball </jats:italic>effect). The fast equator in the simulation is reproduced not due to the low Rossby number regime but due to the strong magnetic field. This study newly finds the role of the magnetic field in the maintenance of differential rotation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this paper, through analyzing data from the Solar Dynamics Observatory (SDO) and the Global Oscillation Network Group (GONG), we present a study on the formation of a double-decker filament in NOAA Active Region 12665 from 2017 July 8 to 14. We find that magnetic reconnection occurs between two smaller filaments to form a longer filament. According to the evolution of the leading sunspot, it is obvious that the sunspot experiences a continuous rotation around its umbra. During the period from 03:00 UT on July 11 to 10:00 UT on July 14, the average speed of sunspot rotation is about 3.°7 hr<jats:sup>–1</jats:sup>. The continuous rotation of sunspot stretches the filament and results in the formation of a reversed S-shaped filament. Due to the motion of the magnetic field and internal magnetic reconnection, the filament splits into two branches and forms a double-decker filament structure. In the process of filament separation, internal magnetic reconnection can also accelerate the filament separation. Nonlinear force-free field extrapolation indicates that there are two magnetic flux ropes, which are consistent with the observed results. Eventually, the upper filament erupts and produces an M-class flare and a halo coronal mass ejection.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The J-region asymptotic giant branch (JAGB) method is a new standard candle that is based on the stable intrinsic <jats:italic>J</jats:italic>-band magnitude of color-selected carbon stars, and has a precision comparable to other primary distance indicators such as Cepheids and the TRGB. We further test the accuracy of the JAGB method in the Local Group galaxy M33. M33's moderate inclination, low metallicity, and nearby proximity make it an ideal laboratory for tests of systematics in local distance indicators. Using high-precision optical BVI and near-infrared JHK photometry, we explore the application of three independent distance indicators: the JAGB method, the Cepheid Leavitt law, and the TRGB. We find: <jats:italic>μ</jats:italic> <jats:sub>0</jats:sub>(TRGB<jats:sub> <jats:italic>I</jats:italic> </jats:sub>) = 24.72 ± 0.02 (stat) ± 0.07 (sys) mag, <jats:italic>μ</jats:italic> <jats:sub>0</jats:sub>(TRGB<jats:sub>NIR</jats:sub>) = 24.72 ± 0.04 (stat) ± 0.10 (sys) mag, <jats:italic>μ</jats:italic> <jats:sub>0</jats:sub>(JAGB) = 24.67 ± 0.03 (stat) ± 0.04 (sys) mag, and <jats:italic>μ</jats:italic> <jats:sub>0</jats:sub>(Cepheid) = 24.71 ± 0.04 (stat) ± 0.01 (sys) mag. For the first time, we also directly compare a JAGB distance using ground-based and space-based photometry. We measure <jats:italic>μ</jats:italic> <jats:sub>0</jats:sub>(JAGB<jats:sub>F110W</jats:sub>) = 24.71 ± 0.06 (stat) ± 0.05 (sys) mag using the (F814W−F110W) color combination to effectively isolate the JAGB stars. In this paper, we measure a distance to M33 accurate to 2% and provide further evidence that the JAGB method is a powerful extragalactic distance indicator that can effectively probe a local measurement of the Hubble constant using spaced-based observations. We expect to measure the Hubble constant via the JAGB method in the near future, using observations from the James Webb Space Telescope.</jats:p>