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<jats:title>Abstract</jats:title> <jats:p>The Orion Kleinmann-Low nebula (Orion KL) is notoriously complex and exhibits a range of physical and chemical components. We conducted high-angular-resolution (subarcsecond) observations of <jats:sup>13</jats:sup>CH<jats:sub>3</jats:sub>OH <jats:italic>ν</jats:italic> = 0 (∼0.″3 and ∼0.″7) and CH<jats:sub>3</jats:sub>CN <jats:italic>ν</jats:italic> <jats:sub>8</jats:sub> = 1 (∼0.″2 and ∼0.″9) line emission with the Atacama Large Millimeter/submillimeter Array (ALMA) to investigate Orion KL’s structure on small spatial scales (≤350 au). Gas kinematics, excitation temperatures, and column densities were derived from the molecular emission via a pixel-by-pixel spectral line fitting of the image cubes, enabling us to examine the small-scale variation of these parameters. Subregions of the Hot Core have a higher excitation temperature in a 0.″2 beam than in a 0.″9 beam, indicative of possible internal sources of heating. Furthermore, the velocity field includes a bipolar ∼7–8 km s<jats:sup>−1</jats:sup> feature with a southeast–northwest orientation against the surrounding ∼4–5 km s<jats:sup>−1</jats:sup> velocity field, which may be due to an outflow. We also find evidence of a possible source of internal heating toward the Northwest Clump, since the excitation temperature there is higher in a smaller beam versus a larger beam. Finally, the region southwest of the Hot Core (Hot Core-SW) presents itself as a particularly heterogeneous region bridging the Hot Core and Compact Ridge. Additional studies to identify the (hidden) sources of luminosity and heating within Orion KL are necessary to better understand the nebula and its chemistry.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Our understanding of the impact of magnetic activity on stellar evolution continues to unfold. This impact is seen in sub-subgiant stars, defined to be stars that sit below the subgiant branch and red of the main sequence in a cluster color–magnitude diagram. Here we focus on S1063, a prototypical sub-subgiant in open cluster M67. We use a novel technique combining a two-temperature spectral decomposition and light-curve analysis to constrain starspot properties over a multiyear time frame. Using a high-resolution near-infrared IGRINS spectrum and photometric data from K2 and ASAS-SN, we find a projected spot filling factor of 32% ± 7% with a spot temperature of 4000 ± 200 K. This value anchors the variability seen in the light curve, indicating the spot filling factor of S1063 ranged from 20% to 45% over a four-year time period with an average spot filling factor of 30%. These values are generally lower than those determined from photometric model comparisons but still indicate that S1063, and likely other sub-subgiants, are magnetically active spotted stars. We find observational and theoretical comparisons of spotted stars are nuanced due to the projected spot coverage impacting estimates of the surface-averaged effective temperature. The starspot properties found here are similar to those found in RS CVn systems, supporting classifying sub-subgiants as another type of active giant star binary system. This technique opens the possibility of characterizing the surface conditions of many more spotted stars than previous methods, allowing for larger future studies to test theoretical models of magnetically active stars.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The water snowline location in protostellar envelopes provides crucial information about the thermal structure and the mass accretion process as it can inform about the occurrence of recent (≲1000 yr) accretion bursts. In addition, the ability to image water emission makes these sources excellent laboratories to test indirect snowline tracers such as H<jats:sup>13</jats:sup>CO<jats:sup>+</jats:sup>. We study the water snowline in five protostellar envelopes in Perseus using a suite of molecular-line observations taken with the Atacama Large Millimeter/submillimeter Array (ALMA) at ∼0.″2−0.″7 (60–210 au) resolution. B1-c provides a textbook example of compact <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{H}}}_{2}^{18}{\rm{O}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>18</mml:mn> </mml:mrow> </mml:msubsup> <mml:mi mathvariant="normal">O</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac3080ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> (3<jats:sub>1,3</jats:sub>−2<jats:sub>2,0</jats:sub>) and HDO (3<jats:sub>1,2</jats:sub>−2<jats:sub>2,1</jats:sub>) emission surrounded by a ring of H<jats:sup>13</jats:sup>CO<jats:sup>+</jats:sup> (<jats:italic>J</jats:italic> = 2−1) and HC<jats:sup>18</jats:sup>O<jats:sup>+</jats:sup> (<jats:italic>J</jats:italic> = 3−2). Compact HDO surrounded by H<jats:sup>13</jats:sup>CO<jats:sup>+</jats:sup> is also detected toward B1-bS. The optically thick main isotopologue HCO<jats:sup>+</jats:sup> is not suited to trace the snowline, and HC<jats:sup>18</jats:sup>O<jats:sup>+</jats:sup> is a better tracer than H<jats:sup>13</jats:sup>CO<jats:sup>+</jats:sup> due to a lower contribution from the outer envelope. However, because a detailed analysis is needed to derive a snowline location from H<jats:sup>13</jats:sup>CO<jats:sup>+</jats:sup> or HC<jats:sup>18</jats:sup>O<jats:sup>+</jats:sup> emission, their true value as a snowline tracer will lie in the application in sources where water cannot be readily detected. For protostellar envelopes, the most straightforward way to locate the water snowline is through observations of <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{H}}}_{2}^{18}{\rm{O}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>18</mml:mn> </mml:mrow> </mml:msubsup> <mml:mi mathvariant="normal">O</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac3080ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> or HDO. Including all subarcsecond-resolution water observations from the literature, we derive an average burst interval of ∼10,000 yr, but high-resolution water observations of a larger number of protostars are required to better constrain the burst frequency.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We use deep narrowband CaHK (F395N) imaging taken with the Hubble Space Telescope (HST) to construct the metallicity distribution function (MDF) of Local Group ultra-faint dwarf galaxy Eridanus <jats:sc>II</jats:sc> (Eri <jats:sc>II</jats:sc>). When combined with archival F475W and F814W data, we measure metallicities for 60 resolved red giant branch stars as faint as <jats:italic>m</jats:italic> <jats:sub>F475W</jats:sub> ∼ 24 mag, a factor of ∼4× more stars than current spectroscopic MDF determinations. We find that Eri <jats:sc>II</jats:sc> has a mean metallicity of [Fe/H] = −2.50<jats:inline-formula> <jats:tex-math> <?CDATA ${}_{-0.07}^{+0.07}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow /> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.07</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.07</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac3665ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> and a dispersion of <jats:inline-formula> <jats:tex-math> <?CDATA ${\sigma }_{[\mathrm{Fe}/{\rm{H}}]}\,=\,{0.42}_{-0.06}^{+0.06}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>σ</mml:mi> </mml:mrow> <mml:mrow> <mml:mo stretchy="false">[</mml:mo> <mml:mi>Fe</mml:mi> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> <mml:mo stretchy="false">]</mml:mo> </mml:mrow> </mml:msub> <mml:mspace width="0.25em" /> <mml:mo>=</mml:mo> <mml:mspace width="0.25em" /> <mml:msubsup> <mml:mrow> <mml:mn>0.42</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.06</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.06</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac3665ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>, which are consistent with spectroscopic MDFs, though more precisely constrained owing to a larger sample. We identify a handful of extremely metal-poor star candidates (EMP; [Fe/H] &lt; −3) that are marginally bright enough for spectroscopic follow-up. The MDF of Eri <jats:sc>II</jats:sc> appears well described by a leaky box chemical evolution model. We also compute an updated orbital history for Eri <jats:sc>II</jats:sc> using Gaia eDR3 proper motions, and find that it is likely on first infall into the Milky Way. Our findings suggest that Eri <jats:sc>II</jats:sc> underwent an evolutionary history similar to that of an isolated galaxy. Compared to MDFs for select cosmological simulations of similar mass galaxies, we find that Eri <jats:sc>II</jats:sc> has a lower fraction of stars with [Fe/H] &lt; −3, though such comparisons should currently be treated with caution due to a paucity of simulations, selection effects, and known limitations of CaHK for EMPs. This study demonstrates the power of deep HST CaHK imaging for measuring the MDFs of UFDs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigate aspects of the co-accretion + giant impact scenario proposed by Morbidelli et al. (2012) for the origin of the Uranian satellites. In this model, a regular satellite system formed during gas accretion is impulsively destabilized by a Uranus-tipping impact, producing debris that ultimately re-orients to the planet’s new equatorial plane and re-accumulates into Uranus’ current large moons. We first investigate the nodal randomization of a disk of debris resulting from disruptive collisions between the hypothesized prior satellites. Consistent with Morbidelli et al., we find that an impact-generated interior c-disk with mass ≥10<jats:sup>−2</jats:sup> Uranus masses is needed to cause sufficient nodal randomization to appropriately realign the outer debris disk. We then simulate the reaccumulation of the outer debris disk into satellites and find that disks with larger initial radii are needed to produce an outer debris disk that extends to Oberon’s distance, and that Uranus’ obliquity prior to the giant impact must have been substantial, ≥40°, if its original co-accreted satellite system was broadly similar in radial scale to those at Jupiter and Saturn today. Finally, we explore the subsequent evolution of a massive, water-dominated inner c-disk as it condenses, collisionally spreads, and spawns new moons beyond the Roche limit. We find that intense tidal dissipation in Uranus (i.e., <jats:inline-formula> <jats:tex-math> <?CDATA ${(Q/{k}_{2})}_{{\rm{U}}}\leqslant {10}^{2}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mi>Q</mml:mi> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>k</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">U</mml:mi> </mml:mrow> </mml:msub> <mml:mo>≤</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac300eieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) is needed to prevent large icy moons spawned from the inner disk from expanding beyond the synchronous orbit, where they would be long lived and inconsistent with the lack of massive inner moons at Uranus today. We conclude that while a co-accretion + giant impact is viable it requires rather specific conditions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present results from a search for radio recombination lines in three H <jats:sc>i</jats:sc> self-absorbing (HISA) clouds at 750 MHz and 321 MHz with the Robert C. Byrd Green Bank Telescope, and in three Galactic plane positions at 327 MHz with the Arecibo Telescope. We detect carbon recombination lines (CRRLs) in the direction of DR4 and DR21, as well as in the Galactic plane position G34.94 + 0.0. We additionally detect hydrogen recombination lines in emission in five of the six sightlines, and a Helium line at 750 MHz toward DR21. Combining our new data with 150 MHz Low Frequency Array detections of CRRL absorption toward DR4 and DR21, we estimate the electron densities of the line-forming regions by modeling the line width as a function of frequency. The estimated densities are in the range 1.4 → 6.5 cm<jats:sup>−3</jats:sup> toward DR4, for electron temperatures 200 → 20 K. A dual line-forming region with densities between 3.5 → 24 cm<jats:sup>−3</jats:sup> and 0.008 → 0.3 cm<jats:sup>−3</jats:sup> could plausibly explain the observed line width as a function of frequency on the DR21 sight line. The central velocities of the CRRLs compare well with CO emission and HISA lines in these directions. The cloud densities estimated from the CO lines are smaller (at least a factor of five) than those of the CRRL-forming regions. It is likely that the CRRL-forming and HISA gas is located in a denser, shocked region either at the boundary of or within the CO emitting cloud.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Compact star-forming clumps observed in distant galaxies are often suggested to play a crucial role in galaxy assembly. In this paper, we use a novel approach of applying finite-resolution deconvolution on ground-based images of the COSMOS field to resolve 20,185 star-forming galaxies (SFGs) at 0.5 &lt; <jats:italic>z</jats:italic> &lt; 2 to an angular resolution of 0.″3 and study their clump fractions. A comparison between the deconvolved images and HST images across four different filters shows good agreement and validates image deconvolution. We model spectral energy distributions using the deconvolved 14-band images to provide resolved surface brightness and stellar-mass density maps for these galaxies. We find that the fraction of clumpy galaxies decreases with increasing stellar masses and with increasing redshift: from ∼30% at <jats:italic>z</jats:italic> ∼ 0.7 to ∼50% at <jats:italic>z</jats:italic> ∼ 1.7. Using abundance matching, we also trace the progenitors for galaxies at <jats:italic>z</jats:italic> ∼ 0.7 and measure the fractional mass contribution of clumps toward their total mass budget. Clumps are observed to have a higher fractional mass contribution toward galaxies at higher redshift: increasing from ∼1% at <jats:italic>z</jats:italic> ∼ 0.7 to ∼5% at <jats:italic>z</jats:italic> ∼ 1.7. Finally, the majority of clumpy SFGs have higher specific star formation rates (sSFR) compared to the average SFGs at fixed stellar mass. We discuss the implication of this result for in situ clump formation due to disk instability.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present results of a search for periodic gravitational wave signals with frequencies between 20 and 400 Hz from the neutron star in the supernova remnant G347.3-0.5 using LIGO O2 public data. The search is deployed on the volunteer computing project Einstein@Home, with thousands of participants donating compute cycles to make this endeavour possible. We find no significant signal candidate and set the most constraining upper limits to date on the amplitude of gravitational wave signals from the target, corresponding to deformations below 10<jats:sup>−6</jats:sup> in a large part of the band. At the frequency of best strain sensitivity, near 166 Hz, we set 90% confidence upper limits on the gravitational wave intrinsic amplitude of <jats:inline-formula> <jats:tex-math> <?CDATA ${h}_{0}^{90 \% }\approx 7.0\times {10}^{-26}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>h</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>90</mml:mn> <mml:mo>%</mml:mo> </mml:mrow> </mml:msubsup> <mml:mo>≈</mml:mo> <mml:mn>7.0</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>26</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac35cbieqn1.gif" xlink:type="simple" /> </jats:inline-formula>. Over most of the frequency range our upper limits are a factor of 20 smaller than the indirect age-based upper limit.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Among the fundamental and most challenging problems of laboratory, space, and astrophysical plasma physics is to understand the relaxation processes of nearly collisionless plasmas toward quasi-stationary states and the resultant states of electromagnetic plasma turbulence. Recently, it has been argued that solar wind plasma <jats:italic>β</jats:italic> and temperature anisotropy observations may be regulated by kinetic instabilities such as the ion cyclotron, mirror, electron cyclotron, and firehose instabilities; and it has been argued that magnetic fluctuation observations are consistent with the predictions of the fluctuation–dissipation theorem, even far below the kinetic instability thresholds. Here, using in situ magnetic field and plasma measurements by the THEMIS satellite mission, we show that such regulation seems to occur also in the Earth’s magnetotail plasma sheet at the ion and electron scales. Regardless of the clear differences between the solar wind and the magnetotail environments, our results indicate that spontaneous fluctuations and their collisionless regulation are fundamental features of space and astrophysical plasmas, thereby suggesting the processes is universal.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Integrated Science Investigation of the Sun instrument suite onboard NASA’s Parker Solar Probe mission continues to measure solar energetic particles and cosmic rays closer to the Sun than ever before. Here, we present the first observations of cosmic rays into 0.1 au (21.5 solar radii), focusing specifically on oxygen from ∼2018.7 to ∼2021.2. Our energy spectra reveal an anomalous cosmic-ray-dominated profile that is comparable to that at 1 au, across multiple solar cycle minima. The galactic cosmic-ray-dominated component is similar to that of the previous solar minimum (Solar Cycle 24/25 compared to 23/24) but elevated compared to the past (Solar Cycle 20/21). The findings are generally consistent with the current trend of unusually weak solar modulation that originated during the previous solar minimum and continues today. We also find a strong radial intensity gradient: 49.4 ± 8.0% au<jats:sup>−1</jats:sup> from 0.1 to 0.94 au, for energies of 6.9–27 MeV nuc<jats:sup>−1</jats:sup>. This value agrees with that measured by Helios nearly 45 yr ago from 0.3 to 1.0 au (48% ± 12% au<jats:sup>−1</jats:sup>; 9–29 MeV nuc<jats:sup>−1</jats:sup>) and is larger than predicted by models. The large anomalous cosmic-ray gradients observed close to the Sun by the Parker Solar Probe Integrated Science Investigation of the Sun instrument suite found here suggest that intermediate-scale variations in the magnetic field’s structure strongly influence cosmic-ray drifts, well inside 1 au.</jats:p>