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<jats:title>Abstract</jats:title> <jats:p>The sub-Saturn (∼4–8 <jats:italic>R</jats:italic> <jats:sub>⊕</jats:sub>) occurrence rate rises with orbital period out to at least ∼300 days. In this work we adopt and test the hypothesis that the decrease in their occurrence toward the star is a result of atmospheric mass loss, which can transform sub-Saturns into sub-Neptunes (≲4 <jats:italic>R</jats:italic> <jats:sub>⊕</jats:sub>) more efficiently at shorter periods. We show that under the mass-loss hypothesis, the sub-Saturn occurrence rate can be leveraged to infer their underlying core mass function, and, by extension, that of gas giants. We determine that lognormal core mass functions peaked near ∼10–20 <jats:italic>M</jats:italic> <jats:sub>⊕</jats:sub> are compatible with the sub-Saturn period distribution, the distribution of observationally inferred sub-Saturn cores, and gas-accretion theories. Our theory predicts that close-in sub-Saturns should be ∼50% less common and ∼30% more massive around rapidly rotating stars; this should be directly testable for stars younger than ≲500 Myr. We also predict that the sub-Jovian desert becomes less pronounced and opens up at smaller orbital periods around M stars compared to solar-type stars (∼0.7 days versus ∼3 days). We demonstrate that exceptionally low-density sub-Saturns, “super-puffs,” can survive intense hydrodynamic escape to the present day if they are born with even larger atmospheres than they currently harbor; in this picture, Kepler 223 d began with an envelope ∼1.5× the mass of its core and is currently losing its envelope at a rate of ∼2 × 10<jats:sup>−3</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊕</jats:sub> Myr<jats:sup>−1</jats:sup>. If the predictions from our theory are confirmed by observations, the core mass function we predict can also serve to constrain core formation theories of gas-rich planets.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Metal-deficient stars are important tracers for understanding the early formation of the Galaxy. Recent large-scale surveys with both photometric and spectroscopic data have reported an increasing number of metal-deficient stars whose kinematic features are consistent with those of the disk stellar populations. We report the discovery of an RR Lyrae variable (hereafter RRL) that is located within the thick disk and has an orbit consistent with the thick-disk kinematics. Our target RRL (HD 331986) is located at around 1 kpc from the Sun and, with <jats:italic>V</jats:italic> ≃ 11.3, is among the ∼130 brightest RRLs known so far. However, this object has scarcely been studied because it is in the midplane of the Galaxy, at a Galactic latitude around –1°. Its near-infrared spectrum (0.91–1.32 <jats:italic>μ</jats:italic>m) shows no absorption line except hydrogen lines of the Paschen series, suggesting [Fe/H] ≲ –2.5. It is the most metal-deficient RRL, at least among RRLs whose orbits are consistent with the disk kinematics, although we cannot determine to which of the disk and the halo it belongs. This unique RRL would provide us with essential clues for studying the early formation of stars in the inner Galaxy with further investigations, including high-resolution optical spectroscopy.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Analysis of inclusions in primitive meteorites reveals that several short-lived radionuclides (SLRs) with half-lives of 0.1–100 Myr existed in the early solar system (ESS). We investigate the ESS origin of <jats:sup>107</jats:sup>Pd, <jats:sup>135</jats:sup>Cs, and <jats:sup>182</jats:sup>Hf, which are produced by <jats:italic>slow</jats:italic> neutron captures (the <jats:italic>s</jats:italic>-process) in asymptotic giant branch (AGB) stars. We modeled the Galactic abundances of these SLRs using the <jats:monospace>OMEGA+</jats:monospace> galactic chemical evolution (GCE) code and two sets of mass- and metallicity-dependent AGB nucleosynthesis yields (Monash and FRUITY). Depending on the ratio of the mean-life <jats:italic>τ</jats:italic> of the SLR to the average length of time between the formations of AGB progenitors <jats:italic>γ</jats:italic>, we calculate timescales relevant for the birth of the Sun. If <jats:italic>τ</jats:italic>/<jats:italic>γ</jats:italic> ≳ 2, we predict self-consistent isolation times between 9 and 26 Myr by decaying the GCE predicted <jats:sup>107</jats:sup>Pd/<jats:sup>108</jats:sup>Pd, <jats:sup>135</jats:sup>Cs/<jats:sup>133</jats:sup>Cs, and <jats:sup>182</jats:sup>Hf/<jats:sup>180</jats:sup>Hf ratios to their respective ESS ratios. The predicted <jats:sup>107</jats:sup>Pd/<jats:sup>182</jats:sup>Hf ratio indicates that our GCE models are missing 9%–73% of <jats:sup>107</jats:sup>Pd and <jats:sup>108</jats:sup>Pd in the ESS. This missing component may have come from AGB stars of higher metallicity than those that contributed to the ESS in our GCE code. If <jats:italic>τ</jats:italic>/<jats:italic>γ</jats:italic> ≲ 0.3, we calculate instead the time (<jats:italic>T</jats:italic> <jats:sub>LE</jats:sub>) from the last nucleosynthesis event that added the SLRs into the presolar matter to the formation of the oldest solids in the ESS. For the 2 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, <jats:italic>Z</jats:italic> = 0.01 Monash model we find a self-consistent solution of <jats:italic>T</jats:italic> <jats:sub>LE</jats:sub> = 25.5 Myr.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Jets and outflows trace the accretion history of protostars. High-velocity molecular jets have been observed from several protostars in the early Class 0 phase of star formation, detected with the high-density tracer SiO. Until now, no clear jet has been detected with SiO emission from isolated evolved Class I protostellar systems. We report a prominent dense SiO jet from a Class I source G205S3 (HOPS-315: <jats:italic>T</jats:italic> <jats:sub>bol</jats:sub> ∼ 180 K, spectral index ∼0.417), with a moderately high mass-loss rate (∼0.59 × 10<jats:sup>−6</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup>) estimated from CO emission. Together, these features suggest that G205S3 is still in a high-accretion phase, similar to that expected of Class 0 objects. We compare G205S3 to a representative Class 0 system G206W2 (HOPS-399) and literature Class 0/I sources to explore the possible explanations behind the SiO emission seen at the later phase. We estimate a high inclination angle (∼40°) for G205S3 from CO emission, which may expose the infrared emission from the central core and mislead the spectral classification. However, the compact 1.3 mm continuum, C<jats:sup>18</jats:sup>O emission, location in the bolometric luminosity to submillimeter fluxes diagram, outflow force (∼3.26 × 10<jats:sup>−5</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> km s<jats:sup>−1</jats:sup> yr<jats:sup>−1</jats:sup>) are also analogous to that of Class I systems. We thus consider G205S3 to be at the very early phase of Class I, and in the late phase of <jats:italic>high accretion</jats:italic>. The episodic ejection could be due to the presence of an unknown binary, a planetary companion, or dense clumps, where the required mass for such high accretion could be supplied by a massive circumbinary disk.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Contamination by polarized foregrounds is one of the biggest challenges for future polarized cosmic microwave background (CMB) surveys and the potential detection of primordial <jats:italic>B</jats:italic>-modes. Future experiments, such as Simons Observatory (SO) and CMB-S4, will aim at very deep observations in relatively small (<jats:italic>f</jats:italic> <jats:sub>sky</jats:sub> ∼ 0.1) areas of the sky. In this work, we investigate the forecasted performance, as a function of the survey field location on the sky, for regions over the full sky, balancing between polarized foreground avoidance and foreground component separation modeling needs. To do this, we simulate observations by an SO-like experiment and measure the error bar on the detection of the tensor-to-scalar ratio, <jats:italic>σ</jats:italic>(<jats:italic>r</jats:italic>), with a pipeline that includes a parametric component separation method, the Correlated Component Analysis, and the use of the Fisher information matrix. We forecast the performance over 192 survey areas covering the full sky and also for optimized low-foreground regions. We find that modeling the spectral energy distribution of foregrounds is the most important factor, and any mismatch will result in residuals and bias in the primordial <jats:italic>B</jats:italic>-modes. At these noise levels, <jats:italic>σ</jats:italic>(<jats:italic>r</jats:italic>) is not especially sensitive to the level of foreground contamination, provided the survey targets the least-contaminated regions of the sky close to the Galactic poles.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We have conducted mapping observations (∼2′ × 2′) of the Class I protostar L1489 IRS using the 7 m array of the Atacama Compact Array and the IRAM 30 m telescope in C<jats:sup>18</jats:sup>O 2–1 emission to investigate the gas kinematics on 1000–10,000 au scales. The C<jats:sup>18</jats:sup>O emission shows a velocity gradient across the protostar in a direction almost perpendicular to the outflow. The radial profile of the peak velocity was measured from a C<jats:sup>18</jats:sup>O position–velocity diagram cut along the disk major axis. The measured peak velocity decreases with radius at radii of ∼1400–2900 au, but increases slightly or is almost constant at radii of <jats:italic>r</jats:italic> ≳ 2900 au. Disk-and-envelope models were compared with the observations to understand the nature of the radial profile of the peak velocity. The measured peak velocities are best explained by a model where the specific angular momentum is constant within a radius of 2900 au but increases with radius outside 2900 au. We calculated the radial profile of the specific angular momentum from the measured peak velocities and compared it to analytic models of core collapse. The analytic models reproduce well the observed radial profile of the specific angular momentum and suggest that material within a radius of ∼4000–6000 au in the initial dense core has accreted to the central protostar. Because dense cores are typically ∼10,000–20,000 au in radius, and as L1489 IRS is close to the end of its mass accretion phase, our result suggests that only a fraction of a dense core eventually forms a star.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We use the observed cumulative statistics of C <jats:sc>iv</jats:sc> absorbers and dark matter halos to infer the distribution of C <jats:sc>iv</jats:sc>-absorbing gas relative to galaxies at redshifts 0 ≤ <jats:italic>z</jats:italic> ≤ 5. We compare the cosmic incidence <jats:italic>dN/dX</jats:italic> of C <jats:sc>iv</jats:sc> absorber populations and galaxy halos, finding that massive <jats:italic>L</jats:italic> ≥ <jats:italic>L</jats:italic> <jats:sub>⋆</jats:sub> halos alone cannot account for all the observed <jats:italic>W</jats:italic> <jats:sub> <jats:italic>r</jats:italic> </jats:sub> ≥ 0.05 Å absorbers. However, the <jats:italic>dN/dX</jats:italic> of lower-mass halos exceeds that of <jats:italic>W</jats:italic> <jats:sub> <jats:italic>r</jats:italic> </jats:sub> ≥ 0.05 Å absorbers. We also estimate the characteristic gas radius of absorbing structures required for the observed C <jats:sc>iv</jats:sc> <jats:italic>dN/dX</jats:italic>, assuming each absorber is associated with a single galaxy halo. The <jats:italic>W</jats:italic> <jats:sub> <jats:italic>r</jats:italic> </jats:sub> ≥ 0.3 Å and <jats:italic>W</jats:italic> <jats:sub> <jats:italic>r</jats:italic> </jats:sub> ≥ 0.6 Å C <jats:sc>iv</jats:sc> gas radii are ∼30%–70% (∼20%–40%) of the virial radius of <jats:italic>L</jats:italic> <jats:sub>⋆</jats:sub> (0.1<jats:italic>L</jats:italic> <jats:sub>⋆</jats:sub>) galaxies, and the <jats:italic>W</jats:italic> <jats:sub> <jats:italic>r</jats:italic> </jats:sub> ≥ 0.05 Å gas radius is ∼100%–150% (∼60%–100%) of the virial radius of <jats:italic>L</jats:italic> <jats:sub>⋆</jats:sub> (0.1<jats:italic>L</jats:italic> <jats:sub>⋆</jats:sub>) galaxies. For stronger absorbers, the gas radius relative to the virial radius rises across Cosmic Noon and falls afterwards, while for weaker absorbers, the relative gas radius declines across Cosmic Noon and then dramatically rises at <jats:italic>z</jats:italic> &lt; 1. A strong luminosity-dependence of the gas radius implies highly extended C <jats:sc>iv</jats:sc> envelopes around massive galaxies before Cosmic Noon, while a luminosity-independent gas radius implies highly extended envelopes around dwarf galaxies after Cosmic Noon. From available absorber-galaxy and C <jats:sc>iv</jats:sc> evolution data, we favor a scenario in which low-mass galaxies enrich the volume around massive galaxies at early epochs and propose that the outer halo gas (&gt;0.5 <jats:italic>R</jats:italic> <jats:sub> <jats:italic>v</jats:italic> </jats:sub>) was produced primarily in ancient satellite dwarf galaxy outflows, while the inner halo gas (&lt;0.5 <jats:italic>R</jats:italic> <jats:sub> <jats:italic>v</jats:italic> </jats:sub>) originated from the central galaxy and persists as recycled accreting gas.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The black hole images obtained with the Event Horizon Telescope (EHT) are expected to be variable at the dynamical timescale near their horizons. For the black hole at the center of the M87 galaxy, this timescale (5–61 days) is comparable to the 6 day extent of the 2017 EHT observations. Closure phases along baseline triangles are robust interferometric observables that are sensitive to the expected structural changes of the images but are free of station-based atmospheric and instrumental errors. We explored the day-to-day variability in closure-phase measurements on all six linearly independent nontrivial baseline triangles that can be formed from the 2017 observations. We showed that three triangles exhibit very low day-to-day variability, with a dispersion of ∼3°–5°. The only triangles that exhibit substantially higher variability (∼90°–180°) are the ones with baselines that cross the visibility amplitude minima on the <jats:italic>u</jats:italic>–<jats:italic>v</jats:italic> plane, as expected from theoretical modeling. We used two sets of general relativistic magnetohydrodynamic simulations to explore the dependence of the predicted variability on various black hole and accretion-flow parameters. We found that changing the magnetic field configuration, electron temperature model, or black hole spin has a marginal effect on the model consistency with the observed level of variability. On the other hand, the most discriminating image characteristic of models is the fractional width of the bright ring of emission. Models that best reproduce the observed small level of variability are characterized by thin ring-like images with structures dominated by gravitational lensing effects and thus least affected by turbulence in the accreting plasmas.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Plasma-filled loop structures are common in the solar corona. Because detailed modeling of the dynamical evolution of these structures is computationally costly, an efficient method for computing approximate but quick physics-based solutions is to rely on space-integrated 0D simulations. The enthalpy-based thermal evolution of loops (<jats:monospace>EBTEL</jats:monospace>) framework is a commonly used method to study the exchange of mass and energy between the corona and transition region. <jats:monospace>EBTEL</jats:monospace> solves for density, temperature, and pressure, averaged over the coronal part of the loop, velocity at coronal base, and the instantaneous differential emission measure distribution in the transition region. The current single-fluid version of the code, <jats:monospace>EBTEL2</jats:monospace>, assumes that at all stages the flows are subsonic. However, sometimes the solutions show the presence of supersonic flows during the impulsive phase of heat input. It is thus necessary to account for this effect. Here, we upgrade <jats:monospace>EBTEL2</jats:monospace> to <jats:monospace>EBTEL3</jats:monospace> by including the kinetic energy term in the Navier–Stokes equation. We compare the solutions from <jats:monospace>EBTEL3</jats:monospace> with those obtained using <jats:monospace>EBTEL2</jats:monospace>, as well as the state-of-the-art field-aligned hydrodynamics code <jats:monospace>HYDRAD</jats:monospace>. We find that the match in pressure between <jats:monospace>EBTEL3</jats:monospace> and <jats:monospace>HYDRAD</jats:monospace> is better than that between <jats:monospace>EBTEL2</jats:monospace> and <jats:monospace>HYDRAD</jats:monospace>. Additionally, the velocities predicted by <jats:monospace>EBTEL3</jats:monospace> are in close agreement with those obtained with <jats:monospace>HYDRAD</jats:monospace> when the flows are subsonic. However, <jats:monospace>EBTEL3</jats:monospace> solutions deviate substantially from <jats:monospace>HYDRAD</jats:monospace>’s when the latter predicts supersonic flows. Using the mismatches in the solution, we propose a criterion to determine the conditions under which <jats:monospace>EBTEL</jats:monospace> can be used to study flows in the system.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report on a search for electron antineutrinos (<jats:inline-formula> <jats:tex-math> <?CDATA ${\bar{\nu }}_{e}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mover accent="true"> <mml:mrow> <mml:mi>ν</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>¯</mml:mo> </mml:mrow> </mml:mover> </mml:mrow> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac32c1ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) from astrophysical sources in the neutrino energy range 8.3–30.8 MeV with the KamLAND detector. In an exposure of 6.72 kton-year of the liquid scintillator, we observe 18 candidate events via the inverse beta decay reaction. Although there is a large background uncertainty from neutral current atmospheric neutrino interactions, we find no significant excess over background model predictions. Assuming several supernova relic neutrino spectra, we give upper flux limits of 60–110 cm<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup> (90% confidence level, CL) in the analysis range and present a model-independent flux. We also set limits on the annihilation rates for light dark matter pairs to neutrino pairs. These data improve on the upper probability limit of <jats:sup>8</jats:sup>B solar neutrinos converting into <jats:inline-formula> <jats:tex-math> <?CDATA ${\bar{\nu }}_{e}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mover accent="true"> <mml:mrow> <mml:mi>ν</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>¯</mml:mo> </mml:mrow> </mml:mover> </mml:mrow> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac32c1ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>, <jats:inline-formula> <jats:tex-math> <?CDATA ${P}_{{\nu }_{e}\to {\bar{\nu }}_{e}}\lt 3.5\times {10}^{-5}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>P</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>ν</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> </mml:msub> <mml:mo>→</mml:mo> <mml:msub> <mml:mrow> <mml:mover accent="true"> <mml:mrow> <mml:mi>ν</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>¯</mml:mo> </mml:mrow> </mml:mover> </mml:mrow> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:msub> <mml:mo>&lt;</mml:mo> <mml:mn>3.5</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>5</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac32c1ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> (90% CL) assuming an undistorted <jats:inline-formula> <jats:tex-math> <?CDATA ${\bar{\nu }}_{e}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mover accent="true"> <mml:mrow> <mml:mi>ν</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>¯</mml:mo> </mml:mrow> </mml:mover> </mml:mrow> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac32c1ieqn4.gif" xlink:type="simple" /> </jats:inline-formula> shape. This corresponds to a solar <jats:inline-formula> <jats:tex-math> <?CDATA ${\bar{\nu }}_{e}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mover accent="true"> <mml:mrow> <mml:mi>ν</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>¯</mml:mo> </mml:mrow> </mml:mover> </mml:mrow> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac32c1ieqn5.gif" xlink:type="simple" /> </jats:inline-formula> flux of 60 cm<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup> (90% CL) in the analysis energy range.</jats:p>