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<jats:title>Abstract</jats:title> <jats:p>We present the results of a single-dish survey toward 95 very low luminosity objects (VeLLOs) in optically thick (HCN 1−0) and thin (N<jats:sub>2</jats:sub>H<jats:sup>+</jats:sup> 1−0) lines performed for the purpose of understanding the physical processes of inward motions in the envelopes of the VeLLOs and characterizing their true nature. The normalized velocity differences (<jats:inline-formula> <jats:tex-math> <?CDATA $\delta {V}_{\mathrm{HCN}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>δ</mml:mi> <mml:msub> <mml:mrow> <mml:mi>V</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>HCN</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabe4d3ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) between the peak velocities of the two lines were derived for 41 VeLLOs detected in both lines. The <jats:italic>δ</jats:italic> <jats:italic>V</jats:italic> distribution of these VeLLOs is found to be significantly skewed to the blue, indicating the dominance of infalling motions in their envelopes. The infall speeds were derived for 15 infall candidates by using the HILL5 radiative transfer model. The speeds were in the range of 0.03−0.3 km s<jats:sup>−1</jats:sup>, with a median value of 0.16 km s<jats:sup>−1</jats:sup>, consistent with the gravitational freefall speeds from pressure-free envelopes. The mass infall rates calculated from the infall speeds are mostly of the order of 10<jats:sup>−6</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup>, with a median value of (3.4 ± 1.5) × 10<jats:sup>−6</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup>. These are found to be also consistent with the values predicted with the inside-out collapse model and show a fairly good correlation with the internal luminosities of the VeLLOs. This again indicates that the infall motions observed toward the VeLLOs are likely to be due to the gravitational infall motions in their envelopes. Our study suggests that most of the VeLLOs are potentially faint protostars, while two of the VeLLOs could possibly be proto−brown dwarf candidates.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Using the data sets of Mars Atmosphere and Volatile EvolutioN and OMNI for the period 2014 October 10–2020 February 14 and the heliocentric distance of 1–1.66 au, we investigate the statistical properties of solar wind upstream of Mars for the first time. The key parameters, including interplanetary magnetic field (IMF), proton density (<jats:italic>N</jats:italic>), bulk velocity (∣<jats:bold> <jats:italic>V</jats:italic> </jats:bold>∣), and dynamic pressure (<jats:italic>P</jats:italic> <jats:sub>dyn</jats:sub>), are surveyed with regard to variations of solar activity level and heliocentric distance. We find that the parameters ∣IMF∣, <jats:italic>N</jats:italic>, and <jats:italic>P</jats:italic> <jats:sub>dyn</jats:sub> monotonously decrease with heliocentric distance. Both ∣IMF∣ and <jats:italic>P</jats:italic> <jats:sub>dyn</jats:sub> are generally stronger at a higher solar activity level (<jats:italic>F</jats:italic> <jats:sub>10.7</jats:sub> ≥ 70 sfu), while such activity has little relevance to <jats:italic>N</jats:italic>. In contrast, ∣<jats:bold> <jats:italic>V</jats:italic> </jats:bold>∣ basically keeps a median of about 370 km s<jats:sup>−1</jats:sup> and is insensitive to the solar activity level and heliocentric distance. We also find that the IMF upstream of Mars at the higher solar activity level has a much smaller spiral angle in the inward sector; thus, IMF seems “straighter” than that in the outward sector, although that is not so for the inward sector of the upstream of Earth. Our statistical survey can be used as a reference for upstream solar wind of Mars at 1.4 ∼ 1.7 au, and could benefit the studies on solar wind as well as the Martian space environment.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Active regions in the inner solar corona, when observed in X-ray emission, consist of bright, hot loops surrounded by unstructured clouds. The emission from the clouds extends to a height of ≈4–5 × 10<jats:sup>4</jats:sup> km at temperatures of ≈2–3 MK. These “hot clouds” are variable, but persist for many days and do not appear to connect directly to the active region streamers or other large-scale structures observed higher in the corona. We present an observational analysis of these diffuse structures to establish basic plasma parameters such as magnetic field strength, particle density, and temperature. The values of <jats:italic>β</jats:italic>, the ratio of the plasma pressure to the magnetic field pressure, were found to be generally less than unity, though often approaching unity in the upper portions of the active region, where the hot clouds are located. The magnetic field may therefore only partially confine these regions and inhibit flare-like instabilities that could otherwise be driven by gradients of plasma pressure and current density.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The collisional growth of dust grains in a protoplanetary nebula is impacted by sintering because this increases the elasticity of the neck between dust grains. The high elasticity of a neck can lead to bouncing and not sticking of dust aggregates. This hinders the formation of planetesimals, and dust aggregates accumulate at a particular location in a protoplanetary nebula. Following sintering, the key parameter is the elasticity of a neck between dust grains. This study determined elasticity using numerical simulation and laboratory experiments. Elasticity was substantially smaller than that of a previous model, in which it was assumed that only the neck between grains was deformed. However, the results of this study demonstrated a change is negligible in the sticking efficiency of sintered dust aggregates compared to the results in a previous study.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Similarities in the chemical composition of two of the closest Milky Way satellites, namely, the Large Magellanic Cloud (LMC) and the Sagittarius (Sgr) dwarf galaxy, have been proposed in the literature, suggesting similar chemical enrichment histories between the two galaxies. This proposition, however, rests on different abundance analyses, which likely introduce various systematics that hamper a fair comparison among the different data sets. In order to bypass this issue (and highlight real similarities and differences between their abundance patterns), we present a homogeneous chemical analysis of 30 giant stars in the LMC, 14 giant stars in Sgr, and 14 giants in the Milky Way, based on high-resolution spectra taken with the spectrograph UVES-FLAMES. The LMC and Sgr stars, in the considered metallicity range ([Fe/H] &gt; −1.1 dex), show very similar abundance ratios for almost all the elements, with differences only in the heavy <jats:italic>s</jats:italic>-process elements Ba, La, and Nd, suggesting a different contribution by asymptotic giant branch stars. On the other hand, the two galaxies have chemical patterns clearly different from those measured in the Galactic stars, especially for the elements produced by massive stars. This finding suggests that the massive stars contributed less to the chemical enrichment of these galaxies with respect to the Milky Way. The derived abundances support similar chemical enrichment histories for the LMC and Sgr.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Subpercent level accuracy in shear measurement is required by the Stage-IV weak lensing surveys. One important challenge is suppressing the shear bias on source images of low signal-to-noise ratios (S/N ≲ 10). Previously, it has been demonstrated that the shear estimators defined in the Fourier_Quad (FQ) method can achieve subpercent accuracy at the very faint end (S/N ≲ 5) through ensemble averaging. Later, it was found that we can approach the minimum statistical error (the Cramer–Rao Bound) by symmetrizing the full probability distribution function (PDF) of the FQ shear estimators (the PDF_SYM approach), instead of taking ensemble averages. Recently, with a large amount of mock galaxy images, we were able to identify some small amount of shear biases in the PDF_SYM approach at the faint end. The multiplicative bias goes up to (1–2) × 10<jats:sup>−2</jats:sup> at S/N ≲ 10, and the anisotropy of the point-spread function causes an additive bias that can reach a few times 10<jats:sup>−4</jats:sup>. We find that these biases originate from the noise-source coupling in the galaxy power spectrum. It turns out that this problem can be largely fixed by adding additional terms to the FQ shear estimators. The resulting multiplicative and additive biases can be significantly suppressed to the level of 10<jats:sup>−3</jats:sup> and 10<jats:sup>−5</jats:sup>, respectively. These corrections substantially extend the available S/N range for accurate shear measurement with the PDF_SYM approach.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present an analysis of UV spectra of 13 quasars believed to belong to extreme Population A (xA) quasars, aimed at the estimation of the chemical abundances of the broad-line-emitting gas. Metallicity estimates for the broad-line-emitting gas of quasars are subject to a number of caveats; xA sources with the strongest Fe <jats:sc>ii</jats:sc> emission offer several advantages with respect to the quasar general population, as their optical and UV emission lines can be interpreted as the sum of a low-ionization component roughly at quasar rest frame (from virialized gas), plus a blueshifted excess (a disk wind), in different physical conditions. Capitalizing on these results, we analyze the component at rest frame and the blueshifted one, exploiting the dependence of several intensity line ratios on metallicity <jats:italic>Z</jats:italic>. We find that the validity of intensity line ratios as metallicity indicators depends on the physical conditions. We apply the measured diagnostic ratios to estimate the physical properties of sources such as density, ionization, and metallicity of the gas. Our results confirm that the two regions (the low-ionization component and the blueshifted excess) of different dynamical conditions also show different physical conditions and suggest metallicity values that are high, and probably the highest along the quasar main sequence, with <jats:italic>Z</jats:italic> ∼ 20−50 <jats:italic>Z</jats:italic> <jats:sub>⊙</jats:sub>, if the solar abundance ratios can be assumed constant. We found some evidence of an overabundance of aluminum with respect to carbon, possibly due to selective enrichment of the broad-line-emitting gas by supernova ejecta.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Using the <jats:italic>N</jats:italic>-body+Smoothed particle hydrodynamics code, ChaNGa, we identify two merger-driven processes—disk disruption and supermassive black hole (SMBH) feedback—which work together to quench <jats:italic>L</jats:italic> <jats:sup>*</jats:sup> galaxies for over 7 Gyr. Specifically, we examine the cessation of star formation in a simulated Milky Way (MW) analog, driven by an interaction with two minor satellites. Both interactions occur within ∼100 Myr of each other, and the satellites both have masses 5–20 times smaller than that of their MW-like host galaxy. Using the genetic modification process of Roth et al., we generate a set of four zoom-in, MW-mass galaxies all of which exhibit unique star formation histories due to small changes to their assembly histories. In two of these four cases, the galaxy is quenched by <jats:italic>z</jats:italic> = 1. Because these are controlled modifications, we are able to isolate the effects of two closely spaced minor merger events, the relative timing of which determines whether the MW-mass main galaxy quenches. This one–two punch works to: (1) fuel the SMBH at its peak accretion rate and (2) disrupt the cold, gaseous disk of the host galaxy. The end result is that feedback from the SMBH thoroughly and abruptly ends the star formation of the galaxy by <jats:italic>z</jats:italic> ≈ 1. We search for and find a similar quenching event in R<jats:sc>omulus</jats:sc>25, a hydrodynamical (25 Mpc)<jats:sup>3</jats:sup> volume simulation, demonstrating that the mechanism is common enough to occur even in a small sample of MW-mass quenched galaxies at <jats:italic>z</jats:italic> = 0.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The detailed observations of GW170817 proved for the first time directly that neutron star mergers are a major production site of heavy elements. The observations could be fit by a number of simulations that qualitatively agree, but can quantitatively differ (e.g., in total r-process mass) by an order of magnitude. We categorize kilonova ejecta into several typical morphologies motivated by numerical simulations, and apply a radiative transfer Monte Carlo code to study how the geometric distribution of the ejecta shapes the emitted radiation. We find major impacts on both spectra and light curves. The peak bolometric luminosity can vary by two orders of magnitude and the timing of its peak by a factor of five. These findings provide the crucial implication that the ejecta masses inferred from observations around the peak brightness are uncertain by at least an order of magnitude. Mixed two-component models with lanthanide-rich ejecta are particularly sensitive to geometric distribution. A subset of mixed models shows very strong viewing angle dependence due to lanthanide “curtaining,” which persists even if the relative mass of lanthanide-rich component is small. The angular dependence is weak in the rest of our models, but different geometric combinations of the two components lead to a highly diverse set of light curves. We identify geometry-dependent P Cygni features in late spectra that directly map out strong lines in the simulated opacity of neodymium, which can help to constrain the ejecta geometry and to directly probe the r-process abundances.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>There is growing evidence that the population of close-in planets discovered by the Kepler mission was sculpted by atmospheric loss, though the typical timescale for this evolution is not well-constrained. Among a highly complete sample of planet hosts of varying ages the age-dependence of the relative fraction of super-Earth and sub-Neptune detections can be used to constrain the rate at which some small planets lose their atmospheres. Using the California-Kepler Survey (CKS) sample, we find evidence that the ratio of super-Earth to sub-Neptune detections rises monotonically from 1 to 10 Gyr. Our results are in good agreement with an independent study focused on stars hotter than the Sun, as well as with forward modeling simulations incorporating the effects of photoevaporation and a CKS-like selection function. We find the observed trend persists even after accounting for the effects of completeness or correlations between age and other fundamental parameters.</jats:p>