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<jats:title>Abstract</jats:title> <jats:p>We analyze five epochs of Neutron star Interior Composition Explorer (NICER) data of the black hole X-ray binary MAXI J1820+070 during the bright hard-to-soft state transition in its 2018 outburst with both reflection spectroscopy and Fourier-resolved timing analysis. We confirm the previous discovery of reverberation lags in the hard state, and find that the frequency range where the (soft) reverberation lag dominates decreases with the reverberation lag amplitude increasing during the transition, suggesting an increasing X-ray emitting region, possibly due to an expanding corona. By jointly fitting the lag-energy spectra in a number of broad frequency ranges with the reverberation model <jats:monospace>reltrans</jats:monospace>, we find the increase in reverberation lag is best described by an increase in the X-ray coronal height. This result, along with the finding that the corona contracts in the hard state, suggests a close relationship between spatial extent of the X-ray corona and the radio jet. We find the corona expansion (as probed by reverberation) precedes a radio flare by ∼5 days, which may suggest that the hard-to-soft transition is marked by the corona expanding vertically and launching a jet knot that propagates along the jet stream at relativistic velocities.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Primordial density perturbations in the radiation-dominated era of the early universe are expected to generate stochastic gravitational waves (GWs) due to nonlinear mode coupling. In this Letter, we report on a search for such a stochastic GW background in the data of the two LIGO detectors during their second observing run (O2). We focus on the primordial perturbations in the range of comoving wavenumbers 10<jats:sup>16</jats:sup>–10<jats:sup>18</jats:sup> Mpc<jats:sup>−1</jats:sup> for which the stochastic background falls within the detectors’ sensitivity band. We do not find any conclusive evidence of this stochastic signal in the data, and thus place the very first GW-based constraints on the amplitude of the power spectrum at these scales. We assume a log-normal shape for the power spectrum and Gaussian statistics for the primordial perturbations, and vary the width of the power spectrum to cover both narrow and broad spectra. Derived upper limits (95%) on the amplitude of the power spectrum are 0.01–0.1. As a byproduct, we are able to infer upper limits on the fraction of the universe’s mass in ultralight primordial black holes (<jats:italic>M</jats:italic> <jats:sub>PBH</jats:sub> ≃ 10<jats:sup>−20</jats:sup>–10<jats:sup>−19</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) at their formation time to be ≲10<jats:sup>−25</jats:sup>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present an independent examination of the parallax zero-point of the Third Gaia Early Data Release (hereafter EDR3), using the LAMOST primary red clump (PRC) stellar sample. A median parallax offset of around 26 <jats:italic>μ</jats:italic>as, slightly larger than that found by examination of distant quasars, is found for both the five- and six-parameter solutions in EDR3, based on samples of over 63,000 and 2000 PRC stars, respectively. Similar to the previous investigation of Lindegren et al., to which we compare our results, the parallax zero-point exhibits clear dependencies on the <jats:italic>G</jats:italic> magnitudes, colors, and positions of the objects. Based on our analysis, the zero-point of the revised parallax can be reduced to a few <jats:italic>μ</jats:italic>as, and some significant patterns, e.g., discontinuities with stellar magnitude, can be properly removed. However, relatively large offsets (&gt;10 <jats:italic>μ</jats:italic>as) are still found for the revised parallaxes over different positions on the sky.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Applying dendrogram analysis to the CARMA-NRO C<jats:sup>18</jats:sup>O (<jats:italic>J</jats:italic> = 1–0) data having an angular resolution of ∼8″, we identified 692 dense cores in the Orion Nebula Cluster region. Using this core sample, we compare the core and initial stellar mass functions in the same area to quantify the step from cores to stars. About 22% of the identified cores are gravitationally bound. The derived core mass function (CMF) for starless cores has a slope similar to Salpeter’s stellar initial mass function (IMF) for the mass range above 1 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, consistent with previous studies. Our CMF has a peak at a subsolar mass of ∼0.1 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, which is comparable to the peak mass of the IMF derived in the same area. We also find that the current star formation rate is consistent with the picture in which stars are born only from self-gravitating starless cores. However, the cores must gain additional gas from the surroundings to reproduce the current IMF (e.g., its slope and peak mass), because the core mass cannot be accreted onto the star with 100% efficiency. Thus, the mass accretion from the surroundings may play a crucial role in determining the final stellar masses of stars.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present constraints on the dust continuum flux and inferred gas content of a gravitationally lensed massive quiescent galaxy at <jats:italic>z</jats:italic> = 1.883 ± 0.001 using AzTEC 1.1 mm imaging with the Large Millimeter Telescope. MRG-S0851 appears to be a prototypical massive compact quiescent galaxy, but evidence suggests that it experienced a centrally concentrated rejuvenation event in the last 100 Myr. This galaxy is undetected in the AzTEC image but we calculate an upper limit on the millimeter flux and use this to estimate the H<jats:sub>2</jats:sub> mass limit via an empirically calibrated relation that assumes a constant molecular-gas-to-dust ratio of 150. We constrain the 3<jats:italic>σ</jats:italic> upper limit of the H<jats:sub>2</jats:sub> fraction from the dust continuum in MRG-S0851 to be <jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{{{\rm{H}}}_{2}}/{M}_{\star }\leqslant 6.8 \% $?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabe132ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>. MRG-S0851 has a low gas fraction limit with a moderately low sSFR owing to the recent rejuvenation episode, which together result in a relatively short depletion time of &lt;0.6 Gyr if no further H<jats:sub>2</jats:sub> gas is accreted. Empirical and analytical models both predict that we should have detected molecular gas in MRG-S0851, especially given the rejuvenation episode; this suggests that cold gas and/or dust is rapidly depleted in at least some early quiescent galaxies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>It is generally believed that the addition of continents cools the climate of an aquaplanet with a similar orbit to Earth; this is because continents have a higher surface albedo than oceans. A similar effect has been shown in climate simulations for exoplanets. Here we demonstrate that the influence of a continent on ocean circulation could have a dominative effect on the climate of a synchronously rotating exoplanet compared with the effect of the surface albedo, especially when the rotation of the exoplanet is relatively slow (e.g., the rotational period is 40 Earth days). The global mean surface temperature could vary by more than 26° C, simply by moving a small continent to a different location. The ocean circulation on a synchronously rotating exoplanet is characterized by a strong westerly jet along the equator and one large gyre in each hemisphere. The surface temperature decreases when the equatorial westerly or the western branch of either of the gyres is blocked by a continent or an island arc chain. However, if the continent blocks the eastern branch of the gyre, the equatorial westerly is strengthened and the climate warms. A large number of potentially habitable exoplanets have been found orbiting around M-dwarfs in a tidally locked manner; our results indicate that their climates, as well as their atmospheric chemistry, may deviate from previous estimates if a small continent, or even an island arc chain, is present.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report the first detection of a hydroxyl radical (OH) emission signature in the planetary atmosphere outside the solar system, in this case, in the dayside of WASP-33b. We analyze high-resolution near-infrared emission spectra of WASP-33b taken using the InfraRed Doppler spectrograph on the 8.2 m Subaru telescope. The telluric and stellar lines are removed using a detrending algorithm, <jats:sc>SysRem</jats:sc>. The residuals are then cross-correlated with OH and H<jats:sub>2</jats:sub>O planetary spectrum templates produced using several different line lists. We check and confirm the accuracy of OH line lists by cross-correlating with the spectrum of GJ 436. As a result, we detect the emission signature of OH at <jats:italic>K</jats:italic> <jats:sub>p</jats:sub> of <jats:inline-formula> <jats:tex-math> <?CDATA ${230.9}_{-7.4}^{+6.9}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabec71ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> km s<jats:sup>−1</jats:sup> and <jats:italic>v</jats:italic> <jats:sub>sys</jats:sub> of −0.3<jats:inline-formula> <jats:tex-math> <?CDATA ${}_{-5.6}^{+5.3}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabec71ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> km s<jats:sup>−1</jats:sup> with a signal-to-noise ratio (S/N) of 5.4 and a significance of 5.5<jats:italic>σ</jats:italic>. Additionally, we marginally detect H<jats:sub>2</jats:sub>O emission in the <jats:italic>H</jats:italic>-band with an S/N of 4.0 and a significance of 5.2<jats:italic>σ</jats:italic> using the POKAZATEL line list. However, no significant signal is detected using the HITEMP 2010, which might be due to differences in line positions and strengths, as well as the incompleteness of the line lists. Nonetheless, this marginal detection is consistent with the prediction that H<jats:sub>2</jats:sub>O is mostly thermally dissociated in the upper atmosphere of the ultra-hot Jupiters. Therefore, along with CO, OH is expected to be one of the most abundant O-bearing molecules in the dayside atmosphere of ultra-hot Jupiters and should be considered when studying their atmospheres.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A solar type-I noise storm is produced by accelerated particle beams generated at active regions undergoing magnetic field restructuring. Their intensity varies by orders of magnitude within subsecond and sub-MHz scales. But the morphological evolution of these sources is not studied at these scales due to the lack of required imaging cadence and fidelity in meterwave bands. Using data from the Murchison Widefield Array, this work explores the coevolution of size, sky-orientation, and intensity of a noise storm source associated with a weak microflare. This work presents the discovery of two correlated modes of evolution in the source parameters: a sausage like “S” mode where the source intensity and size show an anticorrelated evolution; and a torsional like “T” mode where the source size and sky-orientation show a correlated evolution. A flare mediated mode conversion is observed from “T” to “S” for the first time in these sources. These results support the idea of build up of magnetic stress energy in braided active region loops, which later become unstable causing flares and particle acceleration until they relax to a minimally braided state. The discovered mode conversion can be a future diagnostic for such events.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The metastable helium line at 1083 nm can be used to probe the extended upper atmospheres of close-in exoplanets and thus provide insight into their atmospheric mass loss, which is likely to be significant in sculpting their population. We used an ultra-narrow band filter centered on this line to observe two transits of the low-density gas giant HAT-P-18b, using the 200″ Hale Telescope at Palomar Observatory, and report the detection of its extended upper atmosphere. We constrain the excess absorption to be 0.46% ± 0.12% in our 0.635 nm bandpass, exceeding the transit depth from the Transiting Exoplanet Survey Satellite (TESS) by 3.9<jats:italic>σ</jats:italic>. If we fit this signal with a 1D Parker wind model, we find that it corresponds to an atmospheric mass loss rate between <jats:inline-formula> <jats:tex-math> <?CDATA ${8.3}_{-1.9}^{+2.8}\times {10}^{-5}\,{M}_{{\rm{J}}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>8.3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.9</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>2.8</mml:mn> </mml:mrow> </mml:msubsup> <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:mspace width="0.25em" /> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">J</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabe706ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> Gyr<jats:sup>−1</jats:sup> and <jats:inline-formula> <jats:tex-math> <?CDATA ${2.63}_{-0.64}^{+0.46}\times {10}^{-3}\,{M}_{{\rm{J}}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>2.63</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.64</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.46</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em" /> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">J</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabe706ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> Gyr<jats:sup>−1</jats:sup> for thermosphere temperatures ranging from 4000 K to 13,000 K, respectively. With a <jats:italic>J</jats:italic> magnitude of 10.8, this is the faintest system for which such a measurement has been made to date, demonstrating the effectiveness of this approach for surveying mass loss on a diverse sample of close-in gas giant planets.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a detailed study of the molecular gas content and stellar population properties of three massive galaxies at 1 &lt; <jats:italic>z</jats:italic> &lt; 1.3 that are in different stages of quenching. The galaxies were selected to have quiescent optical/near-infrared spectral energy distribution and relatively bright emission at 24 <jats:italic>μ</jats:italic>m, and show remarkably diverse properties. CO emission from each of the three galaxies is detected in deep NOEMA observations, allowing us to derive molecular gas fractions <jats:italic>M</jats:italic> <jats:sub>gas</jats:sub>/<jats:italic>M</jats:italic> <jats:sub>*</jats:sub> of 13%–23%. We also reconstruct the star formation histories by fitting models to the observed photometry and optical spectroscopy, finding evidence for recent rejuvenation in one object, slow quenching in another, and rapid quenching in the third system. To better constrain the quenching mechanism we explore the depletion times for our sample and other similar samples at <jats:italic>z</jats:italic> ∼ 0.7 from the literature. We find that the depletion times are highly dependent on the method adopted to measure the star formation rate: using the UV+IR luminosity we obtain depletion times about 6 times shorter than those derived using dust-corrected [O <jats:sc>ii</jats:sc>] emission. When adopting the star formation rates from spectral fitting, which are arguably more robust, we find that recently quenched galaxies and star-forming galaxies have similar depletion times, while older quiescent systems have longer depletion times. These results offer new, important constraints for physical models of galaxy quenching.</jats:p>