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<jats:title>Abstract</jats:title> <jats:p>We present a high-cadence short term photometric and spectroscopic monitoring campaign of a type Ibn SN 2019wep, which is one of the rare SN Ibn after SNe 2010al and 2019uo to display signatures of flash ionization (He <jats:sc>ii</jats:sc>, C <jats:sc>iii</jats:sc>, N <jats:sc>iii</jats:sc>). We compare the decline rates and rise time of SN 2019wep with other SNe Ibn and fast transients. The post-peak decline in all bands (0.1 mag day<jats:sup>−1</jats:sup>) are consistent with SNe Ibn but less than the fast transients. On the other hand, the Δ<jats:italic>m</jats:italic> <jats:sub>15</jats:sub> values are slightly lower than the average values for SNe Ibn but consistent with the fast transients. The rise time is typically shorter than SNe Ibn but longer than fast transients. SN 2019wep lies at the fainter end of SNe Ibn but possesses an average luminosity among the fast transients sample. The peculiar color evolution places it between SNe Ib and the most extreme SNe Ibn. The bolometric light-curve modeling shows resemblance with SN 2019uo with ejecta masses consistent with SNe Ib. SN 2019wep belongs to the P cygni subclass of SNe Ibn and shows faster evolution in line velocities as compared to the <jats:italic>emission</jats:italic> subclass. The post-maximum spectra show close resemblance with ASASSN-15ed hinting it to be of SN Ib nature. The low He <jats:sc>i</jats:sc> CSM velocities and residual H<jats:italic>α</jats:italic> further justifies it and provide evidence of an intermittent progenitor between Wolf-Rayet and LBV stars.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study the relation between stellar mass (<jats:italic>M</jats:italic> <jats:sub>*</jats:sub>) and star formation rate (SFR) for star-forming galaxies over approximately five decades in stellar mass (<jats:inline-formula> <jats:tex-math> <?CDATA $5.5\ \lesssim \ {\mathrm{log}}_{10}({M}_{* }/{M}_{\odot })\lesssim 10.5$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>5.5</mml:mn> <mml:mspace width="0.33em" /> <mml:mo>≲</mml:mo> <mml:mspace width="0.33em" /> <mml:msub> <mml:mi>log</mml:mi> <mml:mn>10</mml:mn> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>*</mml:mo> </mml:msub> <mml:mo stretchy="true">/</mml:mo> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>⊙</mml:mo> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mo>≲</mml:mo> <mml:mn>10.5</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac5d39ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) at <jats:italic>z</jats:italic> ≈ 3–6.5. This unprecedented coverage has been possible thanks to the joint analysis of blank non-lensed fields (COSMOS/SMUVS) and cluster lensing fields (Hubble Frontier Fields) that allow us to reach very low stellar masses. Previous works have revealed the existence of a clear bimodality in the <jats:italic />SFR–<jats:italic>M</jats:italic> <jats:sub>*</jats:sub> plane with a star formation Main Sequence and a starburst cloud at <jats:italic>z</jats:italic> ≈ 4–5. Here we show that this bimodality extends to all star-forming galaxies and is valid in the whole redshift range <jats:italic>z</jats:italic> ≈ 3–6.5. We find that starbursts constitute at least ≈20% of all star-forming galaxies with <jats:italic>M</jats:italic> <jats:sub>*</jats:sub> ≳ 10<jats:sup>9</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> at these redshifts and reach a peak of 40% at <jats:italic>z</jats:italic> = 4–5. More importantly, 60%–90% of the total SFR budget at these redshifts is contained in starburst galaxies, indicating that the starburst mode of star formation is dominant at high redshifts. Almost all the low stellar mass starbursts with <jats:inline-formula> <jats:tex-math> <?CDATA ${\mathrm{log}}_{10}({M}_{* }/{M}_{\odot })\lesssim 8.5$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>log</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mo>≲</mml:mo> <mml:mn>8.5</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac5d39ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> have ages comparable to the typical timescales of a starburst event, suggesting that these galaxies are being caught in the process of formation. Interestingly, galaxy formation models fail to predict the starburst/main-sequence bimodality and starbursts overall, suggesting that the starburst phenomenon may be driven by physical processes occurring at smaller scales than those probed by these models.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Using high-cadence observations from the Hydrogen-alpha Rapid Dynamics camera imaging system on the Dunn Solar Telescope, we present an investigation of the statistical properties of transverse oscillations in spicules captured above the solar limb. At five equally separated atmospheric heights, spanning approximately 4900–7500 km, we have detected a total of 15,959 individual wave events, with a mean displacement amplitude of 151 ± 124 km, a mean period of 54 ± 45 s, and a mean projected velocity amplitude of 21 ± 13 km s<jats:sup>−1</jats:sup>. We find that both the displacement and velocity amplitudes increase with height above the solar limb, ranging from 132 ± 111 km and 17.7 ± 10.6 km s<jats:sup>−1</jats:sup> at ≈4900 km, and 168 ± 125 km and 26.3 ± 14.1 km s<jats:sup>−1</jats:sup> at ≈7500 km, respectively. Following the examination of neighboring oscillations in time and space, we find 45% of the waves to be upwardly propagating, 49% to be downwardly propagating, and 6% to be standing, with mean absolute phase velocities for the propagating waves on the order of 75–150 km s<jats:sup>−1</jats:sup>. While the energy flux of the waves propagating downwards does not appear to depend on height, we find the energy flux of the upwardly propagating waves decreases with atmospheric height at a rate of −13,200 ± 6500 W m<jats:sup>−2</jats:sup>/Mm. As a result, this decrease in energy flux as the waves propagate upwards may provide significant thermal input into the local plasma.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigate the M6.5 class flare (SOL2015-06-22T18:23) occurring in NOAA Active Region 12371 on 2015 June 22. This eruptive flare is associated with a halo coronal mass ejection with a speed of 1200 km s<jats:sup>−1</jats:sup>. The 94 Å observations by Atmospheric Image Assembly onboard Solar Dynamics Observatory show that one hot channel first rises up, then forms a kinking structure with negative crossing and erupts, which is followed by the eruption of another kinking hot channel with negative crossing at a similar location between the start and peak times of the flare. Consistent with the standard flare model, footpoint drifting of the two hot channels is observed during the eruption. More interestingly, the two footpoints of the first hot channel continue to drift and display an apparent clockwise rotation after leaving the area of the hook-shaped flare ribbons. This apparent rotation is along the high-<jats:italic>Q</jats:italic> region of the log <jats:italic>Q</jats:italic> map derived from the nonlinear force-free field extrapolation. Our analysis suggests that the apparent rotational motion is likely caused by magnetic reconnection between the first hot channel and the surrounding magnetic fields at the high-<jats:italic>Q</jats:italic> region during the unwrithing process. The unwrithing of the second hot channel is accompanied by a significant slipping motion of its right footpoint.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>About 2.5 billion years ago, microbes learned to harness plentiful solar energy to reduce CO<jats:sub>2</jats:sub> with H<jats:sub>2</jats:sub>O, extracting energy and producing O<jats:sub>2</jats:sub> as waste. O<jats:sub>2</jats:sub> production from this metabolic process was so vigorous that it saturated its photochemical sinks, permitting it to reach “runaway” conditions and rapidly accumulate in the atmosphere despite its reactivity. Here we argue that O<jats:sub>2</jats:sub> may not be unique: diverse gases produced by life may experience a “runaway” effect similar to O<jats:sub>2</jats:sub>. This runaway occurs because the ability of an atmosphere to photochemically cleanse itself of trace gases is generally finite. If produced at rates exceeding this finite limit, even reactive gases can rapidly accumulate to high concentrations and become potentially detectable. Planets orbiting smaller, cooler stars, such as the M dwarfs that are the prime targets for the James Webb Space Telescope (JWST), are especially favorable for runaway, due to their lower UV emission compared to higher-mass stars. As an illustrative case study, we show that on a habitable exoplanet with an H<jats:sub>2</jats:sub>–N<jats:sub>2</jats:sub> atmosphere and net surface production of NH<jats:sub>3</jats:sub> orbiting an M dwarf (the “Cold Haber World” scenario), the reactive biogenic gas NH<jats:sub>3</jats:sub> can enter runaway, whereupon an increase in the surface production flux of one order of magnitude can increase NH<jats:sub>3</jats:sub> concentrations by three orders of magnitude and render it detectable by JWST in just two transits. Our work on this and other gases suggests that diverse signs of life on exoplanets may be readily detectable at biochemically plausible production rates.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a new approach for correcting instrumental polarization by modeling the nondepolarizing effects of a complex series of optical elements to determine physically realizable Mueller matrices. Provided that the Mueller matrix of the optical system can be decomposed into a general elliptical diattenuator and general elliptical retarder, it is possible to model the crosstalk between both the polarized and unpolarized states of the Stokes vector and then use the acquired science observations to determine the best-fit free parameters. Here we implement a minimization for solar spectropolarimetric measurements containing photospheric spectral lines sensitive to the Zeeman effect using physical constraints provided by polarized line and continuum formation. This model-based approach is able to provide an accurate correction even in the presence of large amounts of polarization crosstalk and conserves the physically meaningful magnitude of the Stokes vector, a significant improvement over previous ad hoc techniques.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The search for signs of life beyond Earth is a crucial driving motivation of exoplanet science, fueling new work on biosignature gases in habitable exoplanet atmospheres. We study carbonyls, a category of molecules containing the C=O double bond, following our proposal to systematically identify plausible biosignature gas candidates from a list of all small volatile molecules. We rule out carbonyls as biosignature gases due to both their high water solubility and their high photolysis rate, despite their ubiquitous production by life on Earth, their critical importance in Earth’s life biochemistry, and their uniquely identifiable molecular spectral features in mid- to low-resolution spectroscopy. Even in scenarios where life is a large net source of carbonyls, we demonstrate that detection of carbonyls is not possible on even the most ideal habitable exoplanet, because only 10 ppb of carbonyls can accumulate under our most optimistic assumptions. Moreover, high biological fluxes of organic carbon gases, while mathematically possible, are likely biologically unattainable due to the resulting huge waste of carbon—a main building block for life. Our simulations show that photochemical processing of carbonyls leads to generation of CO in quantities that can reengineer the atmosphere, affirming the ambiguity of CO as an antibiosignature. Overall, we find that the expression of a carbonyl-producing biosphere by CO, though potentially detectable by the James Webb Space Telescope, is unable to be uniquely traced back to carbonyls. While carbonyls fail as a bioindicator, by investigating them we have made a significant step toward systematically assessing the biosignature gas potential of all small volatile molecules.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Neutron star–helium white dwarf (NS+He WD) binaries are important evolutionary products of close-orbit binary star systems. They are often observed as millisecond pulsars and may continue evolving into ultracompact X-ray binaries (UCXBs) and continuous gravitational wave (GW) sources that will be detected by space-borne GW observatories, such as LISA, TianQin, and Taiji. Nevertheless, the stability of NS+He WD binaries undergoing mass transfer has not been well studied and is still under debate. In this paper, we model the evolution of NS+He WD binaries with WD masses ranging from 0.17–0.45 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, applying the detailed stellar evolution code <jats:sc>mesa</jats:sc>. Contrary to previous studies based on hydrodynamics, we find that apparently <jats:italic>all</jats:italic> NS+He WD binaries undergo stable mass transfer. We find for such UCXBs that the larger the WD mass, the larger the maximum mass-transfer rate and the smaller the minimum orbital period during their evolution. Finally, we demonstrate numerically and analytically that there is a tight correlation between WD mass and GW frequency for UCXBs, independent of NS mass.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>High-energy emission associated with star formation has been proposed as a significant source of interstellar medium (ISM) ionization in low-metallicity starbursts and an important contributor to the heating of the intergalactic medium (IGM) in the high-redshift (<jats:italic>z</jats:italic> ≳ 8) universe. Using Chandra observations of a sample of 30 galaxies at <jats:italic>D</jats:italic> ≈ 200–450 Mpc that have high specific star formation rates of 3–9 Gyr<jats:sup>−1</jats:sup> and metallicities near <jats:italic>Z</jats:italic> ≈ 0.3<jats:italic>Z</jats:italic> <jats:sub>⊙</jats:sub>, we provide new measurements of the average 0.5–8 keV spectral shape and normalization per unit star formation rate (SFR). We model the sample-combined X-ray spectrum as a combination of hot gas and high-mass X-ray binary (HMXB) populations and constrain their relative contributions. We derive scaling relations of <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}{L}_{0.5\mbox{--}8\ \mathrm{keV}}^{\mathrm{HMXB}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:msubsup> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0.5</mml:mn> <mml:mo>–</mml:mo> <mml:mn>8</mml:mn> <mml:mspace width="0.33em" /> <mml:mi>keV</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>HMXB</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac63a7ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>/SFR = 40.19 ± 0.06 and <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}{L}_{0.5\mbox{--}2\ \mathrm{keV}}^{\mathrm{gas}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:msubsup> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0.5</mml:mn> <mml:mo>–</mml:mo> <mml:mn>2</mml:mn> <mml:mspace width="0.33em" /> <mml:mi>keV</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>gas</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac63a7ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>/SFR <jats:inline-formula> <jats:tex-math> <?CDATA $=\,{39.58}_{-0.28}^{+0.17};$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>=</mml:mo> <mml:mspace width="0.50em" /> <mml:msubsup> <mml:mrow> <mml:mn>39.58</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.28</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.17</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>;</mml:mo> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac63a7ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> significantly elevated compared to local relations. The HMXB scaling is also somewhat higher than <jats:inline-formula> <jats:tex-math> <?CDATA ${L}_{0.5\mbox{--}8\ \mathrm{keV}}^{\mathrm{HMXB}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0.5</mml:mn> <mml:mo>–</mml:mo> <mml:mn>8</mml:mn> <mml:mspace width="0.33em" /> <mml:mi>keV</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>HMXB</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac63a7ieqn4.gif" xlink:type="simple" /> </jats:inline-formula>–SFR-<jats:italic>Z</jats:italic> relations presented in the literature, potentially due to our galaxies having relatively low HMXB obscuration and young and X-ray luminous stellar populations. The elevation of the hot gas scaling relation is at the level expected for diminished attenuation due to a reduction of metals; however, we cannot conclude that an <jats:inline-formula> <jats:tex-math> <?CDATA ${L}_{0.5\mbox{--}2\ \mathrm{keV}}^{\mathrm{gas}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0.5</mml:mn> <mml:mo>–</mml:mo> <mml:mn>2</mml:mn> <mml:mspace width="0.33em" /> <mml:mi>keV</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>gas</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac63a7ieqn5.gif" xlink:type="simple" /> </jats:inline-formula>–SFR-<jats:italic>Z</jats:italic> relation is driven solely by changes in ISM metal content. Finally, we present SFR-scaled spectral models (both emergent and intrinsic) that span the X-ray-to-IR band, providing new benchmarks for studies of the impact of ISM ionization and IGM heating in the early universe.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A large suite of 228 atmospheric retrievals is performed on a curated sample of 19 brown dwarfs spanning the L0–T8 spectral types using the open-source <jats:monospace>Helios-r2</jats:monospace> retrieval code, which implements the method of short characteristics for radiative transfer and a finite-element description of the temperature–pressure profile. Surprisingly, we find that cloud-free and cloudy (both gray and nongray) models are equally consistent with the archival SpeX data from the perspective of Bayesian model comparison. Only upper limits for cloud properties are inferred if log-uniform priors are assumed, but the cloud optical depth becomes constrained if a uniform prior is used. Water is detected in all 19 objects, and methane is detected in all of the T dwarfs, but no obvious trend exists across effective temperature. As carbon monoxide is only detected in a handful of objects, the inferred carbon-to-oxygen ratios are unreliable. The retrieved radius generally decreases with effective temperature, but the values inferred for some T dwarfs are implausibly low and may indicate missing physics or chemistry in the models. For the early L dwarfs, the retrieved surface gravity depends on whether the gray-cloud or non-gray-cloud model is preferred. Future data are necessary for constraining cloud properties and the vertical variation of chemical abundances, the latter of which is needed for distinguishing between the chemical instability and traditional cloud interpretation of the L-T transition.</jats:p>