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<jats:title>Abstract</jats:title> <jats:p>Pure acetonitrile (CH<jats:sub>3</jats:sub>CN) and mixed CO:CH<jats:sub>3</jats:sub>CN and H<jats:sub>2</jats:sub>O:CH<jats:sub>3</jats:sub>CN ices have been irradiated at 15 K with vacuum ultraviolet (VUV) photons in the 7–13.6 eV range using synchrotron radiation. VUV photodesorption yields of CH<jats:sub>3</jats:sub>CN and of photoproducts have been derived as a function of the incident photon energy. The coadsorption of CH<jats:sub>3</jats:sub>CN with CO and H<jats:sub>2</jats:sub>O molecules, which are expected to be among the main constituents of interstellar ices, is found to have no significant influence on the VUV photodesorption spectra of CH<jats:sub>3</jats:sub>CN, CHCN•, HCN, CN•, and CH<jats:sub>3</jats:sub>•. Contrary to what has generally been evidenced for most of the condensed molecules, these findings point toward a desorption process for which the CH<jats:sub>3</jats:sub>CN molecule that absorbs the VUV photon is the one desorbing. It can be ejected in the gas phase as intact CH<jats:sub>3</jats:sub>CN or in the form of its photodissociation fragments. Astrophysical VUV photodesorption yields, applicable to different locations, are derived and can be incorporated into astrochemical modeling. They vary from 0.67(± 0.33) × 10<jats:sup>−5</jats:sup> to 2.0(± 1.0) × 10<jats:sup>−5</jats:sup> molecule photon<jats:sup>−1</jats:sup> for CH<jats:sub>3</jats:sub>CN depending on the region considered, which is high compared to other organic molecules such as methanol. These results could explain the multiple detections of gas-phase CH<jats:sub>3</jats:sub>CN in different regions of the interstellar medium and are well correlated to astrophysical observations of the Horsehead nebula and of protoplanetary disks (such as TW Hya and HD 163296).</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Magnetic flux ropes are the centerpiece of solar eruptions. Direct measurements for the magnetic field of flux ropes are crucial for understanding the triggering and energy release processes, yet they remain heretofore elusive. Here we report microwave imaging spectroscopy observations of an M1.4-class solar flare that occurred on 2017 September 6, using data obtained by the Expanded Owens Valley Solar Array. This flare event is associated with a partial eruption of a twisted filament observed in H<jats:italic>α</jats:italic> by the Goode Solar Telescope at the Big Bear Solar Observatory. The extreme ultraviolet (EUV) and X-ray signatures of the event are generally consistent with the standard scenario of eruptive flares, with the presence of double flare ribbons connected by a bright flare arcade. Intriguingly, this partial eruption event features a microwave counterpart, whose spatial and temporal evolution closely follow the filament seen in H<jats:italic>α</jats:italic> and EUV. The spectral properties of the microwave source are consistent with nonthermal gyrosynchrotron radiation. Using spatially resolved microwave spectral analysis, we derive the magnetic field strength along the filament spine, which ranges from 600 to 1400 Gauss from its apex to the legs. The results agree well with the nonlinear force-free magnetic model extrapolated from the preflare photospheric magnetogram. We conclude that the microwave counterpart of the erupting filament is likely due to flare-accelerated electrons injected into the filament-hosting magnetic flux rope cavity following the newly reconnected magnetic field lines.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>An electron–positron layer can cover the surface of a bare strange star (SS), the electric field in which can excite the vacuum and drive a pair wind by taking away the heat of the star. In order to investigate the pair-emission ability of a proto-SS, we establish a toy model to describe its early thermal evolution, where the initial trapping of neutrinos is specially taken into account. It is found that the early cooling of the SS is dominated by the neutrino diffusion rather than the conventional Urca processes, which leads to the appearance of an initial temperature plateau. During this plateau phase, the surface <jats:italic>e</jats:italic> <jats:sup>±</jats:sup> pair emission can maintain a constant luminosity of 10<jats:sup>48</jats:sup> − 10<jats:sup>50</jats:sup>erg s<jats:sup>−1</jats:sup> for about a few to a few tens of seconds, which is dependent on the value of the initial temperature. The total energy released through this <jats:italic>e</jats:italic> <jats:sup>±</jats:sup> wind can reach as high as ∼10<jats:sup>51</jats:sup> erg. In principle, this pair wind could be responsible for the prompt emission or extended emission of some gamma-ray bursts.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The cosmic origin of carbon, a fundamental building block of life, is still uncertain. Yield predictions for massive stars are almost exclusively based on single-star models, even though a large fraction interact with a binary companion. Using the <jats:monospace>MESA</jats:monospace> stellar evolution code, we predict the amount of carbon ejected in the winds and supernovae of single and binary-stripped stars at solar metallicity. We find that binary-stripped stars are twice as efficient at producing carbon (1.5–2.6 times, depending on choices regarding the slope of the initial mass function and black hole formation). We confirm that this is because the convective helium core recedes in stars that have lost their hydrogen envelope, as noted previously. The shrinking of the core disconnects the outermost carbon-rich layers created during the early phase of helium burning from the more central burning regions. The same effect prevents carbon destruction, even when the supernova shock wave passes. The yields are sensitive to the treatment of mixing at convective boundaries, specifically during carbon-shell burning (variations up to 40%), and improving upon this should be a central priority for more reliable yield predictions. The yields are robust (variations less than 0.5%) across our range of explosion assumptions. Black hole formation assumptions are also important, implying that the stellar graveyard now explored by gravitational-wave detections may yield clues to better understand the cosmic carbon production. Our findings also highlight the importance of accounting for binary-stripped stars in chemical yield predictions and motivates further studies of other products of binary interactions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Kepler’s observation shows that many of the detected planets are super-Earths. They are inside a range of critical masses overlapping the core masses (2–20 <jats:italic>M</jats:italic> <jats:sub>⊕</jats:sub>), which would trigger the runaway accretion and develop the gas giants. Thus, super-Earths/sub-Neptunes can be formed by restraining runaway growth of gaseous envelopes. We assess the effect of planetary rotation in delaying the mass growth. The centrifugal force, induced by spin, will offset a part of the gravitational force and deform the planet. Tracking the change in structure, we find that the temperature at the radiative–convective boundary (RCB) is approximate to the boundary temperature. Since rotation reduces the radiation energy densities in the convective and radiative layers, RCB will penetrate deeper. The cooling luminosity would decrease. Under this condition, the evolutionary timescale can exceed the disk lifetime (10 Myr), and a super-Earth/sub-Neptune could be formed after undergoing additional mass-loss processes. In the dusty atmosphere, even a lower angular velocity can also promote a super-Earth/sub-Neptune forming. Therefore, we conclude that rotation can slow down the planet’s cooling and then promote a super-Earth/sub-Neptune forming.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the characteristics of 2 mm selected sources from the largest Atacama Large Millimeter/submillimeter Array (ALMA) blank-field contiguous survey conducted to date, the Mapping Obscuration to Reionization with ALMA (MORA) survey covering 184 arcmin<jats:sup>2</jats:sup> at 2 mm. Twelve of 13 detections above 5<jats:italic>σ</jats:italic> are attributed to emission from galaxies, 11 of which are dominated by cold dust emission. These sources have a median redshift of <jats:inline-formula> <jats:tex-math> <?CDATA $\langle {z}_{2\,\mathrm{mm}}\rangle ={3.6}_{-0.3}^{+0.4}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">〈</mml:mo> <mml:msub> <mml:mrow> <mml:mi>z</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> <mml:mspace width="0.25em" /> <mml:mi>mm</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">〉</mml:mo> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>3.6</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.4</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac2eb4ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> primarily based on optical/near-infrared photometric redshifts with some spectroscopic redshifts, with 77% ± 11% of sources at <jats:italic>z</jats:italic> &gt; 3 and 38% ± 12% of sources at <jats:italic>z</jats:italic> &gt; 4. This implies that 2 mm selection is an efficient method for identifying the highest-redshift dusty star-forming galaxies (DSFGs). Lower-redshift DSFGs (<jats:italic>z</jats:italic> &lt; 3) are far more numerous than those at <jats:italic>z</jats:italic> &gt; 3 yet are likely to drop out at 2 mm. MORA shows that DSFGs with star formation rates in excess of 300 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup> and a relative rarity of ∼10<jats:sup>−5</jats:sup> Mpc<jats:sup>−3</jats:sup> contribute ∼30% to the integrated star formation rate density at 3 &lt; <jats:italic>z</jats:italic> &lt; 6. The volume density of 2 mm selected DSFGs is consistent with predictions from some cosmological simulations and is similar to the volume density of their hypothesized descendants: massive, quiescent galaxies at <jats:italic>z</jats:italic> &gt; 2. Analysis of MORA sources’ spectral energy distributions hint at steeper empirically measured dust emissivity indices than reported in typical literature studies, with <jats:inline-formula> <jats:tex-math> <?CDATA $\langle \beta \rangle ={2.2}_{-0.4}^{+0.5}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">〈</mml:mo> <mml:mi>β</mml:mi> <mml:mo stretchy="false">〉</mml:mo> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>2.2</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.5</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac2eb4ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>. The MORA survey represents an important step in taking census of obscured star formation in the universe’s first few billion years, but larger area 2 mm surveys are needed to more fully characterize this rare population and push to the detection of the universe’s first dusty galaxies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Interplanetary coronal mass ejections (ICMEs) are known to modify the structure of the solar wind as well as interact with the space environment of planetary systems. Their large magnetic structures have been shown to interact with galactic cosmic rays (GCRs), leading to the Forbush decrease (FD) phenomenon. We revisit in the present article the 17 yr of Advanced Composition Explorer spacecraft ICME detection along with two neutron monitors (McMurdo and Oulu) with a superposed epoch analysis to further analyze the role of the magnetic ejecta in driving FDs. We investigate in the following the role of the sheath and the magnetic ejecta in driving FDs, and we further show that for ICMEs without a sheath, a magnetic ejecta only is able to drive significant FDs of comparable intensities. Furthermore, a comparison of samples with and without a sheath with similar speed profiles enable us to show that the magnetic field intensity, rather than its fluctuations, is the main driver for the FD. Finally, the recovery phase of the FD for isolated magnetic ejecta shows an anisotropy in the level of the GCRs. We relate this finding at 1 au to the gradient of the GCR flux found at different heliospheric distances from several interplanetary missions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The role of whistler-mode waves in the solar wind and the relationship between their electromagnetic fields and charged particles is a fundamental question in space physics. Using high-temporal-resolution electromagnetic field and plasma data from the Magnetospheric MultiScale spacecraft, we report observations of low-frequency whistler waves and associated electromagnetic fields and particle behavior in the Earth’s foreshock. The frequency of these whistler waves is close to half the lower-hybrid frequency (∼2 Hz), with their wavelength close to the ion gyroradius. The electron bulk flows are strongly modulated by these waves, with a modulation amplitude comparable to the solar wind velocity. At such a spatial scale, the electron flows are forcibly separated from the ion flows by the waves, resulting in strong electric currents and anisotropic ion distributions. Furthermore, we find that the low-frequency whistler wave propagates obliquely to the background magnetic field (<jats:bold> <jats:italic>B</jats:italic> </jats:bold> <jats:sub>0</jats:sub>), and results in spatially periodic magnetic gradients in the direction parallel to <jats:bold> <jats:italic>B</jats:italic> </jats:bold> <jats:sub>0</jats:sub>. Under such conditions, large pitch-angle electrons are trapped in wave magnetic valleys by the magnetic mirror force, and may provide free perpendicular electron energy to excite higher-frequency whistler waves. This study offers important clues and new insights into wave–particle interactions, wave generation, and microscale energy conversion processes in the solar wind.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Stellar feedback in dwarf galaxies plays a critical role in regulating star formation via galaxy-scale winds. Recent hydrodynamical zoom-in simulations of dwarf galaxies predict that the periodic outward flow of gas can change the gravitational potential sufficiently to cause radial migration of stars. To test the effect of bursty star formation on stellar migration, we examine star formation observables and sizes of 86 local dwarf galaxies. We find a correlation between the <jats:italic>R</jats:italic>-band half-light radius (<jats:italic>R</jats:italic> <jats:sub> <jats:italic>e</jats:italic> </jats:sub>) and far-UV luminosity (<jats:italic>L</jats:italic> <jats:sub>FUV</jats:sub>) for stellar masses below 10<jats:sup>8</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> and a weak correlation between the <jats:italic>R</jats:italic> <jats:sub> <jats:italic>e</jats:italic> </jats:sub> and H<jats:italic>α</jats:italic> luminosity (<jats:italic>L</jats:italic> <jats:sub>H<jats:italic>α</jats:italic> </jats:sub>). We produce mock observations of eight low-mass galaxies from the FIRE-2 cosmological simulations and measure the similarity of the time sequences of <jats:italic>R</jats:italic> <jats:sub> <jats:italic>e</jats:italic> </jats:sub> and a number of star formation indicators with different timescales. Major episodes of <jats:italic>R</jats:italic> <jats:sub> <jats:italic>e</jats:italic> </jats:sub> time sequence align very well with the major episodes of star formation, with a delay of ∼50 Myr. This correlation decreases toward star formation rate indicators of shorter timescales such that <jats:italic>R</jats:italic> <jats:sub> <jats:italic>e</jats:italic> </jats:sub> is weakly correlated with <jats:italic>L</jats:italic> <jats:sub>FUV</jats:sub> (10–100 Myr timescale) and is completely uncorrelated with <jats:italic>L</jats:italic> <jats:sub>H<jats:italic>α</jats:italic> </jats:sub> (a few Myr timescale), in agreement with the observations. Our findings based on FIRE-2 suggest that the <jats:italic>R</jats:italic>-band size of a galaxy reacts to star formation variations on a ∼50 Myr timescale. With the advent of a new generation of large space telescopes (e.g., JWST), this effect can be examined explicitly in galaxies at higher redshifts, where bursty star formation is more prominent.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We describe the survey design, calibration, commissioning, and emission-line detection algorithms for the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX). The goal of HETDEX is to measure the redshifts of over a million Ly<jats:italic>α</jats:italic> emitting galaxies between 1.88 &lt; <jats:italic>z</jats:italic> &lt; 3.52, in a 540 deg<jats:sup>2</jats:sup> area encompassing a comoving volume of 10.9 Gpc<jats:sup>3</jats:sup>. No preselection of targets is involved; instead the HETDEX measurements are accomplished via a spectroscopic survey using a suite of wide-field integral field units distributed over the focal plane of the telescope. This survey measures the Hubble expansion parameter and angular diameter distance, with a final expected accuracy of better than 1%. We detail the project’s observational strategy, reduction pipeline, source detection, and catalog generation, and present initial results for science verification in the Cosmological Evolution Survey, Extended Groth Strip, and Great Observatories Origins Deep Survey North fields. We demonstrate that our data reach the required specifications in throughput, astrometric accuracy, flux limit, and object detection, with the end products being a catalog of emission-line sources, their object classifications, and flux-calibrated spectra.</jats:p>