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<jats:title>Abstract</jats:title> <jats:p>In this paper, we present a detailed morphological, kinematic, and thermal analysis of two homologous magnetic flux ropes (MFRs) from NOAA 11515 on 2012 July 8–9. The study is based on multiwavelength and dual-perspective imaging observations from the Solar Dynamics Observatory and the Solar Terrestrial Relations Observatory Ahead spacecraft, which can reveal the structure and evolution of the two MFRs. We find that both of the MFRs show up in multiple passbands and their emissions mainly consist of a cold component peaking at a temperature of ∼0.4–0.6 MK and a hot component peaking at ∼7–8 MK. The two MFRs exhibit erupting, expanding, and untwisting motions that manifest distinctive features from two different viewpoints. Their evolution can be divided into two stages—a fast-eruption stage with speeds of about 105–125 km s<jats:sup>−1</jats:sup> for MFR-1 and 50–65 km s<jats:sup>−1</jats:sup> for MFR-2—and a slow-expansion (or untwisting) stage with speeds of about 10–35 km s<jats:sup>−1</jats:sup> for MFR-1 and 10–30 km s<jats:sup>−1</jats:sup> for MFR-2 in the plane of the sky. We also find that during the two-stage evolution, the high-temperature features mainly appear in the interface region between MFRs and ambient magnetic structures and also in the center of MFRs, which suggests that some heating processes take place in such places as magnetic reconnection and plasma compression. These observational results indicate that the eruption and untwisting processes of MFRs are coupled with the heating process, among which an energy conversion exists.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Although large polycyclic aromatic hydrocarbons (PAHs) are likely to be responsible for IR emission of gaseous and dusty regions, their neutral experimental high-resolution gas-phase IR spectra—needed to construct accurate astronomical models—have so far remained out of reach because of their nonvolatility. Applying laser desorption to overcome this problem, we report here the first IR spectra of the jet-cooled large PAHs coronene (C<jats:sub>24</jats:sub>H<jats:sub>12</jats:sub>), peropyrene (C<jats:sub>26</jats:sub>H<jats:sub>14</jats:sub>), ovalene (C<jats:sub>32</jats:sub>H<jats:sub>14</jats:sub>), and hexa(peri)benzocoronene (C<jats:sub>42</jats:sub>H<jats:sub>18</jats:sub>) in the 3–100 <jats:italic>μ</jats:italic>m region. Apart from providing experimental spectra that can be compared directly to astronomical data, such IR spectra are crucial for assessing the accuracy of theoretically predicted spectra used to interpret interstellar IR emission. Here we use the experimental spectra to evaluate the performance of conventional calculations using the harmonic approximation, as well as calculations with an anharmonic (GVPT2) treatment. The harmonic prediction agrees well with the experiment between 100 and 1000 cm<jats:sup>−1</jats:sup> (100 and 10 <jats:italic>μ</jats:italic>m) but shows significant shortcomings in the combination band (1600–2000 cm<jats:sup>−1</jats:sup>, 6.25–5 <jats:italic>μ</jats:italic>m) and CH-stretch (2950–3150 cm<jats:sup>−1</jats:sup>, 3.4–3.17 <jats:italic>μ</jats:italic>m) regions. Especially the CH-stretch region is known to be dominated by the effects of anharmonicity, and we find that large PAHs are no exception. However, for the CH out-of-plane region (667–1000 cm<jats:sup>−1</jats:sup>, 15–10 <jats:italic>μ</jats:italic>m) the anharmonic treatment that significantly improves the predicted spectra for small PAHs leads to large and unrealistic frequency shifts, and intensity changes for large PAHs, thereby rendering the default results unreliable. A detailed analysis of the results of the anharmonic treatment suggests a possible route for improvement, although the underlying cause for the large deviations remains a challenge for theory.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>On Titan, methane is responsible for the complex prebiotic chemistry, the global haze, most of the cloud cover, and the rainfall that models the landscape. Its sources are located in liquid reservoirs at and below the surface, and its sink is the photodissociation at high altitude. Titan’s present and past climates strongly depend on the connection between the surface sources and the atmosphere upper layers. Despite its importance, very little information is available on this topic. In this work, we reanalyze two solar occultations made by Cassini before the northern spring equinox. We find a layer rich in methane at 165 km and at 70°S (mixing ratio 1.62% ± 0.1%) and a dryer background stratosphere (1.1%–1.2%). In the absence of local production, this reveals an intrusion of methane transported into the stratosphere by convective circulation. On the other hand, methane transport through the tropopause at a global scale appears quite inhibited. Leaking through the tropopause is an important bottleneck of Titan’s methane cycle at all timescales. As such, it affects the long-term evolution of Titan’s atmosphere and the exchange fluxes with the surface and subsurface reservoirs in a complex way. Global climate models accounting for cloud physics, thermodynamical feedbacks, and convection are needed to understand the methane cycle, and specifically the humidification of the stratosphere, at the present time, and its evolution under changing conditions at a geological timescale.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The results of the first synoptic survey of novae in the barred spiral and starburst galaxy, M83 (NGC 5236), are presented. A total of 19 novae and one background supernova were discovered during the course of a nearly 7 year survey comprised of over 200 individual nights of observation between 2012 December 12 and 2019 March 14. After correcting for the limiting magnitude and the spatial and temporal coverage of the survey, the nova rate in M83 was found to be <jats:italic>R</jats:italic> = 19<jats:sup>+5</jats:sup> <jats:sub>−3</jats:sub> yr<jats:sup>−1</jats:sup>. This rate, when normalized to the <jats:italic>K</jats:italic>-band luminosity of the galaxy, yields a luminosity-specific nova rate, <jats:italic>ν</jats:italic> <jats:sub> <jats:italic>K</jats:italic> </jats:sub> = 3.0<jats:sup>+0.9</jats:sup> <jats:sub>−0.6</jats:sub> × 10<jats:sup>−10</jats:sup> yr <jats:sup>−1</jats:sup> <jats:italic>L</jats:italic> <jats:sub>⊙,K</jats:sub> <jats:sup>−1</jats:sup>. The spatial distribution of the novae is found to be more extended than the overall galaxy light suggesting that the observed novae are likely dominated by a disk population. This result is consistent with the observed novae light curves, which reveals that the M83 novae are on average more luminous at maximum light and fade faster when compared with novae observed in M31. Generally, the more luminous M83 novae were observed to fade more rapidly, with the complete sample being broadly consistent with a linear maximum magnitude versus rate of decline relation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Using direct numerical simulations (DNSs), the interaction between linear waves and turbulence under the compressible magnetohydrodynamic (CMHD) approach was studied. A set of DNSs in three dimensions for a spatial resolution of 128<jats:sup>3</jats:sup> and 256<jats:sup>3</jats:sup> were performed. A parametric study was carried out varying the sonic Mach number, the mean-magnetic field, and the compressibility amplitude of the forcing. Spatiotemporal spectra of the magnetic energy were built and analyzed, allowing for direct identification of all wave modes in a CMHD turbulent system and quantification of the amount of energy in each mode as a function of the wavenumber. Thus, linear waves were detected, that is Alfvén waves and fast and slow magnetosonic waves. Furthermore, different responses of the plasma were found according to whether the Mach number or the mean-magnetic field was varied. On the other hand, making use of spatiotemporal spectra and two different integration methods, we accurately quantified the amount of energy present in each of the normal modes. Finally, although the presence of linear waves was observed, in all the cases studied the system was mainly dominated by the nonlinear dynamics of the plasma.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the line observations in our Atacama Millimeter-Submillimeter Array imaging spectral scan toward three deeply buried nuclei in <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="object" xlink:href="NGC 4418" xlink:type="simple">NGC 4418</jats:named-content> and <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="object" xlink:href="Arp 220" xlink:type="simple">Arp 220</jats:named-content>. We cover 67 GHz in <jats:italic>f</jats:italic> <jats:sub>rest</jats:sub> = 215–697 GHz at about 0.″2 (30, 80 pc) resolution. All the nuclei show dense line forests; we report our initial line identification using 55 species. The line velocities generally indicate gas rotation around each nucleus, tracing nuclear disks of ∼100 pc in size. We confirmed the counter-rotation of the nuclear disks in Arp 220 and that of the nuclear disk and the galactic disk in NGC 4418. While the brightest lines exceed 100 K, most of the major lines and many <jats:sup>13</jats:sup>C isotopologues show absorption against even brighter continuum cores of the nuclei. The lines with higher upper-level energies, including those from vibrationally excited molecules, tend to arise from smaller areas, indicating radially varying conditions in these nuclei. The outflows from the two Arp 220 nuclei cause blueshifted line absorption below the continuum level. The absorption mostly has small spatial offsets from the continuum peaks to indicate the outflow orientations. The bipolar outflow from the western nucleus is also imaged in multiple emission lines, showing the extent of ∼1″ (400 pc). Redshifted line absorption against the nucleus of NGC 4418 indicates either an inward gas motion or a small collimated outflow slanted to the nuclear disk. We also resolved some previous confusions due to line blending and misidentification.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Helium star–carbon-oxygen white dwarf (CO WD) binaries are potential single-degenerate progenitor systems of thermonuclear supernovae. Revisiting a set of binary evolution calculations using the stellar evolution code <jats:monospace>MESA</jats:monospace>, we refine our previous predictions about which systems can lead to a thermonuclear supernova and then characterize the properties of the helium star donor at the time of explosion. We convert these model properties to near-UV/optical magnitudes assuming a blackbody spectrum and support this approach using a matched stellar atmosphere model. These models will be valuable to compare with pre-explosion imaging for future supernovae, though we emphasize the observational difficulty of detecting extremely blue companions. The pre-explosion source detected in association with SN 2012Z has been interpreted as a helium star binary containing an initially ultra-massive WD in a multiday orbit. However, extending our binary models to initial CO WD masses of up to 1.2<jats:italic> M</jats:italic> <jats:sub>⊙</jats:sub>, we find that these systems undergo off-center carbon ignitions and thus are not expected to produce thermonuclear supernovae. This tension suggests that, if SN 2012Z is associated with a helium star–WD binary, then the pre-explosion optical light from the system must be significantly modified by the binary environment and/or the WD does not have a carbon-rich interior composition.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The results of gamma-ray observations of the binary system HESS J0632 + 057 collected during 450 hr over 15 yr, between 2004 and 2019, are presented. Data taken with the atmospheric Cherenkov telescopes H.E.S.S., MAGIC, and VERITAS at energies above 350 GeV were used together with observations at X-ray energies obtained with Swift-XRT, Chandra, XMM-Newton, NuSTAR, and Suzaku. Some of these observations were accompanied by measurements of the H<jats:italic>α</jats:italic> emission line. A significant detection of the modulation of the very high-energy gamma-ray fluxes with a period of 316.7 ± 4.4 days is reported, consistent with the period of 317.3 ± 0.7 days obtained with a refined analysis of X-ray data. The analysis of data from four orbital cycles with dense observational coverage reveals short-timescale variability, with flux-decay timescales of less than 20 days at very high energies. Flux variations observed over a timescale of several years indicate orbit-to-orbit variability. The analysis confirms the previously reported correlation of X-ray and gamma-ray emission from the system at very high significance, but cannot find any correlation of optical H<jats:italic>α</jats:italic> parameters with fluxes at X-ray or gamma-ray energies in simultaneous observations. The key finding is that the emission of HESS J0632 + 057 in the X-ray and gamma-ray energy bands is highly variable on different timescales. The ratio of gamma-ray to X-ray flux shows the equality or even dominance of the gamma-ray energy range. This wealth of new data is interpreted taking into account the insufficient knowledge of the ephemeris of the system, and discussed in the context of results reported on other gamma-ray binary systems.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigate whether the recently observed 2.6 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> compact object in the gravitational wave event GW190814 can be a bosonic dark matter (DM) admixed compact star. By considering the three constraints of mass, radius, and the stability of such an object, we find that if the DM is made of QCD axions, their particle mass <jats:italic>m</jats:italic> is constrained to a range that has already been ruled out by the independent constraint imposed by the stellar-mass black hole superradiance process. The 2.6 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> object can still be a neutron star admixed with at least 2.0 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> of DM made of axion-like particles (or even a pure axion-like particle star) if 2 × 10<jats:sup>−11</jats:sup> eV ≤ <jats:italic>m</jats:italic> ≤ 2.4 × 10<jats:sup>−11</jats:sup> eV (2.9 × 10<jats:sup>−11</jats:sup> eV ≤ <jats:italic>m</jats:italic> ≤ 3.2 × 10<jats:sup>−11</jats:sup> eV) with a decay constant of <jats:italic>f</jats:italic> ≥ 8 × 10<jats:sup>17</jats:sup> GeV.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Thermal emission has now been observed from dozens of exoplanet atmospheres, opening the gateway to population-level characterization. Here, we provide theoretical explanations for observed trends in Spitzer IRAC channel 1 (3.6 <jats:italic>μ</jats:italic>m) and channel 2 (4.5 <jats:italic>μ</jats:italic>m) photometric eclipse depths (EDs) across a population of 34 hot Jupiters. We apply planet-specific, self-consistent atmospheric models, spanning a range of recirculation factors, metallicities, and C/O ratios, to probe the information content of Spitzer secondary eclipse observations across the hot-Jupiter population. We show that most hot Jupiters are inconsistent with blackbodies from Spitzer observations alone. We demonstrate that the majority of hot Jupiters are consistent with low-energy redistribution between the dayside and nightside (hotter dayside than expected with efficient recirculation). We also see that high-equilibrium temperature planets (<jats:italic>T</jats:italic> <jats:sub>eq</jats:sub> ≥ 1800 K) favor inefficient recirculation in comparison to the low temperature planets. Our planet-specific models do not reveal any definitive population trends in metallicity and C/O ratio with current data precision, but more than 59% of our sample size is consistent with the C/O ratio ≤ 1 and 35% are consistent with whole range (0.35 ≤ C/O ≤ 1.5). We also find that for most of the planets in our sample, 3.6 and 4.5 <jats:italic>μ</jats:italic>m model EDs lie within ±1<jats:italic>σ</jats:italic> of the observed EDs. Intriguingly, few hot Jupiters exhibit greater thermal emission than predicted by the hottest atmospheric models (lowest recirculation) in our grid. Future spectroscopic observations of thermal emission from hot Jupiters with the James Webb Space Telescope will be necessary to robustly identify population trends in chemical compositions with its increased spectral resolution, range, and data precision.</jats:p>