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<jats:title>Abstract</jats:title> <jats:p>Recent observations revealed that several extremely low-density exoplanets show featureless transmission spectra. While atmospheric aerosols are a promising explanation for both the low-density and featureless spectra, there is another attractive possibility: the presence of circumplanetary rings. Previous studies suggested that rings cause anomalously large transit radii. However, it remains poorly understood how rings affect the transmission spectrum. Here, we provide a framework to characterize the transmission spectra of ringed exoplanets. We develop an analytical prescription to include rings in the transmission spectra for arbitrarily viewing geometries. We also establish a simple postprocessing model that can include the ring’s effects on precomputed ring-free spectra. The ring flattens the transmission spectrum for a wide range of viewing geometries, consistent with the featureless spectra of extremely low-density exoplanets. Near-future observations by the James Webb Space Telescope at longer wavelengths would be able to distinguish the aerosol and ring scenarios. We also find that rocky rings might cause a silicate feature at ∼10 <jats:italic>μ</jats:italic>m if the ring’s optical depth is around unity. Thus, the ring’s spectral features, if detected, would provide tight constrains on the physical properties of exoplanetary rings. We also discuss the ring’s stability and suggest that thick rings are sustainable only at the equilibrium temperature of ≲300 K for the ring’s age comparable to Kepler planets. This might indicate the intrinsic deficit of thick rings in the Kepler samples, unless rings are much younger than the planets as suggested for Saturn.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present structural measurements of 145 spectroscopically selected intermediate-redshift (<jats:italic>z</jats:italic> ∼ 0.7), massive (<jats:italic>M</jats:italic> <jats:sub>⋆</jats:sub> ∼ 10<jats:sup>11</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) post-starburst galaxies from the <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{SQuIGG}\vec{L}{\rm{E}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>SQuIGG</mml:mi> <mml:mover accent="true"> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⃗</mml:mo> </mml:mrow> </mml:mover> <mml:mi mathvariant="normal">E</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6096ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> sample measured using wide-depth Hyper Suprime-Cam <jats:italic>i</jats:italic>-band imaging. This deep imaging allows us to probe the sizes and structures of these galaxies, which we compare to a control sample of star-forming and quiescent galaxies drawn from the LEGA-C Survey. We find that post-starburst galaxies systematically lie ∼0.1 dex below the quiescent mass–size (half-light radius) relation, with a scatter of ∼0.2 dex. This finding is bolstered by nonparametric measures, such as the Gini coefficient and the concentration, which also reveal these galaxies to have more compact light profiles than both quiescent and star-forming populations at similar mass and redshift. The sizes of post-starburst galaxies show either negative or no correlation with the time since quenching, such that more recently quenched galaxies are larger or similarly sized. This empirical finding disfavors the formation of post-starburst galaxies via a purely central burst of star formation that simultaneously shrinks the galaxy and shuts off star formation. We show that the central densities of post-starburst and quiescent galaxies at this epoch are very similar, in contrast with their effective radii. The structural properties of <jats:italic>z</jats:italic> ∼ 0.7 post-starburst galaxies match those of quiescent galaxies that formed in the early universe, suggesting that rapid quenching in the present epoch is driven by a similar mechanism to the one at high redshift.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>An ad hoc analytical calculation is presented to infer the duration of injection of 20 MeV protons in 21 selected western solar energetic particle (SEP) events. We convolve the solution of diffusion equation with a “triangle” source to model the time-intensity profiles over the onset and the peaking phase. The effects of “corotating” flux tubes and of solar wind convection are neglected. To accommodate these simplifications, only western events whose associated flares erupted between W15 and W90 are selected. The time-intensity profiles of these events are reconstructed from the timescales presented in Kahler (2005) and Kahler (2013) using the modified Weibull function. From the linear relation between the logarithm of the peak intensity and the logarithm of the fluence of 27–37 MeV protons presented in Kahler &amp; Ling, we derive an optimal radial mean free path (<jats:italic>λ</jats:italic> <jats:sub>mfp</jats:sub>) of 0.08 au and adopt this value to fit all selected events. The inferred duration of injection for the selected events, which in general increases with the initial speed of the associated coronal mass ejection (CME) (<jats:italic>V</jats:italic> <jats:sub>cme</jats:sub>), is less than 1 hr for <jats:italic>V</jats:italic> <jats:sub>cme</jats:sub> &lt; 1000 km s<jats:sup>−1</jats:sup> and varies from a few to ∼10 hr for 1000 km s<jats:sup>−1</jats:sup> &lt; <jats:italic>V</jats:italic> <jats:sub>cme</jats:sub> &lt; 2000 km s<jats:sup>−1</jats:sup>. We then estimate the distance that the associated CMEs have traveled over the duration of injection. Most CMEs in selected events have traveled to less than 60 solar radii by the time the majority of accelerated particles have been injected into the interplanetary space.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Long-term studies on hemispheric asymmetry can help to understand better the solar dynamo. We present the hemispheric sunspot number calculated from daily sunspot observations made at the Madrid Astronomical Observatory for the period 1935–1986 (corresponding approximately to Solar Cycles 17–21). From this data set, we also analyzed the asymmetry index and hemispheric phase shifts. We conclude that the northern hemisphere was predominant in Solar Cycles 17–20, whereas the southern hemisphere was predominant in Solar cycle 21. The strongest asymmetries are found in Solar Cycles 20 (with a relative difference between both hemispheres of 44%) and 19 (39%). A normalization of the Madrid hemispheric sunspot number was also made with respect to the sunspot number (Version 2). Our results agree with previous studies on hemispheric asymmetry around the mid-20th century and their secular trends.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We have modeled the velocity-resolved reverberation response of the H<jats:italic>β</jats:italic> broad emission line in nine Seyfert 1 galaxies from the Lick Active Galactic Nucleus (AGN) Monitoring Project 2016 sample, drawing inferences on the geometry and structure of the low-ionization broad-line region (BLR) and the mass of the central supermassive black hole. Overall, we find that the H<jats:italic>β</jats:italic> BLR is generally a thick disk viewed at low to moderate inclination angles. We combine our sample with prior studies and investigate line-profile shape dependence, such as <jats:inline-formula> <jats:tex-math> <?CDATA ${\mathrm{log}}_{10}(\mathrm{FWHM}/\sigma )$?> </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:mi>FWHM</mml:mi> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mi>σ</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6171ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, on BLR structure and kinematics and search for any BLR luminosity-dependent trends. We find marginal evidence for an anticorrelation between the profile shape of the broad H<jats:italic>β</jats:italic> emission line and the Eddington ratio, when using the rms spectrum. However, we do not find any luminosity-dependent trends, and conclude that AGNs have diverse BLR structure and kinematics, consistent with the hypothesis of transient AGN/BLR conditions rather than systematic trends.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We examine and quantify how hybrid (e.g., UV+IR) star formation rate (SFR) estimators and the <jats:italic>A</jats:italic> <jats:sub>FUV</jats:sub>–<jats:italic>β</jats:italic> relation depend on inclination for disk-dominated galaxies using spectral energy distribution modeling that utilizes the inclination-dependent attenuation curves described in Doore et al. We perform this analysis on a sample of 133 disk-dominated galaxies from the CANDELS fields and 18 disk galaxies from the Spitzer Infrared Nearby Galaxies Survey and Key Insights on Nearby Galaxies: A Far-Infrared Survey with Herschel samples. We find that both the hybrid SFR estimators and the <jats:italic>A</jats:italic> <jats:sub>FUV</jats:sub>–<jats:italic>β</jats:italic> relation present clear dependencies on inclination. To quantify this dependence in the hybrid SFR estimators, we derive an inclination and a far-UV–near-IR color-dependent parametric relation for converting observed UV and IR luminosities into SFRs. For the <jats:italic>A</jats:italic> <jats:sub>FUV</jats:sub>–<jats:italic>β</jats:italic> relation, we introduce an inclination-dependent component that accounts for the majority of the inclination dependence with the scatter of the relation increasing with inclination. We then compare both of these inclination-dependent relations to similar inclination-independent relations found in the literature. From this comparison, we find that the UV+IR correction factor and <jats:italic>A</jats:italic> <jats:sub>FUV</jats:sub> for our hybrid and <jats:italic>A</jats:italic> <jats:sub>FUV</jats:sub>–<jats:italic>β</jats:italic> relations, respectively, result in a reduction in the residual scatter of our sample by approximately a factor of 2. Therefore, we demonstrate that inclination must be considered in hybrid SFR estimators and the <jats:italic>A</jats:italic> <jats:sub>FUV</jats:sub>–<jats:italic>β</jats:italic> relation to produce more accurate SFR estimates in disk-dominated galaxies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report a dramatic, fast X-ray dimming event in a <jats:italic>z</jats:italic> = 2.627 radio-quiet type 1 quasar, which has an estimated supermassive black hole (SMBH) mass of 6.3 × 10<jats:sup>9</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. In the high X-ray state, it showed a typical level of X-ray emission relative to its UV/optical emission. Then its 0.5–2 keV (rest-frame 1.8–7.3 keV) flux dropped by a factor of ≈7.6 within two rest-frame days. The dimming is associated with spectral hardening, as the 2–7 keV (rest-frame 7.3–25.4 keV) flux dropped by only 17%, and the effective power-law photon index of the X-ray spectrum changed from ≈2.3 to ≈0.9. The quasar has an infrared (IR)-to-UV spectral energy distribution and a rest-frame UV spectrum similar to those of typical quasars, and it does not show any significant long-term variability in the IR and UV/optical bands. Such an extremely fast and large-amplitude X-ray variability event has not been reported before in luminous quasars with such massive SMBHs. The X-ray dimming is best explained by a fast-moving absorber crossing the line of sight and fully covering the X-ray emitting corona. Adopting a conservatively small size of 5 <jats:italic>GM</jats:italic> <jats:sub>BH</jats:sub>/<jats:italic>c</jats:italic> <jats:sup>2</jats:sup> for the X-ray corona, the transverse velocity of the absorber is estimated to be ≈0.9<jats:italic>c</jats:italic>. The quasar is likely accreting with a high or even super-Eddington accretion rate, and the high-velocity X-ray absorber is probably related to a powerful accretion-disk wind. Such an energetic wind may eventually evolve into a massive galactic-scale outflow, providing efficient feedback to the host galaxy.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Features at the Sun’s surface and atmosphere are constantly changing due to its magnetic field. The McIntosh Archive provides a long-term (45 yr) record of these features, digitized from hand-drawn synoptic maps by Patrick McIntosh. Utilizing this data, we create stack plots for coronal holes, i.e., Hovmöller-type plots of latitude bands, for all longitudes, stacked in time, allowing tracking of coronal hole movement. Using a newly developed two-step method of centroid calculation, which includes a Fourier descriptor to represent a coronal hole’s boundary and calculate the centroid by the use of Green’s theorem, we calculate the centroids of 31 unique, long-lived equatorial coronal holes for successive Carrington rotations during the entire solar cycle 23, and estimate their slopes (time versus longitude) as the coronal holes evolve. We compute coronal hole centroid drift speeds from these slopes, and find an eastward (prograde) pattern that is actually retrograde with respect to the local differential rotation. By discussing the plausible physical mechanisms which could cause these long-lived equatorial coronal holes to drift retrograde, we identify either classical or magnetically modified westward-propagating solar Rossby waves, with a speed of a few tens to a few hundreds of meters per second, to be the best candidate for governing the drift of deep-rooted, long-lived equatorial coronal holes. To explore plausible physics of why long-lived equatorial coronal holes appear few in number during solar minimum/early rising phase more statistics are required, which will be studied in future.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Binary stars can inflate the observed velocity dispersion of stars in dark matter-dominated systems such as ultrafaint dwarf galaxies (UFDs). However, the population of binaries in UFDs is poorly constrained by observations, with preferred binary fractions for individual galaxies ranging from a few percent to near unity. Searching for wide binaries through nearest neighbor (NN) statistics (or the two-point correlation function) has been suggested in the literature, and we apply this method for the first time to detect wide binaries in a UFD. By analyzing the positions of stars in Reticulum II (Ret II) from Hubble Space Telescope images, we search for angularly resolved wide binaries in Ret II. We find that the distribution of their NN distances shows an enhancement at projected separations of ≲1″ relative to a model containing no binaries. We show that such an enhancement can be explained by a wide binary fraction of <jats:inline-formula> <jats:tex-math> <?CDATA ${f}_{b}\approx {0.007}_{-0.003}^{+0.008}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>b</mml:mi> </mml:mrow> </mml:msub> <mml:mo>≈</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>0.007</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.003</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.008</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac626eieqn1.gif" xlink:type="simple" /> </jats:inline-formula> at separations of more than 3000 au. Under the assumption that the binary separation distribution is similar to that in the Milky Way, the total binary fraction in Ret II may be on the order of 50%. We also use the observed magnitude distribution of stars in Ret II to constrain the initial mass function over the mass range 0.34–0.78 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, finding that a shallow power-law slope of 1.01 ≤ <jats:italic>α</jats:italic> ≤ 1.15 matches the data.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The evolution of a magnetic cloud (MC) from the inner heliosphere to the outer heliosphere has been investigated for decades. Although many studies have reported on the evolution of MCs, there is no relevant statistical study about the continuous parametric evolution of the flux rope model of the Gold–Hoyle solution for MCs from near the Sun to 5.4 au. Based on the velocity-modified uniform-twist force-free flux rope model, in this study we explore the evolution with heliodistance for some parameters from 139 MCs observed by the Helios, Wind, and Ulysses spacecraft. We find a negative/positive correlation between the central axial field strength/the radius of the cross section and the heliodistance. The angle between the axis of the MC and the Sun–spacecraft line (Θ), the expansion velocity (<jats:italic>v</jats:italic> <jats:sub> <jats:italic>e</jats:italic> </jats:sub>), and the poloidal velocity (<jats:italic>v</jats:italic> <jats:sub> <jats:italic>p</jats:italic> </jats:sub>) did not show any evident tendency to increase or decrease with the heliodistance. In addition, the number of turns of the magnetic field lines per unit length winding around the magnetic flux rope, <jats:italic>τ</jats:italic>, shows a weak decrease with heliodistance. Also, there is an evident negative correlation between <jats:italic>τ</jats:italic> and the radius of the flux rope, <jats:italic>R</jats:italic>. The axial magnetic flux (<jats:italic>F</jats:italic> <jats:sub> <jats:italic>z</jats:italic> </jats:sub>) and the magnetic helicity (<jats:italic>H</jats:italic> <jats:sub> <jats:italic>m</jats:italic> </jats:sub>) show a tendency to decrease within 1 au, after which they remain almost unchanged until 5.5 au. Furthermore, we do not find any evident difference in the parametric properties of MCs on and outside the ecliptic.</jats:p>