Table of contents

Energetic neutral atoms (ENAs) are an important tool for investigating the structure of the heliosphere. Recently, it was observed that fluxes of ENAs (with energy ≤55 keV) coming from the upwind and downwind regions of the heliosphere are similar in strength. This led the authors of these observations to hypothesize that the heliosphere is bubble-like rather than comet-like, meaning that it has no extended tail. We investigate the directional distribution of the ENA flux for a wide energy range (3–88 keV) including observations from IBEX (Interstellar Boundary Explorer), INCA (Ion and Neutral Camera, on board Cassini), and HSTOF (High-energy Suprathermal Time Of Flight sensor, on board the Solar and Heliospheric Observatory). An essential element is the model of pickup ion (PUI) acceleration at the termination shock proposed by Zank. We use state-of-the-art models of the global heliosphere, interstellar neutral gas density, and PUI distributions. The results, based on the "comet-like" model of the heliosphere, are close in flux magnitude to ENA observations by IBEX, HSTOF, and partly those by INCA (except for the 5.2–13.5 keV energy channel). We find that the ENA flux from the tail dominates at high energy (in agreement with HSTOF, but not INCA). At low energy, our comet-like model produces ENA fluxes of similar strength from the upwind and downwind directions—which, therefore, removes this as a compelling argument for a bubble-like heliosphere.

Hot Jupiters receive intense incident stellar light on their daysides, which drives vigorous atmospheric circulation that attempts to erase their large dayside-to-nightside flux contrasts. Propagating waves and instabilities in hot Jupiter atmospheres can cause emergent properties of the atmosphere to be time-variable. In this work, we study such weather in hot Jupiter atmospheres using idealized cloud-free general circulation models with double-gray radiative transfer. We find that hot Jupiter atmospheres can be time-variable at the ∼0.1%–1% level in globally averaged temperature and at the ∼1%–10% level in globally averaged wind speeds. As a result, we find that observable quantities are also time-variable: the secondary eclipse depth can be variable at the ≲2% level, the phase-curve amplitude can change by ≲1%, the phase-curve offset can shift by ≲5°, and terminator-averaged wind speeds can vary by ≲2 km s⁻¹. Additionally, we calculate how the eastern and western limb-averaged wind speeds vary with incident stellar flux and the strength of an imposed drag that parameterizes Lorentz forces in partially ionized atmospheres. We find that the eastern limb is blueshifted in models over a wide range of equilibrium temperature and drag strength, while the western limb is only redshifted if equilibrium temperatures are ≲1500 K and drag is weak. Lastly, we show that temporal variability may be observationally detectable in the infrared through secondary eclipse observations with the James Webb Space Telescope, phase-curve observations with future space telescopes (e.g., ARIEL), and/or Doppler wind speed measurements with high-resolution spectrographs.

The Multi-slit Solar Explorer (MUSE) is a proposed mission aimed at understanding the physical mechanisms driving the heating of the solar corona and the eruptions that are at the foundation of space weather. MUSE contains two instruments, a multi-slit extreme ultraviolet (EUV) spectrograph and a context imager. It will simultaneously obtain EUV spectra (along 37 slits) and context images with the highest resolution in space (033–04) and time (1–4 s) ever achieved for the transition region (TR) and corona. The MUSE science investigation will exploit major advances in numerical modeling, and observe at the spatial and temporal scales on which competing models make testable and distinguishable predictions, thereby leading to a breakthrough in our understanding of coronal heating and the drivers of space weather. By obtaining spectra in four bright EUV lines (Fe ix 171 Å, Fe xv 284 Å, Fe xix 108Å, Fe xxi 108 Å) covering a wide range of TR and coronal temperatures along 37 slits simultaneously, MUSE will be able to "freeze" the evolution of the dynamic coronal plasma. We describe MUSE's multi-slit approach and show that the optimization of the design minimizes the impact of spectral lines from neighboring slits, generally allowing line parameters to be accurately determined. We also describe a Spectral Disambiguation Code to resolve multi-slit ambiguity in locations where secondary lines are bright. We use simulations of the corona and eruptions to perform validation tests and show that the multi-slit disambiguation approach allows accurate determination of MUSE observables in locations where significant multi-slit contamination occurs.

We present a detailed analysis of a large sample of spectroscopically confirmed massive quiescent galaxies (MQGs; log(M_*/M_⊙) ∼ 11.5) at z ≳ 2. This sample comprises 15 galaxies selected in the COSMOS and UDS fields by their bright K-band magnitudes and followed up with Very Large Telescope (VLT) X-shooter spectroscopy and Hubble Space Telescope (HST)/WFC3 H_F160W imaging. These observations allow us to unambiguously confirm their redshifts, ascertain their quiescent nature and stellar ages, and reliably assess their internal kinematics and effective radii. We find that these galaxies are compact, consistent with the high-mass end of the stellar mass–size relation for quiescent galaxies at z = 2. Moreover, the distribution of the measured stellar velocity dispersions of the sample is consistent with the most massive local early-type galaxies from the MASSIVE Survey, showing that evolution in these galaxies is dominated by changes in size. The HST images reveal, as surprisingly high, that 40% of the sample has tidal features suggestive of mergers and companions in close proximity, including three galaxies experiencing ongoing major mergers. The absence of velocity dispersion evolution from z = 2 to 0, coupled with a doubling of the stellar mass, with a factor of 4 size increase and the observed disturbed stellar morphologies, supports dry minor mergers as the primary drivers of the evolution of the MQGs over the last 10 billion yr.

The reconnection in nearly symmetric inflow boundary conditions with a strong guide field of three is detected at the magnetopause. The thin current sheet was well resolved by the Magnetospheric Multiscale mission, which revealed that there is a pair of low-density separatrices and a pair of higher-density separatrices. Electron flow is accelerated toward the X-line along the low-density side and ejected out along the higher-density side. All flows are super-Alfvénic, but the outflow velocity is much lower than the inflow velocity. It is further shown that the width of higher-density separatrices is about twice that of the low-density separatrices. Significant and opposite electric field activity is observed on both sides of the current sheet. Our observations show that the separatrix regions between the two sides of strong-guide-field reconnection are significantly different in structure and plasma properties, which in turn affect the acceleration and heating of electrons.

We present evidence that a region of high effective Lyα optical depth at z ∼ 5.7 is associated with an underdense region at the tail end of cosmic reionization. We carried out a survey of Lyman-break Galaxies (LBGs) using Subaru Hyper Suprime-Cam in the field of the z = 5.98 quasar J0148+0600, whose spectrum presents an unusually long (∼160 cMpc) and opaque (τ ≳ 7) Lyα trough at 5.5 ≤ z ≤ 5.9. LBG candidates were selected to lie within the redshift range of the trough, and the projected number densities were measured within 90 cMpc of the quasar sightline. The region within 8' (or ≈19 cMpc) of the quasar position is the most underdense of the whole field. The significance of the presence of the void is estimated to be 99%. This is consistent with the significant deficit of Lyα emitters (LAEs) at z = 5.72 reported by Becker et al. and suggests that the paucity of LAEs is not purely due to the removal of the Lyα emission by the high opacity but reflects a real coherent underdensity of galaxies across the entire redshift range of the trough. These observations are consistent with scenarios in which large optical depth fluctuations arise due to fluctuations in the galaxy-dominant UV background or due to residual neutral islands that are expected from reionization that is completed at redshifts as low as z ≲ 5.5.

We are undertaking a large survey of over 30 disks using the Gemini Planet Imager (GPI) to see whether the observed dust structures match spectral energy distribution predictions and have any correlation with stellar properties. GPI can observe near-infrared light scattered from dust in circumstellar environments using high-resolution Polarimetric Differential Imaging with coronagraphy and adaptive optics. The data have been taken in the J and H bands over two years, with inner working angles of 008 and 011, respectively. Ahead of the release of the complete survey results, here we present five objects with extended and irregular dust structures within 2'' of the central star. These objects are FU Ori, MWC 789, HD 45677, Hen 3-365, and HD 139614. The observed structures are consistent with each object being a pre-main-sequence star with protoplanetary dust. The five objects' circumstellar environments could result from extreme youth and complex initial conditions, from asymmetric scattering patterns due to shadows cast by misaligned disks, or in some cases from interactions with companions. We see complex U_ϕ structures in most objects that could indicate multiple scattering or result from the illumination of companions. Specific key findings include the first high-contrast observation of MWC 789 revealing a newly discovered companion candidate and arc, and two faint companion candidates around Hen 3-365. These two objects should be observed further to confirm whether the companion candidates are comoving. Further observations and modeling are required to determine the causes of the structures.

We report the discovery of a Compton-thick (CT), dust-obscured galaxy at z = 0.89, WISE J082501.48+300257.2 (WISE 0825+3002), observed by the Nuclear Spectroscopic Telescope Array. X-ray analysis with the XCLUMPY model revealed that hard X-ray luminosity in the rest-frame 2–10 keV band of WISE 0825+3002 is L_X (2–10 keV) = ${4.2}_{-1.6}^{+2.8}\times {10}^{44}$ erg s⁻¹ while its hydrogen column density is N_H = ${1.0}_{-0.4}^{+0.8}\times {10}^{24}$ cm⁻², indicating that WISE 0825+3002 is a mildly CT active galactic nucleus (AGN). We performed spectral energy distribution (SED) fitting with CIGALE to derive its stellar mass, star formation rate, and infrared luminosity. The estimated Eddington ratio based on stellar mass and integration of the best-fit SED of the AGN component is λ_Edd = 0.70, which suggests that WISE 0825+3002 harbors an actively growing black hole behind a large amount of gas and dust. We found that the relationship between the luminosity ratio of X-ray and 6 μm, and Eddington ratio, follows an empirical relation for AGNs reported by Toba et al.

Accurate galaxy cluster mass measurements from the gravitational lensing of the cosmic microwave background temperature maps depend on mitigating potential biases from the cluster's own thermal Sunyaev–Zel'dovich (SZ) effect signal. Quadratic lensing estimators use a pair of maps to extract the lensing signal: a large-scale gradient map and a small-scale lensing map. The SZ bias can be eliminated by using an SZ-free map in the pair, with the gradient map being favored for signal-to-noise reasons. However, while this approach eliminates the bias, the SZ power in small-scale lensing map adds extra variance that can become significant for high-mass clusters and low-noise surveys. In this work, we propose projecting out an SZ template to reduce the SZ variance. Any residual SZ signal after template fitting is uncorrelated with the SZ-free gradient map, and thus does not bias the mass measurements. For massive clusters above $4\times {10}^{14}$${M}_{\odot }$ observed by the upcoming CMB-S4 and Simons Observatory experiments, we find that the template fitting approach would increase the cluster lensing signal-to-noise by a factor of 1.4.

Electron excitation collision strengths (Ω) and transition probabilities (A-values) for the iron-peak element Cr ii lines are of high importance for the stellar and nebular abundance studies. Collision and radiative parameters are presented for all possible inelastic transitions between the Cr ii 512 fine-structure levels covering infrared to extreme ultraviolet lines. These parameters should allow a detailed modeling and analysis of the available measured stellar and nebular spectra from different astrophysical objects. Accurate target wave functions have been generated using the multiconfiguration Hartree–Fock method together with term-dependent one-electron orbitals and well-chosen configuration expansions. The wave functions are then used in the calculations of transition probabilities and collision rates. The B-spline Breit–Pauli R-matrix method has been employed for the calculation of electron excitation collision strengths. The semiempirical fine-tuning procedure has been applied to the energies of the local supercluster (LS) terms prior to transformation of the Hamiltonian matrices to intermediate coupling. The Hamiltonian matrices for the calculation of collision rates also include spin–orbit interaction. The 512 fine-structure levels of the Cr ii 3d⁵, 3d⁴4s, $3{d}^{3}4{s}^{2}$, 3d⁴4p, and 3d³4s4p configurations have been considered in our work. The thermally averaged collision strengths have been determined using a Maxwellian distribution for a wide range of temperatures from 10² to 10⁵ K. The accuracy of our results has been estimated by comparison with other calculated collision rates and available measured radiative rates.

A shock tube problem is solved numerically by using one-dimensional full particle-in-cell simulations under the condition that a relatively tenuous and weakly magnetized plasma is continuously pushed by a relatively dense and strongly magnetized plasma having supersonic relative velocity. A forward and a reverse shock and a contact discontinuity are self-consistently reproduced. The spatial width of the contact discontinuity increases as the angle between the discontinuity normal and ambient magnetic field decreases. The inner structure of the discontinuity shows different profiles between magnetic field and plasma density, or pressure, which is caused by a non-MHD effect of the local plasma. The region between the two shocks is turbulent. The fluctuations in the relatively dense plasma are compressible and propagating away from the contact discontinuity, although the fluctuations in the relatively tenuous plasma contain both compressible and incompressible components. The source of the compressible fluctuations in the relatively dense plasma is in the relatively tenuous plasma. Only compressible fast mode fluctuations generated in the relatively tenuous plasma are transmitted through the contact discontinuity and propagate in the relatively dense plasma. These fast mode fluctuations are steepened when passing the contact discontinuity. This wave steepening and probably other effects may cause the broadening of the wave spectrum in the very local interstellar medium plasma. The results are discussed in the context of the heliospheric boundary region or heliopause.

The increasing richness of data related to cold dense matter, from laboratory experiments to neutron-star observations, requires a framework for constraining the properties of such matter that makes use of all relevant information. Here, we present a rigorous but practical Bayesian approach that can include diverse evidence, such as nuclear data and the inferred masses, radii, tidal deformabilities, moments of inertia, and gravitational binding energies of neutron stars. We emphasize that the full posterior probability distributions of measurements should be used rather than, as is common, imposing a cut on the maximum mass or other quantities. Our method can be used with any parameterization of the equation of state (EOS). We use both a spectral parameterization and a piecewise polytropic parameterization with variable transition densities to illustrate the implications of current measurements and show how future measurements in many domains could improve our understanding of cold catalyzed matter. We find that different types of measurements will play distinct roles in constraining the EOS in different density ranges. For example, better symmetry energy measurements will have a major influence on our understanding of matter somewhat below nuclear saturation density but little influence above that density. In contrast, precise radius measurements or multiple tidal deformability measurements of the quality of those from GW170817 or better will improve our knowledge of the EOS over a broader density range.

The IC 5146 cloud is a nearby star-forming region in Cygnus, consisting of molecular gas filaments in a variety of evolutionary stages. We used optical and near-infrared polarization data toward the IC 5146 cloud, reported in the first paper of this series, to reveal the magnetic fields in this cloud. Using the newly released Gaia data, we found that the IC 5146 cloud may contain two separate clouds: a first cloud, including the densest main filament at a distance of ∼600 pc, and a second cloud, associated with the Cocoon Nebula at a distance of ∼800 pc. The spatially averaged H-band polarization map revealed a well-ordered magnetic field morphology, with the polarization segments perpendicular to the main filament but parallel to the nearby subfilaments, consistent with models assuming that the magnetic field is regulating cloud evolution. We estimated the magnetic field strength using the Davis–Chandrasekhar–Fermi method and found that the magnetic field strength scales with volume density with a power-law index of ∼0.5 in the density range from ${N}_{{{\rm{H}}}_{2}}\sim 10$ to 3000 cm⁻³, which indicates an anisotropic cloud contraction with a preferred direction along the magnetic field. In addition, the mass-to-flux ratio of the cloud gradually changes from subcritical to supercritical from the cloud envelope to the deep regions. These features are consistent with strong magnetic field star formation models and suggest that the magnetic field is important in regulating the evolution of the IC 5146 cloud.

We constrain gas inflow speeds in star-forming galaxies with color gradients consistent with inside-out disk growth. Our method combines new measurements of disk orientation with previously described circumgalactic absorption in background quasar spectra. Two quantities, a position angle and an axis ratio, describe the projected shape of each galactic disk on the sky, leaving an ambiguity about which side of the minor axis is tipped toward the observer. This degeneracy regarding the 3D orientation of disks has compromised previous efforts to measure gas inflow speeds. We present Hubble Space Telescope and Keck/LGSAO imaging that resolves the spiral structure in five galaxies at redshift z ≈ 0.2. We determine the sign of the disk inclination for four galaxies, under the assumption that spiral arms trail the rotation. We project models for both radial infall in the disk plane and circular orbits onto each quasar sightline. We compare the resulting line-of-sight velocities to the observed velocity range of Mg ii absorption in spectra of background quasars, which intersect the disk plane at radii between 69 and 115 kpc. For two sightlines, we constrain the maximum radial inflow speeds as 30–40 km s⁻¹. We also rule out a velocity component from radial inflow in one sightline, suggesting that the structures feeding gas to these growing disks do not have unity covering factor. We recommend appropriate selection criteria for building larger samples of galaxy–quasar pairs that produce orientations sensitive to constraining inflow properties.

We present new X-ray observations of the optically obscured protostar HL Tau and the intermediate-mass Herbig Be star HD 100546. Both objects are surrounded by spectacular disks showing complex morphology, including rings and gaps that may have been sculpted by protoplanets. HL Tau was detected as a variable hard X-ray source by Chandra, typical of late-type magnetically active coronal sources. No extended X-ray emission was seen along the HL Tau jet, or along the jet of the T Tauri binary system XZ Tau located 23'' to its east. In contrast, HD 100546 was detected by XMM-Newton as a soft X-ray source (kT ≲ 1 keV) with no short-term (<1 day) variability. Its X-ray properties are remarkably similar to the Herbig stars AB Aur and HD 163296, strongly suggesting that their X-ray emission arises from the same mechanism and is intrinsic to the Herbig stars themselves, not due to unseen late-type companions. We consider several possible emission mechanisms and conclude that the X-ray properties of HD 100546 are consistent with an accretion shock origin, but higher resolution grating spectra capable of providing information on individual emission lines are needed to more reliably distinguish between accretion shocks and alternatives. We show that X-ray ionization and heating are mainly confined to the upper disk layers in both HL Tau and HD 100546, and any exoplanets near the midplane at distances ≥1 au are well-shielded from X-rays produced by the central star.

Various models of solar subsurface stratification are tested in the global EULAG-MHD solver to simulate diverse regimes of near-surface convective transport. Sub- and superadiabacity are altered at the surface of the model (r > 0.95R_⊙) to either suppress or enhance convective flow speeds in an effort to investigate the impact of the near-surface layer on global dynamics. A major consequence of increasing surface convection rates appears to be a significant alteration of the distribution of angular momentum, especially below the tachocline where the rotational frequency predominantly increases at higher latitudes. These hydrodynamic changes correspond to large shifts in the development of the current helicity in this stable layer (r < 0.72R_⊙), significantly altering its impact on the generation of poloidal and toroidal fields at the tachocline and below, acting as a major contributor toward transitions in the dynamo cycle. The enhanced near-surface flow speed manifests in a global shift of the toroidal field (B_ϕ) in the butterfly diagram, from a north–south symmetric pattern to a staggered antisymmetric emergence.

Cosmic rays (CRs) process the matter of the interstellar medium (ISM), not only modifying the interstellar matter but also injecting chemical species in the gas phase. In this work, we study the effect of CRs on astrophysical polycyclic aromatic hydrocarbons (PAHs). For events in which many electrons are stripped out from the PAHs, coulomb explosion takes place and carbon chains are produced. We computed PAH multi-ionization cross sections with a collisional model. We used another model to predict the fragmentation pattern following coulomb explosion. Experimental measurements were used to assess the validity of the calculations. The production rates of carbon chains were calculated using different CR fluxes and elemental compositions, to account for the variations expected in different astrophysical environments. PAHs with a range of sizes and levels of compactness were explored. As an average over the explored PAHs, the PAH lifetime with respect to a standard interstellar CR flux is found to be on the order of a few billion years. The production rates of chains (5–15 carbons) are slightly below the H₂ ionization rate ζ. In the diffuse ISM, with 10% of the available cosmic carbon locked in PAHs, this process leads to carbon chain fractional abundances at steady state, in the range of 10⁻¹⁵–10⁻¹⁴, with a confidence interval of 1 order of magnitude. It reaches 10⁻¹³ in quiescent dense clouds. This is not sufficient to explain the observed abundances of carbon chains and complex organic molecules in dense clouds.

The most energetic flares start with a filament rise followed by magnetic reconnection below this filament. The start of the reconnection corresponds to the beginning of the flare impulsive phase. In this paper we study processes before this phase. During the filament rise we recognize an unusual radio continuum with a starting boundary drifting toward lower frequencies. The estimated velocity of the agent generating this continuum boundary is about 400 km s⁻¹, similar to that of the rising filament. In association with this filament rise, transient X-ray sources and extreme ultraviolet (EUV) brightenings are found near the filament footpoint and outside the locations where later two parallel flare ribbons appear. Moreover, oscillations with a ∼30 s period are found simultaneously in radio, EUV, and X-ray observations. Around the end of these oscillations the flare impulsive phase starts as seen in observations of the drifting pulsation structure and X-ray source located at the upper part of the rising filament. We interpret the unusual radio continuum and transient X-ray sources, which are located outside the two parallel flare ribbons, as those generated during an interaction of the rising filament with the above-lying magnetic loops. The EUV brightening at the filament footpoint could be a signature of the magnetic reconnection inside the magnetic rope carrying the filament. Possible scenarios of the ∼30 s period oscillations in radio, X-ray, and EUV are discussed.

We examine the near-infrared (NIR) emission from low-luminosity active galactic nuclei (LLAGNs). Our galaxy sample includes 15 objects with detected 2–10 keV X-ray emission, dynamical black hole mass estimates from the literature, and available Gemini/NIFS integral field spectroscopy data. We find evidence for red continuum components at the center of most galaxies, consistent with the hot dust emission seen in higher-luminosity AGNs. We decompose the spectral data cubes into a stellar and continuum component, assuming the continuum component comes from thermal emission from hot dust. We detect nuclear thermal emission in 14 out of 15 objects. This emission causes weaker CO absorption lines and redder continuum (2.05–2.28 μm) in our K-band data, as expected from hot dust around an AGN. The NIR emission is clearly correlated with the 2–10 keV X-ray flux, with a Spearman coefficient of r_spearman = 0.69 suggesting a >99% significance of correlation, providing further evidence of an AGN origin. Our sample has typical X-ray and NIR fluxes 3–4 orders of magnitude less luminous than previous work studying the NIR emission from AGNs. We find that the ratio of NIR to X-ray emission increases toward lower Eddington ratios. The NIR emission in our sample is often brighter than the X-ray emission, with our K-band AGN luminosities comparable to or greater than the 2–10 keV X-ray luminosities in all objects with Eddington ratios below 0.01%. The nature of this LLAGN NIR emission remains unclear, with one possibility being an increased contribution from jet emission at these low luminosities. These observations suggest the James Webb Space Telescope will be a useful tool for detecting the lowest-luminosity AGNs.

This paper focuses on point-spread function (PSF) estimation for astronomical images containing only single extended objects captured by adaptive optics systems. The problem is very different from, and much more challenging than, PSF estimation with point-like source images. We propose a new PSF estimation framework based on deep-learning technology. In this framework, PSFs can be estimated "end-to-end" using the original degraded images. Moreover, such a framework can precisely address different sources of blur without requiring accurate prior information about the PSF, image or imaging system. Therefore, the method is practical. We test the proposed method on both simulated and real data, and the favorable results show that the method is valid and performs much better than classical methods do.

The chemical environments of young planets are assumed to be largely influenced by the impacts of bodies lingering on unstable trajectories after the dissolution of the protoplanetary disk. We explore the chemical consequences of impacts within the context of reducing planetary atmospheres dominated by carbon monoxide, methane, and molecular nitrogen. A terawatt high-power laser was selected in order to simulate the airglow plasma and blast wave surrounding the impactor. The chemical results of these experiments are then applied to a theoretical atmospheric model. The impact simulation results in substantial volume mixing ratios within the reactor of 5% hydrogen cyanide (HCN), 8% acetylene (C₂H₂), 5% cyanoacetylene (HC₃N), and 1% ammonia (NH₃). These yields are combined with estimated impact rates for the early Earth to predict surface boundary conditions for an atmospheric model. We show that impacts might have served as sources of energy that would have led to steady-state surface quantities of 0.4% C₂H₂, 400 ppm HCN, and 40 ppm NH₃. We provide simulated transit spectra for an Earth-like exoplanet with this reducing atmosphere during and shortly after eras of intense impacts. We predict that acetylene is as observable as other molecular features on exoplanets with reducing atmospheres that have recently gone through their own "heavy bombardments," with prominent features at 3.05 and 10.5 μm.

Photodissociation regions (PDRs) are parts of the ISM consisting of predominantly neutral gas, located at the interface between H ii regions and molecular clouds. The physical conditions within these regions show variations on very short spatial scales, and therefore PDRs constitute ideal laboratories for investigating the properties and evolution of dust grains. We have mapped IC 63 at high resolution from the UV to the NIR (275 nm to 1.6 μm), using the Hubble Space Telescope WFC3. Using a Bayesian SED fitting tool, we simultaneously derive a set of stellar (T_eff, $\mathrm{log}(g)$, distance) and extinction (A_V, R_V) parameters for 520 background stars. We present maps of A_V and R_V with a resolution of 25 arcsec based on these results. The extinction properties vary across the PDR, with values for A_V between 0.5 and 1.4 mag, and a decreasing trend in R_V, going from 3.7 at the front of the nebula to values as low as 2.5 further in. This provides evidence for evolution of the dust optical properties. We fit two modified blackbodies to the MIR and FIR SED, obtained by combining the A_V map with data from Spitzer and Herschel. We derive effective temperatures (30 and 227 K) and the ratio of opacities at 160 μm to V band κ₁₆₀/κ_V (7.0 × 10⁻⁴ and 2.9 × 10⁻⁹) for the two dust populations. Similar fits to individual pixels show spatial variations of κ₁₆₀/κ_V. The analysis of our HST data, combined with these Spitzer and Herschel data, provides the first panchromatic view of dust within a PDR.

Galaxy color gradients (CGs)—i.e., spectral energy distributions that vary across the galaxy profile—will impact galaxy shape measurements when the modeled point-spread function (PSF) corresponds to that for a galaxy with spatially uniform color. This paper describes the techniques and results of a study of the expected impact of galaxy CGs on weak lensing measurements with the Large Synoptic Survey Telescope (LSST) when the PSF size depends on wavelength. The bias on cosmic shear measurements from CGs is computed both for parametric bulge+disk galaxy simulations and for more realistic chromatic galaxy surface brightness profiles based on Hubble Space Telescope V- and I-band images in the All-Wavelength Extended Groth Strip International Survey (AEGIS). For the parametric galaxies, and for the more realistic galaxies derived from AEGIS galaxies with a sufficient signal-to-noise ratio that CG bias can be isolated, the predicted multiplicative shear biases due to CGs are found to be at least a factor of two below the LSST full-depth requirement on the total systematic uncertainty in the redshift-dependent shear calibration. The analysis code and data products are publicly available (https://github.com/sowmyakth/measure_cg_bias).

Models play an important role in our understanding of the global structure of the solar wind and its interaction with the interstellar medium. A critical ingredient in many types of models is the charge-exchange collisions between ions and neutrals. Some ambiguity exists in the charge-exchange cross-section for protons and hydrogen atoms, depending on which experimental data is used. The differences are greatest at low energies, and for the plasma-neutral interaction in the outer heliosheath may exceed 50%. In this paper we assess a number of existing data sets and formulae for proton–hydrogen charge exchange. We use a global simulation of the heliosphere to quantify the differences between the currently favored cross-section, and we suggest a formulation that more closely matches the majority of available data. We find that in order to make the resulting two heliospheres the same size, the interstellar proton and hydrogen densities need to be adjusted by 10%–15%, which provides a way to link the uncertainty in the cross-section to the uncertainty in the parameters of the pristine interstellar plasma.

The first laboratory evidence of a radiative shock (RS) decelerating during its free expansion phase in an optically thick medium is presented. A shock is generated in a multilayer solid target under the irradiation of a high-power laser at the GEKKO XII laser facility. The rear surface of the target is connected to a gas cell filled with Xe. Upon breakout, an RS, characterized by low Boltzmann number Bo ≪ 1 and Mihalas number R  ≈  10, is generated. Experimental results reveal that radiative losses through the radiative precursor cause the shock to lose energy and decelerate. A model is developed that describes the shock propagation as a function of time. The model is in agreement with both numerical simulations and experimental results. These results have tremendous consequences for astrophysical systems, such as SN 1987A, where radiative deceleration may play a role in the formation of the observed hotspots in the circumstellar ring.

Consistency checks of cosmological data sets are an important tool because they may suggest systematic errors or the type of modifications to ΛCDM necessary to resolve current tensions. In this work, we derive an analytic method for calculating the level of correlations between model parameters from two correlated cosmological data sets, which complements more computationally expensive simulations. This method is an extension of the Fisher analysis that assumes a Gaussian likelihood and a known data covariance matrix. We apply this method to the South Pole Telescope Polarimeter (SPTpol) temperature and polarization cosmic microwave background (CMB) spectra (TE and EE). We find weak correlations between ΛCDM parameters with a 9% correlation between the TE-only and EE-only constraints on H₀ and a 25% and 32% correlation for log(A_s) and n_s respectively. The TE–EE parameter differences are consistent with zero, with a probability to exceed of 0.53. Using simulations we show that this test is independent of the consistency of the SPTpol TE and EE band powers with the best-fit ΛCDM model spectra. Despite the negative correlations between the TE and EE power spectra, the correlations between TE-only and EE-only ΛCDM parameters are positive. Ignoring correlations in the TT–TE and TE–EE comparisons biases the χ² low, artificially making parameters look more consistent. Therefore, we conclude that these correlations need to be accounted for when performing internal consistency checks of the TT versus TE versus EE power spectra for future CMB analyses.

The emission from dark ages halos in the lines of transitions between the lowest rotational levels of hydrogen and hydrogen deuteride molecules is analyzed. It is assumed that molecules are excited by the cosmic microwave background (CMB) and collisions with hydrogen atoms. The physical parameters of halos and the number density of molecules are precalculated assuming that halos are homogeneous top-hat spheres formed from the cosmological density perturbations in the four-component universe with post-Planck cosmological parameters. The differential brightness temperatures and differential spectral fluxes in the rotational lines of H₂–HD molecules are computed for two phenomena: thermal luminescence and resonant scattering of CMB radiation. The results show that the expected maximal values of differential brightness temperature of warm halos (T_K ∼ 200–800 K) are at the level of nanokelvins, are comparable for both phenomena, and are below the sensitivity of modern submillimeter radio telescopes. For hot halos (T_K ∼ 2000–5000 K) the thermal emission of H₂-ortho molecules dominates and the differential brightness temperatures are predicted to be of a few microkelvins at the frequencies 300–600 GHz, which could be detectable with next-generation telescopes.

The surface content of lithium (Li) and beryllium (Be) provides insight into the mixing and circulation mechanisms in stellar interiors. The old open cluster, M67, has been well-studied for Li abundances in both main-sequence and evolved stars. The Be abundances give us a probe to a deeper level in stars. We have taken high-resolution spectra with Keck I with HIRES to determine Be abundances along the subgiant branch of M67, where there are dramatic depletions of Li. These subgiants range in mass from 1.26 to 1.32 M_⊙ and have evolved from main-sequence stars that would have occupied the region of the Li–Be dip found in younger clusters. Lithium abundances have been adjusted to the same scale for 103 stars in M67 by Pace et al. The more massive stars—now the coolest and furthest-evolved from the main sequence—show a drop in Li by a factor of 400 across the subgiant branch. Our new Be abundances also show a decline, but by a factor of ∼50. The two elements decline together with Li showing a steeper decline in these subgiants than it does in the Li–Be dip stars. The relative decline in Be abundance compared to Li is remarkably well fit by the models of Sills & Deliyannis, made specifically for the subgiants in M67. Those models include the effects of mixing induced by stellar rotation. These M67 subgiants show the effects of both main-sequence depletion and post-main-sequence dilution of both Li and Be.

The effects of turbulence in the very local interstellar medium (VLISM) have been proposed by Giacalone & Jokipii to be important in determining the structure of the Interstellar Boundary Explorer (IBEX) ribbon via particle trapping by magnetic mirroring. We further explore this effect by simulating the motion of charged particles in a turbulent magnetic field superposed on a large-scale mean field, which we consider to be either spatially uniform or a draped field derived from a three-dimensional magnetohydrodynamic simulation. We find that the ribbon is not double-peaked, in contrast to Giacalone & Jokipii. However, the magnetic mirror force still plays an important role in trapping particles. Furthermore, the ribbon is considerably thicker if the large-scale mean field is draped around the heliosphere. Voyager 1 observations in the VLISM show a turbulent field component that is stronger than previously thought, which we test in our simulation. We find that the inclusion of turbulent fluctuations at scales ≳100 au and power consistent with Voyager 1 observations produces a ribbon whose large-scale structure is inconsistent with IBEX observations. However, restricting fluctuations to <100 au produces a smoother ribbon structure similar to IBEX observations. Different realizations of turbulence produce different small-scale features (≲10°) in the ribbon, but its large-scale structure is robust if the maximum fluctuation size is ≲50 au. This suggests that the magnetic field structure at scales ≲50 au is determined by the heliosphere–VLISM interaction and cannot entirely be represented by pristine interstellar turbulence.

In order to study short timescale optical variability of γ-ray blazar S5 0716+714, quasi-simultaneous spectroscopic and multiband photometric observations were performed from 2018 November to 2019 March with the 2.4 m optical telescope located at Lijiang Observatory of Yunnan Observatories. The observed spectra are well fitted with a power law F_λ = Aλ^−α (spectral index α > 0). Correlations found between $\dot{\alpha }$, $\dot{A}$, $\dot{A}/A$, $\dot{{F}_{\lambda }}$, and $\dot{{F}_{\lambda }}/{F}_{\lambda }$ are consistent with the trend of bluer-when-brighter (BWB). It is the same case for colors, magnitudes, color variation rates, and magnitude variation rates of photometric observations. The variations of α lead those of F_λ. Also, the color variations lead magnitude variations. The observational data are mostly distributed in the I(+,+) and III(−,−) quadrants of the coordinate system. Both spectroscopic and photometric observations show BWB behaviors in S5 0716+714. The observed BWB may be explained by the shock-jet model, and its appearance may depend on the relative position of the observational frequency ranges with respect to the synchrotron peak frequencies, e.g., at the left of the peak frequencies. Fractional variability amplitudes are F_var ∼ 40% for both spectroscopic and photometric observations. Variations of α indicate variations of relativistic electron distribution producing the optical spectra.

A census of the satellite population around dwarf galaxy primary hosts in environments outside the Local Group is essential to understanding Λ cold dark matter galaxy formation and evolution on the smallest scales. We present deep optical Hubble Space Telescope imaging of the gas-rich, faint dwarf galaxy Antlia B (M_V = −9.4)—a likely satellite of NGC 3109 (D = 1.3 Mpc)—discovered as part of our ongoing survey of primary host galaxies similar to the Magellanic Clouds. We derive a new tip of the red giant branch distance of D = 1.35 ± 0.06 Mpc (m − M = 25.65 ± 0.10), consistent with membership in the nearby NGC 3109 dwarf association. The color–magnitude diagram (CMD) shows both a prominent old, metal-poor stellar component and confirms a small population of young, blue stars with ages ≲1 Gyr. We use the CMD fitting algorithm MATCH to derive the star formation history (SFH) and find that it is consistent with the typical dwarf irregular or transitional dwarf galaxy (dTrans) in the Local Group. Antlia B shows relatively constant stellar mass growth for the first ∼10–11 Gyr and almost no growth in the last ∼2–3 Gyr. Despite being gas-rich, Antlia B shows no evidence of active star formation (i.e., no Hα emission) and should therefore be classified as a dTrans dwarf. Both Antlia B and the Antlia dwarf (dTrans) are likely satellites of NGC 3109, suggesting that the cessation of ongoing star formation in these galaxies may be environmentally driven. Future work studying the gas kinematics and distribution in Antlia B will explore this scenario in greater detail. Our work highlights the fact that detailed studies of nearby dwarf galaxies in a variety of environments may continue to shed light on the processes that drive the SFH and evolution of dwarf galaxies more generally.

We perform a model-independent and comprehensive test on the cosmic distance duality relation (CDDR) by combining the latest observations of strong gravitational lensing (SGL) including a total of 161 well-measured systems from several surveys and observations of Type Ia supernovae (SNe Ia), i.e., the joint light-curve analysis of SNe Ia and the Pantheon SNe Ia. We parameterize the CDDR in the form of ${D}_{{\rm{A}}}{\left(1+z\right)}^{2}/{D}_{{\rm{L}}}=1+{\eta }_{0}z$, and also consider general lens mass models including the dependence on the lens redshift and surface mass density. First, we update tests using the new SGL and the two SNe Ia data sets for the singular isothermal sphere model. The constraint results suggest a moderate tension with the CDDR using the Pantheon SN Ia with a slightly negative η₀. We find that η₀ deviates significantly from the CDDR at more than the 3σ level if the lens mass model depends on redshift. Supplementary tests show that the error from aperture correction and the parameterization method of the CDDR can hardly justify the deviation. Several of the models investigated show some evidence for deviations from the CDDR. However, there is a significant scatter in the inferred level of the CDDR violation, depending on the model describing the population of strong lenses. This variance is too large for us to conclude yet that the CDDR is violated and needs further investigation and future measurements to be verified.

We continue our empirical study of the emission line flux originating in the cool (T ∼ 10⁴ K) gas that populates the halos of galaxies and their environments. Specifically, we present results obtained for a sample of nearly half a million individual galaxies, groups, and clusters of galaxies, intersected by more than two million SDSS lines of sight at projected separations of up to a quarter of the virial radius. Adopting simple power-law relationships between the circumgalactic (CGM) cool gas fraction and either the halo or stellar mass, we present expressions for the CGM cool gas fraction as a function of either halo or stellar mass, ${f}_{{\rm{cool}}}({M}_{h})\,=({0.23}_{-0.07}^{+0.07})$ × ${({M}_{h}/{10}^{12}{M}_{\odot })}^{(-{0.40}_{-0.07}^{+0.06})}$ or ${f}_{{\rm{cool}}}({M}_{\ast })=({0.28}_{-0.04}^{+0.05})$ × ${({M}_{\ast }/{10}^{10.0}{M}_{\odot })}^{(-0.34\pm 0.04)}$. Where we can compare, our results are consistent with previous constraints from absorption line studies, our own previous emission line work, and simulations. The cool gas can be the dominant baryonic CGM component, comprising a fraction as high as >90% of halo gaseous baryons, in low-mass halos, M_h ∼ 10^10.5M_⊙, and a minor fraction, <5%, in groups and clusters, M_h > 10¹⁴M_⊙.

The Kepler Space Telescope observed over 15,000 stars for asteroseismic studies. Of these, 75% of dwarfs (and 8% of giants) were found to show anomalous behavior, such as suppressed oscillations (low amplitude) or no oscillations at all. The lack of solar-like oscillations may be a consequence of multiplicity, due to physical interactions with spectroscopic companions or due to the dilution of oscillation amplitudes from "wide" (AO detected; visual) or spectroscopic companions introducing contaminating flux. We present a search for stellar companions to 327 of the Kepler asteroseismic sample, which were expected to display solar-like oscillations. We used direct imaging with Robo-AO, which can resolve secondary sources at ∼015, and followed up detected companions with Keck AO. Directly imaged companion systems with both separations of ≤05 and amplitude dilutions >10% all have anomalous primaries, suggesting these oscillation signals are diluted by a sufficient amount of excess flux. We also used the high-resolution spectrometer ESPaDOnS at the Canada–France–Hawai'i Telescope to search for spectroscopic binaries. We find tentative evidence for a higher fraction of spectroscopic binaries with high radial velocity scatter in anomalous systems, which would be consistent with previous results suggesting that oscillations are suppressed by tidal interactions in close eclipsing binaries.

We present an iterative method to construct a freeform lens model that self-consistently reproduces the sky positions, geometrically inferred redshifts, and relative brightnesses of all multiply lensed images toward a galaxy cluster. This method is applied to the cluster RXC J2248.7−4431 (z = 0.348) from the Hubble Frontier Fields program, toward which 10 multiply lensed sources with accurate spectroscopic redshifts and 6 others with inexact photometric redshifts have been identified. Using the spectroscopically secure systems to define an initial lens model, we compute the geometric redshifts of the photometric systems. We then iterate the lens model by incorporating the photometric systems at redshifts shifted by incremental amounts toward their geometric redshifts inferred from the previous step; on convergence, we find geometric redshifts in good agreement with the spectroscopically determined redshifts, but they can depart significantly from the photometrically determined redshifts. In the final lens model, all 16 lensed sources tightly follow the cosmological form of the angular diameter distance relation. Furthermore, although they are not used as model constraints, our lens model predicts relative brightnesses between image pairs for a given set of multiply lensed images in reasonable agreement with observations, thus providing independent validation of this model. Our method for inferring the redshifts and intrinsic brightnesses of multiply lensed sources will become especially important in the era of the James Webb Space Telescope, when deep infrared detections will typically be unmatched optically such that photometric redshifts will be very uncertain.

We present a sample of nearby dwarf galaxies with radio-selected accreting massive black holes (BHs), the majority of which are non-nuclear. We observed 111 galaxies using sensitive, high-resolution observations from the Karl G. Jansky Very Large Array (VLA) in its most extended A-configuration at X band (∼8–12 GHz), yielding a typical angular resolution of ∼025 and rms noise of ∼15 μJy. Our targets were selected by crossmatching galaxies with stellar masses M_⋆ ≤ 3 × 10⁹ M_⊙ and redshifts z < 0.055 in the NASA-Sloan Atlas with the VLA Faint Images of the Radio Sky at Twenty centimeters Survey. With our new high-resolution VLA observations, we detect compact radio sources toward 39 galaxies and carefully evaluate possible origins for the radio emission, including thermal H II regions, supernova remnants, younger radio supernovae, background interlopers, and active galactic nuclei (AGNs) in the target galaxies. We find that 13 dwarf galaxies almost certainly host active massive BHs, despite the fact that only one object was previously identified as having optical signatures of an AGN. We also identify a candidate dual radio AGN in a more massive galaxy system. The majority of the radio-detected BHs are offset from the center of the host galaxies, with some systems showing signs of interactions/mergers. Our results indicate that massive BHs need not always live in the nuclei of dwarf galaxies, confirming predictions from simulations. Moreover, searches attempting to constrain BH seed formation using observations of dwarf galaxies need to account for such a population of "wandering" BHs.

Correlations between the mass of a supermassive black hole (SMBH) and the properties of its host galaxy (e.g., total stellar mass M_*, luminosity L_host) suggest an evolutionary connection. A powerful test of a coevolution scenario is to measure the relations ${{ \mathcal M }}_{\mathrm{BH}}$–L_host and ${{ \mathcal M }}_{\mathrm{BH}}$–M_* at high redshift and compare with local estimates. For this purpose, we acquired Hubble Space Telescope (HST) imaging with WFC3 of 32 X-ray-selected broad-line (type 1) active galactic nuclei at 1.2 < z < 1.7 in deep survey fields. By applying state-of-the-art tools to decompose the HST images including available ACS data, we measured the host galaxy luminosity and stellar mass along with other properties through the two-dimensional model fitting. The black hole mass (${{ \mathcal M }}_{\mathrm{BH}}$) was determined using the broad Hα line, detected in the near-infrared with the Subaru Fiber Multi-Object Spectrograph, which potentially minimizes systematic effects using other indicators. We find that the observed ratio of ${{ \mathcal M }}_{\mathrm{BH}}$ to total M_* is 2.7× larger at z ∼ 1.5 than in the local universe, while the scatter is equivalent between the two epochs. A nonevolving mass ratio is consistent with the data at the 2σ–3σ confidence level when accounting for selection effects (estimated using two independent and complementary methods) and their uncertainties. The relationship between ${{ \mathcal M }}_{\mathrm{BH}}$ and host galaxy total luminosity paints a similar picture. Therefore, our results cannot distinguish whether SMBHs and their total host stellar mass and luminosity proceed in lockstep or whether the growth of the former somewhat overshoots the latter, given the uncertainties. Based on a statistical estimate of the bulge-to-total mass fraction, the ratio ${{ \mathcal M }}_{\mathrm{BH}}$/M_*,bulge is offset from the local value by a factor of ∼7, which is significant even accounting for selection effects. Taken together, these observations are consistent with a scenario in which stellar mass is subsequently transferred from an angular momentum–supported component of the galaxy to a pressure-supported one through secular processes or minor mergers at a faster rate than mass accretion onto the SMBH.

Several studies have demonstrated that the cosmic-ray ionization rate is highly variable in the interstellar medium. However, constraints of this rate for several regions, including those that contain hot cores, are lacking. Hot cores are appealing sources to study given their rich chemical complexity. The chemistry of these cores can be influenced by both their cosmic-ray ionization rates and their warm-up timescales; however, understanding the chemical response to these parameters requires further investigation. We study these effects using the astrochemical hot-core modeling code MAGICKAL, in which we construct a grid of 81 models using nine ionization rates and nine warm-up timescales. We also simulate local thermodynamic equilibrium radiative transfer for these models to obtain results that can be directly compared with observations. We compare molecular emission of these models with observations toward NGC 6334 IRS 1, NGC 7538 IRS 1, W3(H₂O), and W33A in an effort to constrain their cosmic-ray ionization rates and warm-up timescales. Our best fits to the observations suggest that these sources possess elevated cosmic-ray ionization rates, compared to the canonical value of 1.3 × 10⁻¹⁷ s⁻¹ used in previous modeling studies, and rapid warm-up timescales. We also demonstrate that there exists a strong correlation between the cosmic-ray ionization rate and the total hydrogen column density of a source and a strong correlation between the warm-up timescale and total source mass. Furthermore, these relationships are in good agreement with other theoretical studies.

The synthesis of chlorine-bearing species in CO ice was studied by the irradiation of CH₃Cl:CO ice at 10 K with vacuum-ultraviolet (VUV) light and energetic electrons. In contrast to the photochemical behavior of CH₃F:CO ice, photolysis of CH₃Cl:CO ice with Lyα or broadband VUV light afforded various products. This discrepancy was attributed to the abundant absorption bands of CH₃Cl in the VUV region, particularly in the Lyα region. The Cl-bearing species including Cl₂O, ClCO, C₃Cl₂, C₃HCl, and HOOCl were characterized by observing their IR features. In contrast, electron bombardment of ice mixtures produced various carbon oxides and primary products, such as CH₂Cl and HCO. In addition, the mechanism of energetic processes in electron bombardment was discussed.

Fast radio bursts (FRBs) are short-lived (∼ms), energetic transients (having a peak flux density of ∼Jy) with no known prompt emission in other energy bands. We present results of a search for prompt X-ray emissions from 41 FRBs using the Cadmium Zinc Telluride Imager on AstroSat, which continuously monitors ∼70% of the sky. Our searches on various timescales in the 20–200 keV range, did not yield any counterparts in this hard X-ray band. We calculate upper limits on hard X-ray flux, in the same energy range and convert them to upper bounds for η: the ratio of X-ray to radio fluence of FRBs. We find η ≤ 10^8–10 for hard X-ray emission. Our results will help constrain the theoretical models of FRBs as the models become more quantitative and nearer, brighter FRBs are discovered.

Recent high angular resolution (≃40 mas) ALMA observations at 1.14 mm resolve a compact (R ≃ 200 au), flattened dust structure perpendicular to the HH 80–81 jet emanating from the GGD 27-MM1 high-mass protostar, making it a robust candidate for a true accretion disk. The jet–disk system (HH 80–81/GGD 27-MM1) resembles those found in association with low- and intermediate-mass protostars. We present radiative transfer models that fit the 1.14 mm ALMA dust image of this disk, which allow us to obtain its physical parameters and predict its density and temperature structure. Our results indicate that this accretion disk is compact (R_disk ≃ 170 au) and massive (≃5 M_⊙), at about 20% of the stellar mass of ≃20 M_⊙. We estimate the total dynamical mass of the star–disk system from the molecular line emission, finding a range between 21 and 30 M_⊙, which is consistent with our model. We fit the density and temperature structures found by our model with power-law functions. These results suggest that accretion disks around massive stars are more massive and hotter than their low-mass siblings, but they still are quite stable. We also compare the temperature distribution in the GGD 27–MM1 disk with that found in low- and intermediate-mass stars and discuss possible implications for the water snow line. We have also carried out a study of the distance based on Gaia DR2 data and the population of young stellar objects in this region and from the extinction maps. We conclude that the source distance is within 1.2 and 1.4 kpc, closer than what was derived in previous studies (1.7 kpc).

We investigated the off-limb spicules observed in the Mg iih and k lines by IRIS in a solar polar coronal hole. We analyzed the large data set of obtained spectra to extract quantitative information about the line intensities, shifts, and widths. The observed Mg ii line profiles are broad and double peaked at lower altitudes, broad but flat topped at middle altitudes, and narrow and single peaked with the largest Doppler shifts at higher altitudes. We use one-dimensional non-LTE vertical slab models (i.e., models that consider departures from local thermodynamic equilibrium) in single-slab and multi-slab configurations to interpret the observations and to investigate how a superposition of spicules along the line of sight (LOS) affects the synthetic Mg ii line profiles. The used multi-slab models either are static, i.e., without any LOS velocities, or assume randomly assigned LOS velocities of individual slabs, representing the spicule dynamics. We conducted such single-slab and multi-slab modeling for a broad set of model input parameters and showed the dependence of the Mg ii line profiles on these parameters. We demonstrated that the observed line widths of the h and k line profiles are strongly affected by the presence of multiple spicules along the LOS. We later showed that the profiles obtained at higher altitudes can be reproduced by single-slab models representing individual spicules. We found that the multi-slab model with a random distribution of the LOS velocities ranging from −25 to 25 km s⁻¹ can well reproduce the width and the shape of Mg ii profiles observed at middle altitudes.

We use models of stellar angular momentum evolution to determine ages for ∼500 stars in the APOGEE-Kepler Cool Dwarfs sample. We focus on lower-main-sequence stars, where other age-dating tools become ineffective. Our age distributions are compared to those derived from asteroseismic and giant samples and solar analogs. We are able to recover gyrochronological ages for old, lower-main-sequence stars, a remarkable improvement over prior work in hotter stars. Under our model assumptions, our ages have a median relative uncertainty of 14%, comparable to the age precision inferred for more massive stars using traditional methods. We investigate trends of Galactic α-enhancement with age, finding evidence of a detection threshold between the age of the oldest α-poor stars and that of the bulk α-rich population. We argue that gyrochronology is an effective tool reaching ages of 10–12 Gyr in K and early M dwarfs. Finally, we present the first effort to quantify the impact of detailed abundance patterns on rotational evolution. We estimate a ∼15% bias in age for cool, α-enhanced (+0.4 dex) stars when standard solar-abundance-pattern rotational models are used for age inference, rather than models that appropriately account for α-enrichment.

We present rest-frame far-infrared (FIR) and optical size measurements of active galactic nucleus (AGN) hosts and star-forming galaxies (SFGs) in the COSMOS field, enabled by high-resolution Atacama Large Millimeter/submillimeter Array (ALMA)/1 mm (01–04) and Hubble Space Telescope (HST)/F814W imaging (∼01). Our sample includes 27 galaxies at z < 2.5, classified as infrared-selected AGN (three sources), X-ray selected AGN (four sources), and non-AGN SFGs (20 sources), for which high-resolution Band 6/7 ALMA images are available at 1 mm from our own observing program as well as archival observations. The sizes and star formation rate surface densities measured from both ALMA/1 mm and HST/F814W images show that obscured AGN host galaxies are more compact than non-AGN SFGs at similar redshift and stellar mass. This result suggests that the obscured accretion phase may be related to galaxies experiencing a compaction of their gaseous component, which could be associated with enhanced central star formation before a subsequent quenching driving the formation of compact passive galaxies. Moreover, most of the detected and stacked rest-frame FIR sizes of AGNs in our sample are similar or more compact than their rest-frame optical sizes, which is consistent with recent results of ALMA-detected sources. This might be explained by the fact that the dusty starbursts take place in the compact regions, and suggests that the star formation mechanisms in the compact regions of AGN hosts are similar to those observed in SFGs observed with ALMA.

For some neutron stars (NSs) in the binary systems, the masses have been accurately measured. While for the isolated neutron stars (INSs), no mass measurement has been reported yet. The situation will change soon thanks to the successful performance of the Neutron Star Interior Composition Explorer (NICER), with which the radius and mass of the isolated PSR J0030+0451 can be simultaneously measured. For most INSs, no mass measurements are possible for NICER because of observational limitations. Benefiting from recent significant progress made on constraining the equation of state of NSs, in this work we propose a way to estimate the masses of the INSs with the measured gravitational redshifts. We apply our method to RX J1856.5-3754, RX J0720.4-3125, and RBS 1223, three members of "The Magnificent Seven" (M7), and estimate their masses to be ${1.24}_{-0.29}^{+0.29}\,{M}_{\odot }$, ${1.23}_{-0.05}^{+0.10}\,{M}_{\odot }$, and ${1.08}_{-0.11}^{+0.20}\,{M}_{\odot }$, respectively. These masses are consistent with that of binary NS systems, suggesting no evidence for experiencing significant accretion of these isolated objects.

In this paper, we investigate the upward overshooting by three-dimensional numerical simulations. We find that the above convectively stable zone can be partitioned into three layers: the thermal adjustment layer (mixing both entropy and material), the turbulent dissipation layer (mixing material but not entropy), and the thermal dissipation layer (mixing neither entropy nor material). The turbulent dissipation layer is separated from the thermal adjustment layer and the thermal dissipation layer by the first and second zero-points of the vertical velocity correlation. The simulation results are in good agreement with the prediction of the one-dimensional turbulent Reynolds stress model. First, the layer structure is similar. Second, the upper boundary of the thermal adjustment layer is close to the peak of the magnitude of the temperature perturbation. Third, the Péclet number at the upper boundary of the turbulent dissipation layer is close to 1. In addition, we have studied the scalings of the overshooting distance on the relative stability parameter S, the Prandtl number Pr, and the Péclet number Pe. The scaling on S is not unique. The trend is that the overshooting distance decreases with S. Fitting on Pr shows that the overshooting distance increases with Pr. Fitting on Pe shows that the overshooting distance decreases with Pe. Finally, we calculate the ratio of the thickness of the turbulent dissipation layer to that of the thermal adjustment layer. The ratio remains almost constant, with an approximate value of 2.4.

We present an eccentric precessing gas disk model designed to study the variable circumstellar absorption features detected for WD 1145+017, a metal polluted white dwarf with an actively disintegrating asteroid around it. This model, inspired by one recently proposed by Cauley et al., calculates explicitly the gas opacity for any predetermined physical conditions in the disk, predicting the strength and shape of all absorption features, from the UV to the optical, at any given phase of the precession cycle. The successes and failures of this simple model provide valuable insight on the physical characteristics of the gas surrounding the star, notably its composition, temperature, and density. This eccentric disk model also highlights the need for supplementary components, most likely circular rings, in order to explain the presence of zero velocity absorption as well as highly ionized Si iv lines. We find that a precession period of 4.6 ± 0.3 yr can successfully reproduce the shape of the velocity profile observed at most epochs from 2015 April to 2018 January, although minor discrepancies at certain times indicate that the assumed geometric configuration may not be optimal yet. Finally, we show that our model can quantitatively explain the change in morphology of the circumstellar features during transiting events.

Solar particle events that are rich in ³He typically also exhibit large overabundances of heavy and ultraheavy ions that increase with the mass of the ions. To explain these observations we apply our charge-consistent acceleration model, which takes into account the acceleration efficiency as a function of the charge to mass ratio of the ion, as well as the charge-dependent Coulomb energy losses, to consider the acceleration of ions within a wide range of their nuclear charge. Because the considerations of particle acceleration were restricted so far by tabulated values of ionization and recombination coefficients that were available only for a limited set of ions, we make use of our method developed earlier and calculate the rates of ions resembling the three representative mass groups of ultraheavy ions. We demonstrate that smaller Coulomb losses together with higher acceleration efficiency result in the enhancements of heavy and ultraheavy ions, in accordance with recent observations. We also conclude that the existing measurements of ultraheavy ions in impulsive solar energetic particle events provide evidence in favor of a magnetic turbulence in the acceleration region with spectral index S ≥ 2.

We report the discovery of two new pulsating extremely low-mass pre-white dwarf (pre-ELMV) candidates in the Transiting Exoplanet Survey Satellite (TESS) eclipsing binaries, TIC 149160359 and TIC 416264037. Their light curves show a typical feature of EL CVn-type binaries. The light-curve modeling indicates that they are both detached systems with very low-mass ratios (q ≃ 0.1). Based on the photometric solutions, the masses and radii of the two main-sequence primary components are estimated, and those of the secondaries are deduced. The results show that the less-massive components of the two binaries are both probably thermally bloated, pre-ELMVs. Apart from the eclipsing light changes, short-period light variations are clearly shown in their residual light curves. We have made the Fourier analysis of their light-curve residuals with the Period04 program. TIC 149160359 was found to pulsate in 21 independent frequencies, 17 of which are between 21 and 35 day⁻¹ and the others are between 63 and 77 day⁻¹. The Fourier amplitude spectrum of TIC 416264037 also shows two frequency concentration ranges. Out of nine independent frequencies, seven reside within the low-frequency range of 12.5–19.9 day⁻¹. Two pulsating signals, f₄ = 122.2698 day⁻¹ and f₁₀ = 112.3603 day⁻¹, were detected in the high-frequency region. These low-frequency signals that are detected on TIC 149160359 and TIC 416264037 are probably due to the intrinsic pulsations of their δ Sct-type primary components. However, the high-frequency signals are likely to come from the pulsations of the pre-ELM WD components. This brings the number of pre-ELMV candidates to 12.

We investigated the relationship between the spectral structures of type II solar radio bursts in the hectometric and kilometric wavelength ranges and solar energetic particles (SEPs). To examine the statistical relationship between type II bursts and SEPs, we selected 26 coronal mass ejection (CME) events with similar characteristics (e.g., initial speed, angular width, and location) observed by the Large Angle and Spectrometric Coronagraph, regardless of the characteristics of the corresponding type II bursts and the SEP flux. Then, we compared associated type II bursts observed by the Radio and Plasma Wave Experiment on board the Wind spacecraft and the SEP flux observed by the Geostationary Operational Environmental Satellite orbiting around the Earth. We found that the bandwidth of the hectometric type II bursts and the peak flux of the SEPs has a positive correlation (with a correlation coefficient of 0.64). This result supports the idea that the nonthermal electrons of type II bursts and the nonthermal ions of SEPs are generated by the same shock and suggests that more SEPs may be generated for a wider or stronger CME shock with a longer duration. Our result also suggests that considering the spectral structures of type II bursts can improve the forecasting accuracy for the peak flux of gradual SEPs.

The ∼200 H i clouds observed to be entrained in the Fermi bubble wind show a trend of increasing maximum $| {V}_{\mathrm{LSR}}|$ with Galactic latitude. We analyze previous observations and present new data from the Green Bank Telescope that rule out systematic effects as the source of this phenomenon. Instead, it is likely evidence for acceleration of the clouds. The data suggest that clouds in the lower 2 kpc of the Fermi bubbles, within the bubble boundaries established from X-ray studies, have an outflow velocity that rises from ≈150 to 200 $\mathrm{km}\,{{\rm{s}}}^{-1}$ close to the Galactic center and reaches ≈330 $\mathrm{km}\,{{\rm{s}}}^{-1}$ at a distance of 2.5–3.5 kpc. These parameters are also consistent with the kinematics of ultraviolet absorption lines from highly ionized species observed against two targets behind the Fermi bubbles at b = −66 and b = +112. The implied neutral cloud lifetime is 4–10 Myr.

In this work, we reexamine sulfur chemistry occurring on and in the ice mantles of interstellar dust grains, and report the effects of two new modifications to standard astrochemical models: namely, (a) the incorporation of cosmic-ray-driven radiation chemistry and (b) the assumption of fast, nondiffusive reactions for key radicals in the bulk. Results from our models of dense molecular clouds show that these changes can have a profound influence on the abundances of sulfur-bearing species in ice mantles, including a reduction in the abundance of solid-phase H₂S and HS, and a significant increase in the abundances of OCS, SO₂, as well as pure allotropes of sulfur, especially S₈. These pure-sulfur species—though nearly impossible to observe directly—have long been speculated to be potential sulfur reservoirs and our results represent possibly the most accurate estimates yet of their abundances in the dense interstellar medium. Moreover, the results of these updated models are found to be in good agreement with available observational data. Finally, we examine the implications of our findings with regard to the as-yet-unknown sulfur reservoir thought to exist in dense interstellar environments.