Table of contents

We report ALMA observations of NGC 1333 IRAS 4A, a young low-mass protostellar binary, whose components are referred to as 4A1 and 4A2. With multiple H₂CO transitions and HNC (4−3) observed at a resolution of 025 (∼70 au), we investigate the gas kinematics of 4A1 and 4A2. Our results show that on the large angular scale (∼10''), 4A1 and 4A2 each display a well-collimated outflow along the N–S direction, and an S-shaped morphology is discerned in the outflow powered by 4A2. On the small scale (∼03), 4A1 and 4A2 exhibit distinct spectral features toward the continuum centroid, with 4A1 showing simple symmetric profiles predominantly in absorption and 4A2 demonstrating rather complicated profiles in emission as well as in absorption. Based on radiative transfer modeling exercises, we find that the physical parameters inferred from earlier low-resolution observations cannot be directly extrapolated down to the inner region of 4A1. Possible reasons for the discrepancies between the observed and modeled profiles are discussed. We constrain the mass infall rate in 4A1 to be at most around 3 × 10⁻⁵M_⊙ yr⁻¹ at the layer of 75 au. For the kinematics of the inner envelope of 4A2, the absorbing dips in the H₂CO spectra are skewed toward the redshifted side and likely signatures of inward motion. These absorbing dips are relatively narrow. This is, like the case for 4A1, significantly slower than the anticipated inflow speed. We estimate a mass infall rate of (3.1–6.2) × 10⁻⁵M_☉ yr⁻¹ at the layer of 100 au in 4A2.

The evolution of an accreting white dwarf (WD) with a strong magnetic field toward a Type Ia supernova (SN Ia) may differ from the classical single-degenerate (SD) channel. In this paper, we perform binary population synthesis simulations for the SD channel with a main-sequence (MS) companion, including the strongly magnetized WD accretion. Under a reasonable assumption that the fraction of such systems is ∼15%, the resulting delay-time distribution roughly follows the t⁻¹ power-law distribution. Within the (WD/MS) SD channel, the contribution from the highly magnetized WD is estimated to be comparable to that from the classical, non-magnetized WD channel. The contribution of the SD channel toward SNe Ia can be at least ∼30% among the whole SN Ia population. We suggest that the SNe Ia resulting from the highly magnetized WD systems would not share the observational properties expected for the classical SD channel; for every (potentially peculiar) SN observationally associated with the SD channel, we expect a comparable number of the "hidden" SD population to be in the normal class.

We present the stellar mass–[Fe/H] and mass–[Mg/H] relation of quiescent galaxies in two galaxy clusters at z ∼ 0.39 and z ∼ 0.54. We derive the age, [Fe/H], and [Mg/Fe] for each individual galaxy using a full-spectrum fitting technique. By comparing with the relations for z ∼ 0 Sloan Digital Sky Survey galaxies, we confirm our previous finding that the mass–[Fe/H] relation evolves with redshift. The mass–[Fe/H] relation at higher redshift has lower normalization and possibly steeper slope. However, based on our sample, the mass–[Mg/H] relation does not evolve over the observed redshift range. We use a simple analytic chemical evolution model to constrain the average outflow that these galaxies experience over their lifetime, via the calculation of mass-loading factor. We find that the average mass-loading factor η is a power-law function of galaxy stellar mass, $\eta \propto {M}_{* }^{-0.21\pm 0.09}$. The measured mass-loading factors are consistent with the results of other observational methods for outflow measurements and with the predictions where outflow is caused by star formation feedback in turbulent disks.

Recent observations show cool, oscillating prominence threads fading when observed in cool spectral lines and appearing in warm spectral lines. A proposed mechanism to explain the observed temperature evolution is that the threads were heated by turbulence driven by the Kelvin–Helmholtz instability that developed as a result of wave-driven shear flows on the surface of the thread. As the Kelvin–Helmholtz instability is an instability that works to mix the two fluids on either side of the velocity shear layer, in the solar corona it can be expected to work by mixing the cool prominence material with that of the hot corona to form a warm boundary layer. In this paper, we develop a simple phenomenological model of nonlinear Kelvin–Helmholtz mixing, using it to determine the characteristic density and temperature of the mixing layer. For the case under study, with constant pressure across the two fluids, these quantities are ${\rho }_{\mathrm{mixed}}=\sqrt{{\rho }_{1}{\rho }_{2}}$ and ${T}_{\mathrm{mixed}}=\sqrt{{T}_{1}{T}_{2}}$. One result from the model is that it provides an accurate—as determined by comparison with simulation results—determination of the kinetic energy in the mean velocity field. A consequence of this is that the magnitude of turbulence—and with it, the energy that can be dissipated on fast timescales—as driven by this instability can be determined. For the prominence–corona system, the mean temperature rise possible from turbulent heating is estimated to be less than 1% of the characteristic temperature (which is found to be T_mixed = 10⁵ K). These results highlight that mixing, and not heating, is likely to be the cause of the observed transition between cool to warm material. One consequence of this result is that the mixing creates a region with higher radiative loss rates on average than either of the original fluids, meaning that this instability could contribute a net loss of thermal energy from the corona, i.e., coronal cooling.

We present an analysis of the kinematic properties of stellar populations in the Galactic halo, making use of over 100,000 main-sequence turnoff (MSTO) stars observed in the Sloan Digital Sky Survey. After dividing the Galactic halo into an inner-halo region (IHR) and outer-halo region (OHR), based on the spatial variation of carbon-to-iron ratios in the sample, we find that stars in the OHR exhibit a clear retrograde motion of −49 ± 4 km s⁻¹ and a more spherical distribution of stellar orbits, while stars in the IHR have zero net rotation (−3 ± 1 km s⁻¹) with a much more radially biased distribution of stellar orbits. Furthermore, we classify the carbon-enhanced metal-poor (CEMP) stars among the MSTO sample in each halo component into CEMP-no and CEMP-s subclasses, based on their absolute carbon abundances, A(C), and examine the spatial distributions and kinematics associated with each subclass. The CEMP-no stars are the majority subclass of CEMP stars in the OHR (∼65%), and the minority subclass in the IHR (∼44%), similar to the results of several previous analyses. The CEMP-no stars in each halo region exhibit slightly higher counterrotation than the CEMP-s stars, but within statistical errors. The CEMP-no stars also show a more spherical distribution of orbits than the CEMP-s stars in each halo region. These distinct characteristics provide strong evidence that numerous low-mass satellite galaxies (similar to the ultra-faint dwarf galaxies) have donated stars to the OHR, while more massive dwarf galaxies provided the dominant contribution to the IHR.

We have studied double-detonation explosions in double-degenerate (DD) systems with different companion white dwarfs (WDs) for modeling Type Ia supernovae (SNe Ia) by means of high-resolution smoothed particle hydrodynamics (SPH) simulations. We have found that only the primary WDs explode in some of the DD systems, while the explosions of the primary WDs induce the explosions of the companion WDs in the other DD systems. The former case is a so-called dynamically-driven double-degenerate double-detonation (D⁶) explosion, or helium-ignited violent merger explosion. The SN ejecta of the primary WDs strip materials from the companion WDs, whose mass is ∼10⁻³M_⊙. The stripped materials contain carbon and oxygen when the companion WDs are carbon–oxygen (CO) WDs with He shells ≲0.04 M_⊙. Since they contribute to low-velocity ejecta components as observationally inferred for iPTF14atg, D⁶ explosions can be counterparts of subluminous SNe Ia. The stripped materials may contribute to low-velocity C seen in several SNe Ia. In the latter case, the companion WDs explode through He detonation if they are He WDs and through the double-detonation mechanism if they are CO WDs with He shells. We name these explosions "triple" and "quadruple" detonation (TD/QD) explosions after the number of detonations. The QD explosion may be counterparts of luminous SNe Ia, such as SN 1991T and SN 1999aa, since they yield a large amount of ⁵⁶Ni, and their He-detonation products contribute to the early emissions accompanying such luminous SNe Ia. On the other hand, the TD explosion may not yield a sufficient amount of ⁵⁶Ni to explain luminous SNe Ia.

Orion BN/KL is an example of a poorly understood phenomena in star-forming regions involving the close encounters of young stellar objects. The explosive structure, the great variety of molecules observed, the energy involved in the event, and the mass of the region suggest a contribution to the chemical diversity of the local interstellar medium. Nevertheless, the frequency and duration of other, similar events have not been determined. In this paper, we explore a recent analytic model that takes into account the interaction of a clump with its molecular environment. We show that the widespread kinematic ages of the Orion fingers—500 to 4000 yr—are a consequence of the interaction of the explosion debris with the surrounding medium. This model explains satisfactorily the age discrepancy of the Orion fingers, and infers the initial conditions together with the lifetime of the explosion. Moreover, our model can explain why some CO streamers do not have an associated H₂ finger.

We present results of our Chandra/ACIS observations of the field centered on the fast, runaway O star AE Aur and its bow shock. Previous XMM-Newton observations revealed an X-ray "blob" near the IR arc tracing the bow shock, possibly a nonthermal source consistent with models of Inverse Compton scattering of dust IR photons by electrons accelerated at the shock. The new, subarcsecond-resolution Chandra data, while confirming the presence of the XMM-Newton source, clearly indicate that the latter is neither extended nor coincident with the IR arc and strongly suggest it is a background active galactic nucleus. Motivated by results published for the bow shock of BD+43°3654, we extended our study to the radio domain by analyzing archival EVLA data. We find no radio emission from the AE Aur bow shock either. The corresponding upper limits for the absorbed (unabsorbed) X-ray flux of 5.9(7.8) × 10⁻¹⁵ erg cm⁻² s⁻¹ (3σ) and, in the radio range of 2 mJy (1.4 GHz) and 0.4 mJy (5.0 GHz), are used to put constraints on model predictions for particle acceleration within the bow shock. In the "classical" framework of diffusive shock acceleration, we find that the predicted X-ray and radio emission by the bow shock is at least two orders of magnitude below the current upper limits, consistent with the systematic nondetections of up to 60 stellar bow shocks. The only exception so far remains that of BD+43°3654, which is probably the result of its very large mass-loss rate among runaway O stars.

With the aim of characterizing the dynamical processes involved in the formation of young protostars, we present high-angular-resolution ALMA dust polarization observations of the Class 0 protostellar cores Serpens SMM1, Emb 8(N), and Emb 8. With spatial resolutions ranging from 150 to 40 au at 870 μm, we find unexpectedly high values of the polarization fraction along the outflow cavity walls in Serpens Emb 8(N). We use 3 mm and 1 mm molecular tracers to investigate outflow and dense-gas properties and their correlation with the polarization. These observations allow us to investigate the physical processes involved in the radiative alignment torques (RATs) acting on dust grains along the outflow cavity walls, which experience irradiation from accretion processes and outflow shocks. The inner core of SMM1-a presents a polarization pattern with a poloidal magnetic field at the bases of the two lobes of the bipolar outflow. To the south of SMM1-a we see two polarized filaments, one of which seems to trace the redshifted outflow cavity wall. The other may be an accretion streamer of material infalling onto the central protostar. We propose that the polarized emission we see at millimeter wavelengths along the irradiated cavity walls can be reconciled with the expectations of RAT theory if the aligned grains present at <500 au scales in Class 0 envelopes have grown larger than the 0.1 μm size of dust grains in the interstellar medium. Our observations allow us to constrain the magnetic field morphologies of star-forming sources within the central cores, along the outflow cavity walls, and in possible accretion streamers.

In this work, archive 1.4 and 4.86 GHz radio continuum data from the Very Large Array were re-reduced and, together with the 1.4 GHz maps from the NRAO VLA Sky Survey, investigated for the presence of detectable, nonthermal continuum radio emission that could be associated with the tidal dwarf galaxy (TDG) candidates in HCG 26, 91, and 96. Radio emission highly coincident with the optical and H_α emission maxima of the TDG candidate HCG 91i (estimated physical separation of less than 150 pc) was revealed. Should this emission be intrinsic to this object, it would imply the presence of a magnetic field as strong as 11–16 μG—comparable to that found in the most radio-luminous, star-forming dwarf galaxies of non-tidal origin. However, the star formation rate derived for this object using the radio flux is about two orders of magnitude higher than the one estimated from the H_α data. Analysis of the auxiliary radio, ultraviolet, and infrared data suggests that either the radio emission originates in a background object with an aged synchrotron spectrum (possibly a GHz-peaked source), or the ${\mathrm{SFR}}_{{{\rm{H}}}_{\alpha }}$ estimate is lower due to the fact that it traces the most recent star formation, while most of the detected radio emission originated when what is known as HCG 91i was still a part of its parent galaxy. The latter scenario is supported by a very large stellar mass derived from 3.6 to 4.5 μm data, implying a high star formation rate in the past.

We report a 3.4σ detection of the warm–hot, massive, extended circumgalactic medium (CGM) around an L^⋆ star-forming spiral galaxy NGC 3221, using deep Suzaku observations. The temperature of the gas is 10^6.1 K, comparable to that of the Milky Way CGM. The spatial extent of the gas is at least 150 kpc. For a β-model of density profile with solar abundance, the central emission measure is EM = (3 ± 1) × 10⁻⁵ cm⁻⁶ kpc and the central electron density is n_eo = (4 ± 1) × 10⁻⁴ cm⁻³, with a slope of β = 0.56. We investigate a range of β values and find that the details of the density profile do not change our results significantly. The mass of the warm–hot gas, assuming a metallicity of $\tfrac{1}{3}$Z_⊙, is (16 ± 3) × 10¹⁰M_⊙, which is the most massive baryon component of NGC 3221. The baryon fraction is f_b = 0.120 ± 0.036 (statistical) ${}_{-0.048}^{+0.104}$ (systematic), consistent with the cosmological mean value, closing the baryon budget of this galaxy. We also investigated the missing metals problem in conjunction with the missing baryons problem and conclude that metals are likely to be preferentially expelled from the galaxy. Ours is the first detection of an extended warm–hot CGM around an external L^⋆ star-forming spiral galaxy, where the CGM likely accounts for the missing galactic baryons.

Supersonic turbulence results in strong density fluctuations in the interstellar medium (ISM), which have a profound effect on the chemical structure. Particularly useful probes of the diffuse ISM are the ArH⁺, OH⁺, H₂O⁺ molecular ions, which are highly sensitive to fluctuations in the density and the H₂ abundance. We use isothermal magnetohydrodynamic simulations of various sonic Mach numbers, ${{ \mathcal M }}_{{\rm{s}}}$, and density decorrelation scales, y_dec, to model the turbulent density field. We post process the simulations with chemical models and obtain the probability density functions (PDFs) for the H₂, ArH⁺, OH⁺, and H₂O⁺ abundances. We find that the PDF dispersions increases with increasing ${{ \mathcal M }}_{{\rm{s}}}$ and y_dec, as the magnitude of the density fluctuations increases, and as they become more coherent. Turbulence also affects the median abundances: when ${{ \mathcal M }}_{{\rm{s}}}$ and y_dec are high, low-density regions with low H₂ abundance become prevalent, resulting in an enhancement of ArH⁺ compared to OH⁺ and H₂O⁺. We compare our models with Herschel observations. The large scatter in the observed abundances, as well as the high observed ArH⁺/OH⁺ and ArH⁺/H₂O⁺ ratios are naturally reproduced by our supersonic $({{ \mathcal M }}_{{\rm{s}}}=4.5)$, large decorrelation scale (y_dec = 0.8) model, supporting a scenario of a large-scale turbulence driving. The abundances also depend on the ultraviolet intensity, cosmic-ray ionization rate, and the cloud column density, and the observed scatter may be influenced by fluctuations in these parameters.

We report the discovery of an exceptional MIR flare in a Type 2 AGN, SDSS J165726.81+234528.1, at z = 0.059. This object brightened by 3 mag in the Wide-field Infrared Survey Explorer (WISE) W1 and W2 bands between 2015 and 2017 (and has been fading since 2018), without significant changes (≲0.2 mag) in the optical over the same period of time. Based on the WISE light curves and near-IR imaging, the flare is more significant at longer wavelengths, suggesting an origin of hot dust emission. The estimated black hole mass (∼10^6.5M_⊙) from different methods places its peak bolometric luminosity around the Eddington limit. The high luminosity of the MIR flare and its multiyear timescale suggest that it most likely originated from reprocessed dust radiation in an extended torus surrounding the AGN, instead of from stellar explosions. The MIR color variability is consistent with known changing-look AGN and tidal disruption events (TDEs), but inconsistent with normal supernovae. We suggest that it is a turning-on Type 2 AGN or TDE, where the optical variability is obscured by the dust torus during the transition. This MIR flare event reveals a population of dramatic nuclear transients that are missed in the optical.

We present a combined radio/X-ray analysis of the poorly studied galaxy cluster A2495 (z = 0.07923) based on new EVLA and Chandra data. We also analyze and discuss Hα emission and optical continuum data retrieved from the literature. We find an offset of ∼6 kpc between the cluster brightest cluster galaxy (BCG) (MCG+02-58-021) and the peak of the X-ray emission, suggesting that the cooling process is not taking place on the central galaxy nucleus. We propose that sloshing of the intracluster medium (ICM) could be responsible for this separation. Furthermore, we detect a second, ∼4 kpc offset between the peak of the Hα emission and that of the X-ray emission. Optical images highlight the presence of a dust filament extending up to ∼6 kpc in the cluster BCG and allow us to estimate a dust mass within the central 7 kpc of 1.7 × 10⁵M_☉. Exploiting the dust-to-gas ratio and the L_Hα–M_mol relation, we argue that a significant amount (up to 10⁹M_☉) of molecular gas should be present in the BCG of this cluster. We also investigate the presence of ICM depressions, finding two putative systems of cavities; the inner pair is characterized by t_age ∼ 18 Myr and P_cav ∼ 1.2 × 10⁴³ erg s⁻¹, the outer one by t_age ∼ 53 Myr and P_cav ∼ 5.6 × 10⁴² erg s⁻¹. Their age difference appears to be consistent with the freefall time of the central cooling gas and with the offset timescale estimated with the Hα kinematic data, suggesting that sloshing is likely playing a key role in this environment. Furthermore, the cavities' power analysis shows that the active galactic nucleus energy injection is able to sustain the feedback cycle, despite cooling being offset from the BCG nucleus.

High inclination black hole X-ray binaries exhibit blueshifted ionized absorption lines from disk winds, whose launching mechanism is still in debate. The lines are predominantly observed in the high/soft state and disappear in the low/hard state, anticorrelated with the jet. We have tested if the thermal winds, which are driven by the irradiation of the outer disk by the X-rays from the inner disk, can explain these observed properties or whether we need a magnetic switch between jet and wind. We use analytic thermal-radiative wind models to predict the column density, ionization parameter, and velocity of the wind given the broadband continuum shape and luminosity determined from the Rossi X-ray Timing Explorer (RXTE) monitoring. We use these to simulate the detailed photoionized absorption features predicted at epochs where there are Chandra high-resolution spectra. These include low/hard, high/soft, and very high states. The model was found to well reproduce the observed lines in the high/soft state, and it also successfully predicts their disappearance in the low/hard state. However, the simplest version of the thermal wind model also predicts that there should be strong features observed in the very high state, which are not seen in the data. Nonetheless, we show this is consistent with thermal winds when we include self-shielding by the irradiated inner disk atmosphere. These results indicate that the evolution of observed wind properties in different states during outbursts in H1743−322 can be explained by the thermal wind model and does not require magnetic driving.

The onset of cool massive winds in evolved giants is correlated with an evolutionary feature on the red giant branch (RGB) known as the "bump." Also at the bump, shear instability in the star leads to magnetic fields that occur preferentially on small length-scales. Pneuman has suggested that the emergence of small-scale flux tubes in the Sun can give rise to enhanced acceleration of the solar wind as a result of plasmoid acceleration (the so-called "melon-seed mechanism"). In this paper, we examine Pneuman's formalism to determine if it may shed some light on the process that drives mass loss in stars above the RGB bump. Because we do not currently have detailed information for some of the relevant physical parameters, we are not yet able to derive a detailed model: instead, our goal in this paper is to explore a "proof of concept." Using parameters that are known to be plausible in cool giants, we find that the total mass-loss rate from such stars can be replicated. Moreover, we find that the radial profile of the wind speed in such stars can be steep or shallow depending on the fraction of the mass-loss rate that is contained in the plasmoids: this is consistent with empirical data that indicate that the velocity profiles of winds from cool giants span a range of steepnesses.

Sulfur is one of the most abundant elements in the universe, with important roles in astro-, geo-, and biochemistry. Its main reservoirs in planet-forming disks have previously eluded detection: gaseous molecules only account for <1% of total elemental sulfur, with the rest likely in either ices or refractory minerals. We use a new method to measure the refractory component. Mechanisms such as giant planets can filter out dust from gas accreting onto disk-hosting stars. For stars above 1.4 solar masses, this leaves a chemical signature on the stellar photosphere that can be used to determine the fraction of each element that is locked in dust. Here, we present an application of this method to sulfur, zinc, and sodium. We analyze the accretion-contaminated photospheres of a sample of young stars and find (89 ± 8)% of elemental sulfur is in refractory form in their disks. The main carrier is much more refractory than water ice, consistent with sulfide minerals such as FeS.

As fireball networks grow, the number of events observed becomes unfeasible to manage by manual efforts. Reducing and analyzing big data requires automated data pipelines. Triangulation of a fireball trajectory can swiftly provide information on positions and, with timing information, velocities. However, extending this pipeline to determine the terminal mass estimate of a meteoroid is a complex next step. Established methods typically require assumptions to be made of the physical meteoroid characteristics (such as shape and bulk density). To determine which meteoroids may have survived entry there are empirical criteria that use a fireball's final height and velocity—low and slow final parameters are likely the best candidates. We review the more elegant approach of the dimensionless coefficient method. Two parameters, α (ballistic coefficient) and β (mass loss), can be calculated for any event with some degree of deceleration, given only velocity and height information. α and β can be used to analytically describe a trajectory with the advantage that they are not mere fitting coefficients; they also represent the physical meteoroid properties. This approach can be applied to any fireball network as an initial identification of key events and determine on which to concentrate resources for more in-depth analyses. We used a set of 278 events observed by the Desert Fireball Network to show how visualization in an α–β diagram can quickly identify which fireballs are likely meteorite candidates.

We present a study of the diffuse X-ray emission from the star-forming region LMC-N 57 in the Large Magellanic Cloud. We use archival XMM-Newton observations to unveil in detail the distribution of hot bubbles in this complex. X-ray emission is detected from the central superbubble (SB) DEM L 229, the supernova remnant (SNR) 0532−675, and the Wolf–Rayet (WR) bubble DEM L 231 around the WR star Br 48. Comparison with infrared (IR) images unveils the powerful effect of massive stars in destroying their nurseries. The distribution of the hot gas in the SNR and the SB display their maxima in regions in contact with the filamentary cold material detected by IR images. Our observations do not reveal extended X-ray emission filling DEM L 231, although several pointlike sources are detected in the field of view of this WR nebula. The X-ray properties of Br 48 are consistent with a binary WN4+O as proposed by other authors. We modeled the X-ray emission from the SB and found that its X-ray emission can be simply explained by pressure-driven wind model—that is, there is no need to invoke the presence of an SN explosion as previously suggested. The pressure calculations of the hot gas confirms that the dynamical evolution of SB DEM L 229 is dominated by the stellar winds from the star cluster LH 76.

The Circinus galaxy is a nearby composite starburst/active galactic nucleus (AGN) system. In this work we re-analyze the GeV emission from Circinus with 10 yr of Fermi-LAT Pass 8 data. In the energy range of 1–500 GeV, the spectrum can be well fitted by a power-law model with a photon index of Γ = 2.20 ± 0.14, and its photon flux is (5.90 ± 1.04) × 10⁻¹⁰ photons cm⁻² s⁻¹. Our 0.1–500 GeV flux is several times lower than that reported in previous literature, which is roughly in compliance with the empirical relation for star-forming and Local Group galaxies and might be reproduced by the interaction between cosmic rays and the interstellar medium. The ratio between the γ-ray luminosity and the total infrared luminosity is near the proton calorimetric limit, indicating that Circinus may be a proton calorimeter. However, marginal evidence for variability of the γ-ray emission is found in the timing analysis, which may indicate the activity of an AGN jet. More Fermi-LAT data and future observation of CTA are required to fully reveal the origin of its γ-ray emission.

Protoplanetary disks are dynamic objects, within which dust grains and gas are expected to be redistributed over large distances. Evidence for this redistribution is seen both in other protoplanetary disks and in our own solar system, with high-temperature materials thought to originate close to the central star found in the cold, outer regions of the disks. While models have shown this redistribution is possible through a variety of mechanisms, these models have generally ignored the possible growth of solids via grain–grain collisions that would occur during transit. Here we investigate the interplay of coagulation and radial and vertical transport of solids in protoplanetary disks, considering cases where growth is limited by bouncing or by fragmentation. We find that, in all cases, growth effectively limits the facility for materials to be carried outward or preserved at large distances from the star. This is due to solids being incorporated into large aggregates which drift inward rapidly under the effects of gas drag. We discuss the implications for mixing in protoplanetary disks, and how the preservation of high-temperature materials in outer disks may require structures or outward flow patterns to avoid them being lost via radial drift.

To extract the information that the Mg ii NUV spectra (observed by the Interface Region Imaging Spectrograph) carry about the chromosphere during solar flares, and to validate models of energy transport via model–data comparison, forward modeling is required. The assumption of statistical equilibrium (SE) is typically used to obtain the atomic level populations from snapshots of flare atmospheres, due to computational necessity. However, it is possible that relying on SE could lead to spurious results. We compare solving the atomic level populations via SE versus a nonequilibrium (NEQ) time-dependent approach. This was achieved using flare simulations from RADYN alongside the minority species version MS_RADYN from which the time-dependent Mg ii atomic level populations and radiation transfer were computed in complete frequency redistribution. The impacts on the emergent profiles, lightcurves, line ratios, and formation heights are discussed. In summary we note that NEQ effects during flares are typically important only in the initial stages and for a short period following the cessation of the energy injection. An analysis of the timescales of ionization equilibrium reveals that for most of the duration of the flare, when the temperatures and densities are sufficiently enhanced, the relaxation timescales are short (τ_relax < 0.1 s), so that the equilibrium solution is an adequate approximation. These effects vary with the size of the flare, however. In weaker flares, effects can be more pronounced. We recommend that NEQ effects be considered when possible but that SE is sufficient at most stages of the flare.

A novel tool aimed to detect solar coronal mass ejections (CMEs) at the Lagrangian point L1 and to forecast their geoeffectiveness is presented in this paper. This approach is based on the analysis of in situ magnetic field and plasma measurements to compute some important magnetohydrodynamic quantities of the solar wind (the total pressure, the magnetic helicity, and the magnetic and kinetic energy), which are used to identify the CME events, that is their arrival and transit times, and to assess their likelihood for impacting the Earths magnetosphere. The method is essentially based on the comparison of the topological properties of the CME magnetic field configuration and of the CME energetic budget with those of the quasi-steady ambient solar wind. The algorithm performances are estimated by testing the tool on solar wind data collected in situ by the Wind spacecraft from 2005 to 2016. In the scanned 12 yr time interval, it results that (i) the procedure efficiency is of 86% for the weakest magnetospheric disturbances, increasing with the level of the geomagnetic storming, up to 100% for the most intense geomagnetic events, (ii) zero false positive predictions are produced by the algorithm, and (iii) the mean delay between the potentially geoeffective CME detection and the geomagnetic storm onset if of 4 hr, with a 98% 2–8 hr confidence interval. Hence, this new technique appears to be very promising in forecasting space weather phenomena associated to CMEs.

The nuclear symmetry energy plays a role in determining both the nuclear properties of terrestrial matter as well as the astrophysical properties of neutron stars. The first measurement of the neutron star tidal deformability, from gravitational-wave event GW170817, provides a new way of probing the symmetry energy. In this work, we report on new constraints on the symmetry energy from GW170817. We focus in particular on the low-order coefficients: namely, the value of the symmetry energy at the nuclear saturation density, S₀, and the slope of the symmetry energy, L₀. We find that the gravitational-wave data are relatively insensitive to S₀, but that they depend strongly on L₀ and point to lower values of L₀ than have previously been reported, with a peak likelihood near L₀ ∼ 23 MeV. Finally, we use the inferred posteriors on L₀ to derive new analytic constraints on higher-order nuclear terms.

Our recent investigations indicate that interplanetary magnetic clouds (MCs) have a high-twist core and a weak-twist outer shell. Utilizing the velocity-modified uniform-twist force-free flux rope model, we further investigate the relationship between the twist profile of magnetic field lines and the distribution of the plasma poloidal angular velocity inside an MC. The poloidal velocity in the MC is 11 km s⁻¹. There are evidently positive correlations between the absolute value of the twist and the plasma poloidal angular velocity in peeled flux ropes or flux rope layers, although the correlation coefficients in flux rope layers are less than those in peeled flux ropes. This finding suggests that plasma flows are frozen-in magnetic field lines as we expected for interplanetary medium, of which the magnetic Reynolds number is large. Furthermore, based on this picture, we infer the axial velocity in the MC frame, which is less than 10 km s⁻¹ and almost uniform in the cross section of the MC. Besides, it is inferred that the plasma flows velocity in the MC is much less than the local Alfvén speed.

The X-ray pulsar SMC X-1 shows a superorbital modulation with an unstable cycle length in the X-ray band. We present its timing behaviors, including the spin, orbital, and superorbital modulations, beyond the end of the Rossi X-ray Timing Explorer mission. The time-frequency maps derived by the wavelet Z-transform and the Hilbert–Huang transform suggest that a new superorbital period excursion event occurred in ∼MJD 57,100 (2015 March). This indicates that the excursion is recurrent and probably (quasi)periodic. The hardness ratio obtained with the Monitor of All-sky X-ray Image (MAXI) suggests increased absorption during the transition from the high to the low state in the superorbital cycle. Compared to the regular epochs, the superorbital profile during the excursion epochs has a shallower and narrower valley, likely caused by a flatter warp. By tracking the spin period evolution with the MAXI Gas Slit Camera in 2–20 keV, we derive an averaged spin-up rate of $\dot{\nu }=2.515(3)\times {10}^{-11}$ s⁻² during the period between MJD 55,141 (2009 November) and 58,526 (2019 February). We obtain no positive correlation between the spin frequency residual and the superorbital frequency, but a torque change accompanying the superorbital period excursion is possible. We suggest that the accretion torque on the neutron star could be changed by various mechanisms, including the change of mass accretion rate and the warp angle. We update the value of the orbital decay as ${\dot{P}}_{\mathrm{orb}}/{P}_{\mathrm{orb}}=-3.380(6)\times {10}^{-6}$ yr⁻¹. Finally, we reconfirm the detection of the superorbital modulation in the optical band and its coherence in phase with the X-ray modulation.

Previous studies have analyzed the energy injection into the interstellar matter due to molecular bubbles. They found that the total kinetic energies of bubbles are comparable to, or even larger than, those of outflows but still less than the gravitational potential and turbulence energies of the hosting clouds. We examined the possibility that previous studies underestimated the energy injection due to being unable to detect dim or incomplete bubbles. We simulated typical molecular bubbles and inserted them into the ¹³CO Five College Radio Astronomical Observatory maps of the Taurus and Perseus Molecular Clouds. We determined bubble identification completeness by applying the same procedures to both simulated and real data sets. We proposed a detectability function for both the Taurus and Perseus molecular clouds based on a multivariate approach. In Taurus, bubbles with kinetic energy less than ∼1 × 10⁴⁴ erg are likely to be missed. We found that the total missing kinetic energy in Taurus is less than a couple of 10⁴⁴ erg, which only accounts for around 0.2% of the total kinetic energy of identified bubbles. In Perseus, bubbles with kinetic energy less than ∼2 × 10⁴⁴ erg are likely to be missed. We found that the total missing kinetic energy in Perseus is less than 10⁴⁵ erg, which only accounts for around 1% of the total kinetic energy of identified bubbles. We thus conclude that previous manual bubble identification routines used in Taurus and Perseus can be considered to be energetically complete. Therefore, we confirm that energy injection from dynamic structures, namely outflows and bubbles, produced by star formation feedback are sufficient to sustain turbulence at a spatial scale from ∼0.1 to ∼2.8 pc.

It is widely believed that water and complex organic molecules (COMs) first form in the ice mantle of dust grains and are subsequently returned into the gas due to grain heating by intense radiation of protostars. Previous research on the desorption of molecules from the ice mantle assumed that grains are at rest, which is contrary to the fact that grains are suprathermally rotating as a result of their interaction with an anisotropic radiation or gas flow. To clearly understand how molecules are released into the gas phase, the effect of grain suprathermal rotation on surface chemistry must be quantified. In this paper, we study the effect of suprathermal rotation of dust grains spun-up by radiative torques on the desorption of molecules from icy grain mantles around protostars. We show that centrifugal potential energy due to grain rotation reduces the potential barrier of molecules and significantly enhances their desorption rate. We term this mechanism rotational-thermal or ro-thermal desorption. We apply the ro-thermal mechanism for studying the desorption of molecules from icy grains that are simultaneously heated to high temperatures and spun-up to suprathermal rotation by an intense radiation of protostars. We find that ro-thermal desorption is much more efficient than thermal desorption for molecules with high binding energy such as water and COMs. Our results have important implications for understanding the origin of COMs detected in star-forming regions and call for attention to the effect of suprathermal rotation of icy grains to use molecules as a tracer of physical conditions of star-forming regions.

Infrared observations of active galactic nuclei (AGNs) reveal emission from the putative dusty circumnuclear "torus" invoked by AGN unification, which is heated up by radiation from the central accreting black hole (BH). The strong 9.7 and 18 μm silicate features observed in the AGN spectra, in both emission and absorption, further indicate the presence of such dusty environments. We present detailed calculations of the chemistry of silicate dust formation in AGN accretion disk winds. The winds considered herein are magnetohydrodynamic winds driven off the entire accretion disk domain that extends from the BH vicinity to the radius of BH influence, of order ∼1–100 pc depending on the mass of the resident BH. Our results indicate that these winds provide conditions conducive to the formation of significant amounts of dust, especially for objects accreting close to their Eddington limit, making AGNs a significant source of dust in the universe, especially for luminous quasars. Our models justify the importance of an r⁻¹ density law in the winds for efficient formation and survival of dust grains. The dust production rate scales linearly with the mass of the central BH and varies as a power law of index between 2 and 2.5 with the dimensionless mass accretion rate. The resultant distribution of the dense dusty gas resembles a toroidal shape, with high column density and optical depths along the equatorial viewing angles, in agreement with the AGN unification picture.

We perform cosmological hydrodynamic simulations to study the effect of gas fragmentation on the formation of supermassive black hole seeds in the context of Direct Collapse. Our setup considers different UV background intensities, host halo spins, and halo merger histories. We observe that our low-spin halos are consistent with the Direct Collapse model when they are irradiated by a UV background of J₂₁ = 10,000. In these cases, a single massive object ∼10⁵M_⊙ is formed in the center of the halo. On the other hand, in our simulations irradiated by a UV background of J₂₁ = 10, we see fragmentation and the formation of various less massive seeds. These fragments have masses of 10³–10⁴M_⊙. These values are still significant if we consider the potential mergers between them and the fact that these minor objects are formed earlier in cosmic time compared to the massive single seeds. Moreover, in one of our simulations, we observe gas fragmentation even in the presence of a strong UV intensity. This structure arises in a dark matter halo that forms after various merger episodes, becoming the structure with the highest spin value. The final black hole seed mass is ∼10⁵M_⊙ for this run. From these results, we conclude that fragmentation produces less massive objects; however, they are still prone to merge. In simulations that form many fragments, they all approach the most massive one as the simulations evolve. We see no uniqueness in the strength of the UV intensity value required to form a DCBH since it depends on other factors like the system dynamics in our cases.

Ejecta from the explosion of massive stars (core-collapse supernovae) make an important contribution to dust in the interstellar medium. However, dust formation around supernovae is not a simple process, with the formation of several components over time. In particular, the exact timing is a matter of debate. Here, we demonstrate that the isotopic composition of barium in supernova grains that survived in primitive meteorites constitutes a potential chronometer. For a subset of supernova silicon carbide grains (X1 grains), the Ba isotopes indicate that they formed at roughly the same time, and that, at this time, a substantial fraction of the freshly produced unstable ¹³⁷Cs (half-life 30 yr) had already decayed into ¹³⁷Ba. Application to the ¹³⁷Cs/¹³⁷Ba system of nucleosynthesis models that replicate the abundance patterns of stable neutron capture isotopes in these grains indicates a surprisingly late (∼20 yr) timescale for condensation, a conclusion that naturally rests on the reliability of these models.

We examine the new Galactic supernova remnant (SNR) candidate, G23.11+0.18, as seen by the Murchison Widefield Array radio telescope. We describe the morphology of the candidate and find a spectral index of −0.63 ± 0.05 in the 70–170 MHz domain. Coincident TeV gamma-ray detection in High Energy Stereoscopic System (HESS) data supports the SNR nature of G23.11+0.18 and suggests that G23.11+0.18 is accelerating particles beyond TeV energies, thus making this object a promising new cosmic-ray hadron source candidate. The remnant cannot be seen in current optical, infrared and X-ray data sets. We do find, however, a dip in CO-traced molecular gas at a line-of-sight velocity of ∼85 km s⁻¹, suggesting the existence of a G23.11+0.18 progenitor wind-blown bubble. Furthermore, the discovery of molecular gas clumps at a neighboring velocity toward HESS J1832−085 adheres to the notion that a hadronic gamma-ray production mechanism is plausible toward the north of the remnant. Based on these morphological arguments, we propose an interstellar medium association for G23.11+0.18 at a kinematic distance of 4.6 ± 0.8 kpc.

Type IIb supernovae (SNe) are important candidates to understand mechanisms that drive the stripping of stripped-envelope (SE) supernova (SN) progenitors. While binary interactions and their high incidence are generally cited to favor them as SN IIb progenitors, this idea has not been tested using models covering a broad parameter space. In this paper, we use non-rotating single- and binary-star models at solar and low metallicities spanning a wide parameter space in primary mass, mass ratio, orbital period, and mass transfer efficiencies. We find that our single- and binary-star models contribute to roughly equal, however small, numbers of SNe IIb at solar metallicity. Binaries only dominate as progenitors at low metallicity. We also find that our models can account for less than half of the observationally inferred rate for SNe IIb at solar metallicity, with computed rates ≲4% of core-collapse (CC) SNe. On the other hand, our models can account for the rates currently indicated by observations at low metallicity, with computed rates as high as 15% of CC SNe. However, this requires low mass transfer efficiencies (≲0.1) to prevent most progenitors from entering contact. We suggest that the stellar wind mass-loss rates at solar metallicity used in our models are too high. Lower mass-loss rates would widen the parameter space for binary SNe IIb at solar metallicity by allowing stars that initiate mass transfer earlier in their evolution to reach CC without getting fully stripped.

We compile and analyze approximately 200 trigonometric parallaxes and proper motions of molecular masers associated with very young high-mass stars. Most of the measurements come from the BeSSeL Survey using the VLBA and the Japanese VERA project. These measurements strongly suggest that the Milky Way is a four-arm spiral, with some extra arm segments and spurs. Fitting log-periodic spirals to the locations of the masers, allowing for "kinks" in the spirals and using well-established arm tangencies in the fourth Galactic quadrant, allows us to significantly expand our view of the structure of the Milky Way. We present an updated model for its spiral structure and incorporate it into our previously published parallax-based distance-estimation program for sources associated with spiral arms. Modeling the three-dimensional space motions yields estimates of the distance to the Galactic center, ${R}_{0}=8.15\pm 0.15\,\mathrm{kpc}$, the circular rotation speed at the Sun's position, ${{\rm{\Theta }}}_{0}=236\pm 7$ km s⁻¹, and the nature of the rotation curve. Our data strongly constrain the full circular velocity of the Sun, ${{\rm{\Theta }}}_{0}+{V}_{\odot }=247\pm 4$ km s⁻¹, and its angular velocity, $({{\rm{\Theta }}}_{0}+{V}_{\odot })/{R}_{0}=30.32\pm 0.27$ km s⁻¹ kpc^–1. Transforming the measured space motions to a Galactocentric frame which rotates with the Galaxy, we find non-circular velocity components typically ≲10 km s⁻¹. However, near the Galactic bar and in a portion of the Perseus arm we find significantly larger non-circular motions. Young high-mass stars within 7 kpc of the Galactic center have a scale height of only 19 pc, and thus are well suited to define the Galactic plane. We find that the orientation of the plane is consistent with the IAU-defined plane to within ±01, and that the Sun is offset toward the north Galactic pole by ${Z}_{\odot }=5.5\pm 5.8$ pc. Accounting for this offset places the central supermassive black hole, Sgr A*, in the midplane of the Galaxy. The measured motions perpendicular to the plane of the Galaxy limit precession of the plane to ≲4 km s⁻¹ at the radius of the Sun. Using our improved Galactic parameters, we predict the Hulse–Taylor binary pulsar to be at a distance of 6.54 ± 0.24 kpc, assuming its orbital decay from gravitational radiation follows general relativity.

Hydrodynamic simulations of a giant impact to proto-Uranus indicated that such an impact could tilt its rotational axis and produce a circumplanetary debris disk beyond the corotation radius of Uranus. However, whether Uranian satellites can actually be formed from such a wide disk remains unclear. Herein, we modeled a wide debris disk of solids with several initial conditions inferred from the hydrodynamic simulations and performed N-body simulations to investigate in situ satellite formation from the debris disk. We also took account of orbital evolutions of satellites due to the planetary tides after the growth of satellites. We found that, in any case, the orbital distribution of the five major satellites could not be reproduced from the disk as long as the power index of its surface density is similar to that of the disk generated just after the giant impact. Satellites in the middle region obtained much larger masses than Ariel or Umbriel, while the outermost satellites did not grow to the mass of Oberon. Our results indicate that we should consider the thermal and viscous evolution of the evaporated disk after the giant impact to form the five major satellites through the in situ formation scenario. On the other hand, the small inner satellites would be formed from the rings produced by the disrupted satellites that migrated from around the corotation radius of Uranus due to the planetary tides.

Supernova detection is a major objective of the Super-Kamiokande (SK) experiment. In the next stage of SK (SK-Gd), gadolinium (Gd) sulfate will be added to the detector, which will improve the ability of the detector to identify neutrons. A core-collapse supernova (CCSN) will be preceded by an increasing flux of neutrinos and antineutrinos, from thermal and weak nuclear processes in the star, over a timescale of hours; some of which may be detected at SK-Gd. This could provide an early warning of an imminent CCSN, hours earlier than the detection of the neutrinos from core collapse. Electron antineutrino detection will rely on inverse beta decay events below the usual analysis energy threshold of SK, so Gd loading is vital to reduce backgrounds while maximizing detection efficiency. Assuming normal neutrino mass ordering, more than 200 events could be detected in the final 12 hr before core collapse for a 15–25 solar mass star at around 200 pc, which is representative of the nearest red supergiant to Earth, α-Ori (Betelgeuse). At a statistical false alarm rate of 1 per century, detection could be up to 10 hr before core collapse, and a pre-supernova star could be detected by SK-Gd up to 600 pc away. A pre-supernova alert could be provided to the astrophysics community following gadolinium loading.

Rate coefficients have been measured for the reaction of CH radicals with formaldehyde, CH₂O, over the temperature range of 31–133 K using a pulsed Laval nozzle apparatus combined with pulsed laser photolysis and laser-induced fluorescence spectroscopy. The rate coefficients are very large and display a distinct decrease with decreasing temperature below 70 K, although classical collision rate theory fails to reproduce this temperature dependence. The measured rate coefficients have been parameterized and used as input for astrochemical models for both dark cloud and Asymptotic Giant Branch stellar outflow scenarios. The models predict a distinct change (up to a factor of two) in the abundance of ketene, H₂CCO, which is the major expected molecular product of the CH + CH₂O reaction.

We investigate the role of the Keplerian tidal field generated by a supermassive black hole (SMBH) on the three-body dynamics of stellar mass black holes. We consider two scenarios occurring close to the SMBH: the breakup of unstable triples and three-body encounters between a binary and a single. These two cases correspond to the hard and soft binary cases, respectively. The tidal field affects the breakup of triples by tidally limiting the system, so that the triples break earlier with lower breakup velocity, leaving behind slightly larger binaries (relative to the isolated case). The breakup direction becomes anisotropic and tends to follow the shape of the Hill region of the triple, favoring breakups in the radial direction. Furthermore, the tidal field can torque the system, leading to angular momentum exchanges between the triple and its orbit around the SMBH. This process changes the properties of the final binary, depending on the initial angular momentum of the triple. Finally, the tidal field also affects binary-single encounters: binaries tend to become both harder and more eccentric with respect to encounters that occur in isolation. Consequently, single-binary scattering in a deep Keplerian potential produces binaries with shorter gravitational wave merger timescales.

We present results from general relativistic calculations of nuclear ignition in white dwarf stars triggered by near encounters with rotating intermediate mass black holes with different spin and alignment parameters. These encounters create thermonuclear environments characteristic of Type Ia supernovae capable of producing both calcium and iron-group elements in arbitrary ratios, depending primarily on the proximity of the interaction which acts as a strong moderator of nucleosynthesis. We explore the effects of black hole spin and spin-orbital alignment on burn-product synthesis to determine whether they might also be capable of moderating reactive flows. When normalized to equivalent impact penetration, accounting for frame-dragging corrections, the influence of spin is weak, no more than 25% as measured by nuclear energy release and mass of burn products, even for near maximally rotating black holes. Stars on prograde trajectories approach closer to the black hole and produce significantly more unbound debris and iron-group elements than is possible by encounters with nonrotating black holes or by retrograde orbits, at more than 50% mass conversion efficiency. The debris contains several radioisotopes, most notably ⁵⁶Ni, made in amounts that produce subluminous (but still observable) light curves compared to branch-normal SNe Ia.

The Hubble constant H₀ and matter density Ω_m of the universe are measured using the latest γ-ray attenuation results from Fermi-LAT and Cerenkov telescopes. This methodology is based upon the fact that the extragalactic background light supplies opacity for very high energy photons via photon–photon interaction. The amount of γ-ray attenuation along the line of sight depends on the expansion rate and matter content of the universe. This novel strategy results in a value of ${H}_{0}={67.4}_{-6.2}^{+6.0}$ km s⁻¹ Mpc⁻¹ and ${{\rm{\Omega }}}_{m}={0.14}_{-0.07}^{+0.06}$. These estimates are independent and complementary to those based on the distance ladder, cosmic microwave background (CMB), clustering with weak lensing, and strong lensing data. We also produce a joint likelihood analysis of our results from γ-rays and those from more mature methodologies, excluding the CMB, yielding a combined value of H₀ = 66.6 ± 1.6 km s⁻¹ Mpc⁻¹ and Ω_m = 0.29 ± 0.02.

A Steady Electron Runaway Model (SERM) is formulated describing plasmas in the astrophysical "condition" having finite (rather than infinitesimal) Knudsen number, ${{\mathbb{K}}}_{\mathrm{Pe}}$, suggesting an omnipresent leptokurtic, nonthermal, and heat-conducting electron velocity distribution function (eVDF) as the replacement for the Maxwellian ansatz typically made. The shape parameters of SERM's eVDFs are functionals of the local dimensionless electric field, ${{\mathbb{E}}}_{\parallel }$, shown to be nearly interchangeable with the pressure Knudsen number, ${{\mathbb{K}}}_{\mathrm{Pe}}$. The eVDF is determined by the total density and pressure, heat flux, and ${{\mathbb{E}}}_{\parallel }$ with the Maxwellian as a special case when ${{\mathbb{E}}}_{\parallel }=0$. The nonthermal part of the eVDF is caused by local and global runaway physics and its density fraction is monotonically dependent on ${{\mathbb{E}}}_{\parallel }$. SERM explains the distinguishable conduction band of suprathermal electrons to be the result of the inhomogeneities of astroplasmas that require ${{\mathbb{E}}}_{\parallel }\ne 0$ to enforce quasi-neutrality. SERM shows that the direction of the heat flow should be that of ${E}_{\parallel }\hat{{\boldsymbol{b}}}$. Almost all reported space age correlations among the shape parameters of the solar wind eVDF are reproduced by this modeling, including scaling of: (i) nonthermal spectral break energy, and (ii) partition of suprathermal density and partial pressure, with solar wind speed. SERM, together with eVDF observations, indirectly bracket $0.2\lt {{\mathbb{E}}}_{\parallel }(1\,\mathrm{au})\lt 0.65$, producing a steady-state eVDF, consistent with in situ (i) heat flows, (ii) strahl pitch angle features in high-speed winds, (iii) ${J}_{\parallel }=0$, and (iv) non-negative probability at all velocities. Because finite ${{\mathbb{K}}}_{\mathrm{Pe}}$ is the identified prerequisite for SERM modeling, nonthermal eVDF's are expected nearly everywhere in astrophysics where ${{\mathbb{K}}}_{\mathrm{Pe}}\gt 0.01$.

The chemical evolution of fluorine is investigated in a sample of Milky Way red giant stars that span a significant range in metallicity from [Fe/H] ∼ −1.3 to 0.0 dex. Fluorine abundances are derived from vibration-rotation lines of HF in high-resolution infrared spectra near 2.335 μm. The red giants are members of the thin and thick disk/halo, with two stars being likely members of the outer disk Monoceros overdensity. At lower metallicities, with [Fe/H] < −0.4 to −0.5, the abundance of F varies as a primary element with respect to the Fe abundance, with a constant subsolar value of [F/Fe] ∼ −0.3 to −0.4 dex. At larger metallicities, however, [F/Fe] increases rapidly with [Fe/H] and displays a near-secondary behavior with respect to Fe. Comparisons with various models of chemical evolution suggest that in the low-metallicity regime (dominated here by thick-disk stars), a primary evolution of ¹⁹F with Fe, with a subsolar [F/Fe] value that roughly matches the observed plateau, can be reproduced by a model incorporating neutrino nucleosynthesis in the aftermath of the core collapse in Type II supernovae. A primary behavior for [F/Fe] at low metallicity is also observed for a model including rapidly rotating low-metallicity massive stars, but this overproduces [F/Fe] at low metallicity. The thick-disk red giants in our sample span a large range of galactocentric distance (R_g ∼ 6–13.7 kpc) yet display a roughly constant value of [F/Fe], indicating a very flat gradient (with a slope of 0.02 ± 0.03 dex kpc⁻¹) of this elemental ratio over a significant portion of the Galaxy having $| Z|$ > 300 pc away from the Galaxy midplane.

The flux of solar type III radio bursts have a time profile of rising and decay phases at a given frequency, which has been actively studied since the 1970s. Several factors that may influence the duration of a type III radio burst have been proposed. In this work, to study the dominant cause of the duration, we investigate the source positions of the front edge, the peak, and the tail edge in the dynamic spectrum of a single and clear type III radio burst. The duration of this type III burst at a given frequency is about 3 s for decameter wave. The beam-formed observations by the LOw-Frequency ARray are used, which can provide the radio source positions and the dynamic spectra at the same time. We find that, for this burst, the source positions of the front edge, the peak, and the tail edge split with each other spatially. The radial speed of the electrons exciting the front edge, the peak, and the tail edge is 0.42c, 0.25c, and 0.16c, respectively. We estimate the influences of the corona density fluctuation and the electron velocity dispersion on the duration, and the scattering effect by comparison with a few short-duration bursts from the same region. The analysis yields that, in the frequency range of 30–41 MHz, the electron velocity dispersion is the dominant factor that determines the time duration of type III radio bursts with long duration, while scattering may play an important role in the duration of short bursts.

The Carnegie-Chicago Hubble Program (CCHP) is building a direct path to the Hubble constant (H₀) using Population II stars as the calibrator of the Type Ia supernova (SN Ia)-based distance scale. This path to calibrate the SNe Ia is independent of the systematics in the traditional Cepheid-based technique. In this paper, we present the distance to M101, the host to SN 2011fe, using the I-band tip of the red giant branch (TRGB) based on observations from the ACS/WFC instrument on the Hubble Space Telescope. The CCHP targets the halo of M101, where there is little to no host galaxy dust, the red giant branch is isolated from nearly all other stellar populations, and there is virtually no source confusion or crowding at the magnitude of the tip. Applying the standard procedure for the TRGB method from the other works in the CCHP series, we find a foreground-extinction-corrected M101 distance modulus of μ₀ = 29.07 ± 0.04_stat ± 0.05_sys mag, which corresponds to a distance of D = 6.52 ± 0.12_stat ± 0.15_sys Mpc. This result is consistent with several recent Cepheid-based determinations, suggesting agreement between Population I and II distance scales for this nearby SN Ia host galaxy. We further analyze four archival data sets for M101 that have targeted its outer disk to argue that targeting in the stellar halo provides much more reliable distance measurements from the TRGB method owing to the combination of multiple structural components and heavy population contamination. Application of the TRGB in complex regions will have sources of uncertainty not accounted for in commonly used uncertainty measurement techniques.

We report NuSTAR and Chandra observations of two X-ray transients, SWIFT J174540.7−290015 (T15) and SWIFT J174540.2−290037 (T37), which were discovered by the Neil Gehrels Swift Observatory in 2016 within r ∼ 1 pc of Sgr A*. NuSTAR detected bright X-ray outbursts from T15 and T37, likely in the soft and hard states, with 3–79 keV luminosities of 8 × 10³⁶ and 3 × 10³⁷ erg s⁻¹, respectively. No X-ray outbursts have previously been detected from the two transients and our Chandra ACIS analysis puts an upper limit of L_X ≲ 2 × 10³¹ erg s⁻¹ on their quiescent 2–8 keV luminosities. No pulsations, significant quasi-periodic oscillations, or type I X-ray bursts were detected in the NuSTAR data. While T15 exhibited no significant red noise, the T37 power density spectra are well characterized by three Lorentzian components. The declining variability of T37 above ν ∼ 10 Hz is typical of black hole (BH) transients in the hard state. NuSTAR spectra of both transients exhibit a thermal disk blackbody, X-ray reflection with broadened Fe atomic features, and a continuum component well described by Comptonization models. Their X-ray reflection spectra are most consistent with high BH spin (a_* ≳ 0.9) and large disk density (n_e ∼ 10²¹ cm⁻³). Based on the best-fit ionization parameters and disk densities, we found that X-ray reflection occurred near the inner-disk radius, which was derived from the relativistic broadening and thermal disk component. These X-ray characteristics suggest the outbursting BH-low-mass X-ray binary scenario for both transients and yield the first BH spin measurements from X-ray transients in the central 100 pc region.

The goal of stellar evolution theory is to predict the structure of stars throughout their lifetimes. Usually, these predictions can be assessed only indirectly, for example by comparing predicted and observed effective temperatures and luminosities. Thanks now to asteroseismology, which can reveal the internal structure of stars, it becomes possible to compare the predictions from stellar evolution theory to actual stellar structures. In this work, we present an inverse analysis of the oscillation data from the solar-type star KIC 6225718, which was observed by the Kepler space observatory during its nominal mission. As its mass is about 20% greater than solar, this star is predicted to transport energy by convection in its nuclear-burning core. We find significant differences between the predicted and actual structure of the star in the radiative interior near to the convective core. In particular, the predicted sound speed is higher than observed in the deep interior of the star, and too low at a fractional radius of 0.25 and beyond. The cause of these discrepancies is unknown, and is not remedied by known physics in the form of convective overshooting or elemental diffusion.

We conduct global three-dimensional radiation magnetohydrodynamic simulations of the inner regions of accretion flows around a 5 × 10⁸M_⊙ black hole, with mass accretion rates reaching 7% and 20% of the Eddington value. We choose initial field topologies that result in an inner disk supported by magnetic pressure, with surface density significantly smaller than the values predicted by the standard thin-disk model as well as a much larger disk scale height. The disks do not show any sign of thermal instability over many thermal timescales. More than half of the accretion is driven by radiation viscosity in the optically thin coronal region for the case of the lower accretion rate, while accretion in the optically thick part of the disk is driven by the Maxwell and Reynolds stresses from turbulence caused by magnetorotational instability. Optically thin plasma with gas temperatures ≳10⁸ K is generated only in the inner ≈10 gravitational radii in both simulations, and is more compact in the case of the higher accretion rate. Such plasma does not form at larger radii because the surface density increases outward with radius, causing less dissipation outside the photosphere. In contrast to standard thin-disk models, the surface density in our simulations increases with increasing mass accretion rate at each radius. This causes a relatively weaker hot plasma component for the simulation with a higher accretion rate. We suggest that these results may provide a physical mechanism for understanding some of the observed properties of coronae and spectra of active galactic nuclei.

The occurrence of planetary nebulae (PNe) in globular clusters (GCs) provides an excellent chance to study low-mass stellar evolution in a special (low-metallicity, high stellar density) environment. We report a systematic spectroscopic survey for the [O iii] 5007 Å emission line of PNe in 1469 Virgo GCs and 121 Virgo ultra-compact dwarfs (UCDs), mainly hosted in the giant elliptical galaxies M87, M49, M86, and M84. We detected zero PNe in our UCD sample and discovered one PN (${M}_{5007}=-4.1\,\mathrm{mag}$) associated with an M87 GC. We used the [O iii] detection limit for each GC to estimate the luminosity-specific frequency of PNe, α, and measured α in the Virgo cluster GCs to be $\alpha \sim {3.9}_{-0.7}^{+5.2}\times {10}^{-8}\,\mathrm{PN}/{L}_{\odot }$. The value of α in the Virgo GCs is among the lowest reported in any environment, due in part to the large sample size, and it is 5–6 times lower than that for the Galactic GCs. We suggest that α decreases toward brighter and more massive clusters, sharing a similar trend as the binary fraction, and the discrepancy between the Virgo and Galactic GCs can be explained by the observational bias in extragalactic surveys toward brighter GCs. This low but nonzero efficiency in forming PNe may highlight the important role played by binary interactions in forming PNe in GCs. We argue that a future survey of less massive Virgo GCs will be able to determine whether PN production in the Virgo GCs is governed by an internal process (mass, density, binary fraction) or if it is largely regulated by the external environment.

We study the effects of grain surface reactions on the chemistry of protoplanetary disks where gas, ice surface layers, and icy mantles of dust grains are considered as three distinct phases. Gas-phase and grain surface chemistry is found to be mainly driven by photoreactions and dust temperature gradients. The icy disk interior has three distinct chemical regions: (i) the inner midplane with low far-UV (FUV) fluxes and warm dust (≳15 K) that lead to the formation of complex organic molecules, (ii) the outer midplane with higher FUV from the interstellar medium and cold dust where hydrogenation reactions dominate, and (iii) a molecular layer above the midplane but below the water condensation front where photodissociation of ices affects gas-phase compositions. Some common radicals, e.g., CN and C₂H, exhibit a two-layered vertical structure and are abundant near the CO photodissociation front and near the water condensation front. The three-phase approximation in general leads to lower vertical column densities than two-phase models for many gas-phase molecules owing to reduced desorption, e.g., H₂O, CO₂, HCN, and HCOOH decrease by roughly two orders of magnitude. Finally, we find that many observed gas-phase species originate near the water condensation front; photoprocesses determine their column densities, which do not vary significantly with key disk properties such as mass and dust/gas ratio.

Rapid rotation is a fundamental characteristic of classical Be stars and a crucial property allowing for the formation of their circumstellar disks. Past evolution in a mass and angular momentum transferring binary system offers a plausible solution to how Be stars attained their fast rotation. Although the subdwarf remnants of mass donors in such systems should exist in abundance, only a few have been confirmed due to tight observational constraints. An indirect method of detecting otherwise hidden companions is offered by their effect on the outer parts of Be star disks, which are expected to be disrupted or truncated. In the context of the infrared and radio continuum excess radiation originating in the disk, the disk truncation can be revealed by a turndown in the spectral energy distribution due to reduced radio flux levels. In this work, we search for signs of spectral turndown in a sample of 57 classical Be stars with radio data, which include new data for 23 stars and the longest-wavelength detections so far (λ ≈ 10 cm) for two stars. We confidently detect the turndown for all 26 stars with sufficient data coverage (20 of which are not known to have close binary companions). For the remaining 31 stars, the data are inconclusive as to whether the turndown is present or not. The analysis suggests that many if not all Be stars have close companions influencing their outer disks. If confirmed to be subdwarf companions, the mass transfer spin-up scenario might explain the existence of the vast majority of classical Be stars.

Coronal and solar wind physics have long used plasma fluid models to motivate physical explanations of observations; the hypothesized model is introduced into a fluid simulation to see if observations are reproduced. This procedure is called Verification of Mechanism (VoM) modeling; it is contingent on the self consistency of the closure that made the simulation possible. Inner corona VoMs typically assume weak gradient Spitzer–Braginskii closures. Four prominent coronal VoMs in place for decades are shown to contradict their closure hypotheses, demonstrably shaping coronal and solar wind research. These findings have been possible since 1953. This unchallenged evolution is worth understanding, so that similarly flawed VoMs do not continue to mislead new research. As a first step in this direction, this paper organizes four a posteriori quantitative tests for the purpose of easily screening the physical integrity of a proposed VoM. A fifth screen involving the thermal force, the tandem of the heat flux, has been shown to be mandatory when VoMs involve species-specific energy equations. VoM modeling will soon be required to advance Parker Solar Probe and Solar Orbiter science. Such modeling cannot advance the physical understanding sought by these missions unless the closures adopted (i) are demonstrated to be self consistent for the VoM plasma Knudsen numbers, (ii) are verified a posteriori as possessing nonnegative VDFs throughout the simulated volume, and (iii) include the physical completeness of thermal force physics when the VoM requires species-specific energy equations.

The properties of fast radio bursts (FRBs) indicate that the physical origin of this type of astrophysical phenomenon is related to neutron stars. The first detected repeating source, FRB 121102, is associated with a persistent radio counterpart. In this paper, we propose that this radio counterpart could arise from a pulsar wind nebula powered by a magnetar without surrounding supernova ejecta. Its medium is a stratified structure produced by a progenitor wind. The model parameters are constrained by the spectrum of the counterpart emission, the size of the nebula, and the large but decreasing rotation measure (RM) of the repeating bursts. In addition, the observed dispersion measure is consistent with the assumption that all of the RM comes from the shocked medium.

The extragalactic background light (EBL), a diffuse photon field in the optical and infrared range, is a record of radiative processes over the universe's history. Spectral measurements of blazars at very high energies (>100 GeV) enable the reconstruction of the spectral energy distribution (SED) of the EBL, as the blazar spectra are modified by redshift- and energy-dependent interactions of the gamma-ray photons with the EBL. The spectra of 14 VERITAS-detected blazars are included in a new measurement of the EBL SED that is independent of EBL SED models. The resulting SED covers an EBL wavelength range of 0.56–56 μm, and is in good agreement with lower limits obtained by assuming that the EBL is entirely due to radiation from cataloged galaxies.

Optical observations of normal stars in binary systems with massive unseen objects have been proposed to search for candidate black holes (BHs) and provide a direct measurement of their dynamical masses. In this paper, we have performed binary population synthesis calculations to simulate the potential population of detached binaries containing BHs and normal-star companions in the Galaxy. We focus on the influence of the BH progenitors. In the traditional model, BHs in binaries evolve from stars more massive than ∼25M_⊙. However, it is difficult for this model to produce BH low-mass X-ray binaries. Recent investigations of massive star evolution have suggested that the BH progenitors have masses as low as ∼15M_⊙. Based on this model, we provide the expected distributions of various parameters for detached BH binaries with normal-star companions, including the component masses, the orbital parameters of the binary systems, the radial velocity semi-amplitudes, and the astrometric signatures of the optical companions. Our calculations show that there are thousands of such detached binaries in the Galaxy, and hundreds of them are potentially observable systems with luminous companions brighter than 20 mag. In addition, detached BH binaries are dominated by those with main-sequence companions and only a small percent of them are expected to have giant companions.

We study the tidal interaction between a low-mass companion (e.g., a protoplanet or a black hole) in orbit about a central mass, and the accretion disk within which it is submerged. We present results for a companion on a coplanar orbit with eccentricity, e, between 0.1 and 0.6. For these eccentricities, dynamical friction arguments in its local approximation, that is, ignoring differential rotation and the curvature of the orbit, provide simple analytical expressions for the rates of energy and angular momentum exchange between the disk and the companion. We examine the range of validity of the dynamical friction approach by conducting a series of hydrodynamical simulations of a perturber with softening radius R_soft embedded in a two-dimensional disk. We find close agreement between predictions and the values in simulations provided that R_soft is chosen sufficiently small, below a threshold value ${\tilde{R}}_{\mathrm{soft}}$, which depends on the disk parameters and on e. We give ${\tilde{R}}_{\mathrm{soft}}$ for both razor-thin disks and disks with a finite scale height. For point-like perturbers, the local approximation is valid if the accretion radius is smaller than ${\tilde{R}}_{\mathrm{soft}}$. This condition imposes an upper value on the mass of the perturber.

We have obtained deep Hubble Space Telescope (HST) imaging of 19 dwarf galaxy candidates in the vicinity of M101. Advanced Camera for Surveys HST photometry for two of these objects showed resolved stellar populations and tip of the red giant branch derived distances (D ∼ 7 Mpc) consistent with M101 group membership. The remaining 17 were found to have no resolved stellar populations, meaning they are either part of the background NGC 5485 group or are distant low surface brightness (LSB) galaxies. It is noteworthy that many LSB objects that had previously been assumed to be M101 group members based on projection have been shown to be background objects, indicating the need for future diffuse dwarf surveys to be very careful in drawing conclusions about group membership without robust distance estimates. In this work we update the satellite luminosity function of M101 based on the presence of these new objects down to M_V = −8.2. M101 is a sparsely populated system with only nine satellites down to M_V ≈ −8, as compared with 26 for M31 and 24.5 ± 7.7 for the median host in the Local Volume. This makes M101 by far the sparsest group probed to this depth, although M94 is even sparser to the depth at which it has been examined (M_V = −9.1). M101 and M94 share several properties that mark them as unusual compared with the other Local Volume galaxies examined: they have a very sparse satellite population but also have high star-forming fractions among these satellites; such properties are also found in the galaxies examined as part of the Satellites around Galactic Analogs survey. We suggest that these properties appear to be tied to the wider galactic environment, with more isolated galaxies showing sparse satellite populations that are more likely to have had recent star formation, while those in dense environments have more satellites that tend to have no ongoing star formation. Overall, our results show a level of halo-to-halo scatter between galaxies of similar mass that is larger than is predicted in the lambda cold dark matter model.

Flare loops form an integral part of eruptive events, being detected in the range of temperatures from X-rays down to cool chromospheric-like plasmas. While hot loops are routinely observed by the Solar Dynamics Observatory's Atmospheric Imaging Assembly, cool loops seen off-limb are rare. In this paper we employ unique observations of the SOL2017-09-10T16:06 X8.2-class flare which produced an extended arcade of loops. The Swedish 1 m Solar Telescope made a series of spectral images of the cool off-limb loops in the Ca ii 8542 Å and the hydrogen Hβ lines. Our focus is on the loop apices. Non-local thermal equilibrium (non-LTE; i.e., departures from LTE) spectral inversion is achieved through the construction of extended grids of models covering a realistic range of plasma parameters. The Multilevel Accelerated Lambda Iterations code solves the non-LTE radiative-transfer problem in a 1D externally illuminated slab, approximating the studied loop segment. Inversion of the Ca ii 8542 Å and Hβ lines yields two similar solutions, both indicating high electron densities around 2 × 10¹² cm⁻³ and relatively large microturbulence around 25 km s⁻¹. These are in reasonable agreement with other independent studies of the same or similar events. In particular, the high electron densities in the range 10¹²–10¹³ cm⁻³ are consistent with those derived from the Solar Dynamics Observatory's Helioseismic and Magnetic Imager white-light observations. The presence of such high densities in solar eruptive flares supports the loop interpretation of the optical continuum emission of stars which manifest superflares.

Given the absence of directly detected dark matter (DM) as weakly interacting massive particles, there is strong interest in the possibility that DM is an ultralight scalar field, here denoted as "fuzzy" DM. Ultra-diffuse galaxies, with the sizes of giant galaxies and the luminosities of dwarf galaxies, have a wide range of DM halo masses, thus providing new opportunities for exploring the connections between galaxies and their DM halos. Following up on new integral field unit spectroscopic observations and dynamics modeling of the DM-dominated ultra-diffuse galaxy Dragonfly 44 in the outskirts of the Coma Cluster, we present models of fuzzy DM constrained by the stellar dynamics of this galaxy. We infer a scalar field mass of $\sim 3\times {10}^{-22}\,\mathrm{eV}$, consistent with other constraints from galaxy dynamics but in tension with constraints from Lyα forest power spectrum modeling. While we are unable to statistically distinguish between fuzzy DM and "normal" cold DM models, we find that the inferred properties of the fuzzy DM halo satisfy a number of predictions for halos in a fuzzy DM cosmology. In particular, we find good agreement with the predicted core size–halo mass relation and the predicted transition radius between the quantum pressure-dominated inner region and the outer halo region.

This study provides a deeper understanding of how the solar wind evolves with increasing distance from the Sun as it encounters an increasing amount of interstellar material. This work extends our prior work by (1) extending the solar wind proton data radial profiles for New Horizons (NH) out to nearly 43 au, (2) quantifying the observed amount of slowing in the solar wind in the outer heliosphere by performing a detailed comparison between the speeds at NH (21–43 au) with speeds at 1 au, and (3) resolving discrepancies between the measured amount of slowing and estimates of the amount of slowing determined from the measured amount of interstellar pickup present in the solar wind. We find that the solar wind density radial profile may decrease at nearly or slightly less than a spherical expansion density profile. However, the temperature profile is well above what would be expected for an adiabatic profile. By comparing outer and inner heliospheric solar wind observations, we find the solar wind speed is reduced by 5%–7% between 30 and 43 au. We find the solar wind polytropic index (γ_sw) steeply decreases toward zero in the outer heliosphere (21–43 au) with a slope of ∼0.031 au⁻¹. Using both this radial variation in γ_sw and the measured amount of interstellar pickup ions, we estimate the slowing in the solar wind and obtain excellent agreement with the observed slowing.

Existing analysis based on spectra from the Reflection Grating Spectrometer (RGS) on board XMM-Newton already shows that the G-ratio of the O vii Heα triplet in the inner bulge of M31 is too high to be consistent with a pure optically thin thermal plasma in collisional ionization equilibrium (CIE). Different processes that may affect properties of diffuse hot plasma were proposed, such as resonance scattering (RS) and charge exchange (CX) with cold gas. To determine which physical process(es) may be responsible for this inconsistency, we present a systematic spectroscopic analysis based on 0.8 Ms XMM-Newton/RGS data, together with complementary Chandra/ACIS-S images. The combination of these data enables us to reveal multiple non-CIE spectroscopic diagnostics, including but not limited to the large G-ratios of Heα triplets (O vii, N vi, and Ne ix) and the high Lyman series line ratios (O viii Lyβ/Lyα and Lyγ/Lyα, and N vii Lyβ/Lyα), which are not expected for a CIE plasma, and the high iron line ratios (Fe xviii 14.2 Å/Fe xvii 17 Å and Fe xvii 15 Å/17 Å), which suggest much higher temperatures than other line ratios, as well as their spatial variations. Neither CX nor RS explains all these spectroscopic diagnostics satisfactorily. Alternatively, we find that an active galactic nucleus (AGN) relic scenario provides a plausible explanation for virtually all the signatures. We estimate that an AGN was present at the center of M31 about half a million years ago and that the initial ionization parameter ξ of the relic plasma is in the range of 3–4.

We use Interface Region Imaging Spectrograph (IRIS) spacecraft data to study a group of Chromospheric ultraviolet bursts (UVBs) associated with an active region. We classify the UVBs into two types: smaller ones that can only be measured once by the scanning slit, and larger UVBs that are measured twice by the slit. The UVBs' optically thin Si iv 1402.77 Å line profiles are studied intensively. By fitting the smaller UVBs' lines with 1–2 Gaussians, we obtain a variety of line-of-sight flow measurements that hint various 3D orientations of small-scale magnetic reconnections, each associated with a UVB. The larger UVBs are, however, unique in a way that they each have two sets of measurements at two slit locations. This makes it possible to unambiguously detect two oppositely directed heated flows jetting out of a single UVB, a signature of magnetic reconnection operating at the heart of the UVB. Here, we report on the first of such an observation. Additionally, all the optically thin Si iv 1402.77 Å line profiles from those UVBs consistently demonstrate excessive broadening, an order of magnitude larger than would be expected from thermal broadening, suggesting that those small-scale reconnections could be driven by large scale (macroscale) turbulence in the active region.

The Sun's corona has interested researchers for multiple reasons, including the search for a solution to the famous coronal heating problem and a purely practical consideration of predicting geomagnetic storms on Earth. There exist numerous different theories regarding the solar corona; therefore, it is important to be able to perform comparative analysis and validation of those theories. One way that could help us move toward the answers to those problems is the search for observational methods that could obtain information about the physical properties of the solar corona and provide means for comparing different solar corona models. In this work we present evidence that very long baseline interferometry (VLBI) observations are, in certain conditions, sensitive to the electron density of the solar corona and are able to distinguish between different electron density models, which makes the technique of VLBI valuable for solar corona investigations. Recent works on the subject used a symmetric power-law model of the electron density in solar plasma; in this work, an improvement is proposed based on a three-dimensional numerical model.

The structure and kinematics of gaseous, disk–halo interfaces are imprinted with the processes that transfer mass, metals, and energy between galactic disks and their environments. We study the extraplanar diffuse ionized gas (eDIG) layer in the interacting, star-forming galaxy NGC 5775 to better understand the consequences of star formation feedback on the dynamical state of the thick-disk interstellar medium. Combining emission-line spectroscopy from the Robert Stobie Spectrograph on the Southern African Large Telescope with radio continuum observations from Continuum Halos in Nearby Galaxies—an EVLA Survey, we ask whether thermal, turbulent, magnetic field, and cosmic-ray pressure gradients can stably support the eDIG layer in dynamical equilibrium. This model fails to reproduce the observed exponential electron scale heights of the eDIG thick disk and halo on the northeast (${h}_{z,e}=0.6,7.5$ kpc) and southwest (${h}_{z,e}=0.8,3.6$ kpc) sides of the galaxy at R < 11 kpc. We report the first definitive detection of an increasing eDIG velocity dispersion as a function of height above the disk. Blueshifted gas along the minor axis at large distances from the midplane hints at a disk–halo circulation and/or ram pressure effects caused by the ongoing interaction with NGC 5774. This work motivates further integral field unit and/or Fabry–Perot spectroscopy of galaxies with a range of star formation rates to develop a spatially resolved understanding of the role of star formation feedback in shaping the kinematics of the disk–halo interface.

We present a Cepheid-based distance to the nearby Seyfert galaxy NGC 6814 from Hubble Space Telescope observations. We obtained F555W and F814W imaging over the course of 12 visits with logarithmic time spacing in 2013 August−October. We detected and made photometric measurements for 16,469 unique sources across all images in both filters, from which we identify 90 excellent Cepheid candidates spanning a range of periods of 13–84 days. We find evidence for incompleteness in the detection of candidates at periods <21 days. Based on the analysis of Cepheid candidates above the incompleteness limit, we determine a distance modulus for NGC 6814 relative to the LMC of ${\mu }_{\mathrm{rel}\mathrm{LMC}}={13.200}_{-0.031}^{+0.031}$ mag. Adopting the recent constraint of the distance modulus to the LMC determined by Pietrzyński et al., we find $m-M={31.677}_{-0.041}^{+0.041}$ which gives a distance of 21.65 ± 0.41 Mpc to NGC 6814.

We report the detection of GeV γ-ray emission from the very-high-energy γ-ray source VER J2227+608 associated with the "tail" region of supernova remnant (SNR) G106.3+2.7. The GeV γ-ray emission is extended and spatially coincident with molecular clouds traced by CO emission. The broadband GeV to TeV emission of VER J2227+608 can be well fitted by a single power-law function with an index of 1.90 ± 0.04, without obvious indication of spectral cutoff toward high energies. The pure leptonic model for the γ-ray emission can be marginally ruled out by the X-ray and TeV data. In the hadronic model, the low energy content of CRs and the hard γ-ray spectrum, in combination with the center bright source structure, suggest that VER J2227+608 may be powered by the Pulsar wind nebula instead of shocks of the SNR. And the cutoff energy of the proton distribution needs to be higher than ∼400 TeV, which makes it an attractive PeVatron candidate. Future observations by the upcoming Large High Altitude Air Shower Observatory and the Cherenkov Telescope Array in the north could distinguish these models and constrain the maximum energy of cosmic rays in SNRs.

Absolute optical oscillator strength (OOS) plays an extremely important role in molecular astrophysics research, especially for hydrogen. In this work, a novel dipole (γ, γ) method is used to determine the absolute OOSs for the Lyman and Werner bands of H₂ with a high energy resolution of 25 meV. A detailed comparison between the obtained results and earlier experimental and theoretical data is presented, and great agreement between the present work and the calculated results is achieved by taking the non-adiabatic effect into account. The total integrated OOSs are also obtained and discussed. The absolute OOSs for the Lyman and Werner bands of H₂ reported in this work can serve as a benchmark to test various theoretical methods and can be applied in molecular astrophysics.

Recent theoretical studies suggest the existence of low-mass, zero-metal stars in the current universe. To study the basic properties of the atmosphere of low-mass first stars, we perform one-dimensional magnetohydrodynamical simulations for the heating of coronal loops on low-mass stars with various metallicities. While the simulated loops are heated up to ≥10⁶ K by the dissipation of Alfvénic waves originating from the convective motion irrespective of metallicity, the coronal properties sensitively depend on the metallicity. Lower-metal stars create hotter and denser coronae because the radiative cooling is suppressed. The zero-metal star gives more than 40 times higher coronal density than the solar-metallicity counterpart, and as a result, the UV and X-ray fluxes from the loop are several times higher than those of the solar-metallicity star. We also discuss the dependence of the coronal properties on the length of the simulated coronal loops.

We are exploring galaxy evolution in low-density environments exploiting smooth particle hydrodynamic simulations, including chemophotometric implementation. From a large grid of simulations of galaxy encounters and mergers starting from triaxial halos of gas and dark matter, we single out the simulations matching the global properties of our targets. These simulations are used to give insights into their evolution. We focus on 11 early-type galaxies selected because of their nearly passive stage of evolution in the nuclear region. However, a variety of UV features are detected in more than half of these galaxies. We find no significant differences in the formation mechanisms between galaxies with or without UV features. Major and minor mergers are able to reproduce their peculiar UV morphologies, and galaxy encounters are more suitable for "normal" early-type galaxies. Their star formation rate self-quenches several gigayears later than the merger/encounter occurred via gas exhaustion and stellar feedback, moving the galaxy from blue to red colors and driving the galaxy transformation. The length of the quenching is mass-dependent and lasts from 1 to 5 Gyr or more in the less massive systems. All of our targets are gas-rich at redshift 1. Three of them assembled at most 40% of their current stellar mass at z > 1, and seven assembled more than 40% between redshift 0.5 and 1. Their stellar mass grows by 4% by crossing the green valley before reaching their current position on the NUV−r versus M_r diagram.

We compare radii based on Gaia parallaxes to radii based on asteroseismic scaling relations for ∼300 dwarfs and subgiants and ∼3600 first-ascent giants from the Kepler mission. Systematics due to temperature, bolometric correction, extinction, asteroseismic radius, and the spatially correlated Gaia parallax zero-point contribute to a 2% systematic uncertainty on the agreement in Gaia–asteroseismic radius. We find that dwarf and giant scaling radii are on a parallactic scale at the level of −2.1% ± 0.5% (rand.) ± 2.0% (syst.) (dwarfs) and +1.7% ± 0.3% (rand.) ± 2.0% (syst.) (giants), supporting the accuracy and precision of scaling relations. In total, the 2% agreement that we find holds for stars spanning radii between 0.8 ${R}_{\odot }$ and 30 ${R}_{\odot }$. We do, however, see evidence for relative errors in scaling radii between dwarfs and giants at the level of 4% ± 0.6%, and find evidence of departures from simple scaling relations for radii above 30 ${R}_{\odot }$. Asteroseismic masses for very metal-poor stars are still overestimated relative to astrophysical priors, but at a reduced level. We see no trend with metallicity in radius agreement for stars with −0.5 < [Fe/H] < +0.5. We quantify the spatially correlated parallax errors in the Kepler field, which globally agree with the Gaia team's published covariance model. We provide Gaia radii, corrected for extinction and the Gaia parallax zero-point, for our full sample of ∼3900 stars, including dwarfs, subgiants, and first-ascent giants.

We studied the dissociation reactions of electron impact on water vapor for several fragment species at optical and near-ultraviolet wavelengths (200–850 nm). The resulting spectrum is dominated by the hydrogen Balmer series, by the OH (A ²Σ⁺ − X ²Π) band, and by the emission of ionic H₂O⁺(A ²A₁ − X ²B₁) and OH⁺(A ³Π − X ³Σ⁻) band systems. Emission cross sections and reaction channel thresholds were determined for energies between 5 and 100 eV. We find that the electron impact dissociation of H₂O results in an emission spectrum of the OH (A ²Σ⁺ − X ²Π) band that is distinctly different from the emission spectra from other excitation mechanisms seen in planetary astronomy. We attribute the change to a strongly non-thermal population of rotational states seen in planetary astronomy. This difference can be utilized for remote probing of the contribution of different physical reactions in astrophysical environments.

Extrasolar satellites are generally too small to be detected by nominal searches. By analogy to the most active body in the solar system, Io, we describe how sodium (Na i) and potassium (K i) gas could be a signature of the geological activity venting from an otherwise hidden exo-Io. Analyzing ∼a dozen close-in gas giants hosting robust alkaline detections, we show that an Io-sized satellite can be stable against orbital decay below a planetary tidal ${{ \mathcal Q }}_{p}\lesssim {10}^{11}$. This tidal energy is also focused into the satellite driving an ∼10^5±2 higher mass-loss rate than Io's supply to Jupiter's Na exosphere based on simple atmospheric loss estimates. The remarkable consequence is that several exo-Io column densities are, on average, more than sufficient to provide the ∼10^10±1 Na cm⁻² required by the equivalent width of exoplanet transmission spectra. Furthermore, the benchmark observations of both Jupiter's extended (∼1000 R_J) Na exosphere and Jupiter's atmosphere in transmission spectroscopy yield similar Na column densities that are purely exogenic in nature. As a proof of concept, we fit the "high-altitude" Na at WASP-49b with an ionization-limited cloud similar to the observed Na profile about Io. Moving forward, we strongly encourage time-dependent ingress and egress monitoring along with spectroscopic searches for other volcanic volatiles.

We investigate the nature of dense gas in the 3–10 pc circumnuclear ring (CNR) in the galactic center of the Milky Way, which is a structure that may be dynamically connecting the supermassive black hole Sgr A* with the central molecular zone at the 100 pc scale, and is the closest reservoir of molecular gas to the massive stars located within the central cluster. In the first of several papers addressing open issues with the CNR, we use far-infrared (FIR) diagnostic emission lines to probe the hot and dense phase of the photodissociation region (PDR) exposed to the radiation field of the central population of massive stars. We use the Far Infrared Field-Imaging Line Spectrometer (FIFI-LS) instrument on board the Stratospheric Observatory For Infrared Astronomy airborne observatory to obtain spatially resolved maps of FIR emission lines of the region with an angular resolution approximately 4 times higher than previous published data. We complement our data with archival continuum images at 19.7, 31.5 and 37.1 μm obtained with FORCAST and 70, 100 and 160 μm archival continuum images from PACS. We use the FIFI-LS emission line flux maps from ionized ([C ii] 157.7 μm), atomic ([O i] 63.2 μm, [O i] 145.5 μm), and molecular (CO J = 14–13 186.0 μm) species for a comparison with model predictions for PDRs. We present a method that dissects emission from the low and from the high excitation phase of the PDR and that also accounts for, e.g., absorption especially in the [O i] 63.2 μm transition. We present spatially resolved maps of dust temperature, atomic hydrogen column density, and FIR flux. The derived atomic hydrogen column density map is aligned with the galactic plane and extends spatially beyond previous near-infrared and radio based A_v determinations. The atomic hydrogen column densities range from 10^22.5 to 10^23.1 cm⁻² resulting in a total enclosed mass of the order of 10^3.5M_⊙. We derive a [O i] 63.2 μm absorption map that is aligned with the galactic plane with no or little absorption in the northern lobe of the CNR but moderate absorption in the southern lobe of the CNR, which is consistent with the picture where the illuminated front surfaces of gas clouds in the northern lobe are directly visible to us, while in the southern lobe the illuminated surfaces are hidden by the clouds within the lobe itself. Local gas densities in the CNR are generally below the Roche limit.