Table of contents

The Ophiuchus galaxy cluster exhibits a curious concave gas density discontinuity at the edge of its cool core. It was discovered in the Chandra X-ray image by Werner and collaborators, who considered the possibility of it being a boundary of an active galactic nucleus (AGN)-inflated bubble located outside the core, but discounted this possibility because it required much too powerful an AGN outburst. Using low-frequency (72–240 MHz) radio data from the Murchison Widefield Array/GLEAM and the Giant Metrewave Radio Telescope, we found that the X-ray structure is, in fact, a giant cavity in the X-ray gas filled with diffuse radio emission with an extraordinarily steep radio spectrum. It thus appears to be a very aged fossil of the most powerful AGN outburst seen in any galaxy cluster (pV ∼ 5 × 10⁶¹ erg for this cavity). There is no apparent diametrically opposite counterpart either in X-ray or in the radio. It may have aged out of the observable radio band because of the cluster asymmetry. At present, the central AGN exhibits only a weak radio source, so it should have been much more powerful in the past to have produced such a bubble. The AGN is currently starved of accreting cool gas because the gas density peak is displaced by core sloshing. The sloshing itself could have been set off by this extraordinary explosion if it had occurred in an asymmetric gas core. This dinosaur may be an early example of a new class of sources to be uncovered by low-frequency surveys of galaxy clusters.

We describe a population of young star clusters (SCs) formed in a hydrodynamical simulation of a gas-rich dwarf galaxy merger resolved with individual massive stars at subparsec spatial resolution. The simulation is part of the griffin (Galaxy Realizations Including Feedback From INdividual massive stars) project. The star formation environment during the simulation spans seven orders of magnitude in gas surface density and thermal pressure, and the global star formation rate surface density (Σ_SFR) varies by more than three orders of magnitude during the simulation. Young SCs more massive than ${M}_{* ,\mathrm{cl}}\sim {10}^{2.5}\,{M}_{\odot }$ form along a mass function with a power-law index α ∼ −1.7 (α ∼ −2 for ${M}_{* ,\mathrm{cl}}\gtrsim {10}^{3}\,{M}_{\odot }$) at all merger phases, while the normalization and the highest SC masses (up to ∼10⁶M_⊙) correlate with Σ_SFR. The cluster formation efficiency varies from Γ ∼ 20% in early merger phases to Γ ∼ 80% at the peak of the starburst and is compared to observations and model predictions. The massive SCs (≳10⁴M_⊙) have sizes and mean surface densities similar to observed young massive SCs. Simulated lower mass clusters appear slightly more concentrated than observed. All SCs form on timescales of a few Myr and lose their gas rapidly resulting in typical stellar age spreads between σ ∼ 0.1–2 Myr (1σ), consistent with observations. The age spreads increase with cluster mass, with the most massive cluster (∼10⁶M_⊙) reaching a spread of 5 Myr once its hierarchical formation finishes. Our study shows that it is now feasible to investigate the SC population of entire galaxies with novel high-resolution numerical simulations.

We report the mass and distance measurements of two single-lens events from the 2017 Spitzer microlensing campaign. The ground-based observations yield the detection of finite-source effects, and the microlens parallaxes are derived from the joint analysis of ground-based observations and Spitzer observations. We find that the lens of OGLE-2017-BLG-1254 is a 0.60 ± 0.03 M_⊙ star with D_LS = 0.53 ± 0.11 kpc, where D_LS is the distance between the lens and the source. The second event, OGLE-2017-BLG-1161, is subject to the known satellite parallax degeneracy, and thus is either a ${0.51}_{-0.10}^{+0.12}\,{M}_{\odot }$ star with D_LS = 0.40 ± 0.12 kpc or a ${0.38}_{-0.12}^{+0.13}\,{M}_{\odot }$ star with D_LS = 0.53 ± 0.19 kpc. Both of the lenses are therefore isolated stars in the Galactic bulge. By comparing the mass and distance distributions of the eight published Spitzer finite-source events with the expectations from a Galactic model, we find that the Spitzer sample is in agreement with the probability of finite-source effects occurring in single-lens events.

We present a new stellar dynamical mass measurement (${M}_{\mathrm{BH}}$) of the supermassive black hole (SMBH) in NGC 1453, a fast-rotating massive elliptical galaxy in the MASSIVE survey. We measure stellar kinematics in 135 spatial bins in the central 1.5 kpc × 2 kpc region of the galaxy using high signal-to-noise ratio (S/N ∼ 130) spectra from the Gemini-North GMOS integral field spectrograph (IFS). Combining with wide-field IFS kinematics out to ∼3 effective radii and stellar light distributions from Hubble Space Telescope Wide Field Camera 3 images, we perform Schwarzschild orbit-based mass modeling in the axisymmetric limit to constrain the mass components in NGC 1453. The best-fit black hole mass is ${M}_{\mathrm{BH}}=(2.9\pm 0.4)\times {10}^{9}\,{M}_{\odot }$; the mass models without a central black hole are excluded at the 8.7σ level. The NGC 1453 black hole lies within the intrinsic scatter of the SMBH and galaxy scaling relations, unlike three other galaxies hosting $\gtrsim {10}^{10}\,{M}_{\odot }$ SMBHs in the MASSIVE sample. The high-S/N GMOS spectra enable us to determine eight moments of the Gauss–Hermite expansion of the line-of-sight velocity distributions (LOSVDs), which are used as constraints in the orbit modeling. The stellar orbits in the mass models are further constrained to produce negligible h₉ through h₁₂ to minimize spurious behavior in the LOSVDs. We show that truncating the series at h₄, as was often done in prior work, leads to a much weaker constraint on the inferred ${M}_{\mathrm{BH}}$ for NGC 1453. Furthermore, we discuss precautions and modifications that are needed to achieve axisymmetry in triaxial orbit codes that use the Schwarzschild method to sample the start space of stellar orbits in triaxial gravitational potentials.

The collapse of degenerate oxygen–neon cores (i.e., electron-capture supernovae or accretion-induced collapse) proceeds through a phase in which a deflagration wave ("flame") forms at or near the center and propagates through the star. In models, the assumed speed of this flame influences whether this process leads to an explosion or to the formation of a neutron star. We calculate the laminar flame speeds in degenerate oxygen–neon mixtures with compositions motivated by detailed stellar evolution models. These mixtures include trace amounts of carbon and have a lower electron fraction than those considered in previous work. We find that trace carbon has little effect on the flame speeds, but that material with electron fraction ${Y}_{{\rm{e}}}\approx 0.48-0.49$ has laminar flame speeds that are $\approx 2$ times faster than those at ${Y}_{{\rm{e}}}=0.5$. We provide tabulated flame speeds and a corresponding fitting function so that the impact of this difference can be assessed via full star hydrodynamical simulations of the collapse process.

Terrestrial planet formation theory is at a bottleneck, with the growing realization that pairwise collisions are treated far too simply. Here, and in our companion paper that introduces the training methodology, we demonstrate the first application of machine learning to more realistically model the late stage of planet formation by giant impacts. We present surrogate models that give fast, reliable answers for the masses and velocities of the two largest remnants of a giant impact, as a function of the colliding masses and their impact velocity and angle, with the caveat that our training data do not yet include pre-impact rotation or variable thermal conditions. We compare canonical N-body scenarios of terrestrial planet formation assuming perfect merger with our more realistic treatment that includes inefficient accretions and hit-and-run collisions. The result is a protracted tail of final events lasting ∼200 Myr, and the conversion of about half the mass of the initial population to debris. We obtain profoundly different solar system architectures, featuring a much wider range of terrestrial planet masses and enhanced compositional diversity.

We present gray gas general circulation model (GCM) simulations of the tidally locked mini-Neptune GJ 1214b. On timescales of 1000–10,000 Earth days, our results are comparable to previous studies of the same planet, in the sense that they all exhibit two off-equatorial eastward jets. Over much longer integration times (50,000–250,000 Earth days) we find a significantly different circulation and observational features. The zonal-mean flow transitions from two off-equatorial jets to a single wide equatorial jet that has higher velocity and extends deeper. The hot spot location also shifts eastward over the integration time. Our results imply a convergence time far longer than the typical integration time used in previous studies. We demonstrate that this long convergence time is related to the long radiative timescale of the deep atmosphere and can be understood through a series of simple arguments. Our results indicate that particular attention must be paid to model convergence time in exoplanet GCM simulations, and that other results on the circulation of tidally locked exoplanets with thick atmospheres may need to be revisited.

We present a study of the ultra-faint Milky Way dwarf satellite galaxy Tucana II using deep photometry from the 1.3 m SkyMapper telescope at Siding Spring Observatory, Australia. The SkyMapper filter set contains a metallicity-sensitive intermediate-band v filter covering the prominent Ca ii K feature at 3933.7 Å. When combined with photometry from the SkyMapper u, g, and i filters, we demonstrate that v-band photometry can be used to obtain stellar metallicities with a precision of ∼0.20 dex when [Fe/H] > −2.5, and ∼0.34 dex when [Fe/H] < −2.5. Since the u and v filters bracket the Balmer Jump at 3646 Å, we also find that the filter set can be used to derive surface gravities. We thus derive photometric metallicities and surface gravities for all stars down to a magnitude of g ∼ 20 within ∼75' of Tucana II. Photometric metallicity and surface gravity cuts remove nearly all foreground contamination. By incorporating Gaia proper motions, we derive quantitative membership probabilities that recover all known members of the red giant branch of Tucana II. Additionally, we identify multiple likely new members in the center of the system, as well as candidate members several half-light radii from the center of the system. Finally, we present a metallicity distribution function derived from the photometric metallicities of likely Tucana II members. This result demonstrates the utility of wide-field imaging with the SkyMapper filter set in studying ultra-faint dwarf galaxies, and in general, low surface brightness populations of metal-poor stars. Upcoming work will clarify the membership status of several distant stars identified as candidate members of Tucana II.

The measurement of diffuse PeV gamma-ray emission from the Galactic plane would provide information about the energy spectrum and propagation of Galactic cosmic rays, and the detection of a pointlike source of PeV gamma-rays would be strong evidence for a Galactic source capable of accelerating cosmic rays up to at least a few PeV. This paper presents several unbinned maximum-likelihood searches for PeV gamma-rays in the Southern Hemisphere using 5 yr of data from the IceTop air shower surface detector and the in-ice array of the IceCube Observatory. The combination of both detectors takes advantage of the low muon content and deep shower maximum of gamma-ray air showers and provides excellent sensitivity to gamma-rays between ∼0.6 and 100 PeV. Our measurements of pointlike and diffuse Galactic emission of PeV gamma-rays are consistent with the background, so we constrain the angle-integrated diffuse gamma-ray flux from the Galactic plane at 2 PeV to 2.61 × 10⁻¹⁹ cm⁻² s⁻¹ TeV⁻¹ at 90% confidence, assuming an E⁻³ spectrum, and we estimate 90% upper limits on pointlike emission at 2 PeV between 10⁻²¹ and 10⁻²⁰ cm⁻² s⁻¹ TeV⁻¹ for an E⁻² spectrum, depending on decl. Furthermore, we exclude unbroken power-law emission up to 2 PeV for several TeV gamma-ray sources observed by the High Energy Spectroscopic System and calculate upper limits on the energy cutoffs of these sources at 90% confidence. We also find no PeV gamma-rays correlated with neutrinos from IceCube's high-energy starting event sample. These are currently the strongest constraints on PeV gamma-ray emission.

Space weather forecasting is very important, and the prediction of space weather, especially for solar flares, has increasingly attracted research interests with the numerous recent breakthroughs in machine learning. In this study, we propose a novel convolutional neural network (CNN) model to make binary class prediction for both ≥C-class and ≥M-class flares within 24 hr. We collect magnetogram samples of solar active regions (ARs) provided by the Space-weather Helioseismic and Magnetic Imager Active Region Patches (SHARP) data from 2010 May to 2018 September. These samples are used to construct 10 separate data sets. Then, after training, validating, and testing our model, we compare the results of our model with previous studies in several metrics, with a focus on the true skill statistic (TSS). The major results are summarized as follows. (1) We propose a method of shuffle and split cross-validation (CV) based on AR segregation, which is the first attempt to verify the validity and stability of the model in flare prediction. (2) The proposed CNN model achieves a relatively high score of TSS = 0.749 ± 0.079 for ≥M-class prediction, and TSS = 0.679 ± 0.045 for ≥C-class prediction, which is greatly improved compared with previous studies. (3) The model trained on 10 CV data sets is considerably robust and stable in making flare prediction for both ≥C class and ≥M class. Our experimental results indicate that our proposed CNN model is a highly effective method for flare forecasting, with quite excellent prediction performance.

NGC 4490/85 (UGC 7651/48) or Arp 269 is well known for being one of the closest interacting/merging galactic systems. NGC 4490 has a high star formation rate (SFR) and is surrounded by an enormous H i feature stretching about 60 kpc north and south of the optically visible galaxies. Both the driver for the high SFR in NGC 4490 and the formation mechanism of the H i structure are puzzling aspects of this system. We have used mid-infrared Spitzer data to show that NGC 4490 has a double nucleus morphology. One nucleus is visible in the optical, while the other is only visible at infrared and radio wavelengths. We find the optical nucleus and the potential infrared visible nucleus have similar sizes, masses, and luminosities. Both are comparable in mass and luminosity to other nuclei found in interacting galaxy pairs and much more massive and luminous compared with typical nonnuclear star-forming complexes. We examine possible origin scenarios for the infrared feature, and conclude that it is likely that NGC 4490 is itself a merger remnant, which is now interacting with NGC 4485. This earlier encounter provides both a possible driver for extended star formation in NGC 4490, and multiple pathways for the formation of the extended H i plume.

The radius–period distribution of exoplanets has been characterized by the Kepler survey, and the empirical mass–radius relation by the subset of Kepler planets with mass measurements. We combine the two in order to constrain the joint mass–radius–period distribution of Kepler transiting planets. We employ hierarchical Bayesian modeling and mixture models to formulate four models with varying complexity and fit these models to the data. We find that the most complex models that treat planets with significant gaseous envelopes, evaporated core planets, and intrinsically rocky planets as three separate populations are preferred by the data and provide the best fit to the observed distribution of Kepler planets. We use these models to calculate occurrence rates of planets in different regimes and to predict masses of Kepler planets, revealing the model-dependent nature of both. When using models with envelope mass loss to calculate η_⊕, we find nearly an order of magnitude drop, indicating that many Earth-like planets discovered with Kepler may be evaporated cores which do not extrapolate out to higher orbital periods. This work provides a framework for higher-dimensional studies of planet occurrence and for using mixture models to incorporate different theoretical populations of planets.

The particle-induced background of X-ray observatories is produced by galactic cosmic ray (GCR) primary protons, electrons, and He ions. Events due to direct interaction with the detector are usually removed by onboard processing. The interactions of these primary particles with the detector environment produce secondary particles that mimic X-ray events from celestial sources, and are much more difficult to identify. The filter-wheel closed data from the XMM-Newton EPIC-pn camera in small window mode (SWM) contains both the X-ray-like background events, and the events due to direct interactions with the primary particles. From this data, we demonstrate that X-ray-like background events are spatially correlated with the primary particle interaction. This result can be used to further characterize and reduce the non-X-ray background in silicon-based X-ray detectors in current and future missions. We also show that spectrum and pattern fractions of secondary particle events are different from those produced by cosmic X-rays.

The topology of the coronal magnetic field has a strong impact on the properties of the solar corona and presumably on the origin of the slow solar wind. To advance our understanding of this impact, we revisit the concept of so-called slip-back mapping and adapt it to determine open, closed, and disconnected flux systems that are formed in the solar corona by magnetic reconnection during a given time interval. In particular, the method we developed allows us to describe magnetic flux transfer between open and closed flux regions via so-called interchange reconnection with an unprecedented level of detail. We illustrate the application of this method to the analysis of the global MHD evolution of the solar corona driven by idealized differential rotation of the photospheric plasma.

Massive stars undergo fundamental mode and first overtone radial pulsations with periods of 100–1000 days as red supergiants (RSGs). At large amplitudes, these pulsations substantially modify the outer envelope's density structure encountered by the outgoing shock wave from the eventual core collapse of these $M\gt 9{M}_{\odot }$ stars. Using Modules for Experiments in Stellar Astrophysics (MESA), we model the effects of fundamental mode and first overtone pulsations in the RSG envelopes and the resulting Type IIP supernovae (SNe) using MESA+STELLA. We find that, in the case of fundamental mode pulsations, SN plateau observables, such as the luminosity at day 50, L₅₀; time-integrated shock energy, ET; and plateau duration, t_p, are consistent with radial scalings derived considering explosions of nonpulsating stars. Namely, most of the effect of the pulsation is consistent with the behavior expected for a star of a different size at the time of explosion. However, in the case of overtone pulsations, the Lagrangian displacement is not monotonic. Therefore, in such cases, excessively bright or faint SN emission at different times reflects the underdense or overdense structure of the emitting region near the SN photosphere.

Direct branching ratio measurements for ¹³C¹⁶O are reported for the three lowest dissociation channels that produce C(³P)+O(³P), C(¹D)+O(³P), and C(³P)+O(¹D) in the vacuum ultraviolet (VUV) region from 102,745 cm⁻¹ (97.33 nm) to 106,360 cm⁻¹ (94.02 nm) and covering six ¹Σ⁺ and six ¹Π states. A time-slice velocity-map ion imaging apparatus with a tunable VUV laser source that is generated by the two-photon resonance-enhanced four-wave mixing technique is used to make these measurements. The results show that the substitution of ¹²C by ¹³C dramatically changes the photodissociation branching ratios into channels that produce C and O atoms in the excited ¹D state for most of the absorption bands in the titled energy range. This isotope effect strongly depends on the specific rovibronic quantum states of CO that are being excited. The branching ratio data from the present study for ¹³C¹⁶O may significantly impact existing photochemical models because of the higher reactivity of the ¹D states of the C and O atoms. In addition to this isotope effect, the rotational dependence of the branching ratios to high J' levels for several vibronic states has been determined. This provides useful information for unraveling the complicated predissociation dynamics of ¹³C¹⁶O.

With machine learning entering into the awareness of the heliophysics community, solar flare prediction has become a topic of increased interest. Although machine-learning models have advanced with each successive publication, the input data has remained largely fixed on magnetic features. Despite this increased model complexity, results seem to indicate that photospheric magnetic field data alone may not be a wholly sufficient source of data for flare prediction. For the first time, we have extended the study of flare prediction to spectral data. In this work, we use Deep Neural Networks to monitor the changes of several features derived from the strong resonant Mg II h and k lines observed by the Interface Region Imaging Spectrograph. The features in descending order of predictive capability are: the triplet emission at 2798.77 Å, line core intensity, total continuum emission between the h and k line cores, the k/h ratio, line width, followed by several other line features such as asymmetry and line center. Regions that are about to flare generate spectra that are distinguishable from non-flaring active region spectra. Our algorithm can correctly identify pre-flare spectra approximately 35 minutes before the start of the flare, with an AUC of 86% and an accuracy, precision, and recall of 80%. The accuracy and AUC monotonically increase to 90% and 97%, respectively, as we move closer in time to the start of the flare. Our study indicates that spectral data alone can lead to good predictive models and should be considered an additional source of information alongside photospheric magnetograms.

We present newly discovered dwarf galaxy candidates in deep and wide-field images of NGC 1291 obtained with the Korea Microlensing Telescope Network. We identify 15 dwarf galaxy candidates by visual inspection. Using imaging simulations, we demonstrate that the completeness rate of our detection is greater than 70% for the central surface-brightness value of μ_0,R ≲ 26 mag arcsec⁻² and for magnitudes M_R ≲ −10 mag. The structural and photometric properties of the dwarf galaxy candidates appear to be broadly consistent with those of ordinary dwarf galaxies in nearby groups and clusters, with μ_0,R ∼ 22.5 to 26.5 mag arcsec⁻² and effective radii of 200 pc to 1 kpc. The dwarf galaxy candidates show a concentration toward NGC 1291 and tend to be redder the closer they are to the center, possibly indicating that they are associated with NGC 1291. The dwarf candidates presented in this paper appear to be bluer than those in denser environments, revealing that the quenching of star formation in dwarf galaxies is susceptible to the environment, while the morphology shaping is not.

We used Very Large Telescope/X-Shooter to target a sample of nearby analogs of Lyman break galaxies (LBGs). These Lyman break analogs are similar to the LBGs in many of their physical properties. We determine electron temperatures using the weak [O iii] λ4363 emission line and determine the oxygen abundance (O/H) using the direct and strong-line methods. We show that the direct and strong-line abundances are consistent with established relations within ∼0.2 dex. The analogs have nitrogen-to-oxygen ratios (N/O) and ionization parameters (q) that are, on average, offset with respect to typical local galaxies but similar to galaxies at z ∼ 2 and other analogs. The N/O and q excesses correlate with the offsets observed in the strong-line ratios, again similar to z ∼ 2. The star formation rate surface densities are consistent with the high electron density and ionization, indicating that the interstellar medium (ISM) pressure is set by feedback from the starbursts. For a given O/H, the apparent N/O excess arises owing to the offset in O/H with respect to the local mass–metallicity relation. This can be explained by recent inflow of relatively metal-poor gas that lowers O/H while leaving N/O unchanged. The difficulties in determining even basic ISM parameters in these nearby analogs illustrate some of the challenges we face at much higher redshifts, where similar rest-frame optical diagnostics for large samples of galaxies can be accessed with the James Webb Space Telescope.

Super-Earths and mini-Neptunes exhibit great diversity in their compositional and orbital properties. Their bulk densities span a large range, from those dense enough to be purely rocky to those needing a substantial contribution from volatiles to their volumes. Their orbital configurations range from compact, circular multitransiting systems like Kepler-11 to systems like our solar system's terrestrial planets with wider spacings and modest but significant eccentricities and mutual inclinations. Here we investigate whether a continuum of formation conditions resulting from variation in the amount of solids available in the inner disk can account for the diversity of orbital and compositional properties observed for super-Earths, including the apparent dichotomy between single and multitransiting systems. We simulate in situ formation of super-Earths via giant impacts and compare to the observed Kepler sample. We find that intrinsic variations among disks in the amount of solids available for in situ formation can account for the orbital and compositional diversity observed among Kepler's transiting planets. Our simulations can account for the planets' distributions of orbital period ratios, transit duration ratios, and transit multiplicity; higher eccentricities for planets in single transiting systems than for those in multitransiting systems; smaller eccentricities for larger planets; scatter in the mass–radius relation, including lower densities for planets with masses measured with transit timing variations instead of with radial velocity; and similarities in planets' sizes and spacings within each system. Our findings support the theory that variation among super-Earth and mini-Neptune properties is primarily locked in by different in situ formation conditions, rather than arising stochastically through subsequent evolution.

Organic molecules may be adsorbed on the ice surfaces of comets or moons. We study the desorption process induced by swift-heavy ion irradiation using a molecular dynamics simulation. Focusing on the amino acid glycine adsorbed on water ice as a prototypical example, we model a 2 MeV sulfur ion impact as it might be typical of magnetospheric ion impact on the surface of Europa. We find that molecules are ejected intact within a radius of up to 25 Å around the ion impact point. Within a core region of around 10 Å, glycine molecules are destroyed and mainly fragments are emitted. Prominent fragments produced are cyanide CN^–, carbon monoxide CO, cyanate OCN^–, and carbon dioxide CO₂, in agreement with experimental studies. In addition, radiolysis of water ice generates the radicals H⁺, H₃O⁺, and HO^– as well as the gases H₂, O₂, and some H₂O₂. While the smaller fragments easily obtain velocities above 2 km s⁻¹—the escape velocity from Europa—most ejected glycine molecules obtain smaller velocities and will thus not leave the moon permanently. Our results thus provide a detailed example that shows to what extent intact emission of organic molecules from Europa's surface by ion irradiation is possible and may be used for modeling the height distribution of ejecta in Europa's exosphere.

The use of infrared spectra to determine molecular abundances of icy astronomical objects and to study their chemistry requires laboratory measurements of reference spectra and related quantities, such as the index of refraction (n) and density (ρ) of candidate ices. Here we present new n and ρ measurements on ices involving over 30 C-, H-, and O-containing compounds, both acyclic and cyclic, representing seven chemical families. We examine the results in a way that is rare in the astrochemical literature, namely one in which data from an ice formed from molecules of a particular chemical family are compared to measurements on another member of the same family, such as of a homologous series or a pair of isomers. Apart from the intrinsic usefulness of the n and ρ data, a structure-based comparison can help establish trends and identify possibly spurious results. As liquid-phase data sometimes are used in low-temperature astrochemical work in the absence of solid-phase measurements, we compare our new ice results to those for the corresponding room-temperature liquids. We emphasize the use of our n and ρ data to compute the molar refraction (R_M) for each of our ices, and how the resulting R_M values compare to those expected from molecular structures. The use of calculated R_M values and measured n values to calculate ice densities, in the absence of direct measurements, is also addressed.

The fundamental stellar atmospheric parameters (T_eff and log g) and 13 chemical abundances are derived for medium-resolution spectroscopy from Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Medium Resolution Survey (MRS) data sets with a deep-learning method. The neural networks we designed, named SPCANet, precisely map LAMOST MRS spectra to stellar parameters and chemical abundances. The stellar labels derived by SPCANet have precisions of 119 K for T_eff and 0.17 dex for log g. The abundance precision of 11 elements including [C/H], [N/H], [O/H], [Mg/H], [Al/H], [Si/H], [S/H], [Ca/H], [Ti/H], [Cr/H], [Fe/H], and [Ni/H] are 0.06 ∼ 0.12 dex, while that of [Cu/H] is 0.19 dex. These precisions can be reached even for spectra with signal-to-noise ratios as low as 10. The results of SPCANet are consistent with those from other surveys such as APOGEE, GALAH, and RAVE, and are also validated with the previous literature values including clusters and field stars. The catalog of the estimated parameters is available at doi:10.12149/101012.

TRAPPIST-1 is an ultracool dwarf hosting a system consisting of seven planets. While orbital properties, radii, and masses of the planets are nowadays well constrained, one of the fascinating open issues is the possibility that an environment hospitable to life could develop on some of these planets. Here, we use a simple formulation of an energy balance model that includes vegetation coverage to investigate the possibility of life affecting the climate of the planets in the TRAPPIST-1 system. Results confirm that planet TRAPPIST-1e has the best chance to be a habitable world and indicate that vegetation coverage significantly affects the resulting temperatures and habitability properties. The influence of vegetation has been evaluated in different scenarios characterized by different vegetation types, land–sea distributions and levels of greenhouse effect. While changes in vegetation type produce small changes, about 0.1%, in the habitable surface fraction, different land–sea distributions, by also affecting the vegetation growth, produce different temperature distributions. Finally, at latitudes where vegetation grows, the lowering of local albedo still represents a relevant contribution in settling the planetary temperature profiles even when levels of greenhouse effect higher than the Earth-like case are considered.

We present MUSE integral field unit (IFU) observations of five individual H ii regions in two giant star-forming complexes in the low-metallicity, nearby dwarf spiral galaxy NGC 300. In combination with high spatial resolution Hubble Space Telescope photometry, we demonstrate the extraction of stellar spectra and classification of individual stars from ground-based IFU data at the distance of 2 Mpc. For the two star-forming complexes, in which no O-type stars had previously been identified, we find a total of 13 newly identified O-type stars and 4 Wolf-Rayet stars (two already-known sources and two Wolf-Rayet star candidates that this work has now confirmed). We use the derived massive stellar content to analyze the impact of stellar feedback on the H ii regions. As already found for H ii regions in the Magellanic Clouds, the dynamics of the analyzed NGC 300 H ii regions are dominated by a combination of the pressure of the ionized gas and stellar winds. Moreover, we analyze the relation between the star formation rate and the pressure of the ionized gas as derived from small (<100 pc) scales, both quantities being systematically overestimated when derived on galactic scales. With the wealth of upcoming IFU instruments and programs, this study serves as a pathfinder for the systematic investigation of resolved stellar feedback in nearby galaxies, delivering the necessary analysis tools to enable massive stellar content and feedback studies sampling an unprecedented range of H ii region properties across entire galaxies in the nearby universe.

The size and structure of the dusty circumnuclear torus in active galactic nuclei (AGNs) can be investigated by analyzing the temporal response of the torus's infrared (IR) dust emission to variations in the AGN ultraviolet/optical luminosity. This method, reverberation mapping, is applicable over a wide redshift range, but the IR response is sensitive to several poorly constrained variables relating to the dust distribution and its illumination, complicating the interpretation of measured reverberation lags. We have used an enhanced version of our torus reverberation mapping code (TORMAC) to conduct a comprehensive exploration of the torus response functions at selected wavelengths, for the standard interstellar medium grain composition. The shapes of the response functions vary widely over the parameter range covered by our models, with the largest variations occurring at shorter wavelengths (≤4.5 μm). The reverberation lag, quantified as the response-weighted delay (RWD), is most affected by the radial depth of the torus, the steepness of the radial cloud distribution, the degree of anisotropy of the AGN radiation field, and the volume filling factor. Nevertheless, we find that the RWD provides a reasonably robust estimate, to within a factor of ∼3, of the luminosity-weighted torus radius, confirming the basic assumption underlying reverberation mapping. However, overall, the models predict radii at 2.2 μm that are typically a factor of ∼2 larger than those derived from K-band reverberation mapping. This is likely an indication that the innermost region of the torus is populated by clouds dominated by large graphite grains.

We present a carefully designed, systematic study of the angular resolution dependence of simulations with the Prometheus-Vertex neutrino-hydrodynamics code. Employing a simplified neutrino heating–cooling scheme in the Prometheus hydrodynamics module allows us to sample the angular resolution between 4° and 05. With a newly implemented static mesh refinement (SMR) technique on the Yin-Yang grid, the angular coordinates can be refined in concentric shells, compensating for the diverging structure of the spherical grid. In contrast to previous studies with Prometheus and other codes, we find that higher angular resolution and therefore lower numerical viscosity provides more favorable explosion conditions and faster shock expansion. We discuss the possible reasons for the discrepant results. The overall dynamics seem to converge at a resolution of about 1°. Applying the SMR setup to marginally exploding progenitors is disadvantageous for the shock expansion, however, because the kinetic energy of downflows is dissipated to internal energy at resolution interfaces, leading to a loss of turbulent pressure support and a steeper temperature gradient. We also present a way to estimate the numerical viscosity on grounds of the measured turbulent kinetic energy spectrum, leading to smaller values that are better compatible with the flow behavior witnessed in our simulations than results following calculations in previous literature. Interestingly, the numerical Reynolds numbers in the turbulent, neutrino-heated postshock layer (some 10 to several hundred) are in the ballpark of expected neutrino drag effects on the relevant length scales. We provide a formal derivation and quantitative assessment of the neutrino drag terms in an appendix.

Interesting chemically peculiar field stars may reflect their stellar evolution history and their possible origin in a different environment from where they are found now; this is one of the most important research fields in Galactic archeology. To explore this further, we have used the CN–CH bands around 4000 Å to identify N-rich metal-poor field stars in LAMOST DR3. Here we expand our N-rich, metal-poor field star sample to ∼100 stars in LAMOST DR5, where 53 of them are newly found in this work. We investigate light elements of common stars between our sample and APOGEE DR14. While Mg, Al, and Si abundances generally agree with the hypothesis that N-rich metal-poor field stars come from enriched populations in globular clusters, it is still inconclusive for C, N, and O. After integrating the orbits of our N-rich field stars and a control sample of normal metal-poor field stars, we find that N-rich field stars have different orbital parameter distributions compared to the control sample—specifically, apocentric distances, maximum vertical amplitude (Z_max), orbital energy, and z-direction angular momentum (L_z). The orbital parameters of N-rich field stars indicate that most of them are inner-halo stars. The kinematics of N-rich field stars support their possible GC origin. The spatial and velocity distributions of our bona fide N-rich field star sample are important observational evidence to constrain simulations of the origin of these interesting objects.

One-dimensional stellar evolution models have been successful at representing the structure and evolution of stars in diverse astrophysical contexts, but complications have been noted in the context of young, magnetically active stars, as well as close binary stars with significant tidal interactions. Numerous puzzles are associated with pre-main-sequence (pre-MS) and active main sequence (MS) stars, relating to their radii, their colors, certain elemental abundances, and the coevality of young clusters, among others. A promising explanation for these puzzles is the distorting effects of magnetic activity and starspots on the structure of active stars. To assist the community in evaluating this hypothesis, we present the Stellar Parameters of Tracks with Starspots (SPOTS) models, a grid of solar-metallicity stellar evolutionary tracks and isochrones that include a treatment of the structural effects of starspots. The models range from 0.1 to 1.3 M_⊙ and from spotless to a surface covering fraction of 85%, and are evolved from the pre-MS to the red giant branch (or 15 Gyr). We also produce two-temperature synthetic colors for our models using empirically calibrated color tables. We describe the physical ingredients included in the SPOTS models and compare their predictions to other modern evolution codes. Finally, we apply these models to several open questions in the field of active stars, including the radii of young eclipsing binaries, the color scale of pre-MS stars, and the existence of sub-subgiants, demonstrating that our models can explain many peculiar features of active stars.

The mechanisms of angular momentum transport and the level of turbulence in protoplanetary disks (PPDs) are crucial for understanding many aspects of planet formation. In recent years, it has been realized that the magneto-rotational instability tends to be suppressed in PPDs due to nonideal magnetohydrodynamic (MHD) effects, and the disk is primarily laminar with accretion driven by magnetized disk winds. In parallel, several hydrodynamic mechanisms have been identified that likely also generate vigorous turbulence and drive disk accretion. In this work, we study the interplay between MHD winds in PPDs with the vertical shear instability (VSI), one of the most promising hydrodynamic mechanisms, through 2D global nonideal MHD simulations with ambipolar diffusion (AD) and ohmic resistivity. For typical disk parameters, MHD winds can coexist with the VSI with accretion primarily wind-driven accompanied by vigorous VSI turbulence. The properties of the VSI remain similar to the unmagnetized case. The wind and overall field configuration are not strongly affected by the VSI turbulence, showing a modest level of variability and corrugation of the midplane current sheet. Weak AD strength or the enhanced coupling between gas and magnetic fields weakens the VSI. The VSI is also weakened with increasing magnetization, and characteristic VSI corrugation modes transition to low-amplitude breathing mode oscillations with strong magnetic fields.

We present quasi-simultaneous radio and X-ray observations of the black hole X-ray binary GRS 1739–278 during the 2015–2016 mini-outbursts, i.e., between 2015 June 10 and 2016 October 31, with the X-ray-to-radio time interval being less than one day. The monitor campaign was run by Swift in the X-rays and by VLA in the radio (at both 5 and 8 GHz). We find that the brightest radio emission is actually achieved during the soft sate, and the spectrum is marginally optically thick with the spectral index α ≈ −0.28 ± 0.17 (flux F_ν ∝ ν^α). For the radio emission in the hard state, we find a large diversity in the spectral index, i.e., a majority of radio spectra are optically thick with −0.5 ≲ α ≲ 0.5, while a few are optically thin, with α being lower than −1 in certain cases. We then investigate the correlation between the luminosities in radio (monochromatic at 5 GHz, ${L}_{{\rm{R}}}$) and 1–10 keV X-rays (${L}_{{\rm{X}}}$) during the hard state. We find that for more than two orders of magnitude variation in the X-ray luminosity, this source exhibits a flat correlation with p ≈ 0.16 (in the form of ${L}_{{\rm{R}}}\propto {L}_{{\rm{X}}}^{p}$), i.e., it belongs to the "outlier" (to the standard correlation with p ≈ 0.6) category that may follow a hybrid correlation. Both the slope and the corresponding luminosity range agree well with those in H1743–322, the prototype of the hybrid correlation. Theoretical implications of our results are discussed.

A galaxy's stellar mass-to-light ratio (${M}_{\star }/L$) is a useful tool for converting luminosity to stellar mass (${M}_{\star }$). However, the practical utility of ${M}_{\star }/L$ inferred from stellar population synthesis (SPS) models is limited by mismatches between the real and assumed models for star-formation history (SFH) and dust geometry, both of which vary within galaxies. Here, we measure spatial variations in ${M}_{\star }/L$ and their dependence on color, SFH, and dust across the disk of M31, using a map of ${M}_{\star }^{\mathrm{CMD}}$ derived from color–magnitude diagrams of resolved stars in the Panchromatic Hubble Andromeda Treasury survey. First, we find comparable scatter in ${M}_{\star }/L$ for the optical and mid-IR, contrary to the common idea that ${M}_{\star }/L$ is less variable in the IR. Second, we confirm that ${M}_{\star }/L$ is correlated with color for both the optical and mid-IR and report color versus ${M}_{\star }/L$ relations (CMLRs) in M31 for filters used in the Sloan Digital Sky Survey and Widefield Infrared Survey Explorer. Third, we show that the CMLR residuals correlate with recent SFH, such that quiescent regions are offset to higher ${M}_{\star }/L$ than star-forming regions at a fixed color. The mid-IR CMLR, however, is not linear due to the high scatter of ${M}_{\star }/L$ in star-forming regions. Finally, we find a flatter optical CMLR than any SPS-based CMLRs in the literature. We show that this is an effect of dust geometry, which is typically neglected but should be accounted for when using optical data to map ${M}_{\star }$.

By conducting three-dimensional hydrodynamical simulations we find that jets that a main-sequence companion launches as it orbits inside the wind acceleration zone of an asymptotic giant branch star can efficiently remove mass from that zone. We assume that during the intensive wind phase a large fraction of the gas in the acceleration zone does not reach the escape velocity. Therefore, in the numerical simulations we blow the wind with a velocity just below the escape velocity. We assume that a main-sequence companion accretes mass from the slow wind via an accretion disk, and launches two opposite jets perpendicular to the equatorial plane. This novel flow interaction shows that, by launching jets, a companion outside a giant star, but close enough to be in the acceleration zone of a slow intensive wind, can enhance the mass-loss rate from the giant star by ejecting some gas that would otherwise fall back onto the giant star. The jets are bent inside the wind acceleration zone and eject mass in a belt on the two sides of the equatorial plane. The jet–wind interaction contains instabilities that mix the shocked jets' gas with the wind, leading to energy transfer from the jets to the wind. Our new simulations add to the rich variety of jet-induced outflow morphologies from evolved stars.

We study the evolution of solar wind entropy based on a conservative formulation of solar wind and turbulence transport model equations, and compare the model results to Voyager 2 measurements. For a polytropic index of γ = 5/3 (>1), entropy increases with distance due to the dissipation of turbulence, being about 12.84% higher at 75 au than at 1 au. However, if the polytropic index satisfies γ < 1, entropy decreases. We show that not only the creation of pickup ions, but also stream-shear leads to a decrease of the solar wind speed. We show that the sum of the solar wind flow energy (kinetic plus enthalpy) and turbulent (magnetic) energy is constant, indicating that kinetic solar wind energy is transferred into turbulent energy via stream-shear and pickup ion isotropization, which then in turn heats the solar wind via the dissipation of turbulence. We compare the theoretical solutions of the solar wind entropy, the solar wind density, the thermal gas pressure, the solar wind proton temperature, and the fluctuating magnetic energy with those measured by Voyager 2. The results show that the theoretical results are in good agreement with the observed results.

Formation of kappa distribution functions and their relaxation to Maxwellian distributions are the main feature of astrophysical and space collisionless plasmas. In this work, we use the magnetosphere of the Earth as a giant plasma laboratory to study the properties of ion kappa distribution functions. Four years of measurements, performed by the multi-satellite Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission during quiet geomagnetic conditions, at geocentric distances from three Earth radii (R_E) to the magnetopause at daytime (of the order of 10R_E), and up to 20R_E at night time are used for the analyses. We find a dependence of the k parameter on the core energy E₀ of a single kappa distribution inside the magnetospheric ring current and in the plasma sheet, for different values of the plasma parameter (the ratio between the plasma and magnetic pressures). We show that k increases with E₀ for all values of plasma parameter, which supports earlier results obtained for the magnetospheres of the Earth, Jupiter, and Saturn, but using lower statistics. However, contrary to previous results, our studies show that the relation between k and E₀ is nonlinear, and most probably is a power law with a nearly constant index. The results obtained are relevant to solve the problem of thermalization of kappa distributions.

Offsets of molecular line emission peaks from continuum peaks are very common but frequently difficult to explain with a single spherical cloud chemical model. We propose that the spatial projection effects of an irregular three-dimensional (3D) cloud structure can be a solution. This work shows that the idea can be successfully applied to the Planck cold clump G224.4-0.6 by approximating it with four individual spherically symmetric cloud cores whose chemical patterns overlap with each other to produce observable line maps. With the empirical physical structures inferred from the observation data of this clump and a gas-grain chemical model, the four cores can satisfactorily reproduce its 850 μm continuum map and the diverse peak offsets of CCS, HC₃N, and N₂H⁺ simultaneously at chemical ages of about 8 × 10⁵ ∼ 3 × 10⁶ yr. The 3D projection effects on chemistry has the potential to explain such asymmetrical distributions of chemicals in many other molecular clouds.

In the present work we analyzed seven globular clusters (GCs) selected from their location in the Galactic bulge and with metallicity values in the range −1.30 ≲ [Fe/H] ≲ −0.50. The aim of this work is first to derive cluster ages assuming single stellar populations and second to identify the stars from first (1G) and second generations (2G) from the main sequence, subgiant, and red giant branches, and to derive their age differences. Based on a combination of UV and optical filters used in this project, we apply the Gaussian mixture models to distinguish the multiple stellar populations. Applying statistical isochrone fitting, we derive self-consistent ages, distances, metallicities, and reddening values for the sample clusters. An average age of 12.3 ± 0.4 Gyr was obtained both using DSED and BaSTI (accounting atomic diffusion effects) isochrones, without a clear distinction between the moderately metal-poor and the more metal-rich bulge clusters, except for NGC 6717 and the inner halo NGC 6362 with ∼13.5 Gyr. We derived a weighted mean age difference between the multiple populations hosted by each GC of 41 ± 170 Myr adopting canonical He abundances; whereas for higher He in 2G stars, this difference reduces to 17 ± 170 Myr, but with individual uncertainties of 500 Myr.

Ice mantles on dust grains play a central role in astrochemistry. Water and complex organic molecules (COMs) are thought to first form on the ice mantles and subsequently are released into the gas phase due to star-formation activity. However, the critical question is whether ice mantles can survive stellar radiation when grains are being heated from ${T}_{d}\sim 10\,{\rm{K}}$ to ≳100 K. In this paper, we first study the effect of suprathermal grain rotation driven by the intense radiation of young stellar objects on the ice mantles. We find that the entire ice mantles can be disrupted into small fragments by centrifugal stress before the water ice and COMs desorb via thermal sublimation. We then study the consequence of resulting ice fragments and find that tiny fragments of radius a ≲ 10 Å exhibit a transient release of COMs due to thermal spikes, whereas larger fragments can facilitate thermal sublimation at much higher rates than from the original icy grain, or the same rate but with temperatures of ∼20–40 K lower. We find that rotational desorption is efficient for hot cores/corinos from the inner to outer regions where the temperature drops to ${T}_{\mathrm{gas}}\sim 40\,{\rm{K}}$ and ${n}_{{\rm{H}}}\sim {10}^{4}\,{\mathrm{cm}}^{-3}$. We discuss the implications of this mechanism for desorption of COMs and water ice in various environments, including outflow cavity walls, photodissociation regions, and protoplanetary disks. Finally, we show that very large aggregate grains can be disrupted into individual icy grains via a rotational disruption mechanism, followed by rotational desorption of ice mantles.

We search for dynamical substructures in the LAMOST DR3 very metal-poor (VMP) star catalog. After cross-matching with Gaia DR2, there are ∼3300 VMP stars with available high-quality astrometric information that have halo-like kinematics. We apply a method based on the self-organizing map StarGO to find groups clustered in the 4D space of orbital energy and angular momentum. We identify 57 dynamically tagged groups (DTGs), which we label DTG-1 to DTG-57. Most of them belong to existing massive substructures in the nearby halo, such as the Gaia Sausage or Sequoia. The stream identified by Helmi et al. is recovered, but the two disjointed portions of the substructure appear to have distinct dynamical properties. The very retrograde substructure Rg5 found previously by Myeong et al. is also retrieved. We report six new DTGs with highly retrograde orbits, two with very prograde orbits, and 12 with polar orbits. By mapping other data sets (APOGEE halo stars, and catalogs of r-process-enhanced and carbon-enhanced metal-poor [CEMP] stars) onto the trained neuron map, we can associate stars with detailed chemical abundances with the DTGs and look for associations with chemically peculiar stars. The highly eccentric Gaia Sausage groups contain representatives of both debris from the satellite itself (which is α-poor) and the Splashed Disk, sent up into eccentric halo orbits from the encounter (and which is α-rich). The new prograde substructures also appear to be associated with the Splashed Disk. The DTGs belonging to the Gaia Sausage host two relatively metal-rich r-II stars and six CEMP stars in different subclasses, consistent with the idea that the Gaia Sausage progenitor is a massive dwarf galaxy. Rg5 is dynamically associated with two highly r-process-enhanced stars with [Fe/H] ∼ −3. This finding indicates that its progenitor might be an ultrafaint dwarf galaxy that has experienced r-process enrichment from neutron star mergers.

The main objective of this paper is to explore abundances of fluorine in hot extreme helium stars (EHes). Overabundance of fluorine is a characteristic feature for cool EHes and R Coronae Borealis stars and further enforces their close connection. For hot EHes this relationship with the cooler EHes, based on their fluorine abundance is unexplored. We present in this paper the first abundance estimates of fluorine determined from singly ionized fluorine lines (F ii) for 10 hot EHe stars from optical spectra. Fluorine abundances were determined using the F ii lines in two windows centered at 3505 Å and 3850 Å. Six of the 10 stars show significant enhancement of fluorine similar to the cool EHes. Two carbon-poor hot EHes show no signature of fluorine and have a significant low upper limit for the F abundance. These fluorine abundances are compared with the other elemental abundances observed in these stars, which provide an idea about the formation and evolution of these stars. The trends of fluorine with C, O, and Ne show that significant helium burning after a CO–He white dwarf merger can account for a majority of the observed abundances. Predictions from simulations of white dwarf mergers are discussed in light of the observed abundances.

The clustering of active galactic nuclei (AGNs) sheds light on their typical large (Mpc-scale) environments, which can constrain the growth and evolution of supermassive black holes. Here we measure the clustering of luminous X-ray-selected AGNs in the Stripe 82X and XMM-XXL-north surveys around the peak epoch of black hole growth, in order to investigate the dependence of luminosity on large-scale AGN environment. We compute the auto-correlation function of AGNs in two luminosity bins, ${10}^{43}\leqslant {L}_{X}\lt {10}^{44.5}$ erg s⁻¹ at z ∼ 0.8 and L_X ≥ 10^44.5 erg s⁻¹ at z ∼ 1.8, and calculate the AGN bias taking into account the redshift distribution of the sources using three different methods. Our results show that while the less luminous sample has an inferred typical halo mass that is smaller than for the more luminous AGNs, the host halo mass may be less dependent on luminosity than suggested in previous work. Focusing on the luminous sample, we calculate a typical host halo mass of ∼10¹³${M}_{\odot }\,{h}^{-1}$, which is similar to previous measurements of moderate-luminosity X-ray AGNs and significantly larger than the values found for optical quasars of similar luminosities and redshifts. We suggest that the clustering differences between different AGN selection techniques are dominated by selection biases, and not due to a dependence on AGN luminosity. We discuss the limitations of inferring AGN triggering mechanisms from halo masses derived by large-scale bias.

An observation of Jupiter's tidal response is anticipated for the ongoing Juno spacecraft mission. We combine self-consistent, numerical models of Jupiter's equilibrium tidal response with observed Doppler shifts from the Juno gravity science experiment to test the sensitivity of the spacecraft to tides raised by the Galilean satellites and the Sun. The concentric Maclaurin spheroid (CMS) method finds the equilibrium shape and gravity field of a rotating, liquid planet with the tide raised by a satellite, expanded in Love numbers (k_nm). We present improvements to the CMS theory that eliminate an unphysical center-of-mass offset and study in detail the convergence behavior of the CMS approach. We demonstrate that the dependence of k_nm with orbital distance is important when considering the combined tidal response for Jupiter. Conversely, the details of the interior structure have a negligible influence on k_nm for models that match the zonal harmonics J₂, J₄, and J₆, already measured to high precision by Juno. As the mission continues, improved coverage of Jupiter's gravity field at different phases of Io's orbit is expected to yield an observed value for the degree-two Love number (k₂₂) and potentially select higher-degree k_nm. We present a test of the sensitivity of the Juno Doppler signal to the calculated k_nm, which suggests the detectability of k₃₃, k₄₂, and k₃₁, in addition to k₂₂. A mismatch of a robust Juno observation with the remarkably small range in calculated Io equilibrium, k₂₂ = 0.58976 ± 0.0001, would indicate a heretofore uncharacterized dynamic contribution to the tides.

We investigate the infrared properties of asymptotic giant branch (AGB) stars in our Galaxy and the Magellanic Clouds using various infrared observational data and theoretical models. We use catalogs for the sample of 4996 AGB stars in our Galaxy and about 39,000 AGB stars in the Magellanic Clouds from the available literature. For each object in the sample, we cross-identify the 2MASS, Wide-field Infrared Survey Explorer, and Spitzer counterparts. To compare the physical properties of O- and C-rich AGB stars in our Galaxy and the Magellanic Clouds, we present IR two-color diagrams (2CDs) using various photometric data. We perform radiative transfer model calculations for AGB stars using various possible parameters of central stars and dust shells. Using the dust opacity functions of amorphous silicate and carbon, the theoretical dust shell models can roughly reproduce the observations of AGB stars on various IR 2CDs. Compared with our Galaxy, we find that the Magellanic Clouds are deficient in AGB stars with thick dust shells. Compared with the Large Magellanic Cloud (LMC), the Small Magellanic Cloud (SMC) is more deficient in AGB stars with thick dust shells. This could be because the Magellanic Clouds are more metal-poor than our Galaxy and the LMC is more metal-rich than the SMC. We also present the IR properties of known pulsating variables. Investigating the magnitude distributions at mid-IR (MIR) bands for AGB stars in the Magellanic Clouds, we find that the SMC is more deficient in bright AGB stars at MIR bands compared with the LMC.

The first pulsating ultraluminous X-ray source (PULX) to be identified is M82 X-2. After the discovery in 2014, NuSTAR observed the M82 field 15 times throughout 2015 and 2016. In this paper, we report the results of pulsation searches in all of these data sets and find only one new detection. This new detection allows us to refine the orbital period of the source and measure an average spin-down rate between 2014 and 2016 of ∼−6 × 10⁻¹¹ Hz s⁻¹, which is in contrast to the strong spin-up seen during the 2014 observations, representing the first detection of spin-down in a PULX system. Thanks to the improved orbital solution allowed by this new detection, we are also able to detect pulsations in additional segments of the original 2014 data set. We find a glitch superimposed on the very strong and variable spin-up already reported—the first positive glitch identified in a PULX system. We discuss the new findings in the context of current leading models for PULXs.

We report the discovery of the first short-period binary in which a hot subdwarf star (sdOB) filled its Roche lobe and started mass transfer to its companion. The object was discovered as part of a dedicated high-cadence survey of the Galactic plane named the Zwicky Transient Facility and exhibits a period of P = 39.3401(1) minutes, making it the most compact hot subdwarf binary currently known. Spectroscopic observations are consistent with an intermediate He-sdOB star with an effective temperature of ${T}_{\mathrm{eff}}$ = 42,400 ± 300 K and a surface gravity of $\mathrm{log}(g)$ = 5.77 ± 0.05. A high signal-to-noise ratio GTC+HiPERCAM light curve is dominated by the ellipsoidal deformation of the sdOB star and an eclipse of the sdOB by an accretion disk. We infer a low-mass hot subdwarf donor with a mass M_sdOB = 0.337 ± 0.015 ${M}_{\odot }$ and a white dwarf accretor with a mass M_WD = 0.545 ± 0.020 ${M}_{\odot }$. Theoretical binary modeling indicates the hot subdwarf formed during a common envelope phase when a 2.5–2.8 ${M}_{\odot }$ star lost its envelope when crossing the Hertzsprung gap. To match its current ${P}_{\mathrm{orb}}$, ${T}_{\mathrm{eff}}$, $\mathrm{log}(g)$, and masses, we estimate a post–common envelope period of ${P}_{\mathrm{orb}}$ ≈ 150 minutes and find that the sdOB star is currently undergoing hydrogen shell burning. We estimate that the hot subdwarf will become a white dwarf with a thick helium layer of ≈0.1 ${M}_{\odot }$, merge with its carbon/oxygen white dwarf companion after ≈17 Myr, and presumably explode as a thermonuclear supernova or form an R CrB star.

Based on imaging and spectroscopic data, we develop a 3D model for the Huygens Region of the Orion Nebula. ${\theta }^{1}$ Ori C, the hottest star in the Trapezium, is surrounded by a wind-blown Central Bubble that opens SW into the Extended Orion Nebula. Outside of this feature lies a layer of ionized gas at about 0.4 pc from ${\theta }^{1}$ Ori C. Both of these features are moving rapidly away from ${\theta }^{1}$ Ori C with an expansion age for the Central Bubble of only 15,000 yr.

This paper explores the mechanisms that regulate the formation and evolution of stellar black hole binaries (BHBs) around supermassive black holes (SMBHs). We show that dynamical interactions can efficiently drive "in situ" BHB formation if the SMBH is surrounded by a massive nuclear cluster, while orbitally segregated star clusters can replenish the BHB reservoir in SMBH-dominated nuclei. We discuss how the combined action of stellar hardening and mass segregation sculpts the BHB orbital properties. We use direct N-body simulations including post-Newtonian corrections up to 2.5 order to study the BHB–SMBH interplay, showing that the Kozai–Lidov mechanism plays a crucial role in shortening the lifetime of binaries. We find that the merging probability weakly depends on the SMBH mass in the ${10}^{6}\mbox{--}{10}^{9}\,{M}_{\odot }$ range, leading to a merger rate ${\rm{\Gamma }}\simeq 3\mbox{--}8$ yr⁻¹ Gpc⁻³ at redshift zero. Nearly 40% of the mergers have masses in the "BH mass gap," $50\mbox{--}140\,{M}_{\odot }$, thus indicating that galactic nuclei are ideal places to form BHs in this mass range. We argue that gravitational wave (GW) sources with component masses m₁ > 40 M_⊙ and ${m}_{2}\lt 30\,{M}_{\odot }$ would represent a strong indicator of a galactic nucleus origin. The majority of these mergers could be multiband GW sources in the local universe: nearly 40% might be seen by LISA as eccentric sources and, a few years later, as circular sources by LIGO and the Einstein Telescope, making decihertz observatories like DECIGO unique instruments to bridge the observations during the binary inspiral.

The protoplanetary disk around the T Tauri star GM Aur was one of the first hypothesized to be in the midst of being cleared out by a forming planet. As a result, GM Aur has had an outsized influence on our understanding of disk structure and evolution. We present 1.1 and 2.1 mm ALMA continuum observations of the GM Aur disk at a resolution of ∼50 mas (∼8 au), as well as HCO⁺J = 3 − 2 observations at a resolution of ∼100 mas. The dust continuum shows at least three rings atop faint, extended emission. Unresolved emission is detected at the center of the disk cavity at both wavelengths, likely due to a combination of dust and free–free emission. Compared to the 1.1 mm image, the 2.1 mm image shows a more pronounced "shoulder" near R ∼ 40 au, highlighting the utility of longer-wavelength observations for characterizing disk substructures. The spectral index α features strong radial variations, with minima near the emission peaks and maxima near the gaps. While low spectral indices have often been ascribed to grain growth and dust trapping, the optical depth of GM Aur's inner two emission rings renders their dust properties ambiguous. The gaps and outer disk (R > 100 au) are optically thin at both wavelengths. Meanwhile, the HCO⁺ emission indicates that the gas cavity is more compact than the dust cavity traced by the millimeter continuum, similar to other disks traditionally classified as "transitional."

In this paper, we present the results of three-dimensional numerical simulation of upward overshooting in turbulent compressible convection at large relative stability parameter S. Similar to the previous simulations at small S, we find that the convectively stable zone can be partitioned into three layers: the thermal adjustment layer, the turbulent dissipation layer, and the thermal dissipation layer. Despite of this similarity, there exist significant differences in several aspects. First, for small S, the thermal structure is altered considerably near the interface between the convectively unstable and stable zones. For extremely large S, the thermal structure is only slightly changed. Second, the overshooting distance decreases at small S, but it can increase when S is large enough. Third, for small S, the fluid motions tend to be less active when S increases. However, the fluid motions can be more active when S is large enough. We find that the structure of counter cells has a significant impact on the penetration depth.

Long-period Mira variable stars are considered to have relatively high initial masses and may be potentially useful as tracers of spiral arm structure of the Milky Way. From 2004 to 2017, we monitored long-period Mira candidates selected from the IRAS color–color diagram in the near-infrared K' band. As an initial result of this study, we found 108 Mira variables and determined their periods, mean magnitudes, and amplitudes. Most of them are located between 0° and 90° in Galactic longitude. The peak of their period distribution is at around 500 days, which is longer than the typical value for Mira variables selected in optical surveys. Distances to our Mira variables have also been estimated using the period–luminosity relation (PLR) in 3.4 μm with the help of a three-dimensional map of interstellar extinction. While the K_s-band PLR has a large scatter at longer periods (log P > 2.6), the PLR based on the Wide-field Infrared Survey Explorer 3.4 μm data has a much smaller scatter. We compare the spatial distribution of our sample to the spiral arms in the literature, and discuss the possible association of the long-period Mira variables with the spiral arms although the limited spatial coverage and the limited distance accuracy of the current sample prevent us from drawing a firm conclusion.

Calculations are made of the energy supplied to the solar wind by the rapid decay of density fluctuations, identified as ion acoustic waves. It is shown that this process supplies an appreciable fraction, perhaps nearly all, of the observed heating of the solar wind. This process may be an important step in the conversion of magnetic turbulence to particle energy.

Inspired by recent observations suggesting that photospheric magnetic flux cancellation occurs much more frequently than previously thought, we analytically estimated the energy released from reconnection driven by photospheric flux cancellation, and propose that it can act as a mechanism for chromospheric and coronal heating. Using two-dimensional simulations we validated the analytical estimates and studied the resulting atmospheric response. In the present work, we set up 3D resistive MHD simulations of two canceling polarities in a stratified atmosphere with a horizontal external field to further validate and improve upon the analytical estimates. The computational evaluation of the parameters associated with the energy release are in good qualitative agreement with the analytical estimates. The computational Poynting energy flux into the current sheet is in good qualitative agreement with the analytical estimates, after correcting the analytical expression to better account for the horizontal extent of the current sheet. The atmospheric response to the cancellation is the formation of hot ejections, cool ejections, or a combination of both hot and cool ejections, which can appear with a time difference and/or be spatially offset, depending on the properties of the canceling region and the resulting height of the reconnection. Therefore, during the cancellation, a wide spectrum of ejections can be formed, which can account for the variety of multi-thermal ejections associated with Ellerman bombs, UV bursts, and IRIS bombs, and also other ejections associated with small-scale canceling regions and spicules.

Broad absorption-line (BAL) features in quasar spectra reveal an unambiguous signature of energetic outflows from central supermassive black holes, and thus, BAL quasars are prime targets for investigating the potential process of luminous quasar feedback on galaxies. We analyzed the rest-UV spectrum of an "overlapping trough" iron low-ionization broad absorption-line quasar (FeLoBAL) SDSS J135246.37+423923.5 using the novel spectral synthesis code SimBAL and discovered an extraordinarily fast and energetic BAL outflow. Our analysis revealed outflow velocities reaching $\sim -{\rm{38,000}}\,\mathrm{km}\,{{\rm{s}}}^{-1}$ with a velocity width of $\sim {\rm{10,000}}\,\mathrm{km}\,{{\rm{s}}}^{-1}$, which is the largest FeLoBAL outflow velocity measured to date. The column density of the outflow gas is log${N}_{{\rm{H}}}\sim 23.2\,({\mathrm{cm}}^{-1})$ with the log kinetic luminosity $\mathrm{log}{L}_{\mathrm{KE}}\sim 48.1$ (erg s⁻¹), which exceeds the bolometric luminosity of the quasar and is energetic enough to effectively drive quasar feedback. The energy estimate for the outflow is far greater than the estimates from any BAL object previously reported. The object also shows "anomalous reddening" and a significant scattered component that we were able to model with SimBAL. We found the first definitive case for radiation filtering in an additional zero-velocity absorption component that required an absorbed continuum to produce the particular absorption lines observed (Mg ii, Al iii, and Al ii) without also producing the high-ionization lines such as C iv.

We recently repeated an earlier analysis by Garcia showing that large (≥M3.0) solar X-ray flares associated with solar energetic particle (SEP) events have significantly lower peak X-ray flux ratios R = (0.04–0.5 nm)/(0.1–0.8 nm), proxies for flare peak temperatures, than those without SEP events. As we expect SEP events to be produced by shocks ahead of fast coronal mass ejections (CMEs), a smaller R for an X-ray flare of a given peak flux Fp should also be more likely to be accompanied by a fast (Vcme > 1000 km s⁻¹) CME. We confirm this expectation, examine the role played by the ratios R in correlations between Fp and CME speeds Vcme, and then compare CME widths W, Vcme, and R with each other. We consider an apparent conflict between a global scaling model of eruptive events showing Vcme scaling with higher R and our confirmation that the Garcia analysis implies that faster CMEs are associated with flares of lower R. The R values are examined for 16 large flares of the well-studied AR 12192, for which nearly all flares had no associated CMEs. Those flares share the same high values of R as other active region (AR) flares with no CMEs. We also find that small (<M3.0) flares of filament eruptions leading to SEP events share the lower R values of larger flares with fast CMEs.

In this study, the detailed magnetic field structure of the dense protostellar core Barnard 335 (B335) was revealed, based on near-infrared polarimetric observations of background stars to measure dichroically polarized light produced by magnetically aligned dust grains in the core. Magnetic fields pervading B335 were mapped using 24 stars after subtracting unrelated ambient polarization components, revealing that they have an axisymmetrically distorted hourglass-shaped structure toward the protostellar core. On the basis of simple two- and three-dimensional magnetic field modeling, magnetic inclination angles in the plane-of-sky and line-of-sight directions were determined to be 90° ± 7° and 50° ± 10°, respectively. The total magnetic field strength of B335 was determined to be 30.2 ± 17.7 μG. The critical mass of B335, evaluated using both magnetic and thermal/turbulent support against collapse, was determined to be M_cr = 3.37 ± 0.94 M_⊙, which is identical to the observed core mass of M_core = 3.67 M_⊙. We thus concluded that B335 started its contraction from a condition near equilibrium. We found a linear relationship in the polarization versus extinction diagram, up to A_V ∼ 15 mag toward the stars with the greatest obscuration, which verified that our observations and analysis provide an accurate depiction of the core.

The Interstellar Boundary Explorer (IBEX) observes the "ribbon" of enhanced energetic neutral atom (ENA) fluxes from the outer heliosphere. The ribbon flux is likely formed from the neutralization of energetic pickup ions (PUIs) gyrating in the interstellar magnetic field outside the heliopause. Voyager 1 crossed the heliopause in 2012 and has observed several shocks in the very local interstellar medium (VLISM) that likely originate from merged interaction regions in the inner heliosphere that propagated outside the heliopause. We simulate the response of PUIs and the IBEX ribbon flux to solar disturbances propagating into the VLISM. First, we show that PUIs outside the heliopause respond significantly to the dynamic neutralized solar wind (SW) via charge exchange and to interactions with shocks via adiabatic heating/cooling. However, the evolution of ribbon fluxes at 1 au is primarily driven by changes in the neutralized SW and not PUI interactions with shocks outside the heliopause. Comparisons with IBEX observations of the ribbon at 1.1 keV show that an abrupt decrease in ENA fluxes observed in 2012 was caused by a drop in SW (and thus neutralized SW) speed by ∼100 km s⁻¹. Our simulation predicts a recovery of 1.1 keV ribbon fluxes starting in 2019 to levels observed early in the mission owing to an increase in SW speed. We also estimate that the presence of interstellar helium in the VLISM reduces the effectiveness of charge-exchange sources for PUIs and reduces the model ribbon flux at 1 au by ∼40%, matching well with IBEX ribbon fluxes.

The tip of the red giant branch (TRGB) method provides one of the most accurate and precise means of measuring the distances to nearby galaxies. Here we present a multi-wavelength, VIJHK absolute calibration of the TRGB based on observations of TRGB stars in the Large Magellanic Cloud (LMC), grounded on a geometric distance, determined by detached eclipsing binaries (DEBs). This paper presents a more detailed description of the method first presented by Freedman et al. for measuring corrections for the total line-of-sight extinction and reddening to the LMC. In this method, we use a differential comparison of the red giant population in the LMC, first with red giants in the Local Group galaxy IC 1613, and then with those in the Small Magellanic Cloud (SMC). As a consistency check, we derive an independent calibration of the TRGB sequence using the SMC alone, invoking its geometric distance also calibrated by DEBs. An additional consistency check comes from near-infrared observations of Galactic globular clusters covering a wide range of metallicities. In all cases we find excellent agreement in the zero-point calibration. We then examine the recent claims by Yuan et al., demonstrating that, in the case of the SMC, they corrected for extinction alone while neglecting the essential correction for reddening. In the case of IC 1613, we show that their analysis contains an incorrect treatment of (over-correction for) metallicity. Using our revised (and direct) measurement of the LMC TRGB extinction, we find a value of H₀ = 69.6 ± 0.8 (±1.1% stat) ± 1.7 (±2.4% sys) km s⁻¹ Mpc⁻¹.

The search for water-rich Earth-sized exoplanets around low-mass stars is rapidly gaining attention because they represent the best opportunity to characterize habitable planets in the near future. Understanding the atmospheres of these planets and determining the optimal strategy for characterizing them through transmission spectroscopy with our upcoming instrumentation is essential in order to constrain their environments. For this study, we present simulated transmission spectra of tidally locked Earth-sized ocean-covered planets around late-M to mid-K stellar spectral types, utilizing the results of general circulation models previously published by Kopparapu et al. as inputs for our radiative transfer calculations performed using NASA's Planetary Spectrum Generator (psg.gsfc.nasa.gov). We identify trends in the depth of H₂O spectral features as a function of planet surface temperature and rotation rate. These trends allow us to calculate the exposure times necessary to detect water vapor in the atmospheres of aquaplanets through transmission spectroscopy with the upcoming James Webb Space Telescope as well as several future flagship space telescope concepts under consideration (the Large UV Optical Infrared Surveyor and the Origins Space Telescope) for a target list constructed from the Transiting Exoplanet Survey Satellite (TESS) Input Catalog (TIC). Our calculations reveal that transmission spectra for water-rich Earth-sized planets around low-mass stars will be dominated by clouds, with spectral features <20 ppm, and only a small subset of TIC stars would allow for the characterization of an ocean planet in the habitable zone. We thus present a careful prioritization of targets that are most amenable to follow-up characterizations with next-generation instrumentation, in order to assist the community in efficiently utilizing precious telescope time.

Long-term 17.6 GHz radio monitoring of the broad absorption-line quasar, Mrk 231, detected a strong flare in late 2017. This triggered four epochs of Very Long Baseline Array (VLBA) observations from 8.4 to 43 GHz over a 10 week period as well as an X-ray observation with NuSTAR. This was the third campaign of VLBA monitoring that we have obtained. The 43 GHz VLBA was degraded in all epochs, with only 7 of 10 antennas available in three epochs and 8 in the first epoch. However, useful results were obtained due to a fortuitous capturing of a complete, short 100 mJy flare at 17.6 GHz, both growth and decay. This provided useful constraints on the physical model of the ejected plasma that were not available in previous campaigns. We consider four classes of models: discrete ejections (both protonic and positronic) and jetted (protonic and positronic). The most viable model is a "dissipative bright knot" in a faint background leptonic jet with an energy flux ∼10⁴³ erg s⁻¹. Inverse Compton scattering calculations (based on these models) in the ambient quasar photon field explains the lack of a detectable increase in X-ray luminosity measured by NuSTAR. We show that the core (the bright knot) moves toward a nearby secondary at ≈0.97c. The background jet is much fainter. Evidently, the high-frequency VLBA core does not represent the point of origin of blazar jets, in general, and optical depth "core shift" estimates of jet points of origin can be misleading.

In the present study, we use the time-dependent wave packet (TDWP) method to calculate the thermal rate constants for the reaction Li + HD⁺(v = 0, 1) → LiH/LiD + H⁺/D⁺ in the temperature range of 200–5000 K on the potential energy surface constructed by Martinazzo et al. Total rate constants for both the v = 0 and v = 1 reactions exhibit simple Arrhenius behavior and are compared with previous isotope reactions. Total rate constants for v = 1 are several times larger than those of v = 0, particularly in the low-temperature region. For the two channels of the reaction, the vibrational excitation of HD⁺ greatly promotes the formation rate of the products LiH and LiD. For v = 0, the rate constants of LiH and LiD are comparable, while for v = 1, the rate constants of LiH are more than two times larger than those of LiD. The state-resolved rate constants show that the products LiH and LiD molecules can be excited to higher vibrational states and are preferably formed with hotter rotational states when the reactant HD⁺ is vibrationally excited. Applications of these rate constants in the modeling of the astrophysical sources are discussed.

The collapse of a protostellar envelope results in the growth of a protostar and the development of a protoplanetary disk, playing a critical role during the early stages of star formation. Characterizing the gas infall in the envelope constrains the dynamical models of star formation. We present unambiguous signatures of infall, probed by optically thick molecular lines, toward an isolated embedded protostar, BHR 71 IRS1. The three-dimensional radiative transfer calculations indicate that a slowly rotating infalling envelope model following the "inside-out" collapse reproduces the observations of both ${\mathrm{HCO}}^{+}$$J=4\to 3$ and CS $J=7\to 6$ lines, as well as the low-velocity emission of the HCN $J=4\to 3$ line. The envelope has a model-derived age of 12,000 ± 3000 yr after the initial collapse. The envelope model underestimates the high-velocity emission at the HCN $J=4\to 3$ and H¹³CN $J=4\to 3$ lines, where outflows or a Keplerian disk may contribute. The ALMA observations serendipitously discover the emission of complex organic molecules (COMs) concentrated within a radius of 100 au, indicating that BHR 71 IRS1 harbors a hot corino. Eight species of COMs are identified, including CH₃OH and CH₃OCHO, along with H₂CS, SO₂ and HCN v₂ = 1. The emission of methyl formate and ¹³C-methanol shows a clear velocity gradient within a radius of 50 au, hinting at an unresolved Keplerian rotating disk.

Magnetic reconnection, a fundamentally important process in astrophysics, is believed to be initiated by the tearing instability of an electric current sheet, a region where magnetic field abruptly changes direction. Recent studies have suggested that the amount of magnetic shear in these structures is a critical parameter for the switch-on nature of magnetic reconnection in the solar atmosphere, at large spatial scales. We present results of visco-resistive magnetohydrodynamic simulations of magnetic reconnection in 3D current sheets with conditions appropriate to the solar corona. We follow the evolution of the linear and nonlinear 3D tearing instability. We find that, depending on the parameter space, magnetic shear can play a vital role in the onset of significant energy release and plasma heating. Two regimes in our study exist, dependent on whether the current sheet is longer or shorter than the wavelength of the fastest growing mode, thus determining whether subharmonics are present in the actual system. In one parameter regime, where the fastest growing parallel mode has subharmonics, the subsequent coalescence of 3D plasmoids dominates the nonlinear evolution, with magnetic shear playing only a weak role in the amount of energy released. In the second parameter regime, where the fastest growing parallel mode has no subharmonics, only strongly sheared current sheets, where 3D effects are strong enough, show any significant energy release. We expect both regimes to exist on the Sun, and so our results have important consequences for the question of reconnection onset in various solar physics applications.

We run three long-timescale general-relativistic magnetohydrodynamic simulations of radiatively inefficient accretion flows (RIAFs) onto non-rotating black holes. Our aim is to achieve steady-state behavior out to large radii and understand the resulting flow structure. A simulation with adiabatic index Γ = 4/3 and small initial alternating poloidal magnetic field loops is run to a time of 440,000 GM/c³, reaching inflow equilibrium inside a radius of 370 GM/c². Variations with larger alternating field loops and with Γ = 5/3 are run to 220,000 GM/c³, attaining equilibrium out to 170 GM/c² and 440 GM/c². There is no universal self-similar behavior obtained at radii in inflow equilibrium: the Γ = 5/3 simulation shows a radial density profile with a power-law index ranging from −1 in the inner regions to −1/2 in the outer regions, while the others have a power-law slope ranging from −1/2 to close to −2. Both simulations with small field loops reach a state with polar inflow of matter, while the more ordered initial field has polar outflows. However, unbound outflows remove only a factor of order unity of the inflowing material over a factor of ∼300 in radius. Our results suggest that the dynamics of RIAFs are sensitive to how the flow is fed from larger radii, and may differ appreciably in different astrophysical systems. Millimeter images appropriate for Sgr A* are qualitatively (but not quantitatively) similar in all simulations, with a prominent asymmetric image due to Doppler boosting.

Gravitational lensing sometimes dominates the observed properties of apparently very bright objects. We present morphological properties in the high-resolution (FWHM ∼ 015) Atacama Large Millimeter/submillimeter Array (ALMA) 1 mm map for an ultraluminous quasar at z = 6.30, SDSS J010013.02+280225.8 (hereafter J0100+2802), whose black hole (BH) mass M_BH is the most massive (∼1.2 × 10¹⁰M_⊙) at z > 6 ever known. We find that the continuum emission of J0100+2802 is resolved into a quadruple system within a radius of 02, which can be interpreted as either multiple dusty star-forming regions in the host galaxy or multiple images due to strong gravitational lensing. The Mg ii absorption and the potential Lyα line features have been identified at z = 2.33 in the near-infrared spectroscopy toward J0100+2802, and a simple mass model fitting well reproduces the positions and flux densities of the quadruple system, both of which are consistent with the latter interpretation. Although a high-resolution map taken in the Advanced Camera for Survey on board Hubble Space Telescope (HST) shows a morphology with an apparently single component, in our fiducial lens mass model it can simply be explained by a ∼50 pc scale offset between the ALMA and HST emission regions. In this case, the magnification factor for the observed HST emission is obtained to ∼450, reducing the intrinsic M_BH estimate to below 10⁹M_⊙. The confirmation or the rejection of the gravitational lensing scenario is important for our understanding of the supermassive BHs in the early universe.

We use high spatial resolution stellar velocity maps from the Gemini integral-field spectrograph (IFS) and wide-field velocity maps from the McDonald Mitchell IFS to study the stellar velocity profiles and kinematic misalignments from ∼200 pc to ∼20 kpc in 20 early-type galaxies (ETGs) with stellar mass M_* > 10^11.7M_⊙ in the MASSIVE survey. While 80% of the galaxies have low spins (λ < 0.1) and low rotational velocities (<50 km s⁻¹) in both the central region and the main body, we find a diverse range of velocity features and misalignment angles. For the 18 galaxies with measurable central kinematic axes, 10 have well aligned kinematic axis and photometric major axis, and the other eight galaxies have misalignment angles that are distributed quite evenly from 15° to the maximal value of 90°. There is a strong correlation between central kinematic misalignment and galaxy spin, where all four galaxies with significant spins have well aligned kinematic and photometric axes, but only 43% of the low-spin galaxies are well aligned. The central and main-body kinematic axes within a galaxy are not always aligned. When the two kinematic axes are aligned (∼60% of the cases), they are either also aligned with the photometric major axis or orthogonal to it. We find 13 galaxies to also exhibit noticeable local kinematic twists, and one galaxy to have a counterrotating core. A diverse assembly history consisting of multiple gas-poor mergers of a variety of progenitor mass ratios and orbits is likely to be needed to account for the predominance of low spins and the wide range of central and main-body velocity features reported here for local massive ETGs.

The non-uniform distribution of gas and protostars in molecular clouds is caused by combinations of various physical processes that are difficult to separate. We explore this non-uniform distribution in the M17 molecular cloud complex that hosts massive star formation activity using the ¹²CO (J = 1–0) and ¹³CO (J = 1–0) emission lines obtained with the Nobeyama 45 m telescope. Differences in clump properties such as mass, size, and gravitational boundedness reflect the different evolutionary stages of the M17-H ii and M17-IRDC clouds. Clumps in the M17-H ii cloud are denser, more compact, and more gravitationally bound than those in M17-IRDC. While M17-H ii hosts a large fraction of very dense gas (27%) that has a column density larger than the threshold of ∼1 g cm⁻² theoretically predicted for massive star formation, this very dense gas is deficient in M17-IRDC (0.46%). Our HCO⁺ (J = 1–0) and HCN (J = 1–0) observations with the Taeduk Radio Astronomy Observatory 14 m telescope trace all gas with a column density higher than 3 × 10²² cm⁻², confirming the deficiency of high-density (≳10⁵ cm⁻³) gas in M17-IRDC. Although M17-IRDC is massive enough to potentially form massive stars, its deficiency of very dense gas and gravitationally bound clumps can explain the current lack of massive star formation.

New Hubble Space Telescope/STIS optical spectra were obtained for a sample of early-type stars with existing International Ultraviolet Explorer UV spectra. These data were used to construct optical extinction curves whose general properties are discussed elsewhere. In this paper, we identify extinction features in the curves that are wider than diffuse interstellar bands (DIBs) but narrower than the well known broadband variability. This intermediate scale structure, or ISS, contains distinct features whose peaks can contribute a few percent to 20% of the total extinction. Most of the ISS variation can be captured by three principal components. We model the ISS with three Drude profiles and show that their strengths and widths vary from one sight line to another, but their central positions are stable, near 4370, 4870, and 6300 Å. The very broad structure (VBS) in optical curves appears to be a minimum between the 4870 and 6300 Å absorption peaks. We find relations among the fit parameters and provide a physical interpretation of them in terms of a simplistic grain model. Finally, we note that the strengths of the 4370 and 4870 Å features are correlated to the strength of the 2175 Å UV bump, but that the 6300 Å feature is not, and that none of the ISS features are related to R(V). However, we verify that the broadband curvature of the continuous optical extinction is strongly related to R(V).

We report on the detection of a statistically significant flare-like event in the Mg ii λ 2798 Å emission line and the UV Fe ii band of CTA 102 during the outburst of fall 2017. The ratio between the maximum and minimum of λ3000 Å continuum flux for the observation period (2010−2017) is 179 ± 15. Respectively, the max/min ratios 8.1 ± 10.5 and 34.0 ± 45.5 confirmed the variability of the Mg ii emission line and of the Fe ii band. The highest levels of emission line fluxes recorded coincide with a superluminal jet component traversing through a stationary component located ∼0.1 mas from the 43 GHz core. Additionally, comparing the Mg ii line profile in the minimum of activity against the one in the maximum, we found that the latter is broader and blueshifted. As a result of these findings, we can conclude that the non-thermal continuum emission produced by material in the jet moving at relativistic speeds is related to the broad emission line fluctuations. Consequently, these fluctuations are also linked to the presence of broad-line region (BLR) clouds located ∼25 pc from the central engine, outside the inner parsec, where the canonical BLR is located. Our results suggest that during strong activity in CTA 102, the source of non-thermal emission and broad-line clouds outside the inner parsec introduces uncertainties in the estimates of black hole (BH) mass. Therefore, it is important to estimate the BH mass, using single-epoch or reverberation mapping techniques, only with spectra where the continuum luminosity is dominated by the accretion disk.

We search for high-redshift (z > 4.5) X-ray active galactic nuclei (AGNs) in the deep central (off-axis angle < 57) region of the 7 Ms Chandra Deep Field-South X-ray image. We compile an initial candidate sample from direct X-ray detections. We then probe more deeply in the X-ray data by using preselected samples with high spatial resolution near-infrared (NIR)/mid-infrared (MIR) (Hubble Space Telescope (HST) 1.6 μm and Spitzer 4.5 μm) and submillimeter (ALMA 850 μm) observations. The combination of the NIR/MIR and submillimeter preselections allows us to find X-ray sources with a wide range of dust properties and spectral energy distributions (SEDs). We use the SEDs from the optical to the submillimeter to determine if previous photometric redshifts were plausible. Only five possible z > 5 X-ray AGNs are found, all of which might also lie at lower redshifts. If they do lie at high redshifts, then two are Compton-thick AGNs. Three of the five are ALMA 850 μm sources, including the two Compton-thick AGN candidates. We find that (i) the number density of X-ray AGN drops rapidly at high redshifts, (ii) the detected AGNs do not contribute significantly to photoionization at z > 5, and (iii) the measured X-ray light density over z = 5–10 implies a very low black hole accretion density with very little growth in the black hole mass density in this redshift range.

The accretion-powered X-ray pulsar GX 301−2 was observed with the balloon-borne X-Calibur hard X-ray polarimeter during late 2018 December, with contiguous observations by the Neutron star Interior Composition Explorer Mission (NICER) X-ray telescope, the Swift X-ray Telescope and Burst Alert Telescope, and the Fermi Gamma-ray Burst Monitor spanning several months. The observations detected the pulsar in a rare apastron flaring state coinciding with a significant spin up of the pulsar discovered with the Fermi Gamma-ray Burst Monitor. The X-Calibur, NICER, and Swift observations reveal a pulse profile strongly dominated by one main peak, and the NICER and Swift data show strong variation of the profile from pulse to pulse. The X-Calibur observations constrain for the first time the linear polarization of the 15–35 keV emission from a highly magnetized accreting neutron star, indicating a polarization degree of $({27}_{-27}^{+38})$% (90% confidence limit) averaged over all pulse phases. We discuss the spin up and the X-ray spectral and polarimetric results in the context of theoretical predictions. We conclude with a discussion of the scientific potential of future observations of highly magnetized neutron stars with the more sensitive follow-up mission XL-Calibur.

In quiescence, Sgr A* is surprisingly dim, shining 100,000 times less than expected for its environment. This problem has motivated a host of theoretical models to explain radiatively inefficient accretion flows. The Chandra Galactic Center X-ray Visionary Program obtained approximately 3 Ms (1 month) of Chandra high-energy transmission grating (HETG) data, offering the only opportunity to examine the quiescent X-ray emission of Sgr A* with high-resolution spectroscopy. Utilizing custom background regions and filters for removing overlapping point sources, this work provides the first-ever look at stacked HETG spectra of Sgr A*. We model the background data sets with a cubic spline and fit the unbinned Sgr A* spectra with a simple parametric model of a power law plus Gaussian lines under the effects of interstellar extinction. We detect a strong 6.7 keV iron emission line in the HEG spectra and a 3.1 keV emission line in the MEG spectra. In all cases, the line centroids and equivalent widths are consistent with those measured from low-resolution CCD spectra. An examination of the unbinned, stacked HEG ± 1 spectrum reveals fine structure in the iron line complex. In addition to resolving the resonant and forbidden lines from He-like iron, there are apparent emission features arising with higher statistical significance at lower energy, potentially associated with Fe xx–xxiv ions in a ∼1 keV plasma arising near the Bondi radius of Sgr A*. With this work, we release the cleaned and stacked Sgr A* and background HETG spectra to the public as a special legacy data set.

Young neutron stars (NSs) born in core-collapse explosions are promising candidates for the central engines of fast radio bursts (FRBs), since the first localized repeating burst FRB 121102 occurs in a star-forming dwarf galaxy similar to the host galaxies of superluminous supernovae and long gamma-ray bursts. However, FRB 180924 and FRB 190523 are localized to massive galaxies with low rates of star formation, compared with the host of FRB 121102. The offsets between the bursts and host centers are about 4 and 29 kpc for FRB 180924 and FRB 190523, respectively. These host properties are similar to those of short gamma-ray bursts (GRBs), which are produced by binary neutron star (BNS) or NS–black hole mergers. Therefore, the NSs powering FRBs may be formed in BNS mergers. In this paper, we study BNS merger rates and merger times, and predict the most likely merger locations for different types of host galaxies using the population synthesis method. We find that the BNS merger channel is consistent with the recently reported offsets of FRB 180924 and FRB 190523. The offset distribution of short GRBs is well reproduced by population synthesis using a galaxy model similar to that of GRB hosts. The event rate of FRBs (including non-repeating and repeating), is larger than those of BNS mergers and short GRBs, and requires a large fraction of observed FRBs emitting several bursts. Using curvature radiation by bunches in NS magnetospheres, we also predict the observational properties of FRBs from BNS mergers, including the dispersion measure and rotation measure. At late times (t ≥ 1 yr), the contribution to dispersion measure and rotation measure from BNS merger ejecta can be neglected.

The detection of complex organic molecules (COMs) toward dense, collapsing prestellar cores has sparked interest in the fields of astrochemistry and astrobiology, yet the mechanisms for COM formation are still debated. It was originally believed that COMs first form in ices, only to be irradiated by UV radiation from the surrounding interstellar radiation field as well as forming protostars, and subsequently photodesorbed into the gas phase. However, starless and prestellar cores do not have internal protostars to heat up and sublimate the ices. Alternative models using chemical energy have been developed to explain the desorption of COMs, yet in order to test these models, robust measurements of COM abundances are needed toward representative samples of cores. We have conducted a large sample survey of 31 starless and prestellar cores in the Taurus molecular cloud, detecting methanol (CH₃OH) in 100% of the cores targeted and acetaldehyde (CH₃CHO) in 70%. At least two transition lines of each molecule were measured, allowing us to place tight constraints on excitation temperature, column density, and abundance. Additional mapping of methanol revealed extended emission detected down to A_V as low as ∼3 mag. We find that COMs are detectable in the gas phase and are being formed early, at least hundreds of thousands of years prior to star and planet formation. The precursor molecule, CH₃OH, may be chemically linked to the more complex CH₃CHO; however, higher spatial resolution maps are needed to further test chemical models.

Recent estimates point to abundances of z > 4 submillimeter galaxies far above model predictions. The matter is still debated. According to some analyses the excess may be substantially lower than initially thought and perhaps accounted for by flux boosting and source blending. However, there is no general agreement on this conclusion. An excess of z > 6 dusty galaxies has also been reported albeit with poor statistics. On the other hand, evidence of a top-heavy initial mass function (IMF) in high-z starburst galaxies has been reported in the past decades. This would translate into a higher submillimeter luminosity of dusty galaxies at fixed star formation rate, i.e., into a higher abundance of bright high-z submillimeter galaxies than expected for a universal Chabrier IMF. Exploiting our physical model for high-z protospheroidal galaxies, we find that part of the excess can be understood in terms of an IMF somewhat top-heavier than Chabrier. Such an IMF is consistent with that recently proposed to account for the low ¹³C/¹⁸O abundance ratio in four dusty starburst galaxies at z = 2–3. However, extreme top-heavy IMFs are inconsistent with the submillimeter counts at z > 4.

Two-dimensional cylindrical magnetohydrodynamic (MHD) simulations are implemented to investigate the dynamical properties of young type Ia supernova remnants (SNRs) undergoing shock acceleration in a turbulent medium. In our simulations, an MHD code is coupled with a semianalytical kinetic treatment of shock acceleration by means of a time-dependent effective adiabatic index. Large-scale density and magnetic field fluctuations are calculated and mapped into the computational domain before simulations. The above configurations allow us to study the time-dependent dynamical properties and magnetic field structure of a benchmark SNR undergoing shock acceleration in a turbulent medium, along with the relative positions of the contact discontinuity. Our simulation results reveal that there is a rippled forward shock, a thinner shocked ejecta layer and a denser, narrower intershock region. The resulting net effect is a higher density difference between the shocked ejecta and the shocked interstellar medium, leading to a growth of the Rayleigh–Taylor instability. The amplified magnetic field occurs not only at the contact discontinuity but also near the immediate downstream of the shock. The spatial location of the maximum magnetic field is in the vicinity of immediate downstream, which is different with Guo et al. Our derived profiles of the relative contact discontinuity positions are compatible with the results of two typical young type Ia SNRs: SN 1006 and Tycho, with the lowest value reaching ∼1.02 for both cases. Moreover, we find no obvious ejecta protrusions beyond the main forward shock.

Knowledge of the black hole mass function (BHMF) and its evolution would help us understand the origin of BHs and how BH binaries formed at different stages in the history of the universe. We demonstrate the ability of a future third-generation gravitational-wave (GW) detector—the Einstein Telescope (ET)—to infer the slope of the BHMF and its evolution with redshift. We perform a Monte Carlo simulation of the measurements of chirp signals from binary BH systems (BBH) that could be detected by ET, including the BH masses and their luminosity distances (d_L). We use the mass of a primary black hole in each binary system to infer the BHMF as a power-law function with slope parameter α. Taking into account the bias that could be introduced by the uncertainty of measurements and by the selection effect, we carried out the numerical tests and found that only 1000 GW events registered by ET (∼1% of its yearly detection rate) could accurately infer the α with a precision of α ∼ 0.1. Furthermore, we investigate the validity of our method to recover a scenario where α evolves with redshift as $\alpha (z)={\alpha }_{0}+{\alpha }_{1}\tfrac{z}{1\,+\,z}$. Taking a thousand GW events and using d_L as the redshift estimator, our tests show that one could infer the value of evolving parameter α₁ accurately at the uncertainty level of ∼0.5. Our numerical tests verify the reliability of our method. The uncertainty levels of the inferred parameters can be trusted directly for several sets of the parameters we assumed, yet they should not be treated as general.

In this paper, we calibrate the coefficients for the one-dimensional Reynolds stress model (RSM) with the data generated from the three-dimensional (3D) numerical simulations of upward overshooting in turbulent compressible convection. It has been found that the calibrated convective and isotropic coefficients are almost the same as those calibrated in the pure convection zone. However, the calibrated diffusive coefficients differ significantly from those calibrated in the pure convection zone. We suspect that the diffusive effect induced by the boundary is stronger than by the adjacent stable zone. We have checked the validity of the downgradient approximation (DGA). We find that the prediction of the DGA on the third-order moments (TOMs) is unsatisfactory. However, the prediction on their derivatives is much better. It explains why the performance of the RSM is reasonable in application to the real stars. With the calibrated coefficients, we have solved the full set of nonlocal turbulent equations on RSM. We find that the RSM has successfully produced the thermal adjustment layer and turbulent dissipation layer, which were identified in the 3D numerical simulations. We suggest to use the inflection point of the auto-correlation of temperature perturbation and the Péclet number as the indicators on measuring the extents of the thermal adjustment layer and turbulent dissipation layer, respectively. This result may offer a practical guidance on the application of the RSM in 1D stellar structure and evolution models.

In this paper we present the differential emission measures (DEMs) of two sub-A class microflares observed in hard X-rays (HXRs) by the FOXSI-2 sounding rocket experiment, on 2014 December 11. The second Focusing Optics X-ray Solar Imager (FOXSI) flight was coordinated with instruments X-ray Telescope (Hinode/XRT) and Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA), which provided observations in soft X-rays and Extreme Ultraviolet. This unique data set offers an unprecedented temperature coverage, useful for characterizing the plasma temperature distribution of microflares. By combining data from FOXSI-2, XRT, and AIA, we determined a well-constrained DEM for the microflares. The resulting DEMs peak around 3 MK and extend beyond 10 MK. The emission measures determined from FOXSI-2 were lower than 10²⁶ cm⁻⁵ for temperatures higher than 5 MK; faint emission in this range is best measured in HXRs. The coordinated FOXSI-2 observations produce one of the few definitive measurements of the distribution and the amount of plasma above 5 MK in microflares. We utilize the multi-thermal DEMs to calculate the amount of thermal energy released during both the microflares as ∼5.0 × 10²⁸ erg for Microflare 1 and ∼1.6 × 10²⁸ erg for Microflare 2. We also show the multi-thermal DEMs provide more comprehensive thermal energy estimates than isothermal approximation, which systematically underestimates the amount of thermal energy released.

Interplanetary coronal mass ejections (ICMEs) could be classified into magnetic clouds (MCs) and non-MCs according to their magnetic field signatures, and into prominence-inside ICMEs (PIs) and non-PIs based on whether they contain colder and higher helium abundance plasmas than the solar wind. It is known that the MCs often lead to magnetic storms. However, whether or not the PIs have significant geoeffectiveness is unclear. This statistical work studies the southward interplanetary magnetic field (IMF) magnitude of the PIs, and the related magnetic storms' level. The data include the IMF and plasma moments measured by ACE and WIND, and the Dst index from 1998 to 2011. The hypothesis test based on the proportions of two groups is used to analyze 95 ICMEs related to single storms (SSs). The results show that the magnetic storms caused by the PIs mostly distribute at a strong level, while that caused by the non-PIs and by all the 95 ICMEs mostly distribute at a moderate level. The PIs have a significantly higher probability of generating SSs than the non-PIs. Moreover, the MCs containing carbon-cold and helium-enhanced materials  (MC&PIs) have the highest fraction of minimum B_z, less than −11 nT. Since the MC&PIs have large-scale magnetic flux rope and prominence material, the stronger southward IMF is probably provided by the prominence. It is in accordance with the observed injection of enhanced twisted flux ropes to prominence. Therefore, the detailed eruption and propagation processes of the three-part coronal mass ejections deserve more concern from a space weather perspective.

We report on two millimeter flares detected by the Atacama Large Millimeter/submillimeter Array at 220 GHz from AU Mic, a nearby M dwarf. The larger flare had a duration of only ∼35 s, with peak L_R = 2 × 10¹⁵ erg s⁻¹ Hz⁻¹, and lower limit on linear polarization of $| Q/I| \gt 0.12\pm 0.04$. We examine the characteristics common to these new AU Mic events and those from Proxima Cen previously reported in MacGregor et al.—namely short durations, negative spectral indices, and significant linear polarization—to provide new diagnostics of conditions in outer stellar atmospheres and details of stellar flare particle acceleration. The event rates (∼20 and 4 events days⁻¹ for AU Mic and Proxima Cen, respectively) suggest that millimeter flares occur commonly but have been undetected until now. Analysis of the flare observing frequency and consideration of possible incoherent emission mechanisms confirms the presence of MeV electrons in the stellar atmosphere occurring as part of the flare process. The spectral indices point to a hard distribution of electrons. The short durations and lack of pronounced exponential decay in the light curve are consistent with formation in a simple magnetic loop, with radio emission predominating from directly precipitating electrons. We consider the possibility of both synchrotron and gyrosynchrotron emission mechanisms, although synchrotron is favored given the linear polarization signal. This would imply that the emission must be occurring in a low density environment of only modest magnetic field strength. A deeper understanding of this newly discovered and apparently common stellar flare mechanism awaits more observations with better-studied flare components at other wavelengths.

Using our deep optical and near-infrared photometry along with multiwavelength archival data, we here present a detailed study of the Galactic H ii region Sh 2-305 to understand the star/star-cluster formation. On the basis of excess infrared emission, we have identified 116 young stellar objects (YSOs) within a field of view of ∼185 × 185 around Sh 2-305. The average age, mass, and extinction (A_V) for this sample of YSOs are 1.8 Myr, 2.9 M_⊙, and 7.1 mag, respectively. The density distribution of stellar sources along with minimal spanning tree calculations on the location of YSOs reveals at least three stellar subclusterings in Sh 2-305. One cluster is seen toward the center (i.e., Mayer 3), while the other two are distributed toward the north and south directions. Two massive O-type stars (VM2 and VM4; ages ∼5 Myr) are located at the center of the Sh 2-305 H ii region. The analysis of the infrared and radio maps traces the photon-dominant regions (PDRs) in Sh 2-305. The association of the younger generation of stars with the PDRs is also investigated in Sh 2-305. This result suggests that these two massive stars might have influenced the star formation history in Sh 2-305. This argument is also supported by the calculation of various pressures driven by massive stars, the slope of the mass function/K-band luminosity function, star formation efficiency, fraction of Class i sources, and mass of the dense gas toward the subclusterings in Sh 2-305.

We explore the burst energy distribution of fast radio bursts (FRBs) in the low-twist magnetar model of Wadiasingh & Timokhin (WT19). Motivated by the power-law fluence distributions of FRB 121102, we propose an elementary model for the FRB luminosity function of individual repeaters with an inversion protocol that directly relates the power-law distribution index of magnetar short burst fluences to that for FRBs. The protocol indicates that the FRB energy scales virtually linearly with crust/field dislocation amplitude, if magnetar short bursts prevail in the magnetoelastic regime. Charge starvation in the magnetosphere during bursts (required in WT19) for individual repeaters implies the predicted burst fluence distribution is narrow, ≲3 decades for yielding strains and oscillation frequencies feasible in magnetar crusts. Requiring magnetic confinement and charge starvation, we obtain a death line for FRBs, which segregates magnetars from the normal pulsar population, suggesting only the former will host recurrent FRBs. We convolve the burst energy distribution for individual magnetars to define the distribution of luminosities in evolved magnetar populations. The broken power-law luminosity function's low-energy character depends on the population model, while the high-energy index traces that of individual repeaters. Independent of the evolved population, the broken power-law isotropic-equivalent energy/luminosity function peaks at ∼10³⁷–10⁴⁰ erg with a low-energy cutoff at ∼10³⁷ erg. Lastly, we consider the local fluence distribution of FRBs and find that it can constrain the subset of FRB-producing magnetar progenitors. Our model suggests that improvements in sensitivity may reveal a flattening of the global FRB fluence distribution and saturation in FRB rates.

We present the detection of CO (5−4) with signal-to-noise ratio (S/N) > 7–13 and a lower CO transition with S/N > 3 (CO (4−3) for four galaxies, and CO (3−2) for one) with the Atacama Large Millimeter/submillimeter Array in bands 3 and 4 in five main-sequence (MS) star-forming galaxies with stellar masses (3–6) × 10¹⁰M_⊙ at 3 < z < 3.5. We find a good correlation between the total far-infrared luminosity L_FIR and the luminosity of the CO (5−4) transition ${L}_{\mathrm{CO}(5-4)}^{{\prime} }$, where ${L}_{\mathrm{CO}(5-4)}^{{\prime} }$ increases with star formation rate (SFR), indicating that CO (5−4) is a good tracer of the obscured SFR in these galaxies. The two galaxies that lie closer to the star-forming MS have CO spectral line energy distribution (SLED) slopes that are comparable to other star-forming populations, such as local submillimeter galaxies and BzK star-forming galaxies; the three objects with higher specific star formation rates have far steeper CO SLEDs, which possibly indicates a more concentrated episode of star formation. By exploiting the CO SLED slopes to extrapolate the luminosity of the CO (1−0) transition and using a classical conversion factor for MS galaxies of ${\alpha }_{\mathrm{CO}}=3.8\,{M}_{\odot }{({\rm{K}}\mathrm{km}{{\rm{s}}}^{-1}{\mathrm{pc}}^{-2})}^{-1}$, we find that these galaxies are very gas-rich, with molecular gas fractions between 60% and 80% and quite long depletion times, between 0.2 and 1 Gyr. Finally, we obtain dynamical masses that are comparable to the sum of stellar and gas mass (at least for four out of five galaxies), allowing us to put a first constraint on the α_CO parameter for MS galaxies at an unprecedented redshift.

Recent observations of global velocity gradients across and along molecular filaments have been interpreted as signs of gas accreting onto and along these filaments, potentially feeding star-forming cores and protoclusters. The behavior of velocity gradients in filaments, however, has not been studied in detail, particularly on small scales (<0.1 pc). In this paper, we present MUFASA, an efficient, robust, and automatic method to fit ammonia lines with multiple velocity components, generalizable to other molecular species. We also present CRISPy, a Python package to identify filament spines in 3D images (e.g., position–position–velocity cubes), along with a complementary technique to sort fitted velocity components into velocity-coherent filaments. In NGC 1333, we find a wealth of velocity gradient structures on a beam-resolved scale of ∼0.05 pc. Interestingly, these local velocity gradients are not randomly oriented with respect to filament spines and their perpendicular, i.e., radial, component decreases in magnitude toward the spine for many filaments. Together with remarkably constant velocity gradients on larger scales along many filaments, these results suggest a scenario in which gas falling onto filaments is progressively damped and redirected to flow along these filaments.

Manganese abundances are sensitive probes of the progenitors of Type Ia supernovae (SNe Ia). In this work, we present a catalog of manganese abundances in dwarf spheroidal satellites of the Milky Way, measured using medium-resolution spectroscopy. Using a simple chemical evolution model, we infer the manganese yield of SNe Ia in the Sculptor dwarf spheroidal galaxy (dSph) and compare to theoretical yields. The sub-solar yield from SNe Ia (${[\mathrm{Mn}/\mathrm{Fe}]}_{\mathrm{Ia}}=-{0.30}_{-0.03}^{+0.03}$ at [Fe/ H] = −1.5 dex, with negligible dependence on metallicity) implies that sub-Chandrasekhar-mass (sub-M_Ch) white dwarf progenitors are the dominant channel of SNe Ia at early times in this galaxy, although some fraction (≳20%) of M_Ch Type Ia or Type Iax SNe are still needed to produce the observed yield. First-order corrections for deviations from local thermodynamic equilibrium increase the inferred ${[\mathrm{Mn}/\mathrm{Fe}]}_{\mathrm{Ia}}$ by as much as ∼0.3 dex. However, our results also suggest that the nucleosynthetic source of SNe Ia may depend on environment. In particular, we find that dSphs with extended star formation histories (Leo I, Fornax dSphs) appear to have higher [Mn/Fe] at a given metallicity than galaxies with early bursts of star formation (Sculptor dSph), suggesting that M_Ch progenitors may become the dominant channel of SNe Ia at later times in a galaxy's chemical evolution.

Kinetic-scale current sheets observed in the solar wind are frequently approximately force-free despite the fact that their plasma β is of the order of one. In situ measurements have recently shown that plasma density and temperature often vary across the current sheets, while the plasma pressure is approximately uniform. In many cases these density and temperature variations are asymmetric with respect to the center of the current sheet. To model these observations theoretically we develop in this paper equilibria of kinetic-scale force-free current sheets that have plasma density and temperature gradients. The models can also be useful for analysis of stability and dissipation of the current sheets in the solar wind.

In the third catalog of active galactic nuclei detected by the Fermi Large Area Telescope Clean (3LAC) sample, there are 402 blazar candidates of uncertain type (BCU). The proposed analysis will help to evaluate the potential optical classification flat spectrum radio quasars (FSRQs) versus BL Lacertae (BL Lac) objects of BCUs, which can help to understand which is the most elusive class of blazar hidden in the Fermi sample. By studying the 3LAC sample, we found some critical values of γ-ray photon spectral index (Γ_ph), variability index (VI), and radio flux (${F}_{{\rm{R}}}$) of the sources separate known FSRQs and BL Lac objects. We further utilize those values to defined an empirical "high-confidence" candidate zone that can be classified as BCUs. Within such a zone (Γ_ph < 2.187, log F_R < 2.258, and log VI < 1.702), we found that 120 BCUs can be classified as BL Lac object candidates with a higher degree of confidence (with a misjudged rate <1%). Our results suggest that an empirical "high-confidence" diagnosis is possible to distinguish the BL Lac objects from the Fermi observations based on only the direct observational data of Γ_ph, VI, and F_R.

On 2012 October 23, a strong white-light emission, associated with an X1.8-class flare, was observed by the Solar Optical Telescope on board the Hinode satellite. White-light kernels were clearly observed along the Ca ii H ribbons. RHESSI also observed hard X-ray emissions that were almost located on the white-light kernels. The total energy of the white-light emission was $\sim {10}^{27-28}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$ and the total energy of the accelerated electrons was almost of the same order when we used 40 keV as the lower energy cutoff. The white-light emission appears to have originated from nonthermal electrons in these energies. Moreover, the EUV imaging spectrometer on board the Hinode satellite performed a raster scan over this flaring active region and the flare occurred during the scan. Over the white-light kernels, we observed redshifts of a few tens of km s⁻¹ in Fe xii. It appears that these EUV responses originated from some accelerated electrons due to the solar flare and they are considered to be the source of the white-light emission. In fact, the electron density of the white-light kernels was less than ${10}^{12}\,{\mathrm{cm}}^{-3}$, which is sufficiently low for nonthermal electrons to penetrate into the photosphere.

Solar S-bursts are short duration (<1 s at decameter wavelengths) radio bursts that have been observed during periods of moderate solar activity, where S stands for short. The frequency drift of S-bursts can reflect the coronal density variation and the motion state of the electron beams. In this work, we investigate the frequency drift and the fine structure of the S-bursts with the Low Frequency Array (LOFAR). We find that the average frequency drift rate of the S-bursts within 20–180 MHz could be described by df/dt = −0.0077f^1.59, combined with previous results in low frequency. With the high time and frequency resolution of LOFAR, we can resolve the fine structures of the observed solar S-bursts. A fine drift variation pattern was found in the structure of S-bursts (referred to as solar Sb-bursts in this paper) during the type-III storm on 2019 April 13, in the frequency band of 120–240 MHz. The Sb-bursts have a quasiperiodic segmented pattern, and the relative flux intensity tends to be large when the frequency drift rate is relatively large. This kind of structure exists in about 20% of the solar S-burst events within the observed frequency range. We propose that the fine structure is due to the density fluctuations of the background coronal density. We performed a simulation based on this theory that can reproduce the shape and relative flux intensity of the Sb-bursts. This work shows that the fine structure of solar radio bursts can be used to diagnose the coronal plasma.

The galaxy cluster Zwicky 3146 is a sloshing cool core cluster at z = 0.291 that in X-ray imaging does not appear to exhibit significant pressure substructure in the intracluster medium (ICM). The published M₅₀₀ values range between ${3.88}_{-0.58}^{+0.62}$ to (22.50 ± 7.58) × 10¹⁴M_⊙, where ICM-based estimates with reported errors <20% suggest that we should expect to find a mass between ${6.53}_{-0.44}^{+0.44}\times {10}^{14}$M_⊙ (from Planck, with an 8.4σ detection) and ${8.52}_{-1.47}^{+1.77}\times {10}^{14}$M_⊙ (from ACT, with a 14σ detection). We investigate the ability to estimate the mass of Zwicky 3146 via the Sunyaev–Zel'dovich (SZ) effect with data taken at 90 GHz by MUSTANG-2 to a noise level better than 15 μK at the center and a cluster detection of 61σ. We derive a pressure profile from our SZ data, which is in excellent agreement with that derived from X-ray data. From our SZ-derived pressure profiles, we infer M₅₀₀ and M₂₅₀₀ via three methods—Y–M scaling relations, the virial theorem, and hydrostatic equilibrium (HE)—where we employ X-ray constraints from XMM-Newton on the electron density profile when assuming HE. Depending on the model and estimation method, our M₅₀₀ estimates range from 6.13 ± 0.69 to (10.6 ± 2.0) × 10¹⁴M_⊙, where our estimate from HE is ${7.69}_{-1.98}^{+2.19}$ (±27% stat) ${}_{-0.59}^{+0.63}$ (±7.9% sys, calibration) × 10¹⁴M_⊙. Our fiducial mass, derived from a Y–M relation is ${8.06}_{-0.61}^{+0.67}$ (±7.9% stat) ${}_{-0.42}^{+0.45}$ (±5.4% sys, Y–M) ${}_{-0.54}^{+0.58}$ (±6.9% sys, cal.) × 10¹⁴M_⊙.

We carry out a theoretical study of the polarization of the solar Mg ii h–k doublet (including its extended wings) and the subordinate ultraviolet (UV) triplet around 280 nm. These lines are of great diagnostic interest, as they encode information on the physical properties of the solar atmosphere from the upper photosphere to the chromosphere–corona transition region. We base our study on radiative transfer calculations of spectral line polarization in one-dimensional models of quiet and plage regions of the solar atmosphere. Our calculations take into account the combined action of atomic polarization, quantum level interference, frequency redistribution, and magnetic fields of arbitrary strength. In particular, we study the sensitivity of the emergent Stokes profiles to changes in the magnetic field through the Zeeman and Hanle effects. We also study the impact of the chromospheric plasma dynamics on the emergent Stokes profiles, taking into account the angle-dependent frequency redistribution in the h–k resonance transitions. The results presented here are of interest for the interpretation of spectropolarimetric observations in this important region of the solar UV spectrum.

We analyzed properties of waves excited by mildly relativistic electron beams propagating along the magnetic field with a ring-shape perpendicular momentum distribution in neutral and current-free solar coronal plasmas. These plasmas are subject to both the beam and the electron cyclotron maser instabilities driven by the positive momentum gradients of the ring-beam electron distribution in the directions parallel and perpendicular to the ambient magnetic field, respectively. To explore the related kinetic processes self-consistently, 2.5D fully kinetic particle-in-cell simulations were carried out. To quantify excited wave properties in different coronal conditions, we investigated the dependences of their energy and polarization on the ring-beam electron density and magnetic field. In general, electrostatic waves dominate the energetics of waves, and nonlinear waves are ubiquitous. In weakly magnetized plasmas, where the electron cyclotron frequency ω_ce is lower than the electron plasma frequency ω_pe, it is difficult to produce escaping electromagnetic waves with frequency ω > ω_pe and small refractive index $| {ck}/\omega | \lt 1$ (k and c are the wavenumber and the light speed, respectively). Highly polarized and anisotropic escaping electromagnetic waves can, however, be effectively excited in strongly magnetized plasmas with ω_ce/ω_pe ≥ 1. The anisotropies of the energy, circular polarization degree (CPD), and spectrogram of these escaping electromagnetic waves strongly depend on the number density ratio of the ring-beam electrons to the background electrons. In particular, their CPDs can vary from left-handed to right-handed with the decrease of the ring-beam density, which may explain some observed properties of solar radio bursts (e.g., radio spikes) from the solar corona.

We explore the galaxy structure of four tidal disruption event (TDE) host galaxies on 30 pc to kiloparsec scales using Hubble Space Telescope WFC3 multiband imaging. The star formation histories of these hosts are diverse, including one post-starburst galaxy (ASASSN-14li), two hosts with recent weak starbursts (ASASSN-14ae and iPTF15af), and one early-type galaxy (PTF09ge). Compared to early-type galaxies of similar stellar masses, the TDE hosts have higher central surface brightnesses and stellar mass surface densities on 30–100 pc scales. The TDE hosts do not show the large, kiloparsec-scale tidal disruptions seen in some post-starburst galaxies; the hosts have low morphological asymmetries similar to those of early-type galaxies. The lack of strong asymmetries is inconsistent with a recent major (∼1:1 mass) merger, although minor (≲1:3) mergers are possible. Given the time elapsed since the end of the starbursts in the three post-burst TDE hosts and the constraints on the merger mass ratios, it is unlikely that a bound supermassive black hole binary (SMBHB) has had time to coalesce. The TDE hosts have low central (<140 pc) ellipticities compared to early-type galaxies. The low central ellipticities disfavor a strong radial anisotropy as the cause for the enhanced TDE rate, although we cannot rule out eccentric disks at the scale of the black hole gravitational radius of influence (∼1 pc). These observations suggest that the high central stellar densities are a more important driver than SMBHBs or radial anisotropies in increasing the TDE rate in galaxies with recent starbursts.

We propose a new mechanism for the growth of supermassive black hole (BH) seeds in the star-forming progenitors of local early-type galaxies (ETGs) at z ≳ 1. This envisages the migration and merging of stellar compact remnants (neutron stars and stellar-mass BHs) via gaseous dynamical friction toward the central high-density regions of such galaxies. We show that, under reasonable assumptions and initial conditions, the process can build up central BH masses of the order of 10⁴–10⁶M_⊙ within some 10⁷ yr, so effectively providing heavy seeds before standard disk (Eddington-like) accretion takes over to become the dominant process for further BH growth. Remarkably, such a mechanism may provide an explanation, alternative to super-Eddington accretion rates, for the buildup of billion-solar-massed BHs in quasar hosts at z ≳ 7, when the age of the universe ≲0.8 Gyr constitutes a demanding constraint; moreover, in more common ETG progenitors at redshift z ∼ 2–6, it can concur with disk accretion to build such large BH masses even at moderate Eddington ratios ≲0.3 within the short star formation duration ≲Gyr of these systems. Finally, we investigate the perspectives to detect the merger events between the migrating stellar remnants and the accumulating central supermassive BH via gravitational-wave emission with future ground- and space-based detectors such as the Einstein Telescope and the Laser Interferometer Space Antenna.

We report, for the first time, both the strengthening and radial velocity increases of a narrow absorption-line (NAL) system (C ivλλ1548, 1551 and N vλλ1239, 1243) from the two-epoch spectra of quasar SDSS J143530.49+142338.4. First, we speculate that the ionization changes of the outflow clouds are likely the cause of the strengthening in its equivalent width (EW) based on the obvious weakening of the ionization continuum, although other interpretations cannot be ruled out based on the current two-epoch spectra. According to the cloudy simulation, the asynchronized variations between the absorption-line EWs and the ionizing continuum indicate that the absorbers are at relatively high degrees of ionization, which is also consistent with the high ionization state revealed by the absence of Si iv NAL in the same system. Second, this NAL system exhibits a kinematic velocity shift of ∼138 $\mathrm{km}\,{{\rm{s}}}^{-1}$ within 445.2 days in the quasar rest frame (corresponding to an average acceleration of ∼0.36 $\mathrm{cm}\,{{\rm{s}}}^{-2}$). We evaluate several possible causes for this kinematic shift. However, the current two-epoch spectra do not provide enough constraints to confirm the possible mechanisms, so future monitoring with high resolution will be helpful to achieve this goal.

Recently published precise stellar photometry of 72 Sun-like stars obtained at the Fairborn Observatory between 1993 and 2017 is used to set limits on the solar forcing of Earth's atmosphere of ±4.5 W m⁻² since 1750. This compares with the +2.2 ± 1.1 W m⁻² IPCC estimate for anthropogenic forcing. Three critical assumptions are made. In decreasing order of importance they are: (a) most of the brightness variations occur within the average time series length of ≈17 yr; (b) the Sun seen from the ecliptic behaves as an ensemble of middle-aged solar-like stars; and (c) narrowband photometry in the Strömgren b and y bands are linearly proportional to the total solar irradiance. Assumption (a) can best be relaxed and tested by obtaining more photometric data of Sun-like stars, especially those already observed. Eight stars with near-solar parameters have been observed from 1999, and two since 1993. Our work reveals the importance of continuing and expanding ground-based photometry, to complement expensive solar irradiance measurements from space.

Stars with excess infrared radiation from circumstellar dust are invaluable for studies of exoplanetary systems, informing our understanding of processes of planet formation and destruction alike. All-sky photometric surveys have made the identification of dusty infrared excess candidates trivial, however, samples that rely on data from Wise Infrared Survey Explorer (WISE) are plagued with source confusion, leading to high false-positive rates. Techniques to limit its contribution to WISE-selected samples have been developed, and their effectiveness is even more important as we near the end-of-life of Spitzer, the only facility capable of confirming the excess. Here, we present a Spitzer follow-up of a sample of 22 WISE-selected infrared excess candidates near the faint-end of the WISE detection limits. Eight of the 22 excesses are deemed the result of source confusion, with the remaining candidates all confirmed by the Spitzer data. We consider the efficacy of ground-based near-infrared imaging and astrometric filtering of samples to limit confusion among the sample. We find that both techniques are worthwhile for vetting candidates, but fail to identify all of the confused excesses, indicating that they cannot be used to confirm WISE-selected infrared excess candidates, but only to rule them out. This result confirms the expectation that WISE-selected infrared excess samples will always suffer from appreciable levels of contamination, and that care should be taken in their interpretation regardless of the filters applied.

In this paper, we present the study of the energy reservoir powering the light curves (LCs) of PS1-12cil and SN 2012aa, which are superluminous and luminous supernovae (SNe), respectively. The multiband and bolometric LCs of these two SNe show unusual secondary bumps after the main peaks. The two-peaked LCs cannot be explained by any simple energy-source models (e.g., the ⁵⁶Ni cascade decay model, the magnetar spindown model, or the ejecta-circumstellar medium interaction model). Therefore, we employ the ⁵⁶Ni plus ejecta-circumstellar medium (CSM) interaction (CSI) model, the magnetar plus CSI model, and the double CSI model to fit their bolometric LCs, and find that both these two SNe can be explained by the double CSI model and the magnetar plus CSI model. Based on the modeling, we calculate the the time when the shells were expelled by the progenitors: provided that they were powered by double ejecta-shell CSI, the inner and outer shells might be expelled ∼0.2–3.6 and ∼2–25 yr before the explosions of the SNe, respectively; the shells were expelled ∼2–20 yr before the explosions of the SNe if they were powered by magnetars plus CSI.

We report the discovery of torsional Alfvénic oscillations in solar flares, which modulate the time evolution of the magnetic free energy E_f(t), while the magnetic potential energy E_p(t) is uncorrelated, and the nonpotential energy varies as E_np(t) = E_p + E_f(t). The mean observed time period of the torsional oscillations is P_obs = 15.1 ± 3.9 minutes, the mean field line length is L = 135 ± 35 Mm, and the mean phase speed is v_phase = 315 ± 120 km s⁻¹, which we interpret as torsional Alfvénic waves in flare loops with enhanced electron densities. Most of the torsional oscillations are found to be decay-less, but exhibit a positive or negative trend in the evolution of the free energy, indicating new emerging flux (if positive), magnetic cancellation, or flare energy dissipation (if negative). The time evolution of the free energy has been calculated in this study with the Vertical-current Approximation (Version 4) Non-linear Force-free Field code, which incorporates automatically detected coronal loops in the solution and bypasses the non-force-freeness of the photospheric boundary condition, in contrast to traditional NLFFF codes.

Pyroxenes ((Ca, Mg, Fe, Mn)₂Si₂O₆) belong to the most abundant rock forming minerals that make up the surface of rocky planets and moons. Therefore, sputtering of pyroxenes by solar wind ions has to be considered as a very important process for modifying the surface of planetary bodies. This is increased due to potential sputtering by multiply charged ions; to quantify this effect, sputtering of wollastonite (CaSiO₃) by He²⁺ ions was investigated. Thin films of CaSiO₃ deposited on a quartz crystal microbalance were irradiated, allowing precise, in situ, real time sputtering yield measurements. Experimental results were compared with SDTrimSP simulations, which were improved by adapting the used input parameters. On freshly prepared surfaces, He²⁺ ions show a significant increase in sputtering, as compared to equally fast He⁺ ions. However, the yield decreases exponentially with fluence, reaching a lower steady state after sputtering of the first few monolayers. Experiments using Ar⁸⁺ ions show a similar behavior, which is qualitatively explained by a preferential depletion of surface oxygen due to potential sputtering. A corresponding quantitative model is applied, and the observed potential sputtering behaviors of both He and Ar are reproduced very well. The results of these calculations support the assumption that mainly O atoms are affected by potential sputtering. Based on our findings, we discuss the importance of potential sputtering for the solar wind eroding the lunar surface. Estimated concentration changes and sputtering yields are both in line with previous modeling for other materials, allowing a consistent perspective on the effects of solar wind potential sputtering.

Observed turbulence in space and astrophysics is expected to involve cascade and subsequent dissipation and heating. Contrary to standard collisional fluid turbulence, the weakly collisional magnetized plasma cascade may involve several channels of energy conversion, interchange, and spatial transport, leading eventually to the production of internal energy. This paper describes these channels of transfer and conversion, collectively amounting to a complex generalization of the Kolmogorov cascade. Channels may be described using compressible magnetohydrodynamic (MHD) and multispecies Vlasov–Maxwell formulations. Key steps are conservative transport of energy in space, parallel incompressible and compressible cascades in scale, electromagnetic work on particles driving macroscopic and microscopic flows, and pressure–strain interactions, both compressive and shear-like, that produce internal energy. A significant contrast with the collisional case is that the steps leading to the disappearance of large-scale energy in favor of internal energy are formally reversible. This property motivates a discussion of entropy, reversibility, and the relationship between dissipation with collisions and in the Vlasov system without collisions. Where feasible, examples are given from MHD and Particle in Cell simulations and from MMS observations.