Table of contents

Using high temporal and high spatial resolution observations taken by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, we present a detailed observational analysis of a high-quality quasi-periodic fast-propagating (QFP) magnetosonic wave that was associated with the eruption of a magnetic flux rope and a GOES C5.0 flare. For the first time, we find that the QFP wave lasted for the entire flare lifetime rather than only during the rising phase of the accompanying flare, as reported in previous studies. In addition, the propagation of the different parts of the wave train showed different kinematics and morphologies. For the southern (northern) part, the speed, duration, and intensity variation are about 875 ± 29 (1485 ± 233) km s⁻¹, 45 (60) minutes, and 4% (2%), and their pronounced periods are 106 ± 12 and 160 ± 18 (75 ± 10 and 120 ± 16) s, respectively. It is interesting that the northern part of the wave train showed an obvious refraction effect when it passed through a region of strong magnetic field. The result of a periodicity analysis indicates that all of the periods of the QFP wave can be found in the period spectrum of the accompanying flare, suggesting their common physical origin. We propose that the quasi-periodic nonlinear magnetohydrodynamics process in the magnetic reconnection that produces the accompanying flare should be important in exciting a QFP wave, and the different magnetic distributions along different paths can account for the different speeds and morphology evolution of the wave fronts.

We report the detection of GeV γ-ray emission from supernova remnant HESS J1731-347 using 9 yr of Fermi Large Area Telescope data. We find a slightly extended GeV source in the direction of HESS J1731-347. The spectrum above 1 GeV can be fitted by a power law with an index of Γ = 1.77 ± 0.14, and the GeV spectrum connects smoothly with the TeV spectrum of HESS J1731-347. Either a hadronic–leptonic or a pure leptonic model can fit the multiwavelength spectral energy distribution of the source. However, the hard GeV γ-ray spectrum is more naturally produced in a leptonic (inverse Compton scattering) scenario, under the framework of diffusive shock acceleration. We also searched for the GeV γ-ray emission from the nearby TeV source HESS J1729-345. No significant GeV γ-ray emission is found, and upper limits are derived.

We study the consistency of 150 GHz data from the South Pole Telescope (SPT) and 143 GHz data from the Planck satellite over the patch of sky covered by the SPT-SZ survey. We first visually compare the maps and find that the residuals appear consistent with noise after accounting for differences in angular resolution and filtering. We then calculate (1) the cross-spectrum between two independent halves of SPT data, (2) the cross-spectrum between two independent halves of Planck data, and (3) the cross-spectrum between SPT and Planck data. We find that the three cross-spectra are well fit (PTE = 0.30) by the null hypothesis in which both experiments have measured the same sky map up to a single free calibration parameter—i.e., we find no evidence for systematic errors in either data set. As a by-product, we improve the precision of the SPT calibration by nearly an order of magnitude, from 2.6% to 0.3% in power. Finally, we compare all three cross-spectra to the full-sky Planck power spectrum and find marginal evidence for differences between the power spectra from the SPT-SZ footprint and the full sky. We model these differences as a power law in spherical harmonic multipole number. The best-fit value of this tilt is consistent among the three cross-spectra in the SPT-SZ footprint, implying that the source of this tilt is a sample variance fluctuation in the SPT-SZ region relative to the full sky. The consistency of cosmological parameters derived from these data sets is discussed in a companion paper.

The Kleinmann–Low nebula in Orion, the closest region of massive star formation, harbors Source I, whose nature is under debate. Knowledge of this source may have profound implications for our understanding of the energetics of the hot core in Orion KL since it might be the main heating source in the region. The spectral energy distribution of this source in the radio is characterized by a positive spectral index close to 2, which is consistent with (i) thermal bremsstrahlung emission of ionized hydrogen gas produced by a central massive protostar, or (ii) photospheric bremsstrahlung emission produced by electrons when deflected by the interaction with neutral and molecular hydrogen like Mira-like variable stars. If ionized hydrogen gas were responsible for the observed continuum emission, its modeling would predict detectable emission from hydrogen radio recombination lines (RRLs). However, our SMA observations were obtained with a high enough sensitivity to rule out that the radio continuum emission arises from a dense hypercompact H ii region because the H26α line would have been detected, in contrast with our observations. To explain the observational constraints, we investigate further the nature of the radio continuum emission from source I. We have compared available radio continuum data with the predictions from our upgraded non-LTE 3D radiative transfer model, MOdel for REcombination LInes, to show that radio continuum fluxes and sizes can only be reproduced by assuming both dust and bremsstrahlung emission from neutral gas. The dust emission contribution is significant at ν ≥ 43 GHz. In addition, our RRL peak intensity predictions for the ionized metals case are consistent with the nondetection of Na and K RRLs at millimeter and submillimeter wavelengths.

We present a study of hierarchical structure in the Perseus molecular cloud, from the scale of the entire cloud ($\gtrsim 10$ pc) to smaller clumps (∼1 pc), cores (∼0.05–0.1 pc), envelopes (∼300–3000 au), and protostellar objects (∼15 au). We use new observations from the Submillimeter Array (SMA) large project "Mass Assembly of Stellar Systems and their Evolution with the SMA (MASSES)" to probe the envelopes, and recent single-dish and interferometric observations from the literature for the remaining scales. This is the first study to analyze hierarchical structure over five scales in the same cloud complex. We compare the number of fragments with the number of Jeans masses in each scale to calculate the Jeans efficiency, or the ratio of observed to expected number of fragments. The velocity dispersion is assumed to arise either from purely thermal motions or from combined thermal and non-thermal motions inferred from observed spectral line widths. For each scale, thermal Jeans fragmentation predicts more fragments than observed, corresponding to inefficient thermal Jeans fragmentation. For the smallest scale, thermal plus non-thermal Jeans fragmentation also predicts too many protostellar objects. However, at each of the larger scales thermal plus non-thermal Jeans fragmentation predicts fewer than one fragment, corresponding to no fragmentation into envelopes, cores, and clumps. Over all scales, the results are inconsistent with complete Jeans fragmentation based on either thermal or thermal plus non-thermal motions. They are more nearly consistent with inefficient thermal Jeans fragmentation, where the thermal Jeans efficiency increases from the largest to the smallest scale.

We introduce a new theoretical model to describe the emitting region in a blazar jet. We adopt a one-zone leptonic picture and construct the particle transport equation for a plasma blob experiencing low-energy, monoenergetic particle injection, energy-dependent particle escape, shock acceleration, adiabatic expansion, stochastic acceleration, synchrotron radiation, and external Compton radiation from the dust torus and broad-line region (BLR). We demonstrate that a one-zone leptonic model is able to explain the IR though $\gamma$-ray spectrum for 3C 279 in 2008–2009. We determine that the BLR seed photons cannot be adequately described by a single average distribution, but rather we find that a stratified BLR provides an improvement in the estimation of the distance of the emitting region from the black hole. We calculate that the jet is not always in equipartition between the particles and magnetic field and find that stochastic acceleration provides more energy to the particles than does shock acceleration, where the latter is also overshadowed by adiabatic losses. We further introduce a novel technique to implement numerical boundary conditions and determine the global normalization for the electron distribution, based on analysis of stiff ordinary differential equations. Our astrophysical results are compared with those obtained by previous authors.

Recently, properties of exoplanet atmospheres have been constrained via multi-wavelength transit observation, which measures an apparent decrease in stellar brightness during planetary transit in front of its host star (called transit depth). Sets of transit depths so far measured at different wavelengths (called transmission spectra) are somewhat diverse: some show steep spectral slope features in the visible, some contain featureless spectra in the near-infrared, some show distinct features from radiative absorption by gaseous species. These facts imply the existence of haze in the atmospheres, especially of warm, relatively low-density super-Earths and mini-Neptunes. Previous studies that addressed theoretical modeling of transmission spectra of hydrogen-dominated atmospheres with haze made some assumptions about the distribution and size of haze particles. In this study, we model the atmospheric chemistry, and derive the spatial and size distributions of haze particles by directly simulating the creation, growth, and settling of hydrocarbon haze particles. We then develop transmission spectrum models of UV-irradiated, solar-abundance atmospheres of close-in warm (∼500 K) exoplanets. We find that the haze is distributed in the atmosphere much more broadly than previously assumed, and consists of particles of various sizes. We also demonstrate that the observed diversity of transmission spectra can be explained by the difference in the production rate of haze monomers, which is related to the UV irradiation intensity from host stars.

We present the analysis of photospheric emission for a set of hydrodynamic simulations of long duration gamma-ray burst jets from massive compact stars. The results are obtained by using the Monte Carlo Radiation Transfer code (MCRaT) to simulate thermal photons scattering through the collimated outflows. MCRaT allows us to study explicitly the time evolution of the photosphere within the photospheric region, as well as the gradual decoupling of the photon and matter counterparts of the jet. The results of the radiation transfer simulations are also used to construct light curves and time-resolved spectra at various viewing angles, which are then used to make comparisons with observed data and outline the agreement and strain points between the photospheric model and long duration gamma-ray burst observations. We find that our fitted time-resolved spectral Band β parameters are in agreement with observations, even though we do not consider the effects of nonthermal particles. Finally, the results are found to be consistent with the Yonetoku correlation, but bear some strain with the Amati correlation.

Linearly polarized emission is described, in general, in terms of the Stokes parameters Q and U, from which the polarization intensity and polarization angle can be determined. Although the polarization intensity and polarization angle provide an intuitive description of the polarization, they are affected by the limitations of interferometric data, such as missing single-dish data in the u–v plane, from which radio-frequency interferometric data is visualized. To negate the effects of these artifacts, it is desirable for polarization diagnostics to be rotationally and translationally invariant in the Q–U plane. One rotationally and translationally invariant quantity, the polarization gradient, has been shown to provide a unique view of spatial variations in the turbulent interstellar medium when applied to diffuse radio-frequency synchrotron emission. In this paper, we develop a formalism to derive additional rotationally and translationally invariant quantities. We present new diagnostics that can be applied to diffuse or point-like polarized emission in any waveband, including a generalization of the polarization gradient, the polarization directional curvature, polarization wavelength derivative, and polarization wavelength curvature. In Paper II, we will apply these diagnostics to observed and simulated images of diffuse radio-frequency synchrotron emission.

We carry out 3D numerical simulations to assess the penetration and bombardment effects of solar energetic particles (SEPs), i.e., high-energy particle bursts during large flares and superflares, on ancient and current Mars. We demonstrate that the deposition of SEPs is non-uniform at the planetary surface, and that the corresponding energy flux is lower than other sources postulated to have influenced the origin of life. Nevertheless, SEPs may have been capable of facilitating the synthesis of a wide range of vital organic molecules (e.g., nucleobases and amino acids). Owing to the relatively high efficiency of these pathways, the overall yields might be comparable to (or even exceed) the values predicted for some conventional sources such as electrical discharges and exogenous delivery by meteorites. We also suggest that SEPs could have played a role in enabling the initiation of lightning. A notable corollary of our work is that SEPs may constitute an important mechanism for prebiotic synthesis on exoplanets around M-dwarfs, thereby mitigating the deficiency of biologically active ultraviolet radiation on these planets. Although there are several uncertainties associated with (exo)planetary environments and prebiotic chemical pathways, our study illustrates that SEPs represent a potentially important factor in understanding the origin of life.

Suprathermal electrons with energy from tens to hundreds of keV are frequently observed in the Earth's magnetotail. The generation of such electrons is typically attributed to magnetic reconnection, dipolarization fronts (DFs), or flux transport. However, which of these contributes more to this generation remains unclear. In this study, we quantitatively compare the electron acceleration by these processes, using the Cluster data. We analyze an event detected in the midtail and find that the suprathermal electrons there are first accelerated by magnetic reconnection and transported earthward, and then further accelerated locally at the DF. The acceleration process by reconnection and transport, resulting in an isotropic pitch angle distribution, contributes ∼70% to the total flux enhancement, while the acceleration process by the DF, resulting in a pancake distribution, contributes ∼30% to the flux enhancement. The electron acceleration at the DF is primarily attributed to a local betatron process that is successfully reproduced using an analytic model. In order to better understand this phenomenon, we examine an additional 16 similar events and find that the DFs and magnetic reconnection statistically contribute 11% ∼ 38% and 62% ∼ 89% to the total flux enhancement, respectively. This study greatly improves our understanding of the electron energization process in the magnetotail.

We compute the concentrations of five transition elements (Cr, Fe, Co, Ni, and Zn) via condensation and implantation in supernova presolar grains (Silicon Carbide Type X) from the time they condense until the end of the free expansion (or pre-Sedov) phase. We consider relative velocities of these elements with respect to grains as they condense and evolve at temperatures ≲2000 K; use zonal nucleosynthesis yields for three core collapse supernovae models −15 M_⊙, 20 M_⊙, and 25 M_⊙; and use an ion target simulator SDTrimSP to model their implantation onto the grains. Simulations from SDTrimSP show that maximal implantation in the core of the grain is possible, contrary to previous studies. Among the available models, we find that the 15 M_⊙ model best explains the measured concentrations of SiC X grains obtained from the Murchison meteorite. For grains where measured concentrations of Fe and Ni are ≳300 ppm, we find the implantation fraction to be ≲0.25 for most probable differential zonal velocities in this phase, which implies that condensation is more dominant than implantation. We show that radioactive corrections and mixing from the innermost Ni and Si zones are required to explain the excess Ni (condensed as well as implanted) in these grains. This mixing also explains the relative abundances of Co and Ni with respect to Fe simultaneously. The model developed can be used to predict concentrations of all other elements in various presolar grains condensed in supernova ejecta and compared with measured concentrations in grains found in meteorites.

We present new Chandra observations of the outer halo of the giant elliptical galaxy NGC 4472 (M49) in the Virgo Cluster. The data extend to 130 kpc (28'), and have a combined exposure time of 150 ks. After identifying optical counterparts using the Next Generation Virgo Cluster Survey to remove background active galactic nuclei and globular cluster (GC) sources, and correcting for completeness, we find that the number of field low-mass X-ray binaries (LMXBs) per unit stellar V-band light increases significantly with the galactocentric radius. Because the flux limit of the complete sample corresponds to the Eddington limit for neutron stars in NGC 4472, many of the ∼90 field LMXBs in this sample could host black holes. The excess of field LMXBs at large galactocentric radii may be partially caused by natal kicks on black holes and neutron stars in binary systems in the inner part of the galaxy. Furthermore, because the metallicity in the halo of NGC 4472 strongly decreases toward larger galactocentric radii, the number of field LMXBs per unit stellar mass is anticorrelated with metallicity, opposite to what is observed in GCs. Another way to explain the spatial distribution of field LMXBs is therefore a reversed metallicity effect, although we have not identified a mechanism to explain this in terms of stellar and binary evolution.

Electric fields provide the major coupling between the turbulence of the solar wind and particles. A large part of the turbulent spectrum of fluctuations in the solar wind is thought to be kinetic Alfvén waves; however, whistlers have recently been found to be important. In this article, we attempt to determine the mode identification of individual waveforms using the three-dimensional antenna system of the SWaves experiments on the STEREO spacecraft. Samples are chosen using waveforms with an apparent periodic structure, selected visually. The short antennas of STEREO respond to density fluctuations and to electric fields. Measurement of four quantities using only three antennas presents a problem. Methods to overcome or to ignore this difficulty are presented. We attempt to decide whether the waveforms correspond to the whistler mode or the Alfvén mode by using the direction of rotation of the signal. Most of the waveforms are so oblique—nearly linearly polarized—that the direction cannot be determined. However, about one third of the waveforms can be identified, and whistlers and Alfvén waves are present in roughly equal numbers. The selected waveforms are very intense but intermittent and are orders of magnitude stronger than the average, yet their accumulated signal accounts for a large fraction of the average. The average, however, is supposed to be the result of a turbulent mixture of many waves, not short coherent events. This presents a puzzle for future work.

Bulge globular clusters (GCs) with metallicities [Fe/H] ≲ −1.0 and blue horizontal branches are candidates to harbor the oldest populations in the Galaxy. Based on the analysis of HST proper-motion-cleaned color–magnitude diagrams in filters F435W and F625W, we determine physical parameters for the old bulge GCs NGC 6522 and NGC 6626 (M28), both with well-defined blue horizontal branches. We compare these results with similar data for the inner halo cluster NGC 6362. These clusters have similar metallicities (−1.3 ≤ [Fe/H] ≤ −1.0) obtained from high-resolution spectroscopy. We derive ages, distance moduli, and reddening values by means of statistical comparisons between observed and synthetic fiducial lines employing likelihood statistics and the Markov chain Monte Carlo method. The synthetic fiducial lines were generated using α-enhanced BaSTI and Dartmouth stellar evolutionary models, adopting both canonical (Y ∼ 0.25) and enhanced (Y ∼ 0.30–0.33) helium abundances. RR Lyrae stars were employed to determine the HB magnitude level, providing an independent indicator to constrain the apparent distance modulus and the helium enhancement. The shape of the observed fiducial line could be compatible with some helium enhancement for NGC 6522 and NGC 6626, but the average magnitudes of RR Lyrae stars tend to rule out this hypothesis. Assuming canonical helium abundances, BaSTI and Dartmouth models indicate that all three clusters are coeval, with ages between ∼12.5 and 13.0 Gyr. The present study also reveals that NGC 6522 has at least two stellar populations, since its CMD shows a significantly wide subgiant branch compatible with 14% ± 2% and 86% ± 5% for first and second generations, respectively.

The γ-ray flares from the Crab Nebula observed by AGILE and Fermi-LAT between 2007 and 2013 reached GeV photon energies and lasted several days. The strongest emission, observed during the 2011 April "superflare", exceeded the quiescent level by more than an order of magnitude. These observations challenge the standard models for particle acceleration in pulsar wind nebulae, because the radiating electrons have energies exceeding the classical radiation-reaction limit for synchrotron emission. Particle-in-cell simulations have suggested that the classical synchrotron limit can be exceeded if the electrons also experience electrostatic acceleration due to shock-driven magnetic reconnection. In this paper, we revisit the problem using an analytic approach based on solving a fully time-dependent electron transport equation describing the electrostatic acceleration, synchrotron losses, and escape experienced by electrons in a magnetically confined plasma "blob" as it encounters and passes through the pulsar wind termination shock. We show that our model can reproduce the γ-ray spectra observed during the rising and decaying phases of each of the two sub-flare components of the 2011 April superflare. We integrate the spectrum for photon energies $\geqslant 100$ MeV to obtain the light curve for the event, which also agrees with the observations. We find that strong electrostatic acceleration occurs on both sides of the termination shock, driven by magnetic reconnection. We also find that the dominant mode of particle escape changes from diffusive escape to advective escape as the blob passes through the shock.

We study the topology of the matter density field in two-dimensional slices and consider how we can use the amplitude A of the genus for cosmological parameter estimation. Using the latest Horizon Run 4 simulation data, we calculate the genus of the smoothed density field constructed from light cone mock galaxy catalogs. Information can be extracted from the amplitude of the genus by considering both its redshift evolution and magnitude. The constancy of the genus amplitude with redshift can be used as a standard population, from which we derive constraints on the equation of state of dark energy ${w}_{\mathrm{de}}$—by measuring A at $z\sim 0.1$ and $z\sim 1$, we can place an order ${\rm{\Delta }}{w}_{\mathrm{de}}\sim { \mathcal O }(15 \% )$ constraint on ${w}_{\mathrm{de}}$. By comparing A to its Gaussian expectation value, we can potentially derive an additional stringent constraint on the matter density ${\rm{\Delta }}{{\rm{\Omega }}}_{\mathrm{mat}}\sim 0.01$. We discuss the primary sources of contamination associated with the two measurements—redshift space distortion (RSD) and shot noise. With accurate knowledge of galaxy bias, we can successfully remove the effect of RSD, and the combined effect of shot noise and nonlinear gravitational evolution is suppressed by smoothing over suitably large scales ${R}_{{\rm{G}}}\geqslant 15\,\mathrm{Mpc}/h$. Without knowledge of the bias, we discuss how joint measurements of the two- and three-dimensional genus can be used to constrain the growth factor $\beta =f/b$. The method can be applied optimally to redshift slices of a galaxy distribution generated using the drop-off technique.

We present a continuum radiative transfer model grid for fitting observed spectral energy distributions (SEDs) of massive protostars. The model grid is based on the paradigm of core accretion theory for massive star formation with pre-assembled gravitationally bound cores as initial conditions. In particular, following the turbulent core model, initial core properties are set primarily by their mass and the pressure of their ambient clump. We then model the evolution of the protostar and its surround structures in a self-consistent way. The model grid contains about 9000 SEDs with four free parameters: initial core mass, the mean surface density of the environment, the protostellar mass, and the inclination. The model grid is used to fit observed SEDs via ${\chi }^{2}$ minimization, with the foreground extinction additionally estimated. We demonstrate the fitting process and results using the example of massive protostar G35.20-0.74. Compared with other SED model grids currently used for massive star formation studies, the properties of the protostar and its surrounding structures are more physically connected in our model grid, which reduces the dimensionality of the parameter spaces and the total number of models. This excludes possible fitting of models that are physically unrealistic or are not internally self-consistent in the context of the turbulent core model. Thus, this model grid serves not only as a fitting tool to estimate properties of massive protostars, but also as a test of core accretion theory. The SED model grid is publicly released with this paper.

Recent multiwavelength work led by the Boston University blazar group (e.g., Marscher et al.) strongly suggests that a fraction of the blazar flares seen by the Fermi Large Area Telescope (LAT) take place a few to several pc away from the central engine. However, at such distances from the central engine, there is no adequate external photon field to provide the seed photons required for producing the observed GeV emission under leptonic inverse Compton (IC) models. A possible solution is a spine-sheath geometry for the emitting region (MacDonald et al., but see Nalewajko et al.). Here we use the current view of the molecular torus (e.g., Elitzur; Netzer), in which the torus extends a few pc beyond the dust sublimation radius with dust clouds distributed with a declining density for decreasing polar angle. We show that for a spine-sheath blazar jet embedded in the torus, the wide beaming pattern of the synchrotron radiation of the relatively slow sheath will heat molecular clouds with subsequent IR radiation that will be highly boosted in the spine comoving frame, and that under reasonable conditions this photon field can dominate over the sheath photons directly entering the spine. If the sheath is sufficiently luminous it will sublimate the dust, and if the sheath synchrotron radiation extends to optical-UV energies (as may happen during flares), this will illuminate the sublimated dust clouds to produce emission lines that will vary in unison with the optical-UV continuum, as has been very recently reported for blazar CTA 102 (Jorstad et al.).

Core helium burning primary red clump (RC) stars are evolved red giant stars that are excellent standard candles. As such, these stars are routinely used to map the Milky Way or determine the distance to other galaxies, among other things. However, distinguishing RC stars from their less evolved precursors, namely red giant branch (RGB) stars, is still a difficult challenge and has been deemed the domain of asteroseismology. In this paper, we use a sample of 1676 RGB and RC stars that have both single epoch infrared spectra from the APOGEE survey and asteroseismic parameters and classification to show that the spectra alone can be used to (1) predict asteroseismic parameters with precision high enough to (2) distinguish core helium burning RC from other giant stars with less than 2% contamination. This will not only allow for a clean selection of a large number of standard candles across our own and other galaxies from spectroscopic surveys, but also will remove one of the primary roadblocks for stellar evolution studies of mixing and mass loss in red giant stars.

We provide the theoretical background for diagnostics of the thermal properties of solar prominences observed by the Atacama Large Millimeter/submillimeter Array (ALMA). To do this, we employ the 3D Whole-Prominence Fine Structure (WPFS) model that produces synthetic ALMA-like observations of a complex simulated prominence. We use synthetic observations derived at two different submillimeter/millimeter (SMM) wavelengths—one at a wavelength at which the simulated prominence is completely optically thin and another at a wavelength at which a significant portion of the simulated prominence is optically thick—as if these were the actual ALMA observations. This allows us to develop a technique for an analysis of the prominence plasma thermal properties from such a pair of simultaneous high-resolution ALMA observations. The 3D WPFS model also provides detailed information about the distribution of the kinetic temperature and the optical thickness along any line of sight. We can thus assess whether the measure of the kinetic temperature derived from observations accurately represents the actual kinetic temperature properties of the observed plasma. We demonstrate here that in a given pixel the optical thickness at the wavelength at which the prominence plasma is optically thick needs to be above unity or even larger to achieve a sufficient accuracy of the derived information about the kinetic temperature of the analyzed plasma. Information about the optical thickness cannot be directly discerned from observations at the SMM wavelengths alone. However, we show that a criterion that can identify those pixels in which the derived kinetic temperature values correspond well to the actual thermal properties in which the observed prominence can be established.

We explore the effects of progenitor pre-stellar core properties on the evolution of disks with external photoevaporation in clusters. Since the strength of external photoevaporation is largely determined by the depth of the gravitational potential well of the disk, the external photoevaporation rate is the function of star mass and disk size. The properties of a core collapse set up the initial conditions of protoplanetary disks, so they influence the evolutions of star mass and disk size. Our calculations show that the core properties can dramatically influence the efficiency of external photoevaporation. For the core with low angular velocity, most core mass directly falls onto the central star or onto the disk near the star. External photoevaporation is suppressed even if external radiation from nearby massive stars are strong. In this case, the disk evolution in clusters is primarily driven by its own internal viscosity. However, if the core angular velocity is high, most core mass falls onto the disk far from the central star. External photoevaporation is so strong that the disk mass is severely evaporated. Finally, the star mass is very low and the disk lifetime is very short. Our calculations could interpret some observational features of disks in clusters, such as the diameter distribution of disks in the Trapezium cluster and the correlation between mass accretion rate and star mass. We suggest that the disk mass determined by (sub)millimeter wavelength observations may be underestimated.

In this paper, the Lorentz invariance violation (LIV) is introduced in the calculations of photon propagation in the universe. LIV is considered in the photon sector, and the mean-free path of the $\gamma \gamma \to {e}^{+}{e}^{-}$ interaction is calculated. The corresponding photon horizon, including LIV effects, is used to predict major changes in the propagation of photons with energy above 10¹⁸ eV. The flux of GZK photons on Earth, considering LIV, is calculated for several source models of ultra-high-energy cosmic rays (UHECRs). The predicted flux of GZK gamma-rays is compared to the new upper limits on the photon flux obtained by the Pierre Auger Observatory in order to impose upper limits on the LIV coefficients of order n = 0, 1, and 2. The limits on the LIV coefficients derived here are more realistic than previous works and in some cases more restrictive. The analysis resulted in LIV upper limits in the photon sector of ${\delta }_{\gamma ,0}^{\mathrm{limit}}\sim -{10}^{-20}$, ${\delta }_{\gamma ,1}^{\mathrm{limit}}\sim -{10}^{-38}\,{\mathrm{eV}}^{-1}$, and ${\delta }_{\gamma ,2}^{\mathrm{limit}}\sim -{10}^{-56}\,{\mathrm{eV}}^{-2}$ in the astrophysical scenario, which best describes UHECR data.

We investigate the X-ray active galactic nucleus (AGN) properties of millimeter galaxies in the Great Observatories Origins Deep Survey South (GOODS-S) field detected with the Atacama Large Millimeter/submillimeter Array (ALMA), by utilizing the Chandra 7-Ms data, the deepest X-ray survey to date. Our millimeter galaxy sample comes from the ASAGAO survey covering 26 arcmin² (12 sources at a 1.2 mm flux-density limit of $\approx 0.6$ mJy), supplemented by the deeper but narrower 1.3 mm survey of a part of the ASAGAO field by Dunlop et al. Ofthe 25 total millimeter galaxies, 14 have Chandra counterparts. The observed AGN fractions at $z=1.5\mbox{--}3$ are found to be ${90}_{-19}^{+8}$% and ${57}_{-25}^{+23}$% for the ultra-luminous and luminous infrared galaxies with log ${L}_{\mathrm{IR}}$/${L}_{\odot }$ = 12–12.8 and log ${L}_{\mathrm{IR}}$/${L}_{\odot }$ = 11.5–12, respectively. The majority (∼2/3) of the ALMA and/or Herschel detected X-ray AGNs at z = 1.5−3 appear to be star-formation-dominant populations, having ${L}_{{\rm{X}}}$/ ${L}_{\mathrm{IR}}$ ratios smaller than the "simultaneous evolution" value expected from the local black-hole-mass-to-stellar-mass (${M}_{\mathrm{BH}}$–M_*) relation. On the basis of the ${L}_{{\rm{X}}}$ and stellar mass relation, we infer that a large fraction of star-forming galaxies at $z=1.5\mbox{--}3$ have black hole masses that are smaller than those expected from the local ${M}_{\mathrm{BH}}$–M_* relation. This contrasts previous reports on luminous AGNs at the same redshifts detected in wider and shallower surveys, which are subject to selection biases against lower luminosity AGNs. Our results are consistent with an evolutionary scenario in which star formation occurs first, and an AGN-dominant phase follows later, in objects that finally evolve into galaxies with classical bulges.

The intrinsic alignment of galaxies is an important systematic effect in weak-lensing surveys, which can affect the derived cosmological parameters. One direct way to distinguish different alignment models and quantify their effects on the measurement is to produce mock weak-lensing surveys. In this work, we use the full-sky ray-tracing technique to produce mock images of galaxies from the ELUCID N-body simulation run with WMAP9 cosmology. In our model, we assume that the shape of the central elliptical galaxy follows that of the dark matter halo, and that of the spiral galaxy follows the halo spin. Using the mock galaxy images, a combination of galaxy intrinsic shape and the gravitational shear, we compare the predicted tomographic shear correlations to the results of the Kilo-Degree Survey (KiDS) and Deep Lens Survey (DLS). We find that our predictions stay between the KiDS and DLS results. We rule out a model in which the satellite galaxies are radially aligned with the center galaxy; otherwise, the shear correlations on small scales are too high. Most importantly, we find that although the intrinsic alignment of spiral galaxies is very weak, they induce a positive correlation between the gravitational shear signal and the intrinsic galaxy orientation (GI). This is because the spiral galaxy is tangentially aligned with the nearby large-scale overdensity, contrary to the radial alignment of the elliptical galaxy. Our results explain the origin of the detected positive GI term in the weak-lensing surveys. We conclude that in future analyses, the GI model must include the dependence on galaxy types in more detail.

Properties of the turbulent cascade from fluid to kinetic scales in collisionless plasmas are investigated by means of large-size 3D hybrid (fluid electrons, kinetic protons) particle-in-cell simulations. Initially isotropic Alfvénic fluctuations rapidly develop a strongly anisotropic turbulent cascade, mainly in the direction perpendicular to the ambient magnetic field. The omnidirectional magnetic field spectrum shows a double power-law behavior over almost two decades in wavenumber, with a Kolmogorov-like index at large scales, a spectral break around ion scales, and a steepening at sub-ion scales. Power laws are also observed in the spectra of the ion bulk velocity, density, and electric field, at both magnetohydrodynamic (MHD) and kinetic scales. Despite the complex structure, the omnidirectional spectra of all fields at ion and sub-ion scales are in remarkable quantitative agreement with those of a 2D simulation with similar physical parameters. This provides a partial, a posteriori validation of the 2D approximation at kinetic scales. Conversely, at MHD scales, the spectra of the density and of the velocity (and, consequently, of the electric field) exhibit differences between the 2D and 3D cases. Although they can be partly ascribed to the lower spatial resolution, the main reason is likely the larger importance of compressible effects in the full 3D geometry. Our findings are also in remarkable quantitative agreement with solar wind observations.

Nova Cen 2013 (V1369 Cen) is the fourth bright nova observed panchromatically through high-resolution UV+optical multiepoch spectroscopy. It is also the nova with the richest set of spectra (in terms of both data quality and number of epochs) thanks to its exceptional brightness. Here, we use the late nebular spectra taken between day ∼250 and day ∼837 after outburst to derive the physical, geometrical, and kinematical properties of the nova. We compare the results with those determined for the other panchromatic studies in this series: T Pyx, V339 Del (nova Del 2013), and V959 Mon (nova Mon 2012). From this we conclude that in all these novae the ejecta geometry and phenomenology can be consistently explained by clumpy gas expelled during a single, brief ejection episode and in ballistic expansion, and not by a wind. For V1369 Cen the ejecta mass (∼1 × 10⁻⁴M⊙) and filling factor (0.1 ≤ f ≤ 0.2) are consistent with those of classical novae but larger (by at least an order of magnitude) than those of T Pyx and the recurrent novae. V1369 Cen has an anomalously high (relative to solar) N/C ratio that is beyond the range currently predicted for a CO nova, and the Ne emission line strengths are dissimilar to those of typical ONe or CO white dwarfs.

V582 Aur is an FU Ori-type young eruptive star in outburst since ∼1985. The eruption is currently in a relatively constant plateau phase, with photometric and spectroscopic variability superimposed. Here we will characterize the progenitor of the outbursting object, explore its environment, and analyze the temporal evolution of the eruption. We are particularly interested in the physical origin of the two deep photometric dips, one that occurred in 2012 and one that is ongoing since 2016. We collected archival photographic plates and carried out new optical, infrared, and millimeter-wave photometric and spectroscopic observations between 2010 and 2018, with a high sampling rate during the current minimum. Besides analyzing the color changes during fading, we compiled multiepoch spectral energy distributions and fitted them with a simple accretion disk model. Based on pre-outburst data and a millimeter continuum measurement, we suggest that the progenitor of the V582 Aur outburst is a low-mass T Tauri star with average properties. The mass of an unresolved circumstellar structure, probably a disk, is 0.04 M_⊙. The optical and near-infrared spectra demonstrate the presence of hydrogen and metallic lines, show the CO band head in absorption, and exhibit a variable Hα profile. The color variations strongly indicate that both the ∼1 yr long brightness dip in 2012 and the current minimum since 2016 are caused by increased extinction along the line of sight. According to our accretion disk models, the reddening changed from A_V = 4.5 to 12.5 mag, while the accretion rate remained practically constant. Similarly to the models of the UXor phenomenon of intermediate- and low-mass young stars, orbiting disk structures could be responsible for the eclipses.

We present wide and deep photometry of the northwestern part of the halo of the Andromeda galaxy (M31) using Hyper Suprime-Cam on the Subaru Telescope. The survey covers a 9.2 deg² field in the g, i, and NB515 bands and shows a clear red giant branch (RGB) of M31's halo stars and a pronounced red clump (RC) feature. The spatial distribution of RC stars shows a prominent stream feature, the Northwestern (NW) Stream, and a diffuse substructure in the southern part of our survey field. We estimate the distances based on the RC method and obtain $(m\mbox{--}M)$ = 24.63 ± 0.191 (random) ± 0.057 (systematic) and 24.29 ± 0.211 (random) ± 0.057 (systematic) mag for the NW Stream and diffuse substructure, respectively, implying that the NW Stream is located behind M31, whereas the diffuse substructure is located in front of it. We also estimate line-of-sight distances along the NW Stream and find that the southern part of the stream is ∼20 kpc closer to us relative to the northern part. The distance to the NW Stream inferred from the isochrone fitting to the color–magnitude diagram favors the RC-based distance, but the tip of the RGB (TRGB)-based distance estimated for NB515-selected RGB stars does not agree with it. The surface number density distribution of RC stars across the NW Stream is found to be approximately Gaussian with an FWHM of ∼25 arcmin (5.7 kpc), with a slight skew to the southwest side. That along the NW Stream shows a complicated structure, including variations in number density and a significant gap in the stream.

TRAPPIST-1 is an ultracool dwarf star transited by seven Earth-sized planets, for which thorough characterization of atmospheric properties, surface conditions encompassing habitability, and internal compositions is possible with current and next-generation telescopes. Accurate modeling of the star is essential to achieve this goal. We aim to obtain updated stellar parameters for TRAPPIST-1 based on new measurements and evolutionary models, compared to those used in discovery studies. We present a new measurement for the parallax of TRAPPIST-1, 82.4 ± 0.8 mas, based on 188 epochs of observations with the TRAPPIST and Liverpool Telescopes from 2013 to 2016. This revised parallax yields an updated luminosity of ${L}_{* }=(5.22\pm 0.19)\times {10}^{-4}\,{L}_{\odot }$, which is very close to the previous estimate but almost two times more precise. We next present an updated estimate for TRAPPIST-1 stellar mass, based on two approaches: mass from stellar evolution modeling, and empirical mass derived from dynamical masses of equivalently classified ultracool dwarfs in astrometric binaries. We combine them using a Monte-Carlo approach to derive a semi-empirical estimate for the mass of TRAPPIST-1. We also derive estimate for the radius by combining this mass with stellar density inferred from transits, as well as an estimate for the effective temperature from our revised luminosity and radius. Our final results are ${M}_{* }=0.089\pm 0.006\,{M}_{\odot }$, ${R}_{* }=0.121\pm 0.003\,{R}_{\odot }$, and ${T}_{\mathrm{eff}}\,=$ 2516 ± 41 K. Considering the degree to which the TRAPPIST-1 system will be scrutinized in coming years, these revised and more precise stellar parameters should be considered when assessing the properties of TRAPPIST-1 planets.

We present the results of near-infrared-to-mid-infrared (NIR-to-MIR) imaging and NIR spectroscopic observations of two galaxy mergers, NGC 2782 (Arp 215) and NGC 7727 (Arp 222), with the Infrared Camera on board AKARI. NGC 2782 shows extended MIR emission in the eastern side of the galaxy, which corresponds to the eastern tidal tail seen in the H i 21 cm map, while NGC 7727 shows extended MIR emission in the north of the galaxy, which is similar to the plumes seen in the residual image at the K-band after subtracting a galaxy model. Both extended structures are thought to have formed in association with their merger events. They show excess emission at 7–15 μm, which can be attributed to emission from polycyclic aromatic hydrocarbons (PAHs), while the observed spectral energy distributions (SEDs) decline longward of 24 μm, suggesting that very small grains (VSGs) are deficient. These characteristics of the observed MIR SED may be explained if PAHs are formed by fragmentation of VSGs during merger events. The star formation rate is estimated from the MIR PAH emission in the eastern tail region of NGC 2782 and it is in fair agreement with those estimated from Hα and [C ii] 158 μm. MIR observations are efficient for the study of dust processing and structures formed during merger events.

Resonant single photoionization cross sections of Feⁿ⁺ (n = 6 to 10) ions have been measured in absolute values using a merged-beams setup at the SOLEIL synchrotron radiation facility. Photon energies were between about 710 and 780 eV, covering the range of the 2p–3d transitions. The experimental cross sections are compared to calculations we performed using a multi-configuration Dirac–Fock code and the OPAS code dedicated to radiative opacity calculations. Comparisons are also done with the Chandra X-ray observatory NGC 3783 spectra and with the results of previously published calculations.

The plasma resistivity was evaluated in an experiment on the collision of two magnetic flux ropes. Whenever the ropes collide, some magnetic energy is lost as a result of reconnection. Volumetric data, in which all the relevant time-varying quantities were recorded in detail, are presented. Ohm's law is shown to be nonlocal and cannot be used to evaluate the plasma resistivity. The resistivity was instead calculated using the AC Kubo resistivity and shown to be anomalously high in certain regions of space.

Rapid flares from blazars in very high-energy (VHE) γ-rays challenge the common understanding of jets of active galactic nuclei (AGNs). The same population of ultra-relativistic electrons is often thought to be responsible for both X-ray and VHE emission. We thus systematically searched for X-ray flares at sub-hour timescales of TeV blazars in the entire Rossi X-ray Timing Explorer archival database. We found rapid flares from PKS 2005−489 and S5 0716+714, and a candidate rapid flare from 1ES 1101−232. In particular, the characteristic rise timescale of PKS 2005−489 is less than half a minute, which, to our knowledge, is the shortest among known AGN flares at any wavelengths. The timescales of these rapid flares indicate that the size of the central supermassive black hole is not a hard lower limit on the physical size of the emission region of the flare. PKS 2005−489 shows possible hard lags in its flare, which could be attributed to particle acceleration (injection); its flaring component has the hardest spectrum when it first appears. For all flares, the flaring components show similar hard spectra with ${\rm{\Gamma }}=1.7\mbox{--}1.9$, and we estimate the magnetic field strength B ∼ 0.1–1.0 G by assuming synchrotron cooling. These flares could be caused by inhomogeneity of the jets. Models that can only produce rapid γ-ray flares but little synchrotron activity are less favorable.

Magnetic twist is thought to play an important role in many structures of the solar atmosphere. One of the effects of twist is to modify the properties of the eigenmodes of magnetic tubes. In the linear regime standing kink solutions are characterized by a change in polarization of the transverse displacement along the twisted tube. In the nonlinear regime, magnetic twist affects the development of shear instabilities that appear at the tube boundary when it is oscillating laterally. These Kelvin–Helmholtz instabilities (KHI) are produced either by the jump in the azimuthal component of the velocity at the edge of the sharp boundary between the internal and external part of the tube or by the continuous small length scales produced by phase mixing when there is a smooth inhomogeneous layer. In this work the effect of twist is consistently investigated by solving the time-dependent problem including the process of energy transfer to the inhomogeneous layer. It is found that twist always delays the appearance of the shear instability, but for tubes with thin inhomogeneous layers the effect is relatively small for moderate values of twist. On the contrary, for tubes with thick layers, the effect of twist is much stronger. This can have some important implications regarding observations of transverse kink modes and the KHI itself.

We present Gemini and Keck spectroscopic redshifts and velocity dispersions for 20 clusters detected via the Sunyaev–Zel'dovich (SZ) effect by the Planck space mission, with estimated masses in the range $2.3\times {10}^{14}\,{M}_{\odot }\lt {M}_{500}^{\mathrm{Pl}}\lt 9.4\times {10}^{14}\,{M}_{\odot }$. Cluster members were selected for spectroscopic follow-up with Palomar, Gemini, and Keck optical and (in some cases) infrared imaging. Seven cluster redshifts were measured for the first time with this observing campaign, including one of the most distant Planck clusters confirmed to date, at $z=0.782\pm 0.010$, PSZ2 G085.95+25.23. The spectroscopic redshift catalogs of members of each confirmed cluster are included as online tables. We show the galaxy redshift distributions and measure the cluster velocity dispersions. The cluster velocity dispersions obtained in this paper were used in a companion paper to measure the Planck mass bias and to constrain the cluster velocity bias.

Celestial bodies with a mass of $M\approx 10\,{M}_{\mathrm{Jup}}$ have been found orbiting nearby stars. It is unknown whether these objects formed like gas-giant planets through core accretion or like stars through gravitational instability. I show that objects with $M\lesssim 4\,{M}_{\mathrm{Jup}}$ orbit metal-rich solar-type dwarf stars, a property associated with core accretion. Objects with $M\gtrsim 10\,{M}_{\mathrm{Jup}}$ do not share this property. This transition is coincident with a minimum in the occurrence rate of such objects, suggesting that the maximum mass of a celestial body formed through core accretion like a planet is less than $10\,{M}_{\mathrm{Jup}}$. Consequently, objects with $M\gtrsim 10\,{M}_{\mathrm{Jup}}$ orbiting solar-type dwarf stars likely formed through gravitational instability and should not be thought of as planets. Theoretical models of giant planet formation in scaled minimum-mass solar nebula Shakura–Sunyaev disks with standard parameters tuned to produce giant planets predict a maximum mass nearly an order of magnitude larger. To prevent newly formed giant planets from growing larger than $10\,{M}_{\mathrm{Jup}}$, protoplanetary disks must therefore be significantly less viscous or of lower mass than typically assumed during the runaway gas accretion stage of giant planet formation. Either effect would act to slow the Type I/II migration of planetary embryos/giant planets and promote their survival. These inferences are insensitive to the host star mass, planet formation location, or characteristic disk dissipation time.

All known extraterrestrial dust (micrometeoroids) entering the Earth's atmosphere is anticipated to have a significant contribution from ordinary chondritic precursors, as seen in meteorites, but this is an apparent contradiction that needs to be addressed. Ordinary chondrites represent a minor contribution to the overall meteor influx compared to carbonaceous chondrites, which are largely dominated by CI and/or CM chondrites. However, the near-Earth asteroid population presents a scenario with sufficient scope for generation of dust-sized debris from ordinary chondritic sources. The bulk chemical composition of 3255 micrometeorites (MMs) collected from Antarctica and deep-sea sediments has shown Mg/Si largely dominated by carbonaceous chondrites, and less than 10% having ordinary chondritic precursors. The chemical ablation model is combined with different initial chondritic compositions (CI, CV, L, LL, H), and the results clearly indicate that high-density (≥2.8 g cm⁻³) precursors, such as CV and ordinary chondrites in the size range 100–700 μm and zenith angle 0°–70°, ablate at much faster rates and lose their identity even before reaching the Earth's surface and hence are under-represented in our collections. Moreover, their ability to survive as MMs remains grim for high-velocity micrometeoroids (>16 km s⁻¹). The elemental ratio for CV and ordinary chondrites are also similar to each other irrespective of the difference in the initial chemical composition. In conclusion, MMs belonging to ordinary chondritic precursors' concentrations may not be insignificant in thermosphere, as they are found on Earth's surface.

The rate of tidal disruption events (TDEs), ${R}_{\mathrm{TDE}}$, is predicted to depend on stellar conditions near the super-massive black hole (SMBH), which are on difficult-to-measure sub-parsec scales. We test whether ${R}_{\mathrm{TDE}}$ depends on kpc-scale global galaxy properties, which are observable. We concentrate on stellar surface mass density, ${{\rm{\Sigma }}}_{{M}_{\star }}$, and velocity dispersion, ${\sigma }_{v}$, which correlate with the stellar density and velocity dispersion of the stars around the SMBH. We consider 35 TDE candidates, with and without known X-ray emission. The hosts range from star-forming to quiescent to quiescent with strong Balmer absorption lines. The last (often with post-starburst spectra) are overrepresented in our sample by a factor of ${35}_{-17}^{+21}$ or ${18}_{-7}^{+8}$, depending on the strength of the Hδ absorption line. For a subsample of hosts with homogeneous measurements, ${{\rm{\Sigma }}}_{{M}_{\star }}={10}^{9}$–${10}^{10}\,{M}_{\odot }/{{\rm{kpc}}}^{2}$, higher on average than for a volume-weighted control sample of Sloan Digital Sky Survey galaxies with similar redshifts and stellar masses. This is because (1) most of the TDE hosts here are quiescent galaxies, which tend to have higher ${{\rm{\Sigma }}}_{{M}_{\star }}$ than the star-forming galaxies that dominate the control, and (2) the star-forming hosts have higher average ${{\rm{\Sigma }}}_{{M}_{\star }}$ than the star-forming control. There is also a weak suggestion that TDE hosts have lower ${\sigma }_{v}$ than for the quiescent control. Assuming that ${R}_{\mathrm{TDE}}\propto {{\rm{\Sigma }}}_{{M}_{\star }}^{\alpha }\times {\sigma }_{v}^{\beta }$, and applying a statistical model to the TDE hosts and control sample, we estimate $\hat{\alpha }=0.9\pm 0.2$ and $\hat{\beta }=-1.0\pm 0.6$. This is broadly consistent with ${R}_{\mathrm{TDE}}$ being tied to the dynamical relaxation of stars surrounding the SMBH.

We analyze a 900 ks stacked Chandra/HETG spectrum of NGC 3783 in the context of magnetically driven accretion-disk wind models in an effort to provide tight constraints on the global conditions of the underlying absorbers. Motivated by the earlier measurements of its absorption measure distribution (AMD) indicating X-ray-absorbing ionic columns that decrease slowly with decreasing ionization parameter, we employ 2D magnetohydrodynamic (MHD) disk wind models to describe the global outflow. We compute its photoionization structure along with the wind kinematic properties, allowing us to further calculate in a self-consistent fashion the shapes of the major X-ray absorption lines. With the wind radial density profile determined by the AMD, the profiles of the ensemble of the observed absorption features are determined by the two global parameters of the MHD wind; i.e., disk inclination ${\theta }_{\mathrm{obs}}$ and wind density normalization n_o. Considering the most significant absorption features in the ∼1.8–20 Å range, we show that the MHD wind is best described by $n{(r)\sim 6.9\times {10}^{11}(r/{r}_{o})}^{-1.15}$ cm⁻³ and ${\theta }_{\mathrm{obs}}=44^\circ$. We argue that winds launched by X-ray heating or radiation pressure, or even MHD winds but with steeper radial density profiles, are strongly disfavored by data. Considering the properties of Fe K-band absorption features (i.e., Fe xxv and Fe xxvi), while typically prominent in the active galactic nucleus X-ray spectra, they appear to be weak in NGC 3783. For the specific parameters of our model obtained by fitting the AMD and the rest of the absorption features, these features are found to be weak, in agreement with observations.

We study the energy release process of a set of 51 flares (32 confined, 19 eruptive) ranging from GOES class B3 to X17. We use Hα filtergrams from Kanzelhöhe Observatory together with Solar Dynamics Observatory HMI and Solar and Heliospheric Observatory MDI magnetograms to derive magnetic reconnection fluxes and rates. The flare reconnection flux is strongly correlated with the peak of the GOES 1–8 Å soft X-ray flux (c = 0.92, in log–log space) for both confined and eruptive flares. Confined flares of a certain GOES class exhibit smaller ribbon areas but larger magnetic flux densities in the flare ribbons (by a factor of 2). In the largest events, up to ≈50% of the magnetic flux of the active region (AR) causing the flare is involved in the flare magnetic reconnection. These findings allow us to extrapolate toward the largest solar flares possible. A complex solar AR hosting a magnetic flux of 2 × 10²³ Mx, which is in line with the largest AR fluxes directly measured, is capable of producing an X80 flare, which corresponds to a bolometric energy of about 7 × 10³² erg. Using a magnetic flux estimate of 6 × 10²³ Mx for the largest solar AR observed, we find that flares of GOES class ≈X500 could be produced (E_bol ≈ 3 × 10³³ erg). These estimates suggest that the present day's Sun is capable of producing flares and related space weather events that may be more than an order of magnitude stronger than have been observed to date.

We performed Very Long Baseline Array (VLBA) observations of SiO masers ($v=1,v=2,J=1\to 0$) toward VX Sgr from 2006 July to 2008 August. With the application of a phase reference technique, the accurate relative positions of maser spots at the two transitions can be acquired. The relative positions enable us to obtain more matched masers in the same coordinate frame to better study the dynamics of the maser shell. We adopt two different methods to investigate the global motions of the maser shell, which is found to expand in a decelerated manner. At the beginning of this process, the decelerative force can be interpreted as a force dominated by the gravitational attraction of the star. However, in the later epochs, the deceleration has a smaller magnitude, suggesting that an outward force is combating the stellar gravity. In addition, we construct a model of a rotating and expanding maser shell. The consistency of the model and observations at the first two epochs suggests approximate Keplerian rotation of the shell with a period of 46.9 years. However, other explanations, such as an axisymmetric outflow, are also possible. We also find two matched maser spots with double-peak spectra moving at a velocity of 6.8 km s⁻¹. The special spectra provide direct observational evidence that the motion of a maser spot reflects the real gas stream, rather than changes in physical conditions. Finally, the distance to VX Sgr is calculated to be 1.10 ± 0.11 kpc using a statistical parallax method. This value is within the range reported in the literature.

The prompt emission spectrum of gamma-ray bursts is characterized by a smoothly joint broken power-law spectrum known as the Band function. The typical low-energy photon index is $\sim -1$, which poses a challenge to standard synchrotron radiation models. We investigate the electron energy spectrum as a result of the interplay among adiabatic stochastic acceleration (ASA), particle injection, and synchrotron cooling. In the ASA-dominated low-energy range, ASA enables an efficient hardening of the injected energy spectrum to approach a spectral index −1. In the synchrotron cooling-dominated high-energy range, the injected high-energy electrons undergo fast synchrotron cooling and have a softer photon spectrum. With the energy range of the injected electrons broadly covering both the ASA- and synchrotron cooling-dominated ranges, the resulting photon number spectrum has low- and high-energy indices of ${\alpha }_{s}\sim -1$ and ${\beta }_{s}\sim -p/2-1$, respectively. The break energy is of the order of ∼100 keV, depending on the turbulence properties.

It is widely believed that relativistic jets in X-ray binaries (XRBs) and active-galactic nuclei are powered by the rotational energy of black holes. This idea is supported by general-relativistic magnetohydrodynamic (GRMHD) simulations of accreting black holes, which demonstrate efficient energy extraction via the Blandford–Znajek mechanism. However, due to uncertainties in the physics of mass loading, and the failure of GRMHD numerical schemes in the highly magnetized funnel region, the matter content of the jet remains poorly constrained. We investigate the observational signatures of mass loading in the funnel by performing general-relativistic radiative transfer calculations on a range of 3D GRMHD simulations of accreting black holes. We find significant observational differences between cases in which the funnel is empty and cases where the funnel is filled with plasma, particularly in the optical and X-ray bands. In the context of Sgr A*, current spectral data constrains the jet filling only if the black hole is rapidly rotating with a ≳ 0.9. In this case, the limits on the infrared flux disfavor a strong contribution from material in the funnel. We comment on the implications of our models for interpreting future Event Horizon Telescope observations. We also scale our models to stellar-mass black holes, and discuss their applicability to the low-luminosity state in XRBs.

To understand why supercritical accretion is feasible onto a neutron star (NS), we carefully examine the accretion flow dynamics by 2.5-dimensional general relativistic radiation magnetohydrodynamic (RMHD) simulations, comparing the cases of accretion onto a non-magnetized NS and that onto a black hole (BH). Supercritical BH accretion is relatively easy, since BHs can swallow excess radiation energy, so that radiation flux can be inward in its vicinity. This mechanism can never work for an NS, which has a solid surface. In fact, we find that the radiation force is always outward. Instead, we found significant reduction in the mass accretion rate due to strong radiation-pressure-driven outflow. The radiation flux F_rad is self-regulated such that the radiation force balances with the sum of gravity and centrifugal forces. Even when the radiation energy density greatly exceeds that expected from the Eddington luminosity ${E}_{\mathrm{rad}}\simeq {F}_{\mathrm{rad}}\tau /c\gt {10}^{2}{L}_{\mathrm{Edd}}/(4\pi {r}^{2}c)$, the radiation flux is always kept below a certain value, which makes it possible not to blow all the gas away from the disk. These effects make supercritical accretion feasible. We also find that a settling region, where accretion is significantly decelerated by a radiation cushion, is formed around the NS surface. In the settling region, the radiation temperature and mass density roughly follow ${T}_{\mathrm{rad}}\propto {r}^{-1}$ and $\rho \propto {r}^{-3}$, respectively. No settling region appears around the BH, so matter can be directly swallowed by the BH with supersonic speed.

We present new evidence that the bright nonthermal X-ray emission features in the interior of the Cassiopeia A supernova remnant are caused by inward-moving shocks, based on Chandra and NuSTAR observations. Several bright inward-moving filaments were identified using monitoring data taken by Chandra in 2000–2014. These inward-moving shock locations are nearly coincident with hard X-ray (15–40 keV) hot spots seen by NuSTAR. From proper-motion measurements, the transverse velocities were estimated to be in the range of ∼2100–3800 km s⁻¹ for a distance of 3.4 kpc. The shock velocities in the frame of the expanding ejecta reach values of ∼5100–8700 km s⁻¹, which is slightly higher than the typical speed of the forward shock. Additionally, we find flux variations (both increasing and decreasing) on timescales of a few years in some of the inward-moving shock filaments. The rapid variability timescales are consistent with an amplified magnetic field of B ∼ 0.5–1 mG. The high speed and low photon cut-off energy of the inward-moving shocks are shown to imply a particle diffusion coefficient that departs from the Bohm regime (k₀ = D₀/D_0,Bohm ∼ 3–8) for the few simple physical configurations we consider in this study. The maximum electron energy at these shocks is estimated to be ∼8–11 TeV, which is smaller than the values of ∼15–34 TeV that were inferred for the forward shock. Cassiopeia A is dynamically too young for its reverse shock to appear to be moving inward in the observer frame. We propose instead that the inward-moving shocks are a consequence of the forward shock encountering a density jump of ≳5–8 in the surrounding material.

Brightest cluster galaxies (BCGs) are believed to have assembled most of their stars early in time and therefore should be passively evolving at low redshifts and appear "red-and-dead." However, there have been reports that a minority of low-redshift BCGs still have ongoing star formation rates (SFRs) of a few to even $\sim 100\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$. Such BCGs are found in "cool-core" ("CC") clusters, and their star formation is thought to be fueled by "cooling flow." To further investigate the implications of low-redshift, star-forming BCGs, we perform a systematic search using the 22 μm data ("W4" band) from the Wide-field Infrared Survey Explorer (WISE) on the GMBCG catalog, which contains 55,424 BCGs at $0.1\lesssim z\lesssim 0.55$ identified in the Sloan Digital Sky Survey (SDSS). Our sample consists of 389 BCGs that are bright in W4 ("W4BCGs"), most being brighter than 5 mJy. While some ($\lesssim 20 \%$) might host active galactic nuclei, most W4BCGs should owe their strong mid-IR emissions to dust-enshrouded star formation. Their median total IR luminosity (L_IR) is $5\times {10}^{11}\,{L}_{\odot }$ (SFR ∼50 ${M}_{\odot }\,{\mathrm{yr}}^{-1})$, and 27% of the whole sample has ${L}_{\mathrm{IR}}\gt {10}^{12}\,{L}_{\odot }$ (SFR >100 ${M}_{\odot }\,{\mathrm{yr}}^{-1}$). Using 10 W4BCGs that have Chandra X-ray data, we show that 7 of them are possibly in CC clusters. However, in most cases (five out of seven) the mass deposition rate cannot account for the observed SFR. This casts doubt on the idea that cooling flows are the cause of the star formation in non-quiescent BCGs.

Nucleosynthetic isotope anomalies in meteorites are useful for investigating the origin of materials in the protoplanetary disk and dynamical processes of planetary formation. In particular, calcium and aluminum-rich inclusions (CAIs) found in chondrites are key minerals for decoding the initial conditions of the solar system before the accretion of small planetary bodies. In this study, we report isotopic analyses for three Allende CAIs, fluffy type A (FTA), type B, and fine-grained spinel rich (FS) inclusions, with a specific emphasis on the measurements of ⁸⁴Sr/⁸⁶Sr ratios. It was found that the average μ⁸⁴Sr values (10⁶ relative deviations from a standard material) were 175, 129, and 56 ppm for the samples of FTA, type B, and FS inclusions, respectively. Additionally, the FTA samples exhibited heterogeneous μ⁸⁴Sr values, while those for the type B and FS inclusions were homogeneous within individual inclusions. The elevated μ⁸⁴Sr values were most likely explained by the relative enrichment of r-process nuclides in the CAI formation region. The variation of μ⁸⁴Sr values between the FTA and type B inclusions, as well as within the FTA inclusion, suggests the presence of multiple CAI source reservoirs with distinct isotopic compositions, which is either inherited from isotopic heterogeneity in the molecular cloud or caused by the selective destruction of r-process-enriched supernova grains via nebular thermal processing. On the other hand, the reaction between a refractory precursor of the FS inclusion and a gaseous reservoir enriched in Mg, Si, and ¹⁶O resulted in the lowest μ⁸⁴Sr values for the FS inclusion.

A massive planet closely orbiting its host star creates tidal forces that distort the typically spherical stellar surface. These distortions, known as ellipsoidal variations, result in changes in the photometric flux emitted by the star, which can be detected within the data from the Kepler Space Telescope. Currently, there exist several models describing such variations and their effect on the photometric flux. By using Bayesian model testing in conjunction with the Bayesian-based exoplanet characterization software package EXONEST, the most probable representation for ellipsoidal variations was determined for synthetic data and the confirmed hot Jupiter exoplanet Kepler-13A b. The most preferred model for ellipsoidal variations observed in the Kepler-13 light curve was determined to be EVIL-MC. Among the trigonometric models, the Modified Kane & Gelino model provided the best representation of ellipsoidal variations for the Kepler-13 system and may serve as a fast alternative to the more computationally intensive EVIL-MC. The computational feasibility of directly modeling the ellipsoidal variations of a star are examined and future work is outlined. Providing a more accurate model of ellipsoidal variations is expected to result in better planetary mass estimations.

We report deep spectroscopy of 10 planetary nebulae (PNe) in the Andromeda Galaxy (M31) using the 10.4 m Gran Telescopio Canarias (GTC). Our targets reside in different regions of M31, including halo streams and the dwarf satellite M32, and kinematically deviate from the extended disk. The temperature-sensitive [O iii] λ4363 line is observed in all PNe. For four PNe, the GTC spectra extend beyond 1 μm, enabling the explicit detection of the [S iii] λ6312 and λλ9069, 9531 lines and thus determination of the [S iii] temperature. Abundance ratios are derived and generally consistent with AGB model predictions. Our PNe probably all evolved from low-mass (<2 M_☉) stars, as analyzed with the most up-to-date post-AGB evolutionary models, and their main-sequence ages are mostly ∼2–5 Gyr. Compared to the underlying, smooth, metal-poor halo of M31, our targets are uniformly metal rich ([O/H] ≳ −0.4), and seem to resemble the younger population in the stream. We thus speculate that our halo PNe formed in the Giant Stream's progenitor through extended star formation. Alternatively, they might have formed from the same metal-rich gas as did the outer-disk PNe but were displaced into their present locations as a result of galactic interactions. These interpretations are, although speculative, qualitatively in line with the current picture, as inferred from previous wide-field photometric surveys, that M31's halo is the result of complex interactions and merger processes. The behavior of the N/O of the combined sample of the outer-disk and our halo/substructure PNe signifies that hot bottom burning might actually occur at <3 M_☉ but careful assessment is needed.

Ultralight axion is a dark matter candidate with mass ${ \mathcal O }({10}^{-22})\mathrm{eV}$ and de Broglie wavelength of order kiloparsec. Such an axion, also called fuzzy dark matter (FDM), thermalizes via gravitational force and forms a Bose–Einstein condensate. Recent studies suggested that the quantum pressure from FDM can significantly affect structure formation in small scales, thus alleviating the so-called "small-scale crisis." In this paper, we develop a new technique to discretize the quantum pressure and illustrate the interactions among FDM particles in an N-body simulation that accurately simulates the formation of the dark matter halo and its inner structure in the region outside the softening length. In a self-gravitationally bound virialized halo, we find a constant density solitonic core, which is consistent with theoretical prediction. The existence of the solitonic core reveals the nonlinear effect of quantum pressure and impacts structure formation in the FDM model.

We investigate the properties of X-ray emission from shock breakout of a supernova in a stellar wind. We consider a simple model describing aspherical explosions, in which the shock front with an ellipsoidal shape propagates into the dense circumstellar matter. For this model, both X-ray light curves and spectra are simultaneously calculated using a Monte Carlo method. We show that the shock breakout occurs simultaneously in all directions in a steady and spherically symmetric wind. As a result, even for the aspherical explosion, the rise and decay timescales of the light curve do not significantly depend on the viewing angles. This fact suggests that the light curve of the shock breakout may be used as a probe of the wind mass-loss rate. We compare our results with the observed spectrum and light curve of X-ray outburst 080109/SN 2008D. The observation can be reproduced by an explosion with a shock velocity of 60% of the speed of light and circumstellar matter with a mass-loss rate of $5\times {10}^{-4}\,{M}_{\odot }$ yr⁻¹.

An interplay of magnetic fields and gravitation drives accretion and outflows near black holes. However, a specific mechanism is still a matter of debate; it is very likely that different processes dominate under various conditions. In particular, for the acceleration of particles and their collimation in jets, an ordered component of the magnetic field seems to be essential. Here we discuss the role of large-scale magnetic fields in transporting the charged particles and dust grains from the bound orbits in the equatorial plane of a rotating (Kerr) black hole and the resulting acceleration along trajectories escaping the system in a direction parallel to the symmetry axis (perpendicular to the accretion disk). We consider a specific scenario of destabilization of circular geodesics of initially neutral matter by charging (e.g., due to photoionization). Some particles may be set on escaping trajectories and attain relativistic velocity. The case of charged particles differs from charged dust grains by their charge-to-mass ratio, but the acceleration mechanism operates in a similar manner. It appears that the chaotic dynamics controls the outflow and supports the formation of near-horizon escape zones. We employ the technique of recurrence plots to characterize the onset of chaos in the outflowing medium. We investigate the system numerically and construct the basin-boundary plots, which show the location and the extent of the escape zones. The effects of black hole spin and magnetic field strength on the formation and location of escape zones are discussed, and the maximal escape velocity is computed.

We present new observations of the late-stage merger galaxy NGC 7727, including Hubble Space Telescope/WFPC2 images and long-slit spectra obtained with the Clay telescope. NGC 7727 is relatively luminous (${M}_{V}$ = −21.7) and features two unequal tidal tails, various bluish arcs and star clusters, and two bright nuclei 480 pc apart in projection. These two nuclei have nearly identical redshifts, yet are strikingly different. The primary nucleus, hereafter Nucleus 1, fits smoothly into the central luminosity profile of the galaxy and appears—at various wavelengths—"red and dead." In contrast, Nucleus 2 is very compact, has a tidal radius of 103 pc, and exhibits three signs of recent activity: a post-starburst spectrum, an [O iii] emission line, and a central X-ray point source. Its emission-line ratios place it among Seyfert nuclei. A comparison of Nucleus 2 (${M}_{V}$ = −15.5) with ultracompact dwarf galaxies (UCDs) suggests that it may be the best case yet for a massive UCD having formed through tidal stripping of a gas-rich disk galaxy. Evidence for this comes from its extended star formation history, long blue tidal stream, and elevated dynamical-to-stellar-mass ratio. While the majority of its stars formed $\gtrsim 10\,\mathrm{Gyr}$ ago, ∼1/3 formed during starbursts in the past 2 Gyr. Its weak active galactic nucleus activity is likely driven by a black hole of mass $3\times \ {10}^{6-8}\,{M}_{\odot }$. We estimate that the former companion's initial mass was less than half that of then NGC 7727, implying a minor merger. By now this former companion has been largely shredded, leaving behind Nucleus 2 as a freshly minted UCD that probably moves on a highly eccentric orbit.

Polaris, the nearest and brightest Cepheid, is a potential anchor point for the Leavitt period–luminosity relation. However, its distance is a matter of contention, with recent advocacy for a parallax of ∼10 mas, in contrast with the Hipparcos measurement of 7.54 ± 0.11 mas. We report an independent trigonometric parallax determination, using the Fine Guidance Sensors (FGS) on the Hubble Space Telescope. Polaris itself is too bright for FGS, so we measured its eighth-magnitude companion Polaris B, relative to a network of background reference stars. We converted the FGS relative parallax to absolute, using estimated distances to the reference stars from ground-based photometry and spectral classification. Our result, 6.26 ± 0.24 mas, is even smaller than that found by Hipparcos. We note other objects for which Hipparcos appears to have overestimated parallaxes, including the well-established case of the Pleiades. We consider possible sources of systematic error in the FGS parallax, but find no evidence they are significant. If our "long" distance is correct, the high luminosity of Polaris indicates that it is pulsating in the second overtone of its fundamental mode. Our results raise several puzzles, including a long pulsation period for Polaris compared to second-overtone pulsators in the Magellanic Clouds, and a conflict between the isochrone age of Polaris B (∼2.1 Gyr) and the much younger age of Polaris A. We discuss possibilities that B is not a physical companion of A, in spite of the strong evidence that it is, or that one of the stars is a merger remnant. These issues may be resolved when Gaia provides parallaxes for both stars.

We use a newly assembled sample of 3545 star-forming galaxies with secure spectroscopic, grism, and photometric redshifts at z = 1.5–2.5 to constrain the relationship between UV slope (β) and dust attenuation (L_IR/L_UV ≡ IRX). Our sample significantly extends the range of L_UV and β probed in previous UV-selected samples, including those as faint as M₁₆₀₀ = −17.4 ($\simeq 0.05{L}_{\mathrm{UV}}^{* }$) and −2.6 ≲ β ≲ 0.0. IRX is measured using stacks of deep Herschel data, and the results are compared with predictions of the IRX−β relation for different assumptions of the stellar population model and obscuration curve. We find that z = 1.5–2.5 galaxies have an IRX−β relation that is consistent with the predictions for an SMC curve if we invoke subsolar-metallicity models currently favored for high-redshift galaxies, while the commonly assumed starburst curve overpredicts the IRX at a given β by a factor of ≳3. IRX is roughly constant with L_UV for L_UV ≳ 3 × 10⁹L_⊙. Thus, the commonly observed trend of fainter galaxies having bluer β may simply reflect bluer intrinsic slopes for such galaxies, rather than lower obscurations. The IRX−β relation for young/low-mass galaxies at z ≳ 2 implies a dust curve that is steeper than the SMC. The lower attenuations and higher ionizing photon output for low-metallicity stellar populations point to Lyman continuum production efficiencies, ξ_ion, that may be elevated by a factor of ≈2 relative to the canonical value for L* galaxies, aiding in their ability to keep the universe ionized at z ∼ 2.

Hydrogen-poor superluminous supernovae (SLSNe-I) have been predominantly found in low-metallicity, star-forming dwarf galaxies. Here we identify Gaia17biu/SN 2017egm as an SLSN-I occurring in a "normal" spiral galaxy (NGC 3191) in terms of stellar mass (several times 10¹⁰M_⊙) and metallicity (roughly solar). At redshift z = 0.031, Gaia17biu is also the lowest-redshift SLSN-I to date, and the absence of a larger population of SLSNe-I in dwarf galaxies of similar redshift suggests that metallicity is likely less important to the production of SLSNe-I than previously believed. With the smallest distance and highest apparent brightness for an SLSN-I, we are able to study Gaia17biu in unprecedented detail. Its pre-peak near-ultraviolet to optical color is similar to that of Gaia16apd and among the bluest observed for an SLSN-I, while its peak luminosity (M_g = −21 mag) is substantially lower than that of Gaia16apd. Thanks to the high signal-to-noise ratios of our spectra, we identify several new spectroscopic features that may help to probe the properties of these enigmatic explosions. We detect polarization at the ∼0.5% level that is not strongly dependent on wavelength, suggesting a modest, global departure from spherical symmetry. In addition, we put the tightest upper limit yet on the radio luminosity of an SLSN-I with <5.4 × 10²⁶ erg s⁻¹ Hz⁻¹ at 10 GHz, which is almost a factor of 40 better than previous upper limits and one of the few measured at an early stage in the evolution of an SLSN-I. This limit largely rules out an association of this SLSN-I with known populations of gamma-ray-burst-like central engines.

With the discovery of ever smaller and colder exoplanets, terrestrial worlds with hazy atmospheres must be increasingly considered. Our solar system's Titan is a prototypical hazy planet, whose atmosphere may be representative of a large number of planets in our Galaxy. As a step toward characterizing such worlds, we present simulations of exoplanets that resemble Titan but orbit three different stellar hosts: G, K, and M dwarf stars. We use general circulation and photochemistry models to explore the circulation and chemistry of these Titan-like planets under varying stellar spectra, in all cases assuming a Titan-like insolation. Due to the strong absorption of visible light by atmospheric haze, the redder radiation accompanying later stellar types produces more isothermal stratospheres, stronger meridional temperature gradients at mbar pressures, and deeper and stronger zonal winds. In all cases, the planets' atmospheres are strongly superrotating, but meridional circulation cells are weaker aloft under redder starlight. The photochemistry of hydrocarbon and nitrile species varies with stellar spectra, with variations in the FUV/NUV flux ratio playing an important role. Our results tentatively suggest that column haze production rates could be similar under all three hosts, implying that planets around many different stars could have similar characteristics to Titan's atmosphere. Lastly, we present theoretical emission spectra. Overall, our study indicates that, despite important and subtle differences, the circulation and chemistry of Titan-like exoplanets are relatively insensitive to differences in the host star. These findings may be further probed with future space-based facilities, like WFIRST, LUVOIR, HabEx, and OST.

We present an analysis of flare activity in wide binary stars using a combination of value-added data sets from the NASA Kepler mission. The target list contains a set of previously discovered wide binary star systems identified by proper motions in the Kepler field. We cross-matched these systems with estimates of flare activity for ∼200,000 stars in the Kepler field, allowing us to compare relative flare luminosity between stars in coeval binaries. From a sample of 184 previously known wide binaries in the Kepler field, we find 58 with detectable flare activity in at least 1 component, 33 of which are similar in mass (q > 0.8). Of these 33 equal-mass binaries, the majority display similar (±1 dex) flare luminosity between both stars, as expected for stars of equal mass and age. However, we find two equal-mass pairs where the secondary (lower mass) star is more active than its counterpart, and two equal-mass pairs where the primary star is more active. The stellar rotation periods are also anomalously fast for stars with elevated flare activity. Pairs with discrepant rotation and activity qualitatively seem to have lower mass ratios. These outliers may be due to tidal spin-up, indicating these wide binaries could be hierarchical triple systems. We additionally present high-resolution adaptive optics images for two wide binary systems to test this hypothesis. The demographics of stellar rotation and magnetic activity between stars in wide binaries may be useful indicators for discerning the formation scenarios of these systems.

We study the evolution of star clusters located in the outer regions of a galaxy undergoing a sudden mass loss through gas expulsion in the framework of Milgromian dynamics (MOND) by means of N-body simulations. We find that, to leave a bound star cluster, the star formation efficiency (SFE) of an embedded cluster dominated by deep MOND gravity can be reduced down to $2.5 \%$. For a given SFE, the star clusters that survive in MOND can bind a larger fraction of mass compared to those of the Newtonian dynamics. Moreover, the more diffuse the embedded cluster is, the less substantial the size expansion of the final star cluster is. The density profiles of a surviving star cluster are more cuspy in the center for more massive embedded clusters, and the central density profiles are flatter for less massive embedded clusters or for lower SFE. This work may help to understand the low concentration and extension of the distant low-density globular clusters and ultra-faint and diffuse satellite galaxies around the Milky Way.

Ubiquitous transverse oscillations observed in spicular waveguides, identified as the kink wave-mode had previously been reported along with periodic structural distortions of the flux tubes, observed as cross-sectional width and associated photometric variations. Previous studies identified these perturbations as the observed signatures of concurrent kink and sausage wave-modes. High-resolution Hα imaging-spectroscopy data from the CRisp Imaging SpectroPolarimeter at the Swedish Solar Telescope are used to analyze the off-limb spicular structures. For the first time, the evolution of the resultant transverse displacement of the flux-tube structure, estimated from the perpendicular velocity components, is analyzed along with longitudinal, cross-sectional width, photometric, and azimuthal shear/torsion variations. The pulse-like nonlinear kink wave-mode shows strong coupling with these observables, with a period-doubling, -tripling aspect, supported by mutual phase relations concentrated around 0° and $\pm 180^\circ$. The three-dimensional ensemble of the observed dynamical components revealed complexities pertinent to the accurate identification and interpretation of, e.g., linear/nonlinear, coupled/uncoupled magnetohydrodynamical wave-modes in spicules.

We present our analysis of the Type II supernova DLT16am (SN 2016ija). The object was discovered during the ongoing $D\lt 40\,\mathrm{Mpc}$ (DLT40) one-day cadence supernova search at $r\sim 20.1\,\mathrm{mag}$ in the "edge-on" nearby ($D=20.0\pm 4.0\,\mathrm{Mpc}$) galaxy NGC 1532. The subsequent prompt and high-cadenced spectroscopic and photometric follow-up revealed a highly extinguished transient, with $E(B-V)=1.95\pm 0.15\,\mathrm{mag}$, consistent with a standard extinction law with R_V = 3.1 and a bright (${M}_{V}=-18.48\pm 0.77\,\mathrm{mag}$) absolute peak magnitude. A comparison of the photometric features with those of large samples of SNe II reveals a fast rise for the derived luminosity and a relatively short plateau phase, with a slope of ${S}_{50V}=0.84\pm 0.04\,\mathrm{mag}/50\,\mathrm{days}$, consistent with the photometric properties typical of those of fast-declining SNe II. Despite the large uncertainties on the distance and the extinction in the direction of DLT16am, the measured photospheric expansion velocity and the derived absolute V-band magnitude at $\sim 50\,\mathrm{days}$ after the explosion match the existing luminosity–velocity relation for SNe II.

While major mergers have long been proposed as a driver of both active galactic nucleus (AGN) activity and the ${M}_{\mathrm{BH}}\mbox{--}{\sigma }_{\mathrm{bulge}}$ relation, studies of moderate to high-redshift Seyfert-luminosity AGN hosts have found little evidence for enhanced rates of interactions. However, both theory and observation suggest that while these AGNs may be fueled by stochastic accretion and secular processes, high-luminosity, high-redshift, and heavily obscured AGNs are the AGNs most likely to be merger-driven. To better sample this population of AGNs, we turn to infrared selection in the CANDELS/COSMOS field. Compared to their lower-luminosity and less obscured X-ray-only counterparts, IR-only AGNs (luminous, heavily obscured AGNs) are more likely to be classified as either irregular (${50}_{-12}^{+12} \%$ versus ${9}_{-2}^{+5} \%$) or asymmetric (${69}_{-13}^{+9} \%$ versus ${17}_{-4}^{+6} \%$) and are less likely to have a spheroidal component (${31}_{-9}^{+13} \%$ versus ${77}_{-6}^{+4} \%$). Furthermore, IR-only AGNs are also significantly more likely than X-ray-only AGNs (${75}_{-13}^{+8} \%$ versus ${31}_{-6}^{+6} \%$) to be classified either as interacting or merging in a way that significantly disturbs the host galaxy or as disturbed, though not clearly interacting or merging, which potentially represents the late stages of a major merger. This suggests that while major mergers may not contribute significantly to the fueling of Seyfert-luminosity AGNs, interactions appear to play a more dominant role in the triggering and fueling of high-luminosity heavily obscured AGNs.

We analyze the interiors of HD 219134 b and c, which are among the coolest super-Earths detected thus far. Without using spectroscopic measurements, we aim at constraining if the possible atmospheres are hydrogen-rich or hydrogen-poor. In the first step, we employ a full probabilistic Bayesian inference analysis to rigorously quantify the degeneracy of interior parameters given the data of mass, radius, refractory element abundances, semimajor axes, and stellar irradiation. We obtain constraints on structure and composition for core, mantle, ice layer, and atmosphere. In the second step, we aim to draw conclusions on the nature of possible atmospheres by considering atmospheric escape. Specifically, we compare the actual possible atmospheres to a threshold thickness above which a primordial (H₂-dominated) atmosphere can be retained against evaporation over the planet's lifetime. The best-constrained parameters are the individual layer thicknesses. The maximum radius fraction of possible atmospheres are 0.18 and 0.13 R (radius), for planets b and c, respectively. These values are significantly smaller than the threshold thicknesses of primordial atmospheres: 0.28 and 0.19 R, respectively. Thus, the possible atmospheres of planets b and c are unlikely to be H₂-dominated. However, whether possible volatile layers are made of gas or liquid/solid water cannot be uniquely determined. Our main conclusions are (1) the possible atmospheres for planets b and c are enriched and thus possibly secondary in nature, and (2) both planets may contain a gas layer, whereas the layer of HD 219134 b must be larger. HD 219134 c can be rocky.

We present results from an analytical model for magnetic buoyancy and rotational instabilities in a full spherical shell tachocline that includes rotation, differential rotation close to that observed helioseismically, and toroidal field. Perturbation solutions are found for the limit of large latitudinal wave number, a limit commonly used to maximize instability due to magnetic buoyancy. We find that at all middle and high latitudes vigorous rotational instability is induced by weak toroidal fields, particularly for high longitudinal wave number, even when the vertical rotation gradient is marginally stable without toroidal field. We infer that this instability will prevent much storage of toroidal fields in the tachocline at these latitudes, but could be responsible for the appearance of ephemeral active regions there. By contrast, the low-latitude vertical rotation gradient, opposite in sign to that at high latitudes, is not only stable itself but also prevents magnetic buoyancy instability until the peak toroidal field is raised above a threshold of about 9 kG at the equator, declining to zero where the vertical rotation gradient changes sign, at $32\buildrel{\circ}\over{.} 3$ in our model. Thus this rotation gradient provides a previously unnoticed mechanism for storage of toroidal fields until they amplify by dynamo action to order 10 kG, whereupon they can overcome the rotation gradient to emerge as sunspots. These results provide a new explanation for why sunspots are seen only at low latitudes. The purely rotational instability at latitudes above 50°, even without toroidal fields, also suggests that the high-latitude tachocline should be much thicker, due to HD turbulence, than has been inferred for lower latitudes from helioseismic measurements.

The study of time-dependent solar active region (AR) morphology and its relation to eruptive events requires analysis of imaging data obtained in multiple wavelength domains with differing spatial and time resolution, ideally in combination with 3D physical models. To facilitate this goal, we have undertaken a major enhancement of our IDL-based simulation tool, GX_Simulator, previously developed for modeling microwave and X-ray emission from flaring loops, to allow it to simulate quiescent emission from solar ARs. The framework includes new tools for building the atmospheric model and enhanced routines for calculating emission that include new wavelengths. In this paper, we use our upgraded tool to model and analyze an AR and compare the synthetic emission maps with observations. We conclude that the modeled magneto-thermal structure is a reasonably good approximation of the real one.

Recent theoretical studies suggest that a significant part of the primordial gas accretes onto forming galaxies as narrow filaments of cold gas without building a shock and experiencing heating. Using a simple model of disk galaxy evolution that combines the growth of dark matter halos predicted by cosmological simulations with a hypothetical form of cold-mode accretion, we investigate how this cold-accretion mode affects the formation process of disk galaxies. It is found that the shock-heating and cold-accretion models produce compatible results for low-mass galaxies owing to the short cooling timescale in such galaxies. However, cold accretion significantly alters the evolution of disk galaxies more massive than the Milky Way and puts observable fingerprints on their present properties. For a galaxy with a virial mass ${M}_{\mathrm{vir}}=2.5\times {10}^{12}\,{M}_{\odot }$, the scale length of the stellar disk is larger by 41% in the cold-accretion model than in the shock-heating model, with the former model reproducing the steep rise in the size–mass relation observed at the high-mass end. Furthermore, the stellar component of massive galaxies becomes significantly redder (0.66 in u − r at ${M}_{\mathrm{vir}}=2.5\times {10}^{12}\,{M}_{\odot }$), and the observed color–mass relation in nearby galaxies is qualitatively reproduced. These results suggest that large disk galaxies with red optical colors may be the product of cold-mode accretion. The essential role of cold accretion is to promote disk formation in the intermediate-evolution phase ($0.5\lt z\lt 1.5$) by providing the primordial gas having large angular momentum and to terminate late-epoch accretion, quenching star formation and making massive galaxies red.

We present 88 multi-epoch Very Long Baseline Array (VLBA) images (most at an observing frequency of 8 GHz) of 20 TeV blazars, all of the high-frequency-peaked BL Lac (HBL) class, that have not been previously studied at multiple epochs on the parsec scale. From these 20 sources, we analyze the apparent speeds of 43 jet components that are all detected at four or more epochs. As has been found for other TeV HBLs, the apparent speeds of these components are relatively slow. About two-thirds of the components have an apparent speed that is consistent (within 2σ) with no motion, and some of these components may be stationary patterns whose apparent speed does not relate to the underlying bulk flow speed. In addition, a superluminal tail to the apparent speed distribution of the TeV HBLs is detected for the first time, with eight components in seven sources having a 2σ lower limit on the apparent speed exceeding $1c$. We combine the data from these 20 sources with an additional 18 sources from the literature to analyze the complete apparent speed distribution of all 38 TeV HBLs that have been studied with very long baseline interferometry at multiple epochs. The highest 2σ apparent speed lower limit considering all sources is $3.6c$. This suggests that bulk Lorentz factors of up to about 4, but probably not much higher, exist in the parsec-scale radio-emitting regions of these sources, consistent with estimates obtained in the radio by other means such as brightness temperatures. This can be reconciled with the high Lorentz factors estimated from the high-energy data if the jet has velocity structures consisting of different emission regions with different Lorentz factors. In particular, we analyze the current apparent speed data for the TeV HBLs in the context of a model with a fast central spine and a slower outer layer.

The Spitzer Matching Survey of the UltraVISTA ultra-deep Stripes (SMUVS) provides unparalleled depth at 3.6 and 4.5 μm over ∼0.66 deg² of the COSMOS field, allowing precise photometric determinations of redshift and stellar mass. From this unique data set we can connect galaxy samples, selected by stellar mass, to their host dark matter halos for $1.5\lt z\lt 5.0$, filling in a large hitherto unexplored region of the parameter space. To interpret the observed galaxy clustering, we use a phenomenological halo model, combined with a novel method to account for uncertainties arising from the use of photometric redshifts. We find that the satellite fraction decreases with increasing redshift and that the clustering amplitude (e.g., comoving correlation length/large-scale bias) displays monotonic trends with redshift and stellar mass. Applying ΛCDM halo mass accretion histories and cumulative abundance arguments for the evolution of stellar mass content, we propose pathways for the coevolution of dark matter and stellar mass assembly. Additionally, we are able to estimate that the halo mass at which the ratio of stellar-to-halo mass is maximized is ${10}^{{12.5}_{-0.08}^{+0.10}}$${M}_{\odot }$ at $z\sim 2.5$. This peak halo mass is here inferred for the first time from stellar mass-selected clustering measurements at $z\gtrsim 2$, and it implies a mild evolution of this quantity for $z\lesssim 3$, consistent with constraints from abundance-matching techniques.

We present the analysis of the binary-microlensing event OGLE-2014-BLG-0289. The event light curve exhibits five very unusual peaks, four of which were produced by caustic crossings and the other by a cusp approach. It is found that the quintuple-peak features of the light curve provide tight constraints on the source trajectory, enabling us to precisely and accurately measure the microlensing parallax ${\pi }_{{\rm{E}}}$. Furthermore, the three resolved caustics allow us to measure the angular Einstein radius ${\theta }_{{\rm{E}}}$. From the combination of ${\pi }_{{\rm{E}}}$ and ${\theta }_{{\rm{E}}}$, the physical lens parameters are uniquely determined. It is found that the lens is a binary composed of two M dwarfs with masses ${M}_{1}=0.52\pm 0.04\ {M}_{\odot }$ and ${M}_{2}=0.42\pm 0.03\ {M}_{\odot }$ separated in projection by ${a}_{\perp }=6.4\pm 0.5\,\mathrm{au}$. The lens is located in the disk with a distance of ${D}_{{\rm{L}}}=3.3\pm 0.3\,\mathrm{kpc}$. The reason for the absence of a lensing signal in the Spitzer data is that the time of observation corresponds to the flat region of the light curve.

Lunar soil spectra differ from pulverized lunar rocks spectra by reddening and darkening effects, and shallower absorption bands. These effects have been described in the past as a consequence of space weathering. In this work, we focus on the effects of nanophase iron (npFe⁰) inclusions on the experimental reflectance spectra of lunar regolith particles. The reflectance spectra are computed using SIRIS3, a code that combines ray optics with radiative-transfer modeling to simulate light scattering by different types of scatterers. The imaginary part of the refractive index as a function of wavelength of immature lunar soil is derived by comparison with the measured spectra of the corresponding material. Furthermore, the effect of adding nanophase iron inclusions on the reflectance spectra is studied. The computed spectra qualitatively reproduce the observed effects of space weathered lunar regolith.

On 2017 August 21, a total solar eclipse swept across the contiguous United States, providing excellent opportunities for diagnostics of the Sun's corona. The Sun's coronal structure is notoriously difficult to observe except during solar eclipses; thus, theoretical models must be relied upon for inferring the underlying magnetic structure of the Sun's outer atmosphere. These models are necessary for understanding the role of magnetic fields in the heating of the corona to a million degrees and the generation of severe space weather. Here we present a methodology for predicting the structure of the coronal field based on model forward runs of a solar surface flux transport model, whose predicted surface field is utilized to extrapolate future coronal magnetic field structures. This prescription was applied to the 2017 August 21 solar eclipse. A post-eclipse analysis shows good agreement between model simulated and observed coronal structures and their locations on the limb. We demonstrate that slow changes in the Sun's surface magnetic field distribution driven by long-term flux emergence and its evolution governs large-scale coronal structures with a (plausibly cycle-phase dependent) dynamical memory timescale on the order of a few solar rotations, opening up the possibility for large-scale, global corona predictions at least a month in advance.

We apply the algorithm published by Liang et al. to describe the Double Pulsar system J0737–3039 and extract the sense of rotation of the first born recycled pulsar PSR J0737–3039A. We find that this pulsar is rotating prograde in its orbit. This is the first direct measurement of the sense of rotation of a pulsar with respect to its orbit and a direct confirmation of the rotating lighthouse model for pulsars. This result confirms that the spin angular momentum vector is closely aligned with the orbital angular momentum, suggesting that the kick of the supernova producing the second born pulsar J0737–3039B was small.

In a protoplanetary disk, dust aggregates in the μm to mm size range possess mean collision velocities of 10–60 m s⁻¹ with respect to dm- to m-sized bodies. We performed laboratory collision experiments to explore this parameter regime and found a size- and velocity-dependent threshold between erosion and growth. By using a local Monte Carlo coagulation calculation and along with a simple semi-analytical timescale approach, we show that erosion considerably limits particle growth in protoplanetary disks and leads to a steady-state dust-size distribution from μm- to dm-sized particles.

We present 2MASS J11151597+1937266, a recently identified low-surface-gravity L dwarf, classified as an L2γ based on Sloan Digital Sky Survey optical spectroscopy. We confirm this spectral type with near-infrared spectroscopy, which provides further evidence that 2MASS J11151597+1937266 is a low-surface-gravity L dwarf. This object also shows significant excess mid-infrared flux, indicative of circumstellar material; and its strong Hα emission (EW_Hα = 560 ± 82 Å) is an indicator of enhanced magnetic activity or weak accretion. Comparison of its spectral energy distribution to model photospheres yields an effective temperature of ${1724}_{-38}^{+184}\,{\rm{K}}$. We also provide a revised distance estimate of 37 ± 6 pc using a spectral type–luminosity relationship for low-surface-gravity objects. The three-dimensional galactic velocities and positions of 2MASS J11151597+1937266 do not match any known young association or moving group. Assuming a probable age in the range of 5–45 Myr, the model-dependent estimated mass of this object is between 7 and 21 M_Jup, making it a potentially isolated planetary-mass object. We also identify a candidate co-moving, young stellar companion, 2MASS J11131089+2110086.

New results on the short-term galactic cosmic-ray (GCR) intensity variation (Forbish decrease) in 2006 December measured by the PAMELA instrument are presented. Forbush decreases are sudden suppressions of the GCR intensities, which are associated with the passage of interplanetary transients such as shocks and interplanetary coronal mass ejections (ICMEs). Most of the past measurements of this phenomenon were carried out with ground-based detectors such as neutron monitors or muon telescopes. These techniques allow only the indirect detection of the overall GCR intensity over an integrated energy range. For the first time, thanks to the unique features of the PAMELA magnetic spectrometer, the Forbush decrease, commencing on 2006 December 14 and following a CME at the Sun on 2006 December 13, was studied in a wide rigidity range (0.4–20 GV) and for different species of GCRs detected directly in space. The daily averaged GCR proton intensity was used to investigate the rigidity dependence of the amplitude and the recovery time of the Forbush decrease. Additionally, for the first time, the temporal variations in the helium and electron intensities during a Forbush decrease were studied. Interestingly, the temporal evolutions of the helium and proton intensities during the Forbush decrease were found to be in good agreement, while the low rigidity electrons ($\lt 2$ GV) displayed a faster recovery. This difference in the electron recovery is interpreted as a charge sign dependence introduced by drift motions experienced by the GCRs during their propagation through the heliosphere.

We present ∼800 days of photometric monitoring of Boyajian's Star (KIC 8462852) from the All-Sky Automated Survey for Supernovae (ASAS-SN) and ∼4000 days of monitoring from the All Sky Automated Survey (ASAS). We show that from 2015 to the present the brightness of Boyajian's Star has steadily decreased at a rate of 6.3 ± 1.4 mmag yr⁻¹, such that the star is now 1.5% fainter than it was in 2015 February. Moreover, the longer time baseline afforded by ASAS suggests that Boyajian's Star has also undergone two brightening episodes in the past 11 years, rather than only exhibiting a monotonic decline. We analyze a sample of ∼1000 comparison stars of similar brightness located in the same ASAS-SN field and demonstrate that the recent fading is significant at ≳99.4% confidence. The 2015–2017 dimming rate is consistent with that measured with Kepler data for the time period from 2009 to 2013. This long-term variability is difficult to explain with any of the physical models for the star's behavior proposed to date.

The relation between X-ray luminosity (L_X) and ambient gas temperature (T) among massive galactic systems is an important cornerstone of both observational cosmology and galaxy-evolution modeling. In the most massive galaxy clusters, the relation is determined primarily by cosmological structure formation. In less massive systems, it primarily reflects the feedback response to radiative cooling of circumgalactic gas. Here we present a simple but powerful model for the L_X–T relation as a function of physical aperture R within which those measurements are made. The model is based on the precipitation framework for AGN feedback and assumes that the circumgalactic medium is precipitation-regulated at small radii and limited by cosmological structure formation at large radii. We compare this model with many different data sets and show that it successfully reproduces the slope and upper envelope of the L_X–T–R relation over the temperature range from ∼0.2 keV through $\gtrsim 10\,\mathrm{keV}$. Our findings strongly suggest that the feedback mechanisms responsible for regulating star formation in individual massive galaxies have much in common with the precipitation-triggered feedback that appears to regulate galaxy-cluster cores.

Recent studies on the temperatures of red supergiants (RSGs) in the local universe provide us with an excellent observational constraint on RSG models. We calibrate the mixing length parameter by comparing model predictions with the empirical RSG temperatures in Small and Large Magellanic Clouds, Milky Way, and M31, which are inferred from the TiO band and the spectral energy distribution (SED). Although our RSG models are computed with the MESA code, our result may be applied to other stellar evolution codes, including the BEC and TWIN codes. We find evidence that the mixing length increases with increasing metallicity for both cases where the TiO and SED temperatures of RSGs are used for the calibration. Together with the recent finding of a similar correlation in low-mass red giants by Tayar et al., this implies that the metallicity dependence of the mixing length is a universal feature in post-main sequence stars of both low and high masses. Our result implies that typical Type IIP supernova (SN IIP) progenitors with initial masses of $\sim 10\mbox{--}16\,{M}_{\odot }$ have a radius range of $400\,{R}_{\odot }\lesssim R\lesssim 800\,{R}_{\odot }$ regardless of metallicity. As an auxiliary result of this study, we find that the hydrogen-rich envelope mass of SN IIP progenitors for a given initial mass is predicted to be largely independent of metallicity if the Ledoux criterion with slow semiconvection is adopted, while the Schwarzschild models predict systematically more massive hydrogen-rich envelopes for lower metallicity.

In this work, we use two decadal sunspot number series reconstructed from cosmogenic radionuclide data (¹⁴C in tree trunks, SN 14C, and ¹⁰Be in polar ice, SN 10Be) and the extreme value theory to study variability of solar activity during the last nine millennia. The peaks-over-threshold technique was used to compute, in particular, the shape parameter of the generalized Pareto distribution for different thresholds. Its negative value implies an upper bound of the extreme SN 10Be and SN 14C timeseries. The return level for 1000 and 10,000 years were estimated leading to values lower than the maximum observed values, expected for the 1000 year, but not for the 10,000 year return levels, for both series. A comparison of these results with those obtained using the observed sunspot numbers from telescopic observations during the last four centuries suggests that the main characteristics of solar activity have already been recorded in the telescopic period (from 1610 to nowadays) which covers the full range of solar variability from a Grand minimum to a Grand maximum.

The galaxies with photometric redshifts observed in a close angular proximity might be either projection coincidences, strongly lensed images of the same galaxy, or separate galaxies that are in a stage of merging. We search for the groups of galaxies in the Hubble Ultra Deep Field (HUDF09) in z ∼ 7 and z ∼ 8 drop-out samples. We find no close pairs among 50 galaxies in the z ∼ 7 sample, while in the z ∼ 8 sample we find that 6 out of 22 galaxies have a companion within ∼1'' (3 pairs). Adopting a numerical simulation and performing forward modeling, we show that even though mergers are unlikely to have such a high fraction, the projection coincidences and the strong lensing are even less likely mechanisms to account for all of three pairs. Alternatively, there is a possibility of the contamination in the drop-out catalog from lower redshifts, which potentially can account for all of the groups. Finally, we make projection on the sensitivity to mergers of the James Webb Space Telescope (JWST), and discuss the possible applications of the high-redshift merging galaxies for decreasing cosmic variance effects on the luminosity function and for improving the accuracy of photometric redshifts in general.

Numerous observations have revealed that power-law distributions are ubiquitous in energetic solar processes. Hard X-rays, soft X-rays, extreme ultraviolet radiation, and radio waves all display power-law frequency distributions. Since magnetic reconnection is the driving mechanism for many energetic solar phenomena, it is likely that reconnection events themselves display such power-law distributions. In this work, we perform numerical simulations of the solar corona driven by simple convective motions at the photospheric level. Using temperature changes, current distributions, and Poynting fluxes as proxies for heating, we demonstrate that energetic events occurring in our simulation display power-law frequency distributions, with slopes in good agreement with observations. We suggest that the braiding-associated reconnection in the corona can be understood in terms of a self-organized criticality model driven by convective rotational motions similar to those observed at the photosphere.

The compositions of stars and planets are connected, but the definition of "habitability" and the "habitable zone" only take into account the physical relationship between the star and planet. Planets, however, are made truly habitable by both chemical and physical processes that regulate climatic and geochemical cycling between atmosphere, surface, and interior reservoirs. Despite this, an "Earth-like" planet is often defined as a planet made of a mixture of rock and Fe that is roughly 1 Earth-density. To understand the interior of a terrestrial planet, the stellar abundances of planet-building elements (e.g., Mg, Si, and Fe) can be used as a proxy for the planet's composition. We explore the planetary mineralogy and structure for fictive planets around the 10 stars closest to the Sun using stellar abundances from the Hypatia Catalog. Although our sample contains stars that are both sub- and super-solar in their abundances, we find that the mineralogies are very similar for all 10 planets—since the error or spread in the stellar abundances create significant degeneracy in the models. We show that abundance uncertainties need to be on the order of [Fe/H] < 0.02 dex, [Si/H] < 0.01 dex, [Al/H] < 0.002 dex, while [Mg/H] and [Ca/H] < 0.001 dex in order to distinguish two unique planetary populations in our sample of 10 stars. While these precisions are high, we believe that they are possible given certain abundance techniques, in addition to methodological transparency, that have recently been demonstrated in the literature. However, without these precisions, the uncertainty in planetary structures will be so high that we will be unable to confidently state that a planet is like the Earth, or unlike anything we have ever seen.

We study the dependence of the galaxy content of dark matter halos on large-scale environment and halo formation time using semi-analytic galaxy models applied to the Millennium simulation. We analyze subsamples of halos at the extremes of these distributions and measure the occupation functions for the galaxies they host. We find distinct differences among these occupation functions. The main effect with environment is that central galaxies (and in one model, also the satellites) in denser regions start populating lower-mass halos. A similar, but significantly stronger, trend exists with halo age, where early-forming halos are more likely to host central galaxies at lower halo mass. We discuss the origin of these trends and the connection to the stellar mass–halo mass relation. We find that, at fixed halo mass, older halos and to some extent also halos in dense environments tend to host more massive galaxies. Additionally, we see a reverse trend for the occupation of satellite galaxies where early-forming halos have fewer satellites, likely due to having more time for them to merge with the central galaxy. We describe these occupancy variations in terms of the changes in the occupation function parameters, which can aid in constructing realistic mock galaxy samples. Finally, we study the corresponding galaxy auto- and cross-correlation functions of the different samples and elucidate the impact of assembly bias on galaxy clustering. Our results can inform theoretical modeling of galaxy assembly bias and attempts to detect it in the real universe.

We study the anisotropy with respect to the local magnetic field of turbulent magnetic fluctuations at magnetofluid scales in the solar wind. Previous measurements in the fast solar wind obtained axisymmetric anisotropy, despite that the analysis method allows nonaxisymmetric structures. These results are probably contaminated by the wind expansion that introduces another symmetry axis, namely, the radial direction, as indicated by recent numerical simulations. These simulations also show that while the expansion is strong, the principal fluctuations are in the plane perpendicular to the radial direction. Using this property, we separate 11 yr of Wind spacecraft data into two subsets characterized by strong and weak expansion and determine the corresponding turbulence anisotropy. Under strong expansion, the small-scale anisotropy is consistent with the Goldreich & Sridhar critical balance. As in previous works, when the radial symmetry axis is not eliminated, the turbulent structures are field-aligned tubes. Under weak expansion, we find 3D anisotropy predicted by the Boldyrev model, that is, turbulent structures are ribbons and not tubes. However, the very basis of the Boldyrev phenomenology, namely, a cross-helicity increasing at small scales, is not observed in the solar wind: the origin of the ribbon formation is unknown.

In this second installment of the series, we look at the internal kinematics of the multiple stellar populations of the globular cluster ω Centauri in one of the parallel Hubble Space Telescope (HST) fields, located at about 3.5 half-light radii from the center of the cluster. Thanks to the over 15 yr long baseline and the exquisite astrometric precision of the HST cameras, well-measured stars in our proper-motion catalog have errors as low as ∼10 μas yr⁻¹, and the catalog itself extends to near the hydrogen-burning limit of the cluster. We show that second-generation (2G) stars are significantly more radially anisotropic than first-generation (1G) stars. The latter are instead consistent with an isotropic velocity distribution. In addition, 1G stars have excess systemic rotation in the plane of the sky with respect to 2G stars. We show that the six populations below the main-sequence (MS) knee identified in our first paper are associated with the five main population groups recently isolated on the upper MS in the core of cluster. Furthermore, we find both 1G and 2G stars in the field to be far from being in energy equipartition, with ${\eta }_{1{\rm{G}}}=-0.007\pm 0.026$ for the former and ${\eta }_{2{\rm{G}}}=0.074\pm 0.029$ for the latter, where η is defined so that the velocity dispersion ${\sigma }_{\mu }$ scales with stellar mass as ${\sigma }_{\mu }\propto {m}^{-\eta }$. The kinematical differences reported here can help constrain the formation mechanisms for the multiple stellar populations in ω Centauri and other globular clusters. We make our astro-photometric catalog publicly available.

We stack the rest-frame ultraviolet spectra of N = 14 highly magnified gravitationally lensed galaxies at redshifts $1.6\lt z\lt 3.6$. The resulting new composite spans $900\lt {\lambda }_{\mathrm{rest}}\lt 3000$ Å, with a peak signal-to-noise ratio (S/N) of 103 per spectral resolution element (∼100 km s⁻¹). It is the highest S/N, highest spectral resolution composite spectrum of z ∼ 2–3 galaxies yet published. The composite reveals numerous weak nebular emission lines and stellar photospheric absorption lines that can serve as new physical diagnostics, particularly at high redshift with the James Webb Space Telescope (JWST). We report equivalent widths to aid in proposing for and interpreting JWST spectra. We examine the velocity profiles of strong absorption features in the composite, and in a matched composite of $z\sim 0$ COS/HST galaxy spectra. We find remarkable similarity in the velocity profiles at $z\sim 0$ and $z\sim 2$, suggesting that similar physical processes control the outflows across cosmic time. While the maximum outflow velocity depends strongly on ionization potential, the absorption-weighted mean velocity does not. As such, the bulk of the high-ionization absorption traces the low-ionization gas, with an additional blueshifted absorption tail extending to at least −2000 km s⁻¹. We interpret this tail as arising from the stellar wind and photospheres of massive stars. Starburst99 models are able to replicate this high-velocity absorption tail. However, these theoretical models poorly reproduce several of the photospheric absorption features, indicating that improvements are needed to match observational constraints on the massive stellar content of star-forming galaxies at $z\sim 2$. We publicly release our composite spectra.

Hierarchical structure in young star fields has been demonstrated in a variety of ways, including two-point correlation functions (TPCFs) that are power laws for spatial scales up to at least several hundred parsecs. As the stars age, this power law decreases in slope until it becomes nearly flat at ∼100 Myr, at which point the hierarchical structure has disappeared. The fact that the TPCF remains nearly a power law during this time implies that the dispersal mechanism is somewhat independent of scale. This rules out dispersal by random stellar motions at either the local gas turbulent speed or a constant speed, because in both cases the hierarchy would disappear at small scales first, causing the TPCF to bend over. Destruction by shear has the right property, as the shear rate in a galaxy is independent of scale for kiloparsec-size regions, but shear converts the hierarchy into an azimuthal stream, which still has a power-law TPCF. What does explain the observation is the overlapping of several independent hierarchies from successive generations of star formation in the same region. If stellar age is determined from magnitude intervals on the main sequence of a color–magnitude diagram, or if cluster ages are grouped together logarithmically into bins, then multiple generations will overlap more and more as the grouped populations age, and this overlap will lower the spatial correlations between group members. Models of these processes illustrate their relative roles in removing the appearance of young stellar hierarchies.

We present two case studies of the in-situ electron acceleration during the 2000 February 11 shock and the 2004 July 22 shock, with the strongest electron flux enhancement at 40 keV across the shock, among all the quasi-perpendicular and quasi-parallel ICME-driven shocks observed by the WIND 3DP instrument from 1995 through 2014 at 1 au. We find that for this quasi-perpendicular (quasi-parallel) shock on 2000 February 11 (2004 July 22), the shocked electron differential fluxes at ∼0.4–50 keV in the downstream generally fit well to a double-power-law spectrum, J ∼ E^−β, with an index of β ∼ 3.15 (4.0) at energies below a break at ∼3 keV (∼1 keV) and β ∼ 2.65 (2.6) at energies above. For both shock events, the downstream electron spectral indices appear to be similar for all pitch angles, which are significantly larger than the index prediction by diffusive shock acceleration. In addition, the downstream electron pitch-angle distributions show the anisotropic beams in the anti-sunward-traveling direction, while the ratio of the downstream over ambient fluxes appears to peak near 90° pitch angles, at all energies of ∼0.4–50 keV. These results suggest that in both shocks, shock drift acceleration likely plays an important role in accelerating electrons in situ at 1 au. Such ICME-driven shocks could contribute to the formation of solar wind halo electrons at energies ≲2 keV, as well as the production of solar wind superhalo electrons at energies ≳2 keV in interplanetary space.

This paper introduces a novel method for flare forecasting, combining prediction accuracy with the ability to identify the most relevant predictive variables. This result is obtained by means of a two-step approach: first, a supervised regularization method for regression, namely, LASSO is applied, where a sparsity-enhancing penalty term allows the identification of the significance with which each data feature contributes to the prediction; then, an unsupervised fuzzy clustering technique for classification, namely, Fuzzy C-Means, is applied, where the regression outcome is partitioned through the minimization of a cost function and without focusing on the optimization of a specific skill score. This approach is therefore hybrid, since it combines supervised and unsupervised learning; realizes classification in an automatic, skill-score-independent way; and provides effective prediction performances even in the case of imbalanced data sets. Its prediction power is verified against NOAA Space Weather Prediction Center data, using as a test set, data in the range between 1996 August and 2010 December and as training set, data in the range between 1988 December and 1996 June. To validate the method, we computed several skill scores typically utilized in flare prediction and compared the values provided by the hybrid approach with the ones provided by several standard (non-hybrid) machine learning methods. The results showed that the hybrid approach performs classification better than all other supervised methods and with an effectiveness comparable to the one of clustering methods; but, in addition, it provides a reliable ranking of the weights with which the data properties contribute to the forecast.

Using a cosmological dark matter simulation of a galaxy-cluster halo, we follow the temporal evolution of its globular cluster population. To mimic the red and blue globular cluster populations, we select at high redshift $(z\sim 1)$ two sets of particles from individual galactic halos constrained by the fact that, at redshift z = 0, they have density profiles similar to observed ones. At redshift z = 0, approximately 60% of our selected globular clusters were removed from their original halos building up the intra-cluster globular cluster population, while the remaining 40% are still gravitationally bound to their original galactic halos. As the blue population is more extended than the red one, the intra-cluster globular cluster population is dominated by blue globular clusters, with a relative fraction that grows from 60% at redshift z = 0 up to 83% for redshift $z\sim 2$. In agreement with observational results for the Virgo galaxy cluster, the blue intra-cluster globular cluster population is more spatially extended than the red one, pointing to a tidally disrupted origin.

Aqueous alteration is one of the primitive activities that occurred on meteorite parent bodies in the early solar system. The Tagish Lake meteorite is known to show an intense parent body aqueous alteration signature. In this study, quantitative analyses of the alkaline elements and isotopic analyses of Sr and Ba from acid leachates of TL (C2-ungrouped) were performed to investigate effects of aqueous alteration. The main purpose of this study is to search for isotopic evidence of extinct ¹³⁵Cs from the Ba isotopic analyses in the chemical separates from the Tagish Lake meteorite. Barium isotopic data from the leachates show variable ¹³⁵Ba isotopic anomalies (ε = −2.6 ∼ +3.6) which correlatewith ¹³⁷Ba and ¹³⁸Ba suggesting a heterogeneous distribution of s- and r-rich nucleosynthetic components in the early solar system. The ⁸⁷Rb–⁸⁷Sr and ¹³⁵Cs–¹³⁵Ba decay systems on TL in this study do not provide any chronological information. The disturbance of the TL chronometers is likely a reflection of the selective dissolution of Cs and Rb given the relatively higher mobility of Cs and Rb compared to Ba and Sr, respectively, during fluid mineral interactions.

Although gravitational waves tend to erase eccentricity of an inspiraling binary system, ellipticity can be generated in the presence of surrounding matter. We present a semianalytical method for understanding the eccentricity distribution of binary black holes (BHs) in the presence of a supermassive BH in a galactic center. Given a matter distribution, we show how to determine the resultant eccentricity analytically in the presence of both tidal forces and evaporation up to one cutoff and one matter-distribution-independent function, paving the way for understanding the environment of detected inspiraling BHs. We furthermore generalize Kozai–Lidov dynamics to situations where perturbation theory breaks down for short time intervals, allowing more general angular momentum exchange, such that eccentricity is generated even when all bodies orbit in the same plane.

Interchange reconnection, specifically magnetic reconnection between open magnetic fields and closed magnetic flux ropes, plays a major role in the heliospheric magnetic flux budget. It is generally accepted that closed magnetic field lines of interplanetary magnetic flux ropes (IMFRs) can gradually open through reconnection between one of its legs and other open field lines until no closed field lines are left to contribute flux to the heliosphere. In this paper, we report an IMFR associated with a magnetic reconnection exhaust, whereby its closed field lines were opening by a magnetic reconnection event near 1 au. The reconnection exhaust and the following IMFR were observed on 2002 February 2 by both the Wind and ACE spacecraft. Observations on counterstreaming suprathermal electrons revealed that most magnetic field lines of the IMFR were closed, especially those after the front boundary of the IMFR, with both ends connected to the Sun. The unidirectional suprathermal electron strahls before the exhaust manifested the magnetic field lines observed before the exhaust was open. These observations provide direct evidence that closed field lines of IMFRs can be opened by interchange reconnection in interplanetary space. This is the first report of the closed field lines of IMFRs being opened by interchange reconnection in interplanetary space. This type of interplanetary interchange reconnection may pose important implications for balancing the heliospheric flux budget.

The spectroscopy of background QSO sightlines passing close to foreground galaxies is a potent technique for studying the circumgalactic medium (CGM). However, QSOs are effectively point sources, limiting their potential to constrain the size of circumgalactic gaseous structures. Here we present the first large Keck/Low-resolution Imaging Spectrometer (LRIS) and Very Large Telescope (VLT)/Focal Reducer/Low-dispersion Spectrograph 2 (FORS2) spectroscopic survey of bright (${B}_{\mathrm{AB}}\lt 22.3$) background galaxies whose lines of sight probe Mg ii$\lambda \lambda 2796,2803$ absorption from the CGM around close projected foreground galaxies at transverse distances $10\,\mathrm{kpc}\lt {R}_{\perp }\,\lt 150\,\mathrm{kpc}$. Our sample of 72 projected pairs, drawn from the PRIsm MUlti-object Survey, includes 48 background galaxies that do not host bright active galactic nuclei, and both star-forming and quiescent foreground galaxies with stellar masses of $9.0\lt \mathrm{log}{M}_{* }/{M}_{\odot }\lt 11.2$ at redshifts of $0.35\lt {z}_{{\rm{f}}/{\rm{g}}}\lt 0.8$. We detect Mg ii absorption associated with these foreground galaxies with equivalent widths of $0.25\,\mathring{\rm{A}} \lt {W}_{2796}\lt 2.6\,\mathring{\rm{A}}$ at $\gt 2\sigma$ significance in 20 individual background sightlines passing within ${R}_{\perp }\lt 50\,\mathrm{kpc}$ and place $2\sigma$ upper limits on W₂₇₉₆ of $\lesssim 0.5\,\mathring{\rm{A}}$ in an additional 11 close sightlines. Within ${R}_{\perp }\lt 50\,\mathrm{kpc}$, W₂₇₉₆ is anticorrelated with R_⊥, consistent with analyses of Mg ii absorption detected along background QSO sightlines. Subsamples of these foreground hosts divided at $\mathrm{log}{M}_{* }/{M}_{\odot }=9.9$ exhibit statistically inconsistent W₂₇₉₆ distributions at $30\,\mathrm{kpc}\lt {R}_{\perp }\lt 50\,\mathrm{kpc}$, with the higher-M_* galaxies yielding a larger median W₂₇₉₆ by $0.9\,\mathring{\rm{A}}$. Finally, we demonstrate that foreground galaxies with similar stellar masses exhibit the same median W₂₇₉₆ at a given R_⊥ to within $\lt 0.2\,\mathring{\rm{A}}$ toward both background galaxies and toward QSO sightlines drawn from the literature. Analysis of these data sets constraining the spatial coherence scale of circumgalactic Mg ii absorption is presented in a companion paper.

We identify velocity channel map intensities as a new way to trace magnetic fields in turbulent media. This work makes use of both the modern theory of magnetohydrodynamic (MHD) turbulence, which predicts that magnetic eddies are aligned with the local direction of the magnetic field, and also the theory of spectral line position–position–velocity (PPV) statistics, which describes how velocity and density fluctuations are mapped onto PPV space. In particular, we use the fact that the fluctuations of the intensity of thin channel maps are mostly affected by the turbulent velocity, while the thick maps are dominated by density variations. We study how contributions of the fundamental MHD modes affect the Velocity Channel Gradients (VChGs), and demonstrate that the VChGs arising from Alfvén and slow modes are aligned perpendicular to the local direction of the magnetic field, while the VChGs produced by the fast mode are aligned parallel to the magnetic field. The dominance of Alfvén and slow modes in interstellar media will therefore allow reliable magnetic field tracing using the VChGs. We explore ways of identifying self-gravitating regions that do not require polarimetric information. In addition, we also introduce a new measure, termed "Reduced Velocity Centroids" (RVCGs), and compare its abilities with those of VChGs. We employed VChGs in analyzing GALFA 21 cm data and successfully compared the magnetic field directions with the Planck polarization observations. The applications of the suggested techniques include both tracing the magnetic field in diffuse interstellar media and star-forming regions, and removing the galactic foreground in the framework of cosmological polarization studies.