Table of contents

Above the top of the solar corona, the young, slow solar wind transitions from low-β, magnetically structured flow dominated by radial structures to high-β, less structured flow dominated by hydrodynamics. This transition, long inferred via theory, is readily apparent in the sky region close to 10° from the Sun in processed, background-subtracted solar wind images. We present image sequences collected by the inner Heliospheric Imager instrument on board the Solar-Terrestrial Relations Observatory (STEREO/HI1) in 2008 December, covering apparent distances from approximately 4° to 24° from the center of the Sun and spanning this transition in the large-scale morphology of the wind. We describe the observation and novel techniques to extract evolving image structure from the images, and we use those data and techniques to present and quantify the clear textural shift in the apparent structure of the corona and solar wind in this altitude range. We demonstrate that the change in apparent texture is due both to anomalous fading of the radial striae that characterize the corona and to anomalous relative brightening of locally dense puffs of solar wind that we term "flocculae." We show that these phenomena are inconsistent with smooth radial flow, but consistent with the onset of hydrodynamic or magnetohydrodynamic instabilities leading to a turbulent cascade in the young solar wind.

We present the first results from MMT and Keck spectroscopy for a large sample of $0.1\leqslant z\leqslant 1$ emission-line galaxies selected from our narrowband imaging in the Subaru Deep Field. We measured the weak [O iii]λ4363 emission line for 164 galaxies (66 with at least 3σ detections, and 98 with significant upper limits). The strength of this line is set by the electron temperature for the ionized gas. Because the gas temperature is regulated by the metal content, the gas-phase oxygen abundance is inversely correlated with [O iii]λ4363 line strength. Our temperature-based metallicity study is the first to span $\approx 8$ Gyr of cosmic time and $\approx 3$ dex in stellar mass for low-mass galaxies, $\mathrm{log}({M}_{\star }/{M}_{\odot })\approx 6.0$–9.0. Using extensive multi-wavelength photometry, we measure the evolution of the stellar mass–gas metallicity relation and its dependence on dust-corrected star formation rate (SFR). The latter is obtained from high signal-to-noise Balmer emission-line measurements. Our mass–metallicity relation is consistent with Andrews & Martini at $z\leqslant 0.3$, and evolves toward lower abundances at a given stellar mass, $\mathrm{log}{({\rm{O/H}})\propto (1+z)}^{-{2.32}_{-0.26}^{+0.52}}$. We find that galaxies with lower metallicities have higher SFRs at a given stellar mass and redshift, although the scatter is large ($\approx 0.3$ dex) and the trend is weaker than seen in local studies. We also compare our mass–metallicity relation against predictions from high-resolution galaxy formation simulations, and find good agreement with models that adopt energy- and momentum-driven stellar feedback. We identified 16 extremely metal-poor galaxies with abundances of less than a tenth of solar; our most metal-poor galaxy at $z\approx 0.84$ is similar to I Zw 18.

Motivated by advances in observational searches for sub-parsec supermassive black hole binaries (SBHBs) made in the past few years, we develop a semi-analytic model to describe spectral emission-line signatures of these systems. The goal of this study is to aid the interpretation of spectroscopic searches for binaries and to help test one of the leading models of binary accretion flows in the literature: SBHB in a circumbinary disk. In this work, we present the methodology and a comparison of the preliminary model with the data. We model SBHB accretion flows as a set of three accretion disks: two mini-disks that are gravitationally bound to the individual black holes and a circumbinary disk. Given a physically motivated parameter space occupied by sub-parsec SBHBs, we calculate a synthetic database of nearly 15 million broad optical emission-line profiles and explore the dependence of the profile shapes on characteristic properties of SBHBs. We find that the modeled profiles show distinct statistical properties as a function of the semimajor axis, mass ratio, eccentricity of the binary, and the degree of alignment of the triple disk system. This suggests that the broad emission-line profiles from SBHB systems can in principle be used to infer the distribution of these parameters and as such merit further investigation. Calculated profiles are more morphologically heterogeneous than the broad emission lines in observed SBHB candidates and we discuss improved treatment of radiative transfer effects, which will allow a direct statistical comparison of the two groups.

Measurements of extinction curves toward young stars are essential for calculating the intrinsic stellar spectrophotometric radiation. This flux determines the chemical properties and evolution of the circumstellar region, including the environment in which planets form. We develop a new technique using H₂ emission lines pumped by stellar Lyα photons to characterize the extinction curve by comparing the measured far-ultraviolet H₂ line fluxes with model H₂ line fluxes. The difference between model and observed fluxes can be attributed to the dust attenuation along the line of sight through both the interstellar and circumstellar material. The extinction curves are fit by a Cardelli et al. (1989) model and the A_V(H₂) for the 10 targets studied with good extinction fits range from 0.5 to 1.5 mag, with R_V values ranging from 2.0 to 4.7. A_V and R_V are found to be highly degenerate, suggesting that one or the other needs to be calculated independently. Column densities and temperatures for the fluorescent H₂ populations are also determined, with averages of log₁₀(N(H₂)) = 19.0 and T = 1500 K. This paper explores the strengths and limitations of the newly developed extinction curve technique in order to assess the reliability of the results and improve the method in the future.

PSR J1509–5850 is a middle-aged pulsar with a period of P ≈ 89 ms and spin-down power of $\dot{E}=5.1\times {10}^{35}$ erg s⁻¹, at a distance of about 3.8 kpc. We report on deep Chandra X-ray Observatory observations of this pulsar and its pulsar wind nebula (PWN). In addition to the previously detected tail extending up to 7' southwest from the pulsar (the southern outflow), the deep images reveal similarly long, faint, diffuse emission stretched toward the north (the northern outflow) and the fine structure of the compact nebula (CN) in the pulsar vicinity. The CN is resolved into two lateral tails and one axial tail pointing southwest (a morphology remarkably similar to that of the Geminga PWN), which supports the assumption that the pulsar moves toward the northeast. The luminosities of the southern and northern outflows are about $1\times {10}^{33}$ and $4\times {10}^{32}$ erg s⁻¹, respectively. The spectra extracted from four regions of the southern outflow do not show any softening with increasing distance from the pulsar. The lack of synchrotron cooling suggests a high flow speed or in situ acceleration of particles. The spectra extracted from two regions of the northern outflow show a hint of softening with distance from the pulsar, which may indicate slower particle propagation. We speculate that the northern outflow is associated with particle leakage from the bow-shock apex into the ISM, while the southern outflow represents the tail of the shocked pulsar wind behind the moving pulsar. We estimate the physical parameters of the observed outflows and compare the J1509–5850 PWN with PWNe of other supersonically moving pulsars.

The escape of ionizing Lyman continuum (LyC) photons requires the existence of low-N_{H i} sightlines, which also promote escape of Lyα. We use a suite of 2500 Lyα Monte-Carlo radiative transfer simulations through models of dusty, clumpy interstellar ("multiphase") media from Gronke & Dijkstra, and compare the escape fractions of Lyα (${f}_{{\rm{esc}}}^{{\rm{Ly}}\alpha }$) and LyC radiation (${f}_{{\rm{esc}}}^{{\rm{ion}}}$). We find that ${f}_{{\rm{esc}}}^{{\rm{ion}}}$ and ${f}_{{\rm{esc}}}^{{\rm{Ly}}\alpha }$ are correlated: galaxies with a low ${f}_{{\rm{esc}}}^{{\rm{Ly}}\alpha }$ consistently have a low ${f}_{{\rm{esc}}}^{{\rm{ion}}}$, while galaxies with a high ${f}_{{\rm{esc}}}^{{\rm{Ly}}\alpha }$ exhibit a large dispersion in ${f}_{{\rm{esc}}}^{{\rm{ion}}}$. We argue that there is increasing observational evidence that Lyα escapes more easily from UV-faint galaxies. The correlation between ${f}_{{\rm{esc}}}^{{\rm{ion}}}$ and ${f}_{{\rm{esc}}}^{{\rm{Ly}}\alpha }$ then implies that UV-faint galaxies contribute more to the ionizing background than implied by the faint-end slope of the UV luminosity function. In multiphase gases, the ionizing escape fraction is most strongly affected by the cloud covering factor, f_cl, which implies that ${f}_{{\rm{esc}}}^{{\rm{ion}}}$ is closely connected to the observed Lyα spectral line shape. Specifically, LyC-emitting galaxies typically having narrower, more symmetric line profiles. This prediction is qualitatively similar to that for "shell models."

Slow MHD waves are important tools for understanding coronal structures and dynamics. In this paper, we report a number of observations from the X-Ray Telescope (XRT) on board HINODE and Solar Dynamic Observatory/Atmospheric Imaging Assembly (AIA) of reflecting longitudinal waves in hot coronal loops. To our knowledge, this is the first report of this kind as seen from the XRT and simultaneously with the AIA. The wave appears after a micro-flare occurs at one of the footpoints. We estimate the density and temperature of the loop plasma by performing differential emission measure (DEM) analysis on the AIA image sequence. The estimated speed of propagation is comparable to or lower than the local sound speed, suggesting it to be a propagating slow wave. The intensity perturbation amplitude, in every case, falls very rapidly as the perturbation moves along the loop and eventually vanishes after one or more reflections. To check the consistency of such reflection signatures with the obtained loop parameters, we perform a 2.5D MHD simulation, which uses the parameters obtained from our observation as inputs, and perform forward modeling to synthesize AIA 94 Å images. Analyzing the synthesized images, we obtain the same properties of the observables as for the real observation. From the analysis we conclude that a footpoint heating can generate a slow wave which then reflects back and forth in the coronal loop before fading. Our analysis of the simulated data shows that the main agent for this damping is anisotropic thermal conduction.

Supermassive black holes (SMBHs) are ubiquitous in galaxies with a sizable mass. It is expected that a pair of SMBHs originally in the nuclei of two merging galaxies would form a binary and eventually coalesce via a burst of gravitational waves. So far, theoretical models and simulations, focusing only on limited phases of the orbital decay of SMBHs under idealized conditions of the galaxy hosts, have been unable to directly predict the SMBH merger timescale from ab-initio galaxy formation theory. The predicted SMBH merger timescales are long, of order Gyrs, which could be problematic for future gravitational wave (GW) searches. Here, we present the first multi-scale ΛCDM cosmological simulation that follows the orbital decay of a pair of SMBHs in a merger of two typical massive galaxies at $z\sim 3$, all the way to the final coalescence driven by GW emission. The two SMBHs, with masses $\sim {10}^{8}$${M}_{\odot }$, settle quickly in the nucleus of the merger remnant. The remnant is triaxial and extremely dense due to the dissipative nature of the merger and the intrinsic compactness of galaxies at high redshift. Such properties naturally allow a very efficient hardening of the SMBH binary. The SMBH merger occurs in only ∼10 Myr after the galactic cores have merged, which is two orders of magnitude smaller than the Hubble time.

We report the Chandra/HRC-S and Swift/XRT observations for the 2015 outburst of the high-mass X-ray binary pulsar in the Small Magellanic Cloud, SMC X-2. While previous studies suggested that either an O star or a Be star in the field is the high-mass companion of SMC X-2, our Chandra/HRC-S image unambiguously confirms the O-type star as the true optical counterpart. Using the Swift/XRT observations, we extracted accurate orbital parameters of the pulsar binary through a time of arrivals analysis. In addition, there were two X-ray dips near the inferior conjunction, which are possibly caused by eclipses or an ionized high-density shadow wind near the companion's surface. Finally, we propose that an outflow driven by the radiation pressure from day ∼10 played an important role in the X-ray/optical evolution of the outburst.

The Galactic bulge is dominated by an old, metal-rich stellar population. The possible presence and the amount of a young (a few gigayears old) minor component is one of the major issues debated in the literature. Recently, the bulge stellar system Terzan 5 was found to harbor three sub-populations with iron content varying by more than one order of magnitude (from 0.2 up to two times the solar value), with chemical abundance patterns strikingly similar to those observed in bulge field stars. Here we report on the detection of two distinct main-sequence turnoff points in Terzan 5, providing the age of the two main stellar populations: 12 Gyr for the (dominant) sub-solar component and 4.5 Gyr for the component at super-solar metallicity. This discovery classifies Terzan 5 as a site in the Galactic bulge where multiple bursts of star formation occurred, thus suggesting a quite massive progenitor possibly resembling the giant clumps observed in star-forming galaxies at high redshifts. This connection opens a new route of investigation into the formation process and evolution of spheroids and their stellar content.

Among the multitude of methods used to investigate coronal heating, the time lag method of Viall & Klimchuk is becoming increasingly prevalent as an analysis technique that is complementary to those that are traditionally used. The time lag method cross correlates light curves at a given spatial location obtained in spectral bands that sample different temperature plasmas. It has been used most extensively with data from the Atmospheric Imaging Assembly on the Solar Dynamics Observatory. We have previously applied the time lag method to entire active regions and surrounding the quiet Sun and created maps of the results. We find that the majority of time lags are consistent with the cooling of coronal plasma that has been impulsively heated. Additionally, a significant fraction of the map area has a time lag of zero. This does not indicate a lack of variability. Rather, strong variability must be present, and it must occur in phase between the different channels. We have previously shown that these zero time lags are consistent with the transition region response to coronal nanoflares, although other explanations are possible. A common misconception is that the zero time lag indicates steady emission resulting from steady heating. Using simulated and observed light curves, we demonstrate here that highly correlated light curves at zero time lag are not compatible with equilibrium solutions. Such light curves can only be created by evolution.

In order to understand the rate of merger of stellar mass black hole binaries (BHBs) by gravitational wave (GW) emission it is important to determine the major pathways to merger. We use numerical simulations to explore the evolution of BHBs inside the radius of influence of supermassive black holes (SMBHs) in galactic centers. In this region, the evolution of binaries is dominated by perturbations from the central SMBH. In particular, as first pointed out by Antonini and Perets, the Kozai–Lidov mechanism trades relative inclination of the BHB to the SMBH for eccentricity of the BHB, and for some orientations can bring the BHB to an eccentricity near unity. At very high eccentricities, GW emission from the BHB can become efficient, causing the members of the BHB to coalesce. We use a novel combination of two N-body codes to follow this evolution. We are required to simulate small systems to follow the behavior accurately. We have completed 400 simulations that range from ∼300 stars around a 10³${M}_{\odot }$ black hole to ∼4500 stars around a 10⁴${M}_{\odot }$ black hole. These simulations are the first to follow the internal orbit of a binary near an SMBH while also following the changes to its external orbit self-consistently. We find that this mechanism could produce mergers at a maximum rate per volume of ∼100 Gpc⁻³ yr⁻¹ or considerably less if the inclination oscillations of the binary remain constant as the BHB inclination to the SMBH changes, or if the binary black hole fraction is small.

From 2013 April to 2014 April, we performed X-ray and optical simultaneous monitoring of the type 1.5 Seyfert galaxy NGC 3516. We employed Suzaku and five Japanese ground-based telescopes—the Pirka, Kiso Schmidt, Nayuta, MITSuME, and the Kanata telescopes. The Suzaku observations were conducted seven times with various intervals ranging from days or weeks to months, with an exposure of ∼50 ks each. The optical B-band observations not only covered those of Suzaku almost simultaneously, but also followed the source as frequently as possible. As a result, NGC 3516 was found in its faint phase with a 2–10 keV flux of 0.21–2.70 × 10⁻¹¹ erg s⁻¹ cm⁻². The 2–45 keV X-ray spectra were composed of a dominant variable hard power-law (PL) continuum with a photon index of ∼1.7 and a non-relativistic reflection component with a prominent Fe–Kα emission line. Producing the B-band light curve by differential image photometry, we found that the B-band flux changed by ∼2.7 × 10⁻¹¹ erg s⁻¹ cm⁻², which is comparable to the X-ray variation, and we detected a significant flux correlation between the hard PL component in X-rays and the B-band radiation, for the first time in NGC 3516. By examining their correlation, we found that the X-ray flux preceded that in the B band by ${2.0}_{-0.6}^{+0.7}$ days (1σ error). Although this result supports the X-ray reprocessing model, the derived lag is too large to be explained by the standard view, which assumes a "lamppost"-type X-ray illuminator located near a standard accretion disk. Our results are better explained by assuming a hot accretion flow and a truncated disk.

In this paper we apply a Bayesian technique to determine the best fit of stellar evolution models to find the main sequence turn-off age and other cluster parameters of four intermediate-age open clusters: NGC 2360, NGC 2477, NGC 2660, and NGC 3960. Our algorithm utilizes a Markov chain Monte Carlo technique to fit these various parameters, objectively finding the best-fit isochrone for each cluster. The result is a high-precision isochrone fit. We compare these results with the those of traditional "by-eye" isochrone fitting methods. By applying this Bayesian technique to NGC 2360, NGC 2477, NGC 2660, and NGC 3960, we determine the ages of these clusters to be 1.35 ± 0.05, 1.02 ± 0.02, 1.64 ± 0.04, and 0.860 ± 0.04 Gyr, respectively. The results of this paper continue our effort to determine cluster ages to a higher precision than that offered by these traditional methods of isochrone fitting.

We provide estimates of atmospheric pressure and surface composition on short-period, rocky exoplanets with dayside magma pools and silicate-vapor atmospheres. Atmospheric pressure tends toward vapor-pressure equilibrium with surface magma, and magma-surface composition is set by the competing effects of fractional vaporization and surface-interior exchange. We use basic models to show how surface-interior exchange is controlled by the planet's temperature, mass, and initial composition. We assume that mantle rock undergoes bulk melting to form the magma pool, and that winds flow radially away from the substellar point. With these assumptions, we find that: (1) atmosphere-interior exchange is fast when the planet's bulk-silicate FeO concentration is low, and slow when the planet's bulk-silicate FeO concentration is high; (2) magma pools are compositionally well mixed for substellar temperatures ≲2400 K, but compositionally variegated and rapidly variable for substellar temperatures ≳2400 K; (3) currents within the magma pool tend to cool the top of the solid mantle ("tectonic refrigeration"); (4) contrary to earlier work, many magma planets have time-variable surface compositions.

The direct measurements of interstellar matter by the Interstellar Boundary Explorer (IBEX) mission have opened a new and important chapter in our study of the interactions that control the boundaries of our heliosphere. Here we derive for the quantitative information about interstellar O flow parameters from IBEX low-energy neutral atom data for the first time. Specifically, we derive a relatively narrow four-dimensional parameter tube along which interstellar O flow parameters must lie. Along the parameter tube, we find a large uncertainty in interstellar O flow longitude, 760 ± 34 from χ² analysis and 765 ± 62 from a maximum likelihood fit, which is statistically consistent with the flow longitude derived for interstellar He, 756 ± 14. The best-fit O and He temperatures are almost identical at a reference flow longitude of 76°, which provides a strong indication that the local interstellar plasma near the Sun is relatively unaffected by turbulent heating. However, key differences include an oxygen parameter tube for the interstellar speed (relation between speed and longitude) that has higher speeds than those in the corresponding parameter tube for He, and an upstream flow latitude for oxygen that is southward of the upstream flow latitude for helium. Both of these differences are likely the result of enhanced filtration of interstellar oxygen due to its charge-exchange ionization rate, which is higher than that for helium. Furthermore, we derive an interstellar O density near the termination shock of ${5.8}_{-0.8}^{+0.9}\times {10}^{-5}$ cm⁻³ that, within uncertainties, is consistent with previous estimates. Thus, we use IBEX data to probe the interstellar properties of oxygen.

We report our implementation of the magneto-frictional method in the Message Passing Interface Adaptive Mesh Refinement Versatile Advection Code (MPI-AMRVAC). The method aims at applications where local adaptive mesh refinement (AMR) is essential to make follow-up dynamical modeling affordable. We quantify its performance in both domain-decomposed uniform grids and block-adaptive AMR computations, using all frequently employed force-free, divergence-free, and other vector comparison metrics. As test cases, we revisit the semi-analytic solution of Low and Lou in both Cartesian and spherical geometries, along with the topologically challenging Titov–Démoulin model. We compare different combinations of spatial and temporal discretizations, and find that the fourth-order central difference with a local Lax–Friedrichs dissipation term in a single-step marching scheme is an optimal combination. The initial condition is provided by the potential field, which is the potential field source surface model in spherical geometry. Various boundary conditions are adopted, ranging from fully prescribed cases where all boundaries are assigned with the semi-analytic models, to solar-like cases where only the magnetic field at the bottom is known. Our results demonstrate that all the metrics compare favorably to previous works in both Cartesian and spherical coordinates. Cases with several AMR levels perform in accordance with their effective resolutions. The magneto-frictional method in MPI-AMRVAC allows us to model a region of interest with high spatial resolution and large field of view simultaneously, as required by observation-constrained extrapolations using vector data provided with modern instruments. The applications of the magneto-frictional method to observations are shown in an accompanying paper.

A magneto-frictional module has been implemented and tested in the Message Passing Interface Adaptive Mesh Refinement Versatile Advection Code (MPI-AMRVAC) in the first paper of this series. Here, we apply the magneto-frictional method to observations to demonstrate its applicability in both Cartesian and spherical coordinates, and in uniform and block-adaptive octree grids. We first reconstruct a nonlinear force-free field (NLFFF) on a uniform grid of 180³ cells in Cartesian coordinates, with boundary conditions provided by the vector magnetic field observed by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) at 06:00 UT on 2010 November 11 in active region NOAA 11123. The reconstructed NLFFF successfully reproduces the sheared and twisted field lines and magnetic null points. Next, we adopt a three-level block-adaptive grid to model the same active region with a higher spatial resolution on the bottom boundary and a coarser treatment of regions higher up. The force-free and divergence-free metrics obtained are comparable to the run with a uniform grid, and the reconstructed field topology is also very similar. Finally, a group of active regions, including NOAA 11401, 11402, 11405, and 11407, observed at 03:00 UT on 2012 January 23 by SDO/HMI is modeled with a five-level block-adaptive grid in spherical coordinates, where we reach a local resolution of $0\buildrel{\circ}\over{.} 06$ pixel⁻¹ in an area of 790 Mm × 604 Mm. Local high spatial resolution and a large field of view in NLFFF modeling can be achieved simultaneously in parallel and block-adaptive magneto-frictional relaxations.

In the well-established theories of polarized line formation with partial frequency redistribution (PRD) for a two-level and two-term atom, it is generally assumed that the lower level of the scattering transition is unpolarized. However, the existence of unexplained spectral features in some lines of the Second Solar Spectrum points toward a need to relax this assumption. There exists a density matrix theory that accounts for the polarization of all the atomic levels, but it is based on the flat-spectrum approximation (corresponding to complete frequency redistribution). In the present paper we propose a numerical algorithm to solve the problem of polarized line formation in magnetized media, which includes both the effects of PRD and the lower level polarization (LLP) for a two-level atom. First we derive a collisionless redistribution matrix that includes the combined effects of the PRD and the LLP. We then solve the relevant transfer equation using a two-stage approach. For illustration purposes, we consider two case studies in the non-magnetic regime, namely, the J_a = 1, J_b = 0 and J_a = J_b = 1, where J_a and J_b represent the total angular momentum quantum numbers of the lower and upper states, respectively. Our studies show that the effects of LLP are significant only in the line core. This leads us to propose a simplified numerical approach to solve the concerned radiative transfer problem.

We propose a new model-independent method to test the cosmic curvature by comparing the proper distance and transverse comoving distance. Using the measurements of the Hubble parameter H(z) and the angular diameter distance d_A, the cosmic curvature parameter ${{\rm{\Omega }}}_{K}$ is constrained to be −0.09 ± 0.19, which is consistent with a flat universe. We also use a Monte Carlo simulation to test the validity and efficiency, and find that our method can give a reliable and efficient constraint on cosmic curvature. Compared with other model-independent methods testing the cosmic curvature, our method can avoid some drawbacks and give a better constraint.

We use the cellular automaton model described in López Fuentes & Klimchuk to study the evolution of coronal loop plasmas. The model, based on the idea of a critical misalignment angle in tangled magnetic fields, produces nanoflares of varying frequency with respect to the plasma cooling time. We compare the results of the model with active region (AR) observations obtained with the Hinode/XRT and SDO/AIA instruments. The comparison is based on the statistical properties of synthetic and observed loop light curves. Our results show that the model reproduces the main observational characteristics of the evolution of the plasma in AR coronal loops. The typical intensity fluctuations have amplitudes of 10%–15% both for the model and the observations. The sign of the skewness of the intensity distributions indicates the presence of cooling plasma in the loops. We also study the emission measure (EM) distribution predicted by the model and obtain slopes in log(EM) versus log(T) between 2.7 and 4.3, in agreement with published observational values.

Almost all superluminous supernovae (SLSNe) whose peak magnitudes are $\lesssim -21$ mag can be explained by the ⁵⁶Ni-powered model, the magnetar-powered (highly magnetized pulsar) model, or the ejecta-circumstellar medium (CSM) interaction model. Recently, iPTF13ehe challenged these energy-source models, because the spectral analysis shows that $\sim 2.5{M}_{\odot }$ of ⁵⁶Ni have been synthesized, but are inadequate to power the peak bolometric emission of iPTF13ehe, while the rebrightening of the late-time light curve (LC) and the Hα emission lines indicate that the ejecta-CSM interaction must play a key role in powering the late-time LC. Here we propose a triple-energy-source model, in which a magnetar together with some amount ($\lesssim 2.5{M}_{\odot }$) of ⁵⁶Ni may power the early LC of iPTF13ehe, while the late-time rebrightening can be quantitatively explained by an ejecta-CSM interaction. Furthermore, we suggest that iPTF13ehe is a genuine core-collapse supernova rather than a pulsational pair-instability supernova candidate. Further studies on similar SLSNe in the future would eventually shed light on their explosion and energy-source mechanisms.

Turbulent motions close to the visible solar surface may generate low-frequency internal gravity waves (IGWs) that propagate through the lower solar atmosphere. Magnetic activity is ubiquitous throughout the solar atmosphere, so it is expected that the behavior of IGWs is to be affected. In this article we investigate the role of an equilibrium magnetic field on propagating and standing buoyancy oscillations in a gravitationally stratified medium. We assume that this background magnetic field is parallel to the direction of gravitational stratification. It is known that when the equilibrium magnetic field is weak and the background is isothermal, the frequencies of standing IGWs are sensitive to the presence of magnetism. Here, we generalize this result to the case of a slowly varying temperature. To do this, we make use of the Boussinesq approximation. A comparison between the hydrodynamic and magnetohydrodynamic cases allows us to deduce the effects due to a magnetic field. It is shown that the frequency of IGWs may depart significantly from the Brunt–Väisälä frequency, even for a weak magnetic field. The mathematical techniques applied here give a clearer picture of the wave mode identification, which has previously been misinterpreted. An observational test is urged to validate the theoretical findings.

The Coronal Multi-channel Polarimeter (CoMP) has previously demonstrated the presence of Doppler velocity fluctuations in the solar corona. The observed fluctuations are thought to be transverse waves, i.e., highly incompressible motions whose restoring force is dominated by the magnetic tension, some of which demonstrate clear periodicity. We aim to exploit CoMP's ability to provide high cadence observations of the off-limb corona to investigate the properties of velocity fluctuations in a range of coronal features, providing insight into how (whether) the properties of the waves are influenced by the varying magnetic topology in active regions, quiet Sun and open field regions. An analysis of Doppler velocity time-series of the solar corona from the 10747 Å Iron xiii line is performed, determining the velocity power spectrum and using it as a tool to probe wave behavior. Further, the average phase speed and density for each region are estimated and used to compute the spectra for energy density and energy flux. In addition, we assess the noise levels associated with the CoMP data, deriving analytic formulae for the uncertainty on Doppler velocity measurements and providing a comparison by estimating the noise from the data. It is found that the entire corona is replete with transverse wave behavior. The corresponding power spectra indicate that the observed velocity fluctuations are predominately generated by stochastic processes, with the spectral slope of the power varying between the different magnetic regions. Most strikingly, all power spectra reveal the presence of enhanced power occurring at ∼3 mHz, potentially implying that the excitation of coronal transverse waves by p-modes is a global phenomenon.

We introduce a new project to understand helium reionization using fully coupled N-body, hydrodynamics, and radiative transfer simulations. This project aims to capture correctly the thermal history of the intergalactic medium as a result of reionization and make predictions about the Lyα forest and baryon temperature–density relation. The dominant sources of radiation for this transition are quasars, so modeling the source population accurately is very important for making reliable predictions. In this first paper, we present a new method for populating dark matter halos with quasars. Our set of quasar models includes two different light curves, a lightbulb (simple on/off) and symmetric exponential model, and luminosity-dependent quasar lifetimes. Our method self-consistently reproduces an input quasar luminosity function given a halo catalog from an N-body simulation, and propagates quasars through the merger history of halo hosts. After calibrating quasar clustering using measurements from the Baryon Oscillation Spectroscopic Survey, we find that the characteristic mass of quasar hosts is ${M}_{h}\sim 2.5\times {10}^{12}\ {h}^{-1}\,{M}_{\odot }$ for the lightbulb model, and ${M}_{h}\sim 2.3\times {10}^{12}\ {h}^{-1}\,{M}_{\odot }$ for the exponential model. In the latter model, the peak quasar luminosity for a given halo mass is larger than that in the former, typically by a factor of 1.5–2. The effective lifetime for quasars in the lightbulb model is 59 Myr, and in the exponential case, the effective time constant is about 15 Myr. We include semi-analytic calculations of helium reionization, and discuss how to include these quasars as sources of ionizing radiation for full hydrodynamics with radiative transfer simulations in order to study helium reionization.

We implement an Ensemble Kalman Filter procedure using the Data Assimilation Research Testbed for assimilating "synthetic" meridional flow-speed data in a Babcock–Leighton-type flux-transport solar dynamo model. By performing several "observing system simulation experiments," we reconstruct time variation in meridional flow speed and analyze sensitivity and robustness of reconstruction. Using 192 ensemble members including 10 observations, each with 4% error, we find that flow speed is reconstructed best if observations of near-surface poloidal fields from low latitudes and tachocline toroidal fields from midlatitudes are assimilated. If observations include a mixture of poloidal and toroidal fields from different latitude locations, reconstruction is reasonably good for $\leqslant 40 \%$ error in low-latitude data, even if observational error in polar region data becomes 200%, but deteriorates when observational error increases in low- and midlatitude data. Solar polar region observations are known to contain larger errors than those in low latitudes; our forward operator (a flux-transport dynamo model here) can sustain larger errors in polar region data, but is more sensitive to errors in low-latitude data. An optimal reconstruction is obtained if an assimilation interval of 15 days is used; 10- and 20-day assimilation intervals also give reasonably good results. Assimilation intervals $\lt 5$ days do not produce faithful reconstructions of flow speed, because the system requires a minimum time to develop dynamics to respond to flow variations. Reconstruction also deteriorates if an assimilation interval $\gt 45$ days is used, because the system's inherent memory interferes with its short-term dynamics during a substantially long run without updating.

Many powerful and variable gamma-ray sources, including pulsar wind nebulae, active galactic nuclei and gamma-ray bursts, seem capable of accelerating particles to gamma-ray emitting energies efficiently over very short timescales. These are likely due to the rapid dissipation of electromagnetic energy in a highly magnetized, relativistic plasma. In order to understand the generic features of such processes, we have investigated simple models based on the relaxation of unstable force-free magnetostatic equilibria. In this work, we make the connection between the corresponding plasma dynamics and the expected radiation signal, using 2D particle-in-cell simulations that self-consistently include synchrotron radiation reactions. We focus on the lowest order unstable force-free equilibrium in a 2D periodic box. We find that rapid variability, with modest apparent radiation efficiency as perceived by a fixed observer, can be produced during the evolution of the instability. The "flares" are accompanied by an increased polarization degree in the high energy band, with rapid variation in the polarization angle. Furthermore, the separation between the acceleration sites and the synchrotron radiation sites for the highest energy particles facilitates acceleration beyond the synchrotron radiation reaction limit. We also discuss the dynamical consequences of the radiation reaction, and some astrophysical applications of this model. Our current simulations with numerically tractable parameters are not yet able to reproduce the most dramatic gamma-ray flares, e.g., from the Crab Nebula. Higher magnetization studies are promising and will be carried out in the future.

We report experimental results on Kelvin–Helmholtz (KH) instability and resultant vortices in laser-produced plasmas. By irradiating a double plane target with a laser beam, asymmetric counterstreaming plasmas are created. The interaction of the plasmas with different velocities and densities results in the formation of asymmetric shocks, where the shear flow exists along the contact surface and the KH instability is excited. We observe the spatial and temporal evolution of plasmas and shocks with time-resolved diagnostics over several shots. Our results clearly show the evolution of transverse fluctuations, wavelike structures, and circular features, which are interpreted as the KH instability and resultant vortices. The relevant numerical simulations demonstrate the time evolution of KH vortices and show qualitative agreement with experimental results. Shocks, and thus the contact surfaces, are ubiquitous in the universe; our experimental results show general consequences where two plasmas interact.

The recent discovery of the unprecedentedly super-luminous transient ASASSN-15lh (or SN 2015L) with its UV-bright secondary peak challenges all the power-input models that have been proposed for super-luminous supernovae. Here we examine some of the few viable interpretations of ASASSN-15lh in the context of a stellar explosion, involving combinations of one or more power inputs. We model the light curve of ASASSN-15lh with a hybrid model that includes contributions from magnetar spin-down energy and hydrogen-poor circumstellar interaction. We also investigate models of pure circumstellar interaction with a massive hydrogen-deficient shell and discuss the lack of interaction features in the observed spectra. We find that, as a supernova, ASASSN-15lh can be best modeled by the energetic core-collapse of an ∼40 M_⊙ star interacting with a hydrogen-poor shell of ∼20 M_⊙. The circumstellar shell and progenitor mass are consistent with a rapidly rotating pulsational pair-instability supernova progenitor as required for strong interaction following the final supernova explosion. Additional energy injection by a magnetar with an initial period of 1–2 ms and magnetic field of 0.1–1 × 10¹⁴ G may supply the excess luminosity required to overcome the deficit in single-component models, but this requires more fine-tuning and extreme parameters for the magnetar, as well as the assumption of efficient conversion of magnetar energy into radiation. We thus favor a single-input model where the reverse shock formed in a strong SN ejecta–circumstellar matter interaction following a very powerful core-collapse SN explosion can supply the luminosity needed to reproduce the late-time UV-bright plateau.

We present near-infrared (NIR) synthetic spectra based on PHOENIX stellar atmosphere models of typical early and mid-M dwarfs with varied C and O abundances. We apply multiple recently published methods for determining M dwarf metallicity to our models to determine the effects of C and O abundances on metallicity indicators. We find that the pseudo-continuum level is very sensitive to C/O and that all metallicity indicators show a dependence on C and O abundances, especially in lower T_eff models. In some cases, the inferred metallicity ranges over a full order of magnitude (>1 dex) when [C/Fe] and [O/Fe] are varied independently by ±0.2. We also find that [(O−C)/Fe], the difference in O and C abundances, is a better tracer of the pseudo-continuum level than C/O. Models of mid-M dwarfs with [C/Fe], [O/Fe], and [M/H] that are realistic in the context of galactic chemical evolution suggest that variation in [(O−C)/Fe] is the primary physical mechanism behind the M dwarf metallicity tracers investigated here. Empirically calibrated metallicity indicators are still valid for most nearby M dwarfs due to the tight correlation between [(O−C)/Fe] and [Fe/H] evident in spectroscopic surveys of solar neighborhood FGK stars. Variations in C and O abundances also affect the spectral energy distribution of M dwarfs. Allowing [O/Fe] to be a free parameter provides better agreement between the synthetic spectra and observed spectra of metal-rich M dwarfs. We suggest that flux-calibrated, low-resolution, NIR spectra can provide a path toward measuring C and O abundances in M dwarfs and breaking the degeneracy between C/O and [Fe/H] present in M dwarf metallicity indicators.

We build a simple physical model to study the high-redshift active galactic nucleus (AGN) evolution within the co-evolution framework of central black holes (BHs) and their host galaxies. The correlation between the circular velocity of a dark halo V_c and the velocity dispersion of a galaxy σ is used to link the dark matter halo mass and BH mass. The dark matter halo mass function is converted to the BH mass function for any given redshift. The high-redshift optical AGN luminosity functions (LFs) are constructed. At $z\sim 4$, the flattening feature is not shown at the faint end of the optical AGN LF. This is consistent with observational results. If the optical AGN LF at $z\sim 6$ can be reproduced in the case in which central BHs have the Eddington-limited accretion, it is possible for the AGN lifetime to have a small value of $2\times {10}^{5}\,{\rm{years}}$. The X-ray AGN LFs and X-ray AGN number counts are also calculated at $2.0\lt z\lt 5.0$ and $z\gt 3$, respectively, using the same parameters adopted in the calculation for the optical AGN LF at $z\sim 4$. It is estimated that about 30 AGNs per ${{\rm{\deg }}}^{2}$ at $z\gt 6$ can be detected with a flux limit of $3\times {10}^{-17}\,\mathrm{erg}\,{\mathrm{cm}}^{-2}\,{{\rm{s}}}^{-1}$ in the 0.5–2 keV band. Additionally, the cosmic reionization is also investigated. The ultraviolet photons emitted from the high-redshift AGNs mainly contribute to the cosmic reionization, and the central BHs of the high-redshift AGNs have a mass range of ${10}^{6}\mbox{--}{10}^{8}{M}_{\odot }$. We also discuss some uncertainties in both the AGN LFs and AGN number counts originating from the ${M}_{{\rm{BH}}}\mbox{--}\sigma$ relation, Eddington ratio, AGN lifetime, and X-ray attenuation in our model.

We present 3D models of biconical outflows combined with a thin dust plane for investigating the physical properties of the ionized gas outflows and their effect on the observed gas kinematics in type 2 active galactic nuclei (AGNs). Using a set of input parameters, we construct a number of models in 3D and calculate the spatially integrated velocity and velocity dispersion for each model. We find that three primary parameters, i.e., intrinsic velocity, bicone inclination, and the amount of dust extinction, mainly determine the simulated velocity and velocity dispersion. Velocity dispersion increases as the intrinsic velocity or the bicone inclination increases, while velocity (i.e., velocity shifts with respect to systemic velocity) increases as the amount of dust extinction increases. Simulated emission-line profiles well reproduce the observed [O iii] line profiles, e.g., narrow core and broad wing components. By comparing model grids and Monte Carlo simulations with the observed [O iii] velocity–velocity dispersion distribution of ∼39,000 type 2 AGNs, we constrain the intrinsic velocity of gas outflows ranging from ∼500 to ∼1000 km s⁻¹ for the majority of AGNs, and up to ∼1500–2000 km s⁻¹ for extreme cases. The Monte Carlo simulations show that the number ratio of AGNs with negative [O iii] velocity to AGNs with positive [O iii] velocity correlates with the outflow opening angle, suggesting that outflows with higher intrinsic velocity tend to have wider opening angles. These results demonstrate the potential of our 3D models for studying the physical properties of gas outflows, applicable to various observations, including spatially integrated and resolved gas kinematics.

The Seyfert 1 galaxy Ark 120 is a prototype example of the so-called class of bare nucleus active galactic nuclei (AGNs), whereby there is no known evidence for the presence of ionized gas along the direct line of sight. Here deep (>400 ks exposure), high-resolution X-ray spectroscopy of Ark 120 is presented from XMM-Newton observations that were carried out in 2014 March, together with simultaneous Chandra/High Energy Transmission Grating exposures. The high-resolution spectra confirmed the lack of intrinsic absorbing gas associated with Ark 120, with the only X-ray absorption present originating from the interstellar medium (ISM) of our own Galaxy, with a possible slight enhancement of the oxygen abundance required with respect to the expected ISM values in the solar neighborhood. However, the presence of several soft X-ray emission lines are revealed for the first time in the XMM-Newton RGS spectrum, associated with the AGN and arising from the He- and H-like ions of N, O, Ne, and Mg. The He-like line profiles of N, O, and Ne appear velocity broadened, with typical FWHMs of ∼5000 km s⁻¹, whereas the H-like profiles are unresolved. From the clean measurement of the He-like triplets, we deduce that the broad lines arise from a gas of density n_e ∼ 10¹¹ cm⁻³, while the photoionization calculations infer that the emitting gas covers at least 10% of 4π steradian. Thus the broad soft X-ray profiles appear coincident with an X-ray component of the optical–UV broad-line region on sub-parsec scales, whereas the narrow profiles originate on larger parsec scales, perhaps coincident with the AGN narrow-line region. The observations show that Ark 120 is not intrinsically bare and substantial X-ray-emitting gas exists out of our direct line of sight toward this AGN.

With each new version of the Kepler pipeline and resulting planet candidate catalog, an updated measurement of the underlying planet population can only be recovered with a corresponding measurement of the Kepler pipeline detection efficiency. Here we present measurements of the sensitivity of the pipeline (version 9.2) used to generate the Q1–Q17 DR24 planet candidate catalog. We measure this by injecting simulated transiting planets into the pixel-level data of 159,013 targets across the entire Kepler focal plane, and examining the recovery rate. Unlike previous versions of the Kepler pipeline, we find a strong period dependence in the measured detection efficiency, with longer (>40 day) periods having a significantly lower detectability than shorter periods, introduced in part by an incorrectly implemented veto. Consequently, the sensitivity of the 9.2 pipeline cannot be cast as a simple one-dimensional function of the signal strength of the candidate planet signal, as was possible for previous versions of the pipeline. We report on the implications for occurrence rate calculations based on the Q1–Q17 DR24 planet candidate catalog, and offer important caveats and recommendations for performing such calculations. As before, we make available the entire table of injected planet parameters and whether they were recovered by the pipeline, enabling readers to derive the pipeline detection sensitivity in the planet and/or stellar parameter space of their choice.

We present observations toward a high-mass ($\gt 40\,{M}_{\odot }$), low-luminosity ($\lt 10\,{L}_{\odot }$) $70\,\mu {\rm{m}}$ dark molecular core G28.34 S-A at 3.4 mm, using the IRAM 30 m telescope and the NOEMA interferometer. We report the detection of $\mathrm{SiO}$$J=2\to 1$ line emission, which is spatially resolved in this source at a linear resolution of ∼0.1 pc, while the 3.4 mm continuum image does not resolve any internal sub-structures. The SiO emission exhibits two W–E oriented lobes centering on the continuum peak. Corresponding to the redshifted and blueshifted gas with velocities up to $40\,\mathrm{km}\,{{\rm{s}}}^{-1}$ relative to the quiescent cloud, these lobes clearly indicate the presence of a strong bipolar outflow from this $70\,\mu {\rm{m}}$ dark core, a source previously considered as one of the best candidates of "starless" core. Our SiO detection is consistent with ALMA archival data of $\mathrm{SiO}$$J=5\to 4$, whose high-velocity blueshifted gas reveals a more compact lobe spatially closer to the dust center. This outflow indicates that the central source may be in an early evolutionary stage of forming a high-mass protostar. We also find that the low-velocity components (in the range of ${\mathrm{Vlsr}}_{-5}^{+3}\,\mathrm{km}\,{{\rm{s}}}^{-1}$) have an extended, NW–SE oriented distribution. Discussing the possible accretion scenarios of the outflow-powering young stellar object, we argue that molecular line emission and the molecular outflows may provide a better indication of the accretion history of the forming young stellar object, than snapshot observations of the present bolometric luminosity. This is particularly significant for cases of episodic accretion, which may occur during the collapse of the parent molecular core.

In the propagating oscillatory shock model, the oscillation of the post-shock region, i.e., the Compton cloud, causes the observed low-frequency quasi-periodic oscillations (QPOs). The evolution of QPO frequency is explained by the systematic variation of the Compton cloud size, i.e., the steady radial movement of the shock front, which is triggered by the cooling of the post-shock region. Thus, analysis of the energy-dependent temporal properties in different variability timescales can diagnose the dynamics and geometry of accretion flows around black holes. We study these properties for the high-inclination black hole source XTE J1550-564 during its 1998 outburst and the low-inclination black hole source GX 339-4 during its 2006–07 outburst using RXTE/PCA data, and we find that they can satisfactorily explain the time lags associated with the QPOs from these systems. We find a smooth decrease of the time lag as a function of time in the rising phase of both sources. In the declining phase, the time lag increases with time. We find a systematic evolution of QPO frequency and hard lags in these outbursts. In XTE J1550-564, the lag changes from hard to soft (i.e., from a positive to a negative value) at a crossing frequency (ν_c) of ∼3.4 Hz. We present possible mechanisms to explain the lag behavior of high and low-inclination sources within the framework of a single two-component advective flow model.

The proposed Carrington-L5 mission would bring instruments to the L5 Lagrange point to provide us with crucial data for space weather prediction. To assess the importance of including a magnetograph, we consider the possible differences in non-potential solar coronal magnetic field simulations when magnetograph observations are available from the L5 point, compared with an L1-based field of view (FOV). A timeseries of synoptic radial magnetic field maps is constructed to capture the emergence of two active regions from the L5 FOV. These regions are initially absent in the L1 magnetic field maps, but are included once they rotate into the L1 FOV. Non-potential simulations for these two sets of input data are compared in detail. Within the bipolar active regions themselves, differences in the magnetic field structure can exist between the two simulations once the active regions are included in both. These differences tend to reduce within 5 days of the active region being included in L1. The delayed emergence in L1 can, however, lead to significant persistent differences in long-range connectivity between the active regions and the surrounding fields, and also in the global magnetic energy. In particular, the open magnetic flux and the location of open magnetic footpoints, are sensitive to capturing the real-time of emergence. These results suggest that a magnetograph at L5 could significantly improve predictions of the non-potential corona, the interplanetary magnetic field, and of solar wind source regions on the Sun.

We report a strong association between the particle acceleration and plasma motions found in the 2010 August 18 solar flare. The plasma motions are tracked in the extreme ultraviolet (EUV) images taken by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory and the Extreme UltraViolet Imager (EUVI) on the Solar Terrestrial Relations Observatory spacecraft Ahead, and the signature of particle acceleration was investigated by using Nobeyama Radioheliograph data. In our previous paper, we reported that in EUV images many plasma blobs appeared in the current sheet above the flare arcade. They were ejected bidirectionally along the current sheet, and the blobs that were ejected sunward collided with the flare arcade. Some of them collided or merged with each other before they were ejected from the current sheet. We discovered impulsive radio bursts associated with such plasma motions (ejection, coalescence, and collision with the post flare loops). The radio bursts are considered to be the gyrosynchrotron radiation by nonthermal high energy electrons. In addition, the stereoscopic observation by AIA and EUVI suggests that plasma blobs had a three-dimensionally elongated structure. We consider that the plasma blobs were three-dimensional plasmoids (i.e., flux ropes) moving in a current sheet. We believe that our observation provides clear evidence of particle acceleration associated with the plasmoid motions. We discuss possible acceleration mechanisms on the basis of our results.

We study 50 cosmic-ray Forbush decreases (FDs) from the Oulu neutron monitor data during 1997–2005 that were associated with Earth-directed interplanetary coronal mass ejections (ICMEs). Such events are generally thought to arise due to the shielding of cosmic rays by a propagating diffusive barrier. The main processes at work are the diffusion of cosmic rays across the large-scale magnetic fields carried by the ICME and their advection by the solar wind. In an attempt to better understand the relative importance of these effects, we analyze the relationship between the FD profiles and those of the interplanetary magnetic field (B) and the solar wind speed (V_sw). Over the entire duration of a given FD, we find that the FD profile is generally  (anti)correlated with the B and V_sw profiles. This trend holds separately for the FD main and recovery phases too. For the recovery phases, however, the FD profile is highly anti-correlated with the V_sw profile, but not with the B profile. While the total duration of the FD profile is similar to that of the V_sw profile, it is significantly longer than that of the B profile. Using the convection–diffusion model, a significant contribution of advection by solar wind is found during the recovery phases of the FD.

We study the X-ray and optical properties of the ultraluminous X-ray source (ULX) X-6 in the nearby galaxy NGC 4258 (M106) based on the archival XMM-Newton, Chandra, Swift, and Hubble Space Telescope (HST) observations. The source has a peak luminosity of L_X ∼ 2 × 10³⁹ erg s⁻¹ in the XMM-Newton observation of 2004 June. Consideration of the hardness ratios and the spectral model parameters shows that the source seems to exhibit possible spectral variations throughout the X-ray observations. In the images from the HST/Advanced Camera for Surveys, three optical sources have been identified as counterpart candidates within the 1σ error radius of 03. The brightest one has an absolute magnitude of M_V ≈ −7.0 and shows extended structure. The remaining two sources have absolute magnitudes of M_V ≈ −5.8 and −5.3. The possible spectral types of the candidates from brightest to dimmest were determined as B6–A5, B0–A7, and B2–A3. The counterparts of the X-ray source possibly belong to a young star cluster. Neither the standard disk model nor the slim disk model provides firm evidence to determine the spectral characteristics of ULX X-6. We argue that the mass of the compact object lies in the range 10–15 M_☉, indicating that the compact source is most likely a stellar-mass black hole.

We fit ∼0.1–500 MeV nucleon⁻¹ H–Fe spectra in 46 large solar energetic particle (SEP) events with the double power-law Band function to obtain a normalization constant, low- and high-energy parameters γ_a and γ_b, and break energy E_B, and derive the low-energy spectral slope γ₁. We find that: (1) γ_a, γ₁, and γ_b are species-independent and the spectra steepen with increasing energy; (2) E_B decreases systematically with decreasing Q/M scaling as (Q/M)^α; (3) α varies between ∼0.2–3 and is well correlated with the ∼0.16–0.23 MeV nucleon⁻¹ Fe/O; (4) in most events, α < 1.4, γ_b–γ_a > 3, and O E_B increases with γ_b–γ_a; and (5) in many extreme events (associated with faster coronal mass ejections (CMEs) and GLEs), Fe/O and ³He/⁴He ratios are enriched, α ≥ 1.4, γ_b–γ_a < 3, and E_B decreases with γ_b–γ_a. The species-independence of γ_a, γ₁, and γ_b and the Q/M dependence of E_B within an event and the α values suggest that double power-law SEP spectra occur due to diffusive acceleration by near-Sun CME shocks rather than scattering in interplanetary turbulence. Using γ₁, we infer that the average compression ratio for 33 near-Sun CME shocks is 2.49 ± 0.08. In most events, the Q/M dependence of E_B is consistent with the equal diffusion coefficient condition and the variability in α is driven by differences in the near-shock wave intensity spectra, which are flatter than the Kolmogorov turbulence spectrum but weaker than the spectra for extreme events. In contrast, in extreme events, enhanced wave power enables faster CME shocks to accelerate impulsive suprathermal ions more efficiently than ambient coronal ions.

We present the first spectroscopic measurements of the shape of the far-ultraviolet (far-UV; $\lambda =950\mbox{--}1500$ Å) dust attenuation curve at high redshift ($z\sim 3$). Our analysis employs rest-frame UV spectra of 933 galaxies at $z\sim 3$, 121 of which have very deep spectroscopic observations ($\gtrsim 7$ hr) at $\lambda =850\mbox{--}1300\,\mathring{\rm{A}}$, with the Low Resolution Imaging Spectrograph on the Keck Telescope. By using an iterative approach in which we calculate the ratios of composite spectra in different bins of continuum color excess, $E(B-V)$, we derive a dust curve that implies a lower attenuation in the far-UV for a given $E(B-V)$ than those obtained with standard attenuation curves. We demonstrate that the UV composite spectra of $z\sim 3$ galaxies can be modeled well by assuming our new attenuation curve, a high covering fraction of H i, and absorption from the Lyman–Werner bands of ${{\rm{H}}}_{2}$ with a small ($\lesssim 20 \%$) covering fraction. The low covering fraction of ${{\rm{H}}}_{2}$ relative to that of the ${\rm{H}}\,{\rm{I}}$ and dust suggests that most of the dust in the ISM of typical galaxies at $z\sim 3$ is unrelated to the catalysis of ${{\rm{H}}}_{2}$, and is associated with other phases of the ISM (i.e., the ionized and neutral gas). The far-UV dust curve implies a factor of $\approx 2$ lower dust attenuation of Lyman continuum (ionizing) photons relative to those inferred from the most commonly assumed attenuation curves for L* galaxies at $z\sim 3$. Our results may be utilized to assess the degree to which ionizing photons are attenuated in H ii regions or, more generally, in the ionized or low column density ($N({\rm{H}}\,{\rm{I}})\lesssim {10}^{17.2}$ cm⁻²) neutral ISM of high-redshift galaxies.

Using a large sample of spectroscopically confirmed $z\sim 3$ galaxies, we establish an empirical relationship between reddening ($E(B-V)$), neutral gas covering fraction (${f}_{{\rm{cov}}}({\rm{H}}\,{\rm{I}})$), and the escape of ionizing (Lyman continuum, LyC) photons. Our sample includes 933 galaxies at $z\sim 3,121$ of which have deep spectroscopic observations ($\gtrsim 7$ hr) at $850\lesssim {\lambda }_{{\rm{rest}}}\lesssim 1300$ Å with the Low Resolution Imaging Spectrograph on Keck. The high covering fraction of outflowing optically thick ${\rm{H}}\,{\rm{I}}$ indicated by the composite spectra of these galaxies implies that photoelectric absorption, rather than dust attenuation, dominates the depletion of LyC photons. By modeling the composite spectra as the combination of an unattenuated stellar spectrum including nebular continuum emission with one that is absorbed by ${\rm{H}}\,{\rm{I}}$ and reddened by a line-of-sight extinction, we derive an empirical relationship between $E(B-V)$ and ${f}_{{\rm{cov}}}({\rm{H}}\,{\rm{I}})$. Galaxies with redder UV continua have larger covering fractions of ${\rm{H}}\,{\rm{I}}$ characterized by higher line-of-sight extinctions. We develop a model which connects the ionizing escape fraction with $E(B-V)$, and which may be used to estimate the ionizing escape fraction for an ensemble of galaxies. Alternatively, direct measurements of the escape fraction for our sample allow us to constrain the intrinsic LyC-to-UV flux density ratio to be $\langle S(900\,\mathring{\rm{A}} )/S(1500\,\mathring{\rm{A}} ){\rangle }_{{\rm{int}}}\gtrsim 0.20$, a value that favors stellar population models that include weaker stellar winds, a flatter initial mass function, and/or binary evolution. Last, we demonstrate how the framework discussed here may be used to assess the pathways by which ionizing radiation escapes from high-redshift galaxies.

The origin of Phobos and Deimos is still an open question. Currently, none of the three proposed scenarios for their origin (intact capture of two distinct outer solar system small bodies, co-accretion with Mars, and accretion within an impact-generated disk) are able to reconcile their orbital and physical properties. Here we investigate the expected mineralogical composition and size of the grains from which the moons once accreted assuming they formed within an impact-generated accretion disk. A comparison of our results with the present-day spectral properties of the moons allows us to conclude that their building blocks cannot originate from a magma phase, thus preventing their formation in the innermost part of the disk. Instead, gas-to-solid condensation of the building blocks in the outer part of an extended gaseous disk is found as a possible formation mechanism as it does allow reproducing both the spectral and physical properties of the moons. Such a scenario may finally reconcile their orbital and physical properties, alleviating the need to invoke an unlikely capture scenario to explain their physical properties.

The largest observed supermassive black holes (SMBHs) have a mass of ${M}_{{\rm{BH}}}\simeq {10}^{10}\,{\text{}}{M}_{\odot }$, nearly independent of redshift, from the local ($z\simeq 0$) to the early ($z\gt 6$) universe. We suggest that the growth of SMBHs above a few $\times {10}^{10}\,{\text{}}{M}_{\odot }$ is prevented by small-scale accretion physics, independent of the properties of their host galaxies or of cosmology. Growing more massive BHs requires a gas supply rate from galactic scales onto a nuclear region as high as $\gtrsim {10}^{3}\,{M}_{\odot }\,{{\rm{yr}}}^{-1}$. At such a high accretion rate, most of the gas converts to stars at large radii (∼10–100 pc), well before reaching the BH. We adopt a simple model for a star-forming accretion disk and find that the accretion rate in the subparsec nuclear region is reduced to the smaller value of at most a few $\times \,{M}_{\odot }\,{{\rm{yr}}}^{-1}$. This prevents SMBHs from growing above $\simeq {10}^{11}\,{\text{}}{M}_{\odot }$ in the age of the universe. Furthermore, once an SMBH reaches a sufficiently high mass, this rate falls below the critical value at which the accretion flow becomes advection dominated. Once this transition occurs, BH feeding can be suppressed by strong outflows and jets from hot gas near the BH. We find that the maximum SMBH mass, given by this transition, is between ${M}_{{\rm{BH,max}}}\simeq (1\mbox{--}6)\times {10}^{10}\,{\text{}}{M}_{\odot }$, depending primarily on the efficiency of angular momentum transfer inside the galactic disk, and not on other properties of the host galaxy.

As new facilities come online, the astronomical community will be provided with extremely large data sets of well-sampled light curves (LCs) of transients. This motivates systematic studies of the LCs of supernovae (SNe) of all types, including the early rising phase. We performed unsupervised k-means clustering on a sample of 59 R-band SN II LCs and find that the rise to peak plays an important role in classifying LCs. Our sample can be divided into three classes: slowly rising (II-S), fast rise/slow decline (II-FS), and fast rise/fast decline (II-FF). We also identify three outliers based on the algorithm. The II-FF and II-FS classes are disjoint in their decline rates, while the II-S class is intermediate and "bridges the gap." This may explain recent conflicting results regarding II-P/II-L populations. The II-FS class is also significantly less luminous than the other two classes. Performing clustering on the first two principal component analysis components gives equivalent results to using the full LC morphologies. This indicates that Type II LCs could possibly be reduced to two parameters. We present several important caveats to the technique, and find that the division into these classes is not fully robust. Moreover, these classes have some overlap, and are defined in the R band only. It is currently unclear if they represent distinct physical classes, and more data is needed to study these issues. However, we show that the outliers are actually composed of slowly evolving SN IIb, demonstrating the potential of such methods. The slowly evolving SNe IIb may arise from single massive progenitors.

We investigate how accurately the total mass of neutrinos is constrained from the magnitude dispersion of SNe Ia due to the effects of gravitational lensing. For this purpose, we use the propagation equation of light bundles in a realistic inhomogeneous universe and propose a sample selection for supernovae to avoid difficulties associated with small-scale effects such as strong lensing or shear effects. With a fitting formula for the nonlinear matter power spectrum taking account of the effects of massive neutrinos, we find that in our model it is possible to obtain the upper limit ${\rm{\Sigma }}{m}_{\nu }\simeq 1.0[{\rm{eV}}]$ for future optical imaging surveys with the Wide-Field InfraRed Survey Telescope and Large Synoptic Survey Telescope. Furthermore, we discuss how far we need to observe SNe Ia and to what extent we have to reduce the magnitude error except for lensing in order to realize the current tightest limit ${\rm{\Sigma }}{m}_{\nu }\lt 0.2[{\rm{eV}}]$.

We present 1.3 mm observations of the Sun-like star τ Ceti with the Atacama Large Millimeter/submillimeter Array that probe angular scales of $\sim 1^{\prime\prime}$ (4 au). This first interferometric image of the τ Ceti system, which hosts both a debris disk and a possible multiplanet system, shows emission from a nearly face-on belt of cold dust with a position angle of $90^\circ$ surrounding an unresolved central source at the stellar position. To characterize this emission structure, we fit parametric models to the millimeter visibilities. The resulting best-fit model yields an inner belt edge of ${6.2}_{-4.6}^{+9.8}$ au, consistent with inferences from lower resolution, far-infrared Herschel observations. While the limited data at sufficiently short baselines preclude us from placing stronger constraints on the belt properties and its relation to the proposed five planet system, the observations do provide a strong lower limit on the fractional width of the belt, ${\rm{\Delta }}R/R\gt 0.75$ with 99% confidence. This fractional width is more similar to broad disks such as HD 107146 than narrow belts such as the Kuiper Belt and Fomalhaut. The unresolved central source has a higher flux density than the predicted flux of the stellar photosphere at 1.3 mm. Given previous measurements of an excess by a factor of ∼2 at 8.7 mm, this emission is likely due to a hot stellar chromosphere.