Table of contents for issue 1, volume 791, The Astrophysical Journal

Extremely large deuteration of several molecules has been observed toward prestellar cores and low-mass protostars for a decade. New observations performed toward low-mass protostars suggest that water presents a lower deuteration in the warm inner gas than in the cold external envelope. We coupled a gas–grain astrochemical model with a one-dimensional model of a collapsing core to properly follow the formation and the deuteration of interstellar ices as well as their subsequent evaporation in the low-mass protostellar envelopes with the aim of interpreting the spatial and temporal evolutions of their deuteration. The astrochemical model follows the formation and the evaporation of ices with a multilayer approach and also includes a state-of-the-art deuterated chemical network by taking the spin states of H₂ and light ions into account. Because of their slow formation, interstellar ices are chemically heterogeneous and show an increase of their deuterium fractionation toward the surface. The differentiation of the deuteration in ices induces an evolution of the deuteration within protostellar envelopes. The warm inner region is poorly deuterated because it includes the whole molecular content of ices, while the deuteration predicted in the cold external envelope scales with the highly deuterated surface of ices. We are able to reproduce the observed evolution of water deuteration within protostellar envelopes, but we are still unable to predict the super-high deuteration observed for formaldehyde and methanol. Finally, the extension of this study to the deuteration of complex organics, important for the prebiotic chemistry, shows good agreement with the observations, suggesting that we can use the deuteration to retrace their mechanisms and their moments of formation.

Recently, Nyland et al. argued that the radio emission observed in the center of the dwarf galaxy NGC 404 originates in a low-luminosity active galactic nucleus powered by a massive black hole (MBH, M ≲ 10⁶ M_☉). High-resolution radio detections of MBHs are rare. Here we present sensitive, contemporaneous Chandra X-ray, and very long baseline interferometry (VLBI) radio observations with the European VLBI Network. The source is detected in the X-rays, and shows no long-term variability. If the hard X-ray source is powered by accretion, the apparent low accretion efficiency would be consistent with a black hole (BH) in the hard state. Hard state BHs are known to show radio emission compact on the milliarcsecond scales. However, the central region of NGC 404 is resolved out on 10 mas (0.15–1.5 pc) scales. Our VLBI non-detection of a compact, partially self-absorbed radio core in NGC 404 implies that either the BH mass is smaller than  M_☉, or the source does not follow the fundamental plane of BH activity relation. An alternative explanation is that the central BH is not in the hard state. The radio emission observed on arcsecond (tens of parsecs) scales may originate in nuclear star formation or extended emission due to AGN activity, although the latter would not be typical considering the structural properties of low-ionization nuclear emission-line region galaxies with confirmed nuclear activity.

We present the results from a Very Large Telescope/SINFONI and Keck/NIRSPEC near-infrared spectroscopic survey of 16 Lyα emitters (LAEs) at z = 2.1–2.5 in the COSMOS and GOODS-N fields discovered from the Hobby Eberly Telescope Dark Energy Experiment Pilot Survey. We detect rest-frame optical nebular lines (Hα and/or [O iii] λ5007) for 10 of the LAEs and measure physical properties, including the star formation rate (SFR), gas-phase metallicity, gas mass fraction, and Lyα velocity offset. We find that LAEs may lie below the mass–metallicity relation for continuum-selected star-forming galaxies at the same redshift. The LAEs all show velocity shifts of Lyα relative to the systemic redshift ranging between +85 and +296 km s⁻¹ with a mean of +180 km s⁻¹. This value is smaller than measured for continuum-selected star-forming galaxies at similar redshifts. The Lyα velocity offsets show a moderate correlation with the measured SFR (2.5σ), but no significant correlations are seen with the SFR surface density, specific SFR, stellar mass, or dynamical mass (≲1.5σ). Exploring the role of dust, kinematics of the interstellar medium (ISM), and geometry on the escape of Lyα photons, we find no signature of selective quenching of resonantly scattered Lyα photons. However, we also find no evidence that a clumpy ISM is enhancing the Lyα equivalent width. Our results suggest that the low metallicity in LAEs may be responsible for yielding an environment with a low neutral hydrogen column density and less dust, easing the escape of Lyα photons over that in continuum-selected star-forming galaxies.

We examine statistically some properties of 96 20 MeV gradual solar energetic proton (SEP) events as a function of three different types of solar wind (SW) as classified by Richardson and Cane. Gradual SEP (E > 10 MeV) events are produced in shocks driven by fast (V ≳ 900 km s⁻¹) and wide (W > 60°) coronal mass ejections (CMEs). We find no differences among the transient, fast, and slow SW streams for SEP 20 MeV proton event timescales. It has recently been found that the peak intensities Ip of these SEP events scale with the ∼2 MeV proton background intensities, which may be a proxy for the near-Sun shock seed particles. Both the intensities Ip and their 2 MeV backgrounds are significantly enhanced in transient SW compared to those of fast and slow SW streams, and the values of Ip normalized to the 2 MeV backgrounds only weakly correlate with CME V for all SW types. This result implies that forecasts of SEP events could be improved by monitoring both the Sun and the local SW stream properties and that the well known power-law size distributions of Ip may differ between transient and long-lived SW streams. We interpret an observed correlation between CME V and the 2 MeV background for SEP events in transient SW as a manifestation of enhanced solar activity.

The tilt angles of sunspot groups represent the poloidal field source in Babcock–Leighton-type models of the solar dynamo and are crucial for the build-up and reversals of the polar fields in surface flux transport (SFT) simulations. The evolution of the polar field is a consequence of Hale's polarity rules, together with the tilt angle distribution which has a systematic component (Joy's law) and a random component (tilt-angle scatter). We determine the scatter using the observed tilt angle data and study the effects of this scatter on the evolution of the solar surface field using SFT simulations with flux input based upon the recorded sunspot groups. The tilt angle scatter is described in our simulations by a random component according to the observed distributions for different ranges of sunspot group size (total umbral area). By performing simulations with a number of different realizations of the scatter we study the effect of the tilt angle scatter on the global magnetic field, especially on the evolution of the axial dipole moment. The average axial dipole moment at the end of cycle 17 (a medium-amplitude cycle) from our simulations was 2.73 G. The tilt angle scatter leads to an uncertainty of 0.78 G (standard deviation). We also considered cycle 14 (a weak cycle) and cycle 19 (a strong cycle) and show that the standard deviation of the axial dipole moment is similar for all three cycles. The uncertainty mainly results from the big sunspot groups which emerge near the equator. In the framework of Babcock–Leighton dynamo models, the tilt angle scatter therefore constitutes a significant random factor in the cycle-to-cycle amplitude variability, which strongly limits the predictability of solar activity.

Although not yet detected, pairs of exoplanets in 1:1 mean motion resonance probably exist. Low eccentricity, near-planar orbits, which in the comoving frame follow horseshoe trajectories, are one of the possible stable configurations. Here we study transit timing variations (TTVs) produced by mutual gravitational interaction of planets in this orbital architecture, with the goal to develop methods that can be used to recognize this case in observational data. In particular, we use a semi-analytic model to derive parametric constraints that should facilitate data analysis. We show that characteristic traits of the TTVs can directly constrain the (1) ratio of planetary masses and (2) their total mass (divided by that of the central star) as a function of the minimum angular separation as seen from the star. In an ideal case, when transits of both planets are observed and well characterized, the minimum angular separation can also be inferred from the data. As a result, parameters derived from the observed transit timing series alone can directly provide both planetary masses scaled to the central star mass.

Most models used to predict or fit exoplanet transmission spectra do not include all the effects of atmospheric refraction. Namely, the angular size of the star with respect to the planet can limit the lowest altitude, or highest density and pressure, probed during primary eclipses as no rays passing below this critical altitude can reach the observer. We discuss this geometrical effect of refraction for all exoplanets and tabulate the critical altitude, density, and pressure for an exoplanet identical to Earth with a 1 bar N₂/O₂ atmosphere as a function of both the incident stellar flux (Venus, Earth, and Mars-like) at the top of the atmosphere and the spectral type (O5–M9) of the host star. We show that such a habitable exo-Earth can be probed to a surface pressure of 1 bar only around the coolest stars. We present 0.4–5.0 μm model transmission spectra of Earth's atmosphere viewed as a transiting exoplanet, and show how atmospheric refraction modifies the transmission spectrum depending on the spectral type of the host star. We demonstrate that refraction is another phenomenon that can potentially explain flat transmission spectra over some spectral regions.

The Milky Way (MW) dwarf satellites, as the smallest galaxies discovered in the present-day universe, are potentially powerful probes to various baryonic processes in galaxy formation occurring in the early universe. In this paper, we study the chemical properties of the stars in the dwarf satellites around the MW-like host galaxies, and explore the possible effects of several baryonic processes, including supernova (SN) feedback, the reionization of the universe, and H₂ cooling, and how current and future observations may put some constraints on these processes. We use a semianalytical model to generate MW-like galaxies, for which a fiducial model can reproduce the luminosity function and the stellar metallicity–stellar mass correlation of the MW dwarfs. Using the simulated MW-like galaxies, we focus on investigating three metallicity properties of their dwarfs: the stellar metallicity–stellar mass correlation of the dwarf population, and the metal-poor and metal-rich tails of the stellar metallicity distribution in individual dwarfs. We find that (1) the slope of the stellar metallicity–stellar mass correlation is sensitive to the SN feedback strength and the reionization epoch; (2) the extension of the metal-rich tails is mainly sensitive to the SN feedback strength; (3) the extension of the metal-poor tails is mainly sensitive to the reionization epoch; (4) none of the three chemical properties are sensitive to the H₂ cooling process; and (5) a comparison of our model results with the current observational slope of the stellar metallicity–stellar mass relation suggests that the local universe is reionized earlier than the cosmic average, local sources may have a significant contribution to the reionization in the local region, and an intermediate to strong SN feedback strength is preferred. Future observations of metal-rich and metal-poor tails of stellar metallicity distributions will put further constraints on the SN feedback and the reionization processes.

We present a panoptic view of the stellar structure in the Galactic disk's outer reaches commonly known as the Monoceros Ring, based on data from Pan-STARRS1. These observations clearly show the large extent of the stellar overdensities on both sides of the Galactic disk, extending between b = −25° and b = +35° and covering over 130° in Galactic longitude. The structure exhibits a complex morphology with both stream-like features and a sharp edge to the structure in both the north and the south. We compare this map to mock observations of two published simulations aimed at explaining such structures in the outer stellar disk, one postulating an origin as a tidal stream and the other demonstrating a scenario where the disk is strongly distorted by the accretion of a satellite. These morphological comparisons of simulations can link formation scenarios to observed structures, such as demonstrating that the distorted-disk model can produce thin density features resembling tidal streams. Although neither model produces perfect agreement with the observations—the tidal stream predicts material at larger distances that is not detected while in the distorted disk model, the midplane is warped to an excessive degree—future tuning of the models to accommodate these latest data may yield better agreement.

We calculate an empirical, non-parametric estimate of the shape of the period–marginalized radius distribution of planets with periods less than 150 days using the small yet well-characterized sample of cool (T_eff < 4000 K) dwarf stars in the Kepler catalog. In particular, we present and validate a new procedure, based on weighted kernel density estimation, to reconstruct the shape of the planet radius function down to radii smaller than the completeness limit of the survey at the longest periods. Under the assumption that the period distribution of planets does not change dramatically with planet radius, we show that the occurrence of planets around these stars continues to increase to below 1 R_⊕, and that there is no strong evidence for a turnover in the planet radius function. In fact, we demonstrate using many iterations of simulated data that a spurious turnover may be inferred from data even when the true distribution continues to rise toward smaller radii. Finally, the sharp rise in the radius distribution below ∼3 R_⊕ implies that a large number of planets await discovery around cool dwarfs as the sensitivities of ground-based transit surveys increase.

In observations, it is important to deproject the two fundamental quantities characterizing a bar, i.e., its length (a) and ellipticity (e), to face-on values before any careful analyses. However, systematic estimation on the uncertainties of the commonly used deprojection methods is still lacking. Simulated galaxies are well suited in this study. We project two simulated barred galaxies onto a two-dimensional (2D) plane with different bar orientations and disk inclination angles (i). Bar properties are measured and deprojected with the popular deprojection methods in the literature. Generally speaking, deprojection uncertainties increase with increasing i. All of the deprojection methods behave badly when i is larger than 60°, due to the vertical thickness of the bar. Thus, future statistical studies of barred galaxies should exclude galaxies more inclined than 60°. At moderate inclination angles (i ⩽ 60°), 2D deprojection methods (analytical and image stretching), and Fourier-based methods (Fourier decomposition and bar–interbar contrast) perform reasonably well with uncertainties ∼10% in both the bar length and ellipticity, whereas the uncertainties of the one-dimensional (1D) analytical deprojection can be as high as 100% in certain extreme cases. We find that different bar measurement methods show systematic differences in the deprojection uncertainties. We further discuss the deprojection uncertainty factors with the emphasis on the most important one, i.e., the three-dimensional structure of the bar itself. We construct two triaxial toy bar models that can qualitatively reproduce the results of the 1D and 2D analytical deprojections; they confirm that the vertical thickness of the bar is the main source of uncertainties.

Using direct numerical simulations of three-dimensional hydromagnetic turbulence, either with helical or non-helical forcing, we show that the kinetic-to-magnetic energy dissipation ratio always increases with the magnetic Prandtl number, i.e., the ratio of kinematic viscosity to magnetic diffusivity. This dependence can always be approximated by a power law, but the exponent is not the same in all cases. For non-helical turbulence, the exponent is around 1/3, while for helical turbulence it is between 0.6 and 2/3. In the statistically steady state, the rate of energy conversion from kinetic into magnetic by the dynamo must be equal to the Joule dissipation rate. We emphasize that for both small-scale and large-scale dynamos, the efficiency of the energy conversion depends sensitively on the magnetic Prandtl number, and thus on the microphysical dissipation process. To understand this behavior, we also study shell models of turbulence and one-dimensional passive and active scalar models. We conclude that the magnetic Prandtl number dependence is qualitatively best reproduced in the one-dimensional model as a result of dissipation via localized Alfvén kinks.

We study thermal convection in a rotating fluid in order to better understand the properties of convection zones in rotating stars and planets. We first derive a mixing-length theory for rapidly rotating convection, arriving at the results of Stevenson via simple physical arguments. The theory predicts the properties of convection as a function of the imposed heat flux and rotation rate, independent of microscopic diffusivities. In particular, it predicts the mean temperature gradient, the rms velocity and temperature fluctuations, and the size of the eddies that dominate heat transport. We test all of these predictions with high resolution three-dimensional hydrodynamical simulations of Boussinesq convection in a Cartesian box. The results agree remarkably well with the theory across more than two orders of magnitude in rotation rate. For example, the temperature gradient is predicted to scale as the rotation rate to the four-fifths power at fixed flux, and the simulations yield 0.75 ± 0.06. We conclude that the mixing-length theory is a solid foundation for understanding the properties of convection zones in rotating stars and planets.

We study with unprecedented detail the chemical composition and stellar parameters of the solar twin 18 Sco in a strictly differential sense relative to the Sun. Our study is mainly based on high-resolution (R ∼ 110,000), high signal-to-noise ratio (800–1,000) Very Large Telescope UVES spectra, which allow us to achieve a precision of about 0.005 dex in differential abundances. The effective temperature and surface gravity of 18 Sco are T_eff = 5823 ± 6 K and log g = 4.45 ± 0.02 dex, i.e., 18 Sco is 46 ± 6 K hotter than the Sun and log g is 0.01 ± 0.02 dex higher. Its metallicity is [Fe/H] = 0.054 ± 0.005 dex, and its microturbulence velocity is +0.02 ± 0.01 km s⁻¹ higher than solar. Our precise stellar parameters and differential isochrone analysis show that 18 Sco has a mass of 1.04 ± 0.02 M_☉ and that it is ∼1.6 Gyr younger than the Sun. We use precise High Accuracy Radial velocity Planet Searcher (HARPS) radial velocities to search for planets, but none are detected. The chemical abundance pattern of 18 Sco displays a clear trend with condensation temperature, thus showing higher abundances of refractories in 18 Sco than in the Sun. Intriguingly, there are enhancements in the neutron-capture elements relative to the Sun. Despite the small element-to-element abundance differences among nearby n-capture elements (∼0.02 dex), we successfully reproduce the r-process pattern in the Solar System. This is independent evidence for the universality of the r process. Our results have important implications for chemical tagging in our Galaxy and nucleosynthesis in general.

Observational evidence is presented for the alignment between the cosmic sheet and the principal axis of the velocity shear field at the position of the Virgo cluster. The galaxies in and around the Virgo cluster from the Extended Virgo Cluster Catalog that was recently constructed by Kim et al. are used to determine the direction of the local sheet. The peculiar velocity field reconstructed from the Sloan Digital Sky Survey Data Release 7 is analyzed to estimate the local velocity shear tensor at the Virgo center. Showing first that the minor principal axis of the local velocity shear tensor is almost parallel to the direction of the line of sight, we detect a clear signal of alignment between the positions of the Virgo satellites and the intermediate principal axis of the local velocity shear projected onto the plane of the sky. Furthermore, the dwarf satellites are found to appear more strongly aligned than their normal counterparts, which is interpreted as an indication of the following. (1) The normal satellites and the dwarf satellites fall in the Virgo cluster preferentially along the local filament and the local sheet, respectively. (2) The local filament is aligned with the minor principal axis of the local velocity shear while the local sheet is parallel to the plane spanned by the minor and intermediate principal axes. Our result is consistent with the recent numerical claim that the velocity shear is a good tracer of the cosmic web.

We study the kilohertz quasi-periodic oscillations (kHz QPOs) in neutron star low-mass X-ray binaries (LMXBs) with a new magnetohydrodynamics (MHD) model, in which the compressed magnetosphere is considered. The previous MHD model is reexamined and the relation between the frequencies of the kHz QPOs and the accretion rate in LMXBs is obtained. Our result agrees with the observations of six sources (4U 0614+09, 4U 1636–53, 4U 1608–52, 4U 1915–15, 4U 1728–34, and XTE 1807–294) with measured spins. In this model, the kHz QPOs originate from the MHD waves in the compressed magnetosphere. The single kHz QPOs and twin kHz QPOs are produced in two different parts of the accretion disk and the boundary is close to the corotation radius. The lower QPO frequency in a frequency–accretion rate diagram is cut off at a low accretion rate and the twin kHz QPOs encounter a top ceiling at a high accretion rate due to the restriction of the innermost stable circular orbit.

We present near-infrared spectroscopy of a sample of 22 Extreme Emission Line Galaxies at redshifts 1.3 < z < 2.3, confirming that these are low-mass (M_⋆ = 10⁸–10⁹ M_☉) galaxies undergoing intense starburst episodes (M_⋆/SFR ∼ 10–100 Myr). The sample is selected by [O iii] or Hα emission line flux and equivalent width using near-infrared grism spectroscopy from the 3D-HST survey. High-resolution NIR spectroscopy is obtained with LBT/LUCI and VLT/X-SHOOTER. The [O iii]/Hβ line ratio is high (≳ 5) and [N ii]/Hα is always significantly below unity, which suggests a low gas-phase metallicity. We are able to determine gas-phase metallicities for seven of our objects using various strong-line methods, with values in the range 0.05–0.30 Z_☉ and with a median of 0.15 Z_☉; for three of these objects we detect [O iii] λ4363, which allows for a direct constraint on the metallicity. The velocity dispersion, as measured from the nebular emission lines, is typically ∼50 km s⁻¹. Combined with the observed star-forming activity, the Jeans and Toomre stability criteria imply that the gas fraction must be large (f_gas ≳ 2/3), consistent with the difference between our dynamical and stellar mass estimates. The implied gas depletion timescale (several hundred Myr) is substantially longer than the inferred mass-weighted ages (∼50 Myr), which further supports the emerging picture that most stars in low-mass galaxies form in short, intense bursts of star formation.

We present the rest-frame UV wavelength dependence of the Petrosian-like half-light radius (r₅₀), and the concentration parameter for a sample of 198 star-forming galaxies at 0.5 < z < 1.5. We find a ∼5% decrease in r₅₀ from 1500 Å to 3000 Å, with half-light radii at 3000 Å ranging from 0.6 kpc to 6 kpc. We also find a decrease in concentration of ∼0.07 (1.9 < C₃₀₀₀ < 3.9). The lack of a strong relationship between r₅₀ and wavelength is consistent with a model in which clumpy star formation is distributed over length scales comparable to the galaxy's rest-frame optical light. While the wavelength dependence of r₅₀ is independent of size at all redshifts, concentration decreases more sharply in the far-UV (∼1500 Å) for large galaxies at z ∼ 1. This decrease in concentration is caused by a flattening of the inner ∼20% of the light profile in disk-like galaxies, indicating that the central regions have different UV colors than the rest of the galaxy. We interpret this as a bulge component with older stellar populations and/or more dust. The size-dependent decrease in concentration is less dramatic at z ∼ 2, suggesting that bulges are less dusty, younger, and/or less massive than the rest of the galaxy at higher redshifts.

We present new spatially resolved 1.3 mm imaging with CARMA of the GV Tau system. GV Tau is a Class I binary protostar system in the Taurus Molecular Cloud, the components of which are separated by 12. Each protostar is surrounded by a protoplanetary disk, and the pair may be surrounded by a circumbinary envelope. We analyze the data using detailed radiative transfer modeling of the system. We create synthetic protostar model spectra, images, and visibilities and compare them with CARMA 1.3 mm visibilities, a Hubble Space Telescope near-infrared scattered light image, and broadband spectral energy distributions from the literature to study the disk masses and geometries of the GV Tau disks. We show that the protoplanetary disks around GV Tau fall near the lower end of estimates of the Minimum Mass Solar Nebula, and may have just enough mass to form giant planets. When added to the sample of Class I protostars from Eisner, we confirm that Class I protostars are on average more massive than their Class II counterparts. This suggests that substantial dust grain processing occurs between the Class I and Class II stages, and may help to explain why the Class II protostars do not appear to have, on average, enough mass in their disks to form giant planets.

We present Atacama Large Millimeter/submillimeter Array continuum and spectral line data at 0.89 mm and 3.2 mm for three disks surrounding young brown dwarfs and very low mass stars in the Taurus star forming region. Dust thermal emission is detected and spatially resolved for all the three disks, while CO(J = 3–2) emission is seen in two disks. We analyze the continuum visibilities and constrain the disks' physical structure in dust. The results of our analysis show that the disks are relatively large; the smallest one has an outer radius of about 70 AU. The inferred disk radii, radial profiles of the dust surface density, and disk to central object mass ratios lie within the ranges found for disks around more massive young stars. We derive from our observations the wavelength dependence of the millimeter dust opacity. In all the three disks, data are consistent with the presence of grains with at least millimeter sizes, as also found for disks around young stars, and confirm that the early stages of the solid growth toward planetesimals occur also around very low-mass objects. We discuss the implications of our findings on models of solids evolution in protoplanetary disks, the main mechanisms proposed for the formation of brown dwarfs and very low-mass stars, as well as the potential of finding rocky and giant planets around very low-mass objects.

Blazars display strong variability on multiple timescales and in multiple radiation bands. Their variability is often characterized by power spectral densities (PSDs) and time lags plotted as functions of the Fourier frequency. We develop a new theoretical model based on the analysis of the electron transport (continuity) equation, carried out in the Fourier domain. The continuity equation includes electron cooling and escape, and a derivation of the emission properties includes light travel time effects associated with a radiating blob in a relativistic jet. The model successfully reproduces the general shapes of the observed PSDs and predicts specific PSD and time lag behaviors associated with variability in the synchrotron, synchrotron self-Compton, and external Compton emission components, from submillimeter to γ-rays. We discuss applications to BL Lacertae objects and to flat-spectrum radio quasars (FSRQs), where there are hints that some of the predicted features have already been observed. We also find that FSRQs should have steeper γ-ray PSD power-law indices than BL Lac objects at Fourier frequencies ≲ 10⁻⁴ Hz, in qualitative agreement with previously reported observations by the Fermi Large Area Telescope.

We analyze the three-dimensional anisotropy of the galactic cosmic ray (GCR) intensities observed independently with a muon detector at Nagoya in Japan and neutron monitors over four solar activity cycles. We clearly see the phase of the free-space diurnal anisotropy shifting toward earlier hours around solar activity minima in A > 0 epochs, due to the reduced anisotropy component parallel to the mean magnetic field. This component is consistent with a rigidity-independent spectrum, while the perpendicular anisotropy component increases with GCR rigidity. We suggest that this harder spectrum of the perpendicular component is due to contribution from the drift streaming. We find that the bi-directional latitudinal density gradient is positive in the A > 0 epoch, while it is negative in the A < 0 epoch, in agreement with the drift model prediction. The radial density gradient of GCRs, on the other hand, varies with a ∼11 yr cycle with maxima (minima) in solar maximum (minimum) periods, but we find no significant difference between the radial gradients in the A > 0 and A < 0 epochs. The corresponding parallel mean free path is larger in A < 0 than in A > 0. We also find, however, that the parallel mean free path (radial gradient) appears to persistently increase (decrease) in the last three cycles of weakening solar activity. We suggest that simple differences between these parameters in A > 0 and A < 0 epochs are seriously biased by these long-term trends.

We present observations of a confined M4.0 flare from NOAA 11302 on 2011 September 26. Observations at high temporal, spatial, and spectral resolution from the Solar Dynamics Observatory, Reuven Ramaty High Energy Solar Spectroscopic Imager, and Nobeyama Radioheliograph observations enabled us to explore the possible triggering and energy release processes of this flare despite its very impulsive behavior and compact morphology. The flare light curves exhibit an abrupt rise of non-thermal emission with co-temporal hard X-ray (HXR) and microwave (MW) bursts that peaked instantly without any precursor emission. This stage was associated with HXR emission up to 200 keV that followed a power law with photon spectral index (γ) ∼ 3. Another non-thermal peak, observed 32 s later, was more pronounced in the MW flux than the HXR profiles. Dual peaked structures in the MW and HXR light curves suggest a two-step magnetic reconnection process. Extreme ultraviolet (EUV) images exhibit a sequential evolution of the inner and outer core regions of magnetic loop systems while the overlying loop configuration remained unaltered. Combined observations in HXR, (E)UV, and Hα provide support for flare models involving the interaction of coronal loops. The magnetograms obtained by the Helioseismic and Magnetic Imager reveal emergence of magnetic flux that began ∼five hr before the flare. However, the more crucial changes in the photospheric magnetic flux occurred about one minute prior to the flare onset with opposite polarity magnetic transients appearing at the early flare location within the inner core region. The spectral, temporal, and spatial properties of magnetic transients suggest that the sudden changes in the small-scale magnetic field have likely triggered the flare by destabilizing the highly sheared pre-flare magnetic configuration.

Continuously time variable sources are often characterized by their power spectral density and flux distribution. These quantities can undergo dramatic changes over time if the underlying physical processes change. However, some changes can be subtle and not distinguishable using standard statistical approaches. Here, we report a methodology that aims to identify distinct but similar states of time variability. We apply this method to the Galactic supermassive black hole, where 2.2 μm flux is observed from a source associated with Sgr A* and where two distinct states have recently been suggested. Our approach is taken from mathematical finance and works with conditional flux density distributions that depend on the previous flux value. The discrete, unobserved (hidden) state variable is modeled as a stochastic process and the transition probabilities are inferred from the flux density time series. Using the most comprehensive data set to date, in which all Keck and a majority of the publicly available Very Large Telescope data have been merged, we show that Sgr A* is sufficiently described by a single intrinsic state. However, the observed flux densities exhibit two states: noise dominated and source dominated. Our methodology reported here will prove extremely useful to assess the effects of the putative gas cloud G2 that is on its way toward the black hole and might create a new state of variability.

In the Jupiter–Io system, the moon's motion produces currents along the field lines that connect it to Jupiter's polar regions. The currents generate and modulate radio emissions along their paths via the electron–cyclotron maser instability. Based on this process, we suggest that such modulation of planetary radio emissions may reveal the presence of exomoons around giant planets in exoplanetary systems. A model explaining the modulation mechanism in the Jupiter–Io system is extrapolated and used to define criteria for exomoon detectability. A cautiously optimistic scenario of the possible detection of such exomoons around Epsilon Eridani b and Gliese 876 b is provided.

Supernova remnant and heliopause termination shock plasmas may contain significant populations of minority heavy ions, with relative number densities n_α/n_i up to 50%. Preliminary kinetic simulations of collisionless shocks in these environments showed that the reformation cycle and acceleration mechanisms at quasi-perpendicular shocks can depend on the value of n_α/n_i. Shock reformation unfolds on ion spatio-temporal scales, requiring fully kinetic simulations of particle dynamics, together with the self-consistent electric and magnetic fields. This paper presents the first set of particle-in-cell simulations for two ion species, protons (n_p) and α-particles (n_α), with differing mass and charge-to-mass ratios, that spans the entire range of n_α/n_i from 0% to 100%. The interplay between the differing gyro length scales and timescales of the ion species is crucial to the time-evolving phenomenology of the shocks, the downstream turbulence, and the particle acceleration at different n_α/n_i. We show how the overall energization changes with n_α/n_i, and relate this to the processes individual ions undergo in the shock region and in the downstream turbulence, and to the power spectra of magnetic field fluctuations. The crossover between shocks dominated by the respective ion species happens when n_α/n_i = 25%, and minority ion energization is strongest in this regime. Energization of the majority ion species scales with injection energy. The power spectrum of the downstream turbulence includes peaks at sequential ion cyclotron harmonics, suggestive of ion ring-beam collective instability.

Observations of molecular clouds reveal a complex structure, with gas and dust often arranged in filamentary, rather than spherical geometries. The association of pre- and proto-stellar cores with the filaments suggests a direct link with the process of star formation. Any study of the properties of such filaments requires representative samples from different environments for an unbiased detection method. We developed such an approach using the Hessian matrix of a surface-brightness distribution to identify filaments and determine their physical and morphological properties. After testing the method on simulated, but realistic, filaments, we apply the algorithms to column-density maps computed from Herschel observations of the Galactic plane obtained by the Hi-GAL project. We identified ∼500 filaments, in the longitude range of l = 2165 to l = 2255, with lengths from ∼1 pc up to ∼30 pc and widths between 0.1 pc and 2.5 pc. Average column densities are between 10²⁰ cm⁻² and 10²² cm⁻². Filaments include the majority of dense material with > 6 × 10²¹ cm⁻². We find that the pre- and proto-stellar compact sources already identified in the same region are mostly associated with filaments. However, surface densities in excess of the expected critical values for high-mass star formation are only found on the filaments, indicating that these structures are necessary to channel material into the clumps. Furthermore, we analyze the gravitational stability of filaments and discuss their relationship with star formation.

Infrared spectra of carbon-rich objects that have evolved off the asymptotic giant branch reveal a range of dust properties, including fullerenes, polycyclic aromatic hydrocarbons (PAHs), aliphatic hydrocarbons, and several unidentified features, including the 21 μm emission feature. To test for the presence of fullerenes, we used the position and width of the feature at 18.7–18.9 μm and examined other features at 17.4 and 6–9 μm. This method adds three new fullerene sources to the known sample, but it also calls into question three previous identifications. We confirm that the strong 11 μm features seen in some sources arise primarily from SiC, which may exist as a coating around carbonaceous cores and result from photo-processing. Spectra showing the 21 μm feature usually show the newly defined Class D PAH profile at 7–9 μm. These spectra exhibit unusual PAH profiles at 11–14 μm, with weak contributions at 12.7 μm, which we define as Class D1, or show features shifted to ∼11.4, 12.4, and 13.2 μm, which we define as Class D2. Alkyne hydrocarbons match the 15.8 μm feature associated with 21 μm emission. Sources showing fullerene emission but no PAHs have blue colors in the optical, suggesting a clear line of sight to the central source. Spectra with 21 μm features and Class D2 PAH emission also show photometric evidence for a relatively clear line of sight to the central source. The multiple associations of the 21 μm feature with aliphatic hydrocarbons suggest that the carrier is related to this material in some way.

Complex organic molecules (COMs) are considered to be crucial molecules, since they are connected with organic chemistry, at the basis of terrestrial life. More pragmatically, they are molecules which in principle are difficult to synthesize in harsh interstellar environments and, therefore, are a crucial test for astrochemical models. Current models assume that several COMs are synthesized on lukewarm grain surfaces (≳30–40 K) and released in the gas phase at dust temperatures of ≳100 K. However, recent detections of COMs in ≲20 K gas demonstrate that we still need important pieces to complete the puzzle of COMs formation. Here, we present a complete census of the oxygen- and nitrogen-bearing COMs, previously detected in different Interstellar Medium (ISM) regions, toward the solar-type protostar IRAS16293-2422. The census was obtained from the millimeter–submillimeter unbiased spectral survey TIMASSS. Of the 29 COMs searched for, 6 were detected: methyl cyanide, ketene, acetaldehyde, formamide, dimethyl ether, and methyl formate. Multifrequency analysis of the last five COMs provides clear evidence that they are present in the cold (≲30 K) envelope of IRAS16293-2422, with abundances of 0.03–2 × 10⁻¹⁰. Our data do not allow us to support the hypothesis that the COMs abundance increases with increasing dust temperature in the cold envelope, as expected if COMs were predominately formed on lukewarm grain surfaces. Finally, when also considering other ISM sources, we find a strong correlation over five orders of magnitude between methyl formate and dimethyl ether, and methyl formate and formamide abundances, which may point to a link between these two couples of species in cold and warm gas.

We present an observational study using high-resolution echelle spectroscopy of collisionless shocks in the Cygnus Loop supernova remnant. Measured Hα line profiles constrain pre-shock heating processes, shock speeds, and electron–ion equilibration (T_e/T_i). The shocks produce faint Hα emission line profiles, which are characterized by narrow and broad components. The narrow component is representative of the pre-shock conditions, while the broad component is produced after charge transfer between neutrals entering the shock and protons in the post-shock gas, thus reflecting the properties of the post-shock gas. We observe a diffuse Hα region extending about 25 ahead of the shock with line width ∼29 km s⁻¹, while the Hα profile of the shock itself consists of broader than expected narrow (36 km s⁻¹) and broad (250 km s⁻¹) components. The observed diffuse emission arises in a photoionization precursor heated to about 18,000 K by He i and He ii emission from the shock, with additional narrow component broadening originating from a thin cosmic-ray precursor. Broad to narrow component intensity ratios of ∼1.0 imply full electron–ion temperature equilibration T_e ≃ T_i in the post-shock region. Broad component line widths indicate shock velocities of about 400 km s⁻¹. Combining the shock velocities with proper motions suggests that the distance to the Cygnus Loop is ∼890 pc, significantly greater than the generally accepted upper limit of 637 pc.

Recent solar flare observations in the sub-terahertz range have provided evidence of a new spectral component with fluxes increasing for larger frequencies, separated from the well-known microwave emission that maximizes in the gigahertz range. Suggested interpretations explain the terahertz spectral component but do not account for the simultaneous microwave component. We present a mechanism for producing the observed “double spectra.” Based on coherent enhancement of synchrotron emission at long wavelengths in laboratory accelerators, we consider how similar processes may occur within a solar flare. The instability known as microbunching arises from perturbations that produce electron beam density modulations, giving rise to broadband coherent synchrotron emission at wavelengths comparable to the characteristic size of the microbunch structure. The spectral intensity of this coherent synchrotron radiation (CSR) can far exceed that of the incoherent synchrotron radiation (ISR), which peaks at a higher frequency, thus producing a double-peaked spectrum. Successful CSR simulations are shown to fit actual burst spectral observations, using typical flaring physical parameters and power-law energy distributions for the accelerated electrons. The simulations consider an energy threshold below which microbunching is not possible because of Coulomb repulsion. Only a small fraction of the radiating charges accelerated to energies above the threshold is required to produce the microwave component observed for several events. The ISR/CSR mechanism can occur together with other emission processes producing the microwave component. It may bring an important contribution to microwaves, at least for certain events where physical conditions for the occurrence of the ISR/CSR microbunching mechanism are possible.

We use the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope to obtain new high-quality spectra covering the 1900 ⩽λ ⩽ 2360 Å wavelength range for two metal-poor stars, HD 108317 and HD 128279. We derive abundances of Cu ii, Zn ii, As i, Se i, Mo ii, and Cd ii, which have not been detected previously in either star. Abundances derived for Ge i, Te i, Os ii, and Pt i confirm those derived from lines at longer wavelengths. We also derive upper limits from the non-detection of W ii, Hg ii, Pb ii, and Bi i. The mean [As/Fe] ratio derived from these two stars and five others in the literature is unchanged over the metallicity range −2.8 < [Fe/H] <−0.6, 〈[As/Fe]〉 = +0.28 ± 0.14 (σ = 0.36 dex). The mean [Se/Fe] ratio derived from these two stars and six others in the literature is also constant, 〈[Se/Fe]〉 = +0.16 ± 0.09 (σ = 0.26 dex). The As and Se abundances are enhanced relative to a simple extrapolation of the iron-peak abundances to higher masses, suggesting that this mass region (75 ⩽A ⩽ 82) may be the point at which a different nucleosynthetic mechanism begins to dominate the quasi-equilibrium α-rich freezeout of the iron peak. 〈[Cu ii/Cu i]〉 = +0.56 ± 0.23 in HD 108317 and HD 128279, and we infer that lines of Cu i may not be formed in local thermodynamic equilibrium in these stars. The [Zn/Fe], [Mo/Fe], [Cd/Fe], and [Os/Fe] ratios are also derived from neutral and ionized species, and each ratio pair agrees within the mutual uncertainties, which range from 0.15 to 0.52 dex.

Over approximately the last five years, we have identified ∼35 black hole candidates (BHCs) in M31 from their X-ray spectra. Our BHCs exhibited 0.3–10 keV spectra consistent with the X-ray binary (XB) hard state at luminosities that are above the upper limit for neutron star (NS) XBs. When our BHC spectra were modeled with a disk blackbody + blackbody model for comparison with bright NS XBs, we found that the BHCs inhabited a different parameter space than the NS XBs. However, BH XBs may also exhibit a thermally dominated (TD) state that has never been seen in NS XBs; this TD state is most often observed in X-ray transients. We examined the ∼50 X-ray transients in our Chandra survey of M31 and found 13 with spectra suitable for analysis. We also examined two BHCs outside the field of view of our survey in the globular clusters B045 and B375. We have 42 strong BHCs and 8 plausible BHCs that may benefit from further observation. Of our 15 BHCs in globular clusters, 12 differ from NS spectra by >5σ. Due to improvements in our analysis, we have upgraded 10 previously identified plausible BHCs to strong BHCs. The mean maximum duty cycle of the 33 X-ray transients within 6′ of M31* is 0.13; we estimate that >40% of the XBs in this region contain BH accretors. Remarkably, we estimate that BHCs contribute >90% of those XBs >10³⁸ erg s⁻¹.

We report Herschel/SPIRE, Spitzer and Wide-field Infrared Survey Explorer observations of 44 z ≃ 4.8 optically selected active galactic nuclei (AGNs). This flux-limited sample contains the highest mass black holes (BHs) at this redshift. Ten of the objects were detected by Herschel and five show emission that is not clearly associated with the AGNs. The star formation (SF) luminosity (L_SF) obtained by fitting the spectral energy distribution (SED) with standard SF templates, taking into account AGN contribution, is in the range 10^46.62–10^47.21 erg s⁻¹ corresponding to SF rates of 1090–4240 M_☉ yr⁻¹. Fitting with very luminous submillimeter galaxy SEDs gives SF rates that are smaller by 0.05 dex when using all bands and 0.1 dex when ignoring the 250 μm band. A 40 K graybody fits to only the 500 μm fluxes reduce L_SF by about a factor of two. A stacking analysis of 29 undetected sources gives significant signals in all three bands. A SF template fit indicates L_SF = 10^{46.19–46.23} erg s⁻¹ depending on the assumed AGN contribution. A 40 K fit to the stacked 500 μm flux gives L_SF = 10^45.95 erg s⁻¹. The mean BH mass (M_BH) and AGN luminosity (L_AGN) of the detected sources are significantly higher than those of the undetected ones. The spectral differences are seen all the way from UV to far infrared wavelengths. The mean optical–UV spectra are similar to those predicted for thin accretion disks around BHs with similar masses and accretion rates. We suggest two alternative explanations to the correlation of L_SF, L_AGN and M_BH, one involving no AGN feedback and the second involving moderate feedback that affects, but does not totally quench, SF in three-quarters of the sources. We compare our L_SF and L_AGN to lower redshift samples and show a new correlation between L_SF and M_BH. We also examine several rather speculative ideas about the host galaxy properties including the possibility that the detected sources are above the SF mass sequence (MS) at z ≃ 4.8, perhaps in mergers, and most of the undetected sources are on the MS.

The Robo-AO Kepler Planetary Candidate Survey is observing every Kepler planet candidate host star with laser adaptive optics imaging to search for blended nearby stars, which may be physically associated companions and/or responsible for transit false positives. In this paper, we present the results from the 2012 observing season, searching for stars close to 715 Kepler planet candidate hosts. We find 53 companions, 43 of which are new discoveries. We detail the Robo-AO survey data reduction methods including a method of using the large ensemble of target observations as mutual point-spread-function references, along with a new automated companion-detection algorithm designed for large adaptive optics surveys. Our survey is sensitive to objects from ≈015 to 25 separation, with magnitude differences up to Δm ≈ 6. We measure an overall nearby-star probability for Kepler planet candidates of 7.4% ± 1.0%, and calculate the effects of each detected nearby star on the Kepler-measured planetary radius. We discuss several Kepler Objects of Interest (KOIs) of particular interest, including KOI-191 and KOI-1151, which are both multi-planet systems with detected stellar companions whose unusual planetary system architecture might be best explained if they are “coincident multiple” systems, with several transiting planets shared between the two stars. Finally, we find 98% confidence evidence that short-period giant planets are two to three times more likely than longer-period planets to be found in wide stellar binaries.

WASP-12b was the first planet reported to have a carbon-to-oxygen ratio (C/O) greater than one in its dayside atmosphere. However, recent work to further characterize its atmosphere and confirm its composition has led to incompatible measurements and divergent conclusions. Additionally, the recent discovery of stellar binary companions ∼1″ from WASP-12 further complicates the analyses and subsequent interpretations. We present a uniform analysis of all available Hubble and Spitzer Space Telescope secondary-eclipse data, including previously unpublished Spitzer measurements at 3.6 and 4.5 μm. The primary controversy in the literature has centered on the value and interpretation of the eclipse depth at 4.5 μm. Our new measurements and analyses confirm the shallow eclipse depth in this channel, as first reported by Campo and collaborators and used by Madhusudhan and collaborators to infer a carbon-rich composition. To explain WASP-12b's observed dayside emission spectrum, we implemented several recent retrieval approaches. We find that when we exclude absorption due to C₂H₂ and HCN, which are not universally considered in the literature, our models require implausibly large atmospheric CO₂ abundances, regardless of the C/O. By including C₂H₂ and HCN in our models, we find that a physically plausible carbon-rich solution achieves the best fit to the available photometric and spectroscopic data. In comparison, the best-fit oxygen-rich models have abundances that are inconsistent with the chemical equilibrium expectations for hydrogen-dominated atmospheres and are 670 times less probable. Our best-fit solution is also 7.3 × 10⁶ times more probable than an isothermal blackbody model.

We present a revised measurement of the mass of the central black hole (M_BH ) in the Seyfert 1 galaxy NGC 4151. The new stellar dynamical mass measurement is derived by applying an axisymmetric orbit-superposition code to near-infrared integral field data obtained using adaptive optics with the Gemini Near-infrared Integral Field Spectrograph (NIFS). When our models attempt to fit both the NIFS kinematics and additional low spatial resolution kinematics, our results depend sensitively on how χ² is computed—probably a consequence of complex bar kinematics that manifest immediately outside the nuclear region. The most robust results are obtained when only the high spatial resolution kinematic constraints in the nuclear region are included in the fit. Our best estimates for the black hole mass and H-band mass-to-light ratio are M_BH  ∼ 3.76  ±  1.15 × 10⁷ M_☉ (1σ error) and ϒ_H ∼ 0.34  ±  0.03 M_☉/L_☉ (3σ error), respectively (the quoted errors reflect the model uncertainties). Our black hole mass measurement is consistent with estimates from both reverberation mapping () and gas kinematics (; 1σ errors), and our best-fit mass-to-light ratio is consistent with the photometric estimate of ϒ_H = 0.4 ± 0.2 M_☉/L_☉. The NIFS kinematics give a central bulge velocity dispersion σ_c = 116 ± 3 km s⁻¹, bringing this object slightly closer to the M_BH–σ relation for quiescent galaxies. Although NGC 4151 is one of only a few Seyfert 1 galaxies in which it is possible to obtain a direct dynamical black hole mass measurement—and thus, an independent calibration of the reverberation mapping mass scale—the complex bar kinematics makes it less than ideally suited for this purpose.

We present deep, wide-field imaging of the M96 galaxy group (also known as the Leo I Group). Down to surface brightness limits of μ_B = 30.1 and μ_V = 29.5, we find no diffuse, large-scale optical counterpart to the “Leo Ring,” an extended H i ring surrounding the central elliptical M105 (NGC 3379). However, we do find a number of extremely low surface brightness (μ_B ≳ 29) small-scale streamlike features, possibly tidal in origin, two of which may be associated with the Ring. In addition, we present detailed surface photometry of each of the group's most massive members—M105, NGC 3384, M96 (NGC 3368), and M95 (NGC 3351)—out to large radius and low surface brightness, where we search for signatures of interaction and accretion events. We find that the outer isophotes of both M105 and M95 appear almost completely undisturbed, in contrast to NGC 3384 which shows a system of diffuse shells indicative of a recent minor merger. We also find photometric evidence that M96 is accreting gas from the H i ring, in agreement with H i data. In general, however, interaction signatures in the M96 Group are extremely subtle for a group environment, and provide some tension with interaction scenarios for the formation of the Leo H i Ring. The lack of a significant component of diffuse intragroup starlight in the M96 Group is consistent with its status as a loose galaxy group in which encounters are relatively mild and infrequent.

Convergent lines of evidence suggest that globular clusters host multiple stellar populations. It appears that they experience at least two episodes of star formation whereby a fraction of first-generation stars contribute astrated ejecta to form the second generation(s). To identify the polluting progenitors, we require distinguishing chemical signatures such as that provided by lithium. Theoretical models predict that lithium can be synthesized in AGB stars, whereas no net Li production is expected from other candidates. It has been shown that in order to reproduce the abundance pattern found in M4, Li production must occur within the polluters, favoring the AGB scenario. Here, we present Li and Al abundances for a large sample of RGB stars in M12 and M5. These clusters have a very similar metallicity, while demonstrating differences in several cluster properties. Our results indicate that the first-generation and second-generation stars share the same Li content in M12; we recover an abundance pattern similar to that observed in M4. In M5, we find a higher degree of complexity, and a simple dilution model fails in reproducing the majority of the stellar population. In both clusters, we require Li production across the different stellar generations, but production seems to have occurred to different extents. We suggest that such a difference might be related to the cluster mass with the Li production being more efficient in less-massive clusters. This is the first time a statistically significant correlation between the Li spread within a GC and its luminosity has been demonstrated. Finally, although Li-producing polluters are required to account for the observed pattern, other mechanisms, such as MS depletion, might have played a role in contributing to the Li internal variation, though at a relatively low level.

Magnetic fields are believed to play an essential role in astrophysical jets with observations suggesting the presence of helical magnetic fields. Here, we present three-dimensional (3D) ideal MHD simulations of the Caltech plasma jet experiment using a magnetic tower scenario as the baseline model. Magnetic fields consist of an initially localized dipole-like poloidal component and a toroidal component that is continuously being injected into the domain. This flux injection mimics the poloidal currents driven by the anode–cathode voltage drop in the experiment. The injected toroidal field stretches the poloidal fields to large distances, while forming a collimated jet along with several other key features. Detailed comparisons between 3D MHD simulations and experimental measurements provide a comprehensive description of the interplay among magnetic force, pressure, and flow effects. In particular, we delineate both the jet structure and the transition process that converts the injected magnetic energy to other forms. With suitably chosen parameters that are derived from experiments, the jet in the simulation agrees quantitatively with the experimental jet in terms of magnetic/kinetic/inertial energy, total poloidal current, voltage, jet radius, and jet propagation velocity. Specifically, the jet velocity in the simulation is proportional to the poloidal current divided by the square root of the jet density, in agreement with both the experiment and analytical theory. This work provides a new and quantitative method for relating experiments, numerical simulations, and astrophysical observation, and demonstrates the possibility of using terrestrial laboratory experiments to study astrophysical jets.

A soft X-ray enhancement has recently been reported toward the high-velocity cloud MS30.7−81.4−118 (MS30.7), a constituent of the Magellanic Stream. In order to investigate the origin of this enhancement, we have analyzed two overlapping XMM-Newton observations of this cloud. We find that the X-ray enhancement is ∼6′ or ∼100 pc across, and is concentrated to the north and west of the densest part of the cloud. We modeled the X-ray enhancement with a variety of spectral models. A single-temperature equilibrium plasma model yields a temperature of and a 0.4–2.0 keV luminosity of 7.9 × 10³³ erg s⁻¹. However, this model underpredicts the on-enhancement emission around 1 keV, which may indicate the additional presence of hotter plasma (T ≳ 10⁷ K), or that recombination emission is important. We examined several different physical models for the origin of the X-ray enhancement. We find that turbulent mixing of cold cloud material with hot ambient material, compression or shock heating of a hot ambient medium, and charge exchange reactions between cloud atoms and ions in a hot ambient medium all lead to emission that is too faint. In addition, shock heating in a cool or warm medium leads to emission that is too soft (for reasonable cloud speeds). We find that magnetic reconnection could plausibly power the observed X-ray emission, but resistive magnetohydrodynamical simulations are needed to test this hypothesis. If magnetic reconnection is responsible for the X-ray enhancement, the observed spectral properties could potentially constrain the magnetic field in the vicinity of the Magellanic Stream.

We present ALMA observations of the 880  μm continuum and CO J = 3–2 line emission from the transition disk around [PZ99] J160421.7-213028, a solar mass star in the Upper Scorpius OB association. Analysis of the continuum data indicates that 80% of the dust mass is concentrated in an annulus extending between 79 and 114 AU in radius. Dust is robustly detected inside the annulus, at a mass surface density 100 times lower than that at 80 AU. The CO emission in the inner disk also shows a significantly decreased mass surface density, but we infer a cavity radius of only 31 AU for the gas. The large separation of the dust and gas cavity edges, as well as the high radial concentration of millimeter-sized dust grains, is qualitatively consistent with the predictions of pressure trap models that include hydrodynamical disk–planet interactions and dust coagulation/fragmentation processes.

Turbulence and magnetic fields are expected to be important for regulating molecular cloud formation and evolution. However, their effects on sub-parsec to 100 parsec scales, leading to the formation of starless cores, are not well understood. We investigate the prestellar core structure morphologies obtained from analysis of the Herschel-SPIRE 350 μm maps of the Lupus I cloud. This distribution is first compared on a statistical basis to the large-scale shape of the main filament. We find the distribution of the elongation position angle of the cores to be consistent with a random distribution, which means no specific orientation of the morphology of the cores is observed with respect to the mean orientation of the large-scale filament in Lupus I, nor relative to a large-scale bent filament model. This distribution is also compared to the mean orientation of the large-scale magnetic fields probed at 350 μm with the Balloon-borne Large Aperture Telescope for Polarimetry during its 2010 campaign. Here again we do not find any correlation between the core morphology distribution and the average orientation of the magnetic fields on parsec scales. Our main conclusion is that the local filament dynamics—including secondary filaments that often run orthogonally to the primary filament—and possibly small-scale variations in the local magnetic field direction, could be the dominant factors for explaining the final orientation of each core.

This work presents an interesting phenomenon of the period variation in quasi-periodic pulsations (QPPs) observed during the impulsive phase of a coronal mass ejection-related X1.1 class flare on 2012 July 6. The period of QPPs was changed from 21 s at soft X-rays (SXR) to 22–23 s at microwaves, to ∼24 s at extreme ultraviolet emissions (EUV), and to 27–32 s at metric–decimetric waves. The microwave, EUV, and SXR QPPs, emitted from flare loops of different heights, were oscillating in phase. Fast kink mode oscillations were proposed to be the modulation mechanism, which may exist in a wide region in the solar atmosphere from the chromosphere to the upper corona or even to the interplanetary space. Changed parameters of flare loops through the solar atmosphere could result in the varying period of QPPs at different wavelengths. The first appearing microwave QPPs and quasi-periodic metric-decimetric type III bursts were generated by energetic electrons. This may imply that particle acceleration or magnetic reconnection were located between these two non-thermal emission sources. Thermal QPPs (in SXR and EUV emissions) occurred later than the nonthermal ones, which would suggest a some time for plasma heating or energy dissipation in flare loops during burst processes. At the beginning of flare, a sudden collapse and expansion of two separated flare loop structures occurred simultaneously with the multi-wavelength QPPs. An implosion in the corona, including both collapse and expansion of flare loops, could be a trigger of loop oscillations in a very large region in the solar atmosphere.

The dense interiors of massive galaxies are among the most intriguing environments in the universe. In this paper,we ask when these dense cores were formed and determine how galaxies gradually assembled around them. We select galaxies that have a stellar mass >3 × 10¹⁰ M_☉ inside r = 1 kpc out to z = 2.5, using the 3D-HST survey and data at low redshift. Remarkably, the number density of galaxies with dense cores appears to have decreased from z = 2.5 to the present. This decrease is probably mostly due to stellar mass loss and the resulting adiabatic expansion, with some contribution from merging. We infer that dense cores were mostly formed at z > 2.5, consistent with their largely quiescent stellar populations. While the cores appear to form early, the galaxies in which they reside show strong evolution: their total masses increase by a factor of 2–3 from z = 2.5 to z = 0 and their effective radii increase by a factor of 5–6. As a result, the contribution of dense cores to the total mass of the galaxies in which they reside decreases from ∼50% at z = 2.5 to ∼15% at z = 0. Because of their early formation, the contribution of dense cores to the total stellar mass budget of the universe is a strong function of redshift. The stars in cores with M_1 kpc > 3 × 10¹⁰ M_☉ make up ∼0.1% of the stellar mass density of the universe today but 10%–20% at z ∼ 2, depending on their initial mass function. The formation of these cores required the conversion of ∼10¹¹ M_☉ of gas into stars within ∼1 kpc, while preventing significant star formation at larger radii.

The evolution of a dilute electron–positron fireball is calculated in the regime of strong magnetization and high compactness (ℓ ∼ 10³–10⁸). Heating is applied at a low effective temperature (<25 keV), appropriate to breakout from a confining medium, so that relaxation to a blackbody is inhibited by pair annihilation. The diffusion equation for Compton scattering by thermal pairs is coupled to a trans-relativistic cyclo-synchrotron source. We find that the photon spectrum develops a quasi-thermal peak at energy ∼0.1 m_ec² in the comoving frame, with a power-law slope below it that is characteristic of gamma-ray bursts (GRBs; F_ω ∼ const). The formation of a thermal high-energy spectrum is checked using the full kinetic equations. Calculations for a baryon-dominated photosphere reveal a lower spectral peak energy, and a harder low-energy spectrum, unless ion rest mass carries ≲ 10⁻⁵ of the energy flux. We infer that (1) the GRB spectrum is inconsistent with the neutron-rich wind emitted by a young magnetar or neutron torus, and points to an event horizon in the engine; (2) neutrons play a negligible role in prompt gamma-ray emission; (3) the relation between observed peak frequency and burst energy is bounded below by the observed Amati relation if the Lorentz factor ∼(opening angle)⁻¹ at breakout, and the jet is surrounded by a broader sheath that interacts with a collapsing stellar core; (4) X-ray flashes are consistent with magnetized jets with ion-dominated photospheres; (5) high-frequency Alfvén waves may become charge starved in the dilute pair gas; (6) limitations on magnetic reconnection from plasma collisionality have been overestimated.

X-ray observations of quiescent X-ray binaries have the potential to provide insight into the structure and the composition of neutron stars. EXO 0748–676 had been actively accreting for over 24 yr before its outburst ceased in late 2008. Subsequent X-ray monitoring revealed a gradual decay of the quiescent thermal emission that can be attributed to cooling of the accretion-heated neutron star crust. In this work, we report on new Chandra and Swift observations that extend the quiescent monitoring to ≃5 yr post-outburst. We find that the neutron star temperature remained at ≃117 eV between 2009 and 2011, but had decreased to ≃110 eV in 2013. This suggests that the crust has not fully cooled yet, which is supported by the lower temperature (≃95 eV) measured ≃4 yr prior to the accretion phase in 1980. Comparing the data to thermal evolution simulations reveals that the apparent lack of cooling between 2009 and 2011 could possibly be a signature of convection driven by phase separation of light and heavy nuclei in the outer layers of the neutron star.

We extend our earlier work on turbulence-induced relative velocity between equal-size particles (Paper I, in this series) to particles of arbitrarily different sizes. The Pan & Padoan (PP10) model shows that the relative velocity between different particles has two contributions, named the generalized shear and acceleration terms, respectively. The generalized shear term represents the particles' memory of the spatial flow velocity difference across the particle distance in the past, while the acceleration term is associated with the temporal flow velocity difference on individual particle trajectories. Using the simulation of Paper I, we compute the root-mean-square relative velocity, 〈w²〉^1/2, as a function of the friction times, τ_p1 and τ_p2, of the two particles and show that the PP10 prediction is in satisfactory agreement with the data, confirming its physical picture. For a given τ_p1 below the Lagrangian correlation time of the flow, T_L, 〈w²〉^1/2 as a function of τ_p2 shows a dip at τ_p2 ≃ τ_p1, indicating tighter velocity correlation between similar particles. Defining a ratio f ≡ τ_{p, l}/τ_{p, h}, with τ_{p, l} and τ_{p, h} the friction times of the smaller and larger particles, we find that 〈w²〉^1/2 increases with decreasing f due to the generalized acceleration contribution, which dominates at f ≲ 1/4. At a fixed f, our model predicts that 〈w²〉^1/2 scales as for τ_{p, h} in the inertial range of the flow, stays roughly constant for T_L ≲ τ_{p, h} ≲ T_L/f, and finally decreases as for τ_{p, h} ≫ T_L/f. The acceleration term is independent of the particle distance, r, and reduces the r dependence of 〈w²〉^1/2 in the bidisperse case.

We report the results of millimeter-wave molecular line observations of the Tornado Nebula (G357.7–0.1), which is a bright radio source behind the Galactic center region. A 15′ × 15′ area was mapped in the J = 1–0 lines of CO, ¹³CO, and HCO⁺ with the Nobeyama Radio Observatory 45 m telescope. The Very Large Array archival data of OH at 1720 MHz were also reanalyzed. We found two molecular clouds with separate velocities, V_LSR = −14 km s⁻¹ and +5 km s⁻¹. These clouds show rough spatial anti-correlation. Both clouds are associated with OH 1720 MHz emissions in the area overlapping with the Tornado Nebula. The spatial and velocity coincidence indicates violent interaction between the clouds and the Tornado Nebula. Modestly excited gas prefers the position of the Tornado “head” in the −14 km s⁻¹ cloud, also suggesting the interaction. Virial analysis shows that the +5 km s⁻¹ cloud is more tightly bound by self-gravity than the −14 km s⁻¹ cloud. We propose a formation scenario for the Tornado Nebula; the +5 km s⁻¹ cloud collided into the −14 km s⁻¹ cloud, generating a high-density layer behind the shock front, which activates a putative compact object by Bondi–Hoyle–Lyttleton accretion to eject a pair of bipolar jets.

We report on the initial results from our deep Chandra observation (450 ks) of O-rich supernova remnant (SNR) B0049–73.6 in the Small Magellanic Cloud. We detect small metal-rich ejecta features extending out to the outermost boundary of B0049–73.6, which were not seen in the previous data with a shorter exposure. The central nebula is dominated by emission from reverse-shocked ejecta material enriched in O, Ne, Mg, and Si. O-rich ejecta distribution is relatively smooth throughout the central nebula. In contrast, the Si-rich material is highly structured. These results suggest that B0049–73.6 was produced by an asymmetric core-collapse explosion of a massive star. The estimated abundance ratios among these ejecta elements are in plausible agreement with the nucleosynthesis products from the explosion of a 13–15 M_☉ progenitor. The central ring-like (in projection) ejecta nebula extends to ∼9 pc from the SNR center. This suggests that the contact discontinuity may be located at a further distance from the SNR center than the previous estimate. We estimate the Sedov age of ∼17,000 yr and an explosion energy of E₀ ∼1.7 × 10⁵¹ erg for B0049–73.6. We place a stringent upper limit on the 2–7 keV band luminosity of L_X ∼ 8.5 × 10³¹ erg s⁻¹ for the embedded compact stellar remnant at the center of B0049–73.6.

The long residence times and small anisotropies of cosmic rays suggest that they are well confined and well scattered by the Galactic magnetic field. Due to the disk-like shape of the confinement volume, transport in the vertical direction, which is perpendicular to the mean Galactic magnetic field, is key to cosmic ray escape. It has long been recognized that this vertical transport depends both on the vertical component of the field lines themselves and on the extent to which the cosmic rays are tied to the field lines. In this paper, we use magnetic fields with very simple spatial and temporal structures to isolate some important features of cross field line transport. We show that even simple magnetic nonuniformities combined with pitch angle scattering can enhance cross field line transport by several orders of magnitude, while pitch angle scattering is unnecessary for enhanced transport if the field is chaotic. Nevertheless, perpendicular transport is much less than parallel transport in all the cases we study. We apply the results to confinement of cosmic rays in the Fermi bubbles.

We analyze the star-forming and structural properties of 45 massive (log(M/M_☉) >10) compact star-forming galaxies (SFGs) at 2 < z < 3 to explore whether they are progenitors of compact quiescent galaxies at z ∼ 2. The optical/NIR and far-IR Spitzer/Herschel colors indicate that most compact SFGs are heavily obscured. Nearly half (47%) host an X-ray-bright active galactic nucleus (AGN). In contrast, only about 10% of other massive galaxies at that time host AGNs. Compact SFGs have centrally concentrated light profiles and spheroidal morphologies similar to quiescent galaxies and are thus strikingly different from other SFGs, which typically are disk-like and sometimes clumpy or irregular. Most compact SFGs lie either within the star formation rate (SFR)–mass main sequence (65%) or below it (30%), on the expected evolutionary path toward quiescent galaxies. These results show conclusively that galaxies become more compact before they lose their gas and dust, quenching star formation. Using extensive HST photometry from CANDELS and grism spectroscopy from the 3D-HST survey, we model their stellar populations with either exponentially declining (τ) star formation histories (SFHs) or physically motivated SFHs drawn from semianalytic models (SAMs). SAMs predict longer formation timescales and older ages ∼2 Gyr, which are nearly twice as old as the estimates of the τ models. Both models yield good spectral energy distribution fits, indicating that the systematic uncertainty in the age due to degeneracies in the SFH is of that order of magnitude. However, SAM SFHs better match the observed slope and zero point of the SFR–mass main sequence. Contrary to expectations, some low-mass compact SFGs (log(M/M_☉) =10–10.6) have younger ages but lower specific SFRs than that of more massive galaxies, suggesting that the low-mass galaxies reach the red sequence faster. If the progenitors of compact SFGs are extended SFGs, state-of-the-art SAMs show that mergers and disk instabilities (DIs) are both able to shrink galaxies, but DIs are more frequent (60% versus 40%) and form more concentrated galaxies. We confirm this result via high-resolution hydrodynamic simulations.

To investigate parsec-scale jet flow conditions during GeV γ-ray flares detected by the Fermi Large Angle Telescope, we obtained centimeter-band total flux density and linear polarization monitoring observations from 2009.5 through 2012.5 with the 26 m Michigan radio telescope for a sample of core-dominated blazars. We use these data to constrain radiative transfer simulations incorporating propagating shocks oriented at an arbitrary angle to the flow direction in order to set limits on the jet flow and shock parameters during flares temporally associated with γ-ray flares in 0420−014, OJ 287, and 1156+295; these active galactic nuclei exhibited the expected signature of shocks in the linear polarization data. Both the number of shocks comprising an individual radio outburst (3 and 4) and the range of the compression ratios of the individual shocks (0.5–0.8) are similar in all three sources; the shocks are found to be forward-moving with respect to the flow. While simulations incorporating transverse shocks provide good fits for 0420−014 and 1156+295, oblique shocks are required for modeling the OJ 287 outburst, and an unusually low value of the low-energy cutoff of the radiating particles' energy distribution is also identified. Our derived viewing angles and shock speeds are consistent with independent Very Long Baseline Array results. While a random component dominates the jet magnetic field, as evidenced by the low fractional linear polarization, to reproduce the observed spectral character requires that a significant fraction of the magnetic field energy is in an ordered axial component. Both straight and low pitch angle helical field lines are viable scenarios.

Comparisons between the planet populations around solar-type stars and those orbiting M dwarfs shed light on the possible dependence of planet formation and evolution on stellar mass. However, such analyses must control for other factors, i.e., metallicity, a stellar parameter that strongly influences the occurrence of gas giant planets. We obtained infrared spectra of 121 M dwarfs stars monitored by the California Planet Search and determined metallicities with an accuracy of 0.08 dex. The mean and standard deviation of the sample are −0.05 and 0.20 dex, respectively. We parameterized the metallicity dependence of the occurrence of giant planets on orbits with a period less than two years around solar-type stars and applied this to our M dwarf sample to estimate the expected number of giant planets. The number of detected planets (3) is lower than the predicted number (6.4), but the difference is not very significant (12% probability of finding as many or fewer planets). The three M dwarf planet hosts are not especially metal rich and the most likely value of the power-law index relating planet occurrence to metallicity is 1.06 dex per dex for M dwarfs compared to 1.80 for solar-type stars; this difference, however, is comparable to uncertainties. Giant planet occurrence around both types of stars allows, but does not necessarily require, a mass dependence of ∼1 dex per dex. The actual planet–mass–metallicity relation may be complex, and elucidating it will require larger surveys like those to be conducted by ground-based infrared spectrographs and the Gaia space astrometry mission.

We report near-infrared spectroscopy of the gas giant planet HD 189733b in transit. We used the Hubble Space Telescope Wide Field Camera 3 (HST WFC3) with its G141 grism covering 1.1 μm to 1.7 μm and spatially scanned the image across the detector at 2″ s⁻¹. When smoothed to 75 nm bins, the local maxima of the transit depths in the 1.15 μm and 1.4 μm water vapor features are, respectively, 83 ± 53 ppm and 200 ± 47 ppm greater than the local minimum at 1.3 μm. We compare the WFC3 spectrum with the composite transit spectrum of HD 189733b assembled by Pont et al., extending from 0.3 μm to 24 μm. Although the water vapor features in the WFC3 spectrum are compatible with the model of non-absorbing, Rayleigh-scattering dust in the planetary atmosphere, we also re-interpret the available data with a clear planetary atmosphere. In the latter interpretation, the slope of increasing transit depth with shorter wavelengths from the near infrared, through the visible, and into the ultraviolet is caused by unocculted star spots, with a smaller contribution of Rayleigh scattering by molecular hydrogen in the planet's atmosphere. At relevant pressures along the terminator, our model planetary atmosphere's temperature is ∼700 K, which is below the condensation temperatures of sodium- and potassium-bearing molecules, causing the broad wings of the spectral lines of Na i and K i at 0.589 μm and 0.769 μm to be weak.

The cross-field diffusion of field lines in stochastic magnetic fields described by the 2D+slab model is studied using a semi-analytic statistical approach, the decorrelation trajectory method. We show that field line trapping and the associated stochastic magnetic islands strongly influence the diffusion coefficients, leading to dependences on the parameters that are different from the quasilinear and Bohm regimes. A strong amplification of the diffusion is produced by a small slab field in the presence of trapping. The diffusion regimes are determined and the corresponding physical processes are identified.

We compare the host galaxies of 902 supernovae (SNe), including SNe Ia, SNe II, and SNe Ibc, which are selected by cross-matching the Asiago Supernova Catalog with the Sloan Digital Sky Survey (SDSS) Data Release 7. We selected an additional 213 galaxies by requiring the light fraction of spectral observations to be >15%, which could represent well the global properties of the galaxies. Among these 213 galaxies, 135 appear on the Baldwin–Phillips–Terlevich diagram, which allows us to compare the hosts in terms of whether they are star-forming (SF) galaxies, active galactic nuclei (AGNs; including composites, LINERs, and Seyfert 2s) or absorption-line galaxies (Absorps; i.e., their related emission lines are weak or non-existent). The diagrams related to the parameters D_n(4000), Hδ_A, stellar masses, star formation rates (SFRs), and specific SFRs for the SNe hosts show that almost all SNe II and most of the SNe Ibc occur in SF galaxies, which have a wide range of stellar masses and low D_n(4000). The SNe Ia hosts as SF galaxies following similar trends. A significant fraction of SNe Ia occurs in AGNs and absorption-line galaxies, which are massive and have high D_n(4000). The stellar population analysis from spectral synthesis fitting shows that the hosts of SNe II have a younger stellar population than hosts of SNe Ia. These results are compared with those of the 689 comparison galaxies where the SDSS fiber captures less than 15% of the total light. These comparison galaxies appear biased toward higher 12+log(O/H) (∼0.1 dex) at a given stellar mass. Therefore, we believe the aperture effect should be kept in mind when the properties of the hosts for different types of SNe are discussed.

We derived atmospheric parameters and spectroscopic abundances for C and O for a large sample of stars located in the Hertzsprung gap in the Hertzsprung–Russell diagram in order to detect chemical peculiarities and get a comprehensive overview of the population of stars in this evolutionary state. We have observed and analyzed high-resolution spectra (R = 60,000) of 188 stars in the mass range 2–5 M_☉ with the 2.7 m Harlan J. Smith Telescope at the McDonald Observatory including 28 stars previously identified as Am/Ap stars. We find that the C and O abundances of the majority of stars in the Hertzsprung gap are in accordance with abundances derived for local lower-mass dwarfs but detect expected peculiarities for the Am/Ap stars. The C and O abundances of stars with T_eff < 6500 K are slightly lower than for the hotter objects but the C/O ratio is constant in the analyzed temperature domain. No indication of an alteration of the C and O abundances of the stars by mixing during the evolution across the Hertzsprung gap could be found before the homogenization of their atmospheres by the first dredge-up.

We attempt to provide a quantitative theoretical explanation for the observations that Ca ii H/K emission and X-ray emission from solar-like stars increase with decreasing Rossby number (i.e., with faster rotation). Assuming that these emissions are caused by magnetic cycles similar to the sunspot cycle, we construct flux transport dynamo models of 1 M_☉ stars rotating with different rotation periods. We first compute the differential rotation and the meridional circulation inside these stars from a mean-field hydrodynamics model. Then these are substituted in our dynamo code to produce periodic solutions. We find that the dimensionless amplitude f_m of the toroidal flux through the star increases with decreasing rotation period. The observational data can be matched if we assume the emissions to go as the power 3–4 of f_m. Assuming that the Babcock–Leighton mechanism saturates with increasing rotation, we can provide an explanation for the observed saturation of emission at low Rossby numbers. The main failure of our model is that it predicts an increase of the magnetic cycle period with increasing rotation rate, which is the opposite of what is found observationally. Much of our calculations are based on the assumption that the magnetic buoyancy makes the magnetic flux tubes rise radially from the bottom of the convection zone. Taking into account the fact that the Coriolis force diverts the magnetic flux tubes to rise parallel to the rotation axis in rapidly rotating stars, the results do not change qualitatively.

It has been suggested that the hot plasma of the solar corona comes primarily from impulsive heating events, or nanoflares, that occur in the lower atmosphere, either in the upper part of the ordinary chromosphere or at the tips of type II spicules. We test this idea with a series of hydrodynamic simulations. We find that synthetic Fe xii (195) and Fe xiv (274) line profiles generated from the simulations disagree dramatically with actual observations. The integrated line intensities are much too faint; the blueshifts are much too fast; the blue-red asymmetries are much too large; and the emission is confined to low altitudes. We conclude that chromospheric nanoflares are not a primary source of hot coronal plasma. Such events may play an important role in producing the chromosphere and powering its intense radiation, but they do not, in general, raise the temperature of the plasma to coronal values. Those cases where coronal temperatures are reached must be relatively uncommon. The observed profiles of Fe xii and Fe xiv come primarily from plasma that is heated in the corona itself, either by coronal nanoflares or a quasi-steady coronal heating process. Chromospheric nanoflares might play a role in generating waves that provide this coronal heating.

There have been ubiquitous observations of wave-like motions in the solar atmosphere for decades. Recent improvements to space- and ground-based observatories have allowed the focus to shift to smaller magnetic structures on the solar surface. In this paper, high-resolution ground-based data taken using the Swedish 1 m Solar Telescope is combined with co-spatial and co-temporal data from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) satellite to analyze running penumbral waves (RPWs). RPWs have always been thought to be radial wave propagation that occurs within sunspots. Recent research has suggested that they are in fact upwardly propagating field-aligned waves (UPWs). Here, RPWs within a solar pore are observed for the first time and are interpreted as UPWs due to the lack of a penumbra that is required to support RPWs. These UPWs are also observed co-spatially and co-temporally within several SDO/AIA elemental lines that sample the transition region and low corona. The observed UPWs are traveling at a horizontal velocity of around 17  ±  0.5 km s⁻¹ and a minimum vertical velocity of 42 ± 21 km s⁻¹. The estimated energy of the waves is around 150 W m⁻², which is on the lower bound required to heat the quiet-Sun corona. This is a new, yet unconsidered source of wave energy within the solar chromosphere and low corona.

The magnetorotational instability (MRI) drives magnetized turbulence in sufficiently ionized regions of protoplanetary disks, leading to mass accretion. The dissipation of the potential energy associated with this accretion determines the thermal structure of accreting regions. Until recently, the heating from the turbulence has only been treated in an azimuthally averaged sense, neglecting local fluctuations. However, magnetized turbulence dissipates its energy intermittently in current sheet structures. We study this intermittent energy dissipation using high resolution numerical models including a treatment of radiative thermal diffusion in an optically thick regime. Our models predict that these turbulent current sheets drive order-unity temperature variations even where the MRI is damped strongly by Ohmic resistivity. This implies that the current sheet structures where energy dissipation occurs must be well-resolved to correctly capture the flow structure in numerical models. Higher resolutions are required to resolve energy dissipation than to resolve the magnetic field strength or accretion stresses. The temperature variations are large enough to have major consequences for mineral formation in disks, including melting chondrules, remelting calcium–aluminum-rich inclusions, and annealing silicates; and may drive hysteresis: current sheets in MRI active regions could be significantly more conductive than the remainder of the disk.

Ultraluminous and luminous infrared galaxies (ULIRGs and LIRGs) are the most extreme star-forming galaxies in the universe and dominate the total star formation rate density at z > 1. In the local universe (z < 0.3), the majority of ULIRGs and a significant portion of LIRGs are triggered by interactions between gas-rich spiral galaxies, yet it is unclear if this is still the case at high z. To investigate the relative importance of galaxy interactions in infrared luminous galaxies, we carry out a comparison of optical morphological properties between local (U)LIRGs and (U)LIRGs at z = 0.5–1.5 based on the same sample selection, morphology classification scheme, and optical morphology at similar rest-frame wavelengths. In addition, we quantify the systematics in comparing local and high-z data sets by constructing a redshifted data set from local (U)LIRGs, in which its data quality mimics the high-z data set. Based on the Gini–M₂₀ classification scheme, we find that the fraction of interacting systems decreases by ∼8% from local to z ≲ 1, and it is consistent with the reduction between local and redshifted data sets (). Based on visual classifications, the merger fraction of local ULIRGs is found to be ∼20% lower compared to published results, and the reduction due to redshifting is . Consequently, the differences of merger fractions between local and z ≲ 1 (U)LIRGs is only ∼17%. These results demonstrate that there is no strong evolution in the fraction of (U)LIRGs classified as mergers at least out to z ∼ 1. At z > 1, the morphology types of ∼30% of (U)LIRGs cannot be determined due to their faintness in the F814W band; thus, the merger fraction measured at z > 1 suffers from large uncertainties.

The methods by which one characterizes the distribution of matter in cosmological simulations is intrinsically different from how one performs the same task observationally. In this paper, we make substantial steps toward comparing simulations and observations of the intergalactic medium (IGM) in a more sensible way. We present a pipeline that generates and fits synthetic QSO absorption spectra using sight lines cast through a cosmological simulation, and simultaneously identifies structure by directly analyzing the variations in H i and O vi number density. We compare synthetic absorption spectra with a less observationally motivated, but more straightforward density threshold-based method for finding absorbers. Our efforts focus on H i and O vi to better characterize the warm/hot IGM, a subset of the IGM that is challenging to conclusively identify observationally. We find that the two methods trace roughly the same quantities of H i and O vi above observable column density limits, but the synthetic spectra typically identify more substructure in absorbers. We use both methods to characterize H i and O vi absorber properties. We find that both integrated and differential column density distributions from both methods generally agree with observations. The distribution of Doppler parameters between the two methods are similar for Lyα and compare reasonably with observational results, but while the two methods agree with each other with O vi systems, they both are systematically different from observations. We find a strong correlation between O vi baryon fraction and O vi column density. We also discuss a possible bimodality in the temperature distribution of the gas traced by O vi.

The J = 2 ← 1 rotational transition of AlH (X¹Σ⁺) near 755 GHz and the J = 4 ← 3 line of AlD (X¹Σ⁺) near 787 GHz have been measured using terahertz direct absorption spectroscopy. Both species were created in an AC discharge of Al(CH₃)₃ and H₂ or D₂ in the presence of argon. This work is the first direct measurement of both transitions. These data were combined with previous submillimeter transition frequencies for both molecules recorded by Halfen & Ziurys in global analyses to refine their spectroscopic parameters. The constants B and D for AlH were determined for the first time based on pure rotational data only, improving their accuracy, while those for AlD were slightly refined. Predictions for higher-lying transitions of AlH must consequently be revised by at least 50 MHz, a significant difference. AlH has been observed via its A¹Π–X¹Σ⁺ electronic transition in stellar photospheres, suggesting that this species may be present in circumstellar gas surrounding late-type stars, where five aluminum-bearing molecules have already been detected.

The properties of asymptotic giant branch (AGB) stars in the Local Group galaxy M32 are investigated using ground- and space-based observations that span the 1–8 μm wavelength interval, with the goal of demonstrating the utility of infrared observations as probes of stellar content. Comparisons with isochrones indicate that the brightest resolved stars in M32 have ages of a few gigayears and are younger on average than AGB stars with the same intrinsic brightness in the outer disk of M31. Accounting for stellar variability is shown to be essential for modeling AGB luminosity functions (LFs). Model LFs that assume the star-forming history measured by Monachesi et al. and the variability properties of Galactic AGB stars match both the K and [5.8] LFs of M32. Models also suggest that the slope of the [5.8] LF between M_[5.8] = −8.5 and −10.0 is sensitive to the mix of stellar ages, and a sizeable fraction of the stars in M32 must have an age older than 7 Gyr in order to match the [5.8] LF. The structural properties of M32 in the infrared are also investigated. The effective radii that are computed from near-infrared and mid-infrared isophotes are similar to those measured at visible wavelengths, suggesting that the stellar content of M32 is well mixed. However, isophotes at radii >16″ (>60 pc) in the near- and mid-infrared are flatter than those at visible wavelengths. The coefficient of the fourth-order cosine term in the Fourier expansion of isophotes changes from “boxy” values at r < 16″ to “disky” values at r > 48″in [3.6] and [4.5]. The mid-infrared colors near the center of M32 do not vary systematically with radius, providing evidence of a well mixed stellar content in this part of the galaxy.

We describe an ongoing search for pulsars and dispersed pulses of radio emission, such as those from rotating radio transients (RRATs) and fast radio bursts, at 350 MHz using the Green Bank Telescope. With the Green Bank Ultimate Pulsar Processing Instrument, we record 100 MHz of bandwidth divided into 4096 channels every 81.92 μs. This survey will cover the entire sky visible to the Green Bank Telescope (δ > −40°, or 82% of the sky) and outside of the Galactic Plane will be sensitive enough to detect slow pulsars and low dispersion measure (<30 pc cm⁻³) millisecond pulsars (MSPs) with a 0.08 duty cycle down to 1.1 mJy. For pulsars with a spectral index of −1.6, we will be 2.5 times more sensitive than previous and ongoing surveys over much of our survey region. Here we describe the survey, the data analysis pipeline, initial discovery parameters for 62 pulsars, and timing solutions for 5 new pulsars. PSR J0214+5222 is an MSP in a long-period (512 days) orbit and has an optical counterpart identified in archival data. PSR J0636+5129 is an MSP in a very short-period (96 minutes) orbit with a very low mass companion (8 M_J). PSR J0645+5158 is an isolated MSP with a timing residual RMS of 500 ns and has been added to pulsar timing array experiments. PSR J1434+7257 is an isolated, intermediate-period pulsar that has been partially recycled. PSR J1816+4510 is an eclipsing MSP in a short-period orbit (8.7 hr) and may have recently completed its spin-up phase.

Results are presented for an initial survey of the Norma Arm gathered with the focusing hard X-Ray Telescope NuSTAR. The survey covers 0.2 deg² of sky area in the 3–79 keV range with a minimum and maximum raw depth of 15 ks and 135 ks, respectively. Besides a bright black-hole X-ray binary in outburst (4U 1630−47) and a new X-ray transient (NuSTAR J163433−473841), NuSTAR locates three sources from the Chandra survey of this region whose spectra are extended above 10 keV for the first time: CXOU J163329.5−473332, CXOU J163350.9−474638, and CXOU J163355.1−473804. Imaging, timing, and spectral data from a broad X-ray range (0.3–79 keV) are analyzed and interpreted with the aim of classifying these objects. CXOU J163329.5−473332 is either a cataclysmic variable or a faint low-mass X-ray binary. CXOU J163350.9−474638 varies in intensity on year-long timescales, and with no multi-wavelength counterpart, it could be a distant X-ray binary or possibly a magnetar. CXOU J163355.1−473804 features a helium-like iron line at 6.7 keV and is classified as a nearby cataclysmic variable. Additional surveys are planned for the Norma Arm and Galactic Center, and those NuSTAR observations will benefit from the lessons learned during this pilot study.

We present the effects of self-gravity on the vertical structure and neutrino luminosity of the neutrino-dominated accretion disks in cylindrical coordinates. It is found that significant changes of the structure appear in the outer region of the disk, especially for high accretion rates (e.g., ≳ 1 M_☉ s⁻¹), and thus cause the slight increase in the neutrino luminosity. Furthermore, the gravitational instability of the disk is reviewed by the vertical distribution of the Toomre parameter, which may account for the late-time flares in gamma-ray bursts and the extended emission in short-duration gamma-ray bursts.

Here we report on Swift and Suzaku observations near the end of an outburst from the black hole transient 4U 1630–47 and Chandra observations when the source was in quiescence. 4U 1630–47 made a transition from a soft state to the hard state ∼50 days after the main outburst ended. During this unusual delay, the flux continued to drop, and one Swift measurement found the source with a soft spectrum at a 2–10 keV luminosity of L = 1.07 × 10³⁵ erg s⁻¹ for an estimated distance of 10 kpc. While such transients usually make a transition to the hard state at L/L_Edd = 0.3%–3%, where L_Edd is the Eddington luminosity, the 4U 1630–47 spectrum remained soft at L/L_Edd = 0.008 % (as measured in the 2–10 keV band), where M₁₀ is the mass of the black hole in units of 10 M_☉. An estimate of the luminosity in the broader 0.5–200 keV bandpass gives L/L_Edd = 0.03 %, which is still an order of magnitude lower than typical. We also measured an exponential decay of the X-ray flux in the hard state with an e-folding time of 3.39 ± 0.06 days, which is much less than previous measurements of 12–15 days during decays by 4U 1630–47 in the soft state. With the ∼100 ks Suzaku observation, we do not see evidence for a reflection component, and the 90% confidence limits on the equivalent width of a narrow iron Kα emission line are <40 eV for a narrow line and <100 eV for a line of any width, which is consistent with a change of geometry (either a truncated accretion disk or a change in the location of the hard X-ray source) in the hard state. Finally, we report a 0.5–8 keV luminosity upper limit of <2 × 10³² erg s⁻¹ in quiescence, which is the lowest value measured for 4U 1630–47 to date.

We use analytic estimates and numerical simulations of test particles interacting with magnetohydrodynamic (MHD) turbulence to show that subsonic MHD turbulence produces efficient second-order Fermi acceleration of relativistic particles. This acceleration is not well described by standard quasi-linear theory but is a consequence of resonance broadening of wave–particle interactions in MHD turbulence. We provide momentum diffusion coefficients that can be used for astrophysical and heliospheric applications and discuss the implications of our results for accretion flows onto black holes. In particular, we show that particle acceleration by subsonic turbulence in radiatively inefficient accretion flows can produce a non-thermal tail in the electron distribution function that is likely important for modeling and interpreting the emission from low-luminosity systems such as Sgr A* and M87.