Table of contents

We present here the results from new Very Long Baseline Array (VLBA) observations at 1.6 and 5 GHz of 19 galaxies of a complete sample of 21 Uppasala General Catalog (UGC) Fanaroff–Riley type I (FRI) radio galaxies. New Chandra data of two sources, viz., UGC 00408 and UGC 08433, are combined with the Chandra archival data of 13 sources. The 5 GHz observations of 10 "core-jet" sources are polarization-sensitive, while the 1.6 GHz observations constitute second-epoch total intensity observations of nine "core-only" sources. Polarized emission is detected in the jets of seven sources at 5 GHz, but the cores are essentially unpolarized, except in M87. Polarization is detected at the jet edges in several sources, and the inferred magnetic field is primarily aligned with the jet direction. This could be indicative of magnetic field "shearing" due to jet-medium interaction, or the presence of helical magnetic fields. The jet peak intensity I_ν falls with distance d from the core, following the relation, I_ν∝d^a, where a is typically ∼ − 1.5. Assuming that adiabatic expansion losses are primarily responsible for the jet intensity "dimming," two limiting cases are considered: (1) the jet has a constant speed on parsec scales and is expanding gradually such that the jet radius r∝d^0.4; this expansion is, however, unobservable in the laterally unresolved jets at 5 GHz, and (2) the jet is cylindrical and is accelerating on parsec scales. Accelerating parsec-scale jets are consistent with the phenomenon of "magnetic driving" in Poynting-flux-dominated jets. While slow jet expansion as predicted by case (1) is indeed observed in a few sources from the literature that are resolved laterally, on scales of tens or hundreds of parsecs, case (2) cannot be ruled out in the present data, provided the jets become conical on scales larger than those probed by VLBA. Chandra observations of 15 UGC FRIs detect X-ray jets in 9 of them. The high frequency of occurrence of X-ray jets in this complete sample suggests that they are a signature of a ubiquitous process in FRI jets. It appears that the FRI jets start out relativistically on parsec scales but decelerate on kiloparsec scales, with the X-ray emission revealing the sites of bulk deceleration and particle reacceleration.

We explore the self-regulation of star formation using a large suite of high-resolution hydrodynamic simulations, focusing on molecule-dominated regions (galactic centers and [U]LIRGS) where feedback from star formation drives highly supersonic turbulence. In equilibrium, the total midplane pressure, dominated by turbulence, must balance the vertical weight of the interstellar medium. Under self-regulation, the momentum flux injected by feedback evolves until it matches the vertical weight. We test this flux balance in simulations spanning a wide range of parameters, including surface density Σ, momentum injected per stellar mass formed (p_*/m_*), and angular velocity. The simulations are two-dimensional radial–vertical slices, and include both self-gravity and an external potential that helps to confine gas to the disk midplane. After the simulations reach a steady state in all relevant quantities, including the star formation rate Σ_SFR, there is remarkably good agreement between the vertical weight, the turbulent pressure, and the momentum injection rate from supernovae. Gas velocity dispersions and disk thicknesses increase with p_*/m_*. The efficiency of star formation per free-fall time at the midplane density, _ff(n₀), is insensitive to the local conditions and to the star formation prescription in very dense gas. We measure _ff(n₀) ∼ 0.004–0.01, consistent with low and approximately constant efficiencies inferred from observations. For Σ ∈ (100–1000) M_☉ pc⁻², we find Σ_SFR ∈ (0.1–4) M_☉ kpc⁻² yr⁻¹, generally following a Σ_SFR ∝ Σ² relationship. The measured relationships agree very well with vertical equilibrium and with turbulent energy replenishment by feedback within a vertical crossing time. These results, along with the observed Σ–Σ_SFR relation in high-density environments, provide strong evidence for the self-regulation of star formation.

We present dynamical and structural scaling relations of quiescent galaxies at z = 2, including the dynamical-mass–size relation and the first constraints on the fundamental plane (FP). The backbone of the analysis is a new, very deep Very Large Telescope/X-shooter spectrum of a massive, compact, quiescent galaxy at z = 2.0389. We detect the continuum between 3700 and 22,000 Å and several strong absorption features (Balmer series, Ca H+K, G band) from which we derive a stellar velocity dispersion of 318 ± 53 km s⁻¹. We perform detailed modeling of the continuum emission and line indices and derive strong simultaneous constraints on the age, metallicity, and stellar mass. The galaxy is a dusty (A_V = 0.77^+0.36_−0.32) solar metallicity (log(Z/Z_☉) = 0.02^+0.20_−0.41) post-starburst galaxy, with a mean-luminosity-weighted log(age/yr) of 8.9 ± 0.1. The galaxy formed the majority of its stars at z > 3 and currently has little or no ongoing star formation. We compile a sample of three other z ∼ 2 quiescent galaxies with measured velocity dispersions, two of which are also post-starburst like. Their dynamical-mass–size relation is offset significantly less than the stellar-mass–size relation from the local early-type relations, which we attribute to a lower central dark matter fraction. Recent cosmological merger simulations agree qualitatively with the data, but cannot fully account for the evolution in the dark matter fraction. The z ∼ 2 FP requires additional evolution beyond passive stellar aging to be in agreement with the local FP. The structural evolution predicted by the cosmological simulations is insufficient, suggesting that additional, possibly non-homologous, structural evolution is needed.

We utilize the Sagittarius Window Eclipsing Extrasolar Planet Search Hubble Space Telescope/Advanced Camera for Surveys data set for a Deep Rapid Archival Flare Transient Search to constrain the flare rate toward the older stellar population in the Galactic bulge. During seven days of monitoring 229,293 stars brighter than V = 29.5, we find evidence for flaring activity in 105 stars between V = 20 and V = 28. We divided the sample into non-variable stars and variable stars whose light curves contain large-scale variability. The flare rate on variable stars is ∼700 times that of non-variable stars, with a significant correlation between the amount of underlying stellar variability and peak flare amplitude. The flare energy loss rates are generally higher than those of nearby well-studied single dMe flare stars. The distribution of proper motions is consistent with the flaring stars being at the distance and age of the Galactic bulge. If they are single dwarfs, then they span a range of ≈1.0–0.25 M_☉. A majority of the flaring stars exhibit periodic photometric modulations with P < 3 days. If these are tidally locked magnetically active binary systems, then their fraction in the bulge is enhanced by a factor of ∼20 compared to the local value. These stars may be useful for placing constraints on the angular momentum evolution of cool close binary stars. Our results expand the type of stars studied for flares in the optical band, and suggest that future sensitive optical time-domain studies will have to contend with a larger sample of flaring stars than the M dwarf flare stars usually considered.

We develop the mid-infrared extinction (MIREX) mapping technique of Butler & Tan (Paper I), presenting a new method to correct for the Galactic foreground emission based on observed saturation in independent cores. Using Spitzer GLIMPSE 8 μm images, this allows us to accurately probe mass surface densities, Σ, up to ≃ 0.5 g cm⁻² with 2'' resolution and mitigate one of the main sources of uncertainty associated with Galactic MIREX mapping. We then characterize the structure of 42 massive starless and early-stage cores and their surrounding clumps, selected from 10 infrared dark clouds, measuring Σ_cl(r) from the core/clump centers. We first assess the properties of the core/clump at a scale where the total enclosed mass as projected on the sky is M_cl = 60 M_☉. We find that these objects have a mean radius of R_cl ≃ 0.1 pc, mean $\bar{\Sigma }_{\rm cl} = 0.3\:\rm g\:cm^{-2}$ and, if fitted by a power-law (PL) density profile $\rho _{\rm cl}\propto r^{-k_{\rm \rho ,cl}}$, a mean value of k_{ρ, cl} = 1.1. If we assume a core is embedded in each clump and subtract the surrounding clump envelope to derive the core properties, then we find a mean core density PL index of k_{ρ, c} = 1.6. We repeat this analysis as a function of radius and derive the best-fitting PL plus uniform clump envelope model for each of the 42 core/clumps. The cores have typical masses of M_c ∼ 100 M_☉ and $\bar{\Sigma }_c\sim 0.1\:\rm g\:cm^{-2}$, and are embedded in clumps with comparable mass surface densities. We also consider Bonnor–Ebert density models, but these do not fit the observed Σ profiles as well as PLs. We conclude that massive starless cores exist and are well described by singular polytropic spheres. Their relatively low values of Σ and the fact that they are IR dark may imply that their fragmentation is inhibited by magnetic fields rather than radiative heating. Comparing to massive star-forming cores and clumps, there is tentative evidence for an evolution toward higher densities and steeper density profiles as star formation proceeds.

We study the effect that non-equilibrium chemistry in dynamical models of collapsing molecular cloud cores has on measurements of the magnetic field in these cores, the degree of ionization, and the mean molecular weight of ions. We find that OH and CN, usually used in Zeeman observations of the line-of-sight magnetic field, have an abundance that decreases toward the center of the core much faster than the density increases. As a result, Zeeman observations tend to sample the outer layers of the core and consistently underestimate the core magnetic field. The degree of ionization follows a complicated dependence on the number density at central densities up to 10⁵ cm⁻³ for magnetic models and 10⁶ cm⁻³ in non-magnetic models. At higher central densities, the scaling approaches a power law with a slope of −0.6 and a normalization which depends on the cosmic-ray ionization rate ζ and the temperature T as (ζT)^1/2. The mean molecular weight of ions is systematically lower than the usually assumed value of 20–30, and, at high densities, approaches a value of 3 due to the asymptotic dominance of the H⁺₃ ion. This significantly lower value implies that ambipolar diffusion operates faster.

Extreme-ultraviolet (EUV) waves have been found for about 15 years. However, significant controversy remains over their physical natures and origins. In this paper, we report an EUV wave that was accompanied by an X1.9 flare and a partial halo coronal mass ejection (CME). Using high temporal and spatial resolution observations taken by the Solar Dynamics Observatory and the Solar-TErrestrial RElations Observatory, we are able to investigate the detailed kinematics of the EUV wave. We find several arguments that support the fast-mode wave scenario. (1) The speed of the EUV wave (570 km s⁻¹) is higher than the sound speed of the quiet-Sun corona. (2) Significant deceleration of the EUV wave (−130 m s⁻²) is found during its propagation. (3) The EUV wave resulted in the oscillations of a loop and a filament along its propagation path, and a reflected wave from the polar coronal hole is also detected. (4) Refraction or reflection effect is observed when the EUV wave was passing through two coronal bright points. (5) The dimming region behind the wavefront stopped to expand when the wavefront started to become diffuse. (6) The profiles of the wavefront exhibited a dispersive nature, and the magnetosonic Mach number of the EUV wave derived from the highest intensity jump is about 1.4. In addition, triangulation indicates that the EUV wave propagated within a height range of about 60–100 Mm above the photosphere. We propose that the EUV wave observed should be a nonlinear fast-mode magnetosonic wave that propagated freely in the corona after it was driven by the CME expanding flanks during the initial period.

Recent observations of power-law time profiles of energetic particles accelerated at interplanetary shocks have shown the possibility of anomalous, superdiffusive transport for energetic particles throughout the heliosphere. Those findings call for an accurate investigation of the magnetic field fluctuation properties at the resonance frequencies upstream of the shock's fronts. Normalized magnetic field variances, indeed, play a crucial role in the determination of the pitch-angle scattering times and then of the transport regime. The present analysis investigates the time behavior of the normalized variances of the magnetic field fluctuations, measured by the Ulysses spacecraft upstream of corotating interaction region (CIR) shocks, for those events which exhibit superdiffusion for energetic electrons. We find a quasi-constant value for the normalized magnetic field variances from about 10 hr to 100 hr from the shock front. This rules out the presence of a varying diffusion coefficient and confirms the possibility of superdiffusion for energetic electrons. A statistical analysis of the scattering times obtained from the magnetic fluctuations upstream of the CIR events has also been performed; the resulting power-law distributions of scattering times imply long range correlations and weak pitch-angle scattering, and the power-law slopes are in qualitative agreement with superdiffusive processes described by a Lévy random walk.

We report the first hard X-ray observation of a solar jet on the limb with flare footpoints occulted, so that faint emission from accelerated electrons in the corona can be studied in detail. In this event on 2003 August 21, RHESSI observed a double coronal hard X-ray source in the pre-impulsive phase at both thermal and nonthermal energies. In the impulsive phase, the first of two hard X-ray bursts consists of a single thermal/nonthermal source coinciding with the lower of the two earlier sources, and the second burst shows an additional nonthermal, elongated source, spatially and temporally coincident with the coronal jet. Analysis of the jet hard X-ray source shows that collisional losses by accelerated electrons can deposit enough energy to generate the jet. The hard X-ray time profile above 20 keV matches that of the accompanying Type III and broadband gyrosynchrotron radio emission, indicating both accelerated electrons escaping outward along the jet path and electrons trapped in the flare loop. The double coronal hard X-ray source, the open field lines indicated by Type III bursts, and the presence of a small post-flare loop are consistent with significant electron acceleration in an interchange reconnection geometry.

We present the results of far ultraviolet (FUV) observations of the broad region around the Aquila Rift including the Galactic plane. As compared with various wavelength data sets, dust scattering is found to be the major origin of the diffuse FUV continuum in this region. The FUV intensity clearly correlates with the dust extinction level for E(B − V) < 0.2, while this correlation disappears for E(B − V) > 0.2 due to heavy dust extinction combined with the effect of nonuniform interstellar radiation fields. The FUV intensity also correlates well with Hα intensity, implying that at least some fraction of the observed Hα emission could be the dust-scattered light of Hα photons originating elsewhere in the Galaxy. Most of the Aquila Rift region is seen devoid of diffuse FUV continuum due to heavy extinction while strong emission is observed in the surrounding regions. Molecular hydrogen fluorescent emission lines are clearly seen in the spectrum of "Aquila-Serpens," while "Aquila-East" does not show any apparent line features. CO emission intensity is also found to be higher in the "Aquila-Serpens" region than in the "Aquila-East" region. In this regard, we note that regions of star formation have been found in "Aquila-Serpens" but not in "Aquila-East."

The X-shooter instrument on the Very Large Telescope was used to obtain spectra of seven moderate-redshift quasars simultaneously covering the spectral range ∼3000 Å to 2.5 μm. At z ≈ 1.5, most of the prominent broad emission lines in the ultraviolet to optical region are captured in their rest frame. We use this unique data set, which mitigates complications from source variability, to intercompare the line profiles of C iv λ1549, C iii] λ1909, Mg ii λ2800, and Hα and evaluate their implications for black hole (BH) mass estimation. We confirm that Mg ii and the Balmer lines share similar kinematics and that they deliver mutually consistent BH mass estimates with minimal internal scatter (≲0.1 dex) using the latest virial mass estimators. Although no virial mass formalism has yet been calibrated for C iii], this line does not appear promising for such an application because of the large spread of its velocity width compared to lines of both higher and lower ionization; part of the discrepancy may be due to the difficulty of deblending C iii] from its neighboring lines. The situation for C iv is complex and, because of the limited statistics of our small sample, inconclusive. On the one hand, slightly more than half of our sample (4/7) have C iv line widths that correlate reasonably well with Hα line widths, and their respective BH mass estimates agree to within ∼0.15 dex. The rest, on the other hand, exhibit exceptionally broad C iv profiles that overestimate virial masses by factors of 2–5 compared to Hα. As C iv is widely used to study BH demographics at high redshifts, we urgently need to revisit our analysis with a larger sample.

The distribution of QSO radio luminosities has long been debated in the literature. Some argue that it is a bimodal distribution, implying that there are two separate QSO populations (normally referred to as "radio-loud" and "radio-quiet"), while others claim it forms a more continuous distribution characteristic of a single population. We use deep observations at 20 GHz to investigate whether the distribution is bimodal at high radio frequencies. Carrying out this study at high radio frequencies has an advantage over previous studies as the radio emission comes predominantly from the core of the active galactic nucleus, and hence probes the most recent activity. Studies carried out at lower frequencies are dominated by the large-scale lobes where the emission is built up over longer timescales (10⁷–10⁸ yr), thereby confusing the sample. Our sample comprises 874 X-ray-selected QSOs that were observed as part of the 6dF Galaxy Survey. Of these, 40% were detected down to a 3σ detection limit of 0.2–0.5 mJy. No evidence of bimodality is seen in either the 20 GHz luminosity distribution or in the distribution of the R₂₀ parameter: the ratio of the radio to optical luminosities traditionally used to classify objects as being either radio-loud or radio-quiet. Previous results have claimed that at low radio luminosities, star formation processes can dominate the radio emission observed in QSOs. We attempt to investigate these claims by stacking the undetected sources at 20 GHz and discuss the limitations in carrying out this analysis. However, if the radio emission was solely due to star formation processes, we calculate that this corresponds to star formation rates ranging from ∼10 M_☉ yr⁻¹ to ∼2300 M_☉ yr⁻¹.

For a solar flare occurring on 2010 November 3, we present observations using several SDO/AIA extreme-ultraviolet (EUV) passbands of an erupting flux rope followed by inflows sweeping into a current sheet region. The inflows are soon followed by outflows appearing to originate from near the termination point of the inflowing motion—an observation in line with standard magnetic reconnection models. We measure average inflow plane-of-sky speeds to range from ∼150 to 690 km s⁻¹ with the initial, high-temperature inflows being the fastest. Using the inflow speeds and a range of Alfvén speeds, we estimate the Alfvénic Mach number which appears to decrease with time. We also provide inflow and outflow times with respect to RHESSI count rates and find that the fast, high-temperature inflows occur simultaneously with a peak in the RHESSI thermal light curve. Five candidate inflow–outflow pairs are identified with no more than a minute delay between detections. The inflow speeds of these pairs are measured to be ∼10² km s⁻¹ with outflow speeds ranging from ∼10² to 10³ km s⁻¹—indicating acceleration during the reconnection process. The fastest of these outflows are in the form of apparently traveling density enhancements along the legs of the loops rather than the loop apexes themselves. These flows could possibly either be accelerated plasma, shocks, or waves prompted by reconnection. The measurements presented here show an order of magnitude difference between the retraction speeds of the loops and the speed of the density enhancements within the loops—presumably exiting the reconnection site.

Since 2008 December, the Interstellar Boundary Explorer (IBEX) has been making detailed observations of neutrals from the boundaries of the heliosphere using two neutral atom cameras with overlapping energy ranges. The unexpected, yet defining feature discovered by IBEX is a Ribbon that extends over the energy range from about 0.2 to 6 keV. This Ribbon is superposed on a more uniform, globally distributed heliospheric neutral population. With some important exceptions, the focus of early IBEX studies has been on neutral atoms with energies greater than ∼0.5 keV. With nearly three years of science observations, enough low-energy neutral atom measurements have been accumulated to extend IBEX observations to energies less than ∼0.5 keV. Using the energy overlap of the sensors to identify and remove backgrounds, energy spectra over the entire IBEX energy range are produced. However, contributions by interstellar neutrals to the energy spectrum below 0.2 keV may not be completely removed. Compared with spectra at higher energies, neutral atom spectra at lower energies do not vary much from location to location in the sky, including in the direction of the IBEX Ribbon. Neutral fluxes are used to show that low energy ions contribute approximately the same thermal pressure as higher energy ions in the heliosheath. However, contributions to the dynamic pressure are very high unless there is, for example, turbulence in the heliosheath with fluctuations of the order of 50–100 km s⁻¹.

We examine a simulation of flux emergence and cancellation, which shows a complex sequence of processes that accumulate free magnetic energy in the solar corona essential for the eruptive events such as coronal mass ejections, filament eruptions, and flares. The flow velocity at the surface and in the corona shows a consistent shearing pattern along the polarity inversion line (PIL), which together with the rotation of the magnetic polarities, builds up the magnetic shear. Tether-cutting reconnection above the PIL then produces longer sheared magnetic field lines that extend higher into the corona, where a sigmoidal structure forms. Most significantly, reconnection and upward-energy–flux transfer are found to occur even as magnetic flux is submerging and appears to cancel at the photosphere. A comparison of the simulated coronal field with the corresponding coronal potential field graphically shows the development of non-potential fields during the emergence of the magnetic flux and formation of sunspots.

We find that a sunspot with positive polarity had an obvious counterclockwise rotation and resulted in the formation and eruption of an inverse S-shaped filament in NOAA Active Region 08858 from 2000 February 9 to 10. The sunspot had two umbrae which rotated around each other by 195° within about 24 hr. The average rotation rate was nearly 8° hr⁻¹. The fastest rotation in the photosphere took place during 14:00 UT to 22:01 UT on February 9, with a rotation rate of nearly 16° hr⁻¹. The fastest rotation in the chromosphere and the corona took place during 15:28 UT to 19:00 UT on February 9, with a rotation rate of nearly 20° hr⁻¹. Interestingly, the rapid increase of the positive magnetic flux occurred only during the fastest rotation of the rotating sunspot, the bright loop-shaped structure, and the filament. During the sunspot rotation, the inverse S-shaped filament gradually formed in the EUV filament channel. The filament experienced two eruptions. In the first eruption, the filament rose quickly and then the filament loops carrying the cool and the hot material were seen to spiral counterclockwise into the sunspot. About 10 minutes later, the filament became active and finally erupted. The filament eruption was accompanied with a C-class flare and a halo coronal mass ejection. These results provide evidence that sunspot rotation plays an important role in the formation and eruption of the sigmoidal active-region filament.

We take advantage of gravitational lensing amplification by A1689 (z = 0.187) to undertake the first space-based census of emission line galaxies (ELGs) in the field of a massive lensing cluster. Forty-three ELGs are identified to a flux of i₇₇₅ = 27.3 via slitless grism spectroscopy. One ELG (at z = 0.7895) is very bright owing to lensing magnification by a factor of ≈4.5. Several Balmer emission lines (ELs) detected from ground-based follow-up spectroscopy signal the onset of a major starburst for this low-mass galaxy (M_* ≈ 2 × 10⁹ M_☉) with a high specific star formation rate (≈20 Gyr⁻¹). From the blue ELs we measure a gas-phase oxygen abundance consistent with solar (12+log(O/H) = 8.8  ±  0.2). We break the continuous line-emitting region of this giant arc into seven ∼1 kpc bins (intrinsic size) and measure a variety of metallicity-dependent line ratios. A weak trend of increasing metal fraction is seen toward the dynamical center of the galaxy. Interestingly, the metal line ratios in a region offset from the center by ∼1 kpc have a placement on the blue H ii region excitation diagram with f ([O iii])/f (Hβ) and f ([Ne iii])/f (Hβ) that can be fitted by an active galactic nucleus (AGN). This asymmetrical AGN-like behavior is interpreted as a product of shocks in the direction of the galaxy's extended tail, possibly instigated by a recent galaxy interaction.

We demonstrate a new technique for determining the physical conditions of the broad-line-emitting gas in quasars, using near-infrared hydrogen emission lines. Unlike higher ionization species, hydrogen is an efficient line emitter for a very wide range of photoionization conditions, and the observed line ratios depend strongly on the density and photoionization state of the gas present. A locally optimally emitting cloud model of the broad emission line region was compared to measured emission lines of four nearby (z ≈ 0.2) quasars that have optical and NIR spectra of sufficient signal to noise to measure their Paschen lines. The model provides a good fit to three of the objects, and a fair fit to the fourth object, an ultraluminous infrared galaxy. We find that low-incident-ionizing fluxes (Φ_H < 10¹⁸ cm⁻² s⁻¹) and high gas densities (n_H > 10¹² cm⁻³) are required to reproduce the observed hydrogen emission line ratios. This analysis demonstrates that the use of composite spectra in photoionization modeling is inappropriate; models must be fitted to the individual spectra of quasars.

We present near-infrared light curves of supernova (SN) 2011fe in M101, including 34 epochs in H band starting 14 days before maximum brightness in the B band. The light curve data were obtained with the WIYN High-Resolution Infrared Camera. When the data are calibrated using templates of other Type Ia SNe, we derive an apparent H-band magnitude at the epoch of B-band maximum of 10.85  ±  0.04. This implies a distance modulus for M101 that ranges from 28.86 to 29.17 mag, depending on which absolute calibration for Type Ia SNe is used.

We present recent contemporaneous X-ray and optical observations of the Be/X-ray binary system A 0535+26 with the Fermi/Gamma-ray Burst Monitor (GBM) and several ground-based observatories. These new observations are put into the context of the rich historical data (since ∼1978) and discussed in terms of the neutron-star–Be-disk interaction. The Be circumstellar disk was exceptionally large just before the 2009 December giant outburst, which may explain the origin of the unusual recent X-ray activity of this source. We found a peculiar evolution of the pulse profile during this giant outburst, with the two main components evolving in opposite ways with energy. A hard 30–70 mHz X-ray quasi-periodic oscillation was detected with GBM during this 2009 December giant outburst. It becomes stronger with increasing energy and disappears at energies below 25 keV. In the long term a strong optical/X-ray correlation was found for this system, however in the medium term the Hα equivalent width and the V-band brightness showed an anti-correlation after ∼2002 August. Each giant X-ray outburst occurred during a decline phase of the optical brightness, while the Hα showed a strong emission. In late 2010 and before the 2011 February outburst, rapid V/R variations are observed in the strength of the two peaks of the Hα line. These had a period of ∼25 days and we suggest the presence of a global one-armed oscillation to explain this scenario. A general pattern might be inferred, where the disk becomes weaker and shows V/R variability beginning ∼6 months following a giant outburst.

Numerical calculations of the linear Rossby wave instability (RWI) in global three-dimensional (3D) disks are presented. The linearized fluid equations are solved for vertically stratified, radially structured disks with either a locally isothermal or polytropic equation of state, by decomposing the vertical dependence of the perturbed hydrodynamic quantities into Hermite and Gegenbauer polynomials, respectively. It is confirmed that the RWI operates in 3D. For perturbations with vertical dependence assumed above, there is little difference in growth rates between 3D and two-dimensional (2D) calculations. Comparison between 2D and 3D solutions of this type suggests the RWI is predominantly a 2D instability and that 3D effects, such as vertical motion, can be interpreted as a perturbative consequence of the dominant 2D flow. The vertical flow around corotation, where vortex formation is expected, is examined. In locally isothermal disks, the expected vortex center remains in approximate vertical hydrostatic equilibrium. For polytropic disks, the vortex center has positive vertical velocity, whose magnitude increases with decreasing polytropic index n.

We present new, full-orbit observations of the infrared phase variations of the canonical hot Jupiter HD 189733b obtained in the 3.6 and 4.5 μm bands using the Spitzer Space Telescope. When combined with previous phase curve observations at 8.0 and 24 μm, these data allow us to characterize the exoplanet's emission spectrum as a function of planetary longitude and to search for local variations in its vertical thermal profile and atmospheric composition. We utilize an improved method for removing the effects of intrapixel sensitivity variations and robustly extracting phase curve signals from these data, and we calculate our best-fit parameters and uncertainties using a wavelet-based Markov Chain Monte Carlo analysis that accounts for the presence of time-correlated noise in our data. We measure a phase curve amplitude of 0.1242% ± 0.0061% in the 3.6 μm band and 0.0982% ± 0.0089% in the 4.5 μm band, corresponding to brightness temperature contrasts of 503 ± 21 K and 264 ± 24 K, respectively. We find that the times of minimum and maximum flux occur several hours earlier than predicted for an atmosphere in radiative equilibrium, consistent with the eastward advection of gas by an equatorial super-rotating jet. The locations of the flux minima in our new data differ from our previous observations at 8 μm, and we present new evidence indicating that the flux minimum observed in the 8 μm is likely caused by an overshooting effect in the 8 μm array. We obtain improved estimates for HD 189733b's dayside planet–star flux ratio of 0.1466% ± 0.0040% in the 3.6 μm band and 0.1787% ± 0.0038% in the 4.5 μm band, corresponding to brightness temperatures of 1328 ± 11 K and 1192 ± 9 K, respectively; these are the most accurate secondary eclipse depths obtained to date for an extrasolar planet. We compare our new dayside and nightside spectra for HD 189733b to the predictions of one-dimensional radiative transfer models from Burrows et al. and conclude that fits to this planet's dayside spectrum provide a reasonably accurate estimate of the amount of energy transported to the night side. Our 3.6 and 4.5 μm phase curves are generally in good agreement with the predictions of general circulation models for this planet from Showman et al., although we require either excess drag or slower rotation rates in order to match the locations of the measured maxima and minima in the 4.5, 8.0, and 24 μm bands. We find that HD 189733b's 4.5 μm nightside flux is 3.3σ smaller than predicted by these models, which assume that the chemistry is in local thermal equilibrium. We conclude that this discrepancy is best explained by vertical mixing, which should lead to an excess of CO and correspondingly enhanced 4.5 μm absorption in this region. This result is consistent with our constraints on the planet's transmission spectrum, which also suggest excess absorption in the 4.5 μm band at the day–night terminator.

The coexistence of Planck and Fermi satellites in orbit has enabled the exploration of the connection between the (sub-)millimeter and γ-ray emission in a large sample of blazars. We find that the γ-ray emission and the (sub-)mm luminosities are correlated over five orders of magnitude, L_γ∝L_(sub-)mm. However, this correlation is not significant at some frequency bands when simultaneous observations are considered. The most significant statistical correlations, on the other hand, arise when observations are quasi-simultaneous within two months. Moreover, we find that sources with an approximate spectral turnover in the middle of the mm-wave regime are more likely to be strong γ-ray emitters. These results suggest a physical relation between the newly injected plasma components in the jet and the high levels of γ-ray emission.

Glycine is the simplest amino acid, and due to the significant astrobiological implications that suppose its detection, the search for it in the interstellar medium (ISM), meteorites, and comets is intensively investigated. In the present work, quantum mechanical calculations based on density functional theory have been used to model the glycine formation on water-ice clusters present in the ISM. The removal of either one H atom or one electron from the water-ice cluster has been considered to simulate the effect of photolytic radiation and of ionizing particles, respectively, which lead to the formation of OH^• radical and H₃O⁺ surface defects. The coupling of incoming CO molecules with the surface OH^• radicals on the ice clusters yields the formation of the COOH^• radicals via ZPE-corrected energy barriers and reaction energies of about 4–5 kcal mol⁻¹ and −22 kcal mol⁻¹, respectively. The COOH^• radicals couple with incoming NH=CH₂ molecules (experimentally detected in the ISM) to form the NHCH₂COOH^• radical glycine through energy barriers of 12 kcal mol⁻¹, exceedingly high at ISM cryogenic temperatures. Nonetheless, when H₃O⁺ is present, one proton may be barrierless transferred to NH=CH₂ to give NH₂=CH₂⁺. This latter may react with the COOH^• radical to give the NH₂CH₂COOH^+• glycine radical cation which can then be transformed into the NH₂CHC(OH)₂^+• species (the most stable form of glycine in its radical cation state) or into the NH₂CHCOOH^• neutral radical glycine. Estimated rate constants of these events suggest that they are kinetically feasible at temperatures of 100–200 K, which indicate that their occurrence may take place in hot molecular cores or in comets exposed to warmer regions of solar systems. Present results provide quantum chemical evidence that defects formed on water ices due to the harsh-physical conditions of the ISM may trigger reactions of cosmochemical interest. The relevance of surface H₃O⁺ ions to facilitate chemical processes by proton transfer (i.e., acting as acidic catalysts) is highlighted, and plausible ways of their formation at the water-ice surface in the ISM are also discussed.

A large sample of spectroscopically confirmed star-forming galaxies at redshifts 1.4 ⩽ z_spec ⩽ 3.7, with complementary imaging in the near- and mid-IR from the ground and from the Hubble Space Telescope and Spitzer Space Telescope, is used to infer the average star formation histories (SFHs) of typical galaxies from z ∼ 2 to 7. For a subset of 302 galaxies at 1.5 ⩽ z_spec < 2.6, we perform a detailed comparison of star formation rates (SFRs) determined from spectral energy distribution (SED) modeling (SFRs[SED]) and those calculated from deep Keck UV and Spitzer/MIPS 24 μm imaging (SFRs[IR+UV]). Exponentially declining SFHs yield SFRs[SED] that are 5–10 times lower on average than SFRs[IR+UV], indicating that declining SFHs may not be accurate for typical galaxies at z ≳ 2. The SFRs of z ∼ 2–3 galaxies are directly proportional to their stellar masses (M_*), with unity slope—a result that is confirmed with Spitzer/IRAC stacks of 1179 UV-faint (${\cal R}>25.5$) galaxies—for M_* ≳ 5 × 10⁸ M_☉ and SFRs ≳ 2 M_☉ yr⁻¹. We interpret this result in the context of several systematic biases that can affect determinations of the SFR–M_* relation. The average specific SFRs at z ∼ 2–3 are remarkably similar within a factor of two to those measured at z ≳ 4, implying that the average SFH is one where SFRs increase with time. A consequence of these rising SFHs is that (1) a substantial fraction of UV-bright z ∼ 2–3 galaxies had faint sub-L* progenitors at z ≳ 4; and (2) gas masses must increase with time from z = 2 to 7, over which time the net cold gas accretion rate—as inferred from the specific SFR and the Kennicutt–Schmidt relation—is ∼2–3 times larger than the SFR. However, if we evolve to higher redshift the SFHs and masses of the halos that are expected to host L* galaxies at z ∼ 2, then we find that ≲ 10% of the baryons accreted onto typical halos at z ≳ 4 actually contribute to star formation at those epochs. These results highlight the relative inefficiency of star formation even at early cosmic times when galaxies were first assembling.

We make use of four galaxy catalogs based on four different semi-analytical models (SAMs) implemented in the Millennium Simulation to study the environmental effects and the model dependence of the galaxy merger rate. We begin the analyses by finding that the galaxy merger rate in SAMs has a mild redshift evolution with luminosity-selected samples in the evolution-corrected B-band magnitude range,−21 ⩽ M^e_B ⩽ −19, consistent with the results of previous works. To study the environmental dependence of the galaxy merger rate, we adopt two estimators, the local overdensity (1 + δ_n), defined as the surface density from the nth nearest neighbor (n = 6 is chosen in this study), and the host halo mass M_h. We find that the galaxy merger rate F_mg shows a strong dependence on the local overdensity (1 + δ_n) and the dependence is similar at all redshifts. For the overdensity estimator, the merger rate F_mg is found to be about twenty times larger in the densest regions than in underdense ones in two of the four SAMs, while it is roughly four times higher in the other two. In other words, the discrepancies of the merger rate difference between the two extremes can differ by a factor of ∼5 depending on the SAMs adopted. On the other hand, for the halo mass estimator, F_mg does not monotonically increase with the host halo mass M_h but peaks in the M_h range between 10¹² and 10¹³ h⁻¹ M_☉, which corresponds to group environments. The high merger rate in high local density regions corresponds primarily to the high merger rate in group environments. In addition, we also study the merger probability of "close pairs" identified using the projected separation and the line-of-sight velocity difference C_mg and the merger timescale T_mg; these are two important quantities for observations to convert the pair fraction N_c into the galaxy merger rate. We discover that T_mg has a weak dependence on environment and different SAMs, and is about 2 Gyr old at z ∼ 1. In contrast, C_mg depends on both environment (declining with density) and different SAMs; its environmental dependence is primarily due to the projection effect. At z ∼ 1, it is found that only ∼31% of projected close pairs will eventually merge by z = 0. We find that the projection effect is the dominant factor in accounting for the low merger probability of projected close pairs.

We report on the long-term X-ray monitoring with Swift, RXTE, Suzaku, Chandra, and XMM-Newton of the outburst of the newly discovered magnetar Swift J1822.3−1606 (SGR 1822−1606), from the first observations soon after the detection of the short X-ray bursts which led to its discovery, through the first stages of its outburst decay (covering the time span from 2011 July until the end of 2012 April). We also report on archival ROSAT observations which detected the source during its likely quiescent state, and on upper limits on Swift J1822.3−1606's radio-pulsed and optical emission during outburst, with the Green Bank Telescope and the Gran Telescopio Canarias, respectively. Our X-ray timing analysis finds the source rotating with a period of P = 8.43772016(2) s and a period derivative $\dot{P}=8.3(2)\times 10^{-14}$ s s⁻¹, which implies an inferred dipolar surface magnetic field of B ≃ 2.7 × 10¹³ G at the equator. This measurement makes Swift J1822.3−1606 the second lowest magnetic field magnetar (after SGR 0418+5729). Following the flux and spectral evolution from the beginning of the outburst, we find that the flux decreased by about an order of magnitude, with a subtle softening of the spectrum, both typical of the outburst decay of magnetars. By modeling the secular thermal evolution of Swift J1822.3−1606, we find that the observed timing properties of the source, as well as its quiescent X-ray luminosity, can be reproduced if it was born with a poloidal and crustal toroidal fields of B_p ∼ 1.5 × 10¹⁴ G and B_tor ∼ 7 × 10¹⁴ G, respectively, and if its current age is ∼550 kyr.

NGC 2392 is a young double-shell planetary nebula (PN). Its intrinsic structure and shaping mechanism are still not fully understood. In this paper we present new spectroscopic observations of NGC 2392. The slits were placed at two different locations to obtain the spectra of the inner and outer regions. Several [Fe iii] lines are clearly detected in the inner region. We infer that NGC 2392 might have an intrinsic structure similar to the bipolar nebula Mz 3, which also exhibits a number of [Fe iii] lines arising from the central regions. In this scenario, the inner and outer regions of NGC 2392 correspond to the inner lobes and the outer outflows of Mz 3, respectively. We construct a three-dimensional morpho-kinematic model to examine our hypothesis. We also compare the physical conditions and chemical composition of the inner and outer regions, and discuss the implications on the formation of this type of PN.

H i spatial power spectra were determined for a sample of 24 nearby dwarf irregular galaxies selected from the Local Irregulars That Trace Luminosity Extremes–The H i Nearby Galaxy Survey sample. The two-dimensional power spectral indices asymptotically become a constant for each galaxy when a significant part of the line profile is integrated. For narrow channel maps, the power spectra become shallower as the channel width decreases, and this shallowing trend continues to our single channel maps. This implies that even the highest velocity resolution of 1.8 km s⁻¹ is not smaller than the thermal dispersion of the coolest, widespread H i component. The one-dimensional power spectra of azimuthal profiles at different radii suggest that the shallower power spectra for narrower channel width is mainly contributed by the inner disks, which indicates that the inner disks have proportionally more cooler H i than the outer disks. Galaxies with lower luminosity (M_B > −14.5 mag) and star formation rate (SFR, log(SFR (M_☉ yr⁻¹)) < −2.1) tend to have steeper power spectra, which implies that the H i line-of-sight depths can be comparable with the radial length scales in low-mass galaxies. A lack of a correlation between the inertial-range spectral indices and SFR surface density implies that either non-stellar power sources are playing a fundamental role in driving the interstellar medium turbulent structure or the nonlinear development of turbulent structures has little to do with the driving sources.

We report on our analysis of the VISTA Orion ZY JHK_s photometric data (completeness magnitudes of Z = 22.6 and J = 21.0 mag) focusing on a circular area of 2798.4 arcmin² around the young σ Orionis star cluster (∼3 Myr, ∼352 pc, and solar metallicity). The combination of the VISTA photometry with optical, WISE and Spitzer data allows us to identify a total of 210 σ Orionis member candidates with masses in the interval 0.25–0.004 M_☉, 23 of which are new planetary-mass object findings. These discoveries double the number of cluster planetary-mass candidates known so far. One object has colors compatible with a T spectral type. The σ Orionis cluster harbors about as many brown dwarfs (69, 0.072–0.012 M_☉) and planetary-mass objects (37, 0.012–0.004 M_☉) as very low mass stars (104, 0.25–0.072 M_☉). Based on Spitzer data, we derive a disk frequency of ∼40% for very low mass stars, brown dwarfs, and planetary-mass objects in σ Orionis. The radial density distributions of these three mass intervals are alike: all are spatially concentrated within an effective radius of 12' (1.2 pc) around the multiple star σ Ori, and no obvious segregation between disk-bearing and diskless objects is observed. Using the VISTA data and the Mayrit catalog, we derive the cluster mass spectrum (ΔN/ΔM ∼ M^−α) from ∼19 to 0.006 M_☉ (VISTA ZJ completeness), which is reasonably described by two power-law expressions with indices of α = 1.7 ± 0.2 for M > 0.35 M_☉, and α = 0.6 ± 0.2 for M < 0.35 M_☉. The σ Orionis mass spectrum smoothly extends into the planetary-mass regime down to 0.004 M_☉. Our findings of T-type sources (<0.004 M_☉) in the VISTA σ Orionis exploration appear to be smaller than what is predicted by the extrapolation of the cluster mass spectrum down to the survey J-band completeness.

Very high intensities of galactic cosmic rays measured by Voyager 1 in the heliosheath appear to be incompatible with the presence of a modulation "wall" near the heliopause produced by a pile up of the heliospheric magnetic field. We propose that the modulation wall is a structure permeable to cosmic rays as a result of a sectored magnetic field topology compressed by plasma slowdown on approach to the heliopause and stretched to high latitudes by latitudinal flows in the heliosheath. The tightly folded warped current sheet permits efficient cosmic-ray transport in the radial direction via a drift-like mechanism. We show that when stochastic variations in the sector widths are taken into account, particle transport becomes predominantly diffusive both along and across the magnetic sectors. Using a test-particle model for cosmic rays in the heliosheath we investigate the dependence of the diffusion coefficients on the properties of the sector structure and on particle energy.

We report a periodicity of ∼1 day in the highly elevated X-ray emission from the protostar V1647 Ori during its two recent multiple-year outbursts of mass accretion. This periodicity is indicative of protostellar rotation at near-break-up speed. Modeling of the phased X-ray light curve indicates that the high-temperature (∼50 MK), X-ray-emitting plasma, which is most likely heated by accretion-induced magnetic reconnection, resides in dense (≳ 5 × 10¹⁰ cm⁻³), pancake-shaped magnetic footprints where the accretion stream feeds the newborn star. The sustained X-ray periodicity of V1647 Ori demonstrates that such protostellar magnetospheric accretion configurations can be stable over timescales of years.

The observations of gamma-ray emission from pulsars with the Fermi-LAT detector and the detection of the Crab pulsar with the VERITAS array of Cherenkov telescopes at energies above 100 GeV make it unlikely that curvature radiation is the main source of photons above GeV energies in the Crab and many other pulsars. We outline a model in which the broad UV–X-ray component and the very high energy γ-ray emission of pulsars are explained within the synchrotron self-Compton framework. We argue that the bulk of the observed radiation is generated by the secondary plasma, which is produced in cascades in the outer gaps of the magnetosphere. We find that the inverse Compton (IC) scattering occurs in the Klein–Nishina regime, which favors synchrotron photons in the UV band as target field for the scattering process. The primary beam is accelerated in a modest electric field, with a field strength that is of the order of a few percent of the magnetic field  near the light cylinder. Overall, for IC scattering occurring in the Klein–Nishina regime, the particle distribution in the gap does not evolve toward a stationary distribution and thus is intrinsically time-dependent. We point out that in a radiation reaction-limited regime of particle acceleration the gamma-ray luminosity L_γ scales linearly with the pulsar spin-down power $\dot{E}$, $L_\gamma \propto \dot{E}$, and not proportional to $\sqrt{\dot{E}}$ as expected from potential-limited acceleration.

We study how the first galaxies were assembled under feedback from the accretion onto a central black hole (BH) that is left behind by the first generation of metal-free stars through self-consistent, cosmological simulations. X-ray radiation from the accretion of gas onto BH remnants of Population III (Pop III) stars, or from high-mass X-ray binaries (HMXBs), again involving Pop III stars, influences the mode of second generation star formation. We track the evolution of the BH accretion rate and the associated X-ray feedback starting with the death of the Pop III progenitor star inside a minihalo and following the subsequent evolution of the BH as the minihalo grows to become an atomically cooling galaxy. We find that X-ray photoionization heating from a stellar-mass BH is able to quench further star formation in the host halo at all times before the halo enters the atomic cooling phase. X-ray radiation from an HMXB, assuming a luminosity close to the Eddington value, exerts an even stronger, and more diverse, feedback on star formation. It photoheats the gas inside the host halo, but also promotes the formation of molecular hydrogen and cooling of gas in the intergalactic medium and in nearby minihalos, leading to a net increase in the number of stars formed at early times. Our simulations further show that the radiative feedback from the first BHs may strongly suppress early BH growth, thus constraining models for the formation of supermassive BHs.

The characteristics of light variation of red supergiant (RSG) stars in the Small Magellanic Cloud (SMC) are analyzed based on the nearly 8–10 year data collected by the ASAS and MACHO projects. The 126 identified RSGs are classified into five categories accordingly: 20 with poor photometry, 55 with no reliable period, 6 with semi-regular variation, 15 with a long secondary period (LSP) and distinguishable short period, and 30 with only an LSP. For the semi-regular variables and the LSP variables with distinguishable short period, the K_S-band period–luminosity (P–L) relation is analyzed and compared with that of the Galaxy, the Large Magellanic Cloud, and M33. It is found that the RSGs in these galaxies obey a similar P–L relation except for those in the Galaxy. In addition, the P–L relations in the infrared bands, namely, the 2MASS JHK_S, Spitzer/IRAC, and Spitzer/MIPS 24 μm bands, are derived with high reliability. The best P–L relation occurs in the Spitzer/IRAC [3.6] and [4.5] bands. Based on the comparison with the theoretical calculation of the P–L relation, the mode of pulsation of RSGs in the SMC is suggested to be the first-overtone radial mode.

We provide additional information on our recent study of the electromagnetic emission produced during the inspiral and merger of supermassive black holes when these are immersed in a force-free plasma threaded by a uniform magnetic field. As anticipated in a recent letter, our results show that although a dual-jet structure is present, the associated luminosity is ∼100 times smaller than the total one, which is predominantly quadrupolar. Here we discuss the details of our implementation of the equations in which the force-free condition is not implemented at a discrete level, but rather obtained via a damping scheme which drives the solution to satisfy the correct condition. We show that this is important for a correct and accurate description of the current sheets that can develop in the course of the simulation. We also study in greater detail the three-dimensional charge distribution produced as a consequence of the inspiral and show that during the inspiral it possesses a complex but ordered structure which traces the motion of the two black holes. Finally, we provide quantitative estimates of the scaling of the electromagnetic emission with frequency, with the diffused part having a dependence that is the same as the gravitational-wave one and that scales as L^non-coll_EM ≈ Ω^10/3−8/3, while the collimated one scales as L^coll_EM ≈ Ω^5/3−6/3, thus with a steeper dependence than previously estimated. We discuss the impact of these results on the potential detectability of dual jets from supermassive black holes and the steps necessary for more accurate estimates.

As part of the Transit Ephemeris Refinement and Monitoring Survey, we present new radial velocities and photometry of the HD 192263 system. Our analysis of the already available Keck-HIRES and CORALIE radial velocity measurements together with the five new Keck measurements we report in this paper results in improved orbital parameters for the system. We derive constraints on the size and phase location of the transit window for HD 192263b, a Jupiter-mass planet with a period of 24.3587 ± 0.0022 days. We use 10 years of Automated Photoelectric Telescope photometry to analyze the stellar variability and search for planetary transits. We find continuing evidence of spot activity with periods near 23.4 days. The shape of the corresponding photometric variations changes over time, giving rise to not one but several Fourier peaks near this value. However, none of these frequencies coincides with the planet's orbital period and thus we find no evidence of star–planet interactions in the system. We attribute the ∼23 day variability to stellar rotation. There are also indications of spot variations on longer (8 years) timescales. Finally, we use the photometric data to exclude transits for a planet with the predicted radius of 1.09 R_J, and as small as 0.79 R_J.

The conventional wisdom that the rate of incidence of Mg ii absorption systems, dN/dz (excluding "associated systems" having a velocity βc relative to the active galactic nucleus (AGN) of less than ∼5000 km s⁻¹), is totally independent of the background AGNs has been challenged by a recent finding that dN/dz for strong Mg ii absorption systems toward distant blazars is 2.2 ± ^0.8_0.6 times the value known for normal optically selected quasars (QSOs). This has led to the suggestion that a significant fraction of even the absorption systems with β as high as ∼0.1 may have been ejected by the relativistic jets in the blazars, which are expected to be pointed close to our direction. Here, we investigate this scenario using a large sample of 115 flat-spectrum radio-loud quasars (FSRQs) that also possess powerful jets, but are only weakly polarized. We show, for the first time, that dN/dz toward FSRQs is, on the whole, quite similar to that known for QSOs and that the comparative excess of strong Mg ii absorption systems seen toward blazars is mainly confined to β < 0.15. The excess relative to FSRQs probably results from a likely closer alignment of blazar jets with our direction; hence, any gas clouds accelerated by them are more likely to be on the line of sight to the active quasar nucleus.

We assess the current membership of the nearby, young TW Hydrae association and examine newly proposed members with the Wide-field Infrared Survey Explorer (WISE) to search for infrared excess indicative of circumstellar disks. Newly proposed members TWA 30A, TWA 30B, TWA 31, and TWA 32 all show excess emission at 12 and 22 μm providing clear evidence for substantial dusty circumstellar disks around these low-mass, ∼8 Myr old stars that were previously shown to likely be accreting circumstellar material. TWA 30B shows large amounts of self-extinction, likely due to an edge-on disk geometry. We also confirm previously reported circumstellar disks with WISE and determine a 22 μm excess fraction of 42⁺¹⁰_{− 9}% based on our results.

To study the effects of interstellar pickup protons and turbulence on the structure and dynamics of the solar wind, we have developed a fully three-dimensional magnetohydrodynamic solar wind model that treats interstellar pickup protons as a separate fluid and incorporates the transport of turbulence and turbulent heating. The governing system of equations combines the mean-field equations for the solar wind plasma, magnetic field, and pickup protons and the turbulence transport equations for the turbulent energy, normalized cross-helicity, and correlation length. The model equations account for photoionization of interstellar hydrogen atoms and their charge exchange with solar wind protons, energy transfer from pickup protons to solar wind protons, and plasma heating by turbulent dissipation. Separate mass and energy equations are used for the solar wind and pickup protons, though a single momentum equation is employed under the assumption that the pickup protons are comoving with the solar wind protons. We compute the global structure of the solar wind plasma, magnetic field, and turbulence in the region from 0.3 to 100 AU for a source magnetic dipole on the Sun tilted by 0°–90° and compare our results with Voyager 2 observations. The results computed with and without pickup protons are superposed to evaluate quantitatively the deceleration and heating effects of pickup protons, the overall compression of the magnetic field in the outer heliosphere caused by deceleration, and the weakening of corotating interaction regions by the thermal pressure of pickup protons.

We study the modification of the classical criterion for the linear onset and growing rate of the Rayleigh–Taylor instability (RTI) in a partially ionized plasma in the two-fluid description. The plasma is composed of a neutral fluid and an electron–ion fluid, coupled by means of particle collisions. The governing linear equations and appropriate boundary conditions, including gravitational terms, are derived and applied to the case of the RTI in a single interface between two partially ionized plasmas. The limits of collisionless, no gravity, and incompressible fluids are checked before addressing the general case. We find that both compressibility and ion–neutral collisions lower the linear growth rate, but do not affect the critical threshold of the onset of the RTI. The configuration is always unstable when a lighter plasma is below a heavier plasma regardless the value of the magnetic field strength, the ionization degree, and the ion–neutral collision frequency. However, ion–neutral collisions have a strong impact on the RTI growth rate, which can be decreased by an order of magnitude compared to the value in the collisionless case. Ion–neutral collisions are necessary to accurately describe the evolution of the RTI in partially ionized plasmas such as prominences. The timescale for the development of the instability is much longer than in the classical incompressible fully ionized case. This result may explain the existence of prominence fine structures with life times of the order of 30 minutes. The timescales derived from the classical theory are about one order of magnitude shorter and incompatible with the observed life times.

We identify a gravitational–dynamical process in near-Keplerian potentials of galactic nuclei that occurs when an intermediate-mass black hole (IMBH) is migrating on an eccentric orbit through the stellar cluster towards the central supermassive black hole. We find that, apart from conventional dynamical friction, the IMBH experiences an often much stronger systematic torque due to the secular (i.e., orbit-averaged) interactions with the cluster's stars. The force which results in this torque is applied, counterintuitively, in the same direction as the IMBH's precession and we refer to its action as "secular dynamical anti-friction" (SDAF). We argue that SDAF, and not the gravitational ejection of stars, is responsible for the IMBH's eccentricity increase seen in the initial stages of previous N-body simulations. Our numerical experiments, supported by qualitative arguments, demonstrate that (1) when the IMBH's precession direction is artificially reversed, the torque changes sign as well, which decreases the orbital eccentricity; (2) the rate of eccentricity growth is sensitive to the IMBH migration rate, with zero systematic eccentricity growth for an IMBH whose orbit is artificially prevented from inward migration; and (3) SDAF is the strongest when the central star cluster is rapidly rotating. This leads to eccentricity growth/decrease for the clusters rotating in the opposite/same direction relative to the IMBH's orbital motion.

We present extreme-ultraviolet multi-wavelength observations with the SDO/AIA instruments of quasi-periodic pulsations (QPPs) propagating along a cusp-shaped loop formed after an M2.2 flare on the Sun. Our motivation is to detect whether there were slow-mode magnetoacoustic waves propagating along its protruding flux tube. To this end, with fast Fourier transform we extract the short (<3 minutes) and long (>3 minutes) period components of the QPPs from time–space diagrams of the tube slices. We find that velocity differences did exist among the short/long-period components of different wavelengths, but only one event in the long-period ones showed they were greater than the measurement errors (e.g., 65 km s⁻¹), which were 330 km s⁻¹ detected in 171 Å, 590 km s⁻¹ in 211 Å, and 180 km s⁻¹ in 304 Å. The intensity modulation in all wavelengths is found to be very large, e.g., ∼60% of the emission trend for an event in the 171 Å passband, which would be an order of magnitude higher than the perturbation of the plasma density in the slow-mode magnetoacoustic waves. Moreover, only the QPPs with upward velocities of 50–300 km s⁻¹ are found in the tube, and the downward ones of several tens of kilometers are never unambiguously detected. Therefore, most of the QPP events under study were likely the episodic outflows along the tube, and the one with a supersonic speed of 590 km s⁻¹ may be a kink wave.

We present the results of an extensive high-resolution imaging survey of M-dwarf multiplicity using the Lucky Imaging technique. The survey made use of the AstraLux Norte camera at the Calar Alto 2.2 m telescope and the AstraLux Sur camera at the ESO New Technology Telescope in order to cover nearly the full sky. In total, 761 stars were observed (701 M-type and 60 late K-type), among which 182 new and 37 previously known companions were detected in 205 systems. Most of the targets have been observed during two or more epochs, and could be confirmed as physical companions through common proper motion, often with orbital motion being confirmed in addition. After accounting for various bias effects, we find a total M-dwarf multiplicity fraction of 27% ± 3% within the AstraLux detection range of 008–6'' (semimajor axes of ∼3–227 AU at a median distance of 30 pc). We examine various statistical multiplicity properties within the sample, such as the trend of multiplicity fraction with stellar mass and the semimajor axis distribution. The results indicate that M-dwarfs are largely consistent with constituting an intermediate step in a continuous distribution from higher-mass stars down to brown dwarfs. Along with other observational results in the literature, this provides further indications that stars and brown dwarfs may share a common formation mechanism, rather than being distinct populations.

We investigate the mid- (MIR) to far-infrared (FIR) properties of a nearly complete sample of local active galactic nuclei (AGNs) detected in the Swift/Burst Alert Telescope (BAT) all-sky hard X-ray (14–195 keV) survey, based on the cross correlation with the AKARI infrared survey catalogs complemented by those with Infrared Astronomical Satellite and Wide-field Infrared Survey Explorer. Out of 135 non-blazer AGNs in the Swift/BAT nine-month catalog, we obtain the MIR photometric data for 128 sources either in the 9, 12, 18, 22, and/or 25 μm band. We find good correlation between their hard X-ray and MIR luminosities over three orders of magnitude (42 < log λL_λ(9, 18 μm) < 45), which is tighter than that with the FIR luminosities at 90 μm. This suggests that thermal emission from hot dusts irradiated by the AGN emission dominate the MIR fluxes. Both X-ray unabsorbed and absorbed AGNs follow the same correlation, implying isotropic infrared emission, as expected in clumpy dust tori rather than homogeneous ones. We find excess signals around 9 μm in the averaged infrared spectral energy distribution from heavy obscured "new type" AGNs with small scattering fractions in the X-ray spectra. This could be attributed to the polycyclic aromatic hydrocarbon emission feature, suggesting that their host galaxies have strong starburst activities.

We present late-time Hubble Space Telescope (HST) imaging of the fields of six Swift gamma-ray bursts (GRBs) lying at 5.0 ≲ z ≲ 9.5. Our data include very deep observations of the field of the most distant spectroscopically confirmed burst, GRB 090423, at z = 8.2. Using the precise positions afforded by their afterglows, we can place stringent limits on the luminosities of their host galaxies. In one case, that of GRB 060522 at z = 5.11, there is a marginal excess of flux close to the GRB position which may be a detection of a host at a magnitude J_AB ≈ 28.5. None of the others are significantly detected, meaning that all the hosts lie below L* at their respective redshifts, with star formation rates (SFRs) ≲ 4 M_☉ yr⁻¹ in all cases. Indeed, stacking the five fields with WFC3-IR data, we conclude a mean SFR <0.17 M_☉ yr⁻¹ per galaxy. These results support the proposition that the bulk of star formation, and hence integrated UV luminosity, at high redshifts arises in galaxies below the detection limits of deep-field observations. Making the reasonable assumption that GRB rate is proportional to UV luminosity at early times allows us to compare our limits with expectations based on galaxy luminosity functions (LFs) derived from the Hubble Ultra-Deep Field and other deep fields. We infer that an LF, which is evolving rapidly toward steeper faint-end slope (α) and decreasing characteristic luminosity (L*), as suggested by some other studies, is consistent with our observations, whereas a non-evolving LF shape is ruled out at ≳ 90% confidence. Although it is not yet possible to make stronger statements, in the future, with larger samples and a fuller understanding of the conditions required for GRB production, studies like this hold great potential for probing the nature of star formation, the shape of the galaxy LF, and the supply of ionizing photons in the early universe.

VX Sgr is a red supergiant at an adopted distance of 1.6 kpc with intense 43 GHz SiO maser emission. In this paper, we present the high-resolution very long baseline interferometry (VLBI) observations of SiO masers toward VX Sgr at five epochs. We used the Very Long Baseline Array to map the J = 1→0 (v = 1, 2) ²⁸SiO masers and confirmed a ring-like structure. In the first two epochs, the v = 1 masers form a ring, but v = 2 maser spots residing only in the southern and northern regions do not form a complete ring. In the third epoch, the two masers are distributed in a ring structure and the v = 2 masers are a bit closer to the central star. In the last two epochs, many new maser spots appear and overlap each other. These overlapping maser spots can be related to the shock waves and reflect the collisional pumping. We compare the observations with the pumping models and speculate that the real pumping mechanism may be complex in VX Sgr and vary with time. The J = 1→0 (v = 0) ²⁹SiO line emission is also detected, but is too weak to produce any VLBI map.

Observations of disk galaxies at z ∼ 2 have demonstrated that turbulence driven by gravitational instability can dominate the energetics of the disk. We present a one-dimensional simulation code, which we have made publicly available, that economically evolves these galaxies from z ∼ 2 to z ∼ 0 on a single CPU in a matter of minutes, tracking column density, metallicity, and velocity dispersions of gaseous and multiple stellar components. We include an H₂-regulated star formation law and the effects of stellar heating by transient spiral structure. We use this code to demonstrate a possible explanation for the existence of a thin and thick disk stellar population and the age–velocity-dispersion correlation of stars in the solar neighborhood: the high velocity dispersion of gas in disks at z ∼ 2 decreases along with the cosmological accretion rate, while at lower redshift the dynamically colder gas forms the low velocity dispersion stars of the thin disk.

We present dynamical modeling of the broad-line region (BLR) in the Seyfert 1 galaxy Mrk 50 using reverberation mapping data taken as part of the Lick AGN Monitoring Project (LAMP) 2011. We model the reverberation mapping data directly, constraining the geometry and kinematics of the BLR, as well as deriving a black hole mass estimate that does not depend on a normalizing factor or virial coefficient. We find that the geometry of the BLR in Mrk 50 is a nearly face-on thick disk, with a mean radius of 9.6^+1.2_−0.9 light days, a width of the BLR of 6.9^+1.2_−1.1 light days, and a disk opening angle of 25 ± 10 deg above the plane. We also constrain the inclination angle to be 9⁺⁷₋₅ deg, close to face-on. Finally, the black hole mass of Mrk 50 is inferred to be log₁₀(M_BH/M_☉) = 7.57^+0.44_−0.27. By comparison to the virial black hole mass estimate from traditional reverberation mapping analysis, we find the normalizing constant (virial coefficient) to be log₁₀f = 0.78^+0.44_−0.27, consistent with the commonly adopted mean value of 0.74 based on aligning the M_BH–σ* relation for active galactic nuclei and quiescent galaxies. While our dynamical model includes the possibility of a net inflow or outflow in the BLR, we cannot distinguish between these two scenarios.

We present eight years of high-precision radial velocity (RV) data for HD 204313 from the 2.7 m Harlan J. Smith Telescope at McDonald Observatory. The star is known to have a giant planet (Msin i = 3.5 M_J) on a ∼1900 day orbit, and a Neptune-mass planet at 0.2 AU. Using our own data in combination with the published CORALIE RVs of Ségransan et al., we discover an outer Jovian (Msin i = 1.6 M_J) planet with P ∼ 2800 days. Our orbital fit suggests that the planets are in a 3:2 mean motion resonance, which would potentially affect their stability. We perform a detailed stability analysis and verify that the planets must be in resonance.

We formulated tidal decay lifetimes for hypothetical moons orbiting extrasolar planets with both lunar and stellar tides. Previous works neglected the effect of lunar tides on planet rotation, and are therefore applicable only to systems in which the moon's mass is much less than that of the planet. This work, in contrast, can be applied to the relatively large moons that might be detected around newly discovered Neptune-mass and super-Earth planets. We conclude that moons are more stable when the planet/moon systems are further from the parent star, the planets are heavier, or the parent stars are lighter. Inclusion of lunar tides allows for significantly longer lifetimes for a massive moon relative to prior formulations. We expect that the semimajor axis of the planet hosting the first detected exomoon around a G-type star is 0.4–0.6 AU and is 0.2–0.4 AU for an M-type star.

We present Submillimeter Array observations of a Keplerian disk around the Class I protobinary system L1551 NE in 335 GHz continuum emission and submillimeter line emission in ¹³CO (J = 3–2) and C¹⁸O (J = 3–2) at a resolution of ∼120 × 80 AU. The 335 GHz dust-continuum image shows a strong central peak closely coincident with the binary protostars and likely corresponding to circumstellar disks, surrounded by a ∼600 × 300 AU feature elongated approximately perpendicular to the [Fe ii] jet from the southern protostellar component suggestive of a circumbinary disk. The ¹³CO and C¹⁸O images confirm that the circumbinary continuum feature is indeed a rotating disk; furthermore, the C¹⁸O channel maps can be well modeled by a geometrically thin disk exhibiting Keplerian rotation. We estimate a mass for the circumbinary disk of ∼0.03–0.12 M_☉, compared with an enclosed mass of ∼0.8 M_☉ that is dominated by the protobinary system. Compared with several other Class I protostars known to exhibit Keplerian disks, L1551 NE has the lowest bolometric temperature (∼91 K), highest envelope mass (∼0.39 M_☉), and the lowest ratio in stellar mass to envelope + disk + stellar mass (∼0.65). L1551 NE may therefore be the youngest protostellar object so far found to exhibit a Keplerian disk. Our observations present firm evidence that Keplerian disks around binary protostellar systems, "Keplerian circumbinary disks," can exist. We speculate that tidal effects from binary companions could transport angular momenta toward the inner edge of the circumbinary disk and create the Keplerian circumbinary disk.

The dominant non-instrumental background source for space-based infrared observatories is the zodiacal light (ZL). We present Spitzer Infrared Array Camera (IRAC) measurements of the ZL at 3.6, 4.5, 5.8, and 8.0 μm, taken as part of the instrument calibrations. We measure the changing surface brightness levels in approximately weekly IRAC observations near the north ecliptic pole over a period of roughly 8.5 years. This long time baseline is crucial for measuring the annual sinusoidal variation in the signal levels due to the tilt of the dust disk with respect to the ecliptic, which is the true signal of the ZL. This is compared to both Cosmic Background Explorer Diffuse Infrared Background Experiment data and a ZL model based thereon. Our data show a few-percent discrepancy from the Kelsall et al. model including a potential warping of the interplanetary dust disk and a previously detected overdensity in the dust cloud directly behind the Earth in its orbit. Accurate knowledge of the ZL is important for both extragalactic and Galactic astronomy including measurements of the cosmic infrared background, absolute measures of extended sources, and comparison to extrasolar interplanetary dust models. IRAC data can be used to further inform and test future ZL models.

With the Coronal Diagnostic Spectrometer operating in rapid cadence (9.8 s) stare mode during a C6.6 flare on the solar disk, we observed a sudden brightening of Fe xix line emission (formed at temperature T ≈ 8 MK) above the pre-flare noise without a corresponding brightening of emission from ions formed at lower temperatures, including He i (0.01 MK), O v (0.25 MK), and Si xii (2 MK). The sudden brightening persisted as a plateau of Fe xix intensity that endured more than 11 minutes. The Fe xix emission at the rise and during the life of the plateau showed no evidence of significant bulk velocity flows, and hence cannot be attributed to chromospheric evaporation. However, the line width showed a significant broadening at the rise of the plateau, corresponding to nonthermal velocities of at least 89 km s⁻¹ due to reconnection outflows or turbulence. During the plateau He i, O v, and Si xii brightened at successively later times starting about 3.5 minutes after Fe xix, which suggests that these brightenings were produced by thermal conduction from the plasma that produced the Fe xix line emission; however, we cannot rule out the possibility that they were produced by a weak beam of nonthermal particles. We interpret an observed shortening of the O v wavelength for about 1.5 minutes toward the middle of the plateau to indicate new upward motions driven by the flare, as occurs during gentle chromospheric evaporation; relative to a quiescent interval shortly before the flare, the O v upward velocity was around −10 km s⁻¹.

We have developed a model for the polarization of curvature radiation by taking into account the polar-cap-current-induced perturbation on the dipolar magnetic field. We present the effects of the polar cap current on the pulsar radio emission in an artificial case when the rotation effects, such as aberration and retardation, are absent. Our model indicates that the intensity components and the polarization angle inflection point can be shifted to either the leading or the trailing side depending upon the prevailing conditions in the viewing geometry, the non-uniformity in source distribution (modulation), and the polar-cap-current-induced perturbation. Also, we find evidence for the origin of symmetric-type circular polarization in addition to the antisymmetric type. Our model predicts a stronger trailing component compared to that on the leading side of a given cone under some specific conditions.

A number of authors have argued that the Sun must have been born in a cluster of no more than several thousand stars, on the basis that, in a larger cluster, close encounters between the Sun and other stars would have truncated the outer solar system or excited the outer planets into eccentric orbits. However, this dynamical limit is in tension with meteoritic evidence that the solar system was exposed to a nearby supernova during or shortly after its formation; a several-thousand-star cluster is much too small to produce a massive star whose lifetime is short enough to have provided the enrichment. In this paper, we revisit the dynamical limit in the light of improved observations of the properties of young clusters. We use a series of scattering simulations to measure the velocity-dependent cross-section for disruption of the outer solar system by stellar encounters, and use this cross-section to compute the probability of a disruptive encounter as a function of birth cluster properties. We find that, contrary to prior work, the probability of disruption is small regardless of the cluster mass, and that it actually decreases rather than increases with cluster mass. Our results differ from prior work for three main reasons: (1) unlike in most previous work, we compute a velocity-dependent cross-section and properly integrate over the cluster mass-dependent velocity distribution of incoming stars; (2) we recognize that ∼90% of clusters have lifetimes of a few crossing times, rather than the 10–100 Myr adopted in many earlier models; and (3) following recent observations, we adopt a mass-independent surface density for embedded clusters, rather than a mass-independent radius as assumed many earlier papers. Our results remove the tension between the dynamical limit and the meteoritic evidence, and suggest that the Sun was born in a massive cluster. A corollary to this result is that close encounters in the Sun's birth cluster are highly unlikely to truncate the Kuiper Belt unless the Sun was born in one of the unusual clusters that survived for tens of Myr. However, we find that encounters could plausibly produce highly eccentric Kuiper Belt objects such as Sedna.

The chance that a planetary system will interact with another member of its host star's nascent cluster would be greatly increased if gas giant planets form in situ on wide orbits. In this paper, we explore the outcomes of planet–planet scattering for a distribution of multi-planet systems that all have one of the planets on an initial orbit of 100 AU. The scattering experiments are run with and without stellar flybys. We convolve the outcomes with distributions for protoplanetary disk and stellar cluster sizes to generalize the results where possible. We find that the frequencies of large mutual inclinations and high eccentricities are sensitive to the number of planets in a system, but not strongly to stellar flybys. However, flybys do play a role in changing the low and moderate portions of the mutual inclination distributions, and erase dynamically cold initial conditions on average. Wide-orbit planets can be mixed throughout the planetary system, and in some cases, can potentially become hot Jupiters, which we demonstrate using scattering experiments that include a tidal damping model. If planets form in situ on wide orbits, then there will be discernible differences in the proper-motion distributions of a sample of wide-orbit planets compared with a pure scattering formation mechanism. Stellar flybys can enhance the frequency of ejections in planetary systems, but autoionization is likely to remain the dominant source of free-floating planets.

For the first time, we study the eastern nucleus in greater detail and search for the more extended emission in the molecular gas in different CO line transitions of the famous ultraluminous infrared galaxy (ULIRG) Arp 220. Furthermore, we present a model of the merger in Arp 220 on large scales with the help of the CO data and an optical and near-infrared composite Hubble Space Telescope image of the prototypical ULIRG. Using the Plateau de Bure interferometer (PdBI), we obtained CO (2–1) and (1–0) data at wavelengths of 1 and 3 mm in 1994, 1996, 1997, and 2006 at different beam sizes and spatial resolutions. The simulations of the merger in Arp 220 were performed with the Identikit modeling tool. The model parameters that describe the galaxy merger best give a mass ratio of 1:2 and result in a merger of ∼6 × 10⁸ yr. The low-resolution CO (1–0) PdBI observations suggest that there are indications for emission ∼10'' toward the south, as well as to the north and to the west of the two nuclei.

Single metal-polluted white dwarfs with no dusty disks are believed to be actively accreting metals from a circumstellar disk of gas caused by the destruction of asteroids perturbed by planetary systems. We report, for the first time, the detection of circumstellar Ca ii gas in absorption around the DAZ WD 1124-293, which lacks an infrared excess. We constrain the gas to >7 R_WD and <32000 AU, and estimate it to be at ∼54 R_WD, well within WD 1124-293's tidal disruption radius. This detection is based on several epochs of spectroscopy around the Ca ii H and K lines (λ = 3968 Å, 3933 Å) with the MIKE spectrograph on the Magellan/Clay Telescope at Las Campanas Observatory. We confirm the circumstellar nature of the gas by observing nearby sightlines and finding no evidence for gas from the local interstellar medium. Through archival data we have measured the equivalent width of the two photospheric Ca lines over a period of 11 years. We see <5%–7% epoch-to-epoch variation in equivalent widths over this time period, and no evidence for long term trends. The presence of a circumstellar gas implies a near edge-on inclination to the system, thus we place limits to short period transiting planetary companions with R > R_⊕ using the Wide Angle Search for Planets survey. The presence of gas in orbit around WD 1124-293 implies that most DAZs could harbor planetary systems. Since 25%–30% of white dwarfs show metal line absorption, the dynamical process for perturbing small bodies must be robust.

We investigate the stability of super-Earth atmospheres around M stars using a seven-parameter, analytical framework. We construct stability diagrams in the parameter space of exoplanetary radius versus semimajor axis and elucidate the regions in which the atmospheres are stable against the condensation of their major constituents, out of the gas phase, on their permanent nightside hemispheres. We find that super-Earth atmospheres that are nitrogen-dominated (Earth-like) occupy a smaller region of allowed parameter space, compared to hydrogen-dominated atmospheres, because of the dual effects of diminished advection and enhanced radiative cooling. Furthermore, some super-Earths which reside within the habitable zones of M stars may not possess stable atmospheres, depending on the mean molecular weight and infrared photospheric pressure of their atmospheres. We apply our stability diagrams to GJ 436b and GJ 1214b, and demonstrate that atmospheric compositions with high mean molecular weights are disfavored if these exoplanets possess solid surfaces and shallow atmospheres. Finally, we construct stability diagrams tailored to the Kepler data set, for G and K stars, and predict that about half of the exoplanet candidates are expected to harbor stable atmospheres if Earth-like conditions are assumed. We include 55 Cancri e and CoRoT-7b in our stability diagram for G stars.

We present an analysis of the full bidimensional optical spectral cube of the nearby spiral galaxy NGC 5668, observed with the Pmas fiber PAcK Integral Field Unit (IFU) at the Calar Alto observatory 3.5 m telescope. We make use of broadband imaging to provide further constraints on the evolutionary history of the galaxy. This data set will allow us to improve our understanding of the mechanisms that drive the evolution of disks. We investigated the properties of 62 H ii regions and concentric rings in NGC 5668 and derived maps in ionized-gas attenuation and chemical (oxygen) abundances. We find that while inward of r ∼36'' ∼ 4.4 kpc ∼ 0.36 (D₂₅/2) the derived O/H ratio follows the radial gradient typical of spiral galaxies, the abundance gradient beyond r ∼ 36'' flattens out. The analysis of the multi-wavelength surface brightness profiles of NGC 5668 is performed by fitting these profiles with those predicted by chemo-spectrophotometric evolutionary models of galaxy disks. From this, we infer a spin and circular velocity of λ = 0.053 and v_c = 167 km s⁻¹, respectively. The metallicity gradient and rotation curve predicted by this best-fitting galaxy model nicely match the values derived from the IFU observations, especially within r ∼36''. The same is true for the colors despite some small offsets and a reddening in the bluest colors beyond that radius. On the other hand, deviations of some of these properties in the outer disk indicate that a secondary mechanism, possibly gas transfer induced by the presence of a young bar, must have played a role in shaping the recent chemical and star formation histories of NGC 5668.

Using the H i emission/absorption method, we resolve the kinematic distance ambiguity and derive distances for 149 of 182 (82%) H ii regions discovered by the Green Bank Telescope H ii Region Discovery Survey (GBT HRDS). The HRDS is an X-band (9 GHz, 3 cm) GBT survey of 448 previously unknown H ii regions in radio recombination line and radio continuum emission. Here, we focus on HRDS sources from 67° ⩾ ℓ ⩾ 18°, where kinematic distances are more reliable. The 25 HRDS sources in this zone that have negative recombination line velocities are unambiguously beyond the orbit of the Sun, up to 20 kpc distant. They are the most distant H ii regions yet discovered. We find that 61% of HRDS sources are located at the far distance, 31% at the tangent-point distance, and only 7% at the near distance. "Bubble" H ii regions are not preferentially located at the near distance (as was assumed previously) but average 10 kpc from the Sun. The HRDS nebulae, when combined with a large sample of H ii regions with previously known distances, show evidence of spiral structure in two circular arc segments of mean Galactocentric radii of 4.25 and 6.0 kpc. We perform a thorough uncertainty analysis to analyze the effect of using different rotation curves, streaming motions, and a change to the solar circular rotation speed. The median distance uncertainty for our sample of H ii regions is only 0.5 kpc, or 5%. This is significantly less than the median difference between the near and far kinematic distances, 6 kpc. The basic Galactic structure results are unchanged after considering these sources of uncertainty.

We study the multi-dimensional geometry of supernova (SN) explosions by means of spectropolarimetric observations of stripped-envelope SNe, i.e., SNe without a hydrogen-rich layer. We perform spectropolarimetric observations of two stripped-envelope SNe, Type Ib SN 2009jf and Type Ic SN 2009mi. Both objects show non-zero polarization at the wavelength of the strong lines. They also show a loop in the Stokes Q – U diagram, which indicates a non-axisymmetric, three-dimensional ion distribution in the ejecta. We show that five out of six stripped-envelope SNe, which have been observed spectropolarimetrically so far, show such a loop. This implies that a three-dimensional geometry is common in stripped-envelope SNe. We find that stronger lines tend to show higher polarization. This effect is not related to the geometry, and must be corrected for to compare the polarization of different lines or different objects. Even after the correction, however, there remains a dispersion of polarization degree among different objects. Such a dispersion might be caused by three-dimensional clumpy ion distributions viewed from different directions.

We present high-resolution, near-infrared NIRSPEC observations of CO absorption toward six class II T Tauri stars: AA Tau, DG Tau, IQ Tau, RY Tau, CW Tau, and Haro 6–5b. ¹²CO overtone absorption lines originating from the circumstellar disk of each object were used to calculate line-of-sight gas column densities toward each source. We measured the gas/dust ratio as a function of disk inclination, utilizing measured visual extinctions and inclinations for each star. The majority of our sources show further evidence for a correlation between the gas/dust column density ratio and disk inclination similar to that found by Rettig et al.

The first ionization potential (FIP) effect is the by now well-known enhancement in abundance over photospheric values of Fe and other elements with FIP below about 10 eV observed in the solar corona and slow speed solar wind. In our model, this fractionation is achieved by means of the ponderomotive force, arising as Alfvén waves propagate through or reflect from steep density gradients in the solar chromosphere. This is also the region where low FIP elements are ionized, and high FIP elements are largely neutral leading to the fractionation as ions interact with the waves but neutrals do not. Helium, the element with the highest FIP and consequently the last to remain neutral as one moves upward, can be depleted in such models. Here, we investigate this depletion for varying loop lengths and magnetic field strengths. Variations in this depletion arise as the concentration of the ponderomotive force at the top of the chromosphere varies in response to Alfvén wave frequency with respect to the resonant frequency of the overlying coronal loop, the magnetic field, and possibly also the loop length. We find that stronger depletions of He are obtained for weaker magnetic field, at frequencies close to or just above the loop resonance. These results may have relevance to observed variations of the slow wind solar He abundance with wind speed, with slower slow speed solar wind having a stronger depletion of He.

The prominence–corona transition region (PCTR) plays a key role in the thermal and pressure equilibrium of solar prominences. Our knowledge of this interface is limited and several major issues remain open, including the thermal structure and, in particular, the maximum temperature of the detectable plasma. The high signal-to-noise ratio of images obtained by the Atmospheric Imaging Assembly (AIA) on NASA's Solar Dynamics Observatory clearly shows that prominences are often seen in emission in the 171 and 131 bands. We investigate the temperature sensitivity of these AIA bands for prominence observations, in order to infer the temperature content in an effort to explain the emission. Using the CHIANTI atomic database and previously determined prominence differential emission measure distributions, we build synthetic spectra to establish the main emission-line contributors in the AIA bands. We find that the Fe ix line always dominates the 171 band, even in the absence of plasma at >10⁶ K temperatures, while the 131 band is dominated by Fe viii. We conclude that the PCTR has sufficient plasma emitting at >4 × 10⁵ K to be detected by AIA.

We use the Marcario Low Resolution Spectrograph at the Hobby–Eberly Telescope to study the kinematics of pseudobulges and classical bulges in the nearby universe. We present major axis rotational velocities, velocity dispersions, and h₃ and h₄ moments derived from high-resolution (σ_inst ≈ 39 km s⁻¹) spectra for 45 S0 to Sc galaxies; for 27 of the galaxies we also present minor axis data. We combine our kinematics with bulge-to-disk decompositions. We demonstrate for the first time that purely kinematic diagnostics of the bulge dichotomy agree systematically with those based on Sérsic index. Low Sérsic index bulges have both increased rotational support (higher v/σ values) and on average lower central velocity dispersions. Furthermore, we confirm that the same correlation also holds when visual morphologies are used to diagnose bulge type. The previously noted trend of photometrically flattened bulges to have shallower velocity dispersion profiles turns out to be significant and systematic if the Sérsic index is used to distinguish between pseudobulges and classical bulges. The anti-correlation between h₃ and v/σ observed in elliptical galaxies is also observed in intermediate-type galaxies, irrespective of bulge type. Finally, we present evidence for formerly undetected counter-rotation in the two systems NGC 3945 and NGC 4736.

Lenticular galaxies with M_B < −21.5 are almost exclusively unbarred, whereas both barred and unbarred objects occur at fainter luminosity levels. This effect is observed both for objects classified in blue light, and for those that were classified in the infrared. This result suggests that the most luminous (massive) S0 galaxies find it difficult to form bars. As a result, the mean luminosity of unbarred lenticular galaxies in both B and IR light is observed to be ∼0.4 mag brighter than that of barred lenticulars. A small contribution to the observed luminosity difference that is found between SA0 and SB0 galaxies may also be due to the fact that there is an asymmetry between the effects of small classification errors on SA0 and SB0 galaxies. An elliptical (E) galaxy might be misclassified as a lenticular (S0) or an S0 as an E. However, an E will never be misclassified as an SB0, nor will an SB0 ever be called an E. This asymmetry is important because E galaxies are typically twice as luminous as S0 galaxies. The present results suggest that the evolution of luminous lenticular galaxies may be closely linked to that of elliptical galaxies, whereas fainter lenticulars might be more closely associated with ram-pressure stripped spiral galaxies. Finally, it is pointed out that fine details of the galaxy formation process might account for some of the differences between the classifications of the same galaxy by individual competent morphologists.

We compare high-resolution ultraviolet spectra of the Sun and thirteen solar-mass main-sequence stars with different rotational periods that serve as proxies for their different ages and magnetic field structures. In this, the second paper in the series, we study the dependence of ultraviolet emission-line centroid velocities on stellar rotation period, as rotation rates decrease from that of the Pleiades star HII314 (P_rot = 1.47 days) to α Cen A (P_rot = 28 days). Our stellar sample of F9 V to G5 V stars consists of six stars observed with the Cosmic Origins Spectrograph on the Hubble Space Telescope (HST) and eight stars observed with the Space Telescope Imaging Spectrograph on HST. We find a systematic trend of increasing redshift with more rapid rotation (decreasing rotation period) that is similar to the increase in line redshift between quiet and plage regions on the Sun. The fastest-rotating solar-mass star in our study, HII314, shows significantly enhanced redshifts at all temperatures above log T = 4.6, including the corona, which is very different from the redshift pattern observed in the more slowly rotating stars. This difference in the redshift pattern suggests that a qualitative change in the magnetic-heating process occurs near P_rot = 2 days. We propose that HII314 is an example of a solar-mass star with a magnetic heating rate too large for the physical processes responsible for the redshift pattern to operate in the same way as for the more slowly rotating stars. HII314 may therefore lie above the high activity end of the set of solar-like phenomena that is often called the "solar–stellar connection."

Distribution of the CH₃OH (J_K = 2_K–1_K, 96.7 GHz) emission has been investigated toward NGC 1333 IRAS4B, a low-mass Class 0 protostar which harbors a hot corino, with Nobeyama Millimeter Array. The CH₃OH emission is found to be prominent in the shocked region caused by an impact of the molecular outflow from the protostars. The direction of the outflow which is responsible for the shock seems to be opposite to that of a compact outflow known previously in the CO (J = 2–1), HCN (J = 1–0), H₂CO (3₁₂–2₁₁), and CH₃OH (J_K = 7_K–6_K) emissions, whereas it is the same as that of the faint second outflow found in the H₂CO emission. This double outflow structure can be interpreted most naturally by the existence of more than two protostars in IRAS4B. On the other hand, a centrally condensed component associated apparently with IRAS4B cannot be recognized in our CH₃OH observation. Our observation suggests that, in this source, the CH₃OH (J_K = 2_K–1_K) emission preferentially traces the shocked regions rather than the hot corino around the protostar.

We report a series of simulations of the formation of a star cluster similar to the Orion Nebula Cluster (ONC), including both radiative transfer and protostellar outflows, and starting from both smooth and self-consistently turbulent initial conditions. Each simulation forms >150 stars and brown dwarfs, yielding a stellar mass distribution that ranges from <0.1 M_☉ to >10 M_☉. We show that a simulation that begins with self-consistently turbulent density and velocity fields embedded in a larger turbulent volume, and that includes protostellar outflows, produces an initial mass function (IMF) that is consistent both with that of the ONC and the Galactic field, at least within the statistical power provided by the number of stars formed in our simulations. This is the first simulation published to date that reproduces the observed IMF in a cluster large enough to contain massive stars, and where the peak of the mass function is determined by a fully self-consistent calculation of gas thermodynamics rather than a hand-imposed equation of state. This simulation also produces a star formation rate that, while still somewhat too high, is much closer to observed values than if we omit either the larger turbulent volume or the outflows. Moreover, we show that the combination of outflows, self-consistently turbulent initial conditions, and turbulence continually fed by motions on scales larger than that of the protocluster yields an IMF that is in agreement with observations and invariant with time, resolving the "overheating" problem in which simulations without these features have an IMF peak that shifts to progressively higher masses over time as more and more of the gas is heated, inconsistent with the observed invariance of the IMF. The simulation that matches the observed IMF also qualitatively reproduces the observed trend of stellar multiplicity strongly increasing with mass. We show that this simulation produces massive stars from distinct massive cores whose properties are consistent with those of observed massive cores. However, the stars formed in these cores also undergo dynamical interactions as they accrete that naturally produce Trapezium-like hierarchical multiple systems of massive stars.

We present high spatial resolution maps of ro-vibrational molecular hydrogen emission from the environment of the GG Tau A binary component in the GG Tau quadruple system. The H₂v = 1–0 S(1) emission is spatially resolved and encompasses the inner binary, with emission detected at locations that should be dynamically cleared on several hundred year timescales. Extensions of H₂ gas emission are seen to ∼100 AU distances from the central stars. The v = 2–1 S(1) emission at 2.24 μm is also detected at ∼30 AU from the central stars, with a line ratio of 0.05 ± 0.01 with respect to the v = 1–0 S(1) emission. Assuming gas in LTE, this ratio corresponds to an emission environment at ∼1700 K. We estimate that this temperature is too high for quiescent gas heated by X-ray or UV emission from the central stars. Surprisingly, we find that the brightest region of H₂ emission arises from a spatial location that is exactly coincident with a recently revealed dust "streamer" which seems to be transferring material from the outer circumbinary ring around GG Tau A into the inner region. As a result, we identify a new excitation mechanism for ro-vibrational H₂ stimulation in the environment of young stars. The H₂ in the GG Tau A system appears to be stimulated by mass accretion infall as material in the circumbinary ring accretes onto the system to replenish the inner circumstellar disks. We postulate that H₂ stimulated by accretion infall could be present in other systems, particularly binaries and "transition disk" systems which have dust-cleared gaps in their circumstellar environments.

Microlensing detections of cool planets are important for the construction of an unbiased sample to estimate the frequency of planets beyond the snow line, which is where giant planets are thought to form according to the core accretion theory of planet formation. In this paper, we report the discovery of a giant planet detected from the analysis of the light curve of a high-magnification microlensing event MOA 2010-BLG-477. The measured planet–star mass ratio is q = (2.181 ± 0.004) × 10⁻³ and the projected separation is s = 1.1228 ± 0.0006 in units of the Einstein radius. The angular Einstein radius is unusually large θ_E = 1.38 ± 0.11 mas. Combining this measurement with constraints on the "microlens parallax" and the lens flux, we can only limit the host mass to the range 0.13 < M/M_☉ < 1.0. In this particular case, the strong degeneracy between microlensing parallax and planet orbital motion prevents us from measuring more accurate host and planet masses. However, we find that adding Bayesian priors from two effects (Galactic model and Keplerian orbit) each independently favors the upper end of this mass range, yielding star and planet masses of M_* = 0.67^+0.33_{− 0.13} M_☉ and m_p = 1.5^+0.8_{− 0.3} M_JUP at a distance of D = 2.3 ± 0.6 kpc, and with a semi-major axis of a = 2⁺³_{− 1} AU. Finally, we show that the lens mass can be determined from future high-resolution near-IR adaptive optics observations independently from two effects, photometric and astrometric.

We explore the evolution of the mass distribution of dust in collision-dominated debris disks, using the collisional code introduced in our previous paper. We analyze the equilibrium distribution and its dependence on model parameters by evolving over 100 models to 10 Gyr. With our numerical models, we confirm that systems reach collisional equilibrium with a mass distribution that is steeper than the traditional solution by Dohnanyi. Our model yields a quasi-steady-state slope of n(m) ∼ m^−1.88 [n(a) ∼ a^−3.65] as a robust solution for a wide range of possible model parameters. We also show that a simple power-law function can be an appropriate approximation for the mass distribution of particles in certain regimes. The steeper solution has observable effects in the submillimeter and millimeter wavelength regimes of the electromagnetic spectrum. We assemble data for nine debris disks that have been observed at these wavelengths and, using a simplified absorption efficiency model, show that the predicted slope of the particle-mass distribution generates spectral energy distributions that are in agreement with the observed ones.

The mid- and the far-infrared spectra of polycyclic aromatic hydrocarbons (PAHs) have been computed using density functional theory. This study has focused on PAHs in the highly symmetric, compact, coronene family with sizes up to 384 carbons. We have identified trends in the peak position and intrinsic strength of the vibrational modes of these species and compared these to trends previously reported for less symmetric and smaller PAHs. The computed spectral modes have been used to calculate the IR emission spectrum of PAHs pumped by UV photons. The results have been compared to observed interstellar spectra to elucidate the characteristics of the interstellar PAH family. The calculations show that highly symmetric PAHs are very stable and, hence, might be favored under the harsh conditions of interstellar space. Our calculated vibrational properties confirm and extend previous studies for small PAHs to the large compact PAHs studied here, specifically in terms of the dependence of the spectral characteristics on ionization and on H-adjacency. The calculations show that for PAHs larger than 150 carbons, the 6.3 μm feature becomes very broad and shifts to longer wavelengths, the 8.6 μm band becomes stronger than the "7.7" μm band, and the 11.0/12.7 band strength ratio gets too large compared with observations. Thus, PAHs with 150 carbons or more are unlikely to be the dominant species in interstellar space. The simplicity of the observed spectra in the 15–20 μm range points toward a preponderance of compact PAHs in the interstellar PAH family.

We present a quantitative study on the properties at death of fast-rotating massive stars evolved at low-metallicity—objects that are proposed as likely progenitors of long-duration γ-ray bursts (LGRBs). We perform one-dimensional+rotation stellar-collapse simulations on the progenitor models of Woosley and Heger, and critically assess their potential for the formation of a black hole and a Keplerian disk (namely, a collapsar) or a proto-magnetar. We note that theoretical uncertainties in the treatment of magnetic fields and the approximate handling of rotation compromise the accuracy of stellar-evolution models. We find that only the fastest rotating progenitors achieve sufficient compactness for black hole formation while the bulk of models possess a core density structure typical of garden-variety core-collapse supernova (SN) progenitors evolved without rotation and at solar metallicity. Of the models that do have sufficient compactness for black hole formation, most of them also retain a large amount of angular momentum in the core, making them prone to a magneto-rotational explosion, therefore preferentially leaving behind a proto-magnetar. A large progenitor angular-momentum budget is often the sole criterion invoked in the community today to assess the suitability for producing a collapsar. This simplification ignores equally important considerations such as the core compactness, which conditions black hole formation, the core angular momentum, which may foster a magneto-rotational explosion preventing black hole formation, or the metallicity and the residual envelope mass which must be compatible with inferences from observed LGRB/SNe. Our study suggests that black hole formation is non-trivial, that there is room for accommodating both collapsars and proto-magnetars as LGRB progenitors, although proto-magnetars seem much more easily produced by current stellar-evolutionary models.

We report on very high energy (E > 100 GeV) gamma-ray observations of V407 Cygni, a symbiotic binary that underwent a nova outburst producing 0.1–10 GeV gamma rays during 2010 March 10–26. Observations were made with the Very Energetic Radiation Imaging Telescope Array System during 2010 March 19–26 at relatively large zenith angles due to the position of V407 Cyg. An improved reconstruction technique for large zenith angle observations is presented and used to analyze the data. We do not detect V407 Cygni and place a differential upper limit on the flux at 1.6 TeV of 2.3 × 10⁻¹² erg cm⁻² s⁻¹ (at the 95% confidence level). When considered jointly with data from Fermi-LAT, this result places limits on the acceleration of very high energy particles in the nova.