Table of contents

A recent cross-correlation between the Sloan Digital Sky Survey (SDSS) Data Release 7 White Dwarf Catalog with the Wide-Field Infrared Survey Explorer (WISE) all-sky photometry at 3.4, 4.6, 12, and 22 μm performed by Debes et al. resulted in the discovery of 52 candidate dusty white dwarfs (WDs). However, the 6'' WISE beam allows for the possibility that many of the excesses exhibited by these WDs may be due to contamination from a nearby source. We present MMT+SAO Wide-Field InfraRed Camera J- and H-band imaging observations (05–15 point spread function) of 16 of these candidate dusty WDs and confirm that four have spectral energy distributions (SEDs) consistent with a dusty disk and are not accompanied by a nearby source contaminant. The remaining 12 WDs have contaminated WISE photometry and SEDs inconsistent with a dusty disk when the contaminating sources are not included in the photometry measurements. We find the frequency of disks around single WDs in the WISE ∩ SDSS sample to be 2.6%–4.1%. One of the four new dusty WDs has a mass of 1.04 M_☉ (progenitor mass 5.4 M_☉) and its discovery offers the first confirmation that massive WDs (and their massive progenitor stars) host planetary systems.

We present a comprehensive high spatial resolution imaging study of globular clusters (GCs) in NGC 1399, the central giant elliptical cD galaxy in the Fornax galaxy cluster, conducted with the Advanced Camera for Surveys (ACS) aboard the Hubble Space Telescope (HST). Using a novel technique to construct drizzled point-spread function libraries for HST/ACS data, we accurately determine the fidelity of GC structural parameter measurements from detailed artificial star cluster experiments and show the superior robustness of the GC half-light radius, r_h, compared with other GC structural parameters, such as King core and tidal radius. The measurement of r_h for the major fraction of the NGC 1399 GC system reveals a trend of increasing r_h versus galactocentric distance, R_gal, out to about 10 kpc and a flat relation beyond. This trend is very similar for blue and red GCs, which are found to have a mean size ratio of r_{h, red}/r_{h, blue} = 0.82 ± 0.11 at all galactocentric radii from the core regions of the galaxy out to ∼40 kpc. This suggests that the size difference between blue and red GCs is due to internal mechanisms related to the evolution of their constituent stellar populations. Modeling the mass density profile of NGC 1399 shows that additional external dynamical mechanisms are required to limit the GC size in the galaxy halo regions to r_h ≈ 2 pc. We suggest that this may be realized by an exotic GC orbit distribution function, an extended dark matter halo, and/or tidal stress induced by the increased stochasticity in the dwarf halo substructure at larger galactocentric distances. We compare our results with the GC r_h distribution functions in various galaxies and find that the fraction of extended GCs with r_h ⩾ 5 pc is systematically larger in late-type galaxies compared with GC systems in early-type galaxies. This is likely due to the dynamically more violent evolution of early-type galaxies. We match our GC r_h measurements with radial velocity data from the literature and split the resulting sample at the median r_h value into compact and extended GCs. We find that compact GCs show a significantly smaller line-of-sight velocity dispersion, 〈σ_cmp〉 = 225  ±  25 km s⁻¹, than their extended counterparts, 〈σ_ext〉 = 317 ± 21 km s⁻¹. Considering the weaker statistical correlation in the GC r_h color and the GC r_h–R_gal relations, the more significant GC size–dynamics relation appears to be astrophysically more relevant and hints at the dominant influence of the GC orbit distribution function on the evolution of GC structural parameters.

Using a large N-body cosmological simulation combined with a subgrid treatment of galaxy formation, merging, and tidal destruction, we study the formation and evolution of the galaxy and cluster population in a comoving volume (100 Mpc)³ in a ΛCDM universe. At z = 0, our computational volume contains 1788 clusters with mass M_cl > 1.1 × 10¹² M_☉, including 18 massive clusters with M_cl > 10¹⁴ M_☉. It also contains 1, 088, 797 galaxies with mass M_gal ⩾ 2 × 10⁹ M_☉ and luminosity L > 9.5 × 10⁵ L_☉. For each cluster, we identified the brightest cluster galaxy (BCG). We then computed two separate statistics: the fraction f_BNC of clusters in which the BCG is not the closest galaxy to the center of the cluster in projection, and the ratio Δv/σ, where Δv is the difference in radial velocity between the BCG and the whole cluster and σ is the radial velocity dispersion of the cluster. We found that f_BNC increases from 0.05 for low-mass clusters (M_cl ∼ 10¹² M_☉) to 0.5 for high-mass clusters (M_cl > 10¹⁴ M_☉) with very little dependence on cluster redshift. Most of this result turns out to be a projection effect and when we consider three-dimensional distances instead of projected distances, f_BNC increases only to 0.2 at high-cluster mass. The values of Δv/σ vary from 0 to 1.8, with median values in the range 0.03–0.15 when considering all clusters, and 0.12–0.31 when considering only massive clusters. These results are consistent with previous observational studies and indicate that the central galaxy paradigm, which states that the BCG should be at rest at the center of the cluster, is usually valid, but exceptions are too common to be ignored. We built merger trees for the 18 most massive clusters in the simulation. Analysis of these trees reveal that 16 of these clusters have experienced 1 or several major or semi-major mergers in the past. These mergers leave each cluster in a non-equilibrium state, but eventually the cluster settles into an equilibrium configuration, unless it is disturbed by another major or semi-major merger. We found evidence that these mergers are responsible for the off-center positions and peculiar velocities of some BCGs. Our results thus support the merging-group scenario, in which some clusters form by the merging of smaller groups in which the galaxies have already formed, including the galaxy destined to become the BCG. Finally, we argue that f_BNC is not a very robust statistics, as it is very sensitive to projection and selection effects, but that Δv/σ is more robust. Still, both statistics exhibit a signature of major mergers between clusters of galaxies.

We have obtained extensive high-quality spectroscopic observations of the OGLE-LMC-CEP-1718 eclipsing binary system in the Large Magellanic Cloud that Soszyński et al. had identified as a candidate system for containing two classical Cepheids in orbit. Our spectroscopic data clearly demonstrate binary motion of the Cepheids in a 413 day eccentric orbit, rendering this eclipsing binary system the first ever known to consist of 2 classical Cepheid variables. After disentangling the four different radial velocity variations in the system, we present the orbital solution and the individual pulsational radial velocity curves of the Cepheids. We show that both Cepheids are extremely likely to be first overtone pulsators and determine their respective dynamical masses, which turn out to be equal to within 1.5%. Since the secondary eclipse is not observed in the orbital light curve, we cannot derive the individual radii of the Cepheids, but the sum of their radii derived from the photometry is consistent with overtone pulsation for both variables. The existence of two equal-mass Cepheids in a binary system having different pulsation periods (1.96 and 2.48 days, respectively) may pose an interesting challenge to stellar evolution and pulsation theories, and a more detailed study of this system using additional data sets should yield deeper insight about the physics of stellar evolution of Cepheid variables. Future analysis of the system using additional near-infrared photometry might also lead to a better understanding of the systematic uncertainties in current Baade–Wesselink techniques of distance determinations to Cepheid variables.

We present a systematic study of the force-free field equation for simple axisymmetric configurations in spherical geometry and apply it to the solar active regions. The condition of separability of solutions in the radial and angular variables leads to two classes of solutions: linear and nonlinear force-free fields (NLFF). We have studied these linear solutions and extended the nonlinear solutions for the radial power law index to the irreducible rational form n = p/q, which is allowed for all cases of odd p and cases of q > p for even p, where the poloidal flux ψ∝1/rⁿ and the field B∝1/r^{n + 2}. We apply these solutions to simulate photospheric vector magnetograms obtained using the spectropolarimeter on board Hinode. The effectiveness of our search strategy is first demonstrated on test inputs of dipolar, axisymmetric, and nonaxisymmetric linear force-free fields. Using the best fit, we build three-dimensional axisymmetric field configurations and calculate the energy and relative helicity with two independent methods, which are in agreement. We have analyzed five magnetograms for AR 10930 spanning a period of three days during which two X-class flares occurred and found the free energy and relative helicity of the active region before and after the flare; our analysis indicates a peak in these quantities before the flare events, which is consistent with the other results. We also analyzed single-polarity regions AR 10923 and 10933, which showed very good fits to potential fields. This method provides useful reconstruction of NLFF and input fields for other numerical techniques.

Strong evidence exists that coronal loops as observed in extreme ultraviolet and soft X-rays may not be monolithic isotropic structures, but can often be more accurately modeled as bundles of independent strands. Modeling the observed active region transient brightenings (ARTBs) within this framework allows for the exploration of the energetic ramifications and characteristics of these stratified structures. Here we present a simple method of detecting and modeling ARTBs observed with the Hinode X-Ray Telescope (XRT) as groups of zero-dimensional strands, which allows us to probe parameter space to better understand the spatial and temporal dependence of strand heating in impulsively heated loops. This partially automated method can be used to analyze a large number of observations to gain a statistical insight into the parameters of coronal structures, including the number of heating events required in a given model to fit the observations. In this article, we present the methodology and demonstrate its use in detecting and modeling ARTBs in a sample data set from Hinode/XRT. These initial results show that, in general, multiple heating events are necessary to reproduce observed ARTBs, but the spatial dependence of these heating events cannot yet be established.

We present numerical results on two- (2D) and three-dimensional (3D) hydrodynamic core-collapse simulations of an 11.2 M_☉ star. By changing numerical resolutions and seed perturbations systematically, we study how the postbounce dynamics are different in 2D and 3D. The calculations were performed with an energy-dependent treatment of the neutrino transport based on the isotropic diffusion source approximation scheme, which we have updated to achieve a very high computational efficiency. All of the computed models in this work, including nine 3D models and fifteen 2D models, exhibit the revival of the stalled bounce shock, leading to the possibility of explosion. All of them are driven by the neutrino-heating mechanism, which is fostered by neutrino-driven convection and the standing-accretion-shock instability. Reflecting the stochastic nature of multi-dimensional (multi-D) neutrino-driven explosions, the blast morphology changes from model to model. However, we find that the final fate of the multi-D models, whether an explosion is obtained or not, is little affected by the explosion stochasticity. In agreement with some previous studies, higher numerical resolutions lead to slower onset of the shock revival in both 2D and 3D. Based on the self-consistent supernova models leading to the possibility of explosions, our results systematically show that the revived shock expands more energetically in 2D than in 3D.

We present the X-ray timing and spectral evolution of the Galactic Center magnetar SGR J1745−2900 for the first ∼4 months post-discovery using data obtained with the Nuclear Spectroscopic Telescope Array and Swift observatories. Our timing analysis reveals a large increase in the magnetar spin-down rate by a factor of 2.60 ± 0.07 over our data span. We further show that the change in spin evolution was likely coincident with a bright X-ray burst observed in 2013 June by Swift, and if so, there was no accompanying discontinuity in the frequency. We find that the source 3–10 keV flux has declined monotonically by a factor of ∼2 over an 80 day period post-outburst accompanied by a ∼20% decrease in the source's blackbody temperature, although there is evidence for both flux and kT having leveled off. We argue that the torque variations are likely to be magnetospheric in nature and will dominate over any dynamical signatures of orbital motion around Sgr A^*.

An important strength of the microlensing method to detect extrasolar planets is its high sensitivity to low-mass planets. However, many believe that microlensing detections of Earth-mass planets from ground-based observation would be difficult because of limits set by finite-source effects. This view comes from the previous estimation of planet detection probability based on the fractional deviation of planetary signals; however, a proper probability estimation is required when considering the source brightness, which is directly related to the photometric precision. In this paper, we reevaluate the feasibility of low-mass planet detections by considering photometric precision for different populations of source stars. From this, we find that the contribution of improved photometric precision to the planetary signal of a giant-source event is large enough to compensate for the decrease in magnification excess caused by finite-source effects. As a result, we conclude that giant-source events are suitable targets for Earth-mass planet detections with significantly higher detection probability than events involved with source stars of smaller radii, and we predict that Earth-mass planets could be detected by prospective high-cadence surveys.

Alfvénic fluctuations in the solar wind exhibit a high degree of velocities and magnetic field correlations consistent with Alfvén waves propagating away and toward the Sun. Two remarkable properties of these fluctuations are the tendencies to have either positive or negative magnetic helicity (−1 ⩽ σ_m ⩽ +1) associated with either left- or right- topological handedness of the fluctuations and to have a constant magnetic field magnitude. This paper provides, for the first time, a theoretical framework for reconstructing both the magnetic and velocity field fluctuations with a divergence-free magnetic field, with any specified power spectral index and normalized magnetic- and cross-helicity spectrum field fluctuations for any plasma species. The spectrum is constructed in the Fourier domain by imposing two conditions—a divergence-free magnetic field and the preservation of the sense of magnetic helicity in both spaces—as well as using Parseval's theorem for the conservation of energy between configuration and Fourier spaces. Applications to the one-dimensional spatial Alfvénic propagation are presented. The theoretical construction is in agreement with typical time series and power spectra properties observed in the solar wind. The theoretical ideas presented in this spectral reconstruction provide a foundation for more realistic simulations of plasma waves, solar wind turbulence, and the propagation of energetic particles in such fluctuating fields.

We use high-resolution cosmological simulations of Milky Way (MW) mass galaxies that include both baryons and dark matter (DM) to show that baryonic physics (energetic feedback from supernovae and subsequent tidal stripping) significantly reduces the DM mass in the central regions of luminous satellite galaxies. The reduced central masses of the simulated satellites reproduce the observed internal dynamics of MW and M31 satellites as a function of luminosity. We use these realistic satellites to update predictions for the observed velocity and luminosity functions of satellites around MW-mass galaxies when baryonic effects are accounted for. We also predict that field dwarf galaxies in the same luminosity range as the MW classical satellites should not exhibit velocities as low as the satellites because the field dwarfs do not experience tidal stripping. Additionally, the early formation times of the satellites compared to field galaxies at the same luminosity may be apparent in the star formation histories of the two populations. Including baryonic physics in cold dark matter (CDM) models naturally explains the observed low DM densities in the MWs dwarf spheroidal population. Our simulations therefore resolve the tension between kinematics predicted in CDM theory and observations of satellites, without invoking alternative forms of DM.

The accumulation of redshifts provides a significant observational bottleneck when using galaxy cluster surveys to constrain cosmological parameters. We propose a simple method to allow the use of samples where there is a fraction of the redshifts that are not known. The simplest assumption is that the missing redshifts are randomly extracted from the catalog, but the method also allows one to take into account known selection effects in the accumulation of redshifts. We quantify the reduction in statistical precision of cosmological parameter constraints as a function of the fraction of missing redshifts for simulated surveys, and also investigate the impact of making an incorrect assumption for the distribution of missing redshifts.

Several studies have suggested that the observed size evolution of massive early-type galaxies (ETGs) can be explained as a combination of dry mergers and progenitor bias, at least since z ∼ 1. In this paper we carry out a new test of the dry-merger scenario based on recent lensing measurements of the evolution of the mass density profile of ETGs. We construct a theoretical model for the joint evolution of the size and mass density profile slope γ' driven by dry mergers occurring at rates given by cosmological simulations. Such dry-merger model predicts a strong decrease of γ' with cosmic time, inconsistent with the almost constant γ' inferred from observations in the redshift range 0 < z < 1. We then show with a simple toy model that a modest amount of cold gas in the mergers—consistent with the upper limits on recent star formation in ETGs—is sufficient to reconcile the model with measurements of γ'. By fitting for the amount of gas accreted during mergers, we find that models with dissipation are consistent with observations of the evolution in both size and density slope, if ∼4% of the total final stellar mass arises from the gas accreted since z ∼ 1. Purely dry merger models are ruled out at >99% CL. We thus suggest a scenario where the outer regions of massive ETGs grow by accretion of stars and dark matter, while small amounts of dissipation and nuclear star formation conspire to keep the mass density profile constant and approximately isothermal.

This paper aims to resolve the problem of formation of young objects observed in the RCW 82 H ii region. In the framework of a classical trigger model the estimated time of fragmentation is larger than the estimated age of the H ii region. Thus the young objects could not have formed during the dynamical evolution of the H ii region. We propose a new model that helps resolve this problem. This model suggests that the H ii region RCW 82 is embedded in a cloud of limited size that is denser than the surrounding interstellar medium. According to this model, when the ionization–shock front leaves the cloud it causes the formation of an accelerating dense gas shell. In the accelerated shell, the effects of the Rayleigh–Taylor (R-T) instability dominate and the characteristic time of the growth of perturbations with the observed magnitude of about 3 pc is 0.14 Myr, which is less than the estimated age of the H ii region. The total time t_∑, which is the sum of the expansion time of the H ii region to the edge of the cloud, the time of the R-T instability growth, and the free fall time, is estimated as 0.44 < t_∑ < 0.78 Myr. We conclude that the young objects in the H ii region RCW 82 could be formed as a result of the R-T instability with subsequent fragmentation into large-scale condensations.

Using one-dimensional models, we show that a helical magnetic field with an appropriate sign of helicity can compensate the Faraday depolarization resulting from the superposition of Faraday-rotated polarization planes from a spatially extended source. For radio emission from a helical magnetic field, the polarization as a function of the square of the wavelength becomes asymmetric with respect to zero. Mathematically speaking, the resulting emission occurs then either at observable or at unobservable (imaginary) wavelengths. We demonstrate that rotation measure (RM) synthesis allows for the reconstruction of the underlying Faraday dispersion function in the former case, but not in the latter. The presence of positive magnetic helicity can thus be detected by observing positive RM in highly polarized regions in the sky and negative RM in weakly polarized regions. Conversely, negative magnetic helicity can be detected by observing negative RM in highly polarized regions and positive RM in weakly polarized regions. The simultaneous presence of two magnetic constituents with opposite signs of helicity is shown to possess signatures that can be quantified through polarization peaks at specific wavelengths and the gradient of the phase of the Faraday dispersion function. Similar polarization peaks can tentatively also be identified for the bi-helical magnetic fields that are generated self-consistently by a dynamo from helically forced turbulence, even though the magnetic energy spectrum is then continuous. Finally, we discuss the possibility of detecting magnetic fields with helical and non-helical properties in external galaxies using the Square Kilometre Array.

We use far-infrared (20–200 μm) data from the Composite Infrared Spectrometer on the Cassini spacecraft to determine the zonal-mean temperature and hydrogen para-fraction in Saturn's upper troposphere from observations taken before and after the large northern hemisphere storm in 2010–2011. During the storm, zonal mean temperatures in the latitude band between approximately 25°N and 45°N (planetographic latitude) increased by about 3 K, while the zonal mean hydrogen para-fraction decreased by about 0.04 over the same latitudes, at pressures greater than about 300 mbar. These changes occurred over the same latitude range as the disturbed cloud band seen in visible images. The observations are consistent with low para-fraction gas being brought up from the level of the water cloud by the strong convective plume associated with the storm, while being heated by condensation of water vapor, and then advected zonally by the winds near the plume tops in the upper troposphere.

Weak lensing provides an important route toward collecting samples of clusters of galaxies selected by mass. Subtle systematic errors in image reduction can compromise the power of this technique. We use the B-mode signal to quantify this systematic error and to test methods for reducing this error. We show that two procedures are efficient in suppressing systematic error in the B-mode: (1) refinement of the mosaic CCD warping procedure to conform to absolute celestial coordinates and (2) truncation of the smoothing procedure on a scale of 10'. Application of these procedures reduces the systematic error to 20% of its original amplitude. We provide an analytic expression for the distribution of the highest peaks in noise maps that can be used to estimate the fraction of false peaks in the weak-lensing κ-signal-to-noise ratio (S/N) maps as a function of the detection threshold. Based on this analysis, we select a threshold S/N = 4.56 for identifying an uncontaminated set of weak-lensing peaks in two test fields covering a total area of ∼3 deg². Taken together these fields contain seven peaks above the threshold. Among these, six are probable systems of galaxies and one is a superposition. We confirm the reliability of these peaks with dense redshift surveys, X-ray, and imaging observations. The systematic error reduction procedures we apply are general and can be applied to future large-area weak-lensing surveys. Our high-peak analysis suggests that with an S/N threshold of 4.5, there should be only 2.7 spurious weak-lensing peaks even in an area of 1000 deg², where we expect ∼2000 peaks based on our Subaru fields.

Magnetic fields govern the plasma dynamics in the outer layers of the solar atmosphere, and electric fields acting on neutral atoms that move across the magnetic field enable us to study the dynamical coupling between neutrals and ions in the plasma. In order to measure the magnetic and electric fields of chromospheric jets, the full Stokes spectra of the Paschen series of neutral hydrogen in a surge and in some active region jets that took place at the solar limb were observed on 2012 May 5, using the spectropolarimeter of the Domeless Solar Telescope at Hida observatory, Japan. First, we inverted the Stokes spectra taking into account only the effect of magnetic fields on the energy structure and polarization of the hydrogen levels. Having found no definitive evidence of the effects of electric fields in the observed Stokes profiles, we then estimated an upper bound for these fields by calculating the polarization degree under the magnetic field configuration derived in the first step, with the additional presence of a perpendicular (Lorentz type) electric field of varying strength. The inferred direction of the magnetic field on the plane of the sky approximately aligns to the active region jets and the surge, with magnetic field strengths in the range 10 G < B < 640 G for the surge. Using magnetic field strengths of 70, 200, and 600 G, we obtained upper limits for possible electric fields of 0.04, 0.3, and 0.8 V cm⁻¹, respectively. This upper bound is conservative, since in our modeling we neglected the possible contribution of collisional depolarization. Because the velocity of neutral atoms of hydrogen moving across the magnetic field derived from these upper limits of the Lorentz electric field is far below the bulk velocity of the plasma perpendicular to the magnetic field as measured by the Doppler shift, we conclude that the neutral atoms must be highly frozen to the magnetic field in the surge.

After the peak intensity of many large solar flares, magnetic and thermodynamic processes give rise to a phenomenon known as supra-arcade downflows (SADs). SADs are sunward flowing density depletions, often observed in post-flare plasma sheets. Some models have suggested that the plasma in the dark lanes is heated to temperatures of 20–80 MK, which is much hotter than temperatures of the surrounding plasma. In this work, we use data from the Atmospheric Imaging Assembly on the Solar Dynamics Observatory and the X-Ray Telescope on the Hinode satellite to determine the thermal structure of SADs in the solar corona. We examine four flares that took place on 2011 October 22, 2012 January 14, 2012 January 16, and 2012 January 27. Differential emission measures are calculated for each flare and we compare the temperatures in the SADs to those of the surrounding plasma. We find that the SADs are hotter than the background, but cooler than the surrounding plasma in most cases, with only 1 out of the 11 SADs examined here having a slightly higher temperature than its surroundings.

We have obtained improved spectra of key fundamental band lines of H$_3^+$, R(1, 1)^l, R(3, 3)^l, and R(2, 2)^l, and ro-vibrational transitions of CO on sightlines toward the luminous infrared sources GCIRS 3 and GCIRS 1W, each located in the Central Cluster of the Galactic center within several arcseconds of Sgr A*. The spectra reveal absorption occurring in three kinds of gaseous environments: (1) cold dense and diffuse gas associated with foreground spiral/lateral arms; (2) warm and diffuse gas absorbing over a wide and mostly negative velocity range, which appears to fill a significant fraction of the Galaxy's Central Molecular Zone (CMZ); and (3) warm, dense and compact clouds with velocities near +50 km s⁻¹ probably within 1–2 pc of the center. The absorptions by the first two cloud types are nearly identical for all the sources in the Central Cluster, and are similar to those previously observed on sightlines from Sgr A* to 30 pc east of it. Cloud type (3), which has only been observed toward the Central Cluster, shows distinct differences between the sightlines to GCIRS 3 and GCIRS 1W, which are separated on the sky by only 0.33 pc in projection. We identify this material as part of an inward extension of the circumnuclear disk previously known from HCN mapping. Lower limits on the products of the hydrogen ionization rate ζ and the path length L are 2.3 × 10⁵ cm s⁻¹ and 1.5 × 10³ cm s⁻¹ for the warm and diffuse CMZ gas and for the warm and dense clouds in the core, respectively. The limits indicate that the ionization rates in these regions are well above 10⁻¹⁵ s⁻¹.

Estimates of the mass and age of young stars from their location in the H-R diagram are limited by not only the typical observational uncertainties that apply to field stars, but also by large systematic uncertainties related to circumstellar phenomena. In this paper, we analyze flux-calibrated optical spectra to measure accurate spectral types and extinctions of 281 nearby T Tauri stars (TTSs). The primary advances in this paper are (1) the incorporation of a simplistic accretion continuum in optical spectral type and extinction measurements calculated over the full optical wavelength range and (2) the uniform analysis of a large sample of stars, many of which are well known and can serve as benchmarks. Comparisons between the non-accreting TTS photospheric templates and stellar photosphere models are used to derive conversions from spectral type to temperature. Differences between spectral types can be subtle and difficult to discern, especially when accounting for accretion and extinction. The spectral types measured here are mostly consistent with spectral types measured over the past decade. However, our new spectral types are one to two subclasses later than literature spectral types for the original members of the TW Hya Association (TWA) and are discrepant with literature values for some well-known members of the Taurus Molecular Cloud. Our extinction measurements are consistent with other optical extinction measurements but are typically 1 mag lower than near-IR measurements, likely the result of methodological differences and the presence of near-IR excesses in most CTTSs. As an illustration of the impact of accretion, spectral type, and extinction uncertainties on the H-R diagrams of young clusters, we find that the resulting luminosity spread of stars in the TWA is 15%–30%. The luminosity spread in the TWA and previously measured for binary stars in Taurus suggests that for a majority of stars, protostellar accretion rates are not large enough to significantly alter the subsequent evolution.

Among many physical processes involved in star formation, radiation transfer is one of the key processes because it dominantly controls the thermodynamics. Because metallicities control opacities, they are one of the important environmental parameters that affect star formation processes. In this work, I investigate protostellar collapse in solar-metallicity and low-metallicity (Z = 0.1 Z_☉) environments using three-dimensional radiation hydrodynamic and magnetohydrodynamic simulations. Because radiation cooling in high-density gas is more effective in low-metallicity environments, first cores are colder and have lower entropies. As a result, first cores are smaller, less massive, and have shorter lifetimes in low-metallicity clouds. Therefore, first cores would be less likely to be found in low-metallicity star forming clouds. This also implies that first cores tend to be more gravitationally unstable and susceptible to fragmentation. The evolution and structure of protostellar cores formed after the second collapse weakly depend on metallicities in the spherical and magnetized models, despite the large difference in the metallicities. Because this is due to the change of the heat capacity by dissociation and ionization of hydrogen, it is a general consequence of the second collapse as long as the effects of radiation cooling are not very large during the second collapse. On the other hand, the effects of different metallicities are more significant in the rotating models without magnetic fields, because they evolve slower than other models and therefore are more affected by radiation cooling.

Neon emission lines are good indicators of high-excitation regions close to a young stellar system because of their high ionization potentials and large critical densities. We have discovered [Ne iii] λ3869 emission from the microjets of Sz 102, a low-mass young star in Lupus III. Spectroastrometric analyses of two-dimensional [Ne iii] spectra obtained from archival high-dispersion (R ≈ 33, 000) Very Large Telescope/UVES data suggest that the emission consists of two velocity components spatially separated by ∼03, or a projected distance of ∼60 AU. The stronger redshifted component is centered at ∼ + 21 km s⁻¹ with a line width of ∼140 km s⁻¹, and the weaker blueshifted component at ∼ − 90 km s⁻¹ with a line width of ∼190 km s⁻¹. The two components trace velocity centroids of the known microjets and show large line widths that extend across the systemic velocity, suggesting their potential origins in wide-angle winds that may eventually collimate into jets. Optical line ratios indicate that the microjets are hot (T ≲ 1.6 × 10⁴ K) and ionized (n_e ≳ 5.7 × 10⁴ cm⁻³). The blueshifted component has ∼13% higher temperature and ∼46% higher electron density than the redshifted counterpart, forming a system of an asymmetric pair of jets. The detection of the [Ne iii] λ3869 line with the distinct velocity profile suggests that the emission originates in flows that may have been strongly ionized by deeply embedded hard X-ray sources, most likely generated by magnetic processes. The discovery of [Ne iii] λ3869 emission along with other optical forbidden lines from Sz 102 supports the picture of wide-angle winds surrounding magnetic loops in the close vicinity of the young star. Future high-sensitivity X-ray imaging and high angular-resolution optical spectroscopy may help confirm the picture proposed.

We present multiwavelength photometry, high angular resolution imaging, and radial velocities of the unique and confounding disintegrating low-mass planet candidate KIC 12557548b. Our high angular resolution imaging, which includes space-based Hubble Space Telescope Wide Field Camera 3 (HST/WFC3) observations in the optical (∼0.53 μm and ∼0.77 μm), and ground-based Keck/NIRC2 observations in K' band (∼2.12 μm), allow us to rule out background and foreground candidates at angular separations greater than 02 that are bright enough to be responsible for the transits we associate with KIC 12557548. Our radial velocity limit from Keck/HIRES allows us to rule out bound, low-mass stellar companions (∼0.2 M_☉) to KIC 12557548 on orbits less than 10 yr, as well as placing an upper limit on the mass of the candidate planet of 1.2 Jupiter masses; therefore, the combination of our radial velocities, high angular resolution imaging, and photometry are able to rule out most false positive interpretations of the transits. Our precise multiwavelength photometry includes two simultaneous detections of the transit of KIC 12557548b using Canada–France–Hawaii Telescope/Wide-field InfraRed Camera (CFHT/WIRCam) at 2.15 μm and the Kepler space telescope at 0.6 μm, as well as simultaneous null-detections of the transit by Kepler and HST/WFC3 at 1.4 μm. Our simultaneous HST/WFC3 and Kepler null-detections provide no evidence for radically different transit depths at these wavelengths. Our simultaneous CFHT/WIRCam detections in the near-infrared and with Kepler in the optical reveal very similar transit depths (the average ratio of the transit depths at ∼2.15 μm compared with ∼0.6 μm is: 1.02 ± 0.20). This suggests that if the transits we observe are due to scattering from single-size particles streaming from the planet in a comet-like tail, then the particles must be ∼0.5 μm in radius or larger, which would favor that KIC 12557548b is a sub-Mercury rather than super-Mercury mass planet.

Many exoplanets in close-in orbits are observed to have relatively high eccentricities and large stellar obliquities. We explore the possibility that these result from planet–planet scattering by studying the dynamical outcomes from a large number of orbit integrations in systems with two and three gas-giant planets in close-in orbits (0.05 AU < a < 0.15 AU). We find that at these orbital separations, unstable systems starting with low eccentricities and mutual inclinations (e ≲ 0.1, i ≲ 0.1) generally lead to planet–planet collisions in which the collision product is a planet on a low-eccentricity, low-inclination orbit. This result is inconsistent with the observations. We conclude that eccentricity and inclination excitation from planet–planet scattering must precede migration of planets into short-period orbits. This result constrains theories of planet migration: the semi-major axis must shrink by 1–2 orders of magnitude without damping the eccentricity and inclination.

Two formation scenarios have been proposed to explain the tight orbits of hot Jupiters. They could be formed in orbits with a small inclination (with respect to the stellar spin) via disk migration, or in more highly inclined orbits via high-eccentricity migration, where gravitational interactions with a companion and tidal dissipation are at play. Here we target hot Jupiter systems where the misalignment λ has been inferred observationally and we investigate whether their properties are consistent with high-eccentricity migration. Specifically, we study whether stellar tides can be responsible for the observed distribution of λ and orbital separations. Improving on previous studies, we use detailed models for each star, thus accounting for how convection (and tidal dissipation) depends on stellar properties. In line with observations suggesting that hotter stars have higher λ, we find that λ increases as the amount of stellar surface convection decreases. This trend supports the hypothesis that tides are the mechanism shaping the observed distribution of λ. Furthermore, we study the past orbital evolution of five representative systems, chosen to cover a variety of temperatures and misalignments. We consider various initial orbital configurations and integrate the equations describing the coupled evolution of the orbital separation, stellar spin, and misalignment. We account for stellar tides and wind mass loss, stellar evolution, and magnetic braking. We show that the current properties of these five representative systems can be explained naturally, given our current understanding of tidal dissipation and with physically motivated assumptions for the effects driving the orbital evolution.

Galaxy mergers play a key role in the evolution of galaxies and the growth of their central supermassive black holes (SMBHs). A search for (active) SMBH binaries (SMBHBs) at the centers of the merger remnants is currently ongoing. Perhaps the greatest challenge is to identify the inactive SMBHBs, which might be the most abundant, but are also the most difficult to identify. Liu et al. predicted characteristic drops in the light curves of tidal disruption events (TDEs), caused by the presence of a secondary SMBH. Here, we apply that model to the light curve of the optically inactive galaxy SDSS J120136.02+300305.5, which was identified as a candidate TDE with XMM-Newton. We show that the deep dips in its evolving X-ray light curve can be well explained by the presence of a SMBHB at its core. A SMBHB model with a mass of the primary of M_BH = 10⁷ M_☉, a mass ratio q ≃ 0.08, and a semi-major axis a_b ≃ 0.6 mpc is in good agreement with the observations. Given that primary mass, introducing an orbital eccentricity is needed, with e_b ≃ 0.3. Alternatively, a lower mass primary of M_BH = 10⁶ M_☉ in a circular orbit fits the light curve well. Tight binaries like this one, which have already overcome the "final parsec problem," are prime sources of gravitational wave radiation once the two SMBHs coalesce. Future transient surveys, which will detect TDEs in large numbers, will place tight constraints on the SMBHB fraction in otherwise non-active galaxies.

We present the most up to date X-ray luminosity function (XLF) and absorption function of active galactic nuclei (AGNs) over the redshift range from 0 to 5, utilizing the largest, highly complete sample ever available obtained from surveys performed with Swift/BAT, MAXI, ASCA, XMM-Newton, Chandra, and ROSAT. The combined sample, including that of the Subaru/XMM-Newton Deep Survey, consists of 4039 detections in the soft (0.5–2 keV) and/or hard (>2 keV) band. We utilize a maximum likelihood method to reproduce the count rate versus redshift distribution for each survey, by taking into account the evolution of the absorbed fraction, the contribution from Compton-thick (CTK) AGNs, and broadband spectra of AGNs, including reflection components from tori based on the luminosity- and redshift-dependent unified scheme. We find that the shape of the XLF at z ∼ 1–3 is significantly different from that in the local universe, for which the luminosity-dependent density evolution model gives much better description than the luminosity and density evolution model. These results establish the standard population synthesis model of the X-ray background (XRB), which well reproduces the source counts, the observed fractions of CTK AGNs, and the spectrum of the hard XRB. The number ratio of CTK AGNs to the absorbed Compton-thin (CTN) AGNs is constrained to be ≈0.5–1.6 to produce the 20–50 keV XRB intensity within present uncertainties, by assuming that they follow the same evolution as CTN AGNs. The growth history of supermassive black holes is discussed based on the new AGN bolometric luminosity function.

The fraction of star-forming to quiescent dwarf galaxies varies from almost infinity in the field to zero in the centers of rich galaxy clusters. What is causing this pronounced morphology–density relation? What do quiescent dwarf galaxies look like when studied in detail, and what conclusions can be drawn about their formation mechanism? Here we study a nearly magnitude-complete sample (−19 < M_r < −16 mag) of 121 Virgo cluster early types with deep near-infrared images from the SMAKCED project. We fit two-dimensional models with optional inner and outer components, as well as bar and lens components (in ∼15% of the galaxies), to the galaxy images. While a single Sérsic function may approximate the overall galaxy structure, it does not entirely capture the light distribution of two-thirds of our galaxies, for which multicomponent models provide a better fit. This fraction of complex galaxies shows a strong dependence on luminosity, being larger for brighter objects. We analyze the global and component-specific photometric scaling relations of early-type dwarf galaxies and discuss similarities with bright early and late types. The dwarfs' global galaxy parameters show scaling relations that are similar to those of bright disk galaxies. The inner components are mostly fitted with Sérsic n values close to 1. At a given magnitude, they are systematically larger than the bulges of spirals, suggesting that they are not ordinary bulges. We argue that the multicomponent structures in early-type dwarfs are mostly a phenomenon inherent to the disks and may indeed stem from environmental processing.

The Palomar Cosmic Web Imager (PCWI), an integral field spectrograph designed to detect and map low surface brightness emission, has obtained imaging spectroscopic maps of Lyα from the circum-QSO medium (CQM) of QSO HS1549+19 at redshift z = 2.843. Extensive extended emission is detected from the CQM, consistent with fluorescent and pumped Lyα produced by the ionizing and Lyα continuum of the QSO. Many features present in PCWI spectral images match those detected in narrow-band images. Filamentary structures with narrow line profiles are detected in several cases as long as 250–400 kpc. One of these is centered at a velocity redshifted with respect to the systemic velocity, and displays a spatially collimated and kinematically cold line profile increasing in velocity width approaching the QSO. This suggests that the filament gas is infalling onto the QSO, perhaps in a cold accretion flow. Because of the strong ionizing flux, the neutral column density is low, typically $N({\rm H}\,\scriptsize{I}) \sim 10^{12}\hbox{--} 10^{15}\, {\rm cm}^{ - 2}$, and the line center optical depth is also low (typically τ₀ < 10), insufficient to display well separated double peak emission characteristic of higher line optical depths. With a simple ionization and cloud model we can very roughly estimate the total gas mass (log M_gas = 12.5 ± 0.5) and the total (log M_tot = 13.3 ± 0.5). We can also calculate a kinematic mass from the total line profile (2 × 10¹³ M_☉), which agrees with the mass estimated from the gas emission. The intensity-binned spectrum of the CQM shows a progression in kinematic properties consistent with heirarchical structure formation.

The intergalactic medium (IGM) is the dominant reservoir of baryons, delineates the large-scale structure of the universe at low to moderate overdensities, and provides gas from which galaxies form and evolve. Simulations of a cold-dark-matter- (CDM-) dominated universe predict that the IGM is distributed in a cosmic web of filaments and that galaxies should form along and at the intersections of these filaments. While observations of QSO absorption lines and the large-scale distribution of galaxies have confirmed the CDM paradigm, the cosmic web of IGM has never been confirmed by direct imaging. Here we report our observation of the Lyα blob 2 (LAB2) in SSA22 with the Cosmic Web Imager (CWI). This is an integral field spectrograph optimized for low surface brightness, extended emission. With 22 hr of total on- and off-source exposure, CWI has revealed that LAB2 has extended Lyα emission that is organized into azimuthal zones consistent with filaments. We perform numerous tests with simulations and the data to secure the robustness of this result, which relies on data with modest signal-to-noise ratios. We have developed a smoothing algorithm that permits visualization of data cube slices along image or spectral image planes. With both raw and smoothed data cubes we demonstrate that the filaments are kinematically associated with LAB2 and display double-peaked profiles characteristic of optically thick Lyα emission. The flux is 10–20 times brighter than expected for the average emission from the IGM but is consistent with boosted fluorescence from a buried QSO or gravitation cooling radiation. Using simple emission models, we infer a baryon mass in the filaments of at least 1–4 × 10¹¹ M_☉, and the dark halo mass is at least 2 × 10¹² M_☉. The spatial-kinematic morphology is more consistent with inflow from the cosmic web than outflow from LAB2, although an outflow feature maybe present at one azimuth. LAB2 and the surrounding gas have significant and coaligned angular momentum, strengthening the case for their association.

We present the discovery of four surprisingly bright (H₁₆₀ ∼ 26–27 mag AB) galaxy candidates at z ∼ 9–10 in the complete HST CANDELS WFC3/IR GOODS-N imaging data, doubling the number of z ∼ 10 galaxy candidates that are known, just ∼500 Myr after the big bang. Two similarly bright sources are also detected in a reanalysis of the GOODS-S data set. Three of the four galaxies in GOODS-N are significantly detected at 4.5σ–6.2σ in the very deep Spitzer/IRAC 4.5 μm data, as is one of the GOODS-S candidates. Furthermore, the brightest of our candidates (at z = 10.2 ± 0.4) is robustly detected also at 3.6 μm (6.9σ), revealing a flat UV spectral energy distribution with a slope β = −2.0 ± 0.2, consistent with demonstrated trends with luminosity at high redshift. Thorough testing and use of grism data excludes known low-redshift contamination at high significance, including single emission-line sources, but as-yet unknown low redshift sources could provide an alternative solution given the surprising luminosity of these candidates. Finding such bright galaxies at z  ∼  9–10 suggests that the luminosity function for luminous galaxies might evolve in a complex way at z > 8. The cosmic star formation rate density still shows, however, an order-of-magnitude increase from z ∼ 10 to z ∼ 8 since the dominant contribution comes from low-luminosity sources. Based on the IRAC detections, we derive galaxy stellar masses at z ∼ 10, finding that these luminous objects are typically 10⁹ M_☉. This allows for a first estimate of the cosmic stellar mass density at z ∼ 10 resulting in $\log _{10}\rho _{*} = 4.7^{+0.5}_{-0.8}$ M_☉ Mpc⁻³ for galaxies brighter than M_UV ∼ −18. The remarkable brightness, and hence luminosity, of these z ∼ 9–10 candidates will enable deep spectroscopy to determine their redshift and nature, and highlights the opportunity for the James Webb Space Telescope to map the buildup of galaxies at redshifts much earlier than z ∼ 10.

We present the redshift evolutions and distributions of the gamma-ray luminosity and photon spectral index of flat spectrum radio quasar (FSRQ) type blazars, using non-parametric methods to obtain the evolutions and distributions directly from the data. The sample we use for analysis consists of almost all FSRQs observed with a greater than approximately 7σ detection threshold in the first-year catalog of the Fermi Gamma-ray Space Telescope's Large Area Telescope, with redshifts as determined from optical spectroscopy by Shaw et al. We find that FSQRs undergo rapid gamma-ray luminosity evolution, but negligible photon index evolution, with redshift. With these evolutions accounted for we determine the density evolution and luminosity function of FSRQs and calculate their total contribution to the extragalactic gamma-ray background radiation, resolved and unresolved, which is found to be 16(+10/−4)%, in agreement with previous studies.

We measure the average temperature decrement on the cosmic microwave background (CMB) produced by voids selected in the Sloan Digital Sky Survey Data Release 7 spectroscopic redshift galaxy catalog, spanning redshifts 0 < z < 0.44. We find an imprint amplitude between 2.6 and 2.9 μK as viewed through a compensated top-hat filter scaled to the radius of each void, we assess the statistical significance of the imprint at ∼2σ, and we make crucial use of N-body simulations to calibrate our analysis. As expected, we find that large voids produce cold spots on the CMB through the integrated Sachs–Wolfe (ISW) effect. However, we also find that small voids in the halo density field produce hot spots, because they reside in contracting, larger-scale overdense regions. This is an important effect to consider when stacking CMB imprints from voids of different radii. We have found that the same filter radius that gives the largest ISW signal in simulations also yields close to the largest detected signal in the observations. However, although it is low in significance, our measured signal has a much higher amplitude than expected from ISW in the concordance ΛCDM universe. The discrepancy is also at the ∼2σ level. We have demonstrated that our result is robust against the varying of thresholds over a wide range.

We present a quantitative model of Lyα emission throughout cosmic history and determine the prospects for intensity mapping spatial fluctuations in the Lyα signal. Since (1) our model assumes at z > 6 the minimum star formation required to sustain reionization and (2) is based at z < 6 on a luminosity function (LF) extrapolated from the few observed bright Lyα emitters, this should be considered a lower limit. Mapping the line emission allows probes of reionization, star formation, and large-scale structure (LSS) as a function of redshift. While Lyα emission during reionization has been studied, we also predict the postreionization signal to test predictions of the intensity and motivate future intensity mapping probes of reionization. We include emission from massive dark matter halos and the intergalactic medium (IGM) in our model. We find agreement with current, measured LFs of Lyα emitters at z < 8. However, diffuse IGM emission, not associated with Lyα emitters, dominates the intensity up to z ∼ 10. While our model is applicable for deep-optical or near-infrared observers like the James Webb Space Telescope, only intensity mapping will detect the diffuse IGM emission. We also construct a three-dimensional power spectrum model of the Lyα emission. Finally, we consider the prospects of an intensity mapper for measuring Lyα fluctuations while identifying interloper contamination for removal. Our results suggest that while the reionization signal is challenging, Lyα fluctuations can be an interesting new probe of LSS at late times when used in conjunction with other lines, e.g., Hα, to monitor low-redshift foreground confusion.

Nuclear reaction rates are among the most important input for understanding primordial nucleosynthesis and, therefore, for a quantitative description of the early universe. An up-to-date compilation of direct cross-sections of ²H(d, p)³H, ²H(d, n)³He, ⁷Li(p, α)⁴He, and ³He(d, p)⁴He reactions is given. These are among the most uncertain cross-sections used and input for big bang nucleosynthesis calculations. Their measurements through the Trojan Horse method are also reviewed and compared with direct data. The reaction rates and the corresponding recommended errors in this work were used as input for primordial nucleosynthesis calculations to evaluate their impact on the ²H, ^{3, 4}He, and ⁷Li primordial abundances, which are then compared with observations.

We determine the extinction law through Cep OB3b, a young cluster of 3000 stars undergoing gas dispersal. The extinction is measured toward 76 background K giants identified with MMT/Hectospec spectra. Color excess ratios were determined toward each of the giants using V and R photometry from the literature, g, r, i, and z photometry from the Sloan Digital Sky Survey and J, H, and K_s photometry from the Two Micron All Sky Survey. These color excess ratios were then used to construct the extinction law through the dusty material associated with Cep OB3b. The extinction law through Cep OB3b is intermediate between the R_V = 3.1 and R_V = 5 laws commonly used for the diffuse atomic interstellar medium and dense molecular clouds, respectively. The dependence of the extinction law on line-of-sight A_V is investigated and we find the extinction law becomes shallower for regions with A_V > 2.5 mag. We speculate that the intermediate dust law results from dust processing during the dispersal of the molecular cloud by the cluster

HH 212 is a nearby (400 pc) Class 0 protostellar system showing several components that can be compared with theoretical models of core collapse. We have mapped it in the 350 GHz continuum and HCO⁺J = 4–3 emission with ALMA at up to ∼04 resolution. A flattened envelope and a compact disk are seen in the continuum around the central source, as seen before. The HCO⁺ kinematics shows that the flattened envelope is infalling with small rotation (i.e., spiraling) into the central source, and thus can be identified as a pseudodisk in the models of magnetized core collapse. Also, the HCO⁺ kinematics shows that the disk is rotating and can be rotationally supported. In addition, to account for the missing HCO⁺ emission at low-redshifted velocity, an extended infalling envelope is required, with its material flowing roughly parallel to the jet axis toward the pseudodisk. This is expected if it is magnetized with an hourglass B-field morphology. We have modeled the continuum and HCO⁺ emission of the flattened envelope and disk simultaneously. We find that a jump in density is required across the interface between the pseudodisk and the disk. A jet is seen in HCO⁺ extending out to ∼500 AU away from the central source, with the peaks upstream of those seen before in SiO. The broad velocity range and high HCO⁺ abundance indicate that the HCO⁺ emission traces internal shocks in the jet.

RadioAstron space–ground very long baseline interferometry observations of the pulsar B0950+08, conducted with the 10 m Space Radio Telescope in conjunction with the Arecibo 300 m telescope and the Westerbork Synthesis Radio Telescope at a frequency of 324 MHz were analyzed in order to investigate plasma inhomogeneities in the direction of this nearby pulsar. The observations were conducted at a spacecraft distance of 330,000 km, resulting in a projected baseline of 220,000 km, providing the greatest angular resolution ever achieved at meter wavelengths. Our analysis is based on fundamental behavior of structure and coherence functions. We find that the pulsar shows scintillation on two frequency scales, both much less than the observing frequency, but modulation is less than 100%. We infer that the scattering is weak, but a refracting wedge disperses the scintillation pattern. The refraction angle of this "cosmic prism" is measured as θ₀ = 1.1–4.4 mas, with the refraction direction being approximately perpendicular to the observer velocity. We show that the observed parameters of scintillation effects indicate that two plasma layers lie along the line of sight to the pulsar, at distances of 4.4–16.4 pc and 26–170 pc, and traveling in different directions relative to the line of sight. Spectra of turbulence for the two layers are found to follow a power law with the indices γ₁ = γ₂ = 3.00 ± 0.08, significantly different from the index expected for a Kolmogorov spectrum of turbulence, γ = 11/3.

We explore the relationship between gas and dust in a massive star-forming region by comparing the physical properties derived from each. We compare the temperatures and column densities in a massive star-forming Infrared Dark Cloud (G32.02+0.05), which shows a range of evolutionary states, from quiescent to active. The gas properties were derived using radiative transfer modeling of the (1,1), (2,2), and (4,4) transitions of NH₃ on the Karl G. Jansky Very Large Array, while the dust temperatures and column densities were calculated using cirrus-subtracted, modified blackbody fits to Herschel data. We compare the derived column densities to calculate an NH₃ abundance, χ$_{{\rm NH}_{3}}$ = 4.6 × 10⁻⁸. In the coldest star-forming region, we find that the measured dust temperatures are lower than the measured gas temperatures (mean and standard deviations T_{dust, avg} ∼ 11.6 ± 0.2 K versus T_{gas, avg} ∼ 15.2 ± 1.5 K), which may indicate that the gas and dust are not well-coupled in the youngest regions (∼0.5 Myr) or that these observations probe a regime where the dust and/or gas temperature measurements are unreliable. Finally, we calculate millimeter fluxes based on the temperatures and column densities derived from NH₃, which suggest that millimeter dust continuum observations of massive star-forming regions, such as the Bolocam Galactic Plane Survey or ATLASGAL, can probe hot cores, cold cores, and the dense gas lanes from which they form, and are generally not dominated by the hottest core.

We present ages and masses for 601 star clusters in M31 from the analysis of the six filter integrated light measurements from near-ultraviolet to near-infrared wavelengths, made as part of the Panchromatic Hubble Andromeda Treasury (PHAT). We derive the ages and masses using a probabilistic technique, which accounts for the effects of stochastic sampling of the stellar initial mass function. Tests on synthetic data show that this method, in conjunction with the exquisite sensitivity of the PHAT observations and their broad wavelength baseline, provides robust age and mass recovery for clusters ranging from ∼10² to 2 × 10⁶ M_☉. We find that the cluster age distribution is consistent with being uniform over the past 100 Myr, which suggests a weak effect of cluster disruption within M31. The age distribution of older (>100 Myr) clusters falls toward old ages, consistent with a power-law decline of index −1, likely from a combination of fading and disruption of the clusters. We find that the mass distribution of the whole sample can be well described by a single power law with a spectral index of −1.9 ± 0.1 over the range of 10³–3 × 10⁵ M_☉. However, if we subdivide the sample by galactocentric radius, we find that the age distributions remain unchanged. However, the mass spectral index varies significantly, showing best-fit values between −2.2 and −1.8, with the shallower slope in the highest star formation intensity regions. We explore the robustness of our study to potential systematics and conclude that the cluster mass function may vary with respect to environment.

In this study, we conduct three-dimensional hydrodynamic simulations systematically to investigate the flow patterns behind the accretion shock waves that are commonly formed in the post-bounce phase of core-collapse supernovae. Adding small perturbations to spherically symmetric, steady, shocked accretion flows, we compute the subsequent evolutions to find what flow pattern emerges as a consequence of hydrodynamical instabilities such as convection and standing accretion shock instability for different neutrino luminosities and mass accretion rates. Depending on these two controlling parameters, various flow patterns are indeed realized. We classify them into three basic patterns and two intermediate ones; the former includes sloshing motion (SL), spiral motion (SP), and multiple buoyant bubble formation (BB); the latter consists of spiral motion with buoyant-bubble formation (SPB) and spiral motion with pulsationally changing rotational velocities (SPP). Although the post-shock flow is highly chaotic, there is a clear trend in the pattern realization. The sloshing and spiral motions tend to be dominant for high accretion rates and low neutrino luminosities, and multiple buoyant bubbles prevail for low accretion rates and high neutrino luminosities. It is interesting that the dominant pattern is not always identical between the semi-nonlinear and nonlinear phases near the critical luminosity; the intermediate cases are realized in the latter case. Running several simulations with different random perturbations, we confirm that the realization of flow pattern is robust in most cases.

We study the temporal and energy spectral properties of the unique neutron star low-mass X-ray binary XTE J1701-462. Assuming the horizontal branch/normal branch (HB/NB) vertex as a reference position of the accretion rate, the horizontal branch oscillation (HBO) of the HB/NB vertex is roughly 50 Hz. It indicates that the HBO is independent of the accretion rate or the source intensity. The spectral analysis shows $R_{\rm {in}}\propto \dot{M}_{\rm {Disk}}^{2.9\pm 0.09}$ in the HB/NB vertex and $R_{\rm {in}}\propto \dot{M}_{\rm {Disk}}^{1.7\pm 0.06}$ in the NB/flaring branch (FB) vertex, which implies that different accretion rates may be produced in the HB/NB and NB/FB vertex. The Comptonization component could be fitted by a constrained broken power law or nthComp. Unlike GX 17+2, the frequencies of HBO positively correlate with the inner disk radius, which contradict with the prediction of the Lense–Thirring precession model. XTE J1701-462, both in the Cyg-like phase and in the Sco-like phase, follows a positive correlation between the break frequency of broadband noise and the characteristic frequency of HBO, which is called the W–K relation. An anticorrelation between the frequency of HBO and photon energy is observed. Moreover, the rms of HBO increases with photon energy until ∼10 keV. We discuss the possible origin of HBO from the corona in XTE J1701-462.

Recent observational and theoretical studies of classical Be stars have established the utility of polarization color diagrams (PCDs) in helping to constrain the time-dependent mass decretion rates of these systems. We expand on our pilot observational study of this phenomenon, and report the detailed analysis of a long-term (1989–2004) spectropolarimetric survey of nine additional classical Be stars, including systems exhibiting evidence of partial disk-loss/disk-growth episodes as well as systems exhibiting long-term stable disks. After carefully characterizing and removing the interstellar polarization along the line of sight to each of these targets, we analyze their intrinsic polarization behavior. We find that many steady-state Be disks pause at the top of the PCD, as predicted by theory. We also observe sharp declines in the Balmer jump polarization for later spectral type, near edge-on steady-state disks, again as recently predicted by theory, likely caused when the base density of the disk is very high, and the outer region of the edge-on disk starts to self absorb a significant number of Balmer jump photons. The intrinsic V-band polarization and polarization position angle of γ Cas exhibits variations that seem to phase with the orbital period of a known one-armed density structure in this disk, similar to the theoretical predictions of Halonen & Jones. We also observe stochastic jumps in the intrinsic polarization across the Balmer jump of several known Be+sdO systems, and speculate that the thermal inflation of part of the outer region of these disks could be responsible for producing this observational phenomenon. Finally, we estimate the base densities of this sample of stars to be between ≈8 × 10⁻¹¹ and ≈4 × 10⁻¹² g cm⁻³ during quasi steady state periods given there maximum observed polarization.

The center of our Galaxy hosts almost two hundred very young stars, a subset of which is orbiting the central supermassive black hole (SMBH) in a relatively thin disk-like structure. First analyses indicated a power-law surface density profile of the disk, Σ∝R^β with β = −2. Recently, however, doubts about this profile arose. In particular, it now seems to be better described by a sort of broken power law. By means of both analytical arguments and numerical N-body modeling, we show that such a broken power-law profile is a natural consequence of the two-body relaxation of the disk. Due to the small relative velocities of the nearby stars in co-planar Keplerian orbits around the SMBH, two-body relaxation is effective enough to affect the evolution of the disk on timescales comparable to its estimated age. In the inner, densest part of the disk, the profile becomes rather flat (β ≈ −1) while the outer parts keep imprints of the initial state. Our numerical models show that the observed projected surface density profile of the young stellar disk can result from two-body relaxation driven evolution of a disk with initial single power-law profile with −2 ≲ β ≲ −1.5. In addition, we suggest that two-body relaxation may have caused a significant radial migration of the S-stars toward the central SMBH, thus playing an important role in their formation scenario.

Three magnetic cloud events, in which solar impulsive electron events occurred in their outer region, are employed to investigate the difference of path lengths L_0eIII traveled by non-relativistic electrons from their release site near the Sun to the observer at 1 AU, where L_0eIII = v_l × (t_l − t_III), v_l and t_l being the velocity and arrival time of electrons in the lowest energy channel (∼27 keV) of the Wind/3DP/SST sensor, respectively, and t_III being the onset time of type III radio bursts. The deduced L_0eIII value ranges from 1.3 to 3.3 AU. Since a negligible interplanetary scattering level can be seen in both L_0eIII > 3 AU and ∼1.2 AU events, the difference in L_0eIII could be linked to the turbulence geometry (slab or two-dimensional) in the solar wind. By using the Wind/MFI magnetic field data with a time resolution of 92 ms, we examine the turbulence geometry in the dissipation range. In our examination, ∼6 minutes of sampled subintervals are used in order to improve time resolution. We have found that, in the transverse turbulence, the observed slab fraction is increased with an increasing L_0eIII value, reaching ∼100% in the L_0eIII > 3 AU event. Our observation implies that when only the slab spectral component exists, magnetic flux tubes (magnetic surfaces) are closed and regular for a very long distance along the transport route of particles.

Transverse, near-circularly polarized, parallel-propagating electromagnetic waves around the proton cyclotron frequency were found sporadically in the solar wind throughout the inner heliosphere. They could play an important role in heating and accelerating the solar wind. These low-frequency waves (LFWs) are intermittent but often occur in prolonged bursts lasting over 10 minutes, named "LFW storms." Through a comprehensive survey of them from Solar Terrestrial Relations Observatory A using dynamic spectral wave analysis, we have identified 241 LFW storms in 2008, present 0.9% of the time. They are left-hand (LH) or right-hand (RH) polarized in the spacecraft frame with similar characteristics, probably due to Doppler shift of the same type of waves or waves of intrinsically different polarities. In rare cases, the opposite polarities are observed closely in time or even simultaneously. Having ruled out interplanetary coronal mass ejections, shocks, energetic particles, comets, planets, and interstellar ions as LFW sources, we discuss the remaining generation scenarios: LH ion cyclotron instability driven by greater perpendicular temperature than parallel temperature or by ring-beam distribution, and RH ion fire hose instability driven by inverse temperature anisotropy or by cool ion beams. The investigation of solar wind conditions is compromised by the bias of the one-dimensional Maxwellian fit used for plasma data calibration. However, the LFW storms are preferentially detected in rarefaction regions following fast winds and when the magnetic field is radial. This preference may be related to the ion cyclotron anisotropy instability in fast wind and the minimum in damping along the radial field.

We present a straightforward model of cosmic-ray propagation in the Galaxy that can account for the observed cosmic-ray positrons entirely as secondary products of cosmic-ray interactions with the interstellar medium. In addition to accounting for the observed energy dependence of the ratio of positrons to total electrons, this model can accommodate both the observed energy dependence of secondary to primary nuclei, like boron/carbon, and the observed bounds on the anisotropy of cosmic rays. This model also predicts the energy dependence of the positron fraction at energies higher than those measured to date, with the ratio rising to ∼0.7 at very high energies. The model presented in this paper arises as a natural extension of the widely used current models and allows one to include the spatial and temporal discreteness of the sources of cosmic rays.

We compare galaxy clusters selected in Chandra and XMM-Newton X-ray observations of the 4 deg² Deep Lens Survey (DLS) F2 field to the cluster samples previously selected in the same field from a sensitive weak-lensing shear map derived from the DLS and from a detailed galaxy redshift survey—the Smithsonian Hectospec Lensing Survey (SHELS). Our Chandra and XMM-Newton observations cover 1.6 deg² of the DLS F2 field, including all 12 weak-lensing peaks above a signal-to-noise ratio of 3.5, along with 16 of the 20 SHELS clusters with published velocity dispersions >500 km s⁻¹. We detect 26 extended X-ray sources in this area and confirm 23 of them as galaxy clusters using the optical imaging. Approximately 75% of clusters detected in either X-ray or spectroscopic surveys are found in both; these follow the previously established scaling relations between velocity dispersion, L_X, and T_X. A lower percentage, 60%, of clusters are in common between X-ray and DLS samples. With the exception of a high false-positive rate in the DLS weak-lensing search (5 out of 12 DLS candidates appear to be false), differences between the three cluster detection methods can be attributed primarily to observational uncertainties and intrinsic scatter between different observables and cluster mass.

We present spectral analysis of two Suzaku observations of the Seyfert 2 galaxy, NGC 2110. This source has been known to show complex, variable absorption which we study in depth by analyzing these two observations set 7 yr apart and by comparing them to previously analyzed observations with the XMM-Newton and Chandra observatories. We find that there is a relatively stable, full-covering absorber with a column density of ∼3× 10²² cm⁻², with an additional patchy absorber that is likely variable in both column density and covering fraction over timescales of years, consistent with clouds in a patchy torus or in the broad line region. We model a soft emission line complex, likely arising from ionized plasma and consistent with previous studies. We find no evidence for reflection from an accretion disk in this source with contribution from neither relativistically broadened Fe Kα line emission, nor from a Compton reflection hump.

The symbiotic X-ray binary (SyXB) 4U 1954+319 is a rare system hosting a peculiar neutron star (NS) and an M-type optical companion. Its ∼5.4 hr NS spin period is the longest among all known accretion-powered pulsars and exhibited large (∼7%) fluctuations over 8 yr. A spin trend transition was detected with Swift/BAT around an X-ray brightening in 2012. The source was in quiescent and bright states before and after this outburst based on 60 ks Suzaku observations in 2011 and 2012. The observed continuum is well described by a Comptonized model with the addition of a narrow 6.4 keV Fe–Kα line during the outburst. Spectral similarities to slowly rotating pulsars in high-mass X-ray binaries, its high pulsed fraction (∼60%–80%), and the location in the Corbet diagram favor high B-field (≳ 10¹² G) over a weak field as in low-mass X-ray binaries. The observed low X-ray luminosity (10³³–10³⁵ erg s⁻¹), probable wide orbit, and a slow stellar wind of this SyXB make quasi-spherical accretion in the subsonic settling regime a plausible model. Assuming a ∼10¹³ G NS, this scheme can explain the ∼5.4 hr equilibrium rotation without employing the magnetar-like field (∼10¹⁶ G) required in the disk accretion case. The timescales of multiple irregular flares (∼50 s) can also be attributed to the free-fall time from the Alfvén shell for a ∼10¹³ G field. A physical interpretation of SyXBs beyond the canonical binary classifications is discussed.

There is a remarkable correlation between the spin periods of the accreting neutron stars (NSs) in Be/X-ray binaries (BeXBs) and their orbital periods. Recently, Knigge et al. showed that the distribution of the spin periods contains two distinct subpopulations peaked at ∼10 s and ∼200 s, respectively, and suggested that they may be related to two types of supernovae for the formation of the NSs, i.e., core-collapse and electron-capture supernovae. Here we propose that the bimodal spin period distribution is likely to be ascribed to different accretion modes of the NSs in BeXBs. When the NS tends to capture material from the warped, outer part of the Be star disk and experiences giant outbursts, a radiatively cooling dominated disk is formed around the NS, which spins up the NS and is responsible for the short-period subpopulation. In BeXBs that are dominated by normal outbursts or are persistent, the accretion flow is advection-dominated or quasi-spherical. The spin-up process is accordingly inefficient, leading to longer periods of the neuron stars. The potential relation between the subpopulations and the supernova mechanism is also discussed.

Blazars, active galactic nuclei with a jet pointing toward the Earth, represent the most abundant class of high-energy extragalactic γ-ray sources. The subset of blazars known as BL Lac objects is on average closer to Earth (i.e., younger) and characterized by harder spectra at high energy than the whole sample. The fraction of BL Lacs that is too dim to be detected and resolved by current γ-ray telescopes is therefore expected to contribute to the high-energy isotropic diffuse γ-ray background (IGRB). The IGRB has been recently measured over a wide energy range by the Large Area Telescope (LAT) on board the Gamma-ray Space Telescope (Fermi). We present a new prediction of the diffuse γ-ray flux due to the unresolved BL Lac blazar population. The model is built upon the spectral energy distribution and the luminosity function derived from the fraction of BL Lacs detected (and spectrally characterized) in the γ-ray energy range. We focus our attention on the ${\cal O}(100)$ GeV energy range, predicting the emission up to the TeV scale and taking into account the absorption on the extragalactic background light. In order to better shape the BL Lac spectral energy distribution, we combine the Fermi-LAT data with Imaging Atmospheric Cerenkov Telescope measurements of the most energetic sources. Our analysis is carried on separately for low- and intermediate-synchrotron-peaked BL Lacs on the one hand and high-synchrotron-peaked BL Lacs on the other hand: we find in fact statistically different features for the two. The diffuse emission from the sum of both BL Lac classes increases from about 10% of the measured IGRB at 100 MeV to ∼100% of the data level at 100 GeV. At energies greater than 100 GeV, our predictions naturally explain the IGRB data, accommodating their softening with increasing energy. Uncertainties are estimated to be within of a factor of two of the best-fit flux up to 500 GeV.

We present a survey of optically emitting supernova remnants (SNRs) in M31 based on Hα and [S ii] images in the Local Group Survey. Using these images, we select objects that have [S ii]:Hα > 0.4 and circular shapes. We identify 156 SNR candidates, of which 76 are newly found objects. We classify these SNR candidates according to two criteria: the SNR progenitor type (Type Ia and core-collapse (CC) SNRs) and the morphological type. Type Ia and CC SNR candidates make up 23% and 77%, respectively, of the total sample. Most of the CC SNR candidates are concentrated in the spiral arms, while the Type Ia SNR candidates are rather distributed over the entire galaxy, including the inner region. The CC SNR candidates are brighter in Hα and [S ii] than the Type Ia SNR candidates. We derive a cumulative size distribution of the SNR candidates, finding that the distribution of the candidates with 17 <D < 50 pc is fitted well by a power law with the power-law index α = 2.53 ± 0.04. This indicates that most of the SNR candidates identified in this study appear to be in the Sedov–Taylor phase. The [S ii]:Hα distribution of the SNR candidates is bimodal, with peaks at [S ii]:Hα ∼ 0.4 and ∼0.9. The properties of these SNR candidates vary little with the galactocentric distance. The Hα and [S ii] surface brightnesses show a good correlation with the X-ray luminosity of the SNR candidates that are center-bright.

We fit the Kepler photometric light curve of the KOI-368 system using an oblate, gravity-darkened stellar model in order to constrain its spin–orbit alignment. We find that the system is relatively well-aligned with a sky-projected spin–orbit alignment of λ  =  10° ± 2°, a stellar obliquity of ψ  =  3° ± 7°, and a true spin–orbit alignment of φ  =  11° ± 3°. Although our measurement differs significantly from zero, the low value for φ is consistent with spin–orbit alignment. We also measure various transit parameters of the KOI-368 system: R_KOI-368 = 2.28  ±  0.02 R_☉, R_p = 1.83 ± 0.02 R_jup, and i = 89221 ± 0013. This work shows that our gravity-darkened model can constrain long-period, well-aligned planets and M-class stars orbiting fast-rotators, allowing for measurement of a new subcategory of transiting bodies.

To date, more than 750 planets have been discovered orbiting stars other than the Sun. Two sub-classes of these exoplanets, "hot Jupiters" and their less massive counterparts "hot Neptunes," provide a unique opportunity to study the extended atmospheres of planets outside of our solar system. We describe here the first far-ultraviolet transit study of a hot Neptune, specifically GJ 436b, for which we use Hubble Space Telescope/Space Telescope Imaging Spectrograph Lyα spectra to measure stellar flux as a function of time, observing variations due to absorption from the planetary atmosphere during transit. This analysis permits us to derive information about atmospheric extent, mass-loss rate from the planet, and interactions between the star and planet. We observe an evolution of the Lyα lightcurve with a transit depth of GJ 436b from 8.8% ± 4.5% near mid-transit, to 22.9% ± 3.9% ∼2 hr after the nominal geometric egress of the planet. Using data from the time-tag mode and considering astrophysical noise from stellar variability, we calculate a post-egress occultation of 23.7% ± 4.5%, demonstrating that the signature is statistically significant and of greater amplitude than can be attributed to stellar fluctuations alone. The extended egress absorption indicates the probable existence of a comet-like tail trailing the exoplanet. We calculate a mass-loss rate for GJ 436b in the range of 3.7 × 10⁶–1.1 × 10⁹ g s⁻¹, corresponding to an atmospheric lifetime of 4 × 10¹¹–2 × 10¹⁴ yr.

Terahertz absorption spectroscopy was employed to detect the ground-state inversion transitions of the hydronium ion (H₃O⁺). The highly excited ions were created with an extended negative glow discharge through a gas mixture of 1 mtorr of H₂O, 2 mtorr of H₂, and 12 mtorr of Ar, which allowed observation of transitions with J and K up to 12. In total, 47 transitions were measured in the 0.9–2.0 THz region and 22 of these were observed for the first time. The experimental uncertainties range from 100 to 300 kHz, which are much better than the range 0.3–1.2 MHz reported in previous work. Differences of up to 25.6 MHz were found between the observed positions and the catalog values that have been used for Herschel data analysis of observations of Sagittarius B2(N), NGC 4418, and Arp 220. The new and improved measurements were fit to experimental accuracies with an updated Hamiltonian, and better H₃O⁺ predictions are reported to support the proper analysis of astronomical observations by high-resolution spectroscopy telescopes, such as Herschel, SOFIA, and ALMA.

We present Hubble Space Telescope (HST) and ground-based optical and near-infrared observations of SN 2005hk and SN 2008A, typical members of the Type Iax class of supernovae (SNe). Here we focus on late-time observations, where these objects deviate most dramatically from all other SN types. Instead of the dominant nebular emission lines that are observed in other SNe at late phases, spectra of SNe 2005hk and 2008A show lines of Fe ii, Ca ii, and Fe i more than a year past maximum light, along with narrow [Fe ii] and [Ca ii] emission. We use spectral features to constrain the temperature and density of the ejecta, and find high densities at late times, with n_e ≳ 10⁹ cm⁻³. Such high densities should yield enhanced cooling of the ejecta, making these objects good candidates to observe the expected "infrared catastrophe," a generic feature of SN Ia models. However, our HST photometry of SN 2008A does not match the predictions of an infrared catastrophe. Moreover, our HST observations rule out a "complete deflagration" that fully disrupts the white dwarf for these peculiar SNe, showing no evidence for unburned material at late times. Deflagration explosion models that leave behind a bound remnant can match some of the observed properties of SNe Iax, but no published model is consistent with all of our observations of SNe 2005hk and 2008A.

We present an integrated thermal–chemical model for the atmosphere of the inner region of a protoplanetary disk that includes irradiation by both far-ultraviolet (FUV) and X-ray radiation. We focus on how the photodissociation of H₂O and OH affects the abundances of these and related species and how it contributes to the heating of the atmosphere. The dust in the atmosphere plays several important roles, primarily as the site of H₂ formation and by absorbing the FUV. Large amounts of water can be synthesized within the inner 4 AU of a disk around a typical classical T Tauri star. OH is found primarily at the top of a warm region where the gas temperature is T_g ≈ 650–1000 K and H₂O is found below it, where the temperature is lower, T_g ≈ 250–650 K. The amounts of H₂O and OH and the temperatures of the regions in which they formed are in agreement with recent Spitzer measurements and support the notion of the in situ production of water in the inner regions of protoplanetary disks. We find that the synthesized water is effective in shielding the disk mid-plane from stellar FUV radiation.

The nature of the mechanisms apparently driving X-rays from intermediate mass stars lacking strong convection zones or massive winds remains poorly understood, and the possible role of hidden, lower mass close companions is still unclear. A 20 ks Chandra HRC-I observation of HR 4796A, an 8 Myr old main sequence A0 star devoid of close stellar companions, has been used to search for a signature or remnant of magnetic activity from the Herbig Ae phase. X-rays were not detected and the X-ray luminosity upper limit was L_X ⩽ 1.3 × 10²⁷ erg s⁻¹. The result is discussed in the context of various scenarios for generating magnetic activity, including rotational shear and subsurface convection. A dynamo driven by natal differential rotation is unlikely to produce observable X rays, chiefly because of the difficulty in getting the dissipated energy up to the surface of the star. A subsurface convection layer produced by the ionization of helium could host a dynamo that should be effective throughout the main sequence but can only produce X-ray luminosities of the order 10²⁵ erg s⁻¹. This luminosity lies only moderately below the current detection limit for Vega. Our study supports the idea that X-ray production in Herbig Ae/Be stars is linked largely to the accretion process rather than the properties of the underlying star, and that early A stars generally decline in X-ray luminosity at least 100,000 fold in only a few million years.

We present the first results of sunspot oscillations from observations by the Interface Region Imaging Spectrograph. The strongly nonlinear oscillation is identified in both the slit-jaw images and the spectra of several emission lines formed in the transition region and chromosphere. We first apply a single Gaussian fit to the profiles of the Mg ii 2796.35 Å, C ii 1335.71 Å, and Si iv 1393.76 Å lines in the sunspot. The intensity change is ∼30%. The Doppler shift oscillation reveals a sawtooth pattern with an amplitude of ∼10 km s⁻¹ in Si iv. The Si iv oscillation lags those of C ii and Mg ii by ∼6 and ∼25 s, respectively. The line width suddenly increases as the Doppler shift changes from redshift to blueshift. However, we demonstrate that this increase is caused by the superposition of two emission components. We then perform detailed analysis of the line profiles at a few selected locations on the slit. The temporal evolution of the line core is dominated by the following behavior: a rapid excursion to the blue side, accompanied by an intensity increase, followed by a linear decrease of the velocity to the red side. The maximum intensity slightly lags the maximum blueshift in Si iv, whereas the intensity enhancement slightly precedes the maximum blueshift in Mg ii. We find a positive correlation between the maximum velocity and deceleration, a result that is consistent with numerical simulations of upward propagating magnetoacoustic shock waves.

The idea that solar system materials were irradiated by solar cosmic rays from the early Sun has long been suggested, but is still questionable. In this study, Sr, Ba, Ce, Nd, Sm, and Gd isotopic compositions of sequential acid leachates from the Kapoeta meteorite (howardite) were determined to find systematic and correlated variations in their isotopic abundances of proton-rich nuclei, leading to an understanding of the irradiation condition by cosmic rays. Significantly large excesses of proton-rich isotopes (p-isotopes), ⁸⁴Sr, ¹³⁰Ba, ¹³²Ba, ¹³⁶Ce, ¹³⁸Ce, and ¹⁴⁴Sm, were observed, particularly in the first chemical separate, which possibly leached out of the very shallow layer within a few μm from the surface of regolith grains in the sample. The results reveal the production of p-isotopes through the interaction of solar cosmic rays with the superficial region of the regolith grains before the formation of the Kapoeta meteorite parent body, suggesting strong activity in the early Sun.

We propose that the reported dearth of Kepler objects of interest (KOIs) with orbital periods P_orb ≲ 2–3 days around stars with rotation periods P_rot ≲ 5–10 days can be attributed to tidal ingestion of close-in planets by their host stars. We show that the planet distribution in this region of the log P_orb–log P_rot plane is qualitatively reproduced with a model that incorporates tidal interaction and magnetic braking as well as the dependence on the stellar core–envelope coupling timescale. We demonstrate the consistency of this scenario with the inferred break in the P_orb distribution of close-in KOIs and point out a potentially testable prediction of this interpretation.

Despite their importance as stellar nurseries and the building blocks of galaxies, very little is known about the formation of the highest mass clusters. The dense clump G0.253+0.016 represents an example of a clump that may form an Arches-like, high-mass cluster. Here we present molecular line maps toward G0.253+0.016 taken as part of the MALT90 molecular line survey, complemented with APEX observations. Combined, these data reveal the global physical properties and kinematics of G0.253+0.016. Recent Herschel data show that while the dust temperature is low (∼19 K) toward its center, the dust temperature on the exterior is higher (∼27 K) due to external heating. Our new molecular line data reveal that, overall, the morphology of dense gas detected toward G0.253+0.016 matches its IR extinction and dust continuum emission very well. An anticorrelation between the dust and gas column densities toward its center indicates that the clump is centrally condensed with a cold, dense interior in which the molecular gas is chemically depleted. The velocity field shows a strong gradient along the clump's major axis, with the blueshifted side at a higher Galactic longitude. The optically thick gas tracers are systematically redshifted with respect to the optically thin and hot gas tracers, indicating radial motions. The gas kinematics and line ratios support the recently proposed scenario in which G0.253+0.016 results from a tidal compression during a recent pericenter passage near Sgr A*. Because G0.253+0.016 represents an excellent example of a clump that may form a high-mass cluster, its detailed study should reveal a wealth of knowledge about the early stages of cluster formation.

The hard X-ray continuum and gamma-ray lines from a Type Ia supernova dominate its integrated photon emissions and can provide unique diagnostics of the mass of the ejecta, the ⁵⁶Ni yield and spatial distribution, its kinetic energy and expansion speed, and the mechanism of explosion. Such signatures and their time behavior "X-ray" the bulk debris field in direct fashion, and do not depend on the ofttimes problematic and elaborate UV, optical, and near-infrared spectroscopy and radiative transfer that have informed the study of these events for decades. However, to date no hard photons have ever been detected from a Type Ia supernova in explosion. With the advent of the supernova SN 2014J in M82, at a distance of ∼3.5 Mpc, this situation may soon change. Both NuSTAR and INTEGRAL have the potential to detect SN 2014J, and, if spectra and light curves can be measured, would usefully constrain the various explosion models published during the last ∼30 yr. In support of these observational campaigns, we provide predictions for the hard X-ray continuum and gamma-line emissions for 15 Type Ia explosion models gleaned from the literature. The model set, containing as it does deflagration, delayed detonation, merger detonation, pulsational delayed detonation, and sub-Chandrasekhar helium detonation models, collectively spans a wide range of properties, and hence signatures. We provide a brief discussion of various diagnostics (with examples), but importantly make the spectral and line results available electronically to aid in the interpretation of the anticipated data.

We study the impact of primordial magnetic fields on the H i absorption from the epoch of reionization. The presence of these fields results in two distinct effects: (1) the heating of the halos from the decay of the magnetic fields owing to ambipolar diffusion, and (2) an increase in the number of halos owing to additional matter fluctuations induced by magnetic fields. We analyze both of these effects and show that the latter is potentially observable because the number of halos along of line of sight can increase by many orders of magnitude. While this effect is not strongly dependent on the magnetic field strength in the range 0.3–0.6 nG, it is extremely sensitive to the magnetic field power spectral index for the near scale-free models. Therefore, the detection of such absorption features could be a sensitive probe of the primordial magnetic field and its power spectrum. We discuss the detectability of these features with the ongoing and future radio interferometers. In particular, we show that LOFAR might be able to detect these absorption features at z ≃ 10 in less than 10 hr of integration if the flux of the background source is 400 mJy.

We study the γ-ray variability of 13 blazars observed with the Fermi/Large Area Telescope (LAT). These blazars have the most complete light curves collected during the first four years of the Fermi sky survey. We model them with the Ornstein–Uhlenbeck (OU) process or a mixture of the OU processes. The OU process has power spectral density (PSD) proportional to 1/f^α with α changing at a characteristic timescale, τ₀, from 0 (τ ≫ τ₀) to 2 (τ ≪ τ₀). The PSD of the mixed OU process has two characteristic timescales and an additional intermediate region with 0 < α < 2. We show that the OU model provides a good description of the Fermi/LAT light curves of three blazars in our sample. For the first time, we constrain a characteristic γ-ray timescale of variability in two BL Lac sources, 3C 66A and PKS 2155-304 (τ₀ ≃ 25 days and τ₀ ≃ 43 days, respectively, in the observer's frame), which are longer than the soft X-ray timescales detected in blazars and Seyfert galaxies. We find that the mixed OU process approximates the light curves of the remaining 10 blazars better than the OU process. We derive limits on their long and short characteristic timescales, and infer that their Fermi/LAT PSD resemble power-law functions. We constrain the PSD slopes for all but one source in the sample. We find hints for sub-hour Fermi/LAT variability in four flat spectrum radio quasars. We discuss the implications of our results for theoretical models of blazar variability.

We report the discovery of a dwarf galaxy in the Leo Triplet. Analysis of the neutral hydrogen distribution shows that it rotates independently of the tidal tail of NGC 3628, with a radial velocity gradient of 35–40 km s⁻¹ over approximately 13 kpc. The galaxy has an extremely high neutral gas content, accounting for a large amount of its total dynamic mass and suggesting a low amount of dark matter. It is located at the tip of the gaseous tail, which strongly suggests a tidal origin. If this is the case, it would be one of the most confident and nearest (to the Milky Way) detections of a tidal dwarf galaxy and, at the same time, the object most detached from its parent galaxy (≈140  kpc) of this type.

We present a detailed investigation of the γ-ray emission in the vicinity of the supernova remnant (SNR) W28 (G6.4−0.1) observed by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. We detected significant γ-ray emission spatially coincident with TeV sources HESS J1800−240A, B, and C, located outside the radio boundary of the SNR. Their spectra in the 2–100 GeV band are consistent with the extrapolation of the power-law spectra of the TeV sources. We also identified a new source of GeV emission, dubbed Source W, which lies outside the boundary of TeV sources and coincides with radio emission from the western part of W28. All of the GeV γ-ray sources overlap with molecular clouds in the velocity range from 0 to 20 km s⁻¹. Under the assumption that the γ-ray emission toward HESS J1800−240A, B, and C comes from π⁰ decay due to the interaction between the molecular clouds and cosmic rays (CRs) escaping from W28, they can be naturally explained by a single model in which the CR diffusion coefficient is smaller than the theoretical expectation in the interstellar space. The total energy of the CRs escaping from W28 is constrained through the same modeling to be larger than ∼2 × 10⁴⁹ erg. The emission from Source W can also be explained with the same CR escape scenario.

Broadband power density spectra offer a window to understanding turbulent behavior in the emission mechanism and, at the highest frequencies, in the putative inner engines powering long gamma-ray bursts (GRBs). We describe a chirp search method alongside Fourier analysis for signal detection in the Poisson noise-dominated, 2 kHz sampled, BeppoSAX light curves. An efficient numerical implementation is described in O(Nnlog n) operations, where N is the number of chirp templates and n is the length of the light-curve time series, suited for embarrassingly parallel processing. For the detection of individual chirps over a 1 s duration, the method is one order of magnitude more sensitive in signal-to-noise ratio than Fourier analysis. The Fourier–chirp spectra of GRB 010408 and GRB 970816 show a continuation of the spectral slope with up to 1 kHz of turbulence identified in low-frequency Fourier analysis. The same continuation is observed in an average spectrum of 42 bright, long GRBs. An outlook on a similar analysis of upcoming gravitational wave data is included.

We present the first detailed study of the RR Lyrae variable population in the Local Group dSph/dIrr transition galaxy, Phoenix, using previously obtained HST/WFPC2 observations of the galaxy. We utilize template light curve fitting routines to obtain best fit light curves for RR Lyrae variables in Phoenix. Our technique has identified 78 highly probable RR Lyrae stars (54 ab-type; 24 c-type) with about 40 additional candidates. We find mean periods for the two populations of 〈P_ab〉 = 0.60 ± 0.03 days and 〈P_c〉 = 0.353 ± 0.002 days. We use the properties of these light curves to extract, among other things, a metallicity distribution function for ab-type RR Lyrae. Our analysis yields a mean metallicity of 〈[Fe/H]〉 = −1.68 ± 0.06 dex for the RRab stars. From the mean period and metallicity calculated from the ab-type RR Lyrae, we conclude that Phoenix is more likely of intermediate Oosterhoff type; however the morphology of the Bailey diagram for Phoenix RR Lyraes appears similar to that of an Oosterhoff type I system. Using the RRab stars, we also study the chemical enrichment law for Phoenix. We find that our metallicity distribution is reasonably well fitted by a closed-box model. The parameters of this model are compatible with the findings of Hidalgo et al., further supporting the idea that Phoenix appears to have been chemically enriched as a closed-box-like system during the early stage of its formation and evolution.

We report on Spitzer Space Telescope Infrared Array Camera observations of near-Earth object 2009 BD that were carried out in support of the NASA Asteroid Robotic Retrieval Mission concept. We did not detect 2009 BD in 25 hr of integration at 4.5 μm. Based on an upper-limit flux density determination from our data, we present a probabilistic derivation of the physical properties of this object. The analysis is based on the combination of a thermophysical model with an orbital model accounting for the non-gravitational forces acting upon the body. We find two physically possible solutions. The first solution shows 2009 BD as a 2.9 ± 0.3 m diameter rocky body (ρ = 2.9 ± 0.5 g cm⁻³) with an extremely high albedo of $0.85_{-0.10}^{+0.20}$ that is covered with regolith-like material, causing it to exhibit a low thermal inertia ($\Gamma =30_{-10}^{+20}$ SI units). The second solution suggests 2009 BD to be a 4 ± 1 m diameter asteroid with $p_V=0.45_{-0.15}^{+0.35}$ that consists of a collection of individual bare rock slabs (Γ = 2000  ±  1000 SI units, $\rho = 1.7_{-0.4}^{+0.7}$ g cm⁻³). We are unable to rule out either solution based on physical reasoning. 2009 BD is the smallest asteroid for which physical properties have been constrained, in this case using an indirect method and based on a detection limit, providing unique information on the physical properties of objects in the size range smaller than 10 m.

In this study, three methods of analysis are compared to test the Walén relation. Method 1 requires a good de Hoffmann–Teller (HT) frame. Method 2 uses three components separately to find the frame that is slightly modified from Method 1. This method is intended to improve the accuracy of the HT frame and able to demonstrate the anisotropic property of the fluctuations. The better the relation is, the closer the slope of a regression fitting the data of plasma versus Alfvén velocities is to 1. However, this criterion is based on an average HT frame, and the fitted slope does not always work for the Walén test because the HT frame can change so fast in the high-speed streams. We propose Method 3 to check the Walén relation using a sequence of data generated by taking the difference of two consecutive values of plasma and Alfvén velocities, respectively. The difference data are independent of the HT frame. We suggest that the ratio of the variances between plasma and Alfvén velocities is a better parameter to qualify the Walén relation. Four cases in two solar wind streams are studied using these three methods. Our results show that when the solar wind HT frame remains stable, all three methods can predict Alfvénic fluctuations well, but Method 3 can better predict the Walén relation when solar wind contains structures with several small streams. A simulated case also demonstrates that Method 3 is better and more robust than Methods 1 and 2. These results are important for a better understanding of Alfvénic fluctuations and turbulence in the solar wind.

F-state interference significantly modifies the polarization produced by scattering processes in the solar atmosphere. Its signature in the emergent Stokes spectrum in the absence of magnetic fields is depolarization in the line core. In the present paper, we derive the partial frequency redistribution (PRD) matrix that includes interference between the upper hyperfine structure states of a two-level atom in the presence of magnetic fields of arbitrary strengths. The theory is applied to the Na i D₂ line that is produced by the transition between the lower J = 1/2 and upper J = 3/2 states which split into F states because of the coupling with the nuclear spin I_s = 3/2. The properties of the PRD matrix for the single-scattering case is explored, in particular, the effects of the magnetic field in the Paschen–Back regime and their usefulness as a tool for the diagnostics of solar magnetic fields.

Winking (oscillating) filaments have been observed for many years. However, observations of successive winking filaments in one event have not yet been reported. In this paper, we present the observations of a chain of winking filaments and a subsequent jet that are observed right after the X2.1 flare in AR11283. The event also produced an extreme-ultraviolet (EUV) wave that has two components: an upward dome-like wave (850 km s⁻¹) and a lateral surface wave (554 km s⁻¹) that was very weak (or invisible) in imaging observations. By analyzing the temporal and spatial relationships between the oscillating filaments and the EUV waves, we propose that all the winking filaments and the jet were triggered by the weak (or invisible) lateral surface EUV wave. The oscillation of the filaments last for two or three cycles, and their periods, Doppler velocity amplitudes, and damping times are 11–22 minutes, 6–14 km s⁻¹, and 25–60 minutes, respectively. We further estimate the radial component magnetic field and the maximum kinetic energy of the filaments, and they are 5–10 G and ∼10¹⁹ J, respectively. The estimated maximum kinetic energy is comparable to the minimum energy of ordinary EUV waves, suggesting that EUV waves can efficiently launch filament oscillations on their path. Based on our analysis results, we conclude that the EUV wave is a good agent for triggering and connecting successive but separated solar activities in the solar atmosphere, and it is also important for producing solar sympathetic eruptions.

The nearby group centered on its bright central galaxy NGC 1407 has been suggested by previous kinematic studies to be an unusually dark system. It is also known for hosting a bright galaxy, NGC 1400, with a large radial velocity (1200 km s⁻¹) with respect to the group center. Previous ROSAT X-ray observations revealed an extended region of enhanced surface brightness just eastward of NGC 1400. We investigate the NGC 1407/1400 complex with XMM-Newton and Chandra observations. We find that the temperature and metallicity of the enhanced region are different (cooler and more metal rich) than those of the surrounding group gas but are consistent with those of the interstellar medium (ISM) in NGC 1400. The relative velocity of NGC 1400 is large enough that much of its ISM could have been ram pressure stripped while plunging through the group atmosphere. We conclude that the enhanced region is likely to be hot gas stripped from the ISM of NGC 1400. We constrain the motion of NGC 1400 using the pressure jump at its associated stagnation front and the total mass profile of the NGC 1407 group. We conclude that NGC 1400 is moving within ∼30° of the line of sight with Mach number $\mathcal {M}\lesssim 3$. We do not detect any obvious shock features in this complex, perhaps because of the high line-of-sight motion of NGC 1400. With an XMM-Newton pointing on the relatively relaxed eastern side of NGC 1407, we derive a hydrostatic mass for this group of ∼1 × 10¹³ M_☉ within 100 kpc. The total mass extrapolated to the virial radius (681 kpc) is 3.8 × 10¹³ M_☉, which puts an upper limit of ∼300 $M_\odot /L_{B_\odot }$ on the mass-to-light ratio of this group. This suggests that the NGC 1407 group is not an unusually dark group.

Many multiple-planet systems have been found by the Kepler transit survey and various radial velocity (RV) surveys. Kepler planets show an asymmetric feature, namely, there are small but significant deficits/excesses of planet pairs with orbital period spacing slightly narrow/wide of the exact resonance, particularly near the first order mean motion resonance (MMR), such as 2:1 and 3:2 MMR. Similarly, if not exactly the same, an asymmetric feature (pileup wide of 2:1 MMR) is also seen in RV planets, but only for massive ones. We analytically and numerically study planets' orbital evolutions near and in the MMR. We find that their orbital period ratios could be asymmetrically distributed around the MMR center regardless of dissipation. In the case of no dissipation, Kepler planets' asymmetric orbital distribution could be partly reproduced for 3:2 MMR but not for 2:1 MMR, implying that dissipation might be more important to the latter. The pileup of massive RV planets just wide of 2:1 MMR is found to be consistent with the scenario that planets formed separately then migrated toward the MMR. The location of the pileup infers a K value of 1–100 on the order of magnitude for massive planets, where K is the damping rate ratio between orbital eccentricity and semimajor axis during planet migration.

The hot Jupiter HD 189733b is probably the best studied of the known extrasolar planets, with published transit and eclipse spectra covering the near UV to mid-IR range. Recent work on the transmission spectrum has shown clear evidence for the presence of clouds in its atmosphere, which significantly increases the model atmosphere parameter space that must be explored in order to fully characterize this planet. In this work, we apply the NEMESIS atmospheric retrieval code to the recently published HST/STIS reflection spectrum, and also to the dayside thermal emission spectrum in light of new Spitzer/IRAC measurements, as well as our own re-analysis of the HST/NICMOS data. We first use the STIS data to place some constraints on the nature of clouds on HD 189733b and explore solution degeneracy between different cloud properties and the abundance of Na in the atmosphere; as already noted in previous work, absorption due to Na plays a significant role in determining the shape of the reflection spectrum. We then perform a new retrieval of the temperature profile and abundances of H₂O, CO₂, CO, and CH₄ from the dayside thermal emission spectrum. Finally, we investigate the effect of including cloud in the model on this retrieval process. We find that the current quality of data does not warrant the extra complexity introduced by including cloud in the model; however, future data are likely to be of sufficient resolution and signal-to-noise that a more complete model, including scattering particles, will be required.

In this paper we present the results of observations of 17 H ii regions in thirteen galaxies from the SIGRID sample of isolated gas-rich irregular dwarf galaxies. The spectra of all but one of the galaxies exhibit the auroral [O iii] 4363 Å line, from which we calculate the electron temperature, T_e, and gas-phase oxygen abundance. Five of the objects are blue compact dwarf galaxies, of which four have not previously been analyzed spectroscopically. We include one unusual galaxy which exhibits no evidence of the [N ii] λλ 6548,6584 Å lines, suggesting a particularly low metallicity (< Z_☉/30). We compare the electron temperature based abundances with those derived using eight of the new strong-line diagnostics presented by Dopita et al. Using a method derived from first principles for calculating total oxygen abundance, we show that the discrepancy between the T_e-based and strong-line gas-phase abundances have now been reduced to within ∼0.07 dex. The chemical abundances are consistent with what is expected from the luminosity–metallicity relation. We derive estimates of the electron densities and find them to be between ∼5 and ∼100 cm⁻³. We find no evidence for a nitrogen plateau for objects in this sample with metallicities 0.5 >  Z_☉ > 0.15.

The Luminous Infrared Galaxy NGC 1614 hosts a prominent circumnuclear ring of star formation. However, the nature of the dominant emitting mechanism in its central ∼100 pc is still under debate. We present sub-arcsecond angular resolution radio, mid-infrared, Paα, optical, and X-ray observations of NGC 1614, aimed at studying in detail both the circumnuclear ring and the nuclear region. The 8.4 GHz continuum emission traced by the Very Large Array and the Gemini/T-ReCS 8.7 μm emission, as well as the Paα line emission, show remarkable morphological similarities within the star-forming ring, suggesting that the underlying emission mechanisms are tightly related. We used a Hubble Space Telescope/NICMOS Paα map of similar resolution to our radio maps to disentangle the thermal free–free and non-thermal synchrotron radio emission, from which we obtained the intrinsic synchrotron power law for each individual region within the central kiloparsec of NGC 1614. The radio ring surrounds a relatively faint, steep-spectrum source at the very center of the galaxy, suggesting that the central source is not powered by an active galactic nucleus (AGN), but rather by a compact (r ≲ 90 pc) starburst (SB). Chandra X-ray data also show that the central kiloparsec region is dominated by SB activity, without requiring the existence of an AGN. We also used publicly available infrared data to model-fit the spectral energy distribution of both the SB ring and a putative AGN in NGC 1614. In summary, we conclude that there is no need to invoke an AGN to explain the observed bolometric properties of the galaxy.

The discovery of rapidly variable Very High Energy (VHE; E > 100 GeV) γ-ray emission from 4C +21.35 (PKS  1222+216) by MAGIC on 2010 June 17, triggered by the high activity detected by the Fermi Large Area Telescope (LAT) in high energy (HE; E > 100 MeV) γ-rays, poses intriguing questions on the location of the γ-ray emitting region in this flat spectrum radio quasar. We present multifrequency data of 4C +21.35 collected from centimeter to VHE during 2010 to investigate the properties of this source and discuss a possible emission model. The first hint of detection at VHE was observed by MAGIC on 2010 May 3, soon after a γ-ray flare detected by Fermi-LAT that peaked on April 29. The same emission mechanism may therefore be responsible for both the HE and VHE emission during the 2010 flaring episodes. Two optical peaks were detected on 2010 April 20 and June 30, close in time but not simultaneous with the two γ-ray peaks, while no clear connection was observed between the X-ray and γ-ray emission. An increasing flux density was observed in radio and mm bands from the beginning of 2009, in accordance with the increasing γ-ray activity observed by Fermi-LAT, and peaking on 2011 January 27 in the mm regime (230 GHz). We model the spectral energy distributions (SEDs) of 4C +21.35 for the two periods of the VHE detection and a quiescent state, using a one-zone model with the emission coming from a very compact region outside the broad line region. The three SEDs can be fit with a combination of synchrotron self-Compton and external Compton emission of seed photons from a dust torus, changing only the electron distribution parameters between the epochs. The fit of the optical/UV part of the spectrum for 2010 April 29 seems to favor an inner disk radius of <six gravitational radii, as one would expect from a prograde-rotating Kerr black hole.

We present our analysis on new limits of the dark matter (DM) halo consisting of primordial black holes (PBHs) or massive compact halo objects. We present a search of the first two yr of publicly available Kepler mission data for potential signatures of gravitational microlensing caused by these objects as well as an extensive analysis of the astrophysical sources of background error. These include variable stars, flare events, and comets or asteroids that are moving through the Kepler field. We discuss the potential of detecting comets using the Kepler light curves, presenting measurements of two known comets and one unidentified object, most likely an asteroid or comet. After removing the background events with statistical cuts, we find no microlensing candidates. We therefore present our Monte Carlo efficiency calculation in order to constrain the PBH DM with masses in the range of 2 × 10⁻⁹ M_☉ to 10⁻⁷ M_☉. We find that PBHs in this mass range cannot make up the entirety of the DM, thus closing a full order of magnitude in the allowed mass range for PBH DM.

We present the first high resolution UV spectra toward Herschel 36, a Trapezium-like system of high-mass stars contained within the Lagoon Nebula (M8, NGC 6523). The spectra reveal extreme rovibrational excitation of molecular hydrogen in material at a single velocity or very small range of velocities, with this component presumably lying near the star system and undergoing fluorescent excitation. The overall H₂ excitation is similar to, but apparently larger than, that seen toward HD 37903 which previously showed the largest vibrationally excited H₂ column densities seen in UV absorption spectra. While the velocities of the highly excited H₂ lines are consistent within each observation, it appears that they underwent a ∼60 km s⁻¹ redshift during the 3.6 yr between observations. In neither case does the velocity of the highly excited material match the velocity of the bulk of the line-of-sight material which appears to mostly be in the foreground of M8. Recent work shows unusually excited CH and CH⁺ lines and several unusually broad diffuse interstellar bands toward Herschel 36. Along with the H₂ excitation, all of these findings appear to be related to the extreme environment within ∼0.1 pc of the massive young stellar system.