Table of contents

Finite source effects can be important in observations of gravitational microlensing of stars. Near caustic crossings, for example, some parts of the source star will be more highly magnified than other parts. The spectrum of the star is then no longer the same as when it is unmagnified, and measurements of the atmospheric parameters and abundances will be affected. The accuracy of abundances measured from spectra taken during microlensing events has become important recently because of the use of highly magnified dwarf stars to probe abundance ratios and the abundance distribution in the Galactic bulge. In this paper, we investigate the importance of finite source effects on spectra by using magnification profiles motivated by two events to synthesize spectra for dwarfs between 5000 K and 6200 K at solar metallicity. We adopt the usual techniques for analyzing the microlensed dwarfs, namely, spectroscopic determination of temperature, gravity, and microturbulent velocity, relying on equivalent widths. We find that ignoring the finite source effects for the more extreme case results in errors in T_eff <45 K, in log g of <0.1 dex, and in ξ of <0.1 km s⁻¹. In total, changes in equivalent widths lead to small changes in atmospheric parameters and changes in abundances of <0.06 dex, with changes in [Fe i/H] of <0.03 dex. For the case with a larger source-lens separation, the error in [Fe i/H] is <0.01 dex. This latter case represents the maximum effect seen in events whose light curves are consistent with a point-source lens, which includes the majority of microlensed bulge dwarfs published so far.

This paper studies the global solar wind between 1 AU and the termination shock, taking into account the highly latitude dependent solar wind at the 1 AU boundary and the ionization of interstellar neutral hydrogen. A system of two-fluid magnetohydrodynamics equations governs the flow of solar wind plasma; the conditions of the solar wind at 1 AU are generated from Ulysses data for the relatively stable state of the wind during the declining phase and solar minimum of the solar cycle. A one-fluid model is used to describe the flow of neutral hydrogen and its condition in the far-field boundary outside the termination shock. Simultaneous solutions are obtained using a high-resolution computational code for the two equation systems coupled by the ionization of neutral hydrogen. The ionization process leads to removal of neutral hydrogen in the heliosphere: a hydrogen cavity forms inside ∼4 AU; the cavity extends on the downwind side to form a long cavity wake. Solutions show how the ionization process and the wind condition at 1 AU boundary affect the spatial variation of the wind speed, temperature, pickup proton, fast Mach number, and plasma β-ratio. The wind properties inside 4 AU are axisymmetrical about the solar rotation axis; this axi-symmetry totally disappears in the outer heliosphere. All wind properties are substantially modified at an increasing heliocentric distance on the upwind side to generate an upwind–downwind asymmetry dictated by the direction of the relative motion between the Sun and the interstellar medium.

HH 211 is a highly collimated jet originating from a nearby young Class 0 protostar. Here is a follow-up study of the jet with our previous observations at unprecedented resolution up to ∼03 in SiO (J = 8–7), CO (J = 3–2), and SO (N_J = 8₉–7₈). SiO, CO, and SO can all be a good tracer of the HH 211 jet, tracing the internal shocks in the jet. Although the emissions of these molecules show roughly the same morphology of the jet, there are detailed differences. In particular, the CO emission traces the jet closer to the source than the SiO and SO emissions. In addition, in the better resolved internal shocks, both the CO and SO emission are seen slightly ahead of the SiO emission. The jet is clearly seen on both sides of the source with more than one cycle of wiggle. The wiggle is reflection-symmetric about the source and can be reasonably fitted by an orbiting source jet model. The best-fit parameters suggest that the source itself could be a very low mass protobinary with a total mass of ∼60 M_Jup and a binary separation of ∼4.6 AU. The abundances of SiO and SO in the gas phase are found to be highly enhanced in the jet as compared to the quiescent molecular clouds, even close to within 300 AU from the source where the dynamical timescale is <10 yr. The abundance enhancements of these molecules are closely related to the internal shocks. The detected SiO is either the consequence of the release of Si-bearing material from dust grains or of its formation via gas chemistry in the shocks. The SO, on the other hand, seems to form via gas chemistry in the shocks.

The presence of massive, compact, quiescent galaxies at z>2 presents a major challenge for theoretical models of galaxy formation and evolution. Using one of the deepest large public near-IR surveys to date, we investigate in detail the correlations between star formation and galaxy structural parameters (size, stellar mass, and surface density) from z = 2 to the present. At all redshifts, massive quiescent galaxies (i.e., those with little or no star formation) occupy the extreme high end of the surface density distribution and follow a tight mass–size correlation, while star-forming galaxies show a broad range of both densities and sizes. Conversely, galaxies with the highest surface densities comprise a nearly homogeneous population with little or no ongoing star formation, while less dense galaxies exhibit high star formation rates and varying levels of dust obscuration. Both the sizes and surface densities of quiescent galaxies evolve strongly from z = 2–0; we parameterize this evolution for both populations with simple power-law functions and present best-fit parameters for comparison to future theoretical models. Higher-mass quiescent galaxies undergo faster structural evolution, consistent with previous results. Interestingly, star-forming galaxies' sizes and densities evolve at rates similar to those of quiescent galaxies. It is therefore possible that the same physical processes drive the structural evolution of both populations, suggesting that "dry mergers" may not be the sole culprit in this size evolution.

In order to explain the inflated radii of some transiting extrasolar giant planets, we investigate a tidal heating scenario for the inflated planets WASP-4b, WASP-6b, WASP-12b, WASP-15b, and TrES-4. To do so, we assume that they retain a nonzero eccentricity, possibly by dint of continuing interaction with a third body. We calculate the amount of extra heating in the envelope that is then required to fit the radius of each planet, and we explore how this additional power depends on the planetary atmospheric opacity and on the mass of a heavy-element central core. There is a degeneracy between the core mass M_core and the heating $\dot{E}_{\rm heating}$. Therefore, in the case of tidal heating, there is for each planet a range of {M_core, e²/Q'_p} that can lead to the same radius, where Q'_p is the tidal dissipation factor and e is the eccentricity. With this in mind, we also investigate the case of the non-inflated planet HAT-P-12b, which can admit solutions combining a heavy-element core and tidal heating. A substantial improvement of the measured eccentricities of such planetary systems could simplify this degeneracy by linking the two unknown parameters {M_core, Q'_p}. Further independent constraints on either of these parameters would, through our calculations, constrain the other.

Jitter radiation is produced by relativistic electrons moving in turbulent small-scale magnetic fields such as those produced by streaming Weibel-type instabilities at collisionless shocks in weakly magnetized media. Here, we present a comprehensive study of the dependence of the jitter radiation spectra on the properties of, in general, anisotropic magnetic turbulence. We have obtained that the radiation spectra do reflect, to some extent, properties of the magnetic field spatial distribution, yet the radiation field is anisotropic and sensitive to the viewing direction with respect to the field anisotropy direction. We explore the parameter space of the magnetic field distribution and its effect on the radiation spectrum. Some important results include: the presence of the harder-than-synchrotron segment below the peak frequency at some viewing angles, the presence of the high-frequency power-law tail even for a monoenergetic distribution of electrons, the dependence of the peak frequency on the field correlation length rather than the field strength, and the strong correlation of the spectral parameters with the viewing angle. In general, we have found that even relatively minor changes in the magnetic field properties can produce very significant effects upon the jitter radiation spectra. We consider these results to be important for accurate interpretation of prompt gamma-ray burst spectra and possibly other sources.

The outer regions of galactic disks have received increased attention since ultraviolet observations with Galaxy Evolution Explorer demonstrated that nearly 30% of galaxies have UV emission beyond their optical extents, indicating star formation activity. These galaxies have been termed extended UV (XUV) disks. Here, we address whether these observations contradict the gas surface density threshold for star formation inferred from $\rm {H}\alpha$ radial profiles of galaxies. We run smoothed particle hydrodynamic simulations of isolated disk galaxies with fiducial star formation prescriptions and show that over-densities owing to the presence of spiral structure can induce star formation in extended gas disks. For direct comparison with observations, we use the three-dimensional radiative transfer code Sunrise to create simulated FUV and K_s-band images. We find that galaxies classified as Type I XUV disks are a natural consequence of spiral patterns, but we are unable to reproduce Type II XUV disks. We also compare our results to studies of the Kennicutt–Schmidt relation in outer disks.

We present axisymmetric hydrodynamical simulations of the long-term accretion of a rotating gamma-ray burst (GRB) progenitor star, a "collapsar," onto the central compact object, which we take to be a black hole. The simulations were carried out with the adaptive-mesh-refinement code FLASH in two spatial dimensions and with an explicit shear viscosity. The evolution of the central accretion rate exhibits phases reminiscent of the long GRB γ-ray and X-ray light curve, which lends support to the proposal by Kumar et al. that the luminosity is modulated by the central accretion rate. In the first "prompt" phase, the black hole acquires most of its final mass through supersonic quasiradial accretion occurring at a steady rate of ∼0.2 M_☉ s⁻¹. After a few tens of seconds, an accretion shock sweeps outward through the star. The formation and outward expansion of the accretion shock is accompanied with a sudden and rapid power-law decline in the central accretion rate $\dot{M}\propto t^{-2.8}$, which resembles the L_X ∝ t⁻³ decline observed in the X-ray light curves. The collapsed, shock-heated stellar envelope settles into a thick, low-mass equatorial disk embedded within a massive, pressure-supported atmosphere. After a few hundred seconds, the inflow of low angular momentum material in the axial funnel reverses into an outflow from the thick disk. Meanwhile, the rapid decline of the accretion rate slows down, which is potentially suggestive of the "plateau" phase in the X-ray light curve. We complement our adiabatic simulations with an analytical model that takes into account the cooling by neutrino emission and estimate that the duration of the prompt phase can be ∼20 s. The model suggests that the steep decline in GRB X-ray light curves is triggered by the circularization of the infalling stellar envelope at radii where the virial temperature is below 10¹⁰ K, such that neutrino cooling is inefficient and an outward expansion of the accretion shock becomes imminent; GRBs with longer prompt γ-ray emission should have more slowly rotating envelopes.

The zodiacal cloud is a thick circumsolar disk of small debris particles produced by asteroid collisions and comets. Their relative contribution and how particles of different sizes dynamically evolve to produce the observed phenomena of light scattering, thermal emission, and meteoroid impacts are unknown. Until now, zodiacal cloud models have been phenomenological in nature, composed of ad hoc components with properties not understood from basic physical processes. Here, we present a zodiacal cloud model based on the orbital properties and lifetimes of comets and asteroids, and on the dynamical evolution of dust after ejection. The model is quantitatively constrained by Infrared Astronomical Satellite (IRAS) observations of thermal emission, but also qualitatively consistent with other zodiacal cloud observations, with meteor observations, with spacecraft impact experiments, and with properties of recovered micrometeorites (MMs). We find that particles produced by Jupiter-family comets (JFCs) are scattered by Jupiter before they are able to orbitally decouple from the planet and drift down to 1 AU. Therefore, the inclination distribution of JFC particles is broader than that of their source comets and leads to good fits to the broad latitudinal distribution of fluxes observed by IRAS. We find that 85%–95% of the observed mid-infrared emission is produced by particles from JFCs and <10% by dust from long-period comets. The JFC particles that contribute to the observed cross section area of the zodiacal cloud are typically D ≈ 100 μm in diameter. Asteroidal dust is found to be present at <10%. We suggest that spontaneous disruptions of JFCs, rather than the usual cometary activity driven by sublimating volatiles, is the main mechanism that liberates cometary particles into the zodiacal cloud. The ejected mm to cm-sized particles, which may constitute the basic grain size in comets, are disrupted on ≲10,000 yr to produce the 10–1000 μm grains that dominate the thermal emission and mass influx. Breakup products with D > 100 μm undergo a further collisional cascade with smaller fragments being progressively more affected by Poynting–Robertson (PR) drag. Upon reaching D < 100 μm, the particles typically drift down to <1 AU without suffering further disruptions. The resulting Earth-impact speed and direction of JFC particles is a strong function of particle size. While 300 μm to 1 mm sporadic meteoroids are still on eccentric JFC-like orbits and impact from antihelion/helion directions, which is consistent with the aperture radar observations, the 10–300 μm particles have their orbits circularized by PR drag, impact at low speeds, and are not detected by radar. Our results imply that JFC particles represent ∼85% of the total mass influx at Earth. Since their atmospheric entry speeds are typically low (≈14.5 km s⁻¹ mean for D = 100–200 μm with ≈12 km s⁻¹ being the most common case), many JFC grains should survive frictional heating and land on Earth's surface. This explains why most MMs collected in antarctic ice have primitive carbonaceous composition. The present mass of the inner zodiacal cloud at <5 AU is estimated to be 1–2 × 10¹⁹ g, mainly in D = 100–200 μm particles. The inner zodiacal cloud should have been >10⁴ times brighter during the Late Heavy Bombardment (LHB) epoch ≈3.8 Gyr ago, when the outer planets scattered numerous comets into the inner solar system. The bright debris disks with a large 24 μm excess observed around mature stars may be an indication of massive cometary populations existing in those systems. We estimate that at least ∼10²², ∼2 × 10²¹, and ∼2 × 10²⁰ g of primitive dark dust material could have been accreted during LHB by the Earth, Mars, and Moon, respectively.

We present a new analysis of the Jupiter+Saturn analog system, OGLE-2006-BLG-109Lb,c, which was the first double planet system discovered with the gravitational microlensing method. This is the only multi-planet system discovered by any method with measured masses for the star and both planets. In addition to the signatures of two planets, this event also exhibits a microlensing parallax signature and finite source effects that provide a direct measure of the masses of the star and planets, and the expected brightness of the host star is confirmed by Keck AO imaging, yielding masses of $M_\ast = 0.51{+0.05\atop -0.04}\,M_\odot$, M_b = 231 ± 19 M_⊕, and M_c = 86 ± 7 M_⊕. The Saturn-analog planet in this system had a planetary light-curve deviation that lasted for 11 days, and as a result, the effects of the orbital motion are visible in the microlensing light curve. We find that four of the six orbital parameters are tightly constrained and that a fifth parameter, the orbital acceleration, is weakly constrained. No orbital information is available for the Jupiter-analog planet, but its presence helps to constrain the orbital motion of the Saturn-analog planet. Assuming co-planar orbits, we find an orbital eccentricity of $\epsilon = 0.15 {+0.17\atop -0.10}$ and an orbital inclination of $i = 64^\circ {+4^\circ \atop -7^\circ }$. The 95% confidence level lower limit on the inclination of i > 49° implies that this planetary system can be detected and studied via radial velocity measurements using a telescope of ≳30 m aperture.

We study the impact of theoretical uncertainty in the dark matter halo mass function and halo bias on dark energy constraints from imminent galaxy cluster surveys. We find that for an optical cluster survey like the Dark Energy Survey, the accuracy required on the predicted halo mass function to make it an insignificant source of error on dark energy parameters is ≈1%. The analogous requirement on the predicted halo bias is less stringent (≈5%), particularly if the observable–mass distribution can be well constrained by other means. These requirements depend upon survey area but are relatively insensitive to survey depth. The most stringent requirements are likely to come from a survey over a significant fraction of the sky that aims to observe clusters down to relatively low mass, M_th ≈ 10^13.7 h⁻¹ M_☉; for such a survey, the mass function and halo bias must be predicted to accuracies of ≈0.5% and ≈1%, respectively. These accuracies represent a limit on the practical need to calibrate ever more accurate halo mass and bias functions. We find that improving predictions for the mass function in the low-redshift and low-mass regimes is the most effective way to improve dark energy constraints.

We investigate high-magnification events caused by planets in wide binary stellar systems under the strong finite-source effect, where the planet orbits one of the companions. From this investigation, we find that the pattern of central perturbations in triple lens systems commonly appears as a combination of individual characteristic patterns of planetary and binary lens systems in a certain range where the sizes of the caustics induced by a planet and a binary companion are comparable, and the range changes with the mass ratio of the planet to the planet-hosting star. The inside and outside edge regions of a circle with a radius corresponding to that of the source star and its center located at the center of the caustic show the binary-lensing pattern, while the outside region of the circle shows the planetary-lensing pattern. Specifically, we find that because of this central perturbation pattern, the characteristic feature of high-magnification events caused by the triple lens systems appears in the residual from the single-lensing light curve despite the strong finite-source effect, and it is discriminated from those of the planetary- and binary-lensing events and thus can be used for the identification of the existence of both planet and binary companion. This characteristic feature is a simultaneous appearance of two features. First, double negative-spike and single positive-spike features caused by the binary companion appear together in the residual, where the double negative spike occurs at both moments when the source enters and exits the caustic center and the single positive spike occurs at the moment just before the source enters into or just after the source exits from the caustic center. Second, the magnification excess before or after the single positive-spike feature is positive due to the planet, and the positive excess has a remarkable increasing or decreasing pattern depending on the source trajectory.

Cygnus OB2 is the nearest example of a massive star-forming region (SFR), containing over 50 O-type stars and hundreds of B-type stars. We have analyzed the properties of young stars in two fields in Cyg OB2 using the recently published deep catalog of Chandra X-ray point sources with complementary optical and near-IR photometry. Our sample is complete to ∼1 M_☉ (excluding A- and B-type stars that do not emit X-rays), making this the deepest study of the stellar properties and star formation history in Cyg OB2 to date. From Siess et al. isochrone fits to the near-IR color–magnitude diagram, we derive ages of 3.5^+0.75_−1.0 and 5.25^+1.5_−1.0 Myr for sources in the two fields, both with considerable spreads around the pre-main-sequence isochrones. The presence of a stellar population somewhat older than the present-day O-type stars, also fits in with the low fraction of sources with inner circumstellar disks (as traced by the K-band excess) that we find to be very low, but appropriate for a population of age ∼5 Myr. We also find that the region lacks a population of highly embedded sources that is often observed in young SFRs, suggesting star formation in the vicinity has declined. We measure the stellar mass functions (MFs) in this limit and find a power-law slope of Γ = −1.09 ± 0.13, in good agreement with the global mean value estimated by Kroupa. A steepening of the slope at higher masses is observed and suggested as due to the presence of the previous generation of stars that have lost their most massive members. Finally, combining our MF and an estimate of the radial density profile of the association suggests a total mass of Cyg OB2 of ∼3 × 10⁴ M_☉, similar to that of many of our Galaxy's most massive SFRs.

In this paper, we present VLT/SINFONI integral field spectroscopy of RCW 34 along with Spitzer/IRAC photometry of the surroundings. RCW 34 consists of three different regions. A large bubble has been detected in the IRAC images in which a cluster of intermediate- and low-mass class II objects is found. At the northern edge of this bubble, an H ii region is located, ionized by 3 OB stars, of which the most massive star has spectral type O8.5V. Intermediate-mass stars (2–3 M_☉) are detected of G- and K-spectral type. These stars are still in the pre-main-sequence (PMS) phase. North of the H ii region, a photon-dominated region is present, marking the edge of a dense molecular cloud traced by H₂ emission. Several class 0/I objects are associated with this cloud, indicating that star formation is still taking place. The distance to RCW 34 is revised to 2.5 ± 0.2 kpc and an age estimate of 2 ± 1 Myr is derived from the properties of the PMS stars inside the H ii region. Between the class II sources in the bubble and the PMS stars in the H ii region, no age difference could be detected with the present data. The presence of the class 0/I sources in the molecular cloud, however, suggests that the objects inside the molecular cloud are significantly younger. The most likely scenario for the formation of the three regions is that star formation propagated from south to north. First the bubble is formed, produced by intermediate- and low-mass stars only, after that, the H ii region is formed from a dense core at the edge of the molecular cloud, resulting in the expansion similar to a champagne flow. More recently, star formation occurred in the rest of the molecular cloud. Two different formation scenarios are possible. (1) The bubble with the cluster of low- and intermediate-mass stars triggered the formation of the O star at the edge of the molecular cloud, which in its turn induces the current star formation in the molecular cloud. (2) An external triggering is responsible for the star formation propagating from south to north.

We present the ultraviolet (UV) and X-ray spectra observed with the Far Ultraviolet Spectroscopic Explorer (FUSE) and the XMM-Newton satellite, respectively, of the low-z Seyfert 1 galaxy IRAS F22456 − 5125. This object shows absorption from five distinct, narrow kinematic components that span a significant range in velocity (∼0 to −700 km s⁻¹) and ionization (Lyman series, C iii, N iii, and O vi). We also show that three of the five kinematic components in these lines appear to be saturated in Lyβ λ1026 and that all five components show evidence of saturation in the O vi doublet lines λλ1032, 1038. Further, all five components show evidence for partial covering due to the absorption seen in the O vi doublet. This object is peculiar because it shows no evidence for corresponding X-ray absorption to the UV absorption in the X-ray spectrum, which violates the 1:1 correlation known for low-z active galactic nuclei (AGNs). We perform photoionization modeling of the UV absorption lines and predict that the O vii column density should be small, which would produce little to no absorption in agreement with the X-ray observation. We also examine the UV variability of the continuum flux for this object (an increase of a factor of 6). As the absorption components lack variability, we find a lower limit of ∼20 kpc for the distance for the absorbers from the central AGN.

We present direct evidence for ammonium ion (NH₄⁺) formation through ultraviolet (UV) photolysis of NH₃–H₂O mixture ice that does not contain acids. NH₄⁺ forms by the reaction of NH₃ with protonic defects (H₃O⁺) in the UV-photolyzed ice. Our observations may explain the deficient counter-anions in interstellar ice relative to the abundance of NH₄⁺. Also, H₃O⁺ may play an important role in the acid–base chemistry of interstellar ice in UV-irradiating environments. IR absorption results suggest that NH₄⁺ is a potential contributor to the interstellar 6.85 μm band but is not a dominant component.

Motivated by a paper of Kirsch et al. on possible use of the Crab Nebula as a standard candle for calibrating X-ray response functions, we examine consequences of intrinsic departures from a single (absorbed) power law upon such calibrations. We limit our analyses to three more modern X-ray instruments—the ROSAT/PSPC, the RXTE/Proportional Counter Array, and the XMM-Newton/EPIC-pn (burst mode). The results indicate a need to refine two of the three response functions studied. We are also able to distinguish between two current theoretical models for the system spectrum.

We apply third-moment theory that describes the energy cascade within the inertial range of magnetohydrodynamic turbulence to observations of large cross-helicity states at 1 AU. We find that in contrast to intervals with smaller helicity that form the bulk of the observations, large helicity states demonstrate a significant back-transfer of energy from small to large scales. This occurs in such a manner as to reinforce the dominance of the outward-propagating fluctuations. We find no evidence of a significant anisotropy in the back-transfer dynamics and conclude that the process must be short-lived in order to be consistent with solar wind observations. We offer this as partial explanation for large helicity states in the solar wind.

We have analyzed data from a multi-site campaign to observe oscillations in the F5 star Procyon. The data consist of high-precision velocities that we obtained over more than three weeks with 11 telescopes. A new method for adjusting the data weights allows us to suppress the sidelobes in the power spectrum. Stacking the power spectrum in a so-called échelle diagram reveals two clear ridges, which we identify with even and odd values of the angular degree (l = 0 and 2, and l = 1 and 3, respectively). We interpret a strong, narrow peak at 446 μHz that lies close to the l = 1 ridge as a mode with mixed character. We show that the frequencies of the ridge centroids and their separations are useful diagnostics for asteroseismology. In particular, variations in the large separation appear to indicate a glitch in the sound-speed profile at an acoustic depth of ∼1000 s. We list frequencies for 55 modes extracted from the data spanning 20 radial orders, a range comparable to the best solar data, which will provide valuable constraints for theoretical models. A preliminary comparison with published models shows that the offset between observed and calculated frequencies for the radial modes is very different for Procyon than for the Sun and other cool stars. We find the mean lifetime of the modes in Procyon to be 1.29^+0.55_−0.49 days, which is significantly shorter than the 2–4 days seen in the Sun.

We have used archival Space Telescope Imaging Spectrograph (STIS) data in the range 2100–2500 Å toward the Trapezium star Θ¹ B Orionis (HD 37021) to estimate the Fe column density and other parameters in the neutral Veil of Orion. The Veil lies 1–3 pc in front of the Orion H⁺ region, it has an estimated volume density of 10^2.5–3.5 cm⁻³, and its H° column density has been previously measured via the STIS-observed Lyα line. We find N(Fe)/N(H°) = 4.4 ± 1.3 × 10⁻⁷, implying a log depletion of −1.81 ± 0.13 relative to solar. Our estimate of N(Fe) comes from direct integration of the moderate optical depth Fe ii λ2249 and λ2260 lines. From this analysis, we are also able to estimate empirically new values for the oscillator strengths of the low optical depth Fe ii λ2234 and λ2367 lines. N(Fe)/N(H) in the Veil is consistent with the most recent estimates of this ratio for the main Orion H⁺ region. Therefore, there is no evidence that significant Fe has been released from grains into the gaseous state in the H⁺ region via grain destruction processes. The Fe/H ratio in the Veil is also comparable to other Fe/H measurements made in the diffuse interstellar medium for lower density gas. Therefore, the present result suggests that depletion is not strongly correlated with local gas density at least up to n ≈ 10³ cm⁻³. Finally, we have identified several outlying velocity components in some of the Fe ii line profiles, components that have been previously identified in optical Ca ii and Na i line profiles. These outlying velocity components are probably small concentrations of cold neutral material lying tens of pc or more in front of the Veil and unrelated to it.

The physical properties of galactic cirrus emission are not well characterized. BOOMERanG is a balloon-borne experiment designed to study the cosmic microwave background at high angular resolution in the millimeter range. The BOOMERanG 245 and 345 GHz channels are sensitive to interstellar signals, in a spectral range intermediate between FIR and microwave frequencies. We look for physical characteristics of cirrus structures in a region at high galactic latitudes (b ∼ −40°) where BOOMERanG performed its deepest integration, combining the BOOMERanG data with other available data sets at different wavelengths. We have detected eight emission patches in the 345 GHz map, consistent with cirrus dust in the Infrared Astronomical Satellite maps. The analysis technique we have developed allows us to identify the location and the shape of cirrus clouds, and to extract the flux from observations with different instruments at different wavelengths and angular resolutions. We study the integrated flux emitted from these cirrus clouds using data from Infrared Astronomical Satellite (IRAS), DIRBE, BOOMERanG and Wilkinson Microwave Anisotropy Probe in the frequency range 23–3000 GHz (13 mm–100 μm wavelength). We fit the measured spectral energy distributions with a combination of a gray body and a power-law spectra considering two models for the thermal emission. The temperature of the thermal dust component varies in the 7–20 K range and its emissivity spectral index is in the 1–5 range. We identified a physical relation between temperature and spectral index as had been proposed in previous works. This technique can be proficiently used for the forthcoming Planck and Herschel missions data.

We present a set of low-resolution empirical spectral energy distribution (SED) templates for active galactic nuclei (AGNs) and galaxies in the wavelength range from 0.03 μm to 30 μm based on the multi-wavelength photometric observations of the NOAO Deep-Wide Field Survey Boötes field and the spectroscopic observations of the AGN and Galaxy Evolution Survey. Our training sample is comprised of 14,448 galaxies in the redshift range 0 ≲ z ≲ 1 and 5347 likely AGNs in the range 0 ≲ z ≲ 5.58. The galaxy templates correspond to the SED templates presented in 2008 by Assef et al. extended into the UV and mid-IR by the addition of FUV and NUV GALEX and MIPS 24 μm data for the field. We use our templates to determine photometric redshifts for galaxies and AGNs. While they are relatively accurate for galaxies (σ_z/(1 + z) = 0.04, with 5% outlier rejection), their accuracies for AGNs are a strong function of the luminosity ratio between the AGN and galaxy components. Somewhat surprisingly, the relative luminosities of the AGN and its host are well determined even when the photometric redshift is significantly in error. We also use our templates to study the mid-IR AGN selection criteria developed by Stern et al. in 2005 and Lacy et al. in 2004. We find that the Stern et al. criterion suffers from significant incompleteness when there is a strong host galaxy component and at z ≃ 4.5, when the broad Hα emission line is redshifted into the [3.6] band, but that it is little contaminated by low- and intermediate-redshift galaxies. The Lacy et al. criterion is not affected by incompleteness at z ≃ 4.5 and is somewhat less affected by strong galaxy host components, but is heavily contaminated by low-redshift star-forming galaxies. Finally, we use our templates to predict the color–color distribution of sources in the upcoming Wide-Field Infrared Survey Explorer (WISE) mission and define a color criterion to select AGNs analogous to those developed for IRAC photometry. We estimate that in between 640,000 and 1,700,000 AGNs will be identified by these criteria, but without additional information, WISE-selected quasars will have serious completeness problems for z ≳ 3.4.

We report on the results of two epochs of Very Long Baseline Array observations of the 22 GHz water masers toward IRAS 19190+1102. The water maser emission from this object shows two main arc-shaped formations perpendicular to their NE–SW separation axis. The arcs are separated by ∼280 mas in position and are expanding outward at an angular rate of 2.35 mas yr⁻¹. We detect maser emission at velocities between −53.3 km s⁻¹ and +78.0 km s⁻¹, and there is a distinct velocity pattern where the NE masers are blueshifted and the SW masers are redshifted. The outflow has a three-dimensional outflow velocity of 99.8 km s⁻¹ and a dynamical age of about 59 yr. A group of blueshifted masers not located along the arcs shows a change in velocity of more than 25 km s⁻¹ between epochs, and may be indicative of the formation of a new lobe. These observations show that IRAS 19190+1102 is a member of the class of "water fountain" pre-planetary nebulae displaying bipolar structure.

We present new mid- to far-infrared images of the two dwarf compact elliptical galaxies that are satellites of M31, NGC 185, and NGC 147, obtained with the Spitzer Space Telescope. Spitzer's high sensitivity and spatial resolution enable us for the first time to look directly into the detailed spatial structure and properties of the dust in these systems. The images of NGC 185 at 8 and 24 μm display a mixed morphology characterized by a shell-like diffuse emission region surrounding a central concentration of more intense infrared emission. The lower resolution images at longer wavelengths show the same spatial distribution within the central 50'' but beyond this radius, the 160 μm emission is more extended than that at 24 and 70 μm. On the other hand, the dwarf galaxy NGC 147, located only a small distance away from NGC 185, shows no significant infrared emission beyond 24 μm and therefore its diffuse infrared emission is mainly stellar in origin. For NGC 185, the derived dust mass based on the best fit to the spectral energy distribution is 1.9 × 10³ M_☉, implying a gas mass of 3.0 × 10⁵ M_☉. These values are in agreement with those previously estimated from infrared as well as CO and H i observations and are consistent with the predicted mass return from dying stars based on the last burst of star formation 1 × 10⁹ yr ago. Based on the 70–160 μm flux density ratio, we estimate a temperature for the dust of ∼17 K. For NGC 147, we obtain an upper limit for the dust mass of 4.5 × 10² M_☉ at 160 μm (assuming a temperature of ∼20 K), a value consistent with the previous upper limit derived using Infrared Space Observatory observations of this galaxy. In the case of NGC 185, we also present full 5–38 μm low-resolution (R  ∼  100) spectra of the main emission regions. The Infrared Spectrograph spectra of NGC 185 show strong polycyclic aromatic hydrocarbons emission, deep silicate absorption features and H₂ pure rotational line ratios consistent with having the dust and molecular gas inside the dust cloud being impinged by the far-ultraviolet radiation field of a relatively young stellar population. Therefore, based on its infrared spectral properties, NGC 185 shows signatures of recent star formation (a few ×10⁸ yr ago), although its current star formation rate is quite low.

We use the observation of an Extreme Ultraviolet Imaging Telescope (EIT) wave in the lower solar corona, seen with the two Solar Terrestrial Relations Observatory (STEREO) spacecraft in extreme ultraviolet light on 2007 May 19, to model the same event with a three-dimensional (3D) time-depending magnetohydrodynamic (MHD) code that includes solar coronal magnetic fields derived with Wilcox Solar Observatory magnetogram data, and a solar wind outflow accelerated with empirical heating functions. The model includes a coronal mass ejection (CME) of Gibson and Low flux rope type above the reconstructed active region with parameters adapted from observations to excite the EIT wave. We trace the EIT wave running as circular velocity enhancement around the launching site of the CME in the direction tangential to the sphere produced by the wave front, and compute the phase velocities of the wave front. We find that the phase velocities are in good agreement with theoretical values for a fast magnetosonic wave, derived with the physical parameters of the model, and with observed phase speeds of an incident EIT wave reflected by a coronal hole and running at about the same location. We also produce in our 3D MHD model the observed reflection of the EIT wave at the coronal hole boundary, triggered by the magnetic pressure difference between the wave front hitting the hole and the boundary magnetic fields of the coronal hole, and the response of the coronal hole, which leads to the generation of secondary reflected EIT waves radiating away in different directions than the incident EIT wave. This is the first 3D MHD model of an EIT wave triggered by a CME that includes realistic solar magnetic field, with results comparing favorably to STEREO Extreme Ultraviolet Imager observations.

We calculate the gravitational wave signal from the growth of 10⁷ M_☉ supermassive black holes (SMBHs) from the remnants of Population III stars. The assembly of these lower mass black holes (BHs) is particularly important because observing SMBHs in this mass range is one of the primary science goals for the Laser Interferometer Space Antenna (LISA), a planned NASA/ESA mission to detect gravitational waves. We use high-resolution cosmological N-body simulations to track the merger history of the host dark matter halos, and model the growth of the SMBHs with a semianalytic approach that combines dynamical friction, gas accretion, and feedback. We find that the most common source in the LISA band from our volume consists of mergers between intermediate-mass BHs and SMBHs at redshifts less than 2. This type of high mass ratio merger has not been widely considered in the gravitational wave community; detection and characterization of this signal will likely require a different technique than is used for SMBH mergers or extreme mass ratio inspirals. We find that the event rate of this new LISA source depends on prescriptions for gas accretion onto the BH as well as an accurate model of the dynamics on a galaxy scale; our best estimate yields ∼40 sources with a signal-to-noise ratio greater than 30 occuring within a volume like the Local Group during SMBH assembly—extrapolated over the volume of the universe yields ∼500 observed events over 10 years, although the accuracy of this rate is affected by cosmic variance.

We present a measurement of the volumetric Type Ia supernova (SN Ia) rate based on data from the Sloan Digital Sky Survey II (SDSS-II) Supernova Survey. The adopted sample of supernovae (SNe) includes 516 SNe Ia at redshift z ≲ 0.3, of which 270(52%) are spectroscopically identified as SNe Ia. The remaining 246 SNe Ia were identified through their light curves; 113 of these objects have spectroscopic redshifts from spectra of their host galaxy, and 133 have photometric redshifts estimated from the SN light curves. Based on consideration of 87 spectroscopically confirmed non-Ia SNe discovered by the SDSS-II SN Survey, we estimate that 2.04^+1.61_−0.95% of the photometric SNe Ia may be misidentified. The sample of SNe Ia used in this measurement represents an order of magnitude increase in the statistics for SN Ia rate measurements in the redshift range covered by the SDSS-II Supernova Survey. If we assume an SN Ia rate that is constant at low redshift (z < 0.15), then the SN observations can be used to infer a value of the SN rate of r_V = (2.69^+0.34+0.21_{−0.30−0.01})×10⁻⁵ SNe yr⁻¹ Mpc⁻³ (H₀/(70 km s⁻¹ Mpc⁻¹))³ at a mean redshift of ∼0.12, based on 79 SNe Ia of which 72 are spectroscopically confirmed. However, the large sample of SNe Ia included in this study allows us to place constraints on the redshift dependence of the SN Ia rate based on the SDSS-II Supernova Survey data alone. Fitting a power-law model of the SN rate evolution, r_V(z) = A_p × ((1 + z)/(1 + z₀))^ν, over the redshift range 0.0 < z < 0.3 with z₀ = 0.21, results in A_p = (3.43^+0.15_−0.15) × 10⁻⁵ SNe yr⁻¹ Mpc⁻³ (H₀/(70 km s⁻¹ Mpc⁻¹))³ and ν = 2.04^+0.90_−0.89.

We investigate the relationship between brightest cluster galaxies (BCGs) and their host clusters using a sample of nearby galaxy clusters from the Representative XMM-Newton Cluster Structure Survey. The sample was imaged with the Southern Observatory for Astrophysical Research in R band to investigate the mass of the old stellar population. Using a metric radius of 12 h⁻¹ kpc, we found that the BCG luminosity depends weakly on overall cluster mass as L_BCG ∝ M^0.18±0.07_cl, consistent with previous work. We found that 90% of the BCGs are located within 0.035 r₅₀₀ of the peak of the X-ray emission, including all of the cool core (CC) clusters. We also found an unexpected correlation between the BCG metric luminosity and the core gas density for non-cool-core (non-CC) clusters, following a power law of n_e ∝ L^2.7±0.4_BCG (where n_e is measured at 0.008 r₅₀₀). The correlation is not easily explained by star formation (which is weak in non-CC clusters) or overall cluster mass (which is not correlated with core gas density). The trend persists even when the BCG is not located near the peak of the X-ray emission, so proximity is not necessary. We suggest that, for non-CC clusters, this correlation implies that the same process that sets the central entropy of the cluster gas also determines the central stellar density of the BCG, and that this underlying physical process is likely to be mergers.

We have acquired NanoSIMS images of the matrices of CI, CM, and CR carbonaceous chondrites to study, in situ, the organic matter trapped during the formation of their parent bodies. D/H ratio images reveal the occurrence of D-rich hot spots, constituting isolated organic particles. Not all the organic particles are D-rich hot spots, indicating that at least two kinds of organic particles have been accreted in the parent bodies. Ratio profiles through D-rich hot spots indicate that no significant self-diffusion of deuterium occurs between the D-rich organic matter and the depleted hydrous minerals that are surrounding them. This is not the result of a physical shielding by any constituent of the chondrites. Ab initio calculations indicate that it cannot be explained by isotopic equilibrium. Then it appears that the organic matter that is extremely enriched in D does not exchange with the hydrous minerals, or this exchange is so slow that it is not significant over the 4.5 billion year history on the parent body. If we consider that the D-rich hot spots are the result of an exposure to intense irradiation, then it appears that carbonaceous chondrites accreted organic particles that have been brought to different regions of the solar nebula. This is likely the result of important radial and vertical transport in the early solar system.

Motivated by a considerable scatter in the observationally inferred lifetimes of the embedded phase of star formation, we study the duration of the Class 0 and Class I phases in upper-mass brown dwarfs and low-mass stars using numerical hydrodynamic simulations of the gravitational collapse of a large sample of cloud cores. We resolve the formation of a star/disk/envelope system and extend our numerical simulations to the late accretion phase when the envelope is nearly totally depleted of matter. We adopt the classification scheme of André et al. and calculate the lifetimes of the Class 0 and Class I phases (τ_C0 and τ_CI, respectively) based on the mass remaining in the envelope. When cloud cores with various rotation rates, masses, and sizes (but identical otherwise) are considered, our modeling reveals a sub-linear correlation between the Class 0 lifetimes and stellar masses in the Class 0 phase with the least-squares fit exponent m = 0.8 ± 0.05. The corresponding correlation between the Class I lifetimes and stellar masses in Class I is super-linear with m = 1.2 ± 0.05. If a wider sample of cloud cores is considered, which includes possible variations in the initial gas temperature, cloud core truncation radii, density enhancement amplitudes, initial gas density and angular velocity profiles, and magnetic fields, then the corresponding exponents may decrease by as much as 0.3. The duration of the Class I phase is found to be longer than that of the Class 0 phase in most models, with a mean ratio τ_CI/τ_C0≈ 1.5–2. A notable exception are young stellar objects that form from cloud cores with large initial density enhancements, in which case τ_C0 may be greater than τ_CI. Moreover, the upper-mass (≳1.0 M_☉) cloud cores with frozen-in magnetic fields and high cloud core rotation rates may have the τ_CI/τ_C0 ratios as large as 3.0–4.0. We calculate the rate of mass accretion from the envelope onto the star/disk system and provide an approximation formula that can be used in semi-analytic models of cloud core collapse.

We present photometric and spectroscopic observations of SN 2007if, an overluminous (M_V = −20.4), red (B − V = 0.16 at B-band maximum), slow-rising (t_rise = 24 days) type Ia supernova (SN Ia) in a very faint (M_g = −14.10) host galaxy. A spectrum at 5 days past B-band maximum light is a direct match to the super-Chandrasekhar-mass candidate SN Ia 2003fg, showing Si ii and C ii at ∼9000 km s⁻¹. A high signal-to-noise co-addition of the SN spectral time series reveals no Na i D absorption, suggesting negligible reddening in the host galaxy, and the late-time color evolution has the same slope as the Lira relation for normal SNe Ia. The ejecta appear to be well mixed, with no strong maximum in I band and a diversity of iron-peak lines appearing in near-maximum-light spectra. SN 2007if also displays a plateau in the Si ii velocity extending as late as +10 days, which we interpret as evidence for an overdense shell in the SN ejecta. We calculate the bolometric light curve of the SN and use it and the Si ii velocity evolution to constrain the mass of the shell and the underlying SN ejecta, and demonstrate that SN 2007if is strongly inconsistent with a Chandrasekhar-mass scenario. Within the context of a "tamped detonation" model appropriate for double-degenerate mergers, and assuming no host extinction, we estimate the total mass of the system to be 2.4 ± 0.2 M_☉, with 1.6 ± 0.1 M_☉ of ⁵⁶Ni and with 0.3–0.5 M_☉ in the form of an envelope of unburned carbon/oxygen. Our modeling demonstrates that the kinematics of shell entrainment provide a more efficient mechanism than incomplete nuclear burning for producing the low velocities typical of super-Chandrasekhar-mass SNe Ia.

The high densities, long lifetimes, and narrow emission measure distributions observed in coronal loops with apex temperatures near 1 MK are difficult to reconcile with physical models of the solar atmosphere. It has been proposed that the observed loops are actually composed of sub-resolution "threads" that have been heated impulsively and are cooling. We apply this heating scenario to nearly simultaneous observations of an evolving post-flare loop arcade observed with EUVI/STEREO, EIS/Hinode, XRT/Hinode, and TRACE. We find that it is possible to reproduce the extended loop lifetime, high electron density, and the narrow differential emission measure with a multi-thread hydrodynamic model provided that the timescale for the energy release is sufficiently short. The model, however, does not reproduce the evolution of the very high temperature emission observed with XRT. In XRT the emission appears diffuse and it may be that this discrepancy is simply due to the difficulty of isolating individual loops at these temperatures. This discrepancy may also reflect fundamental problems with our understanding of post-reconnection dynamics during the conductive cooling phase of loop evolution.

Solar models using the new lower abundances of Asplund et al. or Caffau et al. do not agree as well with helioseismic inferences as models that use the higher Grevesse & Noels or Grevesse & Sauval abundances. Adopting the new abundances leads to models with sound-speed discrepancies of up to 1.4% below the base of the convection zone (CZ) compared to discrepancies of less than 0.4% with the old abundances; a CZ that is too shallow; and a CZ helium abundance that is too low. Here we briefly review recent attempts to restore agreement, and we evaluate three changes to the models: early mass loss, accretion of low-Z material, and convective overshoot. One goal of these attempts is to explore models that could preserve the structure in the interior obtained with the old abundances while accommodating the new abundances at the surface. Although the mass-losing and accretion models show some improvement in agreement with seismic constraints, a satisfactory resolution to the solar abundance problem remains to be found. In addition, we perform a preliminary analysis of models with the Caffau et al. abundances that shows that the sound-speed discrepancy is reduced to only about 0.6% at the CZ base, compared to 1.4% for the Asplund et al. abundances and 0.4% for the Grevesse & Noels abundances. Furthermore, including mass loss in models with the Caffau et al. abundances may improve sound-speed agreement and help resolve the solar lithium problem.

The fragmentation of star-forming interstellar clouds, and the resulting stellar initial mass function (IMF), is strongly affected by the temperature structure of the collapsing gas. Since radiation feedback from embedded stars can modify this as collapse proceeds, feedback plays an important role in determining the IMF. However, the effects and importance of radiative heating are likely to depend strongly on the surface density of the collapsing clouds, which determines both their effectiveness at trapping radiation and the accretion luminosities of the stars forming within them. In this paper, we report a suite of adaptive mesh refinement radiation–hydrodynamic simulations using the ORION code in which we isolate the effect of column density on fragmentation by following the collapse of clouds of varying column density while holding the mass, initial density and velocity structure, and initial virial ratio fixed. We find that radiation does not significantly modify the overall star formation rate or efficiency, but that it suppresses fragmentation more and more as cloud surface densities increase from those typical of low-mass star-forming regions like Taurus, through the typical surface density of massive star-forming clouds in the Galaxy, up to conditions found only in super-star clusters. In regions of low surface density, fragmentation during collapse leads to the formation of small clusters rather than individual massive star systems, greatly reducing the fraction of the stellar population with masses ≳10 M_☉. Our simulations have important implications for the formation of massive stars and the universality of the IMF.

As an initial investigation into the long-term evolution of protostellar disks, we explore the conditions required to explain the large outbursts of disk accretion seen in some young stellar objects. We use one-dimensional time-dependent disk models with a phenomenological treatment of the magnetorotational instability (MRI) and gravitational torques to follow disk evolution over long timescales. Comparison with our previous two-dimensional disk model calculations indicates that the neglect of radial effects and two-dimensional disk structure in the one-dimensional case makes only modest differences in the results; this allows us to use the simpler models to explore parameter space efficiently. We find that the mass infall rates typically estimated for low-mass protostars generally result in AU-scale disk accretion outbursts, as predicted by our previous analysis. We also confirm quasi-steady accretion behavior for high mass infall rates if the values of α-parameter for the MRI are small, while at this high accretion rate convection from the thermal instability may lead to some variations. We further constrain the combinations of the α-parameter and the MRI critical temperature, which can reproduce observed outburst behavior. Our results suggest that dust sublimation may be connected with full activation of the MRI. This is consistent with the idea that small dust captures ions and electrons to suppress the MRI. In a companion paper, we will explore both long-term outburst and disk evolution with this model, allowing for infall from protostellar envelopes with differing angular momenta.

We use one-dimensional two-zone time-dependent accretion disk models to study the long-term evolution of protostellar disks subject to mass addition from the collapse of a rotating cloud core. Our model consists of a constant surface density magnetically coupled active layer, with transport and dissipation in inactive regions only via gravitational instability. We start our simulations after a central protostar has formed, containing ∼10% of the mass of the protostellar cloud. Subsequent evolution depends on the angular momentum of the accreting envelope. We find that disk accretion matches the infall rate early in the disk evolution because much of the inner disk is hot enough to couple to the magnetic field. Later infall reaches the disk beyond ∼10 AU, and the disk undergoes outbursts of accretion in FU Ori-like events as described by Zhu et al. If the initial cloud core is moderately rotating, most of the central star's mass is built up by these outburst events. Our results suggest that the protostellar "luminosity problem" is eased by accretion during these FU Ori-like outbursts. After infall stops, the disk enters the T Tauri phase. An outer, viscously evolving disk has a structure that is in reasonable agreement with recent submillimeter studies and its surface density evolves from Σ ∝ R⁻¹ to R^−1.5. An inner, massive belt of material—the "dead zone"—would not have been observed yet but should be seen in future high angular resolution observations by EVLA and ALMA. This high surface density belt is a generic consequence of low angular momentum transport efficiency at radii where the disk is magnetically decoupled, and would strongly affect planet formation and migration.

Preliminary analysis of the oxygen isotopic composition of the solar wind recorded by the Genesis spacecraft suggests that the Sun is ¹⁶O-rich compared to most chondrules, fine-grained chondrite matrices, and bulk compositions of chondrites, achondrites, and terrestrial planets (Δ¹⁷O = −26.5‰ ± 5.6‰ and −33‰ ± 8‰ (2σ) versus Δ¹⁷O ∼ ±5‰). The inferred ¹⁶O-rich composition of the Sun is similar or slightly lighter than the ¹⁶O-rich compositions of amoeboid olivine aggregates and typical calcium–aluminum-rich inclusions (CAIs) from primitive (unmetamorphosed) chondrites (Δ¹⁷O = −24‰ ± 2‰), which are believed to have condensed from and been melted in a gas of approximately solar composition (dust/gas ratio ∼ 0.01 by weight) within the first 0.1 Myr of the solar system formation. Based on solar system abundances, 26% of the solar system oxygen must be initially contained in dust and 74% in gas. Because solar oxygen is dominated by the gas component, these observations suggest that oxygen isotopic composition of the solar nebula gas was initially ¹⁶O-rich. Due to significant thermal processing of the protosolar molecular cloud silicate dust (primordial dust) in the solar nebula and its possible isotope exchange with the isotopically evolved solar nebula gas, the mean oxygen isotopic composition of the primordial dust is not known. In CO self-shielding models, it is assumed that primordial dust and solar nebula gas had initially identical, ¹⁶O-rich compositions, similar to that of the Sun (Δ¹⁷O ∼ −25‰ or −35‰), and solids subsequently evolved toward the terrestrial value (Δ¹⁷O = 0). However, there is no clear evidence that the oxygen isotopic compositions of the solar system solids evolved in the direction of increasing Δ¹⁷O with time and no ¹⁶O-rich primordial dust have yet been discovered. Here we argue that the assumption of the CO self-shielding models that primordial dust and solar nebula gas had initially identical ¹⁶O-rich compositions is incorrect. We show that igneous CAIs with highly fractionated oxygen isotopic compositions, fractionation and unidentified nuclear effects (FUN), and fractionation (F) CAIs, have Δ¹⁷O ranging from −0.5‰ to −24.8‰. Within an individual FUN or F CAI, oxygen isotopic compositions of spinel, forsterite, and pyroxene define a mass-dependent fractionation trend with a constant Δ¹⁷O value. The degree of mass-dependent fractionation of these minerals correlates with the sequence of their crystallization from the host CAI melt. These observations and evaporation experiments on CAI-like melts indicate that FUN and F CAIs formed by melting of solid precursors with diverse Δ¹⁷O values in vacuum (total pressure < 10⁻⁶ atm). We interpret the observed range of Δ¹⁷O values among FUN and F CAIs as the result of varying degrees of equilibration between ¹⁶O-poor dust and ¹⁶O-rich nebular gas and suggest the former is characteristic of the primordial dust. The distinctly different oxygen isotopic compositions of the primordial solar nebula dust and gas could have resulted from Galactic chemical evolution or from pollution of the protosolar molecular cloud by a massive star (>50_☉) ejecta. The ¹⁶O-depleted compositions of chondrules, fine-grained matrices, chondrites, and achondrites compared to the Sun's value reflect their formation in the protoplanetary disk regions with enhanced dust/gas ratio (up to 10⁵× solar).

Cosmology with Type Ia supernova heretofore has required extensive spectroscopic follow-up to establish an accurate redshift. Though this resource-intensive approach is tolerable at the present discovery rate, the next generation of ground-based all-sky survey instruments will render it unsustainable. Photometry-based redshift determination may be a viable alternative, though the technique introduces non-negligible errors that ultimately degrade the ability to discriminate between competing cosmologies. We present a strictly template-based photometric redshift estimator and compute redshift reconstruction errors in the presence of statistical errors. Under highly degraded photometric conditions corresponding to a statistical error σ of 0.5, the residual redshift error is found to be 0.236 when assuming a nightly observing cadence and a single Large Synoptic Science Telescope (LSST) u-band filter. Utilizing all six LSST bandpass filters reduces the residual redshift error to 9.1 × 10⁻³. Assuming a more optimistic statistical error σ of 0.05, we derive residual redshift errors of 4.2 × 10⁻⁴, 5.2 × 10⁻⁴, 9.2 × 10⁻⁴, and 1.8 × 10⁻³ for observations occuring nightly, every 5th, 20th and 45th night, respectively, in each of the six LSST bandpass filters. Adopting an observing cadence in which photometry is acquired with all six filters every 5th night and a realistic supernova distribution, binned redshift errors are combined with photometric errors with a σ of 0.17 and systematic errors with a σ∼ 0.003 to derive joint errors (σ_w, $\sigma _{w^{\prime }}$) of (0.012, 0.066), respectively, in (w,w') with 68% confidence using Fisher matrix formalism. Though highly idealized in the present context, the methodology is nonetheless quite relevant for the next generation of ground-based all-sky surveys.

Radiative transfer in planetary atmospheres is usually treated in the static limit, i.e., neglecting atmospheric motions. We argue that hot Jupiter atmospheres, with possibly fast (sonic) wind speeds, may require a more strongly coupled treatment, formally in the regime of radiation hydrodynamics. To lowest order in v/c, relativistic Doppler shifts distort line profiles along optical paths with finite wind velocity gradients. This leads to flow-dependent deviations in the effective emission and absorption properties of the atmospheric medium. Evaluating the overall impact of these distortions on the radiative structure of a dynamic atmosphere is non-trivial. We present transmissivity and systematic equivalent width excess calculations which suggest possibly important consequences for radiation transport in hot Jupiter atmospheres. If winds are fast and bulk Doppler shifts are indeed important for the global radiative balance, accurate modeling and reliable data interpretation for hot Jupiter atmospheres may prove challenging: it would involve anisotropic and dynamic radiative transfer in a coupled radiation-hydrodynamical flow. On the bright side, it would also imply that the emergent properties of hot Jupiter atmospheres are more direct tracers of their atmospheric flows than is the case for solar system planets. Radiation hydrodynamics may also influence radiative transfer in other classes of hot exoplanetary atmospheres with fast winds.

GALEX near-ultraviolet (NUV) and far-ultraviolet (FUV) light curves of three extremely low accretion rate polars show distinct modulations in their UV light curves. While these three systems have a range of magnetic fields from 13 to 70 MG, and of late-type secondaries (including a likely brown dwarf in SDSSJ121209.31+013627.7), the accretion rates are similar, and the UV observations imply some mechanism is operating to create enhanced emission zones on the white dwarf. The UV variations match in phase to the two magnetic poles viewed in the optical in WX LMi and to the single poles evident in the optical in SDSSJ1212109.31+013627.7 and SDSSJ103100.55+202832.2. Simple spot models of the UV light curves show that if hot spots are responsible for the UV variations, the temperatures are on the order of 10,000–14,000 K. For the single pole systems, the size of the FUV spot must be smaller than the NUV and in all cases the geometry is likely more complicated than a simple circular spot.

High angular-resolution images of the J = 18_K–17_K emission of CH₃CN in the Orion KL molecular core were observed with the Submillimeter Array (SMA). Our high-resolution observations clearly reveal that CH₃CN emission originates mainly from the Orion Hot Core and the Compact Ridge, both within ∼15'' of the warm and dense part of Orion KL. The clumpy nature of the molecular gas in Orion KL can also be readily seen from our high-resolution SMA images. In addition, a semi-open cavity-like kinematic structure is evident at the location between the Hot Core and the Compact Ridge. We performed excitation analysis with the "population diagram" method toward the Hot Core, IRc7, and the northern part of the Compact Ridge. Our results disclose a non-uniform temperature structure on small scales in Orion KL, with a range of temperatures from 190–620 K in the Hot Core. Near the Compact Ridge, the temperatures are found to be 170–280 K. Comparable CH₃CN fractional abundances of 10⁻⁸ to 10⁻⁷ are found around both in the Hot Core and the Compact Ridge. Such high abundances require that a hot gas phase chemistry, probably involving ammonia released from grain mantles, plays an important role in forming these CH₃CN molecules.

The precision of cosmological parameters derived from galaxy cluster surveys is limited by uncertainty in relating observable signals to cluster mass. We demonstrate that a small mass-calibration follow-up program can significantly reduce this uncertainty and improve parameter constraints, particularly when the follow-up targets are judiciously chosen. To this end, we apply a simulated annealing algorithm to maximize the dark energy information at fixed observational cost, and find that optimal follow-up strategies can reduce the observational cost required to achieve a specified precision by up to an order of magnitude. Considering clusters selected from optical imaging in the Dark Energy Survey, we find that approximately 200 low-redshift X-ray clusters or massive Sunyaev–Zel'dovich clusters can improve the dark energy figure of merit by 50%, provided that the follow-up mass measurements involve no systematic error. In practice, the actual improvement depends on (1) the uncertainty in the systematic error in follow-up mass measurements, which needs to be controlled at the 5% level to avoid severe degradation of the results and (2) the scatter in the optical richness–mass distribution, which needs to be made as tight as possible to improve the efficacy of follow-up observations.

We begin an exploration of the capacity of the stationary accretion shock instability (SASI) to generate magnetic fields by adding a weak, stationary, and radial (but bipolar) magnetic field, and in some cases rotation, to an initially spherically symmetric fluid configuration that models a stalled shock in the post-bounce supernova environment. In axisymmetric simulations, we find that cycles of latitudinal flows into and radial flows out of the polar regions amplify the field parallel to the symmetry axis, typically increasing the total magnetic energy by about 2 orders of magnitude. Non-axisymmetric calculations result in fundamentally different flows and a larger magnetic energy increase: shearing associated with the SASI spiral mode contributes to a widespread and turbulent field amplification mechanism, boosting the magnetic energy by almost 4 orders of magnitude (a result which remains very sensitive to the spatial resolution of the numerical simulations). While the SASI may contribute to neutron star magnetization, these simulations do not show qualitatively new features in the global evolution of the shock as a result of SASI-induced magnetic field amplification.

We observed the Galactic black hole candidate H1743−322 with Suzaku for approximately 32 ks, while the source was in a low/hard state during its 2008 outburst. We collected and analyzed the data with the HXD/PIN, HXD/GSO, and XIS cameras spanning the energy range 0.7–200 keV. Fits to the spectra with simple models fail to detect narrow Fe xxv and Fe xxvi absorption lines, with 90% confidence upper limits of 3.5 and 2.5 eV on the equivalent width, respectively. These limits are commensurate with those in the very high state, but are well below the equivalent widths of lines detected in the high/soft state, suggesting that disk winds are partially state-dependent. We discuss these results in the context of previous detections of ionized Fe absorption lines in H1743−322 and connections to winds and jets in accreting systems. Additionally, we report the possible detection of disk reflection features, including an Fe K emission line.

Dynamical masses have been obtained by Dupuy et al. for the brown dwarf binary HD 130948BC. The components have luminosities log (L/L_☉) of −3.82 and −3.90, and masses of 0.0555 and 0.0530 M_☉. In a luminosity–age diagram, Dupuy et al. found that L_bol for both B and C are brighter than theoretical tracks by factors of 2–3, if the age of the system is as old as their estimate of 0.79 Gyr (based on gyrochronology). Here, we apply our model of magnetic convection, in which the onset of convection is impeded in the presence of a vertical magnetic field: our goal is to replicate the observed properties not only in the luminosity–age diagram, but simultaneously in the T_eff–age diagram and in the H−R diagram. Expressing the internal magnetic pressure as a fraction δ of the gas pressure, we obtain evolutionary tracks which fit both stars in an H−R diagram provided that δ lies in the range 0.007–0.038. With such values of δ, our models replicate the observed luminosities of both B and C, provided that the age is no larger than ∼0.39 Gyr. This is significantly younger than the mean age estimated by Dupuy et al. for the primary star in the system, HD 130948A. However, there is sufficient uncertainty in the empirical parameters that an age as young as the one suggested by our magnetic models (∼0.39 Gyr) is marginally within the permitted range.

We present the analysis of an XMM-Newton observation of the Seyfert galaxy NGC 2992. The source was found in its highest level of X-ray activity yet detected, a factor ∼23.5 higher in the 2–10 keV flux than the historical minimum. NGC 2992 is known to exhibit X-ray flaring activity on timescales of days to weeks, and the XMM-Newton data provide at least a factor of ∼3 better spectral resolution in the Fe K band than any previously measured flaring X-ray state. We find that there is a broad feature in the ∼5–7 keV band that could be interpreted as a relativistic Fe Kα emission line. Its flux appears to have increased in tandem with the 2–10 keV continuum when compared to a previous Suzaku observation when the continuum was a factor of ∼8 lower than that during the XMM-Newton observation. The XMM-Newton data are consistent with the general picture that increased X-ray activity and corresponding changes in the Fe Kα line emission occur in the innermost regions of the putative accretion disk. This behavior contrasts with the behavior of other active galactic nuclei in which the Fe Kα line does not respond to variability in the X-ray.

The installation of the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) will revolutionize the study of high-redshift galaxy populations. Initial observations of the HST Ultra Deep Field (UDF) have yielded multiple z ≳ 7 dropout candidates. Supplemented by the GOODS Early Release Science (ERS) and further UDF pointings, these data will provide crucial information about the most distant known galaxies. However, achieving tight constraints on the z ∼ 7 galaxy luminosity function (LF) will require even more ambitious photometric surveys. Using a Fisher matrix approach to fully account for Poisson and cosmic sample variance, as well as covariances in the data, we estimate the uncertainties on LF parameters achieved by surveys of a given area and depth. Applying this method to WFC3 z ∼ 7 dropout galaxy samples, we forecast the LF parameter uncertainties for a variety of model surveys. We demonstrate that performing a wide area (∼1 deg²) survey to H_AB ∼ 27 depth or increasing the UDF depth to H_AB ∼ 30 provides excellent constraints on the high-z LF when combined with the existing Ultradeep Field Guest Observation and GOODS ERS data. We also show that the shape of the matter power spectrum may limit the possible gain of splitting wide area (≳0.5 deg²) high-redshift surveys into multiple fields to probe statistically independent regions; the increased rms density fluctuations in smaller volumes mostly offset the improved variance gained from independent samples.

We study the velocity field of umbral dots (UDs) at a resolution of 014. Our analysis is based on full Stokes measurements of a pore taken with the Crisp Imaging Spectro-Polarimeter at the Swedish 1 m Solar Telescope. We determine the flow velocity at different heights in the photosphere from a bisector analysis of the Fe i 630 nm lines. In addition, we use the observed Stokes Q, U, and V profiles to characterize the magnetic properties of these structures. We find that most UDs are associated with strong upflows in deep photospheric layers. Some of them also show concentrated patches of downflows at their edges, with sizes of about 025, velocities of up to 1000 m s⁻¹, and enhanced net circular polarization signals. The downflows evolve rapidly and have lifetimes of only a few minutes. These results appear to validate numerical models of magnetoconvection in the presence of strong magnetic fields.

Observational evidence is presented for the merging of a downward-propagating plasmoid with a looptop kernel during an occulted limb event on 2007 January 25. RHESSI light curves in the 9–18 keV energy range, as well as that of the 245 MHz channel of the Learmonth Solar Observatory, show enhanced nonthermal emission in the corona at the time of the merging suggesting that additional particle acceleration took place. This was attributed to a secondary episode of reconnection in the current sheet that formed between the two merging sources. RHESSI images were used to establish a mean downward velocity of the plasmoid of 12 km s⁻¹. Complementary observations from the SECCHI suite of instruments on board STEREO-B showed that this process occurred during the acceleration phase of the associated coronal mass ejection (CME). From wavelet-enhanced EUV Imager, image evidence of inflowing magnetic field lines prior to the CME eruption is also presented. The derived inflow velocity was found to be 1.5 km s⁻¹. This combination of observations supports a recent numerical simulation of plasmoid formation, propagation, and subsequent particle acceleration due to the tearing mode instability during current sheet formation.

The evolution of the galaxy stellar mass function is especially useful to test the current model of galaxy formation. Observational data have revealed a few inconsistencies with predictions from the ΛCDM model. For example, most massive galaxies have already been observed at very high redshifts, and they have experienced only mild evolution since then. In conflict with this, semi-analytical models (SAMs) of galaxy formation predict an insufficient number of massive galaxies at high redshift and a rapid evolution between redshift 1 and 0. In addition, there is a strong correlation between star formation rate (SFR) and stellar mass for star-forming galaxies, which can be roughly reproduced with the model, but with a normalization that is too low at high redshift. Furthermore, the stellar mass density obtained from the integral of the cosmic star formation history is higher than the measured one by a factor of 2. In this paper, we study these issues using an SAM that includes (1) cold gas accretion in massive halos at high redshift; (2) tidal stripping of stellar mass from satellite galaxies; and (3) an evolving stellar initial mass function (IMF; bottom-light) with a higher gas recycle fraction. Our results show that the combined effects from (1) and (2) can predict sufficiently massive galaxies at high redshifts and reproduce their mild evolution at low redshift, while the combined effects of (1) and (3) can reproduce the correlation between SFR and stellar mass for star-forming galaxies across a wide range of redshifts. A bottom-light/top-heavy stellar IMF could partly resolve the conflict between the stellar mass density and cosmic star formation history.

We infer the three-dimensional magnetic structure of a transient horizontal magnetic field (THMF) during its evolution through the photosphere using SIRGAUS inversion code. The SIRGAUS code is a modified version of SIR (Stokes Inversion based on Response function), and allows for retrieval of information on the magnetic and thermodynamic parameters of the flux tube embedded in the atmosphere from the observed Stokes profiles. Spectropolarimetric observations of the quiet Sun at the disk center were performed with the Solar Optical Telescope on board Hinode with Fe i 630.2 nm lines. Using repetitive scans with a cadence of 130 s, we first detect the horizontal field that appears inside a granule, near its edge. On the second scan, vertical fields with positive and negative polarities appear at both ends of the horizontal field. Then, the horizontal field disappears leaving the bipolar vertical magnetic fields. The results from the inversion of the Stokes spectra clearly point to the existence of a flux tube with magnetic field strength of ∼400 G rising through the line-forming layer of the Fe i 630.2 nm lines. The flux tube is located at around log τ₅₀₀ ∼ 0 at Δt = 0 s and around log τ₅₀₀ ∼ −1.7 at Δt = 130 s. At Δt = 260 s, the horizontal part is already above the line-forming region of the analyzed lines. The observed Doppler velocity is maximally 3 km s⁻¹, consistent with the upward motion of the structure as retrieved from the SIRGAUS code. The vertical size of the tube is smaller than the thickness of the line-forming layer. The THMF has a clear Ω-shaped loop structure with the apex located near the edge of a granular cell. The magnetic flux carried by this THMF is estimated to be 3.1 × 10¹⁷ Mx.

Many of the most exciting questions in astrophysics and cosmology, including the majority of observational probes of dark energy, rely on an understanding of the nonlinear regime of structure formation. In order to fully exploit the information available from this regime and to extract cosmological constraints, accurate theoretical predictions are needed. Currently, such predictions can only be obtained from costly, precision numerical simulations. This paper is the third in a series aimed at constructing an accurate calibration of the nonlinear mass power spectrum on Mpc scales for a wide range of currently viable cosmological models, including dark energy models with w ≠ −1. The first two papers addressed the numerical challenges and the scheme by which an interpolator was built from a carefully chosen set of cosmological models. In this paper, we introduce the "Coyote Universe" simulation suite which comprises nearly 1000 N-body simulations at different force and mass resolutions, spanning 38 w CDM cosmologies. This large simulation suite enables us to construct a prediction scheme, or emulator, for the nonlinear matter power spectrum accurate at the percent level out to k ≃ 1 h Mpc⁻¹. We describe the construction of the emulator, explain the tests performed to ensure its accuracy, and discuss how the central ideas may be extended to a wider range of cosmological models and applications. A power spectrum emulator code is released publicly as part of this paper.

Uninhibited radiative cooling in clusters of galaxies would lead to excessive mass accretion rates contrary to observations. One of the key proposals to offset radiative energy losses is thermal conduction from outer, hotter layers of cool core (CC) clusters to their centers. However, thermal conduction is sensitive to magnetic field topology. In CC clusters where temperature decreases inwards, the heat buoyancy instability (HBI) leads to magnetic fields ordered preferentially in the direction perpendicular to that of gravity, which significantly reduces the level of conduction below the classical Spitzer–Braginskii value. However, the CC clusters are rarely in perfect hydrostatic equilibrium. Sloshing motions due to minor mergers and stirring motions induced by cluster galaxies or active galactic nuclei can significantly perturb the gas. The turbulent cascade can then affect the topology of the magnetic field and the effective level of thermal conduction. We perform three-dimensional adaptive mesh refinement magnetohydrodynamical simulations of the effect of turbulence on the properties of the anisotropic thermal conduction in CC clusters. We show that very weak subsonic motions, well within observational constraints, can randomize the magnetic field and significantly boost effective thermal conduction beyond the saturated values expected in the pure unperturbed HBI case. We find that the turbulent motions can essentially restore the conductive heat flow to the CC to level comparable to the theoretical maximum of ∼1/3 Spitzer for a highly tangled field. Runs with radiative cooling show that the cooling catastrophe can be averted and the cluster core stabilized; however, this conclusion may depend on the central gas density. Above a critical Froude number, these same turbulent motions also eliminate the tangential bias in the velocity and magnetic field that is otherwise induced by the trapped g-modes, and possibly allow significant turbulent heat diffusion. Our results can be tested with future radio polarization measurements and have implications for efficient metal dispersal in clusters.

The age distribution of star clusters in nearby galaxies plays a crucial role in evaluating the lifetimes and disruption mechanisms of the clusters. Two very different results have been recently found for the age distribution χ(τ) of clusters in the Large Magellanic Cloud (LMC). We found that χ(τ) can be approximately described by a power law χ(τ) ∝ τ^γ, with γ ≈ −0.8, by counting clusters in the mass–age plane, i.e., by constructing χ(τ) directly from mass-limited samples. Gieles & Bastian inferred a value of γ ≈ 0, based on the slope of the relation between the maximum mass of clusters in equal intervals of log τ, hereafter, the M_max method, an indirect technique that requires additional assumptions about the upper end of the mass function. However, our own analysis shows that the M_max method gives a result consistent with our direct counting method for clusters in the LMC, namely, χ(τ) ∝ τ^−0.8 for τ ≲ 10⁹ yr. The reason for the apparent discrepancy is that our analysis includes many intermediate and high-mass clusters (M > 1.5 × 10³ M_☉), which formed recently (τ ≲ 10⁷ yr), and which are known to exist in the LMC, whereas Gieles & Bastian are missing such clusters. We compile recent results from the literature showing that the age distribution of young star clusters in more than a dozen galaxies, including dwarf and giant galaxies, isolated and interacting galaxies, and irregular and spiral galaxies, has a similar declining shape. We interpret this approximately "universal" shape as primarily due to the progressive disruption of star clusters over their first ∼few × 10⁸ yr, starting soon after formation, and discuss some observational and physical implications of this early disruption for stellar populations in galaxies.

The standing accretion shock instability (SASI) is commonly believed to be responsible for large amplitude dipolar oscillations of the stalled shock during core collapse, potentially leading to an asymmetric supernovae explosion. The degree of asymmetry depends on the amplitude of SASI, but the nonlinear saturation mechanism has never been elucidated. We investigate the role of parasitic instabilities as a possible cause of nonlinear SASI saturation. As the shock oscillations create both vorticity and entropy gradients, we show that both Kelvin–Helmholtz and Rayleigh–Taylor types of instabilities are able to grow on a SASI mode if its amplitude is large enough. We obtain simple estimates of their growth rates, taking into account the effects of advection and entropy stratification. In the context of the advective–acoustic cycle, we use numerical simulations to demonstrate how the acoustic feedback can be decreased if a parasitic instability distorts the advected structure. The amplitude of the shock deformation is estimated analytically in this scenario. When applied to the set up of Fernández & Thompson, this saturation mechanism is able to explain the dramatic decrease of the SASI power when both the nuclear dissociation energy and the cooling rate are varied. Our results open new perspectives for anticipating the effect, on the SASI amplitude, of the physical ingredients involved in the modeling of the collapsing star.

Type II-plateau supernovae (SNe IIP) are the results of the explosions of red supergiants and are the most common subclass of core-collapse supernovae. Past observations have shown that the outer layers of the ejecta of SNe IIP are largely spherical, but the degree of asphericity increases toward the core. We present evidence for high degrees of asphericity in the inner cores of three recent SNe IIP (SNe 2006my, 2006ov, and 2007aa), as revealed by late-time optical spectropolarimetry. The three objects were all selected to have very low interstellar polarization (ISP), which minimizes the uncertainties in ISP removal and allows us to use the continuum polarization as a tracer of asphericity. The three objects have intrinsic continuum polarizations in the range of 0.83%–1.56% in observations taken after the end of the photometric plateau, with the polarization dropping to almost zero at the wavelengths of strong emission lines. Our observations of SN 2007aa at earlier times, taken on the photometric plateau, show contrastingly smaller continuum polarizations (∼0.1%). The late-time Hα and [O i] line profiles of SN 2006ov provide further evidence for asphericities in the inner ejecta. Such high core polarizations in very ordinary core-collapse supernovae provide further evidence that essentially all core-collapse supernova explosions are highly aspherical, even if the outer parts of the ejecta show only small deviations from spherical symmetry.

Theoretical and observational studies on the turbulence of the interstellar medium developed fast in the past decades. The theory of supersonic magnetized turbulence, as well as the understanding of the projection effects of observed quantities, is still in progress. In this work, we explore the characterization of the turbulent cascade and its damping from observational spectral line profiles. We address the difference of ion and neutral velocities by clarifying the nature of the turbulence damping in the partially ionized. We provide theoretical arguments in favor of the explanation of the larger Doppler broadening of lines arising from neutral species compared to ions as arising from the turbulence damping of ions at larger scales. Also, we compute a number of MHD numerical simulations for different turbulent regimes and explicit turbulent damping, and compare both the three-dimensional distributions of velocity and the synthetic line profile distributions. From the numerical simulations, we place constraints on the precision with which one can measure the three-dimensional dispersion depending on the turbulence sonic Mach number. We show that no universal correspondence between the three-dimensional velocity dispersions measured in the turbulent volume and minima of the two-dimensional velocity dispersions available through observations exist. For instance, for subsonic turbulence the correspondence is poor at scales much smaller than the turbulence injection scale, while for supersonic turbulence the correspondence is poor for the scales comparable with the injection scale. We provide a physical explanation of the existence of such a two-dimensional to three-dimensional correspondence and discuss the uncertainties in evaluating the damping scale of ions that can be obtained from observations. However, we show that the statistics of velocity dispersion from observed line profiles can provide the spectral index and the energy transfer rate of turbulence. Also, by comparing two similar simulations with different viscous coefficients, it was possible to constrain the turbulent cut-off scale. This may especially prove useful since it is believed that ambipolar diffusion may be one of the dominant dissipative mechanisms in star-forming regions. In this case, the determination of the ambipolar diffusion scale may be used as a complementary method for the determination of magnetic field intensity in collapsing cores. We discuss the implications of our findings in terms of a new approach to magnetic field measurement proposed by Li & Houde.

Many observations of suprathermal and energetic particles in the solar wind and the inner heliosheath show that distribution functions scale approximately with the inverse of particle speed (v) to the fifth power. Although there are exceptions to this behavior, there is a growing need to understand why this type of distribution function appears so frequently. This paper develops the concept that a superposition of exponential and Gaussian distributions with different characteristic speeds and temperatures show power-law tails. The particular type of distribution function, f ∝ v⁻⁵, appears in a number of different ways: (1) a series of Poisson-like processes where entropy is maximized with the rates of individual processes inversely proportional to the characteristic exponential speed, (2) a series of Gaussian distributions where the entropy is maximized with the rates of individual processes inversely proportional to temperature and the density of individual Gaussian distributions proportional to temperature, and (3) a series of different diffusively accelerated energetic particle spectra with individual spectra derived from observations (1997–2002) of a multiplicity of different shocks. Thus, we develop a proof-of-concept for the superposition of stochastic processes that give rise to power-law distribution functions.

We present low- and high-resolution mid-infrared (mid-IR) spectra and photometry for eight compact symmetric objects (CSOs) taken with the Infrared Spectrograph on the Spitzer Space Telescope. The hosts of these young, powerful radio galaxies show significant diversity in their mid-IR spectra. This includes multiple atomic fine-structure lines, H₂ gas, polycyclic aromatic hydrocarbon (PAH) emission, warm dust from T = 50to150 K, and silicate features in both emission and absorption. There is no evidence in the mid-IR of a single template for CSO hosts, but 5/8 galaxies show similar moderate levels of star formation (<10 M_☉ yr⁻¹ from PAH emission) and silicate dust in a clumpy torus. The total amount of extinction ranges from A_V ∼ 10to30, and the high-ionization [Ne v] 14.3 and 24.3 μm transitions are not detected for any galaxy in the sample. Almost all CSOs show contributions both from star formation and active galactic nuclei (AGNs), suggesting that they occupy a continuum between pure starbursts and AGNs. This is consistent with the hypothesis that radio galaxies are created following a galactic merger; the timing of the radio activity onset means that contributions to the IR luminosity from both merger-induced star formation and the central AGN are likely. Bondi accretion is capable of powering the radio jets for almost all CSOs in the sample; the lack of [Ne v] emission suggests an advection-dominated accretion flow mode as a possible candidate. Merging black holes (BHs) with M_BH > 10⁸ M_☉ likely exist in all of the CSOs in the sample; however, there is no direct evidence from these data that BH spin energy is being tapped as an alternative mode for powering the radio jets.