Table of contents

We present the results of a 400 ks Chandra survey of 29 extended Lyα emitting nebulae (Lyα Blobs, LABs) in the z = 3.09 protocluster in the SS A22 field. We detect luminous X-ray counterparts in five LABs, implying a large fraction of active galactic nuclei (AGN) in LABs, f_AGN = 17⁺¹²₋₇% down to L_2–32 keV ∼ 10⁴⁴ erg s⁻¹. All of the AGN appear to be heavily obscured, with spectral indices implying obscuring column densities of N_H > 10²³ cm⁻². The AGN fraction should be considered a lower limit, since several more LABs not detected with Chandra show AGN signatures in their mid-infrared (mid-IR) emission. We show that the UV luminosities of the AGN are easily capable of powering the extended Lyα emission via photoionization alone. When combined with the UV flux from a starburst component, and energy deposited by mechanical feedback, we demonstrate that "heating" by a central source, rather than gravitational cooling is the most likely power source of LABs. We argue that all LABs could be powered in this manner, but that the luminous host galaxies are often just below the sensitivity limits of current instrumentation, or are heavily obscured. No individual LABs show evidence for extended X-ray emission, and a stack equivalent to a ≳9 Ms exposure of an average LAB also yields no statistical detection of a diffuse X-ray component. The resulting diffuse X-ray/Lyα luminosity limit implies there is no hot (T ≳ 10⁷ K) gas component in these halos, and also rules out inverse Compton scattering of cosmic microwave background photons, or local far-IR photons, as a viable power source for LABs.

We present a model for the dispersal of protoplanetary disks by winds from either the central star or the inner disk. These winds obliquely strike the flaring disk surface and strip away disk material by entraining it in an outward radial-moving flow at the wind–disk interface, which lies several disk scale heights above the midplane. The disk dispersal time depends on the entrainment velocity, v_d = c_s, at which disk material flows into this turbulent shear layer interface, where is a scale factor and c_s is the local sound speed in the disk surface just below the entrainment layer. If ∼ 0.1, a likely upper limit, the dispersal time at 1 AU is ∼6 Myr for a disk with a surface density of 10³ g cm⁻², a solar mass central star, and a wind with an outflow rate $\dot{M}_{w}=10^{-8}\;{M}_{\odot }\mbox{ yr}^{-1}$ and terminal velocity v_w = 200kms⁻¹. When compared with photoevaporation and viscous evolution, wind stripping can be a dominant mechanism only for the combination of low accretion rates (≲10⁻⁸ M_☉ yr⁻¹) and wind outflow rates approaching these accretion rates. This case is unusual since generally outflow rates are ≲0.1 of accretion rates.

We present results of a spectroscopic search for Lyα emitters (LAEs) in the Cl1604 supercluster field using the extensive spectroscopic Keck/DEep Imaging Multi-Object Spectrograph database taken as part of the Observations of Redshift Evolution in Large-Scale Environments survey. A total of 12 slitmasks were observed and inspected in the Cl1604 field, spanning a survey volume of 1.365 × 10⁴ comoving Mpc³. We find a total of 17 high-redshift (4.39 ⩽ z ⩽ 5.67) LAE candidates down to a limiting flux of 1.9 × 10⁻¹⁸ erg s⁻¹ cm⁻² (L(Lyα) = 4.6 × 10⁴¹ erg s⁻¹ or ∼0.1 L_* at z ∼ 5), 13 of which we classify as high quality. The resulting LAE number density is nearly double that of LAEs found in the Subaru deep field at z ∼ 4.9 and nearly an order of magnitude higher than in other surveys of LAEs at similar redshifts, an excess that is essentially independent of LAE luminosity. We also report on the discovery of two possible LAE group structures at z ∼ 4.4 and z ∼ 4.8 and investigate the effects of cosmic variance of LAEs on our results. Fitting a simple truncated single Gaussian model to a composite spectrum of the 13 high-quality LAE candidates, we find a best-fit stellar velocity dispersion of 136 km s⁻¹. Additionally, we see modest evidence of a second peak in the composite spectrum, possibly caused by galactic outflows, offset from the main velocity centroid of the LAE population by ∼440 km s⁻¹ as well as evidence for a nontrivial Lyα escape fraction. We find an average star formation rate density (SFRD) of ∼5 × 10⁻³ M_☉ yr⁻¹ Mpc⁻³ with moderate evidence for negative evolution in the SFRD from z ∼ 4.6 to z ∼ 5.7. By simulating the statistical flux loss due to our observational setup, we measure a best-fit luminosity function characterized by Φ_*L_* = 2.2^+3.9_−1.3 × 10³⁹ erg s⁻¹ Mpc⁻³ for α = −1.6, generally consistent with measurements from other surveys at similar epochs. Finally, we investigate any possible effects from weak or strong gravitational lensing induced by the foreground supercluster, finding that our LAE candidates are minimally affected by lensing processes.

We present black hole masses and accretion rates for 182 Type 1 active galactic nuclei (AGNs) in COSMOS. We estimate masses using the scaling relations for the broad H β, Mg ii, and C iv emission lines in the redshift ranges 0.16 < z < 0.88, 1 < z < 2.4, and 2.7 < z < 4.9. We estimate the accretion rate using an Eddington ratio L_I/L_Edd estimated from optical and X-ray data. We find that very few Type 1 AGNs accrete below L_I/L_Edd ∼ 0.01, despite simulations of synthetic spectra which show that the survey is sensitive to such Type 1 AGNs. At lower accretion rates the broad-line region may become obscured, diluted, or nonexistent. We find evidence that Type 1 AGNs at higher accretion rates have higher optical luminosities, as more of their emission comes from the cool (optical) accretion disk with respect to shorter wavelengths. We measure a larger range in accretion rate than previous works, suggesting that COSMOS is more efficient at finding low accretion rate Type 1 AGNs. However, the measured range in accretion rate is still comparable to the intrinsic scatter from the scaling relations, suggesting that Type 1 AGNs accrete at a narrow range of Eddington ratio, with L_I/L_Edd ∼ 0.1.

This paper describes a near-UV/VIS study of a pyrene:H₂O interstellar ice analogue at 10 K using optical absorption spectroscopy. A new experimental approach makes it possible to irradiate the sample with vacuum ultraviolet (VUV) light (7–10.5 eV) while simultaneously recording spectra in the 240–1000 nm range with subsecond time resolution. Both spectroscopic and dynamic information on VUV processed ices are obtained in this way. This provides a powerful tool to follow, in situ and in real time, the photophysical and photochemical processes induced by VUV irradiation of a polycyclic aromatic hydrocarbon containing inter- and circumstellar ice analogue. Results on the VUV photolysis of a prototype sample—strongly diluted pyrene in H₂O ice—are presented. In addition to the pyrene cation (Py⁺), other products—hydroxypyrene (PyOH), possibly hydroxypyrene cation (PyOH⁺), and pyrene/pyrenolate anion (Py⁻/PyO⁻)—are observed. It is found that the charge remains localized in the ice, also after the VUV irradiation is stopped. The astrochemical implications and observational constraints are discussed.

We study the effects of turbulence on magnetic reconnection using three-dimensional direct numerical simulations. This is the first attempt to test a model of fast magnetic reconnection in the presence of weak turbulence proposed by Lazarian & Vishniac. This model predicts that weak turbulence, which is generically present in most astrophysical systems, enhances the rate of reconnection by reducing the transverse scale for reconnection events and by allowing many independent flux reconnection events to occur simultaneously. As a result, the reconnection speed becomes independent of Ohmic resistivity and is determined by the magnetic field wandering induced by turbulence. We test the dependence of the reconnection speed on turbulent power, the energy injection scale, and resistivity. We apply the open and experiment with the outflow boundary conditions in our numerical model and discuss the advantages and drawbacks of various setups. To test our results, we also perform simulations of turbulence with the same outflow boundaries but without a large-scale field reversal, thus without large-scale reconnection. To quantify the reconnection speed we use both an intuitive definition, i.e., the speed of the reconnected flux inflow, and a more sophisticated definition based on a formally derived analytical expression. Our results confirm the predictions of the Lazarian and Vishniac model. In particular, we find that the reconnection speed is proportional to the square root of the injected power, as predicted by the model. The dependence on the injection scale for some of our models is a bit weaker than expected, i.e., l^3/4_inj, compared to the predicted linear dependence on the injection scale, which may require some refinement of the model or may be due to effects such as the finite size of the excitation region, which are not a part of the model. The reconnection speed was found to depend on the expected rate of magnetic field wandering and not on the magnitude of the guide field. In our models, we see no dependence on the guide field when its strength is comparable to the reconnected component. More importantly, while in the absence of turbulence we successfully reproduce the Sweet–Parker scaling of reconnection, in the presence of turbulence we do not observe any dependence on Ohmic resistivity, confirming that the reconnection of the weakly stochastic field is fast. We also do not observe a dependence on anomalous resistivity, which suggests that the presence of anomalous effects, e.g., Hall MHD effects, may be irrelevant for astrophysical systems with weakly stochastic magnetic fields.

We present high angular resolution observations of the NH₃(1, 1), (2, 2), and (3, 3) inversion transitions from the Egg nebula, the archetypical protoplanetary nebula. The spatial distribution and kinematics of the emission in all three lines show four distinct components or lobes that are aligned with the polar and equatorial directions. The kinematics of the NH₃ emission is also found to follow a clear pattern: redshifted emission in the south and west and blueshifted emission in the north and east. The morphology and spatial kinematics of NH₃ emission are shown to have strong similarity to that observed previously in molecular hydrogen emission and CO emission which arise from the shocked molecular gas. We also find that the higher lying inversion transition NH₃ (2, 2) and (3, 3) are stronger in the polar direction in comparison to the lower transition NH₃ (1, 1). We conclude that the NH₃ emission traces the warm molecular gas, which is shocked and heated by the interaction between the high-velocity outflows and the surrounding envelope. The presence of strong ammonia emission associated with the shock fronts and the lack of the emission at the center of the nebula indicate that the abundance of ammonia is significantly enhanced by shocks, a situation very similar to that found in outflows from protostars.

We revisit the flip-flop instability of two-dimensional planar accretion using high-fidelity numerical simulations. By starting from an initially steady-state axisymmetric solution, we are able to follow the growth of this overstability from small amplitudes. In the small-amplitude limit, before any transient accretion disk is formed, the oscillation period of the accretion shock is comparable to the Keplerian period at the Hoyle–Lyttleton accretion radius (R_a), independent of the size of the accreting object. The growth rate of the overstability increases dramatically with decreasing size of the accretor, but is relatively insensitive to the upstream Mach number of the flow. We confirm that the flip-flop does not require any gradient in the upstream flow. Indeed, a small density gradient as used in the discovery simulations has virtually no influence on the growth rate of the overstability. The ratio of specific heats does influence the overstability, with smaller γ leading to faster growth of the instability. For a relatively large accretor (a radius of 0.037 R_a) planar accretion is unstable for γ = 4/3, but stable for γ ⩾ 1.6. Planar accretion is unstable even for γ = 5/3 provided the accretor has a radius of < 0.0025 R_a. We also confirm that when the accretor is sufficiently small, the secular evolution is described by sudden jumps between states with counter-rotating quasi-Keplerian accretion disks.

We present a result of age estimation for star clusters in M33. We obtain color–magnitude diagrams (CMDs) of resolved stars in 242 star clusters from the Hubble Space Telescope/Wide Field Planetary Camera 2 images. We estimate ages of 100 star clusters among these, by fitting the Padova theoretical isochrones to the observational CMDs. Age distribution of the star clusters shows a dominant peak at log(t) ∼ 7.8. Majority of star clusters are younger than log(t) = 9.0, while 10 star clusters are older than log(t) ∼ 9.0. There is only one cluster younger than log(t) = 7 in this study, which is in contrast with the results based on the integrated photometry of star clusters in the previous studies. Radial distribution of the cluster ages shows that young- to intermediate-age clusters are found from the center to the outer region, while old clusters are distributed farther from the M33 center. We briefly discuss the implication of the results with regard to the formation of the M33 cluster system.

Many of the Mira stars observed with adequate spatial resolution show detectable asymmetry. This asymmetry can be caused by an asymmetric stellar photosphere and/or asymmetric envelope around the star and can be the origin of asymmetries in the subsequent planetary nebula. In this paper, we present the results of long baseline interferometric observations of the Mira-type star U Ori at 1.51 (H₂O band), 1.64 (pseudocontinuum), and 1.78 (H₂O band) μm in 2005. We performed model-independent image reconstruction of the envelope around the star using measured visibilities and closure phases. The images show asymmetric structure of the U Ori envelope that is similar to the structure of 22 GHz H₂O masers obtained by Vlemmings et al. in 2003. Further comparison of near infrared images with available radio maps gives some evidence for differential rotation of the envelope with rotational velocities varying between 3 and 5 km s⁻¹. Finally, we discuss the geometric and kinematic structure of the U Ori envelope based on a model of an almost face-on expanding and rotating disk around the star.

We present infrared (IR) luminosities, star formation rates (SFR), colors, morphologies, locations, and active galactic nuclei (AGNs) properties of 24 μm detected sources in photometrically detected high-redshift clusters in order to understand the impact of environment on star formation (SF) and AGN evolution in cluster galaxies. We use three newly identified z = 1 clusters selected from the IRAC dark field; the deepest ever mid-IR survey with accompanying, 14 band multiwavelength data including deep Hubble Space Telescope imaging and deep wide-area Spitzer MIPS 24 μm imaging. We find 90 cluster members with MIPS detections within two virial radii of the cluster centers, of which 17 appear to have spectral energy distributions dominated by AGNs and the rest dominated by SF. We find that 43% of the star-forming sample have IR luminosities L_IR > 10¹¹L_☉ (luminous IR galaxies). The majority of sources (81%) are spirals or irregulars. A large fraction (at least 25%) show obvious signs of interactions. The MIPS-detected member galaxies have varied spatial distributions as compared to the MIPS-undetected members with one of the three clusters showing SF galaxies being preferentially located on the cluster outskirts, while the other two clusters show no such trend. Both the AGN fraction and the summed SFR of cluster galaxies increase from redshift zero to one, at a rate that is a few times faster in clusters than over the same redshift range in the field. Cluster environment does have an effect on the evolution of both AGN fraction and SFR from redshift one to the present, but does not affect the IR luminosities or morphologies of the MIPS sample. SF happens in the same way regardless of environment making MIPS sources look the same in the cluster and field, however the cluster environment does encourage a more rapid evolution with time as compared to the field.

We are using the Very Long Baseline Array and the Japanese VLBI Exploration of Radio Astronomy project to measure trigonometric parallaxes and proper motions of masers found in high-mass star-forming regions across the Milky Way. Early results from 18 sources locate several spiral arms. The Perseus spiral arm has a pitch angle of 16° ± 3°, which favors four rather than two spiral arms for the Galaxy. Combining positions, distances, proper motions, and radial velocities yields complete three-dimensional kinematic information. We find that star-forming regions on average are orbiting the Galaxy ≈15 km s⁻¹ slower than expected for circular orbits. By fitting the measurements to a model of the Galaxy, we estimate the distance to the Galactic center R₀ = 8.4 ± 0.6 kpc and a circular rotation speed Θ₀ = 254 ± 16 km s⁻¹. The ratio Θ₀/R₀ can be determined to higher accuracy than either parameter individually, and we find it to be 30.3 ± 0.9 km s⁻¹ kpc⁻¹, in good agreement with the angular rotation rate determined from the proper motion of Sgr A*. The data favor a rotation curve for the Galaxy that is nearly flat or slightly rising with Galactocentric distance. Kinematic distances are generally too large, sometimes by factors greater than 2; they can be brought into better agreement with the trigonometric parallaxes by increasing Θ₀/R₀ from the IAU recommended value of 25.9 km s⁻¹ kpc⁻¹ to a value near 30 km s⁻¹ kpc⁻¹. We offer a "revised" prescription for calculating kinematic distances and their uncertainties, as well as a new approach for defining Galactic coordinates. Finally, our estimates of Θ₀ and Θ₀/R₀, when coupled with direct estimates of R₀, provide evidence that the rotation curve of the Milky Way is similar to that of the Andromeda galaxy, suggesting that the dark matter halos of these two dominant Local Group galaxy are comparably massive.

We report the discovery of a 4.5 μm counterpart to the anomalous X-ray pulsar (magnetar) 1E 2259+586 with the Spitzer Space Telescope. The mid-infrared flux density is 6.3 ± 1.0 μJy at 4.5 μm and <20 μJy (at 95% confidence) at 8 μm, or 0.02% of the 2–10 keV X-ray flux (corrected for extinction). Combining our Spitzer measurements with previously published near-infrared data, we show that the overall infrared emission from 1E 2259+586 is qualitatively similar to that from the magnetar 4U 0142+61. Therefore, the passive X-ray-heated dust disk model originally developed for 4U 0142+61 might also apply to 1E 2259+586. However, the IR data from this source can also be fitted by a simple power-law spectrum as might be expected from magnetospheric emission.

We report an observation of the Draco cloud region using the Far-ultraviolet IMaging Spectrograph (FIMS/SPEAR). The spectra show important ionic lines, such as C iv λλ1548, 1551, Si iv+O iv] λ1394, Si ii* λ1533, and Al ii λ1671, indicating the existence of hot and warm interstellar gases toward the region. The map of the continuum is generally in accord with the infrared map, which indicates far-ultraviolet continuum is mostly the starlight scattered off by the dust grains in the Draco cloud. Enhanced C iv emission is seen inside the Draco cloud region and attributed to the turbulent mixing of the interacting cold and warm/hot media. This interpretation is supported by the detection of O iii] λ1661 emission line and the Hα feature in this region. We found slightly fainter C iv and far brighter Si ii* emissions covering the rest of the region outside the Draco cloud, in agreement with previous observations of Galactic halos. Additionally, we also found that the molecular hydrogen fluorescence map is consistent with the morphology of the atomic neutral hydrogen and dust emission of the Draco cloud, direct evidence supporting the notion that substantial amounts of hydrogen nuclei exist in molecular form in the cloud.

Ultraviolet (UV) nonionizing continuum and mid-infrared (IR) emission constitute the basis of two widely used star formation (SF) indicators at intermediate and high redshifts. We study 2430 galaxies with z < 1.4 in the Extended Groth Strip with deep MIPS 24 μm observations from FIDEL, spectroscopy from DEEP2, and UV, optical, and near-IR photometry from the AEGIS. The data are coupled with dust-reddened stellar population models and Bayesian spectral energy distribution (SED) fitting to estimate dust-corrected star formation rates (SFRs). In order to probe the dust heating from stellar populations of various ages, the derived SFRs were averaged over various timescales—from 100 Myr for "current" SFR (corresponding to young stars) to 1–3 Gyr for long-timescale SFRs (corresponding to the light-weighted age of the dominant stellar populations). These SED-based UV/optical SFRs are compared to total IR luminosities extrapolated from 24 μm observations, corresponding to 10–18 μm rest frame. The total IR luminosities are in the range of normal star-forming galaxies and luminous IR galaxies (10¹⁰–10¹²L_☉). We show that the IR luminosity can be estimated from the UV and optical photometry to within a factor of 2, implying that most z < 1.4 galaxies are not optically thick. We find that for the blue, actively star-forming galaxies the correlation between the IR luminosity and the UV/optical SFR shows a decrease in scatter when going from shorter to longer SFR-averaging timescales. We interpret this as the greater role of intermediate age stellar populations in heating the dust than what is typically assumed. Equivalently, we observe that the IR luminosity is better correlated with dust-corrected optical luminosity than with dust-corrected UV light. We find that this holds over the entire redshift range. Many so-called green valley galaxies are simply dust-obscured actively star-forming galaxies. However, there exist 24 μm detected galaxies, some with L_IR>10¹¹L_☉, yet with little current SF. For them a reasonable amount of dust absorption of stellar light (but presumably higher than in nearby early-type galaxies) is sufficient to produce the observed levels of IR, which includes a large contribution from intermediate and old stellar populations. In our sample, which contains very few ultraluminous IR galaxies, optical and X-ray active galactic nuclei do not contribute on average more than ∼50% to the mid-IR luminosity, and we see no evidence for a large population of "IR excess" galaxies.

We analyze a sample of galaxies chosen to have F_24 μm > 0.5 mJy and satisfy a certain IRAC color criterion. Infrared Spectrograph (IRS) spectra yield redshifts, spectral types, and polycyclic aromatic hydrocarbons (PAH) luminosities, to which we add broadband photometry from optical through IRAC wavelengths, MIPS from 24–160 μm, 1.1 mm, and radio at 1.4 GHz. Stellar population modeling and IRS spectra together demonstrate that the double criteria used to select this sample have efficiently isolated massive star-forming galaxies at z ∼ 1.9. This is the first starburst (SB)-dominated ultraluminous infrared galaxies (ULIRG) sample at high redshift with total infrared luminosity measured directly from FIR and millimeter photometry, and as such gives us the first accurate view of broadband spectral energy distributions for SB galaxies at extremely high luminosity and at all wavelengths. Similar broadband data are assembled for three other galaxy samples—local SB galaxies, local active galactic nucleus (AGN)/ULIRGs, and a second 24 μm-luminous z ∼ 2 sample dominated by AGN. L_PAH/L_IR for the new z ∼ 2 SB sample is the highest ever seen, some three times higher than in local SBs, whereas in AGNs this ratio is depressed below the SB trend, often severely. Several pieces of evidence imply that AGNs exist in this SB-dominated sample, except two of which even host very strong AGN, while they still have very strong PAH emission. The Advanced Camera for Surveys images show that most objects have very extended morphologies in the rest-frame ultraviolet band, thus extended distribution of PAH molecules. Such an extended distribution prevents further destruction PAH molecules by central AGNs. We conclude that objects in this sample are ULIRGs powered mainly by SB; and the total infrared luminosity density contributed by this type of objects is 0.9–2.6 × 10⁷ L_☉ Mpc⁻³.

The force-free parameter α, also known as helicity parameter or twist parameter, bears the same sign as the magnetic helicity under some restrictive conditions. The single global value of α for a whole active region gives the degree of twist per unit axial length. We investigate the effect of polarimetric noise on the calculation of global α value and magnetic energy of an analytical bipole. The analytical bipole has been generated using the force-free field approximation with a known value of constant α and magnetic energy. The magnetic parameters obtained from the analytical bipole are used to generate Stokes profiles from the Unno–Rachkovsky solutions for polarized radiative transfer equations. Then we add random noise of the order of 10⁻³ of the continuum intensity (I_c) in these profiles to simulate the real profiles obtained by modern spectropolarimeters such as Hinode (SOT/SP), SVM (USO), ASP, DLSP, POLIS, and SOLIS etc. These noisy profiles are then inverted using a Milne–Eddington inversion code to retrieve the magnetic parameters. Hundred realizations of this process of adding random noise and polarimetric inversion is repeated to study the distribution of error in global α and magnetic energy values. The results show that (1) the sign of α is not influenced by polarimetric noise and very accurate values of global twist can be calculated, and (2) accurate estimation of magnetic energy with uncertainty as low as 0.5% is possible under the force-free condition.

FS CMa type stars are a group of Galactic objects with the B[e] phenomenon. They exhibit strong emission-line spectra and infrared excesses, which are most likely due to recently formed circumstellar dust. The group content and identification criteria were described in the first two papers of the series. In this paper we report our spectroscopic and photometric observations of the optical counterpart of IRAS 00470+6429 obtained in 2003–2008. The optical spectrum is dominated by emission lines, most of which have P Cyg type profiles. We detected significant brightness variations, which may include a regular component, and variable spectral line profiles in both shape and position. The presence of a weak Li i 6708 Å line in the spectrum suggests that the object is most likely a binary system with a B2–B3 spectral-type primary companion of a luminosity log L/L_☉ = 3.9 ± 0.3 and a late-type secondary companion. We estimate a distance toward the object to be 2.0 ± 0.3 kpc from the Sun.

Several recent studies have shown that about half of the massive galaxies at z ∼ 2 are in a quiescent phase. Moreover, these galaxies are commonly found to be ultra-compact with half-light radii of ∼1 kpc. We have obtained a ∼29 hr spectrum of a typical quiescent, ultra-dense galaxy at z = 2.1865 with the Gemini Near-Infrared Spectrograph. The spectrum exhibits a strong optical break and several absorption features, which have not previously been detected in z > 2 quiescent galaxies. Comparison of the spectral energy distribution with stellar population synthesis models implies a low star formation rate (SFR) of 1–3 M_☉ yr⁻¹, an age of 1.3–2.2 Gyr, and a stellar mass of ∼2 × 10¹¹ M_☉. We detect several faint emission lines, with emission-line ratios of [N ii]/Hα, [S ii]/Hα, and [O ii]/[O iii] typical of low-ionization nuclear emission-line regions. Thus, neither the stellar continuum nor the nebular emission implies active star formation. The current SFR is <1% of the past average SFR. If this galaxy is representative of compact quiescent galaxies beyond z = 2, it implies that quenching of star formation is extremely efficient and also indicates that low luminosity active galactic nuclei (AGNs) could be common in these objects. Nuclear emission is a potential concern for the size measurement. However, we show that the AGN contributes ≲8% to the rest-frame optical emission. A possible post-starburst population may affect size measurements more strongly; although a 0.5 Gyr old stellar population can make up ≲10% of the total stellar mass, it could account for up to ∼40% of the optical light. Nevertheless, this spectrum shows that this compact galaxy is dominated by an evolved stellar population.

We study the effects of rotation on standing accretion shock instability (SASI) by performing three-dimensional hydrodynamics simulations. Taking into account a realistic equation of state and neutrino heating/cooling, we prepare a spherically symmetric and steady accretion flow through a standing shock wave onto a proto-neutron star (PNS). When the SASI enters the nonlinear phase, we impose uniform rotation on the flow advecting from the outer boundary of the iron core, whose specific angular momentum is assumed to agree with recent stellar evolution models. Using spherical harmonics in space and Fourier decompositions in time, we perform mode analysis of the nonspherical deformed shock wave to observe rotational effects on the SASI in the nonlinear phase. We find that rotation imposed on the axisymmetric flow does not make any spiral modes and hardly affects sloshing modes, except for steady l = 2, m = 0 modes. In contrast, rotation imposed on the nonaxisymmetric flow increases the amplitude of spiral modes so that some spiral flows accreting on the PNS are more clearly formed inside the shock wave than without rotation. The amplitudes of spiral modes increase significantly with rotation in the progressive direction.

The method of light-curve simulations is a tool that has been applied to X-ray monitoring observations of active galactic nuclei for the characterization of the power density spectrum (PDS) of temporal variability and measurement of associated break frequencies (which appear to be an important diagnostic for the mass of the black hole in these systems as well as their accretion state). It relies on a model for the PDS that is fitted to the observed data. The determination of confidence regions on the fitted model parameters is of particular importance, and we show how the Neyman construction based on distributions of estimates may be implemented in the context of light-curve simulations. We believe that this procedure offers advantages over the method used in earlier reports on PDS model fits, not least with respect to the correspondence between the size of the confidence region and the precision with which the data constrain the values of the model parameters. We plan to apply the new procedure to existing RXTE and XMM-Newton observations of Seyfert I galaxies as well as RXTE observations of the Seyfert II galaxy NGC 4945.

We report our observational results of 870 μm continuum emission and its linear polarization in the massive star formation site W51 e2/e8. Inferred from the linear polarization maps, the magnetic field in the plane of sky (B_⊥) is traced with an angular resolution of 07 with the Submillimeter Array. Whereas previous BIMA observations with an angular resolution of 3'' (0.1 pc) showed a uniform B field, our revealed B_⊥ morphology is hourglass-like in the collapsing core near the ultracompact H ii region e2 and also possibly in e8. The decrease in polarization near the continuum peak seen at lower angular resolution is apparently due to the more complex structures at smaller scales. In e2, the pinched direction of the hourglass-like B-field morphology is parallel to the plane of the ionized accretion flow traced by H53α, suggesting that the massive stars are formed via processes similar to the low-mass stars, i.e., accretion through a disk, except that the mass involved is much larger. Furthermore, our finding that the resolved collapsing cores in e2 and e8 lie within one subcritical 0.5 pc envelope supports the scenario of magnetic fragmentation via ambipolar diffusion. We therefore suggest that magnetic fields control the dynamical evolution of the envelope and cores in W51 e2 and e8.

A general treatment of disk star formation is developed from a dissipative multiphase model, with the dominant dissipation due to cloud collisions. The Schmidt–Kennicutt (SK) law emerges naturally for star-forming disks and starbursts. We predict that there should be an inverse correlation between Tully–Fisher law and SK law residuals. The model is extended to include a multiphase treatment of supernova feedback that leads to a turbulent pressure-regulated generalization of the star formation law and is applicable to gas-rich starbursts. Enhanced pressure, as expected in merger-induced star formation, enhances star formation efficiency. An upper limit is derived for the disk star formation rate in starbursts that depends on the ratio of global ISM to cloud pressures. We extend these considerations to the case where the interstellar gas pressure in the inner galaxy is dominated by outflows from a central active galactic nucleus (AGN). During massive spheroid formation, AGN-driven winds trigger star formation, resulting in enhanced supernova feedback and outflows. The outflows are comparable to the AGN-boosted star formation rate and saturate in the super-Eddington limit. Downsizing of both SMBH and spheroids is a consequence of AGN-driven positive feedback. Bondi accretion feeds the central black hole with a specific accretion rate that is proportional to the black hole mass. AGN-enhanced star formation is mediated by turbulent pressure and relates spheroid star formation rate to black hole accretion rate. The relation between black hole mass and spheroid velocity dispersion has a coefficient (Salpeter time to gas consumption time ratio) that provides an arrow of time. Highly efficient, AGN-boosted star formation can occur at high redshift.

We present the results of a stellar population analysis of 30 Lyα emitting galaxies (LAEs) at z ∼ 0.3, previously discovered with the Galaxy Evolution Explorer. With a few exceptions, we can accurately fit model spectral energy distributions to these objects, representing the first time this has been done for a large sample of LAEs at z < 3, a gap of ∼8 Gyr in the history of the universe. From the 26/30 LAEs which we can fit, we find an age and stellar mass range of 200 Myr–10 Gyr and 10⁹–10¹¹M_☉, respectively. These objects thus appear to be significantly older and more massive than LAEs at high redshift. We also find that these LAEs show a mild trend toward higher metallicity than those at high redshift, as well as a tighter range of dust attenuation and interstellar medium geometry. These results suggest that low-redshift LAEs have evolved significantly from those at high redshift.

Hydrodynamic simulations of granular convection predict the existence of supersonic flows covering ∼3%–4% of the solar surface at any time, but these flows have not been detected unambiguously as yet. Using data from the spectropolarimeter aboard the Hinode satellite, I present direct evidence of fast horizontal plasma motions in quiet-Sun granules. Their visibility increases toward the limb due to more favorable viewing conditions. At the resolution of Hinode, the horizontal flows give rise to asymmetric intensity profiles with very inclined blue wings and even line satellites located blueward of the main absorption feature. Doppler shifts of up to 9 km s⁻¹ are observed at the edges of bright granules, demonstrating that the flows reach supersonic speeds. The strongest velocities occur in patches of 05 or less. They tend to be associated with enhanced continuum intensities, line widths, and equivalent widths, but large values of these parameters do not necessarily imply the existence of supersonic flows. Time series of spectropolarimetric measurements in regions away from the disk center show the transient nature of the strong horizontal motions, which last only for a fraction of the granule lifetime. Supersonic flows are expected to produce shocks at the boundaries between granules and intergranular lanes, and may also play a role in the emergence of small-scale magnetic fields in quiet-Sun internetwork regions.

We present stereoscopic reconstructions of the location and inclination of polar plumes of two data sets based on the two simultaneously recorded images taken by the EUVI telescopes in the SECCHI instrument package onboard the Solar TErrestrial RElations Observatory spacecraft. The 10 plumes investigated show a superradial expansion in the coronal hole in three dimensions (3D) which is consistent with the two-dimensional results. Their deviations from the local meridian planes are rather small with an average of 647. By comparing the reconstructed plumes with a dipole field with its axis along the solar rotation axis, it is found that plumes are inclined more horizontally than the dipole field. The lower the latitude is, the larger is the deviation from the dipole field. The relationship between plumes and bright points has been investigated and they are not always associated. For the first data set, based on the 3D height of plumes and the electron density derived from SUMER/SOHO Si viii line pair, we found that electron densities along the plumes decrease with height above the solar surface. The temperature obtained from the density scale height is 1.6–1.8 times larger than the temperature obtained from Mg ix line ratios. We attribute this discrepancy to a deviation of the electron and the ion temperatures. Finally, we have found that the outflow speeds studied in the O vi line in the plumes corrected by the angle between the line of sight and the plume orientation are quite small with a maximum of 10 km s^-1. It is unlikely that plumes are a dominant contributor to the fast solar wind.

We present photometric and spectroscopic observations of the 2009 February 2 transit of the exoplanet XO-3b. The new data show that the planetary orbital axis and stellar rotation axis are misaligned, as reported earlier by Hébrard and coworkers. We find the angle between the sky projections of the two axes to be 37.3 ±  3.7 deg, as compared to the previously reported value of 70 ±  15 deg. The significance of this discrepancy is unclear because there are indications of systematic effects. XO-3b is the first exoplanet known to have a highly inclined orbit relative to the equatorial plane of its parent star, and as such it may fulfill the predictions of some scenarios for the migration of massive planets into close-in orbits. We revisit the statistical analysis of spin–orbit alignment in hot-Jupiter systems. Assuming the stellar obliquities to be drawn from a single Rayleigh distribution, we find the mode of the distribution to be 13⁺⁵₋₂ deg. However, it remains the case that a model representing two different migration channels—in which some planets are drawn from a perfectly aligned distribution and the rest are drawn from an isotropic distribution—is favored over a single Rayleigh distribution.

We have obtained new spectrophotometric data for 28 H ii regions in the spiral galaxy NGC 300, a member of the nearby Sculptor Group. The detection of several auroral lines, including [O iii] λ4363, [S iii] λ6312, and [N ii] λ5755, has allowed us to measure electron temperatures and direct chemical abundances for the whole sample. We determine for the first time in this galaxy a radial gas-phase oxygen abundance gradient based solely on auroral lines, and obtain the following least-square solution: 12 + log(O/H) = 8.57(±0.02) − 0.41(±0.03)R/R₂₅, where the galactocentric distance is expressed in terms of the isophotal radius R₂₅. The characteristic oxygen abundance, measured at 0.4 × R₂₅, is 12 + log(O/H) = 8.41. The gradient corresponds to −0.077 ± 0.006 dex kpc⁻¹, and agrees very well with the galactocentric trend in metallicity obtained for 29 B and A supergiants in the same galaxy, −0.081 ± 0.011 dex kpc⁻¹. The intercept of the regression for the nebular data virtually coincides with the intercept obtained from the stellar data, which is 8.59(±0.05). This allows little room for depletion of nebular oxygen onto dust grains, although in this kind of comparison we are somewhat limited by systematic uncertainties, such as those related to the atomic parameters used to derive the chemical compositions. We discuss the implications of our result with regard to strong-line abundance indicators commonly used to estimate the chemical compositions of star-forming galaxies, such as R₂₃. By applying a few popular calibrations of these indices based on grids of photoionization models on the NGC 300 H ii region fluxes, we find metallicities that are higher by 0.3 dex (a factor of 2) or more relative to our nebular (T_e based) and stellar ones. We detect Wolf–Rayet stellar emission features in ∼1/3 of our H ii region spectra, and find that in one of the nebulae hosting these hot stars the ionizing field has a particularly hard spectrum, as gauged by the "softness" parameter η = (O⁺/O⁺⁺)/(S⁺/S⁺⁺). We suggest that this is related to the presence of an early WN star. By considering a larger sample of extragalactic H ii regions we confirm, using direct abundance measurements, previous findings of a metallicity dependence of η, in the sense that softer stellar continua are found at high metallicity.

We present multiband photometry of 185 type-Ia supernovae (SNe Ia), with over 11,500 observations. These were acquired between 2001 and 2008 at the F. L. Whipple Observatory of the Harvard-Smithsonian Center for Astrophysics (CfA). This sample contains the largest number of homogeneously observed and reduced nearby SNe Ia (z ≲ 0.08) published to date. It more than doubles the nearby sample, bringing SN Ia cosmology to the point where systematic uncertainties dominate. Our natural system photometry has a precision of ≲0.02 mag in BVRIr'i' and ≲0.04 mag in U for points brighter than 17.5 mag. We also estimate a systematic uncertainty of 0.03 mag in our SN Ia standard system BVRIr'i' photometry and 0.07 mag for U. Comparisons of our standard system photometry with published SN Ia light curves and comparison stars, where available for the same SN, reveal agreement at the level of a few hundredths mag in most cases. We find that 1991bg-like SNe Ia are sufficiently distinct from other SNe Ia in their color and light-curve-shape/luminosity relation that they should be treated separately in light-curve/distance fitter training samples. The CfA3 sample will contribute to the development of better light-curve/distance fitters, particularly in the few dozen cases where near-infrared photometry has been obtained and, together, can help disentangle host-galaxy reddening from intrinsic supernova color, reducing the systematic uncertainty in SN Ia distances due to dust.

We investigate the formation and evolution of giant molecular clouds (GMCs) in a Milky-Way-like disk galaxy with a flat rotation curve. We perform a series of three-dimensional adaptive mesh refinement numerical simulations that follow both the global evolution on scales of ∼20 kpc and resolve down to scales ≲10 pc with a multiphase atomic interstellar medium. In this first study, we omit star formation and feedback, and focus on the processes of gravitational instability and cloud collisions and interactions. We define clouds as regions with n_H ⩾ 100 cm^-3 and track the evolution of individual clouds as they orbit through the galaxy from their birth to their eventual destruction via merger or via destructive collision with another cloud. After ∼140 Myr a large fraction of the gas in the disk has fragmented into clouds with masses ∼10⁶ M_☉ and a mass spectrum similar to that of Galactic GMCs. The disk settles into a quasi-steady-state in which gravitational scattering of clouds keeps the disk near the threshold of global gravitational instability. The cloud collision time is found to be a small fraction, ∼1/5, of the orbital time, and this is an efficient mechanism to inject turbulence into the clouds. This helps to keep clouds only moderately gravitationally bound, with virial parameters of order unity. Many other observed GMC properties, such as mass surface density, angular momentum, velocity dispersion, and vertical distribution, can be accounted for in this simple model with no stellar feedback.

We present the results from an optical and near-infrared (NIR) spectroscopic study of the ultraviolet-luminous z = 2.73 galaxy, the 8 o'clock arc. Due to gravitational lensing, this galaxy is magnified by a factor of μ > 10, allowing in-depth measurements which are usually unfeasible at such redshifts. In the optical spectra, we measured the systemic redshift of the galaxy, z = 2.7322± 0.0012, using stellar photospheric lines. This differs from the redshift of absorption lines in the interstellar medium, z = 2.7302 ± 0.0006, implying gas outflows on the order of 160 km s⁻¹. With H- and K-band NIR spectra, we have measured nebular emission lines of Hα, Hβ, Hγ, [N ii], and [O iii], which have a redshift z = 2.7333 ± 0.0001, consistent with the derived systemic redshift. From the Balmer decrement, we measured the dust extinction in this galaxy to be A₅₅₀₀ = 1.17 ± 36 mag. Correcting the Hα line flux for dust extinction as well as the assumed lensing factor, we measure a star formation rate (SFR) of ∼270 M_☉ yr⁻¹, which is higher than ∼85% of star-forming galaxies at z ∼ 2–3. Using combinations of all detected emission lines, we find that the 8 o'clock arc has a gas-phase metallicity of ∼0.8 Z_☉, showing that enrichment at high redshift is not rare, even in blue, star-forming galaxies. Studying spectra from two of the arc components separately, we find that one component dominates both the dust extinction and SFR, although the metallicities between the two components are similar. We derive the mass via stellar population modeling, and find that the arc has a total stellar mass of ∼4.2 × 10¹¹M_☉, which falls on the mass–metallicity relation at z ∼ 2. Finally, we estimate the total gas mass, and find it to be only ∼12% of the stellar mass, implying that the 8 o'clock arc is likely nearing the end of a starburst.

In the brown dwarf (BD) binary 2M0535 − 05, Stassun et al. have reported that the more massive primary has a lowerT_eff than the less massive secondary. Here, we report results obtained by an evolutionary code in which the criterion for the onset of convection in the primary is modified in the presence of a magnetic field. Structural alterations to the primary lead to a lower T_eff and a larger radius than would occur in a non-magnetic BD of the same age mass and age. The observed value of T_eff can be explained if the field in the primary increases in strength from 120–320 G at the surface to 5–13 MG at the center. With zero field in the secondary, our models indicate that both components can be co-eval with an age of 1.0–1.3 Myr. Because the binary is so young, the components have not yet had time to synchronize their rotations: differences in angular velocity may explain why one component has developed a field while the other has not.

We apply methods from Bayesian inferencing and graph theory to a data set of 102 mid-infrared spectra, and archival data from the optical to the millimeter, to construct an evolutionary paradigm for z < 0.4 infrared-luminous galaxies. We propose that the ultraluminous infrared galaxies (ULIRG) lifecycle consists of three phases. The first phase lasts from the initial encounter until approximately coalescence. It is characterized by homogeneous mid-IR spectral shapes, and IR emission mainly from star formation, with a contribution from an active galactic nucleus (AGN) in some cases. At the end of this phase, a ULIRG enters one of two evolutionary paths depending on the dynamics of the merger, the available quantities of gas, and the masses of the black holes in the progenitors. On one branch, the contributions from the starburst and the AGN to the total IR luminosity decline and increase, respectively. The IR spectral shapes are heterogeneous, likely due to feedback from AGN-driven winds. Some objects go through a brief QSO phase at the end. On the other branch, the decline of the starburst relative to the AGN is less pronounced, and few or no objects go through a QSO phase. We show that the 11.2 μm polycyclic aromatic hydrocarbon feature is a remarkably good diagnostic of evolutionary phase, and identify six ULIRGs that may be archetypes of key stages in this lifecycle.

We have performed monitoring observations of the 3 mm flux density toward the Galactic center compact radio source Sagittarius A* (Sgr A*) with the Australia Telescope Compact Array since 2005 October. Careful calibrations of both elevation-dependent and time-dependent gains have enabled us to establish the variability behavior of Sgr A*. Sgr A* appeared to undergo a high and stable state in the 2006 June session, and a low and variable state in the 2006 August session. We report the results, with emphasis on two detected intraday variation events during its low states. One is on 2006 August 12 when Sgr A* exhibited a 33% fractional variation in about 2.5 hr. The other is on 2006 August 13 when two peaks separated by about 4 hr, with a maximum variation of 21% within 2 hr, were seen. The observed short timescale variations are discussed in light of two possible scenarios, i.e., the expanding plasmon model and the sub-Keplerian orbiting hot spot model. The fitting results indicate that for the adiabatically expanding plasmon model, the synchrotron cooling cannot be ignored, and a minimum mass-loss rate of 9.7 × 10⁻¹⁰ M_☉ yr⁻¹ is obtained based on parameters derived for this modified expanding plasmon model. Simultaneous multiwavelength observation is crucial to our understanding of the physical origin of rapid radio variability in Sgr A*.

We present results of our search for X-ray line emission associated with the radiative decay of the sterile neutrino, a well motivated dark matter candidate, in Suzaku Observatory spectra of the Ursa Minor dwarf spheroidal galaxy. These data represent the first deep observation of one of these extreme mass-to-light systems and the first dedicated dark matter search using an X-ray telescope. No such emission line is positively detected, and we place new constraints on the combination of the sterile neutrino mass, m_st, and the active-sterile neutrino oscillation mixing angle, θ. Line flux upper limits are derived using a maximum-likelihood-based approach that, along with the lack of intrinsic X-ray emission, enables us to minimize systematics and account for those that remain. The limits we derive match or approach the best previous results over the entire 1–20 keV mass range from a single Suzaku observation. These are used to place constraints on the existence of sterile neutrinos with given parameters in the general case and in the case where they are assumed to constitute all of the dark matter. The range allowed implies that sterile neutrinos remain a viable candidate to make up some—or all—of the dark matter and also explain pulsar kicks and various other astrophysical phenomena.

Hierarchical star formation leads to a progressive decrease in the clustering of star clusters both in terms of spatial scale and age. Consistently, statistical analysis of the positions and ages of clusters in the Milky Way disk strongly suggests that a correlation between the duration of star formation in a region and its size does exist. The average age difference between pairs of open clusters increases with their separation as the ∼0.16 power. In contrast, for the Large Magellanic Cloud, Efremov & Elmegreen found that the age difference scales with the ∼0.35 power of the region size. This discrepancy may be tentatively interpreted as an argument in support of intrinsically shorter (faster) star formation timescales in smaller galaxies. However, if both the effects of cluster dissolution and incompleteness are taken into consideration, the average age difference between cluster pairs in the Galaxy increases with their separation as the ∼0.4 power. This result implies that the characteristic timescale for coherent, clustered-mode star formation is nearly 1 Myr. Therefore, the overall consequence of ignoring the effect of cluster dissolution is to overestimate the star formation timescale. On the other hand, in the Galactic disk and for young clusters separated by less than three times the characteristic cluster tidal radius (10 pc), the average age difference is 16 Myr, which suggests common origin. A close pair classification scheme is introduced and a list of 11 binary cluster candidates with physical separation less than 30 pc is compiled. Two of these pairs are likely primordial: ASCC 18/ASCC 21 and NGC 3293/NGC 3324. A triple cluster candidate in a highly hierarchical configuration is also identified: NGC 1981/NGC 1976/Collinder 70 in Orion. We find that binary cluster candidates seem to show a tendency to have components of different size—evidence for dynamical interaction.

We study the contribution of the kinematic Sunyaev–Zel'dovich (kSZ) effect, generated by the warm-hot intergalactic medium, to the cosmic microwave background temperature anisotropies in the five-year Wilkinson Microwave Anisotropy Probe (WMAP) data. We explore the concordance ΛCDM cosmological model, with and without this kSZ contribution, using a Markov chain Monte Carlo algorithm. Our model requires a single extra parameter to describe this new component. Our results show that the inclusion of the kSZ signal improves the fit to the data without significantly altering the best-fit cosmological parameters except Ω_bh². The improvement is localized at the ℓ ≳  500 multipoles. For the best-fit model, this extra component peaks at ℓ ∼  450 with an amplitude of 129 μK², and represents 3.1% of the total power measured by WMAP. Nevertheless, at the 2σ level a null kSZ contribution is still compatible with the data. Part of the detected signal could arise from unmasked point sources and/or Poissonianly distributed foreground residuals. A statistically more significant detection requires the wider frequency coverage and angular resolution of the forthcoming Planck mission.

We present 5 to 15 μm Spitzer Infrared Spectrograph (IRS) low-resolution spectral data of a candidate debris disk around an M4.5 star identified as a likely member of the ∼40 Myr old cluster NGC 2547. The IRS spectrum shows a silicate emission feature, indicating the presence of warm, small, (sub)micron-sized dust grains in the disk. Of the 15 previously known candidate debris disks around M-type stars, the one we discuss in this paper is the first to have an observed mid-infrared spectrum and is also the first to have measured silicate emission. We combined the IRS data with ancillary data (optical, JHK_s, and Spitzer InfraRed Array Camera and 24 μm data) to build the spectral energy distribution (SED) of the source. Monte Carlo radiation transfer modeling of the SED characterized the dust disk as being very flat (h₁₀₀ = 2 AU) and extending inward within at least 0.13 AU of the central star. Our analysis shows that the disk is collisionally dominated and is likely a debris disk.

To explain the flux variabilities of active galactic nuclei, especially blazars, we assume a scenario of multiple injections of ultrahigh energy radiating electrons in powerful cosmic nonthermal radiation sources with dominant magnetic field self-generation leading to a series of bursts. Therefore, we examine analytically the cases of electron energy losses in the form of synchrotron cooling with a constant magnetic field and with a partition condition between the energy densities of the magnetic field and the injected relativistic electrons. Thus, assuming partition conditions, the magnetic field strength becomes time dependent changing both the synchrotron emissivity and the intrinsic temporal evolution of the relativistic particle energy spectrum after injection. In this paper, the linear and nonlinear kinetic equations for the intrinsic temporal evolution of relativistic electrons are solved for the case of multiple instantaneous monoenergetic injections of relativistic electrons. The solutions are applied and compared in the calculations of the optically thin synchrotron radiation intensities and the synchrotron fluences. They show significant differences in the optically thin synchrotron spectral distributions at different times and in the synchrotron light curves at different frequencies.

We propose a plasma experiment to be used to investigate fundamental properties of astrophysical dynamos. The highly conducting, fast-flowing plasma will allow experimenters to explore systems with magnetic Reynolds numbers an order of magnitude larger than those accessible with liquid-metal experiments. The plasma is confined using a ring–cusp strategy and subject to a toroidal differentially rotating outer boundary condition. As proof of principle, we present magnetohydrodynamic simulations of the proposed experiment. When a von Kármán-type boundary condition is specified, and the magnetic Reynolds number is large enough, dynamo action is observed. At different values of the magnetic Prandtl and Reynolds numbers the simulations demonstrate either laminar or turbulent dynamo action.

We use 5000 cosmological N-body simulations of 1 h⁻³ Gpc³ box for the concordance ΛCDM model in order to study the sampling variances of a nonlinear matter power spectrum. We show that the non-Gaussian errors can be important even on large length scales relevant for baryon acoustic oscillations (BAOs). Our findings are the following: (1) the non-Gaussian errors degrade the cumulative signal-to-noise ratios (S/Ns) for the power spectrum amplitude by up to a factor of 2 and 4 for redshifts z = 1 and 0, respectively; (2) there is little information on the power spectrum amplitudes in the quasi-nonlinear regime, confirming the previous results; (3) the distribution of power spectrum estimators at BAO scales, among the realizations, is well approximated by a Gaussian distribution with variance that is given by the diagonal covariance component. (4) For the redshift-space power spectrum, the degradation in S/N by non-Gaussian errors is mitigated due to nonlinear redshift distortions; (5) for an actual galaxy survey, the additional shot noise contamination compromises the cosmological information inherent in the galaxy power spectrum, but also mitigates the impact of non-Gaussian errors. The S/N is degraded by up to 30% for a Wide-Field Fiber-Fed Optical Multi-Object Spectrograph-type survey; (6) the finite survey volume causes additional non-Gaussian errors via the correlations of long-wavelength fluctuations with the fluctuations we want to measure, further degrading the S/N values by about 30% even at high redshift z = 3.

The mid-infrared properties of pre-planetary disks are sensitive to the temperature and flaring profiles of disks for the regions where planet formation is expected to occur. In order to constrain theories of planet formation, we have carried out a mid-infrared (λ = 10.7 μm) size survey of young stellar objects using the segmented Keck telescope in a novel configuration. We introduced a customized pattern of tilts to individual mirror segments to allow efficient sparse-aperture interferometry, allowing full aperture synthesis imaging with higher calibration precision than traditional imaging. In contrast to previous surveys on smaller telescopes and with poorer calibration precision, we find that most objects in our sample are partially resolved. Here, we present the main observational results of our survey of five embedded massive protostars, 25 Herbig Ae/Be stars, 3 T Tauri stars, 1 FU Ori system, and five emission-line objects of uncertain classification. The observed mid-infrared sizes do not obey the size–luminosity relation found at near-infrared wavelengths and a companion paper will provide further modeling analysis of this sample. In addition, we report imaging results for a few of the most resolved objects, including complex emission around embedded massive protostars, the photoevaporating circumbinary disk around MWC 361A, and the subarcsecond binaries T Tau, FU Ori, and MWC 1080.

We present new Spitzer Space Telescope observations of the region NGC 2467, and use these observations to determine how the environment of an H ii region affects the process of star formation. Our observations comprise IRAC (3.6, 4.5, 5.8, and 8.0 μm) and MIPS (24 μm) maps of the region, covering approximately 400 arcmin². The images show a region of ionized gas pushing out into the surrounding molecular cloud, powered by an O6V star and two clusters of massive stars in the region. We have identified as candidate young stellar objects (YSOs) 45 sources in NGC 2467 with infrared excesses in at least two mid-infrared colors. We have constructed color–color diagrams of these sources and have quantified their spatial distribution within the region. We find that the YSOs are not randomly distributed in NGC 2467; rather, over 75% of the sources are distributed at the edge of the H ii region, along ionization fronts driven by the nearby massive stars. The high fraction of YSOs in NGC 2467 that are found in proximity to gas that has been compressed by ionization fronts supports the hypothesis that a significant fraction of the star formation in NGC 2467 is triggered by the massive stars and the expansion of the H ii region. At the current rate of star formation, we estimate at least 25%–50% of the total population of YSOs formed by this process.

We perform an extensive test of theoretical stellar models for main-sequence (MS) stars in ugriz, using cluster fiducial sequences obtained in the previous paper of this series. We generate a set of isochrones using the Yale Rotating Evolutionary Code with updated input physics, and derive magnitudes and colors in ugriz from MARCS model atmospheres. These models match cluster MSs over a wide range of metallicity within the errors of the adopted cluster parameters. However, we find a large discrepancy of model colors at the lower MS (T_eff ≲ 4500 K) for clusters at and above solar metallicity. We also reach similar conclusions using the theoretical isochrones of Girardi et al. and Dotter et al., but our new models are generally in better agreement with the data. Using our theoretical isochrones, we also derive MS-fitting distances and turnoff ages for five key globular clusters, and demonstrate the ability to derive these quantities from photometric data in the Sloan Digital Sky Survey. In particular, we exploit multiple color indices (g − r, g − i, and g − z) in the parameter estimation, which allows us to evaluate internal systematic errors. Our distance estimates, with an error of σ_(m−M) = 0.03–0.11 mag for individual clusters, are consistent with Hipparcos-based subdwarf-fitting distances derived in the Johnson–Cousins or Strömgren photometric systems.

We present an approach for analyzing the morphology and physical properties of H i features near giant OB associations in M33, in the context of a model whereby the H i excess arises from photodissociation of the molecular gas in remnants of the parent giant molecular clouds (GMCs). Examples are presented here in the environs of NGC 604 and CPSDP Z204, two prominent H ii regions in M33. These are the first results of a detailed analysis of the environs of a large number of OB associations in that galaxy. We present evidence for "diffusion" of the far-UV radiation from the OB association through a clumpy remnant GMC, and show further that enhanced CO(1–0) emission appears preferentially associated with GMCs of higher volume density.

This study is based upon plumes seen close to the solar limb within coronal holes in the emission from ions formed in the temperature region of 1 MK, in particular, the band of Fe ix 171 Å from EIT on the Solar and Heliospheric Observatory. It is shown, using geometric arguments, that two distinct classes of structure contribute to apparently similar plume observations. Quasi-cylindrical structures are anchored in discrete regions of the solar surface (beam plumes), and faint extended structures require integration along the line of sight (LOS) in order to reproduce the observed brightness. This second category, sometimes called "curtains," are ubiquitous within the polar holes and are usually more abundant than the beam plumes, which depend more on the enhanced magnetic structures detected at their footpoints. It is here proposed that both phenomena are based on plasma structures in which emerging magnetic loops interact with ambient monopolar fields, involving reconnection. The important difference is in terms of physical scale. It is proposed that curtains are composed of a large number of microplumes, distributed along the LOS. The supergranule network provides the required spatial structure. It is shown by modeling that the observations can be reproduced if microplumes are concentrated within some 5 Mm of the cell boundaries. For this reason, we propose to call this second population "network plumes." The processes involved could represent a major contribution to the heating mechanism of the solar corona.

Flare ribbons are commonly attributed to the low-altitude impact, along the footprints of separatrices or quasi-separatrix layers (QSLs), of particle beams accelerated through magnetic reconnection. If reconnection occurs at a three-dimensional coronal magnetic null point, the footprint of the dome-shaped fan surface would map a closed circular ribbon. This paper addresses the following issues: does the entire circular ribbon brighten simultaneously, as expected because all fan field lines pass through the null point? And since the spine separatrices are singular field lines, do spine-related ribbons look like compact kernels? What can we learn from these observations about current sheet formation and magnetic reconnection in a null-point topology? The present study addresses these questions by analyzing Transition Region and Coronal Explorer and Solar and Heliospheric Observatory/Michelson Doppler Imager observations of a confined flare presenting a circular ribbon. Using a potential field extrapolation, we linked the circular shape of the ribbon with the photospheric mapping of the fan field lines originating from a coronal null point. Observations show that the flare ribbon outlining the fan lines brightens sequentially along the counterclockwise direction and that the spine-related ribbons are elongated. Using the potential field extrapolation as initial condition, we conduct a low-β resistive magnetohydrodynamics simulation of this observed event. We drive the coronal evolution by line-tied diverging boundary motions, so as to emulate the observed photospheric flow pattern associated with some magnetic flux emergence. The numerical analysis allows us to explain several observed features of the confined flare. The vorticity induced in the fan by the prescribed motions causes the spines to tear apart along the fan. This leads to formation of a thin current sheet and induces null-point reconnection. We also find that the null point and its associated topological structure is embedded within QSLs, already present in the asymmetric potential field configuration. We find that the QSL footprints correspond to the observed elongated spine ribbons. Finally, we observe that before and after reconnecting at the null point, all field lines undergo slipping and slip-running reconnection within the QSLs. Field lines, and therefore particle impacts, slip or slip-run according to their distance from the spine, in directions and over distances that are compatible with the observed dynamics of the ribbons.

We present Spitzer Infrared Spectrograph and Infrared Array Camera observations of the young supernova remnant E0102 (SNR 1E0102-7219) in the Small Magellanic Cloud. The infrared spectra show strong lines of Ne and O, with the [Ne ii] line at 12.8 μm having a large velocity dispersion of 2000–4500 km s⁻¹ indicative of fast-moving ejecta. Unlike the young Galactic SNR Cas A, E0102 lacks emission from Ar and Fe. Diagnostics of the observed [Ne iii] line pairs imply that [Ne iii] emitting ejecta have a low temperature of 650 K, while [Ne v] line pairs imply that the infrared [Ne v] emitting ejecta have a high density of ∼10⁴ cm⁻³. We have calculated radiative shock models for various velocity ranges including the effects of photoionization. The shock model indicates that the [Ne v] lines come mainly from the cooling zone, which is hot and dense, whereas [Ne ii] and [Ne iii] come mainly from the photoionization zone, which has a low temperature of 400–1000 K. We estimate an infrared-emitting Ne ejecta mass of 0.04 M_☉ from the infrared observations, and discuss implications for the progenitor mass. The spectra also have a dust continuum feature peaking at 18 μm that coincides spatially with the ejecta, providing evidence that dust formed in the expanding ejecta. The 18 μm peak dust feature is fitted by a mixture of MgSiO₃ and Si dust grains, while the rest of the continuum requires either carbon or Al₂O₃ grains. We measure the total dust mass formed within the ejecta of E0102 to be ∼0.014 M_☉. The dust mass in E0102 is thus a factor of a few smaller than that in Cas A. The composition of the dust is also different, showing relatively less silicate and likely no Fe-bearing dust, as is suggested by the absence of Fe-emitting ejecta.

The first three months of sky-survey operation with the Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Space Telescope reveal 132 bright sources at |b|>10° with test statistic greater than 100 (corresponding to about 10σ). Two methods, based on the CGRaBS, CRATES, and BZCat catalogs, indicate high-confidence associations of 106 of these sources with known active galactic nuclei (AGNs). This sample is referred to as the LAT Bright AGN Sample (LBAS). It contains two radio galaxies, namely, Centaurus A and NGC 1275, and 104 blazars consisting of 58 flat spectrum radio quasars (FSRQs), 42 BL Lac objects, and 4 blazars with unknown classification. Four new blazars were discovered on the basis of the LAT detections. Remarkably, the LBAS includes 10 high-energy-peaked BL Lacs (HBLs), sources which were previously difficult to detect in the GeV range. Another 10 lower-confidence associations are found. Only 33 of the sources, plus two at |b| < 10°, were previously detected with Energetic Gamma-Ray Experiment Telescope(EGRET), probably due to variability. The analysis of the γ-ray properties of the LBAS sources reveals that the average GeV spectra of BL Lac objects are significantly harder than the spectra of FSRQs. No significant correlation between radio and peak γ-ray fluxes is observed. Blazar log N–log S distributions and luminosity functions are constructed to investigate the evolution of the different blazar classes, with positive evolution indicated for FSRQs but none for BL Lacs. The contribution of LAT blazars to the total extragalactic γ-ray intensity is estimated.

We report here the discovery of the first planet around an ultracool dwarf star. It is also the first extrasolar giant planet astrometrically discovered around a main-sequence star. The statistical significance of the detection is shown in two ways. First, there is a 2 × 10⁻⁸ probability that the astrometric motion fits a parallax-and-proper-motion-only model. Second, periodogram analysis shows a false alarm probability of 3 × 10⁻⁵ that the discovered period is randomly generated. The planetary mass is M₂ = 6.4 (+2.6,−3.1) Jupiter-masses (M_J), and the orbital period is P = 0.744 (+0.013,−0.008) yr in the most likely model. In less likely models, companion masses that are higher than the 13 M_J planetary mass limit are ruled out by past radial velocity (RV) measurements unless the system RV is more than twice the current upper limits and the near-periastron orbital phase was never observed. This new planetary system is remarkable, in part, because its star, VB 10, is near the lower mass limit for a star. Our astrometric observations provide a dynamical mass measurement and will in time allow us to confront the theoretical models of formation and evolution of such systems and their members. We thus add to the diversity of planetary systems and to the small number of known M-dwarf planets. Planets such as VB 10b could be the most numerous type of planets because M stars comprise >70% of all stars. To date they have remained hidden since the dominant RV planet-discovery technique is relatively insensitive to these dim, red systems.

We have discovered a correlation between the observed peak spectral energy E_pk,obs and the Euclidean value of 〈V/V_max〉 of gamma-ray bursts (GRBs). We present the evidence for the correlation in the GUSBAD catalog and use it to derive the luminosity function of GRBs without using any redshifts. The procedure involves dividing GUSBAD GRBs into five spectral classes based on their E_pk,obs. The overall luminosity function is derived assuming that each of the spectral classes contributes a Gaussian luminosity function. Their central luminosity is derived from the observed Euclidean 〈V/V_max〉. We explore various forms for the GRB rate function GR(z) in predicting redshift distributions of GRBs detected by Swift. We find that GR(z) peaks at a higher redshift than the typical star formation history currently favored in the literature. We consider two examples of GR(z) that successfully predict the observed redshift distribution of Swift GRBs. With the luminosity functions in hand, we convert the E_pk,obs − V/V_max correlation into an E_pk,obs − L_iso correlation and a rest-frame E_pk − L_iso correlation. By comparing the E_pk − L_iso correlation with a published correlation based on GRBs with known E_pk,obs and redshifts, we discuss the effect of Malmquist bias.

We study the initiation of the detonation in the gravitationally confined detonation (GCD) model of Type Ia supernovae (SNe Ia). In this model, ignition occurs at one or several off-center points, resulting in a burning bubble of hot ash that rises rapidly, breaks through the surface of the star, and collides at a point on the stellar surface opposite the breakout, producing a high-velocity inwardly directed flow. Initiation of the detonation occurs spontaneously in a region where the length scale of the temperature gradient extending from the flow (in which carbon burning is already occurring) into unburned fuel is commensurate to the range of critical length scales which have been derived from one-dimensional simulations that resolve the initiation of a detonation. By increasing the maximum resolution in a truncated cone that encompasses this region, beginning somewhat before initiation of the detonation occurs, we successfully simulate in situ the first gradient-initiated detonation in a whole-star simulation. The detonation emerges when a compression wave overruns a pocket of fuel situated in a Kelvin–Helmholtz cusp at the leading edge of the inwardly directed jet of burning carbon. The compression wave preconditions the temperature in the fuel in such a way that the Zel'dovich gradient mechanism can operate and a detonation ensues. We explore the dependence of the length scale of the temperature gradient on spatial resolution and discuss the implications for the robustness of this detonation mechanism. We find that the time and the location at which initiation of the detonation occurs varies with resolution. In particular, initiation of a detonation had not yet occurred in our highest resolution simulation by the time we ended the simulation because of the computational demand it required. However, it may detonate later. We suggest that the turbulent shear layer surrounding the inwardly directed jet provides the most favorable physical conditions, and therefore the most likely location, for initiation of a detonation in the GCD model.

We present very deep spectrophotometry of 14 bright extragalactic H ii regions belonging to spiral, irregular, and blue compact galaxies. The data for 13 objects were taken with the High Resolution Echelle Spectrometer on the Keck I telescope. We have measured C ii recombination lines in 10 of the objects and O ii recombination lines in eight of them. We have determined electron temperatures from line ratios of several ions, especially those of low ionization potential. We have found a rather tight linear empirical relation between T_e([N ii]) and T_e([O iii]). We have found that O ii lines give always larger abundances than [O iii] lines. Moreover, the difference of both O⁺⁺ abundance determinations—the so-called abundance discrepancy factor—is very similar in all the objects, with a mean value of 0.26 ± 0.09 dex, independent of the properties of the H ii region and of the parent galaxy. Using the observed recombination lines, we have determined the O, C, and C/O radial abundance gradients for three spiral galaxies: M33, M101, and NGC 2403, finding that C abundance gradients are always steeper than those of O, producing negative C/O gradients across the galactic disks. This result is similar to that found in the Milky Way and has important implications for chemical evolution models and the nucleosynthesis of C.

We describe the effect that new atomic calculations, including fully relativistic R-matrix calculations of collisional excitation rates and level-specific dielectronic and radiative recombination rates, have on line ratios from the astrophysically significant ion Ne ix. The new excitation rates systematically change some predicted Ne ix line ratios by 25% at temperatures at or below the temperature of maximum emissivity (4 × 10⁶ K), while the new recombination rates lead to systematic changes at higher temperatures. The new line ratios are shown to agree with observations of Capella and σ² CrB significantly better than older line ratios, showing that 25%–30% accuracy in atomic rates is inadequate for high-resolution X-ray observations from existing spectrometers.

We have investigated the development of current-driven (CD) kink instability through three-dimensional relativistic magnetohydrodynamic simulations. A static force-free equilibrium helical magnetic configuration is considered in order to study the influence of the initial configuration on the linear and nonlinear evolution of the instability. We found that the initial configuration is strongly distorted but not disrupted by the kink instability. The instability develops as predicted by linear theory. In the nonlinear regime, the kink amplitude continues to increase up to the terminal simulation time, albeit at different rates, for all but one simulation. The growth rate and nonlinear evolution of the CD kink instability depend moderately on the density profile and strongly on the magnetic pitch profile. The growth rate of the kink mode is reduced in the linear regime by an increase in the magnetic pitch with radius and reaches the nonlinear regime at a later time than the case with constant helical pitch. On the other hand, the growth rate of the kink mode is increased in the linear regime by a decrease in the magnetic pitch with radius and reaches the nonlinear regime sooner than the case with constant magnetic pitch. Kink amplitude growth in the nonlinear regime for decreasing magnetic pitch leads to a slender helically twisted column wrapped by magnetic field. On the other hand, kink amplitude growth in the nonlinear regime nearly ceases for increasing magnetic pitch.

We explore the properties of selected mid-ultraviolet (1900–3200 Å) spectroscopic indices of simple stellar populations. We incorporate the high-resolution UVBLUE stellar spectral library into an evolutionary population synthesis code, based on the most recent Padova isochrones. We analyze the trends of UV indices with respect to age and chemical composition. As a first test against observations, we compare our results with the empirical mid-UV spectral indices of Galactic globular clusters (GGCs), observed with the International Ultraviolet Explorer. We find that synthetic indices exhibit a variety of properties, the main one being the slight age sensitivity of most of them for ages >2 Gyr. However, for high metallicity, two indices, Fe ii 2332 and Fe ii 2402, display a remarkably different pattern, with a sharp increase within the first two Gyr and, thereafter, a rapid decline. These indices clearly mark the presence of young (∼ 1 Gyr) metal-rich (Z ⩾ Z_☉) stellar populations. We complement existing UV indices of GGCs with new measurements, and carefully identify a subsample of 10 indices suitable for comparison with theoretical models. The comparison shows a fair agreement and, in particular, the strong trend of the indices with metallicity is well reproduced. We also discuss the main improvements that should be considered in future modeling concerning, among others, the effects of α-enhancement in the spectral energy distributions.

We calculate the nonlinear matter power spectrum using the third-order perturbation theory without ignoring the pressure gradient term. We consider a semirealistic system consisting of two matter components with and without pressure, and both are expanded into the third order in perturbations in a self-consistent manner, for the first time. While the pressured component may be identified with baryons or neutrinos, in this paper we mainly explore the physics of the nonlinear pressure effect using a toy model in which the Jeans length does not depend on time, i.e., the sound speed decreases as a^−1/2, where a is the scale factor. The linear analysis shows that the power spectrum below the so-called filtering scale is suppressed relative to the power spectrum of the cold dark matter. Our nonlinear calculation shows that the actual filtering scale for a given sound speed is smaller than the linear filtering scale by a factor depending on the redshift and the Jeans length. A ∼40% change is common, and our results suggest that, when applied to baryons, the temperature of the intergalactic medium inferred from the filtering scale observed in the flux power spectrum of Lyα forests would be underestimated by a factor of 2, if one used the linear filtering scale to interpret the data. The filtering mass, which is proportional to the filtering scale cubed, can also be significantly smaller than the linear theory prediction especially at low redshift, where the actual filtering mass can be smaller than the linear prediction by a factor of 3. Finally, when applied to neutrinos, we find that neutrino perturbations deviate significantly from linear perturbations even below the free-streaming scales, and thus neutrinos cannot be treated as linear perturbations.

Precision laboratory measurements are presented for 1963 Cr i lines spanning the near-ultraviolet into the thermal infrared. Classifications, based on the analysis by Kiess, are presented. The measurements were obtained from Fourier transform spectra in the archives of the National Solar Observatory.

We use the star formation history (SFH) map of the Large Magellanic Cloud recently published by Harris and Zaritsky to study the sites of the eight smallest (and presumably youngest) supernova remnants (SNRs) in the Cloud: SN 1987A, N158A, N49, and N63A (core collapse remnants), 0509 − 67.5, 0519 − 69.0, N103B, and DEM L71 (Type Ia remnants). The local SFHs provide unique insights into the nature of the supernova (SN) progenitors, which we compare with the properties of the SN explosions derived from the remnants themselves and from SN light echoes. We find that all the core collapse SNe that we have studied are associated with vigorous star formation (SF) in the recent past. In the case of SN 1987A, the time of the last peak of SF (12 Myr) matches the lifetime of a star with the known mass of its blue supergiant progenitor (∼20 M_☉). More recent peaks of SF can lead to SNe with more massive progenitors, which opens the possibility of a Type Ib/c origin for SNRs N158A and N63A. Stars more massive than 21.5 M_☉ are very scarce around SNR N49, implying that the magnetar SGR 0526 − 66 in this SNR was either formed elsewhere or came from a progenitor with a mass well below the 30 M_☉ threshold suggested in the literature. Three of our four Ia SNRs are associated with old, metal-poor stellar populations. This includes SNR 0509 − 67.5, which is known to have been originated by an extremely bright Type Ia event, and yet is located very far away from any sites of recent SF, in a population with a mean age of 7.9 Gyr. The Type Ia SNR N103B, on the other hand, is associated with recent SF, and might have had a relatively younger and more massive progenitor with substantial mass loss before the explosion. We discuss these results in the context of our present understanding of core collapse and Type Ia SN progenitors.

Accretion disks are three-dimensional, turbulent, often self-gravitating, magnetohydrodynamic (MHD) flows, which can be modeled with numerical simulations. In this paper, we present a new algorithm that is based on a spectral decomposition method to simulate such flows. Because of the high order of the method, we can solve the induction equation in terms of the magnetic vector potential and, therefore, ensure trivially that the magnetic fields in the numerical solution are divergence free. The spectral method also suffers minimally from numerical dissipation and allows for an easy implementation of models for subgrid physics. Both properties make our method ideal for studying MHD turbulent flows such as those found in accretion disks around compact objects. We verify our algorithm with a series of standard tests and use it to show the development of MHD turbulence in a simulation of an accretion disk. Finally, we study the evolution and saturation of the power spectrum of MHD turbulence driven by the magnetorotational instability.

We have investigated the role of molecular anion chemistry in pseudo-time-dependent chemical models of dark clouds. With oxygen-rich elemental abundances, the addition of anions results in a slight improvement in the overall agreement between model results and observations of molecular abundances in Taurus molecular cloud 1 (TMC-1 (CP)). More importantly, with the inclusion of anions, we see an enhanced production efficiency of unsaturated carbon-chain neutral molecules, especially in the longer members of the families C_nH, C_nH₂, and HC_nN. The use of carbon-rich elemental abundances in models of TMC-1 (CP) with anion chemistry worsens the agreement with observations compared with model results obtained in the absence of anions.

Measurements of the temperature and density structure of the solar corona provide critical constraints on theories of coronal heating. Unfortunately, the complexity of the solar atmosphere, observational uncertainties, and the limitations of current atomic calculations, particularly those for Fe, all conspire to make this task very difficult. A critical assessment of plasma diagnostics in the corona is essential to making progress on the coronal heating problem. In this paper, we present an analysis of temperature and density measurements above the limb in the quiet corona using new observations from the EUV Imaging Spectrometer (EIS) on Hinode. By comparing the Si and Fe emission observed with EIS we are able to identify emission lines that yield consistent emission measure distributions. With these data we find that the distribution of temperatures in the quiet corona above the limb is strongly peaked near 1 MK, consistent with previous studies. We also find, however, that there is a tail in the emission measure distribution that extends to higher temperatures. EIS density measurements from several density sensitive line ratios are found to be generally consistent with each other and with previous measurements in the quiet corona. Our analysis, however, also indicates that a significant fraction of the weaker emission lines observed in the EIS wavelength ranges cannot be understood with current atomic data.

We performed combined focused ion beam/transmission electron microscopy studies to investigate the chemistry and structure of eight presolar silicate grains that were previously detected by NanoSIMS oxygen isotope mapping of the carbonaceous chondrite Acfer 094. The analyzed presolar silicates belong to the O isotope Groups I/II (¹⁷O-enriched and ¹⁸O-depleted) and therefore come from 1–2.5 M_☉ asymptotic giant branch stars of close-to-solar or slightly lower-than-solar metallicity. Three grains are amorphous, Mg-rich, and show a variable, but more pyroxene-like composition. Most probably, these grains have formed under circumstellar low-temperature conditions below the crystallization temperature. Three grains are Fe-bearing glasses similar to the "glass with embedded metal and sulfides" (GEMS) grains found in interplanetary dust particles. However, two of the meteorite GEMS grains from this study lack comparatively large (≳20 nm) Fe-rich inclusions and have sulfur contents <1 at.%, which is different than observed for the majority of GEMS grains. These grains likely condensed under strong non-equilibrium conditions from an Si-enriched gas. One olivine is characterized by a crystalline core and an amorphous, more Fe-rich rim, which is probably the result of interstellar medium sputtering combined with Mg removal. The detection of another olivine with a relatively high Fe content (Mg# 0.9) shows that circumstellar crystalline silicates are more Fe-rich than astrophysical models usually suggest. The overall predominance of olivine among the crystalline silicate stardust population compared to pyroxene indicates preferential formation or survival of this type of mineral. As pyroxene is indeed detected in circumstellar outflows, it remains to be seen how this result is compatible with astrophysical observations and experimental data.

We present HATNet observations of XO-5b, confirming its planetary nature based on evidence beyond that described in the announcement of Burke et al., namely, the lack of significant correlation between spectral bisector variations and orbital phase. In addition, using extensive spectroscopic measurements spanning multiple seasons, we investigate the relatively large scatter in the spectral line bisectors. We also examine possible blended stellar configurations (hierarchical triples, chance alignments) that can mimic the planet signals, and we are able to show that none are consistent with the sum of all the data. The analysis of the S activity index shows no significant stellar activity. Our results for the planet parameters are consistent with values in Burke et al., and we refine both the stellar and the planetary parameters using our data. XO-5b orbits a slightly evolved, late G type star with mass M_⋆ = 0.88 ± 0.03 M_☉, radius R_⋆ = 1.08 ± 0.04 R_☉, and metallicity close to solar. The planetary mass and radius are 1.059 ± 0.028 M_J and 1.109 ± 0.050 R_J, respectively, corresponding to a mean density of $0.96_{-0.11}^{+0.14}\;\rm g\;cm^{-3}$. The ephemeris for the orbit is P = 4.187757 ± 0.000011 days, E = 2454552.67168 ± 0.00029 (BJD) with transit duration of 0.1307 ± 0.0013 days. By measuring four individual transit centers, we found no signs for transit timing variations. The planet XO-5b is notable for its anomalously high Safronov number and has a high surface gravity when compared to other transiting exoplanets with similar period.

We study the galaxy morphology–luminosity–environmental relation and its redshift evolution using a spectroscopic sample of galaxies in the Great Observatories Origins Deep Survey. In the redshift range of 0.4 ⩽ z ⩽ 1.0, we detect conformity in morphology between neighboring galaxies. The realm of conformity is confined within the virialized region associated with each galaxy plus dark matter halo system. When a galaxy is located within the virial radius of its nearest neighbor galaxy, its morphology strongly depends on the neighbor's distance and morphology: the probability for a galaxy to be an early type (f_E) increases as it approaches an early-type neighbor, but decreases as it approaches a late-type neighbor. We find that f_E evolves much faster in high-density regions than in low-density regions, and that the morphology–density relation becomes significantly weaker at z ≈ 1. This may be because the rate of galaxy–galaxy interactions is higher in high-density regions, and a series of interactions and mergers over the course of galaxy life eventually transform late types into early types. We find more isolated galaxies are more luminous, which supports luminosity transformation through mergers at these redshifts. Our results are consistent with those from nearby galaxies, and demonstrate that galaxy–galaxy interactions have been strongly affecting the galaxy evolution over a long period of time.

We present a comparison between the observed color distribution, number, and mass density of massive galaxies at 1.5 < z < 3 and a model by Hopkins et al. that relates the quasar and galaxy population on the basis of gas-rich mergers. In order to test the hypothesis that quiescent red galaxies are formed after a gas-rich merger involving quasar activity, we confront photometry of massive (M>4 × 10¹⁰ M_☉) galaxies extracted from the FIRES, GOODS-South, and MUSYC surveys, together spanning an area of 496 arcmin², with synthetic photometry from hydrodynamical merger simulations. As in the Hopkins et al. model, we use the observed quasar luminosity function to estimate the merger rate. We find that the synthetic U − V and V − J colors of galaxies that had a quasar phase in their past match the colors of observed galaxies that are best characterized by a quiescent stellar population. At z ∼ 2.6, the observed number and mass density of quiescent red galaxies with M>4 × 10¹⁰ M_☉ is consistent with the model in which every quiescent massive galaxy underwent a quasar phase in the past. At z ∼ 1.9, 2.8 times less quiescent galaxies are observed than predicted by the model as descendants of higher redshift quasars. The merger model also predicts a large number and mass density of galaxies undergoing star formation driven by the merger. We find that the predicted number and mass density accounts for 30%–50% of the observed massive star-forming galaxies. However, their colors do not match those of observed star-forming galaxies. In particular, the colors of dusty red galaxies (accounting for 30%–40% of the massive galaxy population) are not reproduced by the simulations. Several possible origins of this discrepancy are discussed. The observational constraints on the validity of the model are currently limited by cosmic variance and uncertainties in stellar population synthesis and radiative transfer.

We calculate simulated images of disks perturbed by embedded small planets. These 10–50 M_⊕ bodies represent the growing cores of giant planets. We examine scattered light and thermal emission from these disks over a range of wavelengths, taking into account the wavelength-dependent opacity of dust in the disk. We also examine the effect of inclination on the observed perturbations. We find that the perturbations are best observed in the visible to mid-infrared (mid-IR). Scattered light images reflect shadows produced at the surface of perturbed disks, while the infrared images follow thermal emission from the surface of the disk, showing cooled/heated material in the shadowed/brightened regions. At still longer wavelengths in the submillimeter, the perturbation fades as the disk becomes optically thin and surface features become overwhelmed by emission closer toward the midplane of the disk. With the construction of telescopes such as TMT, GMT, and ALMA due in the next decade, there is a real possibility of observing planets forming in disks in the optical and submillimeter. However, having the angular resolution to observe the features in the mid-IR will remain a challenge.

Rapid rotation in field red giant stars is a relatively rare but well-studied phenomenon; here we investigate the potential role of planet accretion in spinning up these stars. Using Zahn's theory of tidal friction and stellar evolution models, we compute the decay of a planet's orbit into its evolving host star and the resulting transfer of angular momentum into the stellar convective envelope. This experiment assesses the frequency of planet ingestion and rapid rotation on the red giant branch (RGB) for a sample of 99 known exoplanet host stars. We find that the known exoplanets are indeed capable of creating rapid rotators; however, the expected fraction due to planet ingestion is only ∼ 10% of the total seen in surveys of present-day red giants. Of the planets ingested, we find that those with smaller initial semimajor axes are more likely to create rapid rotators because these planets are accreted when the stellar moment of inertia is smallest. We also find that many planets may be ingested prior to the RGB phase, contrary to the expectation that accretion would generally occur when the stellar radii expand significantly as giants. Finally, our models suggest that the rapid rotation signal from ingested planets is most likely to be seen on the lower RGB, which is also where alternative mechanisms for spin-up, e.g., angular momentum dredged up from the stellar core, do not operate. Thus, rapid rotators on the lower RGB are the best candidates to search for definitive evidence of systems that have experienced planet accretion.

We present projected rotational velocity values for 97 Galactic, 55 SMC, and 106 LMC O-B type stars from archival FUSE observations. The evolved and unevolved samples from each environment are compared through the Kolmogorov–Smirnov test to determine if the distribution of equatorial rotational velocities is metallicity dependent for these massive objects. Stellar interior models predict that massive stars with SMC metallicity will have significantly reduced angular momentum loss on the main sequence compared to their Galactic counterparts. Our results find some support for this prediction but also show that even at Galactic metallicity, evolved and unevolved massive stars have fairly similar fractions of stars with large Vsin i values. Macroturbulent broadening that is present in the spectral features of Galactic evolved massive stars is lower in the LMC and SMC samples. This suggests the processes that lead to macroturbulence are dependent upon metallicity.

The association of an electromagnetic signal with the merger of a pair of supermassive black holes would have many important implications. For example, it would provide new information about gas and magnetic field interactions in dynamical spacetimes as well as a combination of redshift and luminosity distance that would enable precise cosmological tests. A proposal first made by Bode & Phinney is that because radiation of gravitational waves during the final inspiral and merger of the holes is abrupt and decreases the mass of the central object by a few percent, there will be waves in the disk that can steepen into shocks and thus increase the disk luminosity in a characteristic way. We evaluate this process analytically and numerically. We find that shocks only occur when the fractional mass loss exceeds the half-thickness of the disk, hence significant energy release only occurs for geometrically thin disks which are thus at low Eddington ratios. This strongly limits the effective energy release, and in fact our simulations show that the natural variations in disk luminosity are likely to obscure this effect entirely. However, we demonstrate that the reduction of luminosity caused by the retreat of the inner edge of the disk following mass loss is potentially detectable. This decrease occurs even if the disk is geometrically thick, and lasts for a duration on the order of the viscous time of the modified disk. Observationally, the best prospect for detection would be a sensitive future X-ray instrument with a field of view of the order of a square degree, or possibly a wide-field radio array such as the Square Kilometer Array, if the disk changes produce or interrupt radio emission from a jet.

Observations of the high-mass star-forming region AFGL 2591 reveal a large abundance of CO⁺, a molecule known to be enhanced by far-ultraviolet (FUV) and X-ray irradiation. In chemical models assuming a spherically symmetric envelope, the volume of gas irradiated by protostellar FUV radiation is very small due to the high extinction by dust. The abundance of CO⁺ is thus underpredicted by orders of magnitude. In a more realistic model, FUV photons can escape through an outflow region and irradiate gas at the border to the envelope. Thus, we introduce the first two-dimensional axisymmetric chemical model of the envelope of a high-mass star-forming region to explain the CO⁺ observations as a prototypical FUV tracer. The model assumes an axisymmetric power-law density structure with a cavity due to the outflow. The local FUV flux is calculated by a Monte Carlo radiative transfer code taking scattering on dust into account. A grid of precalculated chemical abundances, introduced in the first part of this series of papers, is used to quickly interpolate chemical abundances. This approach allows us to calculate the temperature structure of the FUV-heated outflow walls self-consistently with the chemistry. Synthetic maps of the line flux are calculated using a raytracer code. Single-dish and interferometric observations are simulated and the model results are compared to published and new JCMT and Submillimeter Array (SMA) observations. The two-dimensional model of AFGL 2591 is able to reproduce the JCMT single-dish observations and also explains the nondetection by the SMA. We conclude that the observed CO⁺ line flux and its narrow width can be interpreted by emission from the warm and dense outflow walls irradiated by protostellar FUV radiation.

Remote observing of exoplanetary atmospheres is now possible, offering us access to circulation regimes unlike any of the familiar solar system cases. Atmospheric circulation models are being developed to study these new regimes but model validations and intercomparisons are needed to establish their consistency and accuracy. To this end, we present a simple Earth-like validation of the pseudospectral solver of meteorological equations called Intermediate General Circulation Model (IGCM), based on Newtonian relaxation to a prescribed latitudinal profile of equilibrium temperatures. We then describe a straightforward and idealized model extension to the atmospheric flow on a hot Jupiter with the same IGCM solver. This shallow, three-dimensional hot Jupiter model is based on Newtonian relaxation to a permanent day–night pattern of equilibrium temperatures and the absence of surface drag. The baroclinic regime¹ of the Earth's lower atmosphere is contrasted with the more barotropic regime of the simulated hot Jupiter flow. For plausible conditions at the 0.1–1 bar pressure level on HD 209458b, the simulated flow is characterized by unsteadiness, subsonic wind speeds, a zonally perturbed superrotating equatorial jet and large-scale polar vortices. Violation of the Rayleigh–Kuo inflexion point criterion on the flanks of the accelerating equatorial jet indicates that barotropic (horizontal shear) instabilities may be important dynamical features of the simulated flow. Similarities and differences with previously published simulated hot Jupiter flows are briefly noted.

Erratum

We use one of the highest resolution cosmological smoothed particle hydrodynamic simulations to date to demonstrate that cold gaseous clouds form around Milky Way-size galaxies. We further explore mechanisms responsible for their formation and show that a large fraction of clouds originate as a consequence of late-time filamentary "cold mode" accretion. Here, filaments that are still colder and denser than the surrounding halo gas are not able to connect directly to galaxies, as they do at high redshift, but are instead susceptible to the combined action of cooling and Rayleigh–Taylor instabilities at intermediate radii within the halo leading to the production of cold, dense pressure-confined clouds, without an associated dark matter component. This process is aided through the compression of the incoming filaments by the hot halo gas and expanding shocks during the halo buildup. Our mechanism directly seeds clouds from gas with substantial local overdensity, unlike in previous models, and provides a channel for the origin of cloud complexes. These clouds can later "rain" onto galaxies, delivering fuel for star formation. Owing to the relatively large cross-section of filaments and the net angular momentum carried by the gas, the clouds will be distributed in a modestly flattened region around a galaxy.

We present a correlation between the 2–10 keV spectral slope Γ_X and the Eddington ratio L/L_EDD in a sample of ∼400 Sloan Digital Sky Survey (SDSS) quasars with available hard X-ray spectra from XMM-Newton serendipitous observations. We find that the Γ_X–L/L_EDD correlation is strongest in objects with black hole (BH) masses determined from the Hβ line, and weaker (but still present) for those based on Mg ii. An empirical nonlinear correction of the Mg ii-based masses, obtained by comparing the mass estimates in SDSS quasars having both Hβ and Mg ii measurements, significantly increases the strength of the correlation. No correlation is found among objects with BH masses derived from C iv, confirming that this line is not a reliable indicator of the BH mass. No significant correlation is found with the bolometric luminosity, while a Γ_X–M_BH relation is present, though with a lower statistical significance than between Γ_X and L/L_EDD. Our results imply a physical link between the accretion efficiency in the (cold) accretion disk of active galactic nuclei and the physical status of the (hot) corona responsible for the X-ray emission.

We explore the age distribution of the globular cluster (GC) system of the nearby elliptical galaxy NGC 5128 using ultraviolet (UV) photometry from GALEX observations, with UV–optical colors used as the age indicator. Most GCs in NGC 5128 follow the general trends of GCs in M31 and the Milky Way in the UV–optical color–color diagram, which indicates that the majority of GCs in NGC 5128 are old similar to the age range of old GCs in M31 and the Milky Way. A large fraction of spectroscopically identified intermediate-age GC (IAGC) candidates with ∼3–8 Gyr are not detected in the far-UV (FUV) passband. Considering the nature of intermediate-age populations being faint in the FUV passband, we suggest that many of the spectroscopically identified IAGCs may be truly intermediate in age. This is in contrast to the case of M31 where a large fraction of spectroscopically suggested IAGCs are detected in FUV and therefore may not be genuine IAGCs but rather older GCs with developed blue horizontal branch stars. Our UV photometry strengthens the results previously suggesting the presence of GC and stellar subpopulation with intermediate age in NGC 5128. The existence of IAGCs strongly indicates the occurrence of at least one more major star formation episode after a starburst at high redshift.

The acceleration of ions during magnetic reconnection in solar flares is explored with simulations and analytic analysis. Ions crossing into Alfvénic reconnection outflows can behave like pickup particles and gain an effective thermal velocity equal to the Alfvén speed. However, with a sufficiently strong ambient out-of-plane magnetic field, which is the relevant configuration for flares, the ions can become adiabatic and their heating is then dramatically reduced. The threshold for nonadiabatic behavior, where ions are strongly heated, becomes a condition on the ion mass-to-charge ratio, $m_i/m_pZ_i>10\sqrt{\beta _{0x}/2}/\pi$, where m_i and Z_i are the ion mass and charge state, m_p is the proton mass, and β_0x = 8πnT/B²_0x is the ratio of the plasma pressure to that of the reconnecting magnetic field B_0x. Thus, during flares high mass-to-charge particles gain energy more easily than protons and a simple model reveals that their abundances are enhanced, which is consistent with observations.

We present results of a semianalytic model (SAM) that includes cold accretion and a porosity-based prescription for star formation. We can recover the puzzling observational results of low V/σ seen in various massive disk or disk-like galaxies, if we allow 18% of the accretion energy from cold flows to drive turbulence in gaseous disks at z = 2. The increase of gas mass through cold flows is by itself not sufficient to increase the star formation rate sufficiently to recover the number density of $\dot{M}_*>120 \;M_{\odot }$ yr⁻¹ galaxies in our model. In addition, it is necessary to increase the star formation efficiency. This can be achieved naturally in the porosity model, where star formation efficiency scales ∝σ, which scales as cloud velocity dispersion. As cold accretion is the main driver for gas velocity dispersion in our model, star formation efficiency parallels cold accretion rates and allows fast conversion into stars. At z ∼ 2, we find a space density 10⁻⁴ Mpc⁻³ in star-forming galaxies with $\dot{M}_*>120 \;M_{\odot }$ yr⁻¹, in better agreement than earlier estimates from SAMs. However, the fundamental relation between $\dot{M}_*$ and M_* is still offset from the observed relation, indicating the need for possibly more efficient star formation at high-z perhaps associated with a role for active galactic nucleus (AGN) triggering.

We report the discovery of four rare debris disks with warm excesses around F stars, significantly increasing the number of such systems known in the solar neighborhood. Three of the disks are consistent with the predictions of steady-state planetesimal disk evolution models. The oldest source, HD 169666, displays a dust fractional luminosity too high to be in a steady state and we suggest that this system recently underwent a transient event of dust production. In addition, two spectra of this star separated by approximately three years show silicate emission features, indicative of submicron- to micron-sized grains. We argue that such small grains would be rapidly depleted and their presence in both spectra suggests that the production of small dust is continuous over a timescale of at least a few years. We predict that systems showing variable mid-infrared spectra, if they exist, will provide valuable help in distinguishing the possible scenarios proposed for dust replenishment.

The habitable zones (HZs) of main-sequence stars have traditionally been defined as the range of orbits that intercept the appropriate amount of stellar flux to permit surface water on a planet. Terrestrial exoplanets discovered to orbit M stars in these zones, which are close-in due to decreased stellar luminosity, may also undergo significant tidal heating. Tidal heating may span a wide range for terrestrial exoplanets and may significantly affect conditions near the surface. For example, if heating rates on an exoplanet are near or greater than that on Io (where tides drive volcanism that resurfaces the planet at least every 1 Myr) and produce similar surface conditions, then the development of life seems unlikely. On the other hand, if the tidal heating rate is less than the minimum to initiate plate tectonics, then CO₂ may not be recycled through subduction, leading to a runaway greenhouse that sterilizes the planet. These two cases represent potential boundaries to habitability and are presented along with the range of the traditional HZ for main-sequence, low-mass stars. We propose a revised HZ that incorporates both stellar insolation and tidal heating. We apply these criteria to GJ 581 d and find that it is in the traditional HZ, but its tidal heating alone may be insufficient for plate tectonics.

The supernova remnant G0.9+0.1 has long been inferred to contain a central energetic pulsar. In observations with the NRAO Green Bank Telescope at 2 GHz, we have detected radio pulsations from PSR J1747−2809. The pulsar has a rotation period of 52 ms, and a spin-down luminosity of $\dot{E} = 4.3\times 10^{37}$ erg s⁻¹, the second largest among known Galactic pulsars. With a dispersion measure of DM = 1133 pc cm⁻³, PSR J1747−2809 is distant, at ≈13 kpc according to the NE2001 electron density model, although it could be located as close as the Galactic center. The pulse profile is greatly scatter-broadened at a frequency of 2 GHz, so that it is effectively undetectable at 1.4 GHz, and is very faint, with period-averaged flux density of 40 μJy at 2 GHz.

We study the formation and evolution of a turbulent spectrum of Alfvén waves driven by reflection off the solar wind density gradients, starting from the coronal base up to 17 solar radii, well beyond the Alfvénic critical point. The background solar wind is assigned and two-dimensional shell models are used to describe nonlinear interactions. We find that the turbulent spectra are influenced by the nature of the reflected waves. Close to the base, these give rise to a flatter and steeper spectrum for the outgoing and reflected waves, respectively. At higher heliocentric distance both spectra evolve toward an asymptotic Kolmogorov spectrum. The turbulent dissipation is found to account for at least half of the heating required to sustain the background imposed solar wind and its shape is found to be determined by the reflection-determined turbulent heating below 1.5 solar radii. Therefore, reflection and reflection-driven turbulence are shown to play a key role in the acceleration of the fast solar wind and origin of the turbulent spectrum found at 0.3 AU in the heliosphere.

We compare the results of the unified Monte Carlo chemical model with the new modified-rate equation (MRE) method under a wide range of interstellar conditions, using a full gas–grain chemical network. In most of the explored parameter space, the new MRE method reproduces very well the results of the exact approach. Small disagreements between the methods may be remedied by the use of a more complete surface chemistry network, appropriate to the full range of temperatures employed here.

We numerically analyze the evolution of a long-duration gamma-ray burst jet as it leaves the progenitor star and propagates to the photospheric radius, where radiation can be released. We find that the interaction of the relativistic material with the progenitor star has influences well beyond the stellar surface. Tangential collimation shocks are observed throughout the jet evolution, out to about 100 stellar radii, which is the whole range of our simulation. We find that the jet is internally hot at the photospheric radius and we compute the photospheric emission. The photosphere is a very efficient radiator, capable of converting more than half of the total energy of the jet into radiation. We show that bright photospheres are a common feature of jets born inside massive progenitor stars and that this effect can explain the high radiative efficiency observed in long-duration bursts.

On 2000 April 4–6 the Energetic and Relativistic Nuclei and Electron particle telescope on the Solar and Heliospheric Observatory spacecraft observed a major solar energetic particle (SEP) event associated with two coronal mass ejections (CMEs) separated by approximately 8 hr. The first CME was accompanied by a low-frequency type II radio burst observed by the WAVES receivers on the Wind spacecraft. Analysis of the high-precision measurements of the ∼20 MeV proton flux anisotropy, model fitting of the type II dynamic spectrum, and SEP transport modeling support the idea that the shock wave of the first CME was an efficient accelerator for ∼20 MeV protons during only the first 6 hr after the launch. This shock gradually slowed down, weakened, and became transparent for the protons produced by the second eruption behind the previous CME. The main production of SEPs due to the two successive eruptions continued together for 12 hr. The near-Earth SEP event was additionally amplified by the SEP mirroring in the interplanetary magnetic field draping at the edge of an old CME beyond the Earth's orbit, which made the SEP intensity–time profiles more prolonged than would be expected based on the assumption of SEP transport in the standard solar wind.

We have used Advanced Composition Explorer instruments to survey the period 2007 March through the end of 2008 for ³He-rich solar energetic particle (SEP) events occurring during near solar minimum conditions. Four events were found, all associated with single solar active regions in the western hemisphere. They all show ³He:⁴He ratios of a few percent (i.e., ≳100 times solar system abundances), low intensities, and spectra extending up to at least 1 MeV nucleon⁻¹. Two events, on 2008 February 4 and 2008 June 16, were devoid of signatures associated with ³He-rich SEPs, namely they lacked associations with energetic electrons and type-III bursts. In addition, there were no clear coronal mass ejections and X-ray flare activity was very low or absent. We take this as evidence that the irreducible requirement for ³He-rich SEPs is a western hemisphere solar active region where magnetic and plasma processes preferentially energize ³He and heavy ions.