Table of contents

We obtained ESI/Keck rotation curves of 10 Mg ii absorption-selected galaxies (0.3 ⩽ z ⩽ 1.0) for which we have WFPC-2/HST images and high-resolution HIRES/Keck and UVES/VLT quasar spectra of the Mg ii absorption profiles. We perform a kinematic comparison of these galaxies and their associated halo Mg ii absorption. For all 10 galaxies, the majority of the absorption velocities lie in the range of the observed galaxy rotation velocities. In 7/10 cases, the absorption velocities reside fully to one side of the galaxy systemic velocity and usually align with one arm of the rotation curve. In all cases, a constant rotating thick-disk model poorly reproduces the full spread of observed Mg ii absorption velocities when reasonably realistic parameters are employed. In 2/10 cases, the galaxy kinematics, star formation surface densities, and absorption kinematics have a resemblance to those of high-redshift galaxies showing strong outflows. We find that Mg ii absorption velocity spread and optical depth distribution may be dependent on galaxy inclination. To further aid in the spatial–kinematic relationships of the data, we apply quasar absorption-line techniques to a galaxy (v_c = 180 km s⁻¹) embedded in ΛCDM simulations. In the simulations, Mg ii absorption selects metal-enriched "halo" gas out to ∼100 kpc from the galaxy, tidal streams, filaments, and small satellite galaxies. Within the limitations inherent in the simulations, the majority of the simulated Mg ii absorption arises in the filaments and tidal streams and is infalling toward the galaxy with velocities between −200 km s^-1 ⩽ v_r ⩽ −180 km s⁻¹. The Mg ii absorption velocity offset distribution (relative to the simulated galaxy) spans ∼200 km s⁻¹ with the lowest frequency of detecting Mg ii at the galaxy systematic velocity.

We probe the spatial and dynamical structure of the old open cluster M67 using photometric data from the Sloan Digital Sky Survey's sixth data release. Making use of an optimal contrast, or matched filter, algorithm, we map the distribution of high probability members of M67. We find an extended and elongated halo of likely members to a radius of nearly 60'. Our measured core radius of R_core = 824 ± 060 is somewhat larger than that of previous estimates. We attribute the larger core radius measurement to the SDSS probing lower mass main sequence stars than has been done before for similar studies of M67, and the exclusion of post-main-sequence M67 members in the SDSS sample. We estimate the number of M67 members in our SDSS sample to be 1385 ± 67 stars. A lower limit on the binary fraction in M67 is measured to be 45%. A higher fraction of binary stars is measured in the core as compared to the halo, and the luminosity function of the core is found to be more depleted of low-mass stars. Thus, the halo is consistent with mass segregation within the cluster. The galactic orbit of M67 is calculated from recent proper motion and radial velocity determinations. The elongated halo is roughly aligned to the proper motion of the cluster. This appears to be a result of mass segregation due to the galactic tidal field. Our algorithm is run on Two Micron All Sky Survey photometry to directly compare to previous studies of M67. Decreasing core radii is found for stars with greater masses. We test the accuracy of our algorithm using 1000 artificial cluster Monte Carlo simulations. It is found that the matched filter technique is suitable for recovering low-density spatial structures, as well as measuring the binary fraction of the cluster.

We present the results of a detailed abundance analysis of one of the confirmed building blocks of the Milky Way stellar halo, a kinematically coherent metal-poor stellar stream. We have obtained high-resolution and high signal-to-noise spectra of 12 probable stream members using the Magellan Inamori Kyocera Echelle spectrograph on the Magellan–Clay Telescope at Las Campanas Observatory and the 2dCoude spectrograph on the Smith Telescope at McDonald Observatory. We have derived abundances or upper limits for 51 species of 46 elements in each of these stars. The stream members show a range of metallicity (−3.4 < [Fe/H] <−1.5) but are otherwise chemically homogeneous, with the same star-to-star dispersion in [X/Fe] as the rest of the halo. This implies that, in principle, a significant fraction of the Milky Way stellar halo could have formed from accreted systems like the stream. The stream stars show minimal evolution in the α or Fe-group elements over the range of metallicity. This stream is enriched with material produced by the main and weak components of the rapid neutron-capture process and shows no evidence for enrichment by the slow neutron-capture process.

The early solar system contained a number of short-lived radionuclides (SLRs) such as ²⁶Al with half-lives <15 Myr. The one-time presence of ⁶⁰Fe strongly suggests that the source of these radionuclides was a nearby supernova. In this paper, we investigate the "aerogel" model, which hypothesizes that the solar system's SLRs were injected directly into the solar system's protoplanetary disk from a supernova within the same star-forming region. Previous work has shown that disks generally survive the impact of supernova ejecta, but also that little gaseous ejecta can be injected into the disk. The aerogel model hypothesizes that radionuclides in the ejecta condensed into micron-sized dust grains that were injected directly into the solar nebula disk. Here, we discuss the density structure of supernova ejecta and the observational support for dust condensation in the ejecta. We argue that supernova ejecta are clumpy and describe a model to quantify this clumpiness. We also argue that infrared observations may be underestimating the fraction of material that condenses into dust. Building on calculations of how supernova ejecta interact with protoplanetary disks, we calculate the efficiency with which dust grains in the ejecta are injected into a disk. We find that about 70% of material in grains roughly 0.4 μm in diameter can be injected into disks. If ejecta are clumpy, the solar nebula was struck by a clump with higher-than-average ²⁶Al and ⁶⁰Fe, and these elements condensed efficiently into large grains, then the abundances of SLRs in the early solar system can be explained, even if the disk lies 2 pc from the supernova explosion. The probability that all these factors are met is low, perhaps ∼10⁻³–10⁻², and receiving as much ²⁶Al and ⁶⁰Fe as the solar system did may be a rare event. Still, the aerogel model remains a viable explanation for the origins of the radionuclides in the early solar system, and may be the most plausible one.

HD 179821 is an enigmatic evolved star that possesses characteristics of both a post-asymptotic giant branch (post-AGB) star and a yellow hypergiant, and there has been no evidence that unambiguously defines its nature. These two hypotheses are products of an indeterminate distance, presumed to be 1 kpc or 6 kpc. We have obtained the two-epoch Hubble Space Telescope Wild Field Planetary Camera 2 data of its circumstellar shell, which shows multiple concentric arcs extending out to about 8''. We have performed differential proper-motion measurements on distinct structures within the circumstellar shell of this mysterious star in hopes of determining the distance to the object, and thereby distinguishing the nature of this enigmatic stellar source. Upon investigation, rather than azimuthal radially symmetric expansion, we discovered a bulk motion of the circumstellar shell of (2.41 ± 0.43, 2.97 ± 0.32) mas yr⁻¹. This corresponded to a translational interstellar medium (ISM) flow of (1.28 ± 0.95, 7.27 ± 0.75) mas yr⁻¹ local to the star. This finding implies that the distance to HD 179821 should be rather small in order for its circumstellar shell to preserve its highly intact spherical structure in the presence of the distorting ISM flow, therefore favoring the proposition that HD 179821 is a post-AGB object.

In this paper, we present emission line strengths, abundances, and element ratios (X/O for Ne, S, Cl, and Ar) for a sample of 38 Galactic disk planetary nebulae (PNe) consisting primarily of Peimbert classification Type I. Spectrophotometry for these PNe incorporates an extended optical/near-IR range of λλ3600–9600 Å including the [S iii] lines at 9069 Å and 9532 Å, setting this relatively large sample apart from typical spectral coverage. We have utilized Emission Line Spectrum Analyzer, a five-level atom abundance routine, to determine T_e, N_e, ionization correction factors, and total element abundances, thereby continuing our work toward a uniformly processed set of data. With a compilation of data from >120 Milky Way PNe, we present results from our most recent analysis of abundance patterns in Galactic disk PNe. With a wide range of metallicities, galactocentric distances, and both Type I and non-Type I objects, we have examined the alpha elements against H ii regions and blue compact galaxies (H2BCGs) to discern signatures of depletion or enhancement in PNe progenitor stars, particularly the destruction or production of O and Ne. We present evidence that many PNe have higher Ne/O and lower Ar/Ne ratios compared to H2BCGs within the range of 8.5–9.0 for 12 + log(O/H). This suggests that Ne is being synthesized in the low- and intermediate-mass progenitors. Sulfur abundances in PNe continue to show great scatter and are systematically lower than those found in H2BCG at a given metallicity. Although we find that PNe do show some distinction in alpha elements when compared to H2BCG, within the Peimbert classification types studied, PNe do not show significant differences in alpha elements amongst themselves, at least to an extent that would distinguish in situ nucleosynthesis from the observed dispersion in abundance ratios.

A method for separating coronal mass ejections (CMEs) from the quiescent corona in white-light coronagraph images is presented. Such a separation allows the study of CME structure, as well as enabling a study of the quiescent coronal structure, without contamination by the CME. The fact that the large-scale quiescent corona is very close to radial, whilst CMEs are highly non-radial, enables the separation of the two components. The method is applied to Large Angle Spectrometric Coronagraph/Solar and Heliospheric Observatory C2 and C3 observations, and is successful in revealing CME signal, faint CMEs and blobs, and dark rarefactions within a CME. The success of the separation is tested at solar minimum, a time when streamers are in general most non-radial. The technique is also compared to other commonly used methods. The separation method enables (1) the study of extremely faint CME structure, down to almost the noise level of the coronagraphs, (2) paves the way for automated categorization of CME internal structure, and (3) provides a cleaner basis for tomography of the quiescent corona, without contamination from CMEs.

Long-duration gamma-ray bursts (GRBs) are widely believed to be highly collimated explosions (bipolar conical outflows with half-opening angle θ≈ 1°–10°). As a result of this beaming factor, the true energy release from a GRB is usually several orders of magnitude smaller than the observed isotropic value. Measuring this opening angle, typically inferred from an achromatic steepening in the afterglow light curve (a "jet" break), has proven exceedingly difficult in the Swift era. Here, we undertake a study of five of the brightest (in terms of the isotropic prompt γ-ray energy release, E_γ,iso) GRBs in the Swift era to search for jet breaks and hence constrain the collimation-corrected energy release. We present multi-wavelength (radio through X-ray) observations of GRBs 050820A, 060418, and 080319B, and construct afterglow models to extract the opening angle and beaming-corrected energy release for all three events. Together with results from previous analyses of GRBs 050904 and 070125, we find evidence for an achromatic jet break in all five events, strongly supporting the canonical picture of GRBs as collimated explosions. The most natural explanation for the lack of observed jet breaks from most Swift GRBs is therefore selection effects. However, the opening angles for the events in our sample are larger than would be expected if all GRBs had a canonical energy release of ∼10⁵¹ erg. The total energy release we measure for the "hyper-energetic" (E_tot ≳ 10⁵² erg) events in our sample is large enough to start challenging models with a magnetar as the compact central remnant.

We investigate 35 prestellar cores and 36 protostellar cores in the Perseus molecular cloud. We find a very tight correlation between the physical parameters describing the N₂H⁺ and NH₃ gas. Both the velocity centroids and the line widths of N₂H⁺ and NH₃ correlate much better than either species correlates with CO, as expected if the nitrogen-bearing species are probing primarily the dense core gas where the CO has been depleted. We also find a tight correlation in the inferred abundance ratio between N₂H⁺ and para-NH₃ across all cores, with N(p-NH₃)/N(N₂H⁺) = 22 ± 10. We find a mild correlation between NH₃ (and N₂H⁺) column density and the (sub)millimeter dust continuum derived H₂ column density for prestellar cores, N(p-NH₃)/N(H₂) ∼10⁻⁸, but do not find a fixed ratio for protostellar cores. The observations suggest that in the Perseus molecular cloud the formation and destruction mechanisms for the two nitrogen-bearing species are similar, regardless of the physical conditions in the dense core gas. While the equivalence of N₂H⁺ and NH₃ as powerful tracers of dense gas is validated, the lack of correspondence between these species and the (sub)millimeter dust continuum observations for protostellar cores is disconcerting and presently unexplained.

We present new Keck/DEIMOS spectroscopic observations of hundreds of individual stars along the sightline to the first three of the Andromeda (M31) dwarf spheroidal (dSph) galaxies to be discovered, And I, II, and III, and combine them with recent spectroscopic studies by our team of three additional M31 dSphs, And VII, X, and XIV, as a part of the SPLASH Survey (Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo). Member stars of each dSph are isolated from foreground Milky Way dwarf stars and M31 field contamination using a variety of photometric and spectroscopic diagnostics. Our final spectroscopic sample of member stars in each dSph, for which we measure accurate radial velocities with a median uncertainty (random plus systematic errors) of 4–5 km s⁻¹, includes 80 red giants in And I, 95 in And II, 43 in And III, 18 in And VII, 22 in And X, and 38 in And XIV. The sample of confirmed members in the six dSphs is used to derive each system's mean radial velocity, intrinsic central velocity dispersion, mean abundance, abundance spread, and dynamical mass. This combined data set presents us with a unique opportunity to perform the first systematic comparison of the global properties (e.g., metallicities, sizes, and dark matter masses) of one-third of Andromeda's total known dSph population with Milky Way counterparts of the same luminosity. Our overall comparisons indicate that the family of dSphs in these two hosts have both similarities and differences. For example, we find that the luminosity–metallicity relation is very similar between L ∼ 10⁵ and 10⁷L_☉, suggesting that the chemical evolution histories of each group of dSphs are similar. The lowest luminosity M31 dSphs appear to deviate from the relation, possibly suggesting tidal stripping. Previous observations have noted that the sizes of M31's brightest dSphs are systematically larger than Milky Way satellites of similar luminosity. At lower luminosities between L = 10⁴ and 10⁶L_☉, we find that the sizes of dSphs in the two hosts significantly overlap and that four of the faintest M31 dSphs are smaller than Milky Way counterparts. The first dynamical mass measurements of six M31 dSphs over a large range in luminosity indicate similar mass-to-light ratios compared to Milky Way dSphs among the brighter satellites, and smaller mass-to-light ratios among the fainter satellites. Combined with their similar or larger sizes at these luminosities, these results hint that the M31 dSphs are systematically less dense than Milky Way dSphs. The implications of these similarities and differences for general understanding of galaxy formation and evolution are summarized.

We present the results of a photometric and spectroscopic survey of 321 Lyman break galaxies (LBGs) at z∼ 3 to investigate systematically the relationship between Lyα emission and stellar populations. Lyα equivalent widths (W_Lyα) were calculated from rest-frame UV spectroscopy and optical/near-infrared/Spitzer photometry was used in population synthesis modeling to derive the key properties of age, dust extinction, star formation rate (SFR), and stellar mass. We directly compare the stellar populations of LBGs with and without strong Lyα emission, where we designate the former group (W_Lyα⩾ 20 Å) as Lyα emitters (LAEs) and the latter group (W_Lyα< 20 Å) as non-LAEs. This controlled method of comparing objects from the same UV luminosity distribution represents an improvement over previous studies in which the stellar populations of LBGs and narrowband-selected LAEs were contrasted, where the latter were often intrinsically fainter in broadband filters by an order of magnitude simply due to different selection criteria. Using a variety of statistical tests, we find that Lyα equivalent width and age, SFR, and dust extinction, respectively, are significantly correlated in the sense that objects with strong Lyα emission also tend to be older, lower in SFR, and less dusty than objects with weak Lyα emission, or the line in absorption. We accordingly conclude that, within the LBG sample, objects with strong Lyα emission represent a later stage of galaxy evolution in which supernovae-induced outflows have reduced the dust covering fraction. We also examined the hypothesis that the attenuation of Lyα photons is lower than that of the continuum, as proposed by some, but found no evidence to support this picture.

We introduce a new technique to quantify highly structured spectra for which the definition of continua or spectral features in the observed flux spectra is difficult. The method employs wavelet transformations to decompose the observed spectra into different scales. A procedure is formulated to define the strength of spectral features so that the measured spectral indices are independent of the flux levels and are insensitive to the definition of continuum and also to reddening. This technique is applied to Type Ia supernovae (SNe) spectra, where correlations are revealed between luminosity and spectral features. The current technique may allow for luminosity corrections based on spectral features in the use of Type Ia SNe as cosmological probe.

We report the detection of sub-Saturn-mass planet MOA-2008-BLG-310Lb and argue that it is the strongest candidate yet for a bulge planet. Deviations from the single-lens fit are smoothed out by finite-source effects and therefore are not immediately apparent from the light curve. Nevertheless, we find that a model in which the primary has a planetary companion is favored over the single-lens model by Δχ² ∼ 880 for an additional 3 degrees of freedom. Detailed analysis yields a planet/star mass ratio q = (3.3 ±  0.3) × 10⁻⁴ and an angular separation between the planet and star within 10% of the angular Einstein radius. The small angular Einstein radius, θ_E = 0.155 ± 0.011 mas, constrains the distance to the lens to be D_L>6.0 kpc if it is a star (M_L>0.08 M_☉). This is the only microlensing exoplanet host discovered so far that must be in the bulge if it is a star. By analyzing VLT NACO adaptive optics images taken near the baseline of the event, we detect additional blended light that is aligned to within 130 mas of the lensed source. This light is plausibly from the lens, but could also be due to a companion to the lens or source, or possibly an unassociated star. If the blended light is indeed due to the lens, we can estimate the mass of the lens, M_L = 0.67 ± 0.14 M_☉, planet mass m = 74 ± 17 M_⊕, and projected separation between the planet and host, 1.25 ± 0.10 AU, putting it right on the "snow line." If not, then the planet has lower mass, is closer to its host and is colder. To distinguish among these possibilities on reasonable timescales would require obtaining Hubble Space Telescope images almost immediately, before the source–lens relative motion of $\mu = 5\,\rm mas\,yr^{-1}$ causes them to separate substantially.

Pure ethane ices (C₂H₆) were irradiated at 10, 30, and 50 K under contamination-free, ultrahigh vacuum conditions with energetic electrons generated in the track of galactic cosmic-ray (GCR) particles to simulate the interaction of GCRs with ethane ices in the outer solar system. The chemical processing of the samples was monitored by a Fourier transform infrared spectrometer and a quadrupole mass spectrometer during the irradiation phase and subsequent warm-up phases on line and in situ in order to extract qualitative (products) and quantitative (rate constants and yields) information on the newly synthesized molecules. Six hydrocarbons, methane (CH₄), acetylene (C₂H₂), ethylene (C₂H₄), and the ethyl radical (C₂H₅), together with n-butane (C₄H₁₀) and butene (C₄H₈), were found to form at the radiation dose reaching 1.4 eV per molecule. The column densities of these species were quantified in the irradiated ices at each temperature, permitting us to elucidate the temperature and phase-dependent production rates of individual molecules. A kinetic reaction scheme was developed to fit column densities of those species produced during irradiation of amorphous/crystalline ethane held at 10, 30, or 50 K. In general, the yield of the newly formed molecules dropped consistently for all species as the temperature was raised from 10 K to 50 K. Second, the yield in the amorphous samples was found to be systematically higher than in the crystalline samples at constant temperature. A closer look at the branching ratios indicates that ethane decomposes predominantly to ethylene and molecular hydrogen, which may compete with the formation of n-butane inside the ethane matrix. Among the higher molecular products, n-butane dominates. Of particular relevance to the atmosphere of Saturn's moon Titan is the radiation-induced methane production from ethane—an alternative source of replenishing methane into the atmosphere. Finally, we discuss to what extent the n-butane could be the source of ''higher organics'' on Titan's surface thus resembling a crucial sink of condensed ethane molecules.

We report new single dish CO J = 6–5 line observations for the archetypal Ultra Luminous Infrared Galaxy (ULIRG) Arp 220 with the James Clerk Maxwell Telescope atop Mauna Kea in Hawaii. The J = 6–5 line is found to be faint, with brightness temperature ratios (6–5)/(1–0), (6–5)/(3–2) of R_65/10 = 0.080 ± 0.017 and R_65/32 = 0.082 ± 0.019, suggesting very low excitation conditions that cannot be reconciled with the warm and very dense molecular gas present in one of the most extreme starbursts in the local universe. We find that an optically thick dust continuum, with τ(ν ≳ 350 GHz) ≳ 1 for the bulk of the warm dust and gas in Arp 220, submerges this line to an almost black body curve, reducing its flux, and affecting its CO spectral line energy distribution at high frequencies. This also resolves the C⁺ line deficiency in this object, first observed by Infrared Space Observatory: the near absence of that line is a dust optical depth effect, not a dense photodissociation region phenomenon. Finally, we briefly comment on the possibility of such extreme interstellar medium (ISM) states in other ULIRGs in the distant universe, and their consequences for the diagnostic utility of high frequency molecular and atomic ISM lines in such systems. In the case of Arp 220, we anticipate that the now spaceborne Herschel Space Observatory will find faint high-J CO lines at ν ≳ 690 GHz that would appear as sub-thermally excited with respect to the low-J ones as a result of the effects of dust absorption.

PSR J1802 − 2124 is a 12.6 ms pulsar in a 16.8 hr binary orbit with a relatively massive white dwarf (WD) companion. These properties make it a member of the intermediate-mass class of binary pulsar (IMBP) systems. We have been timing this pulsar since its discovery in 2002. Concentrated observations at the Green Bank Telescope, augmented with data from the Parkes and Nançay observatories, have allowed us to determine the general relativistic Shapiro delay. This has yielded pulsar and WD mass measurements of 1.24 ± 0.11 M_☉ and 0.78 ± 0.04 M_☉ (68% confidence), respectively. The low mass of the pulsar, the high mass of the WD companion, the short orbital period, and the pulsar spin period may be explained by the system having gone through a common-envelope phase in its evolution. We argue that selection effects may contribute to the relatively small number of known IMBPs.

We develop an idealized dynamical model to predict the typical properties of outer extrasolar planetary systems, at radii comparable to the Jupiter-to-Neptune region of the solar system. The model is based upon the hypothesis that dynamical evolution in outer planetary systems is controlled by a combination of planet–planet scattering and planetary interactions with an exterior disk of small bodies ("planetesimals"). Our results are based on 5000 long duration N-body simulations that follow the evolution of three planets from a few to 10 AU, together with a planetesimal disk containing 50 M_⊕ from 10 to 20 AU. For large planet masses (M ≳ M_Sat), the model recovers the observed eccentricity distribution of extrasolar planets. For lower-mass planets, the range of outcomes in models with disks is far greater than that which is seen in isolated planet–planet scattering. Common outcomes include strong scattering among massive planets, sudden jumps in eccentricity due to resonance crossings driven by divergent migration, and re-circularization of scattered low-mass planets in the outer disk. We present the distributions of the eccentricity and inclination that result, and discuss how they vary with planet mass and initial system architecture. In agreement with other studies, we find that the currently observed eccentricity distribution (derived primarily from planets at a ≲ 3 AU) is consistent with isolated planet–planet scattering. We explain the observed mass dependence—which is in the opposite sense from that predicted by the simplest scattering models—as a consequence of strong correlations between planet masses in the same system. At somewhat larger radii, initial planetary mass correlations and disk effects can yield similar modest changes to the eccentricity distribution. Nonetheless, strong damping of eccentricity for low-mass planets at large radii appears to be a secure signature of the dynamical influence of disks. Radial velocity measurements capable of detecting planets with K ≈ 5 m s⁻¹ and periods in excess of 10 years will provide constraints on this regime. Finally, we present an analysis of the predicted separation of planets in two-planet systems, and of the population of planets in mean-motion resonances (MMRs). We show that, if there are systems with ∼ Jupiter-mass planets that avoid close encounters, the planetesimal disk acts as a damping mechanism and populates MMRs at a very high rate (50%–80%). In many cases, resonant chains (in particular the 4:2:1 Laplace resonance) are set up among all three planets. We expect such resonant chains to be common among massive planets in outer planetary systems.

Using the spectral energy distributions (SEDs) of the weak active galactic nuclei (AGNs) in 35 low-ionization nuclear emission regions (LINERs) presented in a companion paper, we assess whether photoionization by the weak AGN can power the emission-line luminosities measured through the large (few-arcsecond) apertures used in ground-based spectroscopic surveys. Spectra taken through such apertures are used to define LINERs as a class and constrain non-stellar photoionization models for LINERs. Therefore, our energy budget test is a self-consistency check of the idea that the observed emission lines are powered by an AGN. We determine the ionizing luminosities and photon rates by integrating the observed SEDs and by scaling a template SED. We find that even if all ionizing photons are absorbed by the line-emitting gas, more than half of the LINERs in this sample suffer from a deficit of ionizing photons. In 1/3 of LINERs the deficit is severe. If only 10% of the ionizing photons are absorbed by the gas, there is an ionizing photon deficit in 85% of LINERs. We disfavor the possibility that additional electromagnetic power, either obscured or emitted in the unobservable far-UV band, is available from the AGN. Therefore, we consider other power sources such as mechanical heating by compact jets from the AGN and photoionization by either young or old stars. Photoionization by young stars may be important in a small fraction of cases. Mechanical heating can provide enough power in most cases but it is not clear how this power would be transferred to the emission-line gas. Photoionization by post asymptotic giant branch stars is an important power source; it provides more ionizing photons than the AGN in more than half of the LINERs and enough ionizing photons to power the emission lines in 1/3 of the LINERs. It appears likely that the emission-line spectra of LINERs obtained from the ground include the sum of emission from different regions where different power sources dominate.

Variable stars have been identified for the first time in the very metal-poor blue compact dwarf galaxy IZw18, using deep multi-band (F606W, F814W) time-series photometry obtained with the Advanced Camera for Surveys on board the Hubble Space Telescope. We detected 34 candidate variable stars in the galaxy. We classify three of them as Classical Cepheids, with periods of 8.71, 125.0, and 130.3 days, respectively, and other two as long period variables with periodicities longer than 100 days. These are the lowest metallicity Classical Cepheids known so far, thus providing the opportunity to explore and fit models of stellar pulsation for Classical Cepheids at previously inaccessible metallicities. The period distribution of the confirmed Cepheids is markedly different from what is seen in other nearby galaxies, which is likely related to the star bursting nature of IZw18. The long period Cepheids we have detected in IZw18 seem to indicate that massive stars at the metallicity of IZw18 (Z = 0.0004) may cross the instability strip long enough to be observed. By applying to the 8.71 days Cepheid theoretical Wesenheit (V, I) relations based on new pulsation models of Classical Cepheids specifically computed for the extremely low metallicity of this galaxy (Z = 0.0004, Y = 0.24), we estimate the distance modulus of IZw18 to be μ₀ = 31.4 ± 0.3 (D = 19.0^+2.8_−2.5 Mpc) for canonical models of Classical Cepheids, and of 31.2 ± 0.3 mag (D = 17.4^+2.6_−2.2 Mpc) using over luminous models. The theoretical modeling of the star's light curves provides μ₀ = 31.4± 0.2 mag, D = 19.0^+1.8_−1.7 Mpc, in good agreement with the results from the theoretical Wesenheit relations. These pulsation distances bracket the distance of 18.2 ±1.5 Mpc inferred by Aloisi et al. using the galaxy's red giant branch tip.

In recent years, we have come to recognize the widespread importance of large-scale winds in the life cycle of galaxies. The onset and evolution of a galactic wind is a highly complex process which must be understood if we are to understand how energy and metals are recycled throughout the galaxy and beyond. Here we present three-dimensional spectroscopic observations of a sample of 10 nearby galaxies with the AAOmega-SPIRAL integral-field spectrograph on the 3.9 m Anglo-Australian Telescope, the largest survey of its kind to date. The double-beam spectrograph provides spatial maps in a range of spectral diagnostics: [O iii]5007, Hβ, Mg b, Na d, [O i]6300, Hα, [N ii]6583, [S ii]6717, 6731. We demonstrate that these flows can often separate into highly ordered structures through the use of ionization diagnostics and kinematics. All of the objects in our survey show extensive wind-driven filamentation along the minor axis, in addition to large-scale disk rotation. Our sample can be divided into either starburst galaxies or active galactic nuclei (AGNs), although some objects appear to be a combination of these. The total ionizing photon budget available to both classes of galaxies is sufficient to ionize all of the wind-blown filamentation out to large radius. We find, however, that while AGN photoionization always dominates in the wind filaments, this is not the case in starburst galaxies where shock ionization dominates. This clearly indicates that after the onset of star formation, there is a substantial delay (≳10 Myr) before a starburst wind develops. We show why this behavior is expected by deriving "ionization" and dynamical timescales for both AGNs and starbursts. We establish a sequence of events that lead to the onset of a galactic wind. The clear signature provided by the ionization timescale is arguably the strongest evidence yet that the starburst phenomenon is an impulsive event. A well-defined ionization timescale is not expected in galaxies with a protracted history of circumnuclear star formation. Our three-dimensional data provide important templates for comparisons with high-redshift galaxies.

We have computed seismic images of magnetic activity on the far surface of the Sun by using a seismic-holography technique. As in previous works, the method is based on the comparison of waves going in and out of a particular point in the Sun, but we have computed here Green's functions from a spherical polar expansion of the adiabatic wave equations in the Cowling approximation instead of using the ray-path approximation previously used in the far-side holography. A comparison between the results obtained using the ray theory and the spherical polar expansion is shown. We use the gravito-acoustic wave equation in the local plane–parallel limit in both cases and for the latter we take the asymptotic approximation for the radial dependences of Green's function. As a result, improved images of the far side can be obtained from the polar-expansion approximation, especially when combining Green's functions corresponding to two and three skips. We also show that the phase corrections in Green's functions due to the incorrect modeling of the uppermost layers of the Sun can be estimated from the eigenfrequencies of the normal modes of oscillation.

We study the outer-shock structure of the oxygen-rich supernova remnant G292.0+1.8 using a deep observation with the Chandra X-ray Observatory. We measure radial variations of the electron temperature and emission measure that we identify as the outer shock propagating into a medium with a radially decreasing density profile. The inferred ambient density structure is consistent with models for the circumstellar wind of a massive progenitor star rather than for a uniform interstellar medium. The estimated wind density (n_H = 0.1–0.3 cm⁻³) at the current outer radius (∼ 7.7 pc) of the remnant is consistent with a slow wind from a red supergiant (RSG) star. The total mass of the wind is estimated to be ∼15–40 M_☉ (depending on the estimated density range), assuming that the wind extended down to near the surface of the progenitor. The overall kinematics of G292.0+1.8 are consistent with the remnant expanding through the RSG wind.

We present a multi-wavelength study of GRB 081008, at redshift 1.967, by Swift, ROTSE-III, and Gamma-Ray Burst Optical/NearInfrared Detector. Compared to other Swift GRBs, GRB 081008 has a typical gamma-ray isotropic equivalent energy output (∼10⁵³ erg) during the prompt phase, and displayed two temporally separated clusters of pulses. The early X-ray emission seen by the Swift X-Ray Telescope was dominated by the softening tail of the prompt emission, producing multiple flares during and after the Swift Burst Alert Telescope detections. Optical observations that started shortly after the first active phase of gamma-ray emission showed two consecutive peaks. We interpret the first optical peak as the onset of the afterglow associated with the early burst activities. A second optical peak, coincident with the later gamma-ray pulses, imposes a small modification to the otherwise smooth light curve and thus suggests a minimal contribution from a probable internal component. We suggest the early optical variability may be from continuous energy injection into the forward shock front by later shells producing the second epoch of burst activities. These early observations thus provide a potential probe for the transition from the prompt phase to the afterglow phase. The later light curve of GRB 081008 displays a smooth steepening in all optical bands and X-ray. The temporal break is consistent with being achromatic at the observed wavelengths. Our broad energy coverage shortly after the break constrains a spectral break within optical. However, the evolution of the break frequency is not observed. We discuss the plausible interpretations of this behavior.

In planetary nebulae (PNe), abundances of oxygen and other heavy elements derived from optical recombination lines are systematically higher than those derived from collisionally excited lines. We investigate the hypothesis that the destruction of solid bodies may produce pockets of cool, high-metallicity gas that could explain these abundance discrepancies. Under the assumption of maximally efficient radiative ablation, we derive two fundamental constraints that the solid bodies must satisfy in order that their evaporation during the PN phase should generate a high enough gas-phase metallicity. A local constraint implies that the bodies must be larger than tens of meters, while a global constraint implies that the total mass of the solid body reservoir must exceed a few hundredths of a solar mass. This mass greatly exceeds the mass of any population of comets or large debris particles expected to be found orbiting evolved low- to intermediate-mass stars. We therefore conclude that contemporaneous solid body destruction cannot explain the observed abundance discrepancies in PNe. However, similar arguments applied to the sublimation of solid bodies during the preceding asymptotic giant branch phase do not lead to such a clear-cut conclusion. In this case, the required reservoir of volatile solids is only one ten-thousandth of a solar mass, which is comparable to the most massive debris disks observed around solar-type stars, implying that this mechanism may contribute to abundance discrepancies in at least some PNe, so long as mixing of the high-metallicity gas is inefficient.

We present an analysis of X-ray high-quality grating spectra of the Seyfert 1 galaxy NGC 5548 using archival Chandra-High Energy Transmission Grating Spectrometer and Low Energy Transmission Grating Spectrometer observations for a total exposure time of 800 ks. The continuum emission (between 0.2 keV and 8 keV) is well represented by a power law (Γ = 1.6) plus a blackbody component (kT = 0.1 keV). We find that the well-known X-ray warm absorber (WA) in this source consists of two different outflow velocity systems. One absorbing system has a velocity of −1110 ±  150 km s⁻¹ and the other of −490 ±  150 km s⁻¹. Recognizing the presence of these kinematically distinct components allows each system to be fitted independently, each with two absorption components with different ionization levels. The high-velocity system consists of two components, one with a temperature of 2.7 ± 0.6 × 10⁶ K, log  U = 1.23, and another with a temperature of 5.8 ± 1.0 × 10⁵ K, log  U = 0.67. The high-velocity, high-ionization component produces absorption by charge states Fe xxi–xxiv, while the high-velocity, low-ionization component produces absorption by Ne ix–x, Fe xvii–xx, and O vii–viii. The low-velocity system also required two absorbing components, one with a temperature of 5.8 ± 0.8 × 10⁵ K, log  U = 0.67, producing absorption by Ne ix–x, Fe xvii–xx, and O vii–viii, and the other with a lower temperature of 3.5 ± 0.35 × 10⁴ K and a lower ionization of log  U = −0.49, producing absorption by O vi–vii and the Fe vii–xii M-shell Unresolved Transitions Array. Once these components are considered, the data do not require any further absorbers. In particular, a model consisting of a continuous radial range of ionization structures (as suggested by a previous analysis) is not required. The two absorbing components in each velocity system are in pressure equilibrium with each other. This suggests that each velocity system consists of a multi-phase medium. This is the first time that different outflow velocity systems have been modeled independently in the X-ray band for this source. The kinematic components and column densities found from the X-rays are in agreement with the main kinematic components found in the UV absorber. This supports the idea that the UV and X-ray absorbing gas is part of the same phenomenon. NGC 5548 can now be seen to fit in a pattern established for other WAs: two or three discrete phases in pressure equilibrium. There are no remaining cases of a well-studied WA in which a model consisting of a multi-phase medium is not viable.

A classic method for computing the mass function of dark matter halos is provided by excursion set theory, where density perturbations evolve stochastically with the smoothing scale, and the problem of computing the probability of halo formation is mapped into the so-called first-passage time problem in the presence of a barrier. While the full dynamical complexity of halo formation can only be revealed through N-body simulations, excursion set theory provides a simple analytic framework for understanding various aspects of this complex process. In this series of papers we propose improvements of both technical and conceptual aspects of excursion set theory, and we explore up to which point the method can reproduce quantitatively the data from N-body simulations. In Paper I of the series, we show how to derive excursion set theory from a path integral formulation. This allows us both to derive rigorously the absorbing barrier boundary condition, that in the usual formulation is just postulated, and to deal analytically with the non-Markovian nature of the random walk. Such a non-Markovian dynamics inevitably enters when either the density is smoothed with filters such as the top-hat filter in coordinate space (which is the only filter associated with a well-defined halo mass) or when one considers non-Gaussian fluctuations. In these cases, beside "Markovian" terms, we find "memory" terms that reflect the non-Markovianity of the evolution with the smoothing scale. We develop a general formalism for evaluating perturbatively these non-Markovian corrections, and in this paper we perform explicitly the computation of the halo mass function for Gaussian fluctuations, to first order in the non-Markovian corrections due to the use of a top-hat filter in coordinate space. In Paper II of this series we propose to extend excursion set theory by treating the critical threshold for collapse as a stochastic variable, which better captures some of the dynamical complexity of the halo formation phenomenon, while in Paper III we use the formalism developed in this paper to compute the effect of non-Gaussianities on the halo mass function.

We construct a sample of low-redshift Lyα emission-line selected sources from Galaxy Evolution Explorer (GALEX) grism spectroscopy of nine deep fields to study the role of Lyα emission in galaxy populations with cosmic time. Our final sample consists of 119 (141) sources selected in the redshift interval z = 0.195–0.44 (z = 0.65–1.25) from the FUV (NUV) channel. We classify the Lyα sources as active galactic nuclei (AGNs) if high-ionization emission lines are present in their UV spectra and as possible star-forming galaxies otherwise. We classify additional sources as AGNs using line widths for our Lyα emitter (LAE) analysis. These classifications are broadly supported by comparisons with X-ray and optical spectroscopic observations, though the optical spectroscopy identifies a small number of additional AGNs. Defining the GALEX LAE sample in the same way as high-redshift LAE samples, we show that LAEs constitute only about 5% of NUV-continuum selected galaxies at z ∼ 0.3. We also show that they are less common at z ∼ 0.3 than they are at z ∼ 3. We find that the z ∼ 0.3 optically confirmed Lyα galaxies lie below the metallicity–luminosity relation of the z ∼ 0.3 NUV-continuum selected galaxies but have similar Hα velocity widths at similar luminosities, suggesting that they also lie below the metallicity–mass relation of the NUV-continuum selected galaxies. We show that, on average, the Lyα galaxies have bluer colors, lower extinctions as measured from the Balmer line ratios, and more compact morphologies than the NUV-continuum selected galaxies. Finally, we confirm that the z ∼ 2 Lyman break galaxies have relatively low metallicities for their luminosities, and we find that they lie in the same metallicity range as the z ∼ 0.3 Lyα galaxies.

We explore the parameter dependence of inner disk stress in black hole accretion by contrasting the results of a number of simulations, all employing three-dimensional general relativistic MHD in a Schwarzschild spacetime. Five of these simulations were performed with the intrinsically conservative code HARM3D, which allows careful regulation of the disk aspect ratio, H/R; our simulations span a range in H/R from 0.06 to 0.17. We contrast these simulations with two previously reported simulations in a Schwarzschild spacetime in order to investigate possible dependence of the inner disk stress on magnetic topology. In all cases, much care was devoted to technical issues: ensuring adequate resolution and azimuthal extent, and averaging only over those time periods when the accretion flow is in approximate inflow equilibrium. We find that the time-averaged radial dependence of fluid-frame electromagnetic stress is almost completely independent of both disk thickness and poloidal magnetic topology. It rises smoothly inward at all radii (exhibiting no feature associated with the innermost stable circular orbit, ISCO) until just outside the event horizon, where the stress plummets to zero. Reynolds stress can also be significant near the ISCO and in the plunging region; the magnitude of this stress, however, depends on both disk thickness and magnetic topology. The two stresses combine to make the net angular momentum accreted per unit rest mass 7%–15% less than the angular momentum of the ISCO.

We present an 880 μm Submillimeter Array (SMA) detection of the submillimeter galaxy SXDF 850.6. SXDF 850.6 is a bright source (S_850 μm = 8 mJy) detected in the SCUBA Half Degree Extragalactic Survey and has multiple possible radio counterparts in its deep radio image obtained at the VLA. Our new SMA detection finds that the submillimeter emission coincides with the brightest radio emission that is found ∼8'' north of the coordinates determined from SCUBA. Despite the lack of detectable counterparts in deep UV/optical images, we find a source at the SMA position in near-infrared and longer wavelength images. We perform spectral energy distribution (SED) model fits to UV–optical–IR photometry (u, B, V, R, i', z', J, H, K, 3.6 μm, 4.5 μm, 5.8 μm, and 8.0 μm) and to submillimeter–radio photometry (850 μm, 880 μm, 1100 μm, and 21 cm) independently, and we find both are well described by starburst templates at a redshift of z ≃ 2.2 ± 0.3. The best-fit parameters from the UV–optical–IR SED fit are a redshift of z = 1.87^+0.15_−0.07, a stellar mass of M_⋆ = 2.5^+2.2_−0.3 × 10¹¹ M_☉, an extinction of A_V = 3.0^+0.3_−1.0 mag, and an age of 720⁺¹⁸⁸⁰₋₂₁₀ Myr. The submillimeter–radio SED fit provides a consistent redshift of z ∼ 1.8–2.5, an IR luminosity of L_IR = (7–26) ×10¹² L_☉, and a star formation rate of 1300–4500 M_☉ yr⁻¹. These results suggest that SXDF 850.6 is a mature system already having a massive amount of old stellar population constructed before its submillimeter bright phase and is experiencing a dusty starburst, possibly induced by major mergers.

In recent observations by the Advanced Composition Explorer, the intensity of solar energetic particles exhibits sudden, large changes known as dropouts. These have been explained in terms of turbulence or a flux tube structure in the solar wind. Dropouts are believed to indicate filamentary magnetic connection to a localized particle source near the solar surface, and computer simulations of a random-phase model of magnetic turbulence have indicated a spatial association between dropout features and local trapping boundaries (LTBs) defined for a two-dimensional (2D) + slab model of turbulence. Previous observations have shown that dropout features are not well associated with sharp magnetic field changes, as might be expected in the flux tube model. Random-phase turbulence models do not properly treat sharp changes in the magnetic field, such as current sheets, and thus cannot be tested in this way. Here, we explore the properties of a more realistic magnetohydrodynamic (MHD) turbulence model (2D MHD), in which current sheets develop and the current and magnetic field have characteristic non-Gaussian statistical properties. For this model, computer simulations that trace field lines to determine magnetic connection from a localized particle source indicate that sharp particle gradients should frequently be associated with LTBs, sometimes with strong 2D magnetic fluctuations, and infrequently with current sheets. Thus, the 2D MHD + slab model of turbulent fluctuations includes some realistic features of the flux tube view and is consistent with the lack of an observed association between dropouts and intense magnetic fields or currents.

Observations have revealed ubiquitous transverse velocity perturbation waves propagating in the solar corona. However, there is ongoing discussion regarding their interpretation as kink or Alfvén waves. To investigate the nature of transverse waves propagating in the solar corona and their potential for use as a coronal diagnostic in MHD seismology, we perform three-dimensional numerical simulations of footpoint-driven transverse waves propagating in a low β plasma. We consider the cases of both a uniform medium and one with loop-like density structure and perform a parametric study for our structuring parameters. When density structuring is present, resonant absorption in inhomogeneous layers leads to the coupling of the kink mode to the Alfvén mode. The decay of the propagating kink wave as energy is transferred to the local Alfvén mode is in good agreement with a modified interpretation of the analysis of Ruderman & Roberts for standing kink modes. Numerical simulations support the most general interpretation of the observed loop oscillations as a coupling of the kink and Alfvén modes. This coupling may account for the observed predominance of outward wave power in longer coronal loops since the observed damping length is comparable to our estimate based on an assumption of resonant absorption as the damping mechanism.

The transport of charged particles (e.g., cosmic rays) in astrophysically relevant, turbulent magnetic fields (like they exist, e.g., in the solar wind) is investigated. Generic theoretical models—using concepts and insights developed recently in the context of magnetic confinement fusion research—are applied to the present problem and confirmed by means of numerical simulations. At high energies, a novel transport regime is found, in which the particles decorrelate on a gyro-orbit timescale. Explicit scaling laws for the cross-field diffusivities in various limits are derived.

We report on five Chandra observations of the X-ray afterglow of the gamma-ray burst (GRB) 060729 performed between 2007 March and 2008 May. In all five observations, the afterglow is clearly detected. The last Chandra pointing was performed on 2008 May 4, 642 days after the burst—the latest detection of a GRB X-ray afterglow ever. A reanalysis of the Swift XRT light curve together with the three detections by Chandra in 2007 reveals a break at ∼1.0 Ms after the burst with a slight steepening of the decay slope from α = 1.32 to 1.61. This break coincides with a significant hardening of the X-ray spectrum, consistent with a cooling break in the wind medium scenario, in which the cooling frequency of the afterglow crosses the X-ray band. The last two Chandra observations in 2007 December and 2008 May provide evidence for another break at about one year after the burst. If interpreted as a jet break, this late-time break implies a jet half-opening angle of ∼14° for a wind medium. Alternatively, this final break may have a spectral origin, in which case no jet break has been observed and the half-opening angle of the jet of GRB 060729 must be larger than ∼15° for a wind medium. We compare the X-ray afterglow of GRB 060729 in a wind environment with other bright X-ray afterglows, in particular GRBs 061121 and 080319B, and discuss why the X-ray afterglow of GRB 060729 is such an exceptionally long-lasting event.

We describe the first three-dimensional simulation of the gravitational collapse of a massive, rotating molecular cloud that includes heating by both non-ionizing and ionizing radiation. These models were performed with the FLASH code, incorporating a hybrid, long characteristic, ray-tracing technique. We find that as the first protostars gain sufficient mass to ionize the accretion flow, their H ii regions are initially gravitationally trapped, but soon begin to rapidly fluctuate between trapped and extended states, in agreement with observations. Over time, the same ultracompact H ii region can expand anisotropically, contract again, and take on any of the observed morphological classes. In their extended phases, expanding H ii regions drive bipolar neutral outflows characteristic of high-mass star formation. The total lifetime of H ii regions is given by the global accretion timescale, rather than their short internal sound-crossing time. This explains the observed number statistics. The pressure of the hot, ionized gas does not terminate accretion. Instead, the final stellar mass is set by fragmentation-induced starvation. Local gravitational instabilities in the accretion flow lead to the build-up of a small cluster of stars, all with relatively high masses due to heating from accretion radiation. These companions subsequently compete with the initial high-mass star for the same common gas reservoir and limit its mass growth. This is in contrast to the classical competitive accretion model, where the massive stars are never hindered in growth by the low-mass stars in the cluster. Our findings show that the most significant differences between the formation of low-mass and high-mass stars are all explained as the result of rapid accretion within a dense, gravitationally unstable, ionized flow.

The observations of circularly polarized thermal radio emission from solar coronal streamers at two low frequencies, viz., 77 and 109 MHz, are used to estimate the magnetic field strength (B) at their corresponding radial distances r≈ 1.7 and 1.5 solar radii given by the electron density model of Newkirk. The estimated values of B at the above two distances are ≈5 ± 1 G and 6 ± 2 G, respectively.

We compare X-ray hydrostatic and weak-lensing mass estimates for a sample of 12 clusters that have been observed with both XMM-Newton and Subaru. At an over-density of Δ = 500, we obtain 1 − M^X/M^WL = 0.01 ± 0.07 for the whole sample. We also divided the sample into undisturbed and disturbed sub-samples based on quantitative X-ray morphologies using asymmetry and fluctuation parameters, obtaining 1 − M^X/M^WL = 0.09 ± 0.06 and −0.06 ± 0.12 for the undisturbed and disturbed clusters, respectively. In addition to non-thermal pressure support, there may be a competing effect associated with adiabatic compression and/or shock heating which leads to overestimate of X-ray hydrostatic masses for disturbed clusters, for example, in the famous merging cluster A1914. Despite the modest statistical significance of the mass discrepancy, on average, in the undisturbed clusters, we detect a clear trend of improving agreement between M^X and M^WL as a function of increasing over-density, $M^{\rm X}/M^{\rm WL}=(0.908 \pm 0.004)+(0.187 \pm 0.010) \cdot \log_{10} (\Delta /500)$. We also examine the gas mass fractions, f_gas = M^gas/M^WL, finding that they are an increasing function of cluster radius, with no dependence on dynamical state, in agreement with predictions from numerical simulations. Overall, our results demonstrate that XMM-Newton and Subaru are a powerful combination for calibrating systematic uncertainties in cluster mass measurements.

The present work uses observations and theoretical considerations to provide both qualitative and quantitative arguments that hydromagnetic waves, whether turbulent or not, cannot produce the acceleration of the fast solar wind and the related heating of the open solar corona. Waves do exist, and can play a role in the differential heating and acceleration of minor ions, but their amplitudes are not sufficient to power the wind, as demonstrated by extrapolation of magnetic spectra from Helios and Ulysses observations. Dissipation mechanisms invoked to circumvent this conclusion cannot be effective for a variety of reasons. In particular, turbulence does not play a strong role in the corona as shown both by observations of coronal striations and other features, and by theoretical considerations of line tying to a nonturbulent photosphere, nonlocality of interactions, and the nature of the kinetic dissipation. We consider possible "ways out" of the arguments presented, and suggest that in the absence of wave or turbulent heating and acceleration, the chromosphere and transition region become the natural source, if yet unproven, of open coronal energization through the production of nonthermal particle distributions.

Galaxy Evolution Explorer (GALEX) observations of comet 9P/Tempel 1 using the near-ultraviolet (NUV) objective grism were made before, during and after the Deep Impact event that occurred on 2005 July 4 at 05:52:03 UT when a 370 kg NASA spacecraft was maneuvered into the path of the comet. The NUV channel provides usable spectral information in a bandpass covering 2000–3400 Å with a point source spectral resolving power of R ≈ 100. The primary spectral features in this range include solar continuum scattered from cometary dust and emissions from OH and CS molecular bands centered near 3085 and 2575 Å, respectively. In particular, we report the only cometary CS emission detected during this event. The observations allow the evolution of these spectral features to be tracked over the period of the encounter. In general, the NUV emissions observed from Tempel 1 are much fainter than those that have been observed by GALEX from other comets. However, it is possible to derive production rates for the parent molecules of the species detected by GALEX in Tempel 1 and to determine the number of these molecules liberated by the impact. The derived quiescent production rates are Q(H₂O) = 6.4 × 10²⁷ molecules s⁻¹ and Q(CS₂) = 6.7 × 10²⁴ molecules s⁻¹, while the impact produced an additional 1.6 × 10³² H₂O molecules and 1.3 × 10²⁹ CS₂ molecules, a similar ratio as in quiescent outgassing.

We present an observation of a filament eruption caused by recurrent chromospheric plasma injections (surges/jets) on 2006 July 6. The filament eruption was associated with an M2.5 two-ribbon flare and a coronal mass ejection (CME). There was a light bridge in the umbra of the main sunspot of NOAA 10898; one end of the filament was terminated at the region close to the light bridge, and recurrent surges were observed to be ejected from the light bridge. The surges occurred intermittently for about 8 hr before the filament eruption, and finally a clear jet was found at the light bridge to trigger the filament eruption. We analyzed the evolutions of the relative darkness of the filament and the loaded mass by the continuous surges quantitatively. It was found that as the occurrence of the surges, the relative darkness of the filament body continued growing for about 3–4 hr, reached its maximum, and kept stable for more than 2 hr until it erupted. If suppose 50% of the ejected mass by the surges could be trapped by the filament channel, then the total loaded mass into the filament channelwill be about 0.57×10¹⁶ g with a momentum of 0.57×10²² g cm s⁻¹ by 08:08 UT, which is a non-negligible effect on the stability of the filament. Based on the observations, we present a model showing the important role that recurrent chromospheric mass injection play in the evolution and eruption of a flux rope. Our study confirms that the surge activities can efficiently supply the necessary material for some filament formation. Furthermore, our study indicates that the continuous mass with momentum loaded by the surge activities to the filament channel could make the filament unstable and cause it to erupt.

The Soft X-ray Telescope (SXT) on board Yohkoh revealed that the ejection of X-ray emitting plasmoid is sometimes observed in a solar flare. It was found that the ejected plasmoid is strongly accelerated during a peak in the hard X-ray (HXR) emission of the flare. In this paper, we present an examination of the GOES X 2.3 class flare that occurred at 14:51 UT on 2000 November 24. In the SXT images, we found "multiple" plasmoid ejections with velocities in the range of 250–1500 km s⁻¹, which showed blob-like or loop-like structures. Furthermore, we also found that each plasmoid ejection is associated with an impulsive burst of HXR emission. Although some correlation between plasmoid ejection and HXR emission has been discussed previously, our observation shows similar behavior for multiple plasmoid ejection such that each plasmoid ejection occurs during the strong energy release of the solar flare. As a result of temperature-emission measure analysis of such plasmoids, it was revealed that the apparent velocities and kinetic energies of the plasmoid ejections show a correlation with the peak intensities in the HXR emissions.

Spectral lag, the time difference between the arrival of high-energy and low-energy photons, is a common feature in gamma-ray bursts (GRBs). Norris et al. reported a correlation between the spectral lag and the isotropic peak luminosity of GRBs based on a limited sample. More recently, a number of authors have provided further support for this correlation using arbitrary energy bands of various instruments. In this paper, we report on a systematic extraction of spectral lags based on the largest Swift sample to date of 31 GRBs with measured redshifts. We extracted the spectral lags for all combinations of the standard Swift hard X-ray energy bands: 15–25 keV, 25–50 keV, 50–100 keV, and 100–200 keV and plotted the time dilation corrected lag as a function of isotropic peak luminosity. The mean value of the correlation coefficient for various channel combinations is −0.68 with a chance probability of ∼0.7 × 10⁻³. In addition, the mean value of the power-law index is 1.4 ± 0.3. Hence, our study lends support to the existence of a lag–luminosity correlation, albeit with large scatter.

We present the results of a three year monitoring program of a sample of very low mass (VLM) field binaries using both astrometric and spectroscopic data obtained in conjunction with the laser guide star adaptive optics system on the W. M. Keck II 10 m telescope. Among the 24 systems studied, 15 have undergone sufficient orbital motion, allowing us to derive their relative orbital parameters and hence their total system mass. These measurements more than double the number of mass measurements for VLM objects, and include the most precise mass measurement to date (<2%). Among the 11 systems with both astrometric and spectroscopic measurements, six have sufficient radial velocity variations to allow us to obtain individual component masses. This is the first derivation of the component masses for five of these systems. Altogether, the orbital solutions of these low mass systems show a correlation between eccentricity and orbital period, consistent with their higher mass counterparts. In our primary analysis, we find that there are systematic discrepancies between our dynamical mass measurements and the predictions of theoretical evolutionary models (TUCSON and LYON) with both models either underpredicting or overpredicting the most precisely determined dynamical masses. These discrepancies are a function of spectral type, with late-M through mid-L systems tending to have their masses underpredicted, while one T-type system has its mass overpredicted. These discrepancies imply that either the temperatures predicted by evolutionary and atmosphere models are inconsistent for an object of a given mass, or the mass–radius relationship or cooling timescales predicted by the evolutionary models are incorrect. If these spectral-type trends are correct and hold into the planetary mass regime, the implication is that the masses of directly imaged extrasolar planets are overpredicted by the evolutionary models.

Background Imaging of Cosmic Extragalactic Polarization (Bicep) is a bolometric polarimeter designed to measure the inflationary B-mode polarization of the cosmic microwave background (CMB) at degree angular scales. During three seasons of observing at the South Pole (2006 through 2008), Bicep mapped ∼2% of the sky chosen to be uniquely clean of polarized foreground emission. Here, we present initial results derived from a subset of the data acquired during the first two years. We present maps of temperature, Stokes Q and U, E and B modes, and associated angular power spectra. We demonstrate that the polarization data are self-consistent by performing a series of jackknife tests. We study potential systematic errors in detail and show that they are sub-dominant to the statistical errors. We measure the E-mode angular power spectrum with high precision at 21 ⩽ ℓ ⩽ 335, detecting for the first time the peak expected at ℓ ∼ 140. The measured E-mode spectrum is consistent with expectations from a ΛCDM model, and the B-mode spectrum is consistent with zero. The tensor-to-scalar ratio derived from the B-mode spectrum is r = 0.02^+0.31_−0.26, or r < 0.72 at 95% confidence, the first meaningful constraint on the inflationary gravitational wave background to come directly from CMB B-mode polarization.

The Background Imaging of Cosmic Extragalactic Polarization (Bicep) experiment was designed specifically to search for the signature of inflationary gravitational waves in the polarization of the cosmic microwave background (CMB). Using a novel small-aperture refractor and 49 pairs of polarization-sensitive bolometers, Bicep has completed three years of successful observations at the South Pole beginning in 2006 February. To constrain the amplitude of the inflationary B-mode polarization, which is expected to be at least 7 orders of magnitude fainter than the 3 K CMB intensity, precise control of systematic effects is essential. This paper describes the characterization of potential systematic errors for the Bicep experiment, supplementing a companion paper on the initial cosmological results. Using the analysis pipelines for the experiment, we have simulated the impact of systematic errors on the B-mode polarization measurement. Guided by these simulations, we have established benchmarks for the characterization of critical instrumental properties including bolometer relative gains, beam mismatch, polarization orientation, telescope pointing, sidelobes, thermal stability, and timestream noise model. A comparison of the benchmarks with the measured values shows that we have characterized the instrument adequately to ensure that systematic errors do not limit Bicep's two-year results, and identifies which future refinements are likely necessary to probe inflationary B-mode polarization down to levels below a tensor-to-scalar ratio r = 0.1.

If a dynamical system is long-lived and non-resonant (that is, if there is a set of tracers that have evolved independently through many orbital times), and if the system is observed at any non-special time, it is possible to infer the dynamical properties of the system (such as the gravitational force or acceleration law) from a snapshot of the positions and velocities of the tracer population at a single moment in time. In this paper, we describe a general inference technique that solves this problem while allowing (1) the unknown distribution function of the tracer population to be simultaneously inferred and marginalized over, and (2) prior information about the gravitational field and distribution function to be taken into account. As an example, we consider the simplest problem of this kind: we infer the force law in the solar system using only an instantaneous kinematic snapshot (valid at 2009 April 1.0) for the eight major planets. We consider purely radial acceleration laws of the form a_r = −A [r/r₀]^−α, where r is the distance from the Sun. Using a probabilistic inference technique, we infer 1.989 < α < 2.052 (95% interval), largely independent of any assumptions about the distribution of energies and eccentricities in the system beyond the assumption that the system is phase-mixed. Generalizations of the methods used here will permit, among other things, inference of Milky Way dynamics from Gaia-like observations.

The vicinity of the unidentified EGRET source 3EG J1420–6038 has undergone extensive study in the search for counterparts, revealing the energetic young pulsar PSR J1420–6048 and its surrounding wind nebula as a likely candidate for at least part of the emission from this bright and extended gamma-ray source. We report on new Suzaku observations of PSR J1420–6048 along with analysis of archival XMM-Newton data. The low background of Suzaku permits mapping of the extended X-ray nebula, indicating a tail stretching ∼8' north of the pulsar. The X-ray data, along with archival radio and very high energy data, hint at a pulsar birthsite to the north, and yield insights into its evolution and the properties of the ambient medium. We further explore such properties by modeling the spectral energy distribution of the extended nebula.

We present the detection of extremely broad, double-peaked, highly polarized Hα emission lines in the nuclei of the well-known Seyfert 2 galaxies NGC 2110 and NGC 5252. These hidden broad Hα emission lines, visible only in scattered light, are shown to display significant variability in strength and profile on timescales of ≲1 yr. That the broad emission line exhibits variability in polarized flux also suggests that the scattering region must be very compact, possibly confined in a small number of electron clouds ≲1 lt-yr in size. Our observational constraints place these clouds within ∼10 pc of the nucleus with temperatures T_e ≲ 10⁶ K and densities n_e ∼ 10⁷ cm⁻³, consistent with a region just outside the obscuring torus between the broad-line region and narrow-line region. These scattering clouds could arise from the clumpy torus itself. These findings and other properties indicate that NGC 2110 and NGC 5252 are the hidden counterparts to the broad-line double-peaked emission-line active galactic nuclei, whose examples include Arp 102B and 3C 332.

The Spitzer Adaptation of the Red-sequence Cluster Survey (SpARCS) is a z'-passband imaging survey of the 50 deg²Spitzer SWIRE Legacy fields, designed with the primary aim of creating the first large, homogeneously selected sample of massive clusters at z > 1. SpARCS uses an infrared adaptation of the two-filter cluster red-sequence technique. In this paper, we report Keck/LRIS spectroscopic confirmation of two new exceptionally rich galaxy clusters, SpARCS J161315+564930 at z = 0.871 ± 0.002, with 14 high-confidence members and a rest-frame velocity dispersion of σ_v = 1230 ± 320 km s⁻¹, and SpARCS J161641+554513 at z = 1.161 ± 0.003, with seven high-confidence members (including one active galactic nucleus) and a rest-frame velocity dispersion of σ_v = 950 ± 330 km s⁻¹. We also report confirmation of a third new system, SpARCS J161037+552417 at z = 1.210 ± 0.002, with seven high-confidence members and a rest-frame velocity dispersion of σ_v = 410 ± 300 km s⁻¹. These three new spectroscopically confirmed clusters further demonstrate the efficiency and effectiveness of two-filter imaging for detecting bona fide galaxy clusters at high redshift. We conclude by demonstrating that prospects are good for the current generation of surveys aiming to estimate cluster redshifts and masses at z ≳ 1 directly from optical-infrared imaging.

Cosmological simulations of galaxy formation often rely on prescriptions for star formation and feedback that depend on halo properties such as halo mass, central overdensity, and virial temperature. In this paper, we address the convergence of individual halo properties, based on their number of particles N, focusing, in particular, on the mass of halos near the resolution limit of a simulation. While it has been established that the halo mass function is sampled on average down to N ∼ 20–30 particles, we show that individual halo properties exhibit significant scatter, and some systematic biases, as one approaches the resolution limit. We carry out a series of cosmological simulations using the Gadget2 and Enzo codes with N_p = 64³ to N_p = 1024³ total particles, keeping the same large-scale structure in the simulation box. We consider boxes of small (l_box = 8 Mpc h⁻¹), medium (l_box = 64 Mpc h⁻¹), and large (l_box = 512 Mpc h⁻¹) size to probe different halo masses and formation redshifts. We cross-identify dark matter halos in boxes at different resolutions and measure the scatter in their properties. The uncertainty in the mass of single halos depends on the number of particles (scaling approximately as N^−1/3), but the rarer the density peak, the more robust its identification. The virial radius of halos is very stable and can be measured without bias for halos with N ≳ 30. In contrast, the average density within a sphere containing 25% of the total halo mass is severely underestimated (by more than a factor 2) and the halo spin is moderately overestimated for N ≲ 100. If sub-grid physics is implemented upon a cosmological simulation, we recommend that rare halos (∼3σ peaks) be resolved with N ≳ 100 particles and common halos (∼1σ peaks) with N ≳ 400 particles to avoid excessive numerical noise and possible systematic biases in the results.

Galactic neutral hydrogen (H i) within a few hundred parsecs of the Sun contains structure with an angular distribution that is similar to small-scale structure observed by the Wilkinson Microwave Anisotropy Probe (WMAP). A total of 108 associated pairs of associated H i and WMAP features have now been cataloged using H i data mapped in 2 km s⁻¹ intervals and these pairs show a typical offset of 08. A large-scale statistical test for a direct association is carried out that casts little additional light on whether the these small offsets are merely coincidental or carry information. To pursue the issue further, the nature of several of the features within the foreground H i most closely associated with WMAP structure is examined in detail and it is shown that the cross-correlation coefficient for well-matched pairs of structures is of order unity. It is shown that free–free emission from electrons in unresolved density enhancements in interstellar space could theoretically produce high-frequency radio continuum radiation at the levels observed by WMAP and that such emission will appear nearly flat across the WMAP frequency range. Evidence for such structure in the interstellar medium already exists in the literature. Until higher angular resolution observations of the high-frequency continuum emission structure as well as the apparently associated H i structure become available, it may be difficult to rule out the possibility that some if not all the small-scale structure usually attributed to the cosmic microwave background may have a galactic origin.

Five new planets orbiting G and K dwarfs have emerged from the Magellan velocity survey. These companions are Jovian-mass planets in eccentric (e ⩾ 0.24) intermediate- and long-period orbits. HD 86226b orbits a solar metallicity G2 dwarf. The M_Psin i mass of the planet is 1.5 M_JUP, the semimajor axis is 2.6 AU, and the eccentricity is 0.73. HD 129445b orbits a metal-rich G6 dwarf. The minimum mass of the planet is M_Psin i = 1.6 M_JUP, the semimajor axis is 2.9 AU, and the eccentricity is 0.70. HD 164604b orbits a K2 dwarf. The M_Psin i mass is 2.7 M_JUP, the semimajor axis is 1.3 AU, and the eccentricity is 0.24. HD 175167b orbits a metal-rich G5 star. The M_Psin i mass is 7.8 M_JUP, the semimajor axis is 2.4 AU, and the eccentricity is 0.54. HD 152079b orbits a G6 dwarf. The M_Psin i mass of the planet is 3 M_JUP, the semimajor axis is 3.2 AU, and the eccentricity is 0.60.

The Far Ultraviolet Spectroscopic Explorer (FUSE) has allowed precise determinations of the column densities of molecular hydrogen (H₂) in Galactic lines of sight with a wide range of pathlengths and extinction properties. However, survey studies of lines of sight with greater extinction have been mostly restricted to the low-J states (lower total angular momentum) in which most molecular hydrogen is observed. This paper presents a survey of column densities for the molecular hydrogen in states of greater rotational excitation (J ⩾ 2) in Galactic lines of sight with log N(H₂) ≳ 20. This study is comprehensive through the highest excited state detectable in each line of sight. J = 5 is observed in every line of sight, and we detect J = 7 in four lines of sight, J = 8 in one line of sight, and vibrationally excited H₂ in two lines of sight. We compared the apparent b-values and velocity offsets of the higher-J states relative to the dominant low-J states and we found no evidence of any trends that might provide insight into the formation of higher-J H₂, although these results are the most affected by the limits of the FUSE resolution. We also derive excitation temperatures based on the column densities of the different states. We confirm that at least two distinct temperatures are necessary to adequately describe these lines of sight, and that more temperatures are probably necessary. Total H₂ column density is known to be correlated with other molecules; we explore if correlations vary as a function of J for several molecules, most importantly CH and CH⁺. Finally, we briefly discuss interpretations of selected lines of sight by comparing them to models computed using the Meudon PDR code.

We compare new results of models of the interplanetary H Lyα intensity background in the outer heliosphere with scans performed by the Voyager1/2 UV spectrometer (UVS) instruments between 1993 and 2003. This study shows that the excess intensity initially reported by Quémerais et al. can be explained by models of the hydrogen atom distribution including effects of the heliospheric interface. The models of the hydrogen atom distribution in the interplanetary medium used in this work have been developed following the numerical scheme presented by Baranov & Malama. Recent improvements are described by Izmodenov et al. Radiative transfer computations of the interplanetary Lyα intensity are made following a Monte Carlo approach presented by Quémerais and Quémerais & Izmodenov. We find that the upwind intensity excess observed in the outer heliosphere initially reported by Quémerais et al. can be explained by a full radiative transfer computation. This computation must include a full description of the velocity distributions of the different hydrogen populations that enter the heliosphere after crossing the interface. The excess upwind intensity observed by UVS on Voyager 1 and Voyager 2 can be explained as an emission of the decelerated hydrogen atoms near the stagnation point of the heliopause. Because those atoms are slowed down relative to the main hydrogen flow, photons they scatter suffer less absorption and are visible at a much larger distance than is the case for photons scattered by atoms in the main flow. The shape and extent of the excess emission gives information about the decelerated population near the heliopause stagnation point. A detailed comparison between the data and our present model does not show a complete agreement. The modeled intensity excess is larger than the observed one. We discuss possible improvements to the H distribution model in order to decrease the size of the excess in the model, for example, by decreasing the density of H atoms in the hydrogen wall.

We compare the observed bivariate distribution of masses (M) and ages (τ) of star clusters in the Large Magellanic Cloud (LMC) with the predicted distributions g(M, τ) from three idealized models for the disruption of star clusters: (1) sudden mass-dependent disruption, (2) gradual mass-dependent disruption, and (3) gradual mass-independent disruption. The model with mass-independent disruption provides a good, first-order description of these cluster populations, with g(M, τ) ∝ M^βτ^γ, β = −1.8 ± 0.2 and γ = −0.8 ± 0.2, at least for clusters with ages τ ≲ 10⁹ yr and masses M ≳ 10³M_☉ (more specifically, τ ≲ 10⁷(M/10²M_☉)^1.3 yr). This model predicts that the clusters should have a power-law luminosity function, dN/dL ∝ L^−1.8, in agreement with observations. The first two models, on the other hand, fare poorly when describing the observations, refuting previous claims that mass-dependent disruption of star clusters is observed in the LMC over the studied M–τ domain. Clusters in the SMC can be described by the same g(M, τ) distribution as for the LMC, but with smaller samples and hence larger uncertainties. The successful g(M, τ) model for clusters in the Magellanic Clouds is virtually the same as the one for clusters in the merging Antennae galaxies, but extends the domain of validity to lower masses and to older ages. This indicates that the dominant disruption processes are similar in these very different galaxies over at least τ ≲ 10⁸ yr and possibly τ ≲ 10⁹ yr. The mass functions for young clusters in the LMC are power laws, while that for ancient globular clusters is peaked. We show that the observed shapes of these mass functions are consistent with expectations from the simple evaporation model presented by McLaughlin & Fall.

The 10 μm silicate feature is an essential diagnostic of dust-grain growth and planet formation in young circumstellar disks. The Spitzer Space Telescope has revolutionized the study of this feature, but due to its small (85 cm) aperture, it cannot spatially resolve small/medium-separation binaries (≲3''; ≲ 420 AU) at the distances of the nearest star-forming regions (∼140 pc). Large, 6–10 m ground-based telescopes with mid-infrared instruments can resolve these systems. In this paper, we spatially resolve the 088 binary, UY Aur, with MMTAO/BLINC-MIRAC4 mid-infrared spectroscopy. We then compare our spectra to Spitzer/IRS (unresolved) spectroscopy, and resolved images from IRTF/MIRAC2, Keck/OSCIR, and Gemini/Michelle, which were taken over the past decade. We find that UY Aur A has extremely pristine, interstellar medium (ISM)-like grains and that UY Aur B has an unusually shaped silicate feature, which is probably the result of blended emission and absorption from foreground extinction in its disk. We also find evidence for variability in both UY Aur A and UY Aur B by comparing synthetic photometry from our spectra with resolved imaging from previous epochs. The photometric variability of UY Aur A could be an indication that the silicate emission itself is variable, as was recently found in EX Lupi. Otherwise, the thermal continuum is variable, and either the ISM-like dust has never evolved, or it is being replenished, perhaps by UY Aur's circumbinary disk.

We present [O iii 5007 Å] observations of the star-forming galaxy (SFG) HDF-BMZ1299 (z = 1.598) using Keck Observatory's adaptive optics system with the near-infrared integral field spectrograph OSIRIS. Using previous Hα and [N ii] measurements of the same source, we are able for the first time to use spatially resolved observations to place a high-redshift galaxy's substructure on a traditional H ii diagnostic diagram. We find that HDF-BMZ1299's spatially concentrated nebular ratios in the central ∼1.5 kpc (02) are best explained by the presence of an active galactic nucleus (AGN): log ([N ii]/Hα) = −0.22 ± 0.05 and 2σ limit of log ([O iii]/Hβ) ≳0.26. The dominant energy source of this galaxy is star formation, and integrating a single aperture across the galaxy yields nebular ratios that are composite spectra from both AGN and H ii regions. The presence of an embedded AGN in HDF-BMZ1299 may suggest a potential contamination in a fraction of other high-redshift SFGs, and we suggest that this may be a source of the "elevated" nebular ratios previously seen in seeing-limited metallicity studies. HDF-BMZ1299's estimated AGN luminosity is L_Hα = (3.7 ± 0.5) × 10⁴¹ erg s⁻¹ and $L_{[\rm O\,\mathsc {iii}]}$ = (5.8 ± 1.9) × 10⁴¹ erg s⁻¹, making it one of the lowest luminosity AGNs discovered at this early epoch.

Na i D lines in the spectrum of the young binary KH 15D have been analyzed in detail. We find an excess absorption component that may be attributed to foreground interstellar absorption, and to gas possibly associated with the solids in the circumbinary disk. The derived column density is log $N_{\rm Na\,\mathsc{i}}$ = 12.5 cm⁻², centered on a radial velocity that is consistent with the systemic velocity. Subtracting the likely contribution of the interstellar medium leaves log $N_{\rm Na\,\mathsc{i}} \sim$ 12.3 cm⁻². There is no detectable change in the gas column density across the "knife edge" formed by the opaque grain disk, indicating that the gas and solids have very different scale heights, with the solids being highly settled. Our data support a picture of this circumbinary disk as being composed of a very thin particulate grain layer composed of millimeter-sized or larger objects that are settled within whatever remaining gas may be present. This phase of disk evolution has been hypothesized to exist as a prelude to the formation of planetesimals through gravitational fragmentation, and is expected to be short-lived if much gas were still present in such a disk. Our analysis also reveals the presence of excess Na i emission relative to the comparison spectrum at the radial velocity of the currently visible star that plausibly arises within the magnetosphere of this still-accreting young star.

We present the discovery of the orbital period of Swift J1626.6−5156. Since its discovery in 2005, the source has been monitored with Rossi X-Ray Timing Explorer, especially during the early stage of the outburst and into the X-ray modulating episode. Using a data span of ∼700 days, we obtain the orbital period of the system as 132.9 days. We find that the orbit is close to a circular shape with an eccentricity 0.08, that is one of the smallest among Be/X-ray binary systems. Moreover, we find that the timescale of the X-ray modulations varied, which led to earlier suggestions of orbital periods at about a third and half of the orbital period of Swift J1626.6−5156.

We calculate the cosmic microwave background (CMB) bispectrum due to inhomogeneous reionization. We calculate all the terms that can contribute to the bispectrum that are products of first-order terms on all scales in conformal Newtonian gauge. We also correctly account for the de-correlation between the matter density and initial conditions using perturbation theory up to third order. We find that the bispectrum is of local type as expected. For a reasonable model of reionization, in which the universe is completely ionized by redshift z_ri ∼ 8 with optical depth to the last scattering surface τ₀ = 0.087, the signal-to-noise ratio (S/N) for detection of the CMB temperature bispectrum is S/N ∼ 0.1 and confusion in the estimation of primordial non-Gaussianity is f_NL ∼ −0.1. For an extreme model with z_ri ∼ 12.5 and τ₀ = 0.14, we get S/N ∼ 0.5 and f_NL ∼ −0.2.

We use Chandra X-ray observations of the hot gas in and around NGC 6868 and NGC 6861 in the Telescopium galaxy group (AS0851) to probe the interaction history between these galaxies. Mean surface brightness profiles for NGC 6868 and NGC 6861 are each well described by double β-models, suggesting that they are each the dominant galaxy in a galaxy subgroup about to merge. Surface brightness and temperature maps of the brightest group galaxy NGC 6868 show a cold front edge ∼23 kpc to the north, and a cool 0.62 keV spiral-shaped tail to the south. Analysis of the temperature and density across the cold front constrains the relative motion between NGC 6868 and the ambient group gas to be at most transonic; while the spiral morphology of the tail strongly suggests that the cold front edge and tail are the result of gas sloshing due to the subgroup merger. The cooler central region of NGC 6861 is surrounded by a sheath of hot gas to the east and hot, bifurcated tails of X-ray emission to the west and northwest. We discuss supersonic infall of the NGC 6861 subgroup, sloshing from the NGC 6868 and NGC 6861 subgroup merger, and AGN heating as possible explanations for these features, and discuss possible scenarios that may contribute to the order of magnitude discrepancy between the Margorrian and black hole mass–σ predictions for its central black hole.

We present the first results from a long (496 ks) Chandra High Energy Transmission Grating observation of the intermediate polar EX Hydrae (EX Hya). In addition to the narrow emission lines from the cooling post-shock gas, for the first time we have detected a broad component in some of the X-ray emission lines, namely, O viii λ18.97, Mg xii λ8.42, Si xiv λ6.18, and Fe xvii λ16.78. The broad and narrow components have widths of ${\sim }1600 \rm \;km \;s^{-1}$ and ${\sim }150 \rm \;km \;s^{-1}$, respectively. We propose a scenario where the broad component is formed in the pre-shock accretion flow, photoionized by radiation from the post-shock flow. Because the photoionized region has to be close to the radiation source in order to produce strong photoionized emission lines from ions such as O viii, Fe xvii, Mg xii, and Si xiv, our photoionization model constrains the height of the standing shock above the white dwarf surface. Thus, the X-ray spectrum from EX Hya manifests features of both magnetic and non-magnetic cataclysmic variables.

The formation of CH⁺ in the interstellar medium (ISM) has long been an outstanding problem in chemical models. In order to probe the physical conditions of the ISM in which CH⁺ forms, we propose the use of CH⁺₃ observations. The pathway to forming CH⁺₃ begins with CH⁺, and a steady-state analysis of CH⁺₃ and the reaction intermediary CH⁺₂ results in a relationship between the CH⁺ and CH⁺₃ abundances. This relationship depends on the molecular hydrogen fraction, $f_{\rm H_2}$, and gas temperature, T, so observations of CH⁺ and CH⁺₃ can be used to infer the properties of the gas in which both species reside. We present observations of both molecules along the diffuse cloud sight line toward Cyg OB2 No. 12. Using our computed column densities and upper limits, we put constraints on the $f_{\rm H_2}$ versus T parameter space in which CH⁺ and CH⁺₃ form. We find that average, static, diffuse molecular cloud conditions (i.e., $f_{\rm H_2}\gtrsim 0.2$, T ∼ 60 K) are excluded by our analysis. However, current theory suggests that non-equilibrium effects drive the reaction C⁺ + H₂ → CH⁺ + H, endothermic by 4640 K. If we consider a higher effective temperature due to collisions between neutrals and accelerated ions, the CH⁺₃ partition function predicts that the overall population will be spread out into several excited rotational levels. As a result, observations of more CH⁺₃ transitions with higher signal-to-noise ratios are necessary to place any constraints on models where magnetic acceleration of ions drives the formation of CH⁺.