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We consider the horizontal branch (HB) of the globular cluster Terzan 5, recently shown to be split into two parts, the fainter one (δM_K ∼ 0.3 mag) having a lower metallicity than the more luminous. Both features show that it contains at least two stellar populations. The separation in magnitude has been ascribed to an age difference of ∼6 Gyr and interpreted as the result of an atypical evolutionary history for this cluster. We show that the observed HB morphology is also consistent with a model in which the bright HB is composed of second generation stars that are metal enriched and with a helium mass fraction larger (by δY ∼ 0.07) than that of first generation stars populating the fainter part of the HB. Terzan 5 would therefore be anomalous, compared to most "normal" clusters hosting multiple populations, only because its second generation is strongly contaminated by supernova ejecta; the previously proposed prolonged period of star formation, however, is not required. The iron enrichment of the bright HB can be ascribed either to contamination from Type Ia supernova ejecta of the low-iron, helium-rich, ejecta of the massive asymptotic giant branch stars of the cluster, or to its mixing with gas, accreting on the cluster from the environment, that has been subject to fast metal enrichment due to its proximity with the galactic bulge. The model proposed here requires only a small age difference of ∼100 Myr.

Outward migration of low-mass planets has recently been shown to be a possibility in non-barotropic disks. We examine the consequences of this result in evolutionary models of protoplanetary disks. Planet migration occurs toward equilibrium radii with zero torque. These radii themselves migrate inwards because of viscous accretion and photoevaporation. We show that as the surface density and temperature fall the planet orbital migration and disk depletion timescales eventually become comparable, with the precise timing depending on the mass of the planet. When this occurs, the planet decouples from the equilibrium radius. At this time, however, the gas surface density is already too low to drive substantial further migration. A higher mass planet, of 10 M_⊕, can open a gap during the late evolution of the disk, and stops migrating. Low-mass planets, with 1 or 0.1 M_⊕, released beyond 1 AU in our models avoid migrating into the star. Our results provide support for the reduced migration rates adopted in recent planet population synthesis models.

We present the first ultraviolet (UV) and multi-epoch optical spectroscopy of 30 Dor 016, a massive O2-type star on the periphery of 30 Doradus in the Large Magellanic Cloud. The UV data were obtained with the Cosmic Origins Spectrograph on the Hubble Space Telescope as part of the Servicing Mission Observatory Verification program after Servicing Mission 4, and reveal #016 to have one of the fastest stellar winds known. From analysis of the C iv λλ1548-51 doublet we find a terminal velocity, v_∞ = 3450 ± 50 km s^-1. Optical spectroscopy is from the VLT-FLAMES Tarantula Survey, from which we rule out a massive companion (with 2 days < P < 1 yr) to a confidence of 98%. The radial velocity of #016 is offset from the systemic value by −85 km s^-1, suggesting that the star has traveled the 120 pc from the core of 30 Doradus as a runaway, ejected via dynamical interactions.

This Letter presents the first theoretical study of the dynamics of a coronal mass ejection (CME) observed by STEREO-A/B. The CME was continuously tracked by SECCHI-A, providing position-time data from eruption to 1 AU. The ejecta was intersected by STEREO-B at 1 AU, where the magnetic field and plasma parameters were measured. The observed CME trajectory and the evolution of the CME magnetic field are modeled using the semianalytic erupting flux-rope model. It is shown that the best-fit theoretical solution is in good agreement—within 1% of the measured CME trajectory in the 1 AU field of view—and is consistent with the in situ magnetic field and plasma data at 1 AU.

The brightest and most surprising feature in the first all-sky maps of energetic neutral atom (ENA) emissions (0.2–6 keV) produced by the Interstellar Boundary Explorer (IBEX) is an almost circular ribbon of a ∼140° opening angle, centered at (l, b) = (33°, 55°), covering the part of the celestial sphere with the lowest column densities of the Local Interstellar Cloud (LIC). We propose a novel interpretation of the IBEX results based on the idea of ENA produced by charge exchange between the neutral H atoms at the nearby edge of the LIC and the hot protons of the Local Bubble (LB). These ENAs can reach the Sun's vicinity because of very low column density of the intervening LIC material. We show that a plane-parallel or slightly curved interface layer of contact between the LIC H atoms (n_H = 0.2 cm⁻³, T = 6000–7000 K) and the LB protons (n_p = 0.005 cm⁻³, T ∼ 10⁶ K), together with an indirect contribution coming from multiply scattered ENAs from the LB, may be able to explain both the shape of the ribbon and the observed intensities, provided that the edge is <(500–2000) AU away, the LIC proton density is (correspondingly) < (0.04–0.01) cm⁻³, and the LB contains ∼1% of non-thermal protons over the IBEX energy range. If this model is correct, then IBEX, for the first time, has imaged in ENAs a celestial object beyond the confines of the heliosphere and can directly diagnose the plasma conditions in the LB.

We present a new high-resolution N-body/smoothed particle hydrodynamics simulation of an encounter of two gas-rich disk galaxies that closely matches the morphology and kinematics of the interacting Antennae galaxies (NGC 4038/39). The simulation includes radiative cooling, star formation, and feedback from Type II supernovae. The large-scale morphology and kinematics are determined by the internal structure and the orbit of the progenitor disks. The properties of the central region, in particular the starburst in the overlap region, only match the observations for a very short time interval (Δt ≈ 20 Myr) after the second encounter. This indicates that the Antennae galaxies are in a special phase only about 40 Myr after the second encounter and 50 Myr before their final collision. This is the only phase in the simulation when a gas-rich overlap region between the nuclei is forming accompanied by enhanced star formation. The star formation rate as well as the recent star formation history in the central region agree well with observational estimates. For the first time, this new model explains the distributed extra-nuclear star formation in the Antennae galaxies as a consequence of the recent second encounter. The proposed model predicts that the Antennae are in a later merger stage than the Mice (NGC 4676) and would therefore lose their first place in the classical Toomre sequence.

An analysis of the fluorine abundance in Galactic asymptotic giant branch (AGB) carbon stars (24 N-type, 5 SC-type, and 5 J-type) is presented. This study uses the state-of-the-art carbon-rich atmosphere models and improved atomic and molecular line lists in the 2.3 μm region. Significantly lower F abundances are obtained in comparison to previous studies in the literature. This difference is mainly due to molecular blends. In the case of carbon stars of SC-type, differences in the model atmospheres are also relevant. The new F enhancements are now in agreement with the most recent theoretical nucleosynthesis models in low-mass AGB stars, solving the long-standing problem of F in Galactic AGB stars. Nevertheless, some SC-type carbon stars still show larger F abundances than predicted by stellar models. The possibility that these stars are of larger mass is briefly discussed.

Previous studies of the active galactic nuclei (AGNs) contribution to the cosmic X-ray background (CXB) consider only observable parameters such as luminosity and absorbing column. Here, for the first time, we extend the study of the CXB to physical parameters including the Eddington ratio of the sources and the black hole mass. In order to calculate the contribution to the CXB of AGN accreting at various Eddington ratios, an evolving Eddington ratio space density model is calculated. In particular, Compton thick (CT) AGNs are modeled as accreting at specific, physically motivated Eddington ratios instead of as a simple extension of the Compton thin type 2 AGN population. Comparing against the observed CT AGN space densities and log N–log S relation indicates that CT AGNs are likely a composite population of AGNs made up of sources accreting either at >90% or <1% of their Eddington rate.

We examine and reconstruct the interplanetary coronal mass ejection (ICME) first seen in space-based coronagraph white-light difference images on 2008 June 1 and 2. We use observations of interplanetary scintillation (IPS) taken with the Solar-Terrestrial Environment Laboratory (STELab), Japan, in our three-dimensional (3D) tomographic reconstruction of density and velocity. The coronal mass ejection (CME) was first observed by the LASCO C3 instrument at around 04:17 UT on 2008 June 2. Its motion subsequently moved across the C3 field of view with a plane-of-the-sky velocity of 192 km s⁻¹. The 3D reconstructed ICME is consistent with the trajectory and extent of the CME measurements taken from the CDAW CME catalog. However, excess mass estimates vary by an order of magnitude from Solar and Heliospheric Observatory and Solar Terrestrial Relations Observatory coronagraphs to our 3D IPS reconstructions of the inner heliosphere. We discuss the discrepancies and give possible explanations for these differences as well as give an outline for future studies.

We report a mass and rotational broadening (vsin i) for the pulsating white dwarf (WD) component of the WZ Sge type Dwarf Nova GW Lib based on high-resolution Very Large Telescope spectroscopy that resolves the Mg ii 4481 Å absorption feature. Its gravitational redshift combined with WD mass–radius models provides us with a direct measurement of the WD mass of M₁ = 0.84 ± 0.02 M_☉. The line is clearly resolved and if associated with rotational broadening gives vsin i = 87.0 ± 3.4 km s⁻¹, equivalent to a spin period of 97 ± 12 s.

SDSS J094857.3+002225 is a very radio-loud narrow-line Seyfert 1 (NLS1) galaxy. Here, we report our discovery of the intranight optical variability (INOV) of this galaxy through the optical monitoring in the B and R bands that covered seven nights in 2009. Violent rapid variability in the optical bands was identified in this RL-NLS1 for the first time, and the amplitudes of the INOV reaches 0.5 mag in both the B and R bands on the timescale of several hours. The detection of the INOV provides a piece of strong evidence supporting the fact that the object carries a relativistic jet with a small viewing angle, which confirms the conclusion drawn from the previous multi-wavelength studies.

We report the discovery of H i 21 cm absorption toward the well-studied Gigahertz peaked spectrum source CTA 21 (4C 16.09) using the Arecibo telescope on 2009 September 20 and 21. Recently, the frequency band between 700 and 800 MHz was temporarily opened up to radio astronomy when US TV stations were mandated to switch from analog to digital transmissions, with new frequency allocations. The redshifted H i frequency for CTA 21 falls within this band. CTA 21 has a complex radio structure on a range of scales. The innermost prominent components are separated by ∼12 mas while weak diffuse emission extends for up to ∼300 mas. The H i absorption profile that we find has two main components, one narrow and the other wider and blueshifted. The total H i column density is 7.9 × 10²⁰ cm⁻², assuming a covering factor of unity and a spin temperature of 100 K. This H i absorption confirms the recently determined optical redshift of this faint galaxy of z ∼ 0.907. We discuss this new detection in light of H i absorption studies toward compact radio sources, and also the possibility that CTA 21 may be exhibiting multiple cycles of nuclear activity. This new detection in CTA 21 is consistent with a strong trend for detection of H i absorption in radio galaxies with evidence of episodic nuclear/jet activity.

Employing solar wind measurements from the Advanced Composition Explorer and Ulysses, photospheric magnetic data, and conservation laws along open field lines, we confirm that the energy and mass flux densities at the Sun increase roughly linearly with the footpoint field strength, B₀. This empirical result has a number of important physical implications. First, it supports the assumption that the magnetic field is the source of the heating in coronal holes. Second, because B₀ may vary by over 2 orders of magnitude, depending on how close the footpoint is located to active regions, the heating rate in coronal holes varies over a very wide range, with active-region holes being characterized by much stronger heating and much larger mass fluxes at low heights than the large, weak-field polar holes. Third, the variation of the mass flux density at 1 AU remains very modest because the mass flux density at the Sun and the net flux-tube expansion both increase almost linearly with B₀, so that the two effects offset each other.

We have investigated the oxygen and nitrogen chemical abundances in extremely compact star-forming galaxies (SFGs) with redshifts between ∼0.11 and 0.35, popularly referred to as "green peas." Direct and strong-line methods sensitive to the N/O ratio applied to their Sloan Digital Sky Survey (SDSS) spectra reveal that these systems are genuine metal-poor galaxies, with mean oxygen abundances ∼20% solar. At a given metallicity these galaxies display systematically large N/O ratios compared to normal galaxies, which can explain the strong difference between our metallicities measurements and previous ones. While their N/O ratios follow the relation with stellar mass of local SFGs in the SDSS, we find that the mass–metallicity relation of the "green peas" is offset ≳0.3 dex to lower metallicities. We argue that recent interaction-induced inflow of gas, possibly coupled with a selective metal-rich gas loss, driven by supernova winds, may explain our findings and the known galaxy properties, namely high specific star formation rates, extreme compactness, and disturbed optical morphologies. The "green pea" galaxy properties seem to be uncommon in the nearby universe, suggesting a short and extreme stage of their evolution. Therefore, these galaxies may allow us to study in great detail many processes, such as starburst activity and chemical enrichment, under physical conditions approaching those in galaxies at higher redshifts.

We report on a global magnetohydrodynamical simulation of the solar convection zone, which succeeds in generating a large-scale axisymmetric magnetic component, antisymmetric about the equatorial plane and undergoing regular polarity reversals on decadal timescales. We focus on a specific simulation run covering 255 years, during which 8 polarity reversals are observed, with a mean period of 30 years. Time–latitude slices of the zonally averaged toroidal magnetic component at the base of the convecting envelope show a well-organized toroidal flux system building up in each solar hemisphere, peaking at mid-latitudes and migrating toward the equator in the course of each cycle, in remarkable agreement with inferences based on the sunspot butterfly diagram. The simulation also produces a large-scale dipole moment, varying in phase with the internal toroidal component, suggesting that the simulation may be operating as what is known in mean-field theory as an αΩ dynamo.

Data from the Sloan Digital Sky Survey (∼300,000 galaxies) indicate that recent star formation (within the last 1 billion years) is bimodal: half of the stars form from gas with high amounts of metals (solar metallicity) and the other half form with small contribution of elements heavier than helium (∼10%–30% solar). Theoretical studies of mass loss from the brightest stars derive significantly higher stellar-origin black hole (BH) masses (∼30–80 M_☉) than previously estimated for sub-solar compositions. We combine these findings to estimate the probability of detecting gravitational waves (GWs) arising from the inspiral of double compact objects. Our results show that a low-metallicity environment significantly boosts the formation of double compact object binaries with at least one BH. In particular, we find the GW detection rate is increased by a factor of 20 if the metallicity is decreased from solar (as in all previous estimates) to a 50–50 mixture of solar and 10% solar metallicity. The current sensitivity of the two largest instruments to neutron star–neutron star (NS–NS) binary inspirals (VIRGO: ∼9 Mpc; LIGO: ∼18) is not high enough to ensure a first detection. However, our results indicate that if a future instrument increased the sensitivity to ∼50–100 Mpc, a detection of GWs would be expected within the first year of observation. It was previously thought that NS–NS inspirals were the most likely source for GW detection. Our results indicate that BH–BH binaries are ∼25 times more likely sources than NS–NS systems and that we are on the cusp of GW detection.

Recently reported observations of magnetar glitches and coincident X-ray long-term brightening events establish enough of a database to indicate that the brightening events are accompanied by glitches at their outset, and that they are probably triggered by the same event that triggers the glitch. We suggest, on the basis of various observational clues, that (1) these are caused by energy releases at depths below 100 m and (2) the unpinning is due to global mechanical motion triggered by the energy release, not by heat. Because mechanical triggering of a glitch requires less energy than a detectable long-term X-ray brightening, the latter does not necessarily accompany every glitch, but it is predicted, when it does occur, to be heralded by a glitch. Crustal oscillation associated with the mechanical energy release may cause short (≪10³ s) flares.

We report on the results from Hα imaging observations of the eastern limb of Tycho's supernova remnant (SN1572) using the Wide Field Planetary Camera 2 on the Hubble Space Telescope. We resolve the detailed structure of the fast, collisionless shock wave into a delicate structure of nearly edge-on filaments. We find a gradual increase of Hα intensity just ahead of the shock front, which we interpret as emission from the thin (∼1'') shock precursor. We find that a significant amount of the Hα emission comes from the precursor and that this could affect the amount of temperature equilibration derived from the observed flux ratio of the broad and narrow Hα components. The observed Hα emission profiles are fit using simple precursor models, and we discuss the relevant parameters. We suggest that the precursor is likely due to cosmic rays and discuss the efficiency of cosmic-ray acceleration at this position.

We report Hubble Space Telescope images of Jupiter during the aftermath of an impact by an unknown object in 2009 July. The 2009 impact-created debris field evolved more slowly than those created in 1994 by the collision of the tidally disrupted comet D/Shoemaker-Levy 9 (SL9). The slower evolution, in conjunction with the isolated nature of this single impact, permits a more detailed assessment of the altitudes and meridional motion of the debris than was possible with SL9. The color of the 2009 debris was markedly similar to that seen in 1994, thus this dark debris is likely to be Jovian material that is highly thermally processed. The 2009 impact site differed from the 1994 SL9 sites in UV morphology and contrast lifetime; both are suggestive of the impacting body being asteroidal rather than cometary. Transport of the 2009 Jovian debris as imaged by Hubble shared similarities with transport of volcanic aerosols in Earth's atmosphere after major eruptions.

On 2009 July 19, we observed a single, large impact on Jupiter at a planetocentric latitude of 55°S. This and the Shoemaker-Levy 9 (SL9) impacts on Jupiter in 1994 are the only planetary-scale impacts ever observed. The 2009 impact had an entry trajectory in the opposite direction and with a lower incidence angle than that of SL9. Comparison of the initial aerosol cloud debris properties, spanning 4800 km east–west and 2500 km north–south, with those produced by the SL9 fragments and dynamical calculations of pre-impact orbit indicates that the impactor was most probably an icy body with a size of 0.5–1 km. The collision rate of events of this magnitude may be five to ten times more frequent than previously thought. The search for unpredicted impacts, such as the current one, could be best performed in 890 nm and K (2.03–2.36 μm) filters in strong gaseous absorption, where the high-altitude aerosols are more reflective than Jupiter's primary clouds.

We have discovered strong gravitational lensing features in the core of the nearby cluster Abell 3827 by analyzing Gemini South GMOS images. The most prominent strong lensing feature is a highly magnified, ring-shaped configuration of four images around the central cD galaxy. GMOS spectroscopic analysis puts this source at z ∼ 0.2. Located ∼20'' away from the central galaxy is a secondary tangential arc feature which has been identified as a background galaxy with z ∼ 0.4. We have modeled the gravitational potential of the cluster core, taking into account the mass from the cluster, the brightest cluster galaxy (BCG), and other galaxies. We derive a total mass of (2.7 ±  0.4) × 10¹³ M_☉ within 37 h⁻¹ kpc. This mass is an order of magnitude larger than that derived from X-ray observations. The total mass derived from lensing data suggests that the BCG in this cluster is perhaps the most massive galaxy in the nearby universe.

We present spectral and kinematic evidence that 2MASS J06085283−2753583 (M8.5γ) is a member of the β Pictoris Moving Group (BPMG, age ∼12 Myr), making it the latest-type known member of this young, nearby association. We confirm low-gravity spectral morphology at both medium and high resolutions in the near-infrared. We present new radial velocity and proper motion measurements, and use these to calculate galactic location and space motion consistent with other high-probability members of the BPMG. The predicted mass range consistent with the object's effective temperature, surface gravity, spectral type, and age is 15–35 M_Jup, placing 2MASS 0608−27 well within the brown dwarf mass regime. 2MASS J06085283−2753583 is thus confidently added to the short list of very low mass, intermediate age benchmark objects that inform ongoing searches for the lowest-mass members of nearby young associations.

We explore a technique for identifying the highest redshift (z>4) sources in Herschel/SPIRE and BLAST submillimeter surveys by localizing the position of the far-infrared dust peak. Just as Spitzer/IRAC was used to identify stellar "bump" sources, the far-IR peak is also a redshift indicator; although the latter also depends on the average dust temperature. We demonstrate the wide range of allowable redshifts for a reasonable range of dust temperatures and show that it is impossible to constraint the redshift of individual objects using solely the position of the far-IR peak. By fitting spectral energy distribution models to simulated Herschel/SPIRE photometry we show the utility of radio and/or far-infrared data in breaking this degeneracy. With prior knowledge of the dust temperature distribution it is possible to obtain statistical samples of high redshift submillimeter galaxy (SMG) candidates. We apply this technique to the BLAST survey of ECDFS to constrain the number of dusty galaxies at z>4. We find 8 ± 2 galaxies with flux density ratios of S₅₀₀>S₃₅₀; this sets an upper limit of 17 ± 4 deg⁻² if we assume all are at z>4. This is <35 % of all 500 μm-selected galaxies down to S₅₀₀>45 mJy (L_IR>2 × 10¹³ L_☉ for z>4). Modeling with conventional temperature and redshift distributions estimates the percentage of these 500 μm peak galaxies at z>4 to be between 10% and 85%. Our results are consistent with other estimates of the number density of very high redshift SMGs and follow the decline in the star formation rate density at z>4.

Numerical simulations show that box-shaped bulges of edge-on galaxies are not bulges: they are bars seen side-on. Therefore, the two components that are seen in edge-on Sb galaxies such as NGC 4565 are a disk and a bar. But face-on SBb galaxies always show a disk, a bar, and a (pseudo)bulge. Where is the (pseudo)bulge in NGC 4565? We use archival Hubble Space TelescopeH-band images and Spitzer Space Telescope 3.6 μm wavelength images, both calibrated to Two Micron All Sky Survey K_s band, to penetrate the prominent dust lane in NGC 4565. We find a high surface brightness, central stellar component that is clearly distinct from the boxy bar and from the disk. Its brightness profile is a Sérsic function with index n = 1.55 ± 0.07 along the major axis and 1.33 ± 0.12 along the minor axis. Therefore, it is a pseudobulge. It is much less luminous than the boxy bar, so the true pseudobulge-to-total luminosity ratio of the galaxy is PB/T = 0.06 ± 0.01, much less than the previously believed value of B/T = 0.4 for the "boxy bulge." We infer that published B/T luminosity ratios of edge-on galaxies with boxy bulges have been overestimated. Therefore, more galaxies than we thought contain little or no evidence of a merger-built classical bulge. From a formation point of view, NGC 4565 is a giant, pure-disk galaxy. This presents a challenge to our picture of galaxy formation by hierarchical clustering: it is difficult to grow galaxies as big as NGC 4565 without also making big classical bulges.

We present the first comparison of virial masses of galaxy clusters with their Sunyaev–Zel'dovich Effect (SZE) signals. We study 15 clusters from the Hectospec Cluster Survey (HeCS) with MMT/Hectospec spectroscopy and published SZE signals. We measure virial masses of these clusters from an average of 90 member redshifts inside the radius r₁₀₀. The virial masses of the clusters are strongly correlated with their SZE signals (at the 99% confidence level using a Spearman rank-sum test). This correlation suggests that Y_SZ can be used as a measure of virial mass. Simulations predict a power-law scaling of Y_SZ ∝ M^α₂₀₀ with α ≈ 1.6. Observationally, we find α = 1.11 ± 0.16, significantly shallower (given the formal uncertainty) than the theoretical prediction. However, the selection function of our sample is unknown and a bias against less massive clusters cannot be excluded (such a selection bias could artificially flatten the slope). Moreover, our sample indicates that the relation between velocity dispersion (or virial mass estimate) and SZE signal has significant intrinsic scatter, comparable to the range of our current sample. More detailed studies of scaling relations are therefore needed to derive a robust determination of the relation between cluster mass and SZE.

We propose to use the large-scale structure (LSS) of the universe as a cosmic standard ruler. This is possible because the pattern of large-scale distribution of matter is scale-dependent and does not change in comoving space during the linear-regime evolution of structure. By examining the pattern of LSS in several redshift intervals it is possible to reconstruct the expansion history of the universe, and thus to measure the cosmological parameters governing the expansion of the universe. The features of the large-scale matter distribution that can be used as standard rulers include the topology of LSS and the overall shapes of the power spectrum and correlation function. The genus, being an intrinsic topology measure, is insensitive to systematic effects such as the nonlinear gravitational evolution, galaxy biasing, and redshift-space distortion, and thus is an ideal cosmic ruler when galaxies in redshift space are used to trace the initial matter distribution. The genus remains unchanged as far as the rank order of density is conserved, which is true for linear and weakly nonlinear gravitational evolution, monotonic galaxy biasing, and mild redshift-space distortions. The expansion history of the universe can be constrained by comparing the theoretically predicted genus corresponding to an adopted set of cosmological parameters with the observed genus measured by using the redshift–comoving distance relation of the same cosmological model.