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We have recently discovered a new starless core with bright radio emissions of long carbon-chain molecules in the Lupus molecular cloud, which we have named as Lupus-1A. Toward this source, the peak intensities of the C₆H and C₈H lines are found to be higher than toward TMC-1 by a factor of 2–3. Even the lines of their anions, C₆H⁻ and C₈H⁻, are also brighter than in TMC-1. Moreover, the line of C₄H⁻ has been detected for the first time in a starless core. The column densities of these long carbon-chain molecules are almost comparable to those in TMC-1, and hence, this source can be regarded as the second "TMC-1 like cloud." TMC-1 has long been an outstanding molecular cloud with rich carbon-chain molecules since its discovery in 1976. In spite of extensive efforts, no comparable sources have been found so far. Lupus-1A will be used for hunting of new interstellar molecules as well as understanding of carbon-chain chemistry through critical comparison of physical and chemical properties with TMC-1. This source is important not only for astronomy but also for molecular science as an ideal spectroscopic laboratory because of narrow line shapes and bright intensities.

Spectra of Triton between 1.8 and 5.5 μm, obtained in 2007 May and 2009 November, have been analyzed to determine the global surface composition. The spectra were acquired with the grism and the prism of the Infrared Camera on board AKARI with spectral resolutions of 135 and 22, respectively. The data from 4 to 5 μm are shown in this Letter and compared to the spectra of N₂, CO, and CO₂, i.e., all the known ices on this moon that have distinct bands in this previously unexplored wavelength range. We report the detection of a 4σ absorption band at 4.76 μm (2101 cm⁻¹), which we attribute tentatively to the presence of solid HCN. This is the sixth ice to be identified on Triton and an expected component of its surface because it is a precipitating photochemical product of Triton's thin N₂ and CH₄ atmosphere. It is also formed directly by irradiation of mixtures of N₂ and CH₄ ices. Here we consider only pure HCN, although it might be dissolved in N₂ on the surface of Triton because of the evaporation and recondensation of N₂ over its seasonal cycle. The AKARI spectrum of Triton also covers the wavelengths of the fundamental (1–0) band of β-phase N₂ ice (4.296 μm, 2328 cm⁻¹), which has never been detected in an astronomical body before, and whose presence is consistent with the overtone (2–0) band previously reported. Fundamental bands of CO and CO₂ ices are also present.

We use resistive magnetohydrodynamical (MHD) simulations with the nested grid technique to study the formation of protoplanetary disks around protostars from molecular cloud cores that provide the realistic environments for planet formation. We find that gaseous planetary-mass objects are formed in the early evolutionary phase by gravitational instability in regions that are decoupled from the magnetic field and surrounded by the injection points of the MHD outflows during the formation phase of protoplanetary disks. Magnetic decoupling enables massive disks to form and these are subject to gravitational instability, even at ∼10 AU. The frequent formation of planetary-mass objects in the disk suggests the possibility of constructing a hybrid planet formation scenario, where the rocky planets form later under the influence of the giant planets in the protoplanetary disk.

The dominant component of the GeV gamma-ray burst emission detected by the Large Area Telescope begins after the prompt soft (sub-MeV) gamma rays and lasts longer. This has led to the intriguing suggestion that the GeV emission is generated via synchrotron emission of the external shock. Moreover, the limits on the MeV afterglow emission lead to the suggestion that at least in bright GeV bursts the field is not amplified beyond compression in the shock. We show here that considerations of confinement (within the decelerating shock), efficiency, and cooling of the emitting electrons constrain, within this model, the magnetic fields that arise in both the upstream (unshocked circumburst) and downstream (shocked circumburst) regions, allowing us to put direct limits on their values. The well-known limit on the maximal synchrotron emission, when combined with the blast wave evolution, implies that late photons (arriving more than ∼100 s after the burst) with energies higher than ∼10 GeV do not arise naturally from an external shock synchrotron and almost certainly have a different origin. Finally, even a modest seed flux (a few mJy) in IR–optical would quench, via Inverse Compton cooling, the GeV emission unless the magnetic field is significantly amplified behind the shock. An observation of a burst with simultaneous IR–optical and GeV emission will rule out this model.

Cosmological simulations of dark matter (DM) structures have identified a set of universal profiles, and similar characteristics have been seen in non-cosmological simulations. There has therefore been speculation as to whether these profiles of collisionless systems relate to accretion and merger history, or if there is an attractor for the DM systems. Here, we identify such a one-dimensional attractor in the three-dimensional space spanned by the two radial slopes of the density and velocity dispersion, and the velocity anisotropy. This attractor effectively removes 1 degree of freedom from the Jeans equation. It also allows us to speculate on a new fluid interpretation for the Jeans equation, with an effective polytropic index for the DM particles between 1/2 and 3/4. If this attractor solution holds for other collisionless structures, then it may hold the key to breaking the mass-anisotropy degeneracy, which presently prevents us from uniquely measuring the mass profiles in dwarf galaxies.

We present HST/WFC3 grism near-IR spectroscopy of the brightest galaxy at z > 1.5 in the GOODS-South WFC3 ERS grism pointing. The spectrum is of remarkable quality and shows the redshifted Balmer lines Hβ, Hγ, and Hδ in absorption at z = 1.902 ± 0.002. The absorption lines can be produced by a post-starburst stellar population with a luminosity-weighted age of ≈0.5 Gyr. The mass-to-light ratio inferred from the spectrum implies a stellar mass of (4 ±  1) ×  10¹¹ M_☉. We determine the morphology of the galaxy from a deep WFC3 H₁₆₀ image. Similar to other massive galaxies at z ∼  2 the galaxy is compact, with an effective radius of 2.1 ±  0.3 kpc. Although most of the light is in a compact core, the galaxy has two red, smooth spiral arms that appear to be tidally induced. The spatially resolved spectroscopy demonstrates that the center of the galaxy is quiescent whereas the surrounding disk is forming stars, as it shows Hβ in emission. The galaxy interacts with a companion at a projected distance of 18 kpc, which also shows prominent tidal features. The companion is a factor of ∼10 fainter than the primary galaxy and may have a lower metallicity. It is tempting to interpret these observations as evidence for the growth of compact, quiescent high-redshift galaxies through minor mergers, which has been proposed by several recent observational and theoretical studies. Interestingly both objects host luminous active galactic nuclei, which implies that these mergers can be accompanied by significant black hole growth.

We use high spatial and spectral resolution observations obtained with the CRisp Imaging SpectroPolarimeter at the Swedish 1 m Solar Telescope to analyze the velocity profile of granular light bridges (LBs) in a sunspot. We find upflows associated with the central dark lanes of the LBs. From bisectors in the Fe i 630.15 nm line we find that the magnitude of the upflows varies with height, with the strongest upflows being deeper in the atmosphere. Typical upflow velocities measured from the 70% bisector are around 500 m s⁻¹ with peaks above 1 km s⁻¹. The upflows in the central dark lane are surrounded by downflows of weaker magnitude, sometimes concentrated in patches with enhanced velocities reaching up to 1.1 km s⁻¹. A small spatial offset between the upflows and the continuum dark lane is interpreted as a line-of-sight effect due to the elevated nature of the dark lane and the LB above the umbral surroundings. Our observations show that the central dark lane in granular LBs is not equivalent to the intergranular lanes of normal photospheric granulation that host convective downflows. These results support recent MHD simulations of magneto-convection in sunspot atmospheres.

We propose a new mechanism for the delivery of gas to the heart of galactic nuclei. We show that warm halo clouds (WHCs) must periodically impact galactic centers and potentially deliver a large (∼10⁴–10⁶ M_☉) mass of gas to the galactic nucleus in a singular event. The impact of an accreting WHC originating far in the galactic halo can, depending on mixing, produce a nuclear starburst of low-metallicity stars as well as low-luminosity accretion onto the central black hole. Based on multiphase cooling around a ΛCDM distribution of halos, we calculate the nuclear impact rate, the mass captured by the central black hole, and the fraction of active nuclei for impacting cloud masses in the range 10⁴–10⁶ M_☉. If there is moderate braking during cloud infall, our model predicts an average fraction of low-luminosity active nuclei consistent with observations.

We present H- and K_s-band imaging data resolving the gap in the transitional disk around LkCa 15, revealing the surrounding nebulosity. We detect sharp elliptical contours delimiting the nebulosity on the inside as well as the outside, consistent with the shape, size, ellipticity, and orientation of starlight reflected from the far-side disk wall, whereas the near-side wall is shielded from view by the disk's optically thick bulk. We note that forward scattering of starlight on the near-side disk surface could provide an alternate interpretation of the nebulosity. In either case, this discovery provides confirmation of the disk geometry that has been proposed to explain the spectral energy distributions of such systems, comprising an optically thick disk with an inner truncation radius of ∼46 AU enclosing a largely evacuated gap. Our data show an offset of the nebulosity contours along the major axis, likely corresponding to a physical pericenter offset of the disk gap. This reinforces the leading theory that dynamical clearing by at least one orbiting body is the cause of the gap. Based on evolutionary models, our high-contrast imagery imposes an upper limit of 21 M_Jup on companions at separations outside of 01 and of 13 M_Jup outside of 02. Thus, we find that a planetary system around LkCa 15 is the most likely explanation for the disk architecture.

We report the discovery of several large "propeller" moons in the outer part of Saturn's A ring, objects large enough to be followed over the 5 year duration of the Cassini mission. These are the first objects ever discovered that can be tracked as individual moons, but do not orbit in empty space. We infer sizes up to 1–2 km for the unseen moonlets at the center of the propeller-shaped structures, though many structural and photometric properties of propeller structures remain unclear. Finally, we demonstrate that some propellers undergo sustained non-Keplerian orbit motion.

We present a seismic analysis of the pulsating hot B subdwarf KPD 1943+4058 (KIC 005807616) on the basis of the long-period, gravity-mode pulsations recently uncovered by Kepler. This is the first time that g-mode seismology can be exploited quantitatively for stars on the extreme horizontal branch, all previous successful seismic analyses having been confined so far to short-period, p-mode pulsators. We demonstrate that current models of hot B subdwarfs can quite well explain the observed g-mode periods, while being consistent with independent constraints provided by spectroscopy. We identify the 18 pulsations retained in our analysis as low-degree (ℓ = 1 and 2), intermediate-order (k = −9 through −58) g-modes. The periods (frequencies) are recovered, on average, at the 0.22% level, which is comparable to the best results obtained for p-mode pulsators. We infer the following structural and core parameters for KPD 1943+4058 (formal fitting uncertainties only): T_eff = 28,050 ± 470 K, log g = 5.52 ± 0.03, M_* = 0.496 ± 0.002 M_☉, log (M_env/M_*) = −2.55 ± 0.07, log (1 − M_core/M_*) = −0.37 ± 0.01, and X_core(C+O) = 0.261 ± 0.008. We additionally derive the age of the star since the zero-age extended horizontal branch 18.4 ± 1.0 Myr, the radius R = 0.203 ± 0.007 R_☉, the luminosity L = 22.9 ± 3.13 L_☉, the absolute magnitude M_V = 4.21 ± 0.11, the reddening index E(B − V) = 0.094 ± 0.017, and the distance d = 1180 ± 95 pc.

In this Letter, we establish clear evidence for the resonant absorption damping mechanism by analyzing observational data from the novel Coronal Multi-Channel Polarimeter. This instrument has established that in the solar corona there are ubiquitous propagating low-amplitude (≈1 km s⁻¹) Alfvénic waves with a wide range of frequencies. Realistically interpreting these waves as the kink mode from magnetohydrodynamic wave theory, they should exhibit a frequency-dependent damping length due to resonant absorption, governed by the Terradas–Goossens–Verth relation showing that transverse plasma inhomogeneity in coronal magnetic flux tubes causes them to act as natural low-pass filters. It is found that the observed frequency dependence on damping length (up to about 8 mHz) can be explained by the kink wave interpretation; and furthermore, the spatially averaged equilibrium parameter describing the length scale of transverse plasma density inhomogeneity over a system of coronal loops is consistent with the range of values estimated from Transition Region and Coronal Explorer observations of standing kink modes.

We discovered a large population of previously unknown Galactic H ii regions by using the Green Bank Telescope to detect their hydrogen radio recombination line emission. Since recombination lines are optically thin at 3 cm wavelength, we can detect H ii regions across the entire Galactic disk. Our targets were selected based on spatially coincident 24 μm and 21 cm continuum emission. For the Galactic zone −16 ° ⩽ ℓ ⩽ 67° and |b| ⩽ 1°, we detected 602 discrete recombination line components from 448 lines of sight, 95% of the sample targets, which more than doubles the number of known H ii regions in this part of the Milky Way. We found 25 new first quadrant nebulae with negative LSR velocities, placing them beyond the solar orbit. Because we can detect all nebulae inside the solar orbit that are ionized by O-stars, the Discovery Survey targets, when combined with existing H ii region catalogs, give a more accurate census of Galactic H ii regions and their properties. The distribution of H ii regions across the Galactic disk shows strong, narrow (∼1 kpc wide) peaks at Galactic radii of 4.3 and 6.0 kpc. The longitude–velocity distribution of H ii regions now gives unambiguous evidence for Galactic structure, including the kinematic signatures of the radial peaks in the spatial distribution, a concentration of nebulae at the end of the Galactic Bar, and nebulae located on the kinematic locus of the 3 Kpc Arm.

Many observational studies have revealed the presence of multiple stellar generations in Galactic globular clusters. These studies suggest that second-generation stars make up a significant fraction of the current mass of globular clusters, with the second-generation mass fraction ranging from ∼50% to 80% in individual clusters. In this Letter, we carry out hydrodynamical simulations to explore the dependence of the mass of second-generation stars on the initial mass and structural parameters and stellar initial mass function (IMF) of the parent cluster. We then use the results of these simulations to estimate the fraction f_SG,H of the mass of the Galactic stellar halo composed of second-generation stars that originated in globular clusters. We study the dependence of f_SG,H on the parameters of the IMF of the Galactic globular cluster system. For a broad range of initial conditions, we find that the fraction of mass of the Galactic stellar halo in second-generation stars is always small, f_SG,H < 4%–6% for a Kroupa-1993 IMF and f_SG,H < 7%–9% for a Kroupa-2001 IMF.

The black hole binary system LMC X-3 has been observed by virtually every X-ray mission since the inception of X-ray astronomy. Among the persistent sources, LMC X-3 is uniquely both habitually soft and highly variable. Using a fully relativistic accretion disk model, we analyze hundreds of spectra collected during eight X-ray missions that span 26 years. For a selected sample of 391 RXTE spectra, we find that to within ≈2% the inner radius of the accretion disk is constant over time and unaffected by source variability. Even considering an ensemble of eight X-ray missions, we find consistent values of the radius to within ≈4%–6%. Our results provide strong evidence for the existence of a fixed inner-disk radius. The only reasonable inference is that this radius is closely associated with the general relativistic innermost stable circular orbit. Our findings establish a firm foundation for the measurement of black hole spin.

During its year-long outburst in 1975–76, the transient source A0620–00 reached an intensity of 50 Crab, an all-time record for any X-ray binary. The source has been quiescent since then. We have recently determined accurate values for the black hole (BH) mass, orbital inclination angle, and distance. Building on these results, we have measured the radius of the inner edge of the accretion disk around the BH primary by fitting its thermal continuum spectrum to our version of the relativistic Novikov–Thorne thin-disk model. We have thereby estimated the spin of the BH. Although our spin estimate depends on a single high-quality spectrum, which was obtained in 1975 by OSO-8, we are confident of our result because of the consistent values of the inner-disk radius that we have obtained for hundreds of observations of other sources: H1743-322, XTE J1550-564, and notably LMC X-3. We have determined the dimensionless spin parameter of the BH to be a_* = 0.12 ± 0.19, with a_* < 0.49 and a_*> − 0.59 at the 3σ level of confidence. This result takes into account all sources of observational and model-parameter uncertainties. Despite the low spin, the intensity and properties of the radio counterpart, both in outburst and quiescence, attest to the presence of a strong jet. If jets are driven by BH spin, then current models indicate that jet power should be a steeply increasing function of a_*. Consequently, the low spin of A0620–00 suggests that its jet may be disk driven.

We report on the discovery and initial observations of the energetic type IIn supernova 2008fz. This object was discovered at redshift z = 0.133 and reached an apparent magnitude of V ∼ 17. After correcting for Galactic extinction and redshift, we determine the peak absolute magnitude of the event to be M_V = −22.3, placing it among the most luminous supernovae discovered. The optical energy emitted by SN 2008fz (based on the light curve over an 88 day period) is possibly the most ever observed for a supernova (>1.4 × 10⁵¹ erg). The event was more luminous than the type IIn SN 2006gy, but exhibited the same smooth, slowly evolving light curve. As is characteristic of type IIn supernova, the early spectra of SN 2008fz initially exhibited narrow Balmer lines which were replaced by a broader component at later times. The spectra also show a blue continuum with no signs of Ca or Na absorption, suggesting that there is little extinction due to dust in the host or circumstellar material. No host galaxy is identified in prior co-added images reaching R ∼ 22. From the supernova's redshift, we place an upper limit on the brightness of the host of M_R ∼ −17 (similar to the brightness of the Small Magellanic Cloud). The presence of the supernova within such a faint galaxy follows the majority of recently discovered highly luminous supernovae. A possible reason for this is the combination of a high star formation rate in low-mass galaxies with a low-metallicity environment.

The dust ejecta of Main-Belt Comet P/2010 A2 (LINEAR) have been observed with several telescopes at the Observatorio del Roque de los Muchachos on La Palma, Spain. Application of an inverse dust tail Monte Carlo method to the images of the dust ejecta from the object indicates that a sustained, likely water-ice-driven, activity over some eight months is the mechanism responsible for the formation of the observed tail. The total amount of the dust released is estimated to be 5 × 10⁷ kg, which represents about 0.3% of the nucleus mass. While the event could have been triggered by a collision, this cannot be determined from the currently available data.

We investigate the ν-process in an energetic Type Ic supernova (SN Ic) and the resultant productions of the light elements including boron and its stable isotopes. SN Ic is a very unique boron source because it can produce boron not only through spallation reactions as discussed in Nakamura & Shigeyama but also the ν-process. The ν-process is considered to occur in core-collapse supernovae and previous studies were limited to SNe II. Although the progenitor star of an SN Ic does not posses an He envelope so that ⁷Li production via the ν-process is unlikely, ¹¹B can be produced in the C-rich layers. We demonstrate a hydrodynamic simulation of a SN Ic explosion and estimate the amounts of the light elements produced via the ν-process for the first time, and also the subsequent spallation reactions between the outermost layers of the compact SN Ic progenitor and the ambient medium. We find that the ν-process in the current SN Ic model produces a significant amount of ¹¹B, which is diluted by ¹⁰B from spallation reactions to get closer to B isotopic ratios observed in meteorites. We also confirm that high-temperature μ and τ neutrinos and their anti-neutrinos, reasonably suggested from the compact structure of SN Ic progenitors, enhance the light-element production through the neutral current reactions, which may imply an important role of SNe Ic in the Galactic chemical evolution.

We present the first observations of diffuse radiation in the far-ultraviolet (FUV; 1000–1150 Å) from the Large Magellanic Cloud based on observations made with the Far Ultraviolet Spectroscopic Explorer. The fraction of the total radiation in the field emitted as diffuse radiation is typically 5%–20% with a high of 45% near N70 where there are few exciting stars, indicating that much of the emission is not due to nearby stars. Much less light is scattered in the FUV than at longer wavelengths, with the stellar radiation going into heating the interstellar dust.

We show that stars with transiting planets for which the stellar obliquity is large are preferentially hot (T_eff > 6250 K). This could explain why small obliquities were observed in the earliest measurements, which focused on relatively cool stars drawn from Doppler surveys, as opposed to hotter stars that emerged more recently from transit surveys. The observed trend could be due to differences in planet formation and migration around stars of varying mass. Alternatively, we speculate that hot-Jupiter systems begin with a wide range of obliquities, but the photospheres of cool stars realign with the orbits due to tidal dissipation in their convective zones, while hot stars cannot realign because of their thinner convective zones. This in turn would suggest that hot Jupiters originate from few-body gravitational dynamics and that disk migration plays at most a supporting role.

We report SMARTS, Gemini, and Swift-UVOT observations of the optical transient (OT) associated with gamma-ray burst (GRB) 091127, at redshift 0.49, taken between 0.9 hr and 102 days following the Swift trigger. In our early-time observations, the OT fades in a manner consistent with previously observed GRB afterglows. However, after nine days post-burst, the OT is observed to brighten for a period of ∼two weeks, after which the source resumes fading. A comparison of this late-time "bump" to SN 1998bw (the broad-lined Type Ic supernova associated with GRB 980425), and several other GRB supernovae (SNe), indicates that the most straightforward explanation is that GRB 091127 was accompanied by a contemporaneous SN (SN 2009nz) that peaked at a magnitude of M_V = −19.0 ± 0.2. SN 2009nz is globally similar to other GRB SNe, but evolves slightly faster than SN 1998bw and reaches a slightly dimmer peak magnitude. We also analyze the early-time UV–optical–IR spectral energy distribution of the afterglow of GRB 091127 and find that there is little to no reddening in the host galaxy along the line of sight to this burst.

We report two detections of deuterated molecular hydrogen (HD) in QSO absorption-line systems at z>2. Toward J2123−0500, we find N(HD) =13.84 ± 0.2 for a sub-Damped Lyman Alpha system (DLA) with metallicity ≃0.5Z_☉ and N(H₂) = 17.64 ± 0.15 at z = 2.0594. Toward FJ0812+32, we find N(HD) =15.38 ± 0.3 for a solar-metallicity DLA with N(H₂) = 19.88 ± 0.2 at z = 2.6265. These systems have ratios of HD to H₂ above that observed in dense clouds within the Milky Way disk and apparently consistent with a simple conversion from the cosmological ratio of D/H. These ratios are not readily explained by any available model of HD chemistry, and there are no obvious trends with metallicity or molecular content. Taken together, these two systems and the two published z>2 HD-bearing DLAs indicate that HD is either less effectively dissociated or more efficiently produced in high-redshift interstellar gas, even at low molecular fraction and/or solar metallicity. It is puzzling that such diverse systems should show such consistent HD/H₂ ratios. Without clear knowledge of all the aspects of HD chemistry that may help determine the ratio HD/H₂, we conclude that these systems are potentially more revealing of gas chemistry than of D/H itself and that it is premature to use such systems to constrain D/H at high redshift.

Non-thermal hard X-ray and high-energy (HE; 1 MeV ⩽ E ⩽ 100 GeV) γ-ray emission in the direction of η Carina has been recently detected using the INTEGRAL, AGILE, and Fermi satellites. So far this emission has been interpreted in the framework of particle acceleration in the colliding wind region between the two massive stars. However, the existence of a very fast moving blast wave which originates in the historical 1843 "Great Eruption" provides an alternative particle acceleration site in this system. Here, we explore an alternate scenario and find that inverse Compton emission from electrons accelerated in the blast wave can naturally explain both the flux and spectral shape of the measured hard X-ray and HE γ-ray emission. This scenario is further supported by the lack of significant variability in the INTEGRAL and Fermi measured fluxes.

The Fermi Large Area Telescope (LAT) discovered a new gamma-ray source near the Galactic plane, Fermi J0109+6134, when it flared brightly in 2010 February. The low Galactic latitude (b = −12) indicated that the source could be located within the Galaxy, which motivated rapid multi-wavelength follow-up including radio, optical, and X-ray observations. We report the results of analyzing all 19 months of LAT data for the source, and of X-ray observations with both Swift and the Chandra X-ray Observatory. We determined the source redshift, z = 0.783, using a Keck Low-Resolution Imaging Spectrometer observation. Finally, we compiled a broadband spectral energy distribution (SED) from both historical and new observations contemporaneous with the 2010 February flare. The redshift, SED, optical line width, X-ray absorption, and multi-band variability indicate that this new GeV source is a blazar seen through the Galactic plane. Because several of the optical emission lines have equivalent width >5 Å, this blazar belongs in the flat-spectrum radio quasar category.

We obtained a long-exposure vector magnetogram of the quiet Sun photosphere at the disk center with a wide field of view of 51'' × 82''. The observation was performed at Fe i 525.0 nm with the shutterless mode of the Narrow Band Filter Imager of the Solar Optical Telescope (SOT) on board the Hinode satellite. We summed the linear polarization (LP) maps taken with a time cadence of 60 s for 2 hr to obtain a map with as long of an exposure as possible. The polarization sensitivity would be more than 4.6 (21.2 in exposure time) times the standard observation with the SOT Spectropolarimeter. The LP map shows a cellular structure with a typical scale of 5''–10''. We find that the enhanced LP signals essentially consist of the isolated sporadic transient horizontal magnetic fields (THMFs) with a lifetime of 1–10 minutes and are not contributed by long-duration weak horizontal magnetic fields. The cellular structure coincides in position with the negative divergence of the horizontal flow field, i.e., mesogranular boundaries with downflows. Azimuth distribution appears to be random for the scale size of the mesogranules. Some pixels have two separate appearances of THMFs, and the measured time intervals are consistent with the random appearance. THMFs tend to appear at the mesogranular boundaries, but appear randomly in time. We discuss the origin of THMFs based on these observations.

New images from the Cassini spacecraft reveal optically thick clumps, capable of casting shadows, and associated structures in regions of Saturn's F ring that have recently experienced close passage by the adjacent moon Prometheus. Using these images and modeling, we show that Prometheus' perturbations create regions of enhanced density and low relative velocity that are susceptible to gravitational instability and the formation of distended, yet long-lived, gravitationally coherent clumps. Subsequent collisional damping of these low-density clumps may facilitate their collapse into ∼10–20 km contiguous moonlets. The observed behavior of the F ring is analogous to the case of a marginally stable gas disk being driven to instability and collapse via perturbations from an embedded gas giant planet.

We present high-resolution images of the bipolar outflow from W51e2, which are produced from the Submillimeter Array archival data observed for CO(3–2) and HCN(4–3) lines with angular resolutions of 08 × 06 and 03 × 02, respectively. The images show that the powerful outflow originates from the protostellar core W51e2-E rather than from the ultracompact H ii region W51e2-W. The kinematic timescale of the outflow from W51e2-E is about 1000 yr, younger than the age (∼5000 yr) of the ultracompact H ii region W51e2-W. A large mass-loss rate of ∼1 × 10⁻³ M_☉ yr⁻¹ and a high mechanical power of 120 L_☉ are inferred, suggesting that an O star or a cluster of B stars are forming in W51e2-E. The observed outflow activity along with the inferred large accretion rate indicates that at present W51e2-E is in a rapid phase of star formation.

Using results of remote sensing by energetic neutral atoms from IBEX, SOHO/HSTOF, and Cassini/INCA, in situ measurements of ∼40–4000 keV protons in the heliosheath (HS) from Low Energy Charged Particle on Voyager 1 and Voyager 2, and outputs from numerical modeling of the termination shock, we estimate L, the characteristic thickness of the HS in the "upwind" direction (±45° in ecliptic longitude of the Nose at λ = 255°). A simple steady-state, internally consistent model gives L = 21 ± 6 AU for Voyager 1, L = 28 ± 8 AU for Voyager 2, and L = 25 ± 8 AU assuming that the same L value is valid for both spacecraft. We recognize that this is a very coarse cut at a very dynamic region of the heliosphere; but if the lower value L = 21 AU applies, one could expect Voyager 1 to cross the heliopause as early as late 2010.

We present new atomic data (radiative transitions rates and collision strengths) from large-scale calculations and a non-LTE spectral model for Fe iii. This model is in very good agreement with observed astronomical emission spectra, in contrast with previous models that yield large discrepancies in observations. The present atomic computations employ a combination of atomic physics methods, e.g., relativistic Hartree–Fock, the Thomas–Fermi–Dirac potential, and Dirac–Fock computation of A-values and the R-matrix with intermediate coupling frame transformation and the Dirac R-matrix. We study advantages and shortcomings of each method. It is found that the Dirac R-matrix collision strengths yield excellent agreement with observations, much improved over previously available models. By contrast, the transformation of the LS-coupling R-matrix fails to yield accurate effective collision strengths at around 10⁴ K, despite using very large configuration expansions, due to the limited treatment of spin–orbit effects in the near-threshold resonances of the collision strengths. The present work demonstrates that accurate atomic data for low-ionization iron-peak species are now within reach.

We report the first observation of an anisotropy in the arrival direction of cosmic rays with energies in the multi-TeV region in the Southern sky using data from the IceCube detector. Between 2007 June and 2008 March, the partially deployed IceCube detector was operated in a configuration with 1320 digital optical sensors distributed over 22 strings at depths between 1450 and 2450 m inside the Antarctic ice. IceCube is a neutrino detector, but the data are dominated by a large background of cosmic-ray muons. Therefore, the background data are suitable for high-statistics studies of cosmic rays in the southern sky. The data include 4.3 billion muons produced by downward-going cosmic-ray interactions in the atmosphere; these events were reconstructed with a median angular resolution of 3° and a median energy of ∼20 TeV. Their arrival direction distribution exhibits an anisotropy in right ascension with a first-harmonic amplitude of (6.4 ± 0.2 stat. ± 0.8 syst.) × 10⁻⁴.

The disk around AB Aur was imaged and resolved at 24.6 μm using the Cooled Mid-infrared Camera and Spectrometer on the 8.2 m Subaru Telescope. The Gaussian full width at half-maximum of the source size is estimated to be 90 ± 6 AU, indicating that the disk extends further out at 24.6 μm than at shorter wavelengths. In order to interpret the extended 24.6 μm image, we consider a disk with a reduced surface density within a boundary radius R_c, which is motivated by radio observations that suggest a reduced inner region within about 100 AU from the star. Introducing the surface density reduction factor f_c for the inner disk, we determine that the best match with the observed radial intensity profile at 24.6 μm is achieved with R_c = 88 AU and f_c = 0.01. We suggest that the extended emission at 24.6 μm is due to the enhanced emission from a wall-like structure at the boundary radius (the inner edge of the outer disk), which is caused by a jump in the surface density at R_c. Such a reduced inner disk and geometrically thick outer disk structure can also explain the more point-like nature at shorter wavelengths. We also note that this disk geometry is qualitatively similar to a pre-transitional disk, suggesting that the AB Aur disk is in a pre-transitional disk phase.