Accretion of dense clumps in the periastron passage of η Carinae

We perform 3D hydrodynamical numerical simulations of the winds interaction process in the massive binary system η Carinae, and find the secondary star to accrete mass from the dense primary wind close to periastron passage. This accretion is thought to result in the spectroscopic event and X-ray minimum observed in the system every revolution. In this study we limit ourselves to explore the role of clumps in the primary wind in triggering the accretion process. We include the gravity of the secondary star and the orbital motion starting 19 days (90°) before periastron passage. The accretion process is triggered by dense clumps that cannot be decelerated by the ram pressure of the secondary wind. The dense clumps are formed by instabilities in the thin dense shell formed by the shocked primary wind gas. We explore the role of the numerical viscosity and some physical parameters on the initiation of the accretion process, and explain the unique properties of η Car that allow for the periastron accretion process to occur. The accretion starts about a week before periastron passage, as is required to explain the several weeks long X-ray minimum.     

Double globular clusters in the Galaxy?

Four pairs of visual double star clusters with the lowest mass-to-luminosity ratio have been selected among globular clusters of our Galaxy. By taking into accounts the effects of dynamical friction and compressive gravitational shocks, we conclude that the probability for the pairs to be gravitationally bound is very low.     

CGCG 292-057: A Near-Distance Merger Galaxy with Double–Double Radio Lobes and X-shape Structure

J1159+5820 is an extended radio galaxy with a quite unusual morphology, featuring two pairs of radio lobes. Such sources, called double–double radio galaxies, constitute a very rare class of extragalactic radio sources. Furthermore, the extended radio structure of this source shows an X-shape form. According to a much likely scenario, such a morphology is due to interrupting nuclear activity in its central active galactic nucleus. Interestingly, the host of this source is a near-distance bright galaxy named CGCG 292-057, which is clearly disturbed, with tidal features and shells as plausible signs of a recent merger.     

Accretion disks in bimetric theory of gravitation. A strong field test of general relativity?

The sensitivity of accretion disk models with respect to its inner boundary conditions, being located in the strong gravity region of a highly compact central body, is used to discuss a possibility of strong field tests of gravitation via compact source observations. Within the bimetric theory of gravitation the optically thin bremsstrahlung model is calculated as an example for this possibility. Using this model to describe the innermost region of the “bimetric disk”, significant differences with respect to the corresponding results in Einstein's theory were found. The more massiv and compact “bimetric disk” radiates softer with higher luminosity.     

Merger Dynamics of the Pair of Galaxy Clusters——A399 and A401

Convincing evidence for a past interaction between the two rich clusters A399 and A401 was recently found in the X-ray imaging observations. We examine the structure and dynamics of this pair of galaxy clusters. A mixture-modeling algorithm was applied to obtain a robust partition into two clusters, which allowed us to discuss the virial mass and velocity distribution of each cluster. Assuming that these two clusters follow a linear orbit and they have once experienced a close encounter, we model the binary cluster as a two-body system. As a result, four gravitationally bound solutions are obtained. The recent X-ray observations seem to favor a scenario in which the two clusters with a true separation of 5.4h-1 Mpc are currently expanding at 583 km s-1 along a direction with a projection angle of 67.5°, and they will reach a maximum extent of 5.65 h-1 Mpc in about 1.0 h-1 Gyr.     

Modeling of the Turbulent Transport Coefficients in a Gas–Dust Accretion Disk

An heuristic way of modeling the turbulent exchange coefficients for Keplerian accretion disks surrounding solar-type stars is considered. The formulas for these coefficients, taking into account the inverse effects of dust transfer and potential temperature on the maintenance of shear turbulence, generalize to protoplanetary gas–dust clouds the expression for the turbulent viscosity coefficient in so-called a-disks which was obtained in a classic work by Shakura and Syunyaev (1973). The defining relationships are derived for turbulent diffusion and heat flows, which describe, for the two-phase mixture rotating differentially at an angular velocity O(r, z), the dust and heat transfer in the direction perpendicular to the central plane of the disk. The regime of limiting saturation by small dust particles of the layer of “cosmic fluid” located slightly above (or below) the dust subdisk is analyzed.     

Formation of Extrasolar Giant Planets: Core Accretion or Disk Instability?

Earth, Moon, and Planets -     

Evidence for Stellar Streaming in the Cores of Elliptical Galaxies: A Kinematic Signature of Mergers?

We present evidence for non-Gaussian velocity fields within the cores of luminous elliptical galaxies. This evidence is based on high signal-to-noise ratio, medium-resolution spectroscopy of the cores of early-type members of the Virgo and Coma Clusters obtained with the Wisconsin-Indiana-Yale-NOAO 3.5 m telescope. The Virgo data were acquired using an integral-field unit (DensePak), which allows the velocity field to be sampled over a variety of spatial scales. The Coma data were obtained through single 2&arcsec; diameter fibers. The cross-correlation profiles of luminous elliptical galaxies show considerable structure, often having several features with amplitudes as high as 10% that of the cross-correlation peak itself. This structure is most obvious within a radius of 1&farcs;5 (at Virgo), or 相似文献   

High-Resolution Mapping of Flows in the Solar Interior: Fully Consistent OLA Inversion of Helioseismic Travel Times

To recover the flow information encoded in travel-time data of time?–?distance helioseismology, accurate forward modeling and a robust inversion of the travel times are required. We accomplish this using three-dimensional finite-frequency travel-time sensitivity kernels for flows along with a (2+1)-dimensional (2+1D) optimally localized averaging (OLA) inversion scheme. Travel times are measured by ridge filtering MDI full-disk Doppler data and the corresponding Born sensitivity kernels are computed for these particular travel times. We also utilize the full noise-covariance properties of the travel times, which allow us to accurately estimate the errors for all inversions. The whole procedure is thus fully consistent. Because of ridge filtering, the kernel functions separate in the horizontal and vertical directions, motivating our choice of a 2+1D inversion implementation. The inversion procedure also minimizes cross-talk effects among the three flow components, and the averaging kernels resulting from the inversion show very small amounts of cross-talk. We obtain three-dimensional maps of vector solar flows in the quiet Sun at horizontal spatial resolutions of 7?10 Mm using generally 24 hours of data. For all of the flow maps we provide averaging kernels and the noise estimates. We present examples to test the inferred flows, such as a comparison with Doppler data, in which we find a correlation of 0.9. We also present results for quiet-Sun supergranular flows at different depths in the upper convection zone. Our estimation of the vertical velocity shows good qualitative agreement with the horizontal vector flows. We also show vertical flows measured solely from f-mode travel times. In addition, we demonstrate how to directly invert for the horizontal divergence and flow vorticity. Finally we study inferred flow-map correlations at different depths and find a rapid decrease in this correlation with depth, consistent with other recent local helioseismic analyses.     

Substructure in clusters of galaxies: A clue to the ‘missing’ mass?

The influence of subclustering in rich clusters of galaxies is examined using results from numericaln-body experiments. It is found that, under some conditions, the standard virial theorem is satisfied. No physical missing mass is needed because its role is replaced by the gravitational energy of the subclustering. We find that, in the Coma cluster, this effect masquerades as a missing mass about 7 times that of the physical mass, so that the apparent extant virial discrepancy (M _VT/M8) in this cluster is explained.     

How Many CMEs Have Flux Ropes? Deciphering the Signatures of Shocks, Flux Ropes, and Prominences in Coronagraph Observations of CMEs

We intend to provide a comprehensive answer to the question on whether all Coronal Mass Ejections (CMEs) have flux rope structure. To achieve this, we present a synthesis of the LASCO CME observations over the last 16 years, assisted by 3D MHD simulations of the breakout model, EUV and coronagraphic observations from STEREO and SDO, and statistics from a revised LASCO CME database. We argue that the bright loop often seen as the CME leading edge is the result of pileup at the boundary of the erupting flux rope irrespective of whether a cavity or, more generally, a three-part CME can be identified. Based on our previous work on white light shock detection and supported by the MHD simulations, we identify a new type of morphology, the ‘two-front’ morphology. It consists of a faint front followed by diffuse emission and the bright loop-like CME leading edge. We show that the faint front is caused by density compression at a wave (or possibly shock) front driven by the CME. We also present highly detailed multi-wavelength EUV observations that clarify the relative positioning of the prominence at the bottom of a coronal cavity with a clear flux rope structure. Finally, we visually check the full LASCO CME database for flux rope structures. In the process, we classify the events into two clear flux rope classes (‘three-part’, and ‘Loop’), jets and outflows (no clear structure). We find that at least 40 % of the observed CMEs have clear flux rope structures and that ～?29 % of the database entries are either misidentifications or inadequately measured and should be discarded from statistical analyses. We propose a new definition for flux rope CMEs (FR-CMEs) as a coherent magnetic, twist-carrying coronal structure with angular width of at least 40^° and able to reach beyond 10 R_⊙ which erupts on a time scale of a few minutes to several hours. We conclude that flux ropes are a common occurrence in CMEs and pose a challenge for future studies to identify CMEs that are clearly not FR-CMEs.     

Evidence of the Link between Broad Emission Line Regions and Accretion Disks in Active Galactic Nuclei

1 INTRODUCTION Most bright active galactic nuclei (AGNs) exhibit broad emission lines, with full width at half maximum (FWHM ≥ 103 km s?1) (Peterson et al. 1999). Some type 1 AGNs could have very broad emission lines (FWHM≥ 20 000 km s?1). Type 2 AGNs s…     

Effects of Random Flows on the Solar f Mode: I. Horizontal Flow

We examine the effect of random horizontal flows on the dispersion relation of high-degree solar f modes. We follow the approach of Murawski and Roberts (Astron. Astrophys. 272, 595, 1993), addressing some limitations of that paper, and extending the results to include damping and to apply for a general turbulent spectrum. We find a reduction in frequency below the classical result that is about three times that observed. For large wavenumber the damping rate is larger than the frequency correction by a factor of the order of the nondimensional wavenumber, which appears to be consistent with observation.     

Outflows at the Edges of an Active Region in a Coronal Hole: A Signature of Active Region Expansion?

Outflows of plasma at the edges of active regions surrounded by quiet Sun are now a common observation with the Hinode satellite. While there is observational evidence to suggest that the outflows are originating in the magnetic field surrounding the active regions, there is no conclusive evidence that reveals how they are driven. Motivated by observations of outflows at the periphery of a mature active region embedded in a coronal hole, we have used a three-dimensional simulation to emulate the active region’s development in order to investigate the origin and driver of these outflows. We find that outflows are accelerated from a site in the coronal hole magnetic field immediately surrounding the active region and are channelled along the coronal hole field as they rise through the atmosphere. The plasma is accelerated simply as a result of the active region expanding horizontally as it develops. Many of the characteristics of the outflows generated in the simulation are consistent with those of observed outflows: velocities up to 45 km s⁻¹, properties akin to the coronal hole, proximity to the active region’s draining loops, expansion with height, and projection over monopolar photospheric magnetic concentrations. Although the horizontal expansion occurs as a consequence of the active region’s development in the simulation, expansion is also a general feature of established active regions. Hence, it is entirely possible and plausible that the expansion acceleration mechanism displayed in the simulation is occurring in active regions on the Sun and, in addition to reconnection, is driving the outflows observed at their edges.     

The orientations of molecular clouds in the outer Galaxy: evidence for the scale of the turbulence driver?

Supernova (SN) explosions inject a considerable amount of energy into the interstellar medium (ISM) in regions with high-to-moderate star formation rates. In order to assess whether the driving of turbulence by supernovae is also important in the outer Galactic disc, where the star formation rates are lower, we study the spatial distribution of molecular cloud (MC) inclinations with respect to the Galactic plane. The latter contains important information on the nature of the mechanism of energy injection into the ISM. We analyse the spatial correlations between the position angles (PAs) of a selected sample of MCs (the largest clouds in the catalogue of the outer Galaxy published by Heyer et al). Our results show that when the PAs of the clouds are all mapped to values into the  [0°, 90°]  interval, there is a significant degree of spatial correlation between the PAs on spatial scales in the range of 100–800 pc. These scales are of the order of the sizes of individual SN shells in low-density environments such as those prevailing in the outer Galaxy and where the metallicity of the ambient gas is of the order of the solar value or smaller. These findings suggest that individual SN explosions, occurring in the outer regions of the Galaxy and in likewise spiral galaxies, albeit at lower rates, continue to play an important role in shaping the structure and dynamics of the ISM in those regions. The SN explosions we postulate here are likely associated with the existence of young stellar clusters in the far outer regions of the Galaxy and the ultraviolet emission and low levels of star formation observed with the Galaxy Evolution Explorer (GALEX) satellite in the outer regions of local galaxies.     

Detection of methane in the martian atmosphere: evidence for life?

Using the Fourier Transform Spectrometer at the Canada-France-Hawaii Telescope, we observed a spectrum of Mars at the P-branch of the strongest CH₄ band at 3.3 μm with resolving power of 180,000 for the apodized spectrum. Summing up the spectral intervals at the expected positions of the 15 strongest Doppler-shifted martian lines, we detected the absorption by martian methane at a 3.7 sigma level which is exactly centered in the summed spectrum. The observed CH₄ mixing ratio is 10±3 ppb. Total photochemical loss of CH₄ in the martian atmosphere is equal to , the CH₄ lifetime is 340 years and methane should be uniformly mixed in the atmosphere. Heterogeneous loss of atmospheric methane is probably negligible, while the sink of CH₄ during its diffusion through the regolith may be significant. There are no processes of CH₄ formation in the atmosphere, so the photochemical loss must therefore be balanced by abiogenic and biogenic sources. Outgassing from Mars is weak, the latest volcanism is at least 10 million years old, and thermal emission imaging from the Mars Odyssey orbiter does not reveal any hot spots on Mars. Hydrothermal systems can hardly be warmer than the room temperature at which production of methane is very low in terrestrial waters. Therefore a significant production of hydrothermal and magmatic methane is not very likely on Mars. The calculated average production of CH₄ by cometary impacts is 2% of the methane loss. Production of methane by meteorites and interplanetary dust does not exceed 4% of the methane loss. Methane cannot originate from an extinct biosphere, as in the case of “natural gas” on Earth, given the exceedingly low limits on organic matter set by the Viking landers and the dry recent history which has been extremely hostile to the macroscopic life needed to generate the gas. Therefore, methanogenesis by living subterranean organisms is a plausible explanation for this discovery. Our estimates of the biomass and its production using the measured CH₄ abundance show that the martian biota may be extremely scarce and Mars may be generally sterile except for some oases.     

A Hidden Radio Halo in the Galaxy Cluster A 1682?

High sensitivity observations of radio halos in galaxy clusters at frequencies ν ≤ 330 MHz are still relatively rare, and very little is known compared to the classical 1.4 GHz images. The few radio halos imaged down to 150–240 MHz show a considerable spread in size, morphology and spectral properties. All clusters belonging to the GMRT Radio Halo Survey with detected or candidate cluster-scale diffuse emission have been imaged at 325 MHz with the GMRT. Few of them were also observed with the GMRT at 240 MHz and 150 MHz. For A 1682, imaging is particularly challenging due to the presence of strong and extended radio galaxies at the center. Our data analysis suggests that thew radio galaxies are superposed to very low surface brightness radio emission extended on the cluster scale, which we present here.     

A Monte Carlo Study of the Evolution of the Scale Height of Normal Pulsars in the Galaxy

Based on the undisturbed, finite thickness disk gravitational potential, we carried out 3-D Monte Carlo simulations of normal pulsars. We find that their scale height evolves in a similar way for different velocity dispersions (σv): it first increases linearly with time, reaches a peak, then gradually decreases, and finally approaches a stable asymptotic value. The initial velocity dispersion has a very large influence on the scale height. The time evolution of the scale height is studied. When the magnetic decay age is used as the time variable, the observed scale height has a similar trend as the simulated results in the linear stage, from which we derive velocity dispersions in the range 70- 178km s-1, which are near the statistical result of 90 - 270km s-1 for 92 pulsars with known transverse velocities. If the characteristic age is used as the time variable, then the observed and theoretical curves roughly agree for t > 108 yr only if σv < 25km s-1.     

Magnetodynamic Formation of Jets in Accretion Process of Magnetized Mass onto the Central Gravitator — Cases of Forming Stars and Active Galactic Nuclei

A magnetodynamic model to deal with the acceleration and collimation of jets as a part of the global process of gravitational contraction of the magnetized gas to the central gravitator is discussed. We first review its application to the star forming jet case with several observational supporting evidence. Then, a justification will be given for the extension of this to the AGN jet case, despite of the difference in orders of magnitudes in the scales as well as in the physical parameters. The results of actual application of this magnetodynamic mechanism to the AGN case will be presented together with the discussions for the origin of the radio lobes and hotspots, and we show that this mechanism can explain the enhancement of accretion and the formation of the jet + lobe system consistently with the genetic consideration of the system. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the generation of envelope solitons in?the?presence of?excess superthermal electrons and?positrons

A theoretical model is presented to investigate the existence, formation, and possible realization of nonlinear envelope ion acoustic solitary waves which accompany collisionless electron-positron-ion plasmas with high-energy electrons and positrons (represented by kappa distribution). By employing the reductive perturbation method, the hydrodynamic model and the Poisson equation are reduced to nonlinear Schr?dinger equation. The effects of the superthermal parameters, as well as ion-to-electron temperature ratio on the propagation and stability of the envelope solitary waves are examined. The superthermal parameters (ion-to-electron temperature ratio) give rise to instability (stability) of the solitary excitations, since the instability window is strongly modified. Finally, the present results should elucidate the excitation of the nonlinear ion-acoustic solitary wave packets in superthermal electron-positron-ion plasmas, particularly in interstellar medium.