A 3D dynamical model of the colliding winds in binary systems

We present a three-dimensional (3D) dynamical model of the orbital-induced curvature of the wind–wind collision region in binary star systems. Momentum balance equations are used to determine the position and shape of the contact discontinuity between the stars, while further downstream the gas is assumed to behave ballistically. An Archimedean spiral structure is formed by the motion of the stars, with clear resemblance to high-resolution images of the so-called 'pinwheel nebulae'. A key advantage of this approach over grid or smoothed particle hydrodynamic models is its significantly reduced computational cost, while it also allows the study of the structure obtained in an eccentric orbit. The model is relevant to symbiotic systems and γ-ray binaries, as well as systems with O-type and Wolf–Rayet stars.
As an example application, we simulate the X-ray emission from hypothetical O+O and WR+O star binaries, and describe a method of ray tracing through the 3D spiral structure to account for absorption by the circumstellar material in the system. Such calculations may be easily adapted to study observations at wavelengths ranging from the radio to γ-ray.     

On the 3D dynamics and morphology of inner rings

We argue that inner rings in barred spiral galaxies are associated with specific 2D and 3D families of periodic orbits located just beyond the end of the bar. These are families located between the inner radial ultraharmonic 4 : 1 resonance and corotation. They are found in the upper part of a type-2 gap of the x1 characteristic, and can account for the observed ring morphologies without any help from families of the x1-tree. Due to the evolution of the stability of all these families, the ring shapes that are favoured are mainly ovals, as well as polygons with 'corners' on the minor axis, on the sides of the bar. On the other hand, pentagonal rings, or rings of the NGC 7020-type hexagon, should be less probable. The orbits that make the rings belong in their vast majority to 3D families of periodic orbits and orbits trapped around them.     

Few projections astrotomography: radio astronomical approach to 3D reconstruction

We develop a radio astronomical approach to 3D‐reconstruction in few projections tomography. It is based on the 2‐CLEAN DSA method which consists of two clean algorithms by using a synthesized beam. In complex cases two extreme solutions are used for the analysis of the image structure. These solutions determine the limits of permissible energy redistribution on the image among the components of small and large scales. Two variants of 3D‐reconstruction proceeding from a set of two‐dimensional projections (3D_2D) and from a set of one‐dimensional ones (3D_1D) are considered. It is shown that the quality of 3D_2D‐reconstruction should be similar to the quality of 2D_1D‐reconstruction if the same number of equally spaced scans is used. But a doubled number of projections is required for 3D_1D‐reconstruction. We have simulated 3D‐reconstruction of an optically thin emitting object. The present technique is a component of astrotomography and it has good prospects for a wide range of remote sensing. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

3D NIR spectroscopy at subarcsecond resolution

We present a scientific case approached through high quality 3D NIR spectroscopy performed with CIRPASS, attached to the Gemini South telescope. A binary mass concentration at the nucleus of the galaxy M 83 was suggested by Thatte et al. [A&A 364 (2000) L47] and Mast et al. [BAAA 45 (2002) 98. Astroph#0505264] determined the possible position of the hidden secondary mass concentration with 2D H-alpha kinematics. The preliminary results of the NIR study presented here are based in almost 1500 spectra centered in the wavelength 1.3 μm, with a spectral resolving power of 3200. They allow us to unveil, with 0.36″ (6.4 pc) sampling and subarcsecond resolution, the velocity field in a region of 13″ × 9″ around the optical nucleus. We confirm that the optical nucleus is not located at the most important center of symmetry of the ionized gas velocity field. The largest black hole that could fit to the circular motion in this kinematic center should have a mass not larger than 3 × 10⁶(sin i)⁻¹ M solar masses.     

Crowded field 3D spectroscopy

The quantitative spectroscopy of stellar objects in complex environments is mainly limited by the ability of separating the object from the background. Standard slit spectroscopy, restricting the field of view to one dimension, is obviously not the proper technique in general. The emerging Integral Field (3D) technique with spatially resolved spectra of a two‐dimensional field of view provides a great potential for applying advanced subtraction methods. In this paper an image reconstruction algorithm to separate point sources and a smooth background is applied to 3D data. Several performance tests demonstrate the photometric quality of the method. The algorithm is applied to real 3D observations of a sample Planetary Nebula in M31, whose spectrum is contaminated by the bright and complex galaxy background. The ability of separating sources is also studied in a crowded field in M33. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A New Method of Identifying 3D Null Points in Solar Vector Magnetic Fields

Employing the Poincare index of isolated null-points in a vector field, we worked out a mathematical method of searching for 3D null-points in coronal magnetic fields. After introducing the relevant differential topology, we test the method by using the analytical model of Brown & Priest. The location of null-point identified by our method coincides precisely with the analytical solution. Finally we apply the method to the 3D coronal magnetic fields reconstructed from an observed MDI magnetogram of a super-active region (NOAA 10488). We find that the 3D null-point seems to be a key element in the magnetic topology associated with flare occurrence.     

3D spectroscopy of merger Seyfert galaxy Mrk 334: nuclear starburst, superwind and the circumnuclear cavern

We are presenting new results on kinematics and structure of the Mrk 334 Seyfert galaxy. Panoramic (3D) spectroscopy is performed at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences using the integral-field Multi-Pupil Fiber Spectrograph (MPFS) and scanning Fabry–Pérot interferometer. The deep images have revealed that Mrk 334 is observed during the final stage of its merging with a massive companion. A possible mass ratio ranges from 1/5 to 1/3. The merger has triggered mass redistribution in the disc resulting in an intensification of nuclear activity and in a burst of star formation in the inner region of the galaxy. The circumnuclear starburst is so intense that its contribution to the gas ionization exceeds that contribution of the active galactic nuclei (AGN). We interpret the nuclear gas outflow with velocities of  ∼200 km s⁻¹  as a galactic superwind that accompanies the violent star formation. This suggestion is consistent with the asymmetric X-ray brightness distribution in Mrk 334. The trajectory of the fragments of the disrupted satellite in the vicinity of the main galaxy nucleus can be traced. In the galaxy disc, a cavern is found that is filled with a low-density ionized gas. We consider this region to be the place where the remnants of the companion have recently penetrated through the gaseous disc of the main galaxy.     

E3D,the Euro3D visualization tool II: Mosaics,VIMOS data and large IFUs of the future

In this paper, we describe the capabilities of E3D, the Euro3D visualization tool, to handle and display data created by large Integral Field Units (IFUs) and by mosaics consisting of multiple pointings. The reliability of the software has been tested with real data, originating from the PMAS instrument in mosaic mode and from the VIMOS instrument, which features the largest IFU currently available. The capabilities and limitations of the current software are examined in view of future large IFUs, which will produce extremely large datasets. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

3D spectroscopy of z ∼ 1galaxies with gemini

Area spectroscopy has significant advantages over both traditional imaging and long-slit spectroscopy: it is more efficient in observing time, and yields substantially more information. Through Integral Field Units, area spectroscopy is becoming an essential part of new facility instruments on the latest large telescopes. We have been undertaking a programme on the Gemini 8-m telescopes to demonstrate the power of integral field spectroscopy, using the optical GMOS spectrograph, and the new CIRPASS instrument in the near-infrared. Here we present some preliminary results from 3D spectroscopy of z ∼ 1 objects, mapping the emission lines in a 3CR radio galaxy and in a gravitationally lensed arc. This revised version was published online in August 2006 with corrections to the Cover Date.     

Reflected light from 3D exoplanetary atmospheres and simulation of HD 209458b

We present radiation transfer models that demonstrate that reflected light levels from 3D exoplanetary atmospheres can be more than 50 per cent lower than those predicted by models of homogeneous or smooth atmospheres. Compared to smooth models, 3D atmospheres enable starlight to penetrate to larger depths resulting in a decreased probability for the photons to scatter back out of the atmosphere before being absorbed. The increased depth of penetration of starlight in a 3D medium is a well-known result from theoretical studies of molecular clouds and planetary atmospheres. For the first time we study the reflectivity of 3D atmospheres as a possible explanation for the apparent low geometric albedos inferred for extrasolar planetary atmospheres. Our models indicate that 3D atmospheric structure may be an important contributing factor to the non-detections of scattered light from exoplanetary atmospheres. We investigate the self-shadowing radiation transfer effects of patchy cloud cover in 3D scattered light simulations of the atmosphere of HD 209458b. We find that, for a generic planet, geometric albedos can be as high as 0.45 in some limited situations, but that in general the geometric albedo is much lower. We conclude with some explanations on why extrasolar planets are likely dark at optical wavelengths.     

High-Resolution Simulations of the Impacts of Asteroids into the Venusian Atmosphere II: 3D Models

We compare high-resolution 2D and 3D numerical hydrocode simulations of asteroids striking the atmosphere of Venus. Our focus is on aerobraking and its effect on the size of impact craters. We consider impacts both by spheres and by the real asteroid 4769 Castalia, a severely nonspherical body in a Venus-crossing orbit. We compute mass and momentum fluxes as functions of altitude as global measures of the asteroid's progress. We find that, on average, the 2D and 3D simulations are in broad agreement over how quickly an asteroid slows down, but that the scatter about the average is much larger for the 2D models than for the 3D models. The 2D models appear to be rather strongly susceptible to the “butterfly effect,” in which tiny changes in initial conditions (e.g., 0.05% change in the impact velocity) produce quite different chaotic evolutions. By contrast, the global properties of the 3D models appear more reproducible despite seemingly large differences in initial conditions. We argue that this difference between 2D and 3D models has its root in the greater geometrical constraints present in any 2D model, and in particular in the global conservation of enstrophy in 2D that forces energy to pool in large-scale structures. It is the interaction of these artificial large-scale structures that causes slightly different 2D models to diverge so greatly. These constraints do not apply in 3D and large scale structures are not observed to form. A one-parameter modified pancake model reproduces the expected crater diameters of the 3D Castalias reasonably well.     

3D simulations of rotationally-induced line variability from a classical T Tauri star with a misaligned magnetic dipole

We present 3D simulations of rotationally induced line variability arising from complex circumstellar environment of classical T Tauri stars (CTTS) using the results of the 3D magnetohydrodynamics (MHD) simulations of Romanova et al., who considered accretion on to a CTTS with a misaligned dipole magnetic axis with respect to the rotational axis. The density, velocity and temperature structures of the MHD simulations are mapped on to the radiative transfer grid, and corresponding line source function and the observed profiles of neutral hydrogen lines (Hβ, Paβ and Brγ) are computed using the Sobolev escape probability method. We study the dependency of line variability on inclination angles ( i ) and magnetic axis misalignment angles (Θ). We find the line profiles are relatively insensitive to the details of the temperature structure of accretion funnels, but are influenced more by the mean temperature of the flow and its geometry. By comparing our models with the Paβ profiles of 42 CTTS observed by Folha & Emerson, we find that models with a smaller misaligngment angle  (Θ < ∼15°)  are more consistent with the observations which show that majority of Paβ are rather symmetric around the line centre. For a high inclination system with a small dipole misalignment angle  (Θ≈ 15°)  , only one accretion funnel (on the upper hemisphere) is visible to an observer at any given rotational phase. This can cause an anticorrelation of the line equivalent to the width in the blue wing  ( v < 0)  and that in the red wing  ( v > 0)  over half of a rotational period, and a positive correlation over the other half. We find a good overall agreement of the line variability behaviour predicted by our model and those from observations.     

The 3D skeleton: tracing the filamentary structure of the Universe

The skeleton formalism, which aims at extracting and quantifying the filamentary structure of our Universe, is generalized to 3D density fields. A numerical method for computing a local approximation of the skeleton is presented and validated here on Gaussian random fields. It involves solving equation     , where  ∇ρ  and     are the gradient and Hessian matrix of the field. This method traces well the filamentary structure in 3D fields such as those produced by numerical simulations of the dark matter distribution on large scales, and is insensitive to monotonic biasing.
Two of its characteristics, namely its length and differential length, are analysed for Gaussian random fields. Its differential length per unit normalized density contrast scales like the probability distribution function of the underlying density contrast times the total length times a quadratic Edgeworth correction involving the square of the spectral parameter. The total length-scales like the inverse square smoothing length, with a scaling factor given by  0.21 (5.28 + n )  where n is the power index of the underlying field. This dependency implies that the total length can be used to constrain the shape of the underlying power spectrum, hence the cosmology.
Possible applications of the skeleton to galaxy formation and cosmology are discussed. As an illustration, the orientation of the spin of dark haloes and the orientation of the flow near the skeleton is computed for cosmological dark matter simulations. The flow is laminar along the filaments, while spins of dark haloes within 500 kpc of the skeleton are preferentially orthogonal to the direction of the flow at a level of 25 per cent.     

High spatial resolution Galactic 3D extinction mapping with IPHAS

We present an algorithm (MEAD, for 'Mapping Extinction Against Distance') which will determine intrinsic  ( r '− i ')  colour, extinction, and distance for early-A to K4 stars extracted from the IPHAS   r '/ i '/Hα  photometric data base. These data can be binned up to map extinction in three dimensions across the northern Galactic plane. The large size of the IPHAS data base (∼200 million unique objects), the accuracy of the digital photometry it contains and its faint limiting magnitude  ( r '∼ 20)  allow extinction to be mapped with fine angular (∼10 arcmin) and distance (∼ 0.1 kpc) resolution to distances of up to 10 kpc, outside the solar circle. High reddening within the solar circle on occasion brings this range down to ∼2 kpc. The resolution achieved, both in angle and depth, greatly exceeds that of previous empirical 3D extinction maps, enabling the structure of the Galactic Plane to be studied in increased detail. MEAD accounts for the effect of the survey magnitude limits, photometric errors, unresolved interstellar medium (ISM) substructure and binarity. The impact of metallicity variations, within the range typical of the Galactic disc is small. The accuracy and reliability of MEAD are tested through the use of simulated photometry created with Monte Carlo sampling techniques. The success of this algorithm is demonstrated on a selection of fields and the results are compared to the literature.     

3D eccentric discs around Be stars

One-armed oscillation modes in the circumstellar discs of Be stars may explain the cyclical variations in their emission lines. We show that a 3D effect, involving vertical motion and neglected in previous treatments, profoundly influences the dynamics. Using a secular theory of eccentric discs that reduces the problem to a second-order differential equation, we show that confined prograde modes are obtained for all reasonable disc temperatures and stellar rotation rates. We confirm these results using a numerical analysis of the full set of linearized equations for 3D isothermal discs including viscous terms that couple the horizontal motions at different altitudes. In order to make these modes grow, viscous damping must be overcome by an excitation mechanism such as viscous overstability.     

一种针对MWISP项目分子云团块的3D CNN证认方法

分子云团块是恒星的诞生地. 分子团块的普查和其性质的全面研究将有助于了解恒星的形成乃至星系和宇宙的演化过程. 随着银河画卷计划(MWISP)项目的深入进行, 这类研究方案变得切实可行. 但是项目产生的分子云观测数据是海量的, 因此迫切需要一种能够自动识别和证认分子团块的方法. 目前应用广泛的3维分子云数据处理方法有很多, 典型的包括GaussClumps、ClumpFind、FellWalker、Reinhold等, 但都需要输入多个参数来控制它们的性能, 并且进行反复的参数优化和目测才能得到比较满意的结果. 对于大规模的观测数据, 利用现有方法进行分子团块的证认将是一项耗时耗力的任务. 为了克服传统分子云团块检测算法的局限性, 人工智能(AI)的方法将提供一个很好的解决方案. 提出了一种3D CNN (Convolutional Neural Network)方法, 它可以自动处理3D分子谱线数据, 整个过程分为检出和验证两个步骤. 首先, 通过设置较低阈值使用ClumpFind以检出候选对象, 然后通过训练好的3D CNN模型进行验证. 利用仿真数据所做的一系列的实验结果表明, 该方法的综合表现优于4种传统方法. 将该方法应用于实际的MWISP数据表明, 3D CNN方法的性能也令人满意.     

Recovering 3D particle size distributions from 2D sections

We discuss different ways to convert observed, apparent particle size distributions from 2D sections (thin sections, SEM maps on planar surfaces, etc.) into true 3D particle size distributions. We give a simple, flexible, and practical method to do this; show which of these techniques gives the most faithful conversions; and provide (online) short computer codes to calculate both 2D‐3D recoveries and simulations of 2D observations by random sectioning. The most important systematic bias of 2D sectioning, from the standpoint of most chondrite studies, is an overestimate of the abundance of the larger particles. We show that fairly good recoveries can be achieved from observed size distributions containing 100–300 individual measurements of apparent particle diameter.     

Calculations and physical properties of the D3 emission lines of a prominence

The D3 emission lines observed on a prominence over the solar east limb on 1984 May 5, which were found to consist of two components, i.e. the main and the broadened components, have been successfully calculated using the two-cloud model method with the multiplet of helium (3 ³D_3,2,1–2 ³P_2,1,0) taken into account. The results obtained show that the ejecta in front of the prominence are formed by the intermittent ejections of the matter from the plage region around the prominence, because there exist at least three distinguishable phases of the line-of-sight velocity, increasing during the observations. The turbulent velocity of the ejecta is rather large, about 29 km s⁻¹. The Doppler width of the ejecta is mainly the result of the non-thermal effect, and the thermal effect can be neglected compared with the non-thermal effect. The prominence is quiet and characterized by typical properties .     

Orbit classification in arbitrary 2D and 3D potentials

A method of classifying generic orbits in arbitrary 2D and 3D potentials is presented. It is based on the concept of spectral dynamics introduced by Binney &38; Spergel that uses the Fourier transform of the time series of each coordinate. The method is tested using a number of potentials previously studied in the literature and is shown to distinguish correctly between regular and irregular orbits, to identify the various families of regular orbits (boxes, loops, tubes, boxlets, etc.), and to recognize the second-rank resonances that bifurcate from them. The method returns the position of the potential centre and, for 2D potentials, the orientation of the principal axes as well, should this be unknown. A further advantage of the method is that it has been encoded in a FORTRAN program that does not require user intervention, except for 'fine tuning' of search parameters that define the numerical limits of the code. The automatic character makes the program suitable for classifying large numbers of orbits.