Reconstruction of the brightness distribution across a stellar disk from gravitational lensing caustic passage observations

This paper describes a method for analyzing observations of the passage of a star through a gravitational lensing caustic that enables the derivation of information about the brightness distribution across the stellar disk without knowledge of the lens parameters. The ill-posed inverse problem of reconstructing a one-dimensional strip brightness distribution across the stellar disk is solved using a regularization method, taking into account the non-negative nature of this function. Assuming the source is circularly symmetric, the search for the radial brightness distribution is carried out over compact sets of upward-convex, non-negative functions or functions that do not grow with distance from the stellar center. The method is used to analyze the gravitational microlensing event MACHO 98-SMC-1, of a star in the Small Magellanic Cloud, obtained by the PLANET international group. The resulting brightness distribution is compared with computations of limb darkening for model stellar atmospheres.     

Reconstruction of the strip brightness distribution in a quasar accretion disk from gravitational microlensing data

A technique is proposed for the successive reconstruction of the branches of the strip brightness distribution for a quasar accretion disk via the analysis of observations of high magnification flux events in the multiple quasar images produced by a gravitational lens. The distribution branches are searched for on compact sets of nonnegative, monotonically nonincreasing, convex downward functions. The results of numerical simulations and application of the technique to real observations show that the solution obtained is stable against random noise. Analysis of the light curve of a high magnification event in image C of the gravitational lens QSO 2237+0305 observed by the OGLE group in summer 1999 has yielded the form of the strip brightness distribution in the accretion disk of the lensed quasar. The results are consistent with the hypothesis that the quasar disk was scanned by a fold caustic. The form of the strip distribution is consistent with the expected appearance of an accretion disk rotating around a supermassive black hole.     

Mathematical modeling of the structure of an accretion disk in a stellar binary system

Numerical simulations of gas-dynamical processes taking place in the accretion disk of a stellar binary system are presented. The initial state of the disk is an equilibrium gaseous configuration. Mechanisms for the development of spiral waves and associated variations in the angular momentum of the gas are considered. The influence of the ratio of the binary-component masses and the initial disk configuration are investigated. It is concluded that the existence of a steady-state disk is impossible without a flow of gas from the donor star.     

Power spectrum of brightness temperature fluctuations derived from solar eclipse observations at 2.8 GHz

In this paper we report on the MEM power spectrum analysis of brightness temperature fluctuations observed at 2.8 GHz during the total solar eclipse of 16 February 1980. The observed periodicities range from 3.5 min to 64 min. These periodicities may arise due to spatial and/or temporal variations in the solar radio emission. The observed periodicities imply presence of scale sizes ranging from 70,000 to 600,000 km assuming that the brightness fluctuations arise because of spatial variation only. On the other hand, if these fluctuations are due to temporal variation, the observed periodicities correspond well to predicted modes of solar global oscillations.     

Analysis of brightness variations in the massive close binary system UU Cassiopeia

We derive the parameters of the hot, massive close binary system UU Cas from earlier and recent photoelectric UBVR observations: M ₁ = 34.5M _⊙, M ₂ = 25.7M _⊙, A = 69R _⊙, and i=68°; the components' limb darkening coefficients are close to 1. Our fitting of the light curves provides evidence for a high degree of over-contact: the components fill their inner critical surfaces by 132% and 100%. It is possible that the appearance of the light curve is determined not only by the distorted shapes of the components and their eclipses but, to a considerable extent, by screening by a complex envelope and the envelope's contribution to the system's total luminosity.     

Comparison between two-and three-dimensional modeling of the structure of an accretion disk in a binary system

We compare two-and three-dimensional modeling of gas-dynamical processes in the accretion disk of a binary system. The origin of spiral waves and the loss of the angular momentum related to them are considered. It is concluded that a steady state of the disk cannot exist without taking into account t he gas inflow from the donor star.     

Morphology of the interaction between the stream and cool accretion disk in a semidetached binary system

We analyze heating and cooling processes in accretion disks in binaries. For realistic parameters of the accretion disks in close binaries (\(\dot M \simeq 10^{ - 12} - 10^7 M_ \odot /yr\) and α?10^?1–10^?2), the gas temperature in the outer parts of the disk is from ～10⁴ to ～10⁶ K. Our previous gas-dynamical studies of mass transfer in close binaries indicate that, for hot disks (with temperatures for the outer parts of the disk of several hundred thousand K), the interaction between the stream from the inner Lagrange point and the disk is shockless. To study the morphology of the interaction between the stream and a cool accretion disk, we carried out three-dimensional modeling of the flow structure in a binary for the case when the gas temperature in the outer parts of the forming disk does not exceed 13 600 K. The flow pattern indicates that the interaction is again shockless. The computations provide evidence that, as is the case for hot disks, the zone of enhanced energy release (the “hot line”) is located beyond the disk and originates due to the interaction between the circumdisk halo and the stream.     

Regional soil moisture retrievals and simulations from assimilation of satellite microwave brightness temperature observations

Low-frequency microwave satellite observations are sensitive to land surface soil moisture (SM). Using satellite microwave brightness temperature observations to improve SM simulations of numerical weather, climate and hydrological predictions is one of the most active research areas of the geoscience community. In this paper, Yan and Jins’ (J Radio Sci 19(4):386–392, 2004) theory on the relationship between satellite microwave remote sensing polarization index and SM is used to estimate land surface SM values from the advanced microwave scanning radiometer-E (AMSR-E) brightness temperature data. With consideration of soil texture, surface roughness, optical thickness, and the monthly means of NASA AMSR-E SM data products, the regional daily land surface SM values are estimated over the eastern part of the Qinghai-Tibet Plateau. The resulting SM retrievals are better than the NASA daily AMSR-E SM product. The retrieved SM values are generally lower than the ground measurements from the Maqu Station (33.85°N, 102.57°E) and the Tanglha Station (33.07°N, 91.94°E) and the US NCEP reanalysis data, but the temporal variations of the retrieved SM demonstrate more realistic response to the observed precipitation events. In order to improve the land surface SM simulating ability of the weather research and forecasting model, the retrieved SM was assimilated into the Noah land surface model by the Newtonian relaxation (NR) method. A direct insertion method was also applied for comparison. The results indicate that fine-tuning the quality factor in the NR method improves the simulated SM values most for desert areas, followed by grasslands, and shrub and grass mixed zones at the regional scale. At the temporal scale, the NR method decreased the root mean square error between the simulated SM and actual observed SM by 0.03 and 0.07 m³/m³ at the Maqu and Tanglha Stations, respectively, and the temporal variation of simulated SM values was much closer to the ground-measured SM values.     

Gamma-ray bursts from a close pulsar binary system?

The close neutron-star binary system comprised of the radio pulsars PSR J0737-3039 A,B is discussed. An analysis of the observational data indicates that the wind from pulsar A, which is more powerful than the wind from pulsar B, strongly distorts the magnetosphere of pulsar B. A shock separating the relativistic wind from pulsar A and the corotating magnetosphere of pulsar B should form inside the light cylinder of pulsar B. A weakly diverging “tail” of magnetic field is also formed, which stores a magnetic energy on the order of 10³⁰ erg. This energy could be liberated over a short time on the order of 0.1 s as a result of reconnection of the magnetic-force lines in this “tail,” leading to an outburst of electromagnetic radiation with energies near 100 keV, with an observed flux at the Earth of 4 × 10^?11 erg cm^?2 s^?2. Such outbursts would occur sporadically, as in the case of magnetic substorms in the Earth’s magnetosphere.     

The wavelet-smoothed distribution of young stellar objects in the Galactic plane

We have analyzed the distribution of young objects (open clusters, classical Cepheids, and HII regions) projected onto the plane of the Galaxy using wavelet smoothing. This smoothing technique enables investigation of the large-scale structure of the distribution of young objects. All the studied objects display a similar spiral structure, whose appearance essentially corresponds to a regular alternation of young and older stellar complexes along sections of the spiral arms. A four-arm spiral structure with its arms originating at the Galactic center is obtained if the major arms are taken to be the Carina-Sagittarius arm and an outer arm behind the Perseus arm. If all the observed arms are taken to be major arms, we obtain a 12-arm structure, in contradiction with the size of the region in which the structure is observed in the Galaxy. This discrepancy can be removed if the arms originate from a ring formed by a sufficiently long bar-like structure, rather then from the Galactic center.     

Structure of CB 26 protoplanetary disk derived from millimeter dust continuum maps

Observations of the circumstellar disk in the Bok globule CB 26 at 110, 230, and 270 GHz are presented together with the results of the simulations and estimates of the disk parameters. These observations were obtained using the SMA, IRAM Plateau de Bure, and OVRO interferometers. The maps have relatively high angular resolutions (0.4??-1??), making it possible to study the spatial structure of the gas-dust disk. The disk parameters are reconstructed via a quantitative comparison of observational and theoretical intensity maps. The disk model used to construct the theoretical maps is based on the assumption of hydrostatic and radiative equilibrium in the vertical direction, while the radial surface-density profile is described phenomenologically. The system of equations for the transfer of the infrared and ultraviolet radiation is solved in the vertical direction, in order to compute the thermal structure of the disk. The disk best-fit parameters are derived for the each map and all the maps simultaneously, using a conjugate gradient method. The degrees of degeneracy of the parameters describing the thermal structure and density distribution of the disk are analyzed in detail. All three maps indicate the presence of an inner dust-free region with a diameter of approximately 35 AU, in agreement with the conclusions of other studies. The inclination of the disk is 78°, which is smaller than the value adopted in our earlier study of rotating molecular outflows from CB 26. The model does not provide any evidence for the growth of dust particles above a _max ?? 0.02 cm.     

Observed effects of gravitational microlensing of stars by a spatial-temporal tunnel

We consider microlensing of stars by a spacetime tunnel (wormhole), which is manifest as a gravitational lens with negative mass and a circular caustic in the source plane. If a source with a small angular size does not cross the circular caustic, it is impossible to discriminate between gravitational lenses with positive and negative mass. Even for comparatively large stellar angular diameters, differences from a Schwarzschild lensing curve are on the order of the observational errors. When the angular size of a star is comparable to the radius of the Einstein cone, for a sufficiently large impact parameter, the shape of the observed light curves can be similar to that due to microlensing of a compact object surrounded by an extended gaseous envelope. Such an object can be easily distinguished from a negative-mass gravitational lens via analysis of chromatic and polarization effects of the lensing.     

Three-dimensional hydrodynamical modeling of the formation of the accretion disk in the SS 433 binary system

Three-dimensional hydrodynamical modeling of the formation of the accretion disk in the SS 433 binary system is carried out with various types of cooling and numerical grids. These computations show that a thick accretion disk with a height of 0.25–0.30 (in units of the component separation) is formed around the compact object, from a flow with a large radius (0.2–0.3 in the same units) that forms in the vicinity of the inner Lagrangian point. This disk has the form of a flattened torus. The number of orbits of a particle of gas in the disk is 100–150, testifying to a minimal influence of numerical viscosity in these computations. The computations also show that the stream flowing from L₁ is nearly conservative, and spirals in the disk are not formed due to the influence of the donor gravitation.     

基于Micromine软件的澳大利亚某矿床铅锌品位分布规律研究

基于三维模型的矿床地质统计学研究,可以准确反应矿体的空间结构变化和品位的空间变化规律,在矿床评价中具有不可替代的作用。本文在已有的钻探工程数据基础上,借助三维建模软件以地质统计学思维对澳大利亚某矿床铅锌品位的空间分布特征及内在规律进行了揭示,通过对矿体铅锌品位在走向、倾向和厚度三个方向的理论变异函数的拟合,表明矿体呈明显的各向异性,在走向方向变程值较大,连续性较好,倾向方向次之。对矿体块体模型空间赋值,并进行投影分析,结果表明矿体沿走向向东矿化范围和强度均有扩大趋势,且在815800E线以东深部倾向方向铅锌品位逐渐增强,高品位矿化断续出现。因此矿区下一步勘查重点应该在矿体走向东部和815800E线以东的倾向延伸方向。     

The structure of the common envelope in a close binary system

As a result of the interaction between an elliptical accretion disk and gas flowing into it from the circumbinary envelope in a close binary in the course of its orbital motion, the matter of the disk and the circum-disk halo is periodically ejected from the vicinity of the Lagrange point L₃, and a common envelope is formed in the system. Three-dimensional numerical gas-dynamical modeling is used to study the structure and dynamics of the envelope and determine its basic parameters. The evolution of the envelope is followed on timescales of the order of several orbital periods. The matter flow ejected through the vicinity of L₃ displays a spiral shape. The maximum size of the forming spiral structure is restricted by the self-intersection point, and is of the order of four to five times the component separation. We consider the dynamics of the regions directly adjacent to the spiral structure: an inner, rarified and outer, fragmented region, which further makes a transition to an expanding diffuse ring.     

Velocity field of the stellar wind of the wolf-rayet star in the V 444 Cyg binary system: A parametric model

An analysis of the λ4244 Å continuum light curve of the eclipsing variable V444 Cyg is used to reconstruct the velocity law v(r) of the stellar wind of the WR star in terms of Lamers parametric and powerlaw models. Both models are inconsistent with the observed light curve, and can be rejected at the <2% significance level. Departures of the Lamers parametric relation from the empirical v(r) law reconstructed in previous papers from the same λ 4244 Å light curve on sets of concave and convexo-concave functions are statistically significant. The stellar wind of the WN5 star continues to accelerate at a considerable distance from the star’s center. This corresponds to an acceleration parameter β>1 in terms of a coarse Lamers-law approximation for the empirical v(r) field.     

Influence of mass-loss due to stellar wind on the orbits of binary stars to a second order theory

We examine the influence of mass-loss due to stellar wind using the celestial mechanics of variable mass, and derive first-and second-order solutions, taking into account the decreasing mass due to the stellar wind. The theoretical results show that the semi-major axis exhibits secular and periodic variations in the first-and second-order theory. The orbital eccentricity exhibits periodic, but no secular variation or changes. The longitude of periastron exhibits only periodic variations in the first-order solution, but also secular variations in the second-order solution. The theoretical results are applied to the binary star HD 698, and variability of the orbital elements of this star due to stellar-wind mass loss calculated. Published in Russian in Astronomicheskiĭ Zhurnal, 2008, Vol. 85, No. 10, pp. 896–900. The article was translated by the authors.     

Elliptical motion of a star in a close binary system

The motion of a rotating star in a close binary system with conservative mass exchange is considered. In contrast to the Paczyński-Huang model, the new model applied examines the relative motion of a star along an elliptical orbit in a close binary system, taking into account the mutual gravitation between the stars, reactive forces, the gravitation exered on the stars by the mass-transfer stream, and perturbations due to the rotation of the accreting star. The variations of the semi-major axis and eccentricity of the orbit and the orbital angular velocity of the accreting star as a function of the component-mass ratio q are determined. The results are applied to the BF Aurigae system.     

Information derived from soil maps: Areal distribution of bedrock landslide distribution and slope steepness

Soil maps can be used to generate maps showing the areal distribution of bedrock. This technique is especially useful in heavily vegetated areas where weathering is intense and outcrops sparse. Broad lithologic categories that are readily distinguished include: diabase/basalt, sandstone, shale, limestone, conglomerate, and hornfels. Using soil maps is not a substitute for field work, but is a valuable tool to aid in making geologic maps. Soil maps can also be used to produce derivative maps showing slope steepness and landslide distribution.     

Kinematics of the Cerca del Cielo, Puerto Rico landslide derived from GPS observations

Global positioning system (GPS) technologies have been increasingly employed to monitor landslide movements. This paper demonstrates the use of GPS in the study of a creeping landslide in Ponce, Puerto Rico. The landslide is primarily composed of chalk colluvium that extends to depths of about 30 m at the head zone and 2 to 3 m at the toe zone. The slip surface lies at the base of the chalk colluvium, which slides southeast over a weathered brown mudstone unit. GPS monitoring of the landslide began in March 2008. Both campaign rapid static and continuous static GPS surveying methods were applied. Precision at the level of 0.5 mm horizontally and 1.3 mm vertically was achieved through 24-h continuous GPS monitoring. Rainfall data from a local weather station was also integrated into the study. Rainfall heavily influenced the movements of the landslide. A heavy rainfall in September 2008, which dumped 50 cm rain on the landslide area over a 4-day period, temporarily accelerated the sliding and generated rapid movement of 1 m horizontally and 0.5 m vertically. The slide slowed markedly after this significant movement. A prolonged moderate rainfall in November 2009 also temporarily accelerated the sliding. The landslide remains active. The creeping appears likely to continue in the future with short bursts of rainfall-induced rapid movements. Potential landslide causes are investigated, and two measures to minimize future risk are proposed at the end of the article.