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1.
A statistical study of motions of images of distant extragalactic sources, such as quasars on the celestial sphere, due to
the action of weak gravitational microlensing is presented. It was assumed that the parallax of the lens was 10 milliarcseconds
(mas), the mass of the lens was 1 M
⊙, and the proper motion was μ = 30 mas. The initial point for the motion of the lens (a star in our Galaxy) was taken to be
the boundary of a region with a radius of ϑ = 100 mas and its center coincident with the distant source. The simulations for
each trajectory were carried out in steps, with the time step being 0.1 year. The number of sources “launched” over the computational
period was 5000. The appearance of the trajectories for the source images is presented; 57% of the total number of sources
that participated in the simulations showed motions of 0.7–1.0 mas.
Original Russian Text ? T.A. Kalinina, M.S. Pshirkov, 2006, published in Astronomicheskiĭ Zhurnal, 2006, Vol. 83, No. 6, pp.
483–488. 相似文献
2.
A. T. Bajkova 《Astronomy Reports》2005,49(12):973-983
We consider the problem of mapping with ultra-high angular resolution using a space—ground radio interferometer with a space antenna in a high orbit, whose apogee height exceeds the radius of the Earth by a factor of ten. In this case, a multielement interferometer essentially degenerates into a two-element interferometer. The degeneracy of the close-phase relations prevents the use of standard methods for hybrid mapping and self-calibration for the correct reconstruction of images. We propose a new phaseless mapping method based on methods for the reconstruction of images in the complete absence of phase information, using only the amplitudes of the spatial-coherence function of the source. In connection with this problem, we propose a new method for the reliable solution of the phase problem, based on optimizing information-carrying nonlinear functionals, in particular, the Shannon entropy. Results of simulations of mapping radio sources with various structures with ultra-high angular resolution in the framework of the RADIOASTRON mission are presented. 相似文献
3.
The Arp-Burbidge paradox (the enhanced density of distant quasars in the vicinity of some nearby galaxies) can potentially be explained as an effect of gravitational lensing within the existing cosmological paradigm. Distant, rich X-ray clusters, or even superclusters, of galaxies are observed along the lines of sight toward many of the objects on which this “paradox” is based. Such clusters can act as complex, transparent gravitational lenses, which can change the observed surface density of background objects due to the gravitational fields of both the cluster as a whole and of massive member galaxies, as well as of possible intergalactic globular clusters that may contain an appreciable fraction (～10%) of the dark matter in galaxy clusters. We have verified the statistical basis for the supposedly “paradoxical” observational facts using data from the SDSS catalog, and used the minimal spanning tree method to search for inhomogeneities in the surface distributions of 32 800 quasars in one region of the celestial sphere (α = 120°–260°, δ = 20°–70°). 相似文献
4.
《Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy》1999,24(2):101-104
An underground low-noise high-sensitivity laser strainmeter, crossing a fault in the Gran Sasso massif (central Italy), is discontinuously operating since late May 1994, after a few years of mechanical stabilization of end monuments. A swift extensional strain transient reaching a peak of at least 1 μϵ occurred in about one month from the beginning of the operating time, followed by a four-month-long coarsely stable period, and a slower decay. On June 2nd 1994, in coincidence with two local earthquakes, permanent extensional offsets of about 10 ne have been recorded. A further aseismic slip of the same order of magnitude and sign has been observed about thirty minutes after the last preceding local event, and ten minutes before the next following one. At the same time, the arrival of seismic waves from a distant earthquake has been recorded by the interferometer. No similar signal behaviour has been observed any more since then. 相似文献
5.
A method for studying the physical conditions in compact components of extragalactic radio sources displaying variability on time scales of hundreds of days is proposed. The method can be used to estimate the relative variations of the magnetic-field strength and number density of relativistic electrons in superluminal jets from the cores of quasars and radio galaxies. Results are presented for the jets of the quasars 3C 120, 3C 273, 3C 279, and 3C 345. The energies of the magnetic field and relativistic particles in these objects are not in equipartition. As a rule, the magnetic-field strength decreases appreciably during the evolution of an expanding jet, while the number of relativistic electrons grows. 相似文献
6.
The properties of giant radio sources (GRS’s) are considered with the aim of identifying conditions contributing to their
formation, using data from the literature, the Sloan Digital Sky Survey (SDSS), and the APM catalog. The optical and radio
properties of normal-size radio sources, (≤1 Mpc), are compared. The following conclusions are reached. (1) The fraction of
objects with broad emission lines among GRS’s with high-excitation spectra is the same as for isotropic samples of radio sources;
in the framework of the “unified scheme,” this testifies to an isotropic distribution of angles between the radio jets of
GRS’s and the line of sight, i.e., GRS’s do not represent a population of objects whose radio jets are in the plane of the
sky. (2) Giant radio sources do not differ from normal radio sources in the distributions of various asymmetry parameters
for their extended radio components; in the unified scheme, the similarity of the asymmetry distributions for giant radio
galaxies and giant radio quasars suggests that the origin of the asymmetry of their extended radio components is inhomogeneity
of the external conditions. (3) The observed powers of the radio jets of giant and normal radio sources do not differ, making
it unlikely that the large sizes of the GRS’s are due to this factor. (4) The richness and character of the environments of
giant and normal radio sources do not differ: giant host galaxies are found in both isolated fields and in clusters of up
to Abell class 1 in richness. This argues against the idea that a low density of the environment is the only origin of GRS’s.
(5) The relatively large fraction of radio sources with two pairs of extended radio components (so-called double-double radio
sources) among GRS’s testifies that the lifetimes of GRS’s are approximately an order of magnitude longer than those of normal
radio sources.Given the equal spatial densities of nearby (z < 0.1) GRS’s and FR II radio sources with powers P
1.4 MHz > 1025 W/Hz, this indicates that ∼10% of FR II radio sources have lifetimes an order of magnitude longer, and evolve into GRS’s.
(6) The small (∼0.1) ratio of the number of known GRS’s to the number of normal FR II radio sources, together with the observed
spatial density of GRS’s at z ∼ 0.6, which is an order of magnitude lower than the predicted value, suggests that a considerable number of GRS’s were missed
by surveys at z > 0.1, possibly due to observational selection effects because of their relatively low radio powers and radio surface brightnesses.
(7) The absence of “double-double” giant quasars suggests that these objects have a shorter activity time scale than GRS’s.
In an evolutionary scenario that is an alternative to the unified scheme uniting “radio loud” quasars and radio galaxies,
radio quasars evolve with time into radio galaxies, and the observed relative number of radio quasars among the GRS’s (∼10%)
can be interpreted as reflecting the existence of a long-lived population of “radio loud” quasars comprising ∼10% of all radio
quasars, with such a population of long-lived radio quasars being the parent population for giant radio galaxies. 相似文献
7.
The results of dual-frequency polarization observations of 12 gamma-ray quasars are presented (as a continuation of a study of six blazars carried out earlier). The observations were obtained with the American Very Long Baseline Array. The distributions of intensity and polarization were obtained at 5 and 15 GHz. The degrees of polarization in the cores and jets of the 18 gamma-ray quasars do not stand out from those of other quasars. The brightness temperatures of the core components do not strongly exceed 1012 K. 相似文献
8.
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. 相似文献
9.
According to current observations, the relative abundance of gas-phase metals in distant quasars with ages of only ～109 yr (z～5) can be appreciably higher than the solar abundance. We show that there are two main ways to explain the high metallicity of these galactic nuclei: a high gas density in the central regions, or an increase in the minimum masses of forming stars to several solar masses. The results of numerical modeling confirm this conclusion. 相似文献
10.
Observational data on the evolution of quasars and galaxies of various morphological types and numerical simulations carried out by various groups are used to argue that low-redshift (z < 0.5) quasars of types I and II, identified with massive elliptical and spiral galaxies with classical bulges, cannot be undergoing a single, late phase of activity; i.e., their activity cannot be “primordial,” and must have “flared up” at multiple times in the past. This means that their appearance at low z is associated with recurrence of their activity—i.e., with major mergers of gas-rich galaxies (so-called wet major mergers)—since their lifetimes in the active phase do not exceed a few times 107 yrs. Only objects we have referred to earlier as AGN III, which are associated with the nuclei of isolated, late-type spiral galaxies with low-mass, rapidly-rotating “pseudobulges,” could represent primordial AGNs at low z. The black holes in such galaxies have masses M BH < 107 M ⊙, and the peculiarities of their nuclear spectra suggest that they may have very high specific rotational angular momenta per unit mass. Type I narrow-line (widths less than 2000 km/s) Seyfert galaxies (NLSyIs) with pseudobulges and black-hole masses M BH < 107 M ⊙ may be characteristic representatives of the AGN III population. Since NLSyI galaxies have pseudobulges while Type I broad-line Seyfert galaxies have classical bulges, these two types of galaxies cannot represent different evolutionary stages of a single type of object. It is possible that the precursors of NLSyIs are “Population A” quasars. 相似文献
11.
P. K. Sikdar P. Sahu S. P. Sinha Ray A. Sarkar S. Chakraborty 《Environmental Earth Sciences》2013,70(4):1863-1879
A heterogeneous anisotropic steady-state groundwater flow model for the multi-aquifer system of a part of southern Bengal Basin shows that human intervention has changed the natural groundwater flow system. At present, the shallow groundwater flow is restricted within the aquifer, with very short travel time of tens of years and vertical path length. The deep aquifer is fed by surface water or rainwater from distant locations with travel time of thousands of years and has no hydraulic connection with the arsenic-rich shallow aquifer. Numerical simulations indicate that the future pumping of deep groundwater is not likely to drive in arsenic from the shallow aquifer. Therefore, new wells may be installed in the deep aquifer. High pumping of shallow unpolluted aquifer consisting of brown sand will drive in groundwater containing organic matter from the post-Last Glacial Maximum aquifer-aquitard system. The organic matter drives reduction of manganese oxides at strip interfaces between palaeo-channel and palaeo-interfluve. After the completion of manganese reduction, FeOOH reduction may take place in the marginal palaeo-interfluvial aquifer and release sorbed arsenic. Arsenic then moves into the interior of palaeo-interfluvial aquifer polluting its fresh groundwater. Arsenic migration rates ranges between 0.21 and 6.3 and 1.3 × 10?2 and 0.4 m/year in horizontal and vertical directions, respectively. Therefore, palaeo-interfluvial aquifer will remain arsenic-free for hundreds to thousands of years to supply safe drinking water. 相似文献
12.
13.
The effect of weak microlensing on the apparent velocities of extragalactic sources is considered; in particular, the apparent
motions of sources from the ICRF list are discussed. We expect from two to seven cases of apparent motions of extragalactic
sources due to weak microlensing by stars or dark bodies in our Galaxy to be detected over the next 30 years. 相似文献
14.
采用沉积物再悬浮振荡器在0.2~0.5N/m2的切应力和60~1800s的持续振荡时间下,对太湖沉积物原状芯样的再悬浮特征开展模拟实验研究,揭示切应力大小和外力作用时间对沉积物再悬浮的影响。实验结果表明,振荡初期,上覆水中悬浮物浓度上升速率较快,随振荡时间延长,上升速率减缓,浓度趋于稳定;且浓度上升速率随切应力增加呈显著增大趋势。此外,悬浮物沉降通量随振荡时间而增大,而再悬浮通量呈相反变化趋势,两者的时间变化曲线逐渐接近,最终达到动态平衡。室内模拟试验观测值与太湖现场观测结果的对比表明,该模拟装置能够在室内可控条件下较好地反映太湖沉积物再悬浮特征。 相似文献
15.
We consider observable effects during the gravitational microlensing of stars of finite angular size with a given brightness distribution across their disks by exotic objects whose space-time environment is described with the NUT metric. We demonstrate that, under certain conditions, the microlensing light curves and chromatic effects due to the wavelength dependence of the disk brightness distributions can differ considerably from those observed for a Schwarzschild gravitational lens, so that their analysis can facilitate the identification of such objects. 相似文献
16.
M. S. Butuzova 《Astronomy Reports》2016,60(3):313-321
The X-ray emission of the kiloparsec-scale jets of core-dominant quasars is usually interpreted as inverse Compton scattering on the cosmic microwave background (CMB) emission (Sample I). By analogy with the situation on parsec scales, ultrarelativistic motion along a jet oriented at a small angle to the line of sight is usually invoked to explain the X-ray emission while also satisfying the condition of equipartition between the energies associated with the relativistic particles and the magnetic field on kiloparsec scales. This leads to an increase in the energy flux of the CMB radiation in the rest frame of the kiloparsec-scale jets. Consequently, the intensity of the CMB radiation is enhanced to the level required for detectable X-ray emission. This suggests that kiloparsec jets of quasars with similar extents and radio flux densities that are not detected in the X-ray (Sample II) could have subrelativistic speeds and larger angles to the line of sight, due to deceleration and bending of the jet between parsec and kiloparsec scales. This suggests the possible presence of differences in the distributions of the difference between the position angle for the parsec-scale and kiloparsec-scale jets for these two groups of quasars; this is not confirmed by a statistical analysis of the data for Samples I and II. It is deduced that most of the sources considered exhibit bending of their jets by less than about 1.5 times the angle of the parsec-scale jet to the line of sight. This suggests that the X-ray emission is generated by other mechanisms that there is no equipartition. 相似文献
17.
Interaction of organic compounds with calcium carbonate—III. Amino acid composition of sorbed layers
Nitrogenous organic compounds in sorbed surface layers and in calcified organic matter associated with calcium carbonate sediment particles consist of 40–50% amino acids, 2% amino sugars and 25% ammonia. In grain size classes > 20 μm these compounds are mainly contained in the calcified protein of carbonate secreting organisms but with smaller grain sizes—and consequently increased specific surface area—they are contained in sorbed layers at the mineral surface. The composition of the sorbed layer is characterized by a predominance of neutral amino acids, a relative enrichment of basic and weakly polar amino acids, and a deficiency of acidic amino acids in comparison with the proteinaceous matter of calcifying organisms. The respective abundances for sorbed and calcified matter are: 505 and 380 Res./ of neutral amino acids, 262 and 450 Res./1000 of acidic amino acids, 92 and 51 Res./l000 of basic amino acids, and 141 and 129 Res./1000 of weakly polar amino acids.The composition of the sorbed layer appears to be the result of sorption of proteinaceous matter from solution since it reflects the free and peptide-bound amino acid composition of seawater. The characteristic amino acid assemblage could also be the result of preferential decomposition of protein and subsequent enrichment of neutral and basic amino acids; however, sorption from solution appears more likely since the total amount of amino acids sorbed to calcium carbonate (0.58 mg m ?2) corresponds closely to the amount of protein known to cover one m2 of aqueous substrate in monolayer arrangement. Sorption from solution is further supported by the low arginine/ornithine ratios in both the sorbed layer and the natural dissolved organic matter. This process might lead to a characteristic amino acid spectrum in fine grained calcareous sediments that reflects the composition of the dissolved organic matter in seawater rather than that of the carbonate secreting proteinaceous matter. 相似文献
18.
Numerical simulations of the dynamical evolution of a galaxy cluster in the framework of the N-body problem taking into account dark matter are presented. These simulations are aimed at studying the role of intergalactic
gas in the cluster (the ICM) in the formation of a central, supermassive cD galaxy. The numerical models indicate that deceleration
of the galaxies by intergalactic gas supports the observed high temperature of this gas, and accelerates the formation of
a supermassive cD galaxy in the cluster core. The accretion of interstellar gas by the cluster core can support a high accretion
rate by the central, supermassive black hole associated with the nucleus of the cD galaxy. As a result, this nucleus harbors
a bright quasar. The mass of the black hole can grow with time to values 1010
M
⊙, as are observed for the brightest quasars. 相似文献
19.
Approximately 20% of weak sources in a scintillation survey at 102 MHz were not identified in other, more sensitive, low-frequency surveys. These sources had very high compactness and steep spectra. Since, as shown earlier, these sources are probably quasars, the epoch of the radio birth of quasars should correspond to flux densities of ～0.01 Jy. 相似文献
20.
A star located in the close vicinity of a supermassive black hole (SMBH) in a galactic nucleus or a globular-cluster core could form a close binary with the SMBH, with the star possibly filling its Roche lobe. The evolution of such binary systems is studied assuming that the SMBH mainly accretes matter from the companion star and that the presence of gas in the vicinity of the SMBH does not appreciably influence variations in the star’s orbit. The evolution of the star–SMBH system is mainly determined by the same processes as those determining the evolution of ordinary binaries. The main differences are that the star is subject to an incident flux of hard radiation arising during the accretion of matter by the SMBH, and, in detached systems, the SMBH captures virtually all the wind emitted by its stellar companion, which appreciably influences the evolution of the major axis of the orbit. Moreover, the exchange between the orbital angular momentum and the angular momentum of the overflowing matter may not be entirely standard in such systems. The computations assume that there will be no such exchange of angular momentum if the characteristic timescale for mass transfer is shorter than the thermal time scale of the star. The absorption of external radiation in the stellar envelope was computed using the same formalism applied when computing the opacity of the stellar matter. The numerical simulations show that, with the adopted assumptions, three types of evolution are possible for such a binary system, depending on the masses and the initial separation of the SMBH and star. Type I evolution leads to the complete destruction of the star. Only this type of evolution is realized for low-mass main-sequence (MS) stars, even those with large initial separations from their SMBHs. Massive MS stars will also be destroyed if the initial separation is sufficiently small. However, two other types of evolution are possible for massive stars, with a determining role in the time variations of the parameters of the star–SMBH system being played by the possible growth of the massive star into a red giant during the time it is located in the close vicinity of the SMBH. Type II evolution can be realized for massive MS stars that are initially farther from the SMBH than in the case of disruption. In this case, the massive star fills its Roche lobe during its expansion, but is not fully destroyed; the star retreats inside its Roche lobe after a period of intense mass loss. This type of evolution is characterized by an increase in the orbital period of the system with time. As a result, the remnant of the star (its former core) is preserved as a white dwarf, and can end up at a fairly large distance from the SMBH. Type III evolution can be realized formassiveMSstars that are initially located still farther from their SMBHs, and also for massive stars that are already evolved at the initial time. In these cases, the star moves away from the SMBH without filling its Roche lobe, due to its intense stellar wind. The remnants of such stars can also end up at a fairly large distances from their SMBHs. 相似文献