共查询到20条相似文献，搜索用时 609 毫秒
1.
We present an analysis of a high-amplitude event in the flux curve of component A of the gravitational lens QSO 2237+0305 observed by the OGLE and GLITP groups in autumn 1999. Hypothesizing this event to be associated with microlensing of a fold caustic, we analyzed the observational data using a method for the successive reconstruction of branches of the one-dimensional strip brightness distribution across the source corresponding to positive and negative arguments. The search for the branches was carried out on compact sets of nonnegative, monotonically nonincreasing, convex downward functions. The resulting shape of the strip brightness distribution for the accretion disk of the quasar is in agreement with results obtained earlier via model fitting. Features in the lensing curve that could be associated with curvature of the caustic, nearness of a cusp, or the influence of nearby caustics are noted. 相似文献
2.
Using a model-independent technique, we have reconstructed a one-dimensional strip distribution of the brightness over a stellar disk from observations of microlensing of a Galactic bulge star by a caustic of the binary gravitational lens OGLE-1999-BUL-23, obtained by the international PLANET group. The ill-posed inverse problem was solved using a regularization method taking into account the non-negativity of the brightness distribution. The radial brightness distribution was searched for on a compact set of convex-upward, monotonically non-increasing, non-negative functions, assuming that the source is circularly symmetrical. The reconstructed brightness distribution is compared with the results of model fitting and limb-darkening calculations based on models of stellar atmospheres. 相似文献
3.
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. 相似文献
4.
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
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8.
V. N. Shalyapin 《Astronomy Reports》2006,50(9):699-707
A procedure for calculating two-dimensional power spectra of microlensing magnification fields is presented. In the absence of a shift, the one-dimensional projections of the power spectra P(k) corresponding to the light curve of a point source moving in a linear trajectory can be approximated by the expression (a 2 + k 2)?1/2 (where a = const). The power spectrum of an extended source is treated like the product of the power spectrum of a point source and the power spectrum of the brightness distribution of the extended source. The effect of the extent of the source is that it acts like a filter, suppressing high-frequency components in the spectrum. Based on eight years of monitoring of the quad gravitational lens Q2237+0305 by the OGLE group, power spectra for all four images are constructed and the (temporal) size of the radiating region of the quasar in the V filter is estimated to be 24 ± 6 days; given the constraints on the transverse velocity of the lensing galaxy (<600 km/s), the linear size turns out to be <1015 cm. 相似文献
9.
We have studied the relationships between the brightness, color, and emission-line profiles for the classical T Tauri star RW Aur, which displays an intense emission spectrum and signs of accretion and outflow. Spectral and photometric observations carried out from 1995 to 1999 have been analyzed in the framework of magnetospheric accretion concept, where the brightness of the star depends on the level of the non-photospheric continuum (veiling), which, in turn, depends on the accretion rate. We found that (1) the equivalent widths and profiles of broad emission lines vary independently of the brightness of the star, the brightness and color variations are due primarily to absorption in dust clouds formed by the disk wind; (2) at times when the accretion in the line of sight becomes stronger, all broad emission lines are weakened substantially due to the asymmetry of the magnetosphere and screening of the radiating region; (3) the periodic variations of the U-B and B-V color indices are due to the variable contribution of broad emission lines in the photometric bands; (4) the veiling of the photospheric spectrum is not correlated with either the brightness of the star or the intensity of the accretion components. 相似文献
10.
A. N. Sazonov 《Astronomy Reports》2011,55(2):142-158
We present the results of WBVR observations of the low-mass X-ray binary V1341 Cyg = Cyg X-2. Our observations include a total of 2375 individual measurements
in four bands on 478 nights in 1986–1992. We tied the comparison and check stars used for the binary to the WBVR catalog using their JHK magnitudes. The uncertainty of this procedure was 3% in the B and V bands and 8%–10% for the W and R bands. In quiescence, the amplitude of the periodic component in the binary’s B brightness variations is within 0.265
m
–0.278
m
(0.290
m
–0.320
m
in W); this is due to the ellipsoidal shape of the optical component, which is distorted with gravitational forces from the X-ray
component. Some of the system’s active states (long flares) may be due to instabilities in the accretion disk, and possibly
to instabilities of gas flows and other accretion structures. The binary possesses a low-luminosity accretion disk. The light
curves reveal no indications of an eclipse near the phases of the upper and lower conjunctions in quiescence or in active
states during the observed intervals. We conclude that the optical star in the close binary V1341 Cyg = Cyg X-2 is a red giant
rather than a blue straggler. We studied the longterm variability of the binary during the seven years covered by our observations.
The optical observations presented in this study are compared to X-ray data from the Ginga observatory for the same time intervals. 相似文献
11.
B. B. Krissinel’ 《Astronomy Reports》2005,49(11):939-945
The radio brightness distribution at 5.2 cm has been obtained along the entire solar limb down to a level of 0.01 of brightness temperature at the disk center T 0 c during the solar minimum. The measurements are based on strip scans from the Siberian Solar Radio Telescope. Data reduction included model fitting of an actual solar scan for each position angle. The maximum limb brightness, 1.37 T 0 c , in the derived distribution is at equatorial direction, where the radio radius exceeds the photosphere radius by 7%. Toward the poles, the brightness peak and radio radius gradually decrease to 1.01 T 0 c and 1.005 R0. The derived two-dimensional brightness distribution was used to calculate radio radius as a function of position angle for several wavelengths from 4 to 31.6 cm. These dependences are consistent with RATAN-600 observations at position angles 0° and 25°. 相似文献
12.
The structure and magnitude of the electric field created by a rotating accretion disk with a poloidal magnetic field is found for the case of a vacuum approximation along the axis. The accretion disk is modeled as a torus filled with plasma and a frozen-in magnetic field. The dimensions and location of the maximum electric field as well as the energy of the accelerated particles are found. The gravitational field is assumed to be weak. 相似文献
13.
Results of spectral observations of the isolated Ae Herbig star CQ Tau obtained in 1995–1998 in the Hα line and near the sodium resonance doublet are presented, together with simultaneous photometric monitoring of the star. CQ Tau is a member of the family of young UX Ori stars with nonperiodic Algol-like brightness decreases. The star is surrounded by an accretion disk, in which its emission-line spectrum and part of its absorption-line spectrum are formed. The strong variability of the Hα, D NaI, and HeI 5876 Å lines testifies that the gaseous disk is appreciably inhomogeneous in both the radial and azimuthal directions. This inhomogeneity probably results from uneven feeding by the circumstellar material from the peripheral regions of the circumstellar disk. Over the four years of observations, we observed the star in deep minima three times (ΔV～2). On these nights, an increase in the Hα equivalent width followed the decrease in radiation flux. In the two deepest minima, the normally two-component line profile had only a single component with a nearly symmetrical profile. This behavior of the Hα line is in good agreement with the results of numerical modeling of Algol-like minima and can be used to estimate the parameters of the dust clouds eclipsing the star and inner accretion disk. These estimates suggest that the circumstellar dust clouds can approach very close to the star and be sublimated there. 相似文献
14.
Astronomy Reports - The scenario of a merger of two black holes surrounded by an accretion disk is considered. As a result of the emission of gravitational waves, the mass of the central object... 相似文献
15.
ASCA, RXTE, and Chandra observations of Seyfert galaxies indicate the presence in their spectra of broad emission lines with characteristic double-peaked pro files, which could arise in the inner regions of an accretion disk. In such regions, general relativistic effects must be taken into account, and may even dominate. In connection with this, we have constructed the radiation spectrum for an individual spectral line for a model isothermal Kerr accretion disk. This demonstrates the manifestation of general relativistic effects in pure form, unclouded by effects associated with models for the structure of the disk itself. It is assumed that matter in the disk moves in circular geodesics in the equatorial plane. The spectrum retains a characteristic two-peaked profile for wide ranges of values of the radial coordinate of the radiating region, angular momentum of the black hole, and viewing angle. The inner regions of the disk make an appreciable contribution to the red wing of the spectrum. 相似文献
16.
E. P. Velikhov K. R. Sychugov V. M. Chechetkin A. Yu. Lugovskii A. V. Koldoba 《Astronomy Reports》2012,56(2):84-95
We investigate the role of the magnetic field in the collapse of a gas-dust cloud into a massive gravitating object. Observations
of one such object (G31.41) indicate that the magnetic field has an hourglass shape oriented along the rotation axis of the
matter, due to the freezing-in of the magnetic-field lines in the accreting matter. It is believed that accretion in stellar
disks is associated with the transport of angular momentum from the center to the periphery, which could be initiated by large-scale
vortex structures arising in the presence of unstable rotational flows of matter. The numerical simulations have established
that the equilibrium configuration of a gas-dust disk rotating in a spherically symmetrical gravitational potential is subject
to the development of strong instability in the presence of a weak magnetic field. It is shown that the development of instability
leads to a transport of angular momentum to the disk periphery by large-scale vortex structures, together with the accretion
of matter onto the gravitating object. The magnetic-field lines near the equator take on a chaotic character, but an hourglass
configuration is observed near the rotation axis, in agreement with observations. 相似文献
17.
E. P. Pavlenko I. B. Voloshina M. V. Andreev S. Yu. Shugarov A. V. Baklanov O. I. Antonyuk N. A. Parakhin D. A. Samsonov V. G. Metlov 《Astronomy Reports》2010,54(1):6-16
We analyze photometry of the dwarf nova MN Dra carried out using various instruments at four observatories on 18 nights between
May 20 and June 28, 2009. The observations cover a variety of activity states of the system: a superoutburst, three normal
outbursts, and quiescence. Analysis of the system’s light curve during the superoutburst decline reveals positive superhumps
that recur, on average, with a period of 0.105 days and are due to the direct apsidal precession of the accretion disk. These
are observed until the end of the superoutburst, but their period decreases at a rate of −24.5 × 10−5 of the period per period. Both the positive-superhump period and its derivative are in good agreement with estimates made
during previous superoutbursts. At the brightness minimum and in normal outbursts, MN Dra displays brightness variations with
a period of 0.096 days, whose amplitude is much larger during the brightness minimum (0.8
m
–1.5
m
) than during normal outbursts (0.1
m
–0.2
m
). We suggest that these brightness variations could be negative superhumps due to nodal precession of the oblique accretion
disk. 相似文献
18.
A.G.W. Cameron 《Earth》1973,9(2):125-137
A brief introduction is given to the various approaches which have been followed in attempting to construct models of the origin of the solar system. The author then outlines in more detail one of the more recent approaches, involving models of a massive primitive solar nebula. In this approach a massive gaseous disk is first formed during the course of star formation, and the Sun must subsequently form from the disk as a result of hydrodynamical dissipation processes. Both the dissipation and the accompanying formation of the planets are estimated to require only a few thousand years. As a consequence, there was little time for the Earth to radiate its energy of gravitational accretion, and the primitive Earth must have been extremely hot. 相似文献
19.
V. P. Grinin O. Yu. Barsunova S. G. Sergeev A. A. Arkharov S. Yu. Shugarov A. O. Semenov N. V. Efimova 《Astronomy Reports》2018,62(10):677-688
The results of many-year photometric observations of the weak-line T Tauri star V715 Per in the optical (V RI) and infrared (JHK) photometric bands are presented. The period of the star’s lowamplitude brightness variations in the V RI bands detected earlier, 5.23d, is confirmed. This period persists during the entire 14-year time interval of the observations, but its amplitude varies with time. The same period was found in the variations of JHK infrared fluxes, with the brightness variations in the two ranges being almost synchronous. The most probable origin of these variations is periodic eclipses of the star by its own disk, perturbed by its interaction with the magnetosphere (AA Tau-type variations). In addition to the periodic brightness variations, the star also displayed sporadic Algol-like minima characteristic of UX Ori stars during several years (2005–2011). The amplitude of these variations increasedmonotonically, reaching approximately 1m in the V band by the end of 2010, after which the deep fadings ended. During this entire time interval, the amplitude of the periodic variations was observed to decrease. After 2011, the periodic component began to become stronger again. These changes of the photometric activity of V715 Per can be explained by an increasing rate of gas accretion onto the star, decreasing the radius of warped regions of the disk and leading to accompanying Algol-like fadings. This model assumes a low inclination of the circumstellar disk in V715 Per to the line of sight. 相似文献
20.
A. M. Fridman D. V. Bisikalo A. A. Boyarchuk Yu. M. Torgashin L. A. Pustil’nik 《Astronomy Reports》2009,53(8):750-768
The results of studies of the over-reflection mechanism for the development of hydrodynamical instability in the accretion disks of close binary stars are presented. The driving of this instability is shown to result in the generation of regular, large-scale, spiral-vortex structures and the development of turbulence in the disk. The derived estimates of the coefficient of turbulent viscosity are in good agreement with the observations, and are able to explain the high rate of angular-momentum transfer and the measured accretion rate. The developed theoretical model is used with the observational data to derive a power-law spectrum for the developed turbulence. 相似文献