共查询到20条相似文献，搜索用时 31 毫秒
1.
简单地介绍了CCD相机的读出噪声、电荷转移效率(CTE)的常用测试和归算方法,指出了其中的不足之处。在此基础上,提出了改进的噪声和CTE的测试和归算方法。也就是,读出噪声的测量以过扫描区的方差为基础来进行。而在CTE的归算时,先采用人-机交互方式确定一条适当的初始转移直线(X射线的单像元事件线)和相应的区间,在此区间中进行的第一次线性拟合得到一条较准确的转移直线,以后根据前一次的结果自动选取区间并进行线性拟合。以此方式就可以归算出较为精确的CTE数据。 相似文献
2.
Probhas Raychaudhuri 《Astrophysics and Space Science》1972,19(1):145-149
It is pointed out that the all old supernova remnants are not in general sources of soft X-ray emission. Again it is pointed out that the galactic radio spur (Cetus arc) may be an old supernova remnant but it has already ceased to be a source of X-ray emission. Finally X-ray flux from Vela is ostimated from cooling rate of neutron star by neutrino emission. The results agree approximately with the observed X-ray flux from Vela X. 相似文献
3.
The multicollinearity among regression variables is a common phenomenon in the reduction of astronomical data. The phenomenon
of multicollinearity and the diagnostic factors are introduced first. As a remedy, a new method, called adaptive ridge regression
(ARR), which is an improved method of choosing the departure constant θ in ridge regression, is suggested and applied in a
case that the Earth orientation parameters (EOP) are determined by lunar laser ranging (LLR). It is pointed out, via a diagnosis,
the variance inflation factors (VIFs), that there exists serious multicollinearity among the regression variables. It is shown
that the ARR method is effective in reducing the multicollinearity and makes the regression coefficients more stable than
that of using ordinary least squares estimation (LS), especially when there is serious multicollinearity.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
M.J. Yerbury 《Icarus》1971
Radio emission from the planet Saturn was detected and measured by an unusually efficient observing technique at a wavelength of 49.5cm. The corresponding equivalent disk brightness temperature was hence determined to be 390 ± 65°K, providing further evidence for a mild enhancement in the emission at long wavelengths. It is pointed out that the currently available measurements of the disk brightness temperature in the wavelength range 1mm-1m are, as a whole, inadequate for estimating with confidence the detailed shape of the spectrum and that the exiguous, long wavelength observations should be supplemented with more and accurate measurements. 相似文献
5.
W. Wenzel 《Astronomische Nachrichten》1987,308(1):75-80
The mean cycle length of the catalysmic binary HT Cas, which is remarkable because of the shortness of its orbital period, has been determined as 400d±50d. The hitherto assuixed value of 30d proved unfounded. Some aspects arising when classifying long-cycle objects and SU Ursae Majoris variables are pointed out, a s well as the relation between large cycle length and small accretion rate. 相似文献
6.
Assigning to the equivalent gravitational parameter of a two-body dynamic system, a periodic change of a small amplitude B and arbitrary frequency and phase, the behaviour of an elliptic-type orbit is studied. The first order (in B) perturbations of the orbital elements are determined by using Delaunay's canonical variables. According to the value of the ratio between oscillation frequency and dynamic frequency, three cases (non-resonant (NR), quasi-resonant (QR), and resonant (R) ones) are pointed out. The solution of motion equations shows that only in the QR and R cases there are elements (argument of pericentre and mean anomaly) affected by secular perturbations. The solutions are valid over prediction times of order of pericentre and mean anomaly) affected by secular perturbations. The solutions are valid over prediction times of order B−1 in the NR case and B−1/2 in the QR and R cases. 相似文献
7.
For the dynamics of general-relativistic adiabatic fluids a reduced Hamiltonian formalism is presented. For slowly moving fluids an approximation scheme is defined. The first steps of the scheme are worked out explicitly. Radiation damping and emission, and backscattering are discussed. The usefulness of the formalism for numerical relativity is pointed out. 相似文献
8.
Ramesh Chander Kapoor 《Astrophysics and Space Science》1983,93(1):79-85
It is argued that accreting supermassive black holes ejected from centers of galaxies are the likely models for the quasars
observed in association with galaxies. Also pointed out are the implications of a recent suggestion by Horák (1982) to account
for the excess redshifts of such quasars due to a combined effect of peculiar Doppler-motion and the gravitational field. 相似文献
9.
The ability of magnetic reconnection solutions to explain statistical flare data is discussed. It is assumed that flares occur at well-defined, isolated sites within an active region, determined by the null points and separators of the coronal magnetic field (Craig, 2001). Statistical flare observations then derive from a multiplicity of independent sites, flaring in parallel, that produce events of widely varying output (Wheatland, 2002). Given that the `separator length' at an individual site controls the event frequency and the mean energy release, it is shown that the observed frequency-energy spectrum N(E)can be inverted to yield a source function that relates directly to the distribution of separator lengths. It is also pointed out that, under the parallel flaring model, inferred waiting-time distributions are naturally interpreted as a superposition of individual point processes. Only a modest number of flaring separators is required to mimic a Poisson process. 相似文献
10.
M. E. Alexander 《Astrophysics and Space Science》1976,45(1):105-117
The precession of the orbital plane in a close binary system can provide an important observational tool for investigating dynamical properties of the components. Tidal evolution will always tend to align the rotation axes perpendicular to the orbital plane, thereby eliminating precession. It is pointed out, however, that if observations indicate the existence of a circular orbit and synchronous rotation of the components-which is the outcome of tidal evolution-then precession may still be present, provided the interior of one of the components is, or recently has been, radiative, and is not strongly coupled to the surface layers (where tidal dissipation is greatest). The equations governing precession and nutation are derived in a concise form, and applied to the numerical study of two binary systems. The observational effects are also discussed. Finally, it is pointed out that precession may be present in a subclass of the X-ray binary systems, and its observational significance is briefly discussed. 相似文献
11.
In this paper we study the coexisting low frequency oscillations in strongly degenerate, magnetized, (electron-positron) pair and warm pair-ion plasma. The dispersion relations are obtained for both the cases in macroscopic quantum hydrodynamics approximation. In pair-ion case, the dispersion equation shows coupling of electrostatic and (shear) electromagnetic modes under certain circumstances with important role of ion temperature. Domain of existence of such waves and their relevance to dense degenerate astrophysical plasmas is pointed out. Results are analyzed numerically for typical systems with variation of ion concentration and ion temperature. 相似文献
12.
On the base of a photographic plate in system V, which was taken with the 134/200/400 cm Schmidt camera of the Karl-Schwarzschild-Observatorium Tautenburg maximal diameters of galaxies in the centre of the Coma cluster are determined by photographic equidensitometry. An other system of diameters is determined for medium densities of the objects. The results are compared with ROOD and BAUM'S who derived the diameters by visual measurements on plates taken with the 5-metre telescope of the Hale Observatories. Both statistics contain galaxies up to 19m. They are complete up to 17m.5. It is pointed out that the Tautenburg diameters are in the mean 3 times larger than those derived by ROOD and BAUM. Diameter-magnitude diagrams and ellipticities of the objects are derived, further photometric corrections for tilted objects. For describing the general structure of the cluster diameter functions are derived instead of magnitude functions. The accuracy of a brightness determination by the equidensity method from the diameter-magnitude diagrams is nearly twice better than according to ROOD and BAUM. 相似文献
13.
The kink instability in a coronal loop is a possible explanation of a compact loop flare as it may cause a current sheet to form allowing reconnection to take place and release the free magnetic energy stored in the loop. However, current sheets do not form in all cases. Ali and Sneyd (2001) investigated three different classes of equilibrium (determined by the form of the twist) using a magneto-frictional code. They searched for the equilibria to which the loop might evolve once it had become unstable to the kink instability. They found indications of current-sheet formation for only one class of equilibrium studied. However, as they pointed out, since their code searched for equilibria they were unable to say for certain that the loop would evolve in this way. In this paper we have considered the same three classes of equilibria but have used a code which follows the non-linear 3D MHD (magnetohydrodynamic) evolution of the loop. We have investigated whether or not there are indications of current-sheet formation. In the cases where there is evidence of this we have found that reconnection does occur and releases sufficient magnetic energy to explain a compact loop flare. 相似文献
14.
The periodic motion of a test particle (dust, grain, or a larger body) around a pulsating star with a luminosity oscillation of small amplitude (featured by a small parameterB) is being studied. The perturbations of all orbital elements are determined to first order inB, by using Delaunay-type canonical variables and a method whose bases were put forth by von Zeipel. According to the value of the ratio oscillation frequency/dynamic frequency, three possible situations are pointed out: nonresonant (NR), quasi-resonant (QR), and resonant (R). The solution of motion equations shows that only in the (QR) and (R) cases there are orbital parameters (argument of periastron and mean anomaly) affected by secular perturbations. These solutions (which indicate a secularly stable motion in a first approximation) are valid over prediction times of orderB
–1 in the (NR) case andB
–1/2 in the (QR) and (R) cases. The theory may be applied to various astronomical situations. 相似文献
15.
C. Sivaram 《Astrophysics and Space Science》1994,215(2):185-189
Some consequences of MOND (Modification of Newtonian dynamics) proposed as an alternative hypothesis to dark matter for various astrophysical situations is discussed. The ubiquitous occurrence of the fundamental acceleration invoked is pointed out. 相似文献
16.
E. M. Drobyshevski 《Earth, Moon, and Planets》1978,18(2):145-194
If the solar system origin is considered within the framework of the author's hypothesis on the binary stars formation as a result of rotational-exchange break-up of the rotating protostar, then difficulties involved in the usual nebular hypotheses are automatically removed (unclear aspects of the possibility of formation of the gas disc proper, the problems of the angular momentum including slow rotation of the Sun and coplanarity of the planetary orbits, of differences in planetary masses and composition, the need, for the disc remnants to be swept out, the long time of planetary formation as compared with the possible lifetime of a turbulized disc etc.).The major stages of division and evolution of the Jupiter-Sun system are described. Similarities between the massive rotating proto-Jupiter (PJ) and the classical protoplanetary discs are pointed out. The process of planetoid condensation inside PJ is discussed. The most probable site of the condensation is the region of the first Lagrangian point. The planetoids condensed were lost by PJ as a result of its fast mass decrease. A gas dynamic consideration of the motion of planetoids in PJ yields 1000–3000 yr as a time scale for the PJ's mass loss. The number of the moonlike bodies lost (the remaining Galilean satellites fixing their lower mass limit) could reach 104.Evolution of such interacting bodies results in the formation beyond Neptune of a cloud (up to 103) of moonlike (and more massive) planets.The excess concentration of the long-period comets aphelia in this area implies their genetic relation to the planets. A concept of a joint planeto-cometary cloud is introduced. A concrete hydrodynamic mechanism of ice ejection from planets into space, viz. the formation of cumulative (Monroe) jets, is pointed out.A program of further investigations is outlined and recommendations given for an experimental check on the implications of the new cosmogonic concepts. 相似文献
17.
18.
Uniformly Redundant Arrays (URA's) are two–dimensional binary arrays with constant sidelobes of their periodic autocorrelation function. They are widely agreed upon to be optimum mask patterns for coded aperture imaging, particularly in imaging systems with a cyclic coded mask. In this paper, a survey of all currently known construction methods for URA's is given and the sizes and open fractions of the arrays resulting from each construction method are pointed out. Alternatives to URA's for situations in which a URA does not exist, are discussed. 相似文献
19.
UBV measurements of early‐type stars, mostly eclipsing binaries, obtained at La Silla in the years 1990 to 1994 with the ESO 50 cm telescope are presented. Most of these data were already used in our individual studies of several binaries. Now all photometric measurements were reduced again with an advanced technique and are made available electronically. Our data for MY Ser have not yet been published; new light curve is given and solved. The result is that MY Ser is a contact binary, with very large fill‐out parameter. Also a light curve and its solution for V1051 Cen are provided, and the problem of the period of V871 Cen is pointed out. Besides binaries (and the comparison and check stars) data for several stars in southern H II regions are included. Extinction and transformation coefficients are given (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
20.
L. Stenflo 《Planetary and Space Science》1973,21(3):391-397
The coupled equations for the resonant nonlinear interaction between three waves in cold magnetized plasmas are derived and written in a comparatively simple and symmetric form. The deficiencies of previous papers are pointed out and the possibility of explosive interactions in the solar corona is suggested. 相似文献