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1.
Claims continue to be made that detector selection effects can explain the deviation of the gamma-ray burst brightness distributions from the -3/2 power law expected for homogeneous burst sources. However, these effects are insufficient to explain the BATSE observations. The BATSE sensitivity threshold does vary with time, independent of the burst brightness; however, a homogeneous distribution of standard candle sources would still produce a -3/2 power law. The variation in the threshold does affect inhomogeneous source models. As an example, the effect of a time-varyingC min on theC max/C min distribution of an extended Galactic halo model is shown here. To fit the BATSEC max/C min distribution including a varyingC min requires a larger observing distance (relative to the scale-height of the halo) than for a constantC min; however, the observations can still be fit using the halo models.  相似文献   

2.
We have performed a series ofN-body experiments including the effects of a massive dominant background which follows Schuster's density law in order to simulate clusters of galaxies in which a smoothly distributed dark component is present. The existence of this background is inferred from the weak luminosity segregation observed in clusters which, however, show several characteristics of well-relaxed systems. The comparison of the velocity dispersion profiles of three clusters of galaxies (Coma, Perseus, and Virgo) with those obtained in the numerical experiments allows us to place some constraints on both the distribution and amount of distributed dark material in these clusters. The profiles are rather insensitive to variations in the ratio of the background mass to the mass attached to galaxies (M b/Mg), but exhibit a strong dependence on their relative concentration. We conclude that highly concentrated background models are not consistent with observations. We find a maximum value for the ratio of the gravitational radius of the galaxies and the background (R g/Rb) (approximately 0.6) and using previous results (Navarroet al., 1986) we conclude that virial theorem masses underestimate the total mass (M b+M g) of the clusters. As a final result, we derive a minimum value for theM b/Mg ratio. All these conclusions could apply in general if Coma, Perseus, and Virgo constitute a fair sample of the rich clusters of galaxies in the Universe.  相似文献   

3.
Analysis of the available observational data for the α-Persei cluster members shows that rotation effects on the intermediate-band indices c1 and (u-b) are considerable. In c1, rotation produces a reddening of 0.040 magnitudes per 100 km s-1 In (u-b) the effect for B stars is found to be 0.06 magnitudes per 100 km s-1 ofV sin i. The binaries and peculiar stars are found to behave differently in the colour excess (due to rotation) versusV sin i diagrams. These empirical effects can be utilised to recalibrate these colour indices and also to separate members that are either chemically peculiar or in binary systems.  相似文献   

4.
High‐resolution mass spectrometry (HRMS) imaging by desorption electrospray ionization (DESI) coupled with Orbitrap MS using methanol (MeOH) spray was performed on a fragment of the Murchison (CM2) meteorite in this study. Homologues of CnH2n–1N2+ (n = 7–9) and CnH2nNO+ (n = 9–14) were detected on the sample surface by the imaging. A high‐performance liquid chromatography (HPLC)/HRMS analysis of MeOH extracts from the sample surface after DESI/HRMS imaging indicated that the CnH2n–1N2+ homologues corresponds to alkylimidazole, and that a few isomers of the CnH2nNO+ homologues present in the sample. The alkylimidazoles and CnH2nNO+ homologues displayed different spatial distributions on the surface of the Murchison fragment, indicating chromatographic separation effects during aqueous alteration. Moreover, the distribution pattern of compounds is also different among homologues. This is probably also resulting from the separation of isomers by similar chromatographic effects, or different synthetic pathways. Alkylimidazoles and the CnH2nNO+ homologues are mainly distributed in the matrix region of the Murchison by mineralogical observations, which is consistent with previous reports. Altered minerals (e.g., Fe‐oxide, Fe‐sulfide, and carbonates) occurred in this region. However, no clear relationship was found between these minerals and the organic compounds detected by DESI/HRMS imaging. Although this result might be due to scale differences between the spatial resolution of DESI/HRMS imaging and the grain size in the matrix of the Murchison, our results would indicate that alkylimidazoles and the CnH2nNO+ homologues in the Murchison fragment were mainly synthesized by different processes from hydrothermal alteration on the parent body.  相似文献   

5.
The effects of partial frequency redistribution on the formation of spectral lines have been studied. We considered the angle-averaged RII, RIII andR v types of redistribution with isotropic phase function, Transfer equation with plane-parallel geometry is solved in isothermal atmospheres. For an atmosphere with constant thermal sources, the frequency-dependent source function SL (R v) lies below SL (RIII) but above SL(R III) in the line wings.  相似文献   

6.
We study the effects of a non-singular gravitational potential on satellite orbits by deriving the corresponding time rates of change of its orbital elements. This is achieved by expanding the non-singular potential into power series up to second order. This series contains three terms, the first been the Newtonian potential and the other two, here R 1 (first order term) and R 2 (second order term), express deviations of the singular potential from the Newtonian. These deviations from the Newtonian potential are taken as disturbing potential terms in the Lagrange planetary equations that provide the time rates of change of the orbital elements of a satellite in a non-singular gravitational field. We split these effects into secular, low and high frequency components and we evaluate them numerically using the low Earth orbiting mission Gravity Recovery and Climate Experiment (GRACE). We show that the secular effect of the second-order disturbing term R 2 on the perigee and the mean anomaly are 4″.307×10−9/a, and −2″.533×10−15/a, respectively. These effects are far too small and most likely cannot easily be observed with today’s technology. Numerical evaluation of the low and high frequency effects of the disturbing term R 2 on low Earth orbiters like GRACE are very small and undetectable by current observational means.  相似文献   

7.
We report on the statistical analysis of a sample of AGNs (Seyferts and LINERs) selected from an RBSC-NVSS sample of the brightest X-ray sources. The sample is large enough and unbiased for a detailed study of multi-frequency (radio to X-ray) properties of AGN. There are no significant differences in X-ray, optical, far-infrared, and radio powers, core dominance, radio loudness, radio spectral index, and two-point radio-to-optical and optical-to-X-ray spectral indices of Seyfert types 1 and 2. These findings strongly support the unification model, and the observed differences between Sy1 and Sy2 are due to both the variable obscuration and different geometric orientation effects. The correlation between the X-ray and radio emission over many decades is primary and indicates the intrinsically similar origin of both radiations in Seyfert galaxies, powered mainly by AGN, rather than compact starbursts. For Seyfert galaxies we found that the slopes of the relations L X - L R and L X - L B are flat, which indicate the existence of components unrelated with X-ray. Perhaps only for LINERs is the observed L X - L R relation completely due to AGNs. The Sy1, Sy2, and LINER galaxies show different slopes in the relation L X - L 1.4, and the relative contribution of extended radio components may be the cause of these differences. The possible effects of unresolved extended radio and X-ray components are quantitatively discussed.  相似文献   

8.
We have measured the decorrelation frequency (f v ) and decorrelation time (t v ) for 15 pulsars. We show by combining our data with those of others thatfv∫ DM-1.79±0.14 andt v ∫ DM-0.80±0.15 up to a dispersion measure (DM) of about 60 cm3 pc. The combined data set does not form a complete sample, but the relations obtained from our measurements on 14 pulsars, which form almost a complete sample up to 41 cm3 pc, are consistent with the above relations, suggesting that these relations are not seriously affected by selection effects. The relations are broadly in agreement with those expected from a homogeneous interstellar medium and are in disagreement with earlier conclusions by others that these relations steepen even for low-DM pulsars. The agreement suggests that the local interstellar medium is homogeneous at least up to a distance of about 2 kpc.  相似文献   

9.
We report the Mueller matrix elements for RATAN-600 computed with the allowance for the diffraction effects in the space between the main, secondary, and flat mirrors in the Souther sector with a flat reflector (“South+flat”) observing mode and in the mode of single-sector observations at the horizon throughout the entire operating wavelength range. We show that the vertical size of the M 41 and M 32 elements decreases, the elements shift relative to the central horizontal section, and the lobe structure of the elements changes with increasing wavelength. In the “South+flat’ mode these changes, which are due to diffraction effects, begin to show up at shorter wavelength compared to the single-sector mode. We investigated the variation of the structure of the elements M 41 and M 32 with the elevation angle of the flat reflector and in the case of longitudinal and transversal off-focus offsets of the primary feed.  相似文献   

10.
In a previous work we studied the effects of (I) the J 2 and C 22 terms of the lunar potential and (II) the rotation of the primary on the critical inclination orbits of artificial satellites. Here, we show that, when 3rd-degree gravity harmonics are taken into account, the long-term orbital behavior and stability are strongly affected, especially for a non-rotating central body, where chaotic or collision orbits dominate the phase space. In the rotating case these phenomena are strongly weakened and the motion is mostly regular. When the averaged effect of the Earth’s perturbation is added, chaotic regions appear again for some inclination ranges. These are more important for higher values of semi-major axes. We compute the main families of periodic orbits, which are shown to emanate from the ‘frozen eccentricity’ and ‘critical inclination’ solutions of the axisymmetric problem (‘J 2 + J 3’). Although the geometrical properties of the orbits are not preserved, we find that the variations in e, I and g can be quite small, so that they can be of practical importance to mission planning.  相似文献   

11.
The treatment followed by Coxet al. (1973) for the estimation of the effects of thermal imbalance on the pulsational stability of stars is applied to Roche and point source (Chandrika Prashad) model. The calculations suggest that the eigenvalues obtained for the above model are correct to 0(t ff/ts). The expressions for stability coefficients and corresponding eigenfunctions for the stars in thermal imbalance for the above models have also been derived.  相似文献   

12.
Results from kinematic solar dynamo models employing α ‐effect and turbulent pumping from local convection calculations are presented. We estimate the magnitude of these effects to be around 2–3 m s–1, having scaled the local quantities with the convective velocity at the bottom of the convection zone from a solar mixing‐length model. Rotation profile of the Sun as obtained from helioseismology is applied in the models; we also investigate the effects of the observed surface shear layer on the dynamo solutions. With these choices of the small‐ and large‐scale velocity fields, we obtain estimate of the ratio of the two induction effects, C α /C Ω ≈ 10–3, which we keep fixed in all models. We also include a one‐cell meridional circulation pattern having a magnitude of 10–20 m s–1 near the surface and 1–2 m s–1 at the bottom of the convection zone. The model essentially represents a distributed turbulent dynamo, as the α ‐effect is nonzero throughout the convection zone, although it concentrates near the bottom of the convection zone obtaining a maximum around 30° of latitude. Turbulent pumping of the mean fields is predominantly down‐ and equatorward. The anisotropies in the turbulent diffusivity are neglected apart from the fact that the diffusivity is significantly reduced in the overshoot region. We find that, when all these effects are included in the model, it is possible to correctly reproduce many features of the solar activity cycle, namely the correct equatorward migration at low latitudes and the polar branch at high latitudes, and the observed negative sign of B r B ϕ . Although the activity clearly shifts towards the equator in comparison to previous models due to the combined action of the α ‐effect peaking at midlatitudes, meridional circulation and latitudinal pumping, most of the activity still occurs at too high latitudes (between 5° … 60°). Other problems include the relatively narrow parameter space within which the preferred solution is dipolar (A0), and the somewhat too short cycle lengths of the solar‐type solutions. The role of the surface shear layer is found to be important only in the case where the α ‐effect has an appreciable magnitude near the surface. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

13.
The analytical stability criterion applicable to coplanar hierarchical three-body systems described in the first paper of this series, Walkeret al. (1980), is modified to give an exact representation ofHill-type stability in all such cases. The dependence of the stability on all orbital parameters (in the coplanar case) is taken into account. The criterion for stability is now dependant upon the participating masses, the elements of the initial osculating Keplerian orbits of the system (viz. the orbits ofm 2 aboutm 1 andm 3 about the mass-centre of the (m 1,m 2) system) and the positions within these orbits.The behaviour of the stability of such systems is demonstrated (both analytically and numerically) with respect to certain of the parameters involved to consider effects not dealt with in the above-mentioned paper. In particular two interesting real cases of triple systems in the Solar System are discussed, namely Sun-Jupiter-Saturn and Earth-Moon-Sun. The results of the present paper are compared with those of past authors who considered the same systems.Finally some general features arising out of our analysis are discussed.  相似文献   

14.
An exact analysis of the mass transfer effects on the free convection flow of an incompressible viscous fluid past an impulsively started infinite vertical (wall) limiting surface (Stokes's or Rayleigh's problem) has been carried out. Expressions for the velocity, temperature, species concentration and skin friction are obtained by using the Laplace transform technique. The velocity field and the skin friction are shown graphically for air (P=0.71) and mercury (P=0.025). The effects ofG (Grashof number),G c (the modified Grashof number) andS c (Schmidt number) are considered qualitatively during the course of discussion.  相似文献   

15.
We have investigated the effects of increasing optical depths on spectral lines formed in a rotating and expanding spherical shell. We have assumed a shell whose outer radius is 3 times the inner radius, with the radial optical depths equal to 10, 50, 100, 500. We have employed a constant velocity with no velocity gradients in the shell. The shell is assumed to be rotating with velocities varying as 1/ρ, whereρ is the perpendicular distance from the axis of rotation, implying the conservation of angular momentum. Two expansion (radial) velocities are treated: (1)V = 0 (static case) and (2)V = 10 mean thermal units. The maximum rotational velocities areV rot = 0, 5, 10 and 20. In the shell where there are no radial motions, we obtain symmetric lines with emission in the wings forV rot = 0 and 5 while forV rot ≥ 10 we obtain symmetric absorption lines. In the case of an expanding shell, we obtain lines with central emission.  相似文献   

16.
We report on first results of a comprehensive study of interacting andmerging processes between spiral galaxies and small satellites to investigatethe effects of such events on the disk component of spirals. Analysis ofour newly obtained photometric data of about 125 edge-on galaxiesin optical and in NIR shows that there are considerable differencesbetween interacting and non-interacting galaxies concerning their absolutedisk scale parameters as well as their ratios (h/z 0).In comparison with normal spirals, the average heating factor perpendicular tothe disk plane of mergers is about 1.5. The most striking feature of thedistributions of (h/z 0) for both normal galaxies and mergers, is thetotal lack of typical flat disk axis ratios (i.e. that of late type ones)of (h/z 0) > 6 for mergers. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

17.
Hall effects on the flow of electrically conducting rarefied gas due to combined buoyant effects of thermal and mass diffusion past an infinite porous plate with constant suction in the presence of strong transverse magnetic field have been investigated. The equations governing the flow poblem have been solved for primary, secondary velocities and temperature. The effects of Hall current, magnetic field and the effect of rarefication have been discussed graphically followed by a discussion.Nomenclature x,y coordinate system - u velocity inx direction - v 0 suction velocity - w velocity inz direction - E Eckert number - G, G* Grashof numbers - h 1 velocity slip coefficient - h 2 temperature jump coefficient - h 3 concentration jump coefficient - M, m magnetic field parameter, Hall parameter - Pr Prandtl number - Sc Schmidt number - T, T w, T temperature in flow regime, plate temperature, temperature outside the boundary layer very away from the plate - C, C w, C concentration of the gas in flow, concentration at the plate, concentration far away from the plate - thermal conductivity - D coefficient of chemical molecular diffusion - coefficient of kinematic viscosity - coefficient of viscosity - electrical conductivity - C p specific heat of gas at constant pressure density  相似文献   

18.
Altimetric measurements of the GEOSAT satellite were used for the determination of geopotential scale factorR 0. The geopotential valueW 0 on the geoid surface was then computed (W 0 =GM/R 0).The GEOSAT Geophysical Data Records (GDR's) covering an initial period of the Exact Repeat Mission (ERM) were filtered and processed. The necessary corrections were made in order to allow a precise detection of the sea surface. Gravitational geopotential, rotation and permanent tides were taken into account and the equipotential surface which is the best approximation of the sea surface was found.The determination of the potential valueW 0 on the mean geoid surface in this way is very promising. An associated value withW 0 - the geopotential scale factorR 0 - seems to be a very good Earth dimension defining quantity. Moreover, there are many possible applications ofW 0 (R 0) in modern geophysics.The incorporation of one of these parameters - we now recommendR 0 - into the set of the Primary Geodetic Parameters (PGP) is discussed and suggested.  相似文献   

19.
Earlier models of compressible, rotating, and homogeneous ellipsoids with gas pressure are generalized to include the presence of radiation pressure. Under the assumptions of a linear velocity field of the fluid and a bounded ellipsoidal surface, the dynamical behaviour of these models can be described by ordinary differential equations. These equations are used to study the finite oscillations of massive radiative models with masses 10M and 30M in which the effects of radiation pressure are expected to be important.Models with two different degrees of equilibrium are chosen: an equilibrium (i.e., dynamically stable) model with an initial asymmetric inward velocity, and a nonequilibrium model with a nonequilibrium central temperature and which falls inwards from rest. For each of these two degrees of equilibrium, two initial configurations are considered: rotating spheroidal and nonrotating spherical models.From the numerical integration of the differential equations for these models, we obtain the time evolution of their principal semi-diametersa 1 anda 3, and of their central temperatures, which are graphically displayed by making plots of the trajectories in the (a 1,a 3) phase space, and of botha 1 and the total central pressureP c against time.It is found that in all the equilibrium radiative models (in which radiation pressure is taken into account), the periods of the oscillations of botha 1 andP c are longer than those of the corresponding nonradiative models, while the reverse is true for the nonequilibrium radiative models. The envelopes of thea 1 oscillations of the equilibrium radiative models also have much longer periods; this result also holds for the nonequilibrium models whenever the envelope is well defined. Further, as compared to the nonradiative models, almost all the radiative models collapse to smaller volumes before rebouncing, with the more massive model undergoing a larger collapse and attaining a correspondingly larger peakP c.When the mass is increased, the dynamical behavior of the radiative model generally becomes more nonperiodic. The ratio of the central radiation pressure to the central gas pressure, which is small for low mass models, increases with mass, and at the center of the more massive model, the radiation pressure can be comparable in magnitude to the gas pressure. In all the radiative models, the average periods as well as the average amplitudes of both thea 1 andP c oscillations also increase with mass.When either rotation or radiation pressure effects or both are included in the equilibrium nonradiative model, the period of the envelope of thea 1 oscillations is increased. The presence of rotation in the equilibrium radiative model, however, decreases this period.Some astrophysical implications of this work are briefly discussed.  相似文献   

20.
To form the Hubble diagram for quasi-stellar objects (QSOs),we have made use of the recently published data on X-ray fluxes of 159 QSOs observed from the Einstein Observatory. The scatter in the Hubble diagram and the lack of an obvious redshift-flux density correlation for these QSOs have been attributed to the observational selection effect that the intrinsically less luminous QSOs can be detected only in the nearby region of space. When the optical, radio and X-ray selection effects are removed, keeping only the intrinsically brighter sources, we obtain a sample of 16 QSOs having a small dispersion in X-ray luminosities (〈 logL x〉) = 46.12 ± 0.28), a statistically significant linear correlation between (logf x, logcz) pairs and a slopeA =-1.906 ± 0.061 of the linear regression oflog f x on logcz. This slope is consistent, at a confidence level of 95 per cent or greater, with the slope of-2.0 expected theoretically based on the assumption that the redshifts of QSOs are cosmological in nature.  相似文献   

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