A momentum distribution of high energy particles around Crab pulsar

We determine the momentum distribution of the relativistic particles near the Crab pulsar from the observed X- and -ray spectra (10³10⁹ eV), provided that the curvature radiation is responsible for it. The power law spectrum for the relativistic electrons,f() ^–5, reproduces a close fit to the observed high-energy photon spectrum. The theoretically determined upper limit to the momentum (due to radiation damping), _M 8×10⁶, corresponds to the upper cut-off energy of the -ray spectrum, 10⁹ eV. The lower limit to the momentum, _m 1.8×10⁵, is chosen such that flattening of the X-ray spectrum below 10 keV is simulated. The number density of these electrons is found to be much higher than the Goldreich-Julian density. We also discuss pulse shape and polarization of high-energy photons. The extremely high density of particles and the steep momentum spectrum are difficult to understand. This may imply that another, more efficient, mechanism is in operation.     

Evidence for a low-density inflationary universe?

The inflationary unvierse model predicts the density parameter ₀ to be 1.0 with the cosmological constant ₀ usually taken to be zero, whereas observational estimates give ₀0.2 and ₀10^-57 cm^–2. It was found, however, that the observed variation of angular diameter with redshift for extragalactic radio sources could be interpreted in terms of a low density universe with linear size evolution of the sources for either an inflationary model with 0 or an open model with =0.     

Quasi-stationary solar wind in ray structures of the streamer belt

It is shown on the basis of analyzing the LASCO/SOHO data that the main quasi-stationary solar wind (SW), with a typical lifetime of up to 10 days, flows in the rays of the streamer belt. Depending on R, its velocity increases gradually from V3 km s^–1 at R1.3 R to V170 km s^–1 at R15 R . We have detected and investigated the movement of the leading edge of the main solar wind at the stage when it occupied the ray, i.e., at the formative stage of a quasi-stationary plasma flow in the ray. It is shown that the width of the leading edge of the main SW increases almost linearly with its distance from the Sun. It is further shown that the initial velocity of the inhomogeneities (`blobs') that travel in the streamer belt rays increases with the distance from the Sun at which they originate, and is approximately equal to the velocity of the main solar wind which carries them away. The characteristic width of the leading edge of the `blob' R , and remains almost unchanging as it moves away from the Sun. Estimates indicate that the main SW in the brightest rays of the streamer belt to within distances at least of order R3 R represents a flow of collisional magnetized plasma along a radial magnetic field.     

The effect of chemical abundance oscillations on the pulsational properties of A 5M ⊙ hydrogen-helium star

A model of a first generation intermediate star of 5M , with Z=0 has been considered. The model is at an advanced stage of its evolution and has a double shell burning. It burns helium in the inner shell, and hydrogen, via CNO cycle, in the outer shell. =(log/log) _T and _T =(log/logT) were computed allowing for the oscillations of the relative mass abundance of the reagents in nuclear reactions. Including =(log/log) _T and =(log/logT) of mean molecular weight and the effect of the oscillations of abundances due to nuclear reactions, stability was studied. Contrary to the results of the static calculations, we found that instability due to the excitation mechanism provided by the high temperature sensitivity of energy generation rate propagates up to the surface. Thus the model in question was found to be unstable against radial adiabatic pulsations, in its fundamental mode.     

Effects of mass transfer on the unsteady free convection flow past an accelerated vertical porous plate with variable suction

An exact analysis of the effects of mass transfer on the flow of a viscous incompressible fluid past an uniformly accelerated vertical porous and non-porous plate has been presented on taking into account the free convection currents. The results are discussed with the effects of the Grashof number Gr, the modified Grashof number Sc, the Schmidt number Sc, and the suction parametera for Pr (the Prandtl number)=0.71 representating air at 20°C.Nomenclature a suction parameter - C species concentration - C species concentration at the free stream - g acceleration due gravity - Gc modified Grashof number (vg^*(C –C )/U ₀ ³ ) - Pr Prandtl number (C _p/K) - T temperature of the fluid near the plate - T dimensionless temperature near the plate ((T-T )/(T -T )) - U(t) dimensionless velocity of the plate (U/U ₀) - v normal velocity component - v ₀ suction/injection velocity - x, y coordinate along and normal to the plate - v kinematic viscosity (/gr) - C _p specific heat at constant pressure - C _w species concentration at the plate - C non-dimensional species concentration ((C-C )/(C _w -C )) - Gr Grashof number (g(T _w -T )/U ₀ ³ ) - D chemical molecular diffusivity - K thermal conductivity - Sc Schmidt number (/D) - T _w temperature of the plate - T free stream temperature - t time variable - t dimensionless time (tU ₀ ² /) - U ₀ reference velocity - u velocity of the fluid near the plate - u non-dimensional velocity (u/U ₀) - v dimensionless velocity (v/U ₀) - v ₀ non-dimensionalv ₀ (v ₀ /U₀)=–at^–1/2 - y dimensionless ordinate (yU ₀/) - density of the fluid - coefficient of viscosity     

Massive accretion disks

Recent high resolution near infrared (HST-NICMOS) and mm-interferometric imaging have revealed dense gas and dust accretion disks in nearby ultra-luminous galactic nuclei. In the best studied ultraluminousIR galaxy, Arp 220, the 2m imaging shows dust disks in both of the merging galactic nuclei and mm-CO line imaging indicates molecular gasmasses 10⁹M for each disk. The two gas disks in Arp 220 are counterrotating and their dynamical masses are 2×10⁹ M , that is, only slightly largerthan the gas masses. These disks have radii 100 pc and thickness 10-50 pc. The high brightness temperatures of the CO lines indicatethat the gas in the disks has area filling factors 25-50% and mean densitiesof 10⁴ cm^-3. Within these nuclear disks, the rate of massive star formation is undoubtedly prodigious and, given the high viscosity of the gas, there will also be high radial accretion rates, perhaps 10 M yr ^-1. If this inflow persists to very small radii, it is enough to feed even the highest luminosity AGNs.     

A Molecular Ring in the Liner Ngc 5218

High resolution OVRO CO 1–0 observations of the inner 30 in the LINER galaxy NGC 5218 reveal the presence of a double centrally peaked molecular concentration with extensions out to a radius of 12. The molecular mass detected is 2.4 × 10⁹ M and the gas surface density is high, 3000 M pc square in the inner 500 pc. The SFR is 2–3 M yr^–1 and the SFE is 13, which are low or moderate values for that gas surface density. We interpret the inner feature as a rotating molecular ring with a radius of 200 pc. We furthermore suggest that the LINER activity in NGC 5218 is not caused by an aging starburst, but by a buried AGN.     

Lunar properties from transient and steady magnetic field measurements

The electrical conductivity of the lunar interior has been determined from magnetic field step transients measured on the lunar dark side. The simplest model which best fits the data is a spherically symmetric three layer model having a nonconducting outer crust of radial thickness 0.03R _moon; an intermediate layer of thicknessR0.37R _moon, with electrical conductivity ₁ 3.5 × 10^–4 mhos/m; and an inner core of radiusR ₂ 0.6R _m with conductivity ₂ 10^–2 mhos/m. Temperatures calculated from these conductivities in the three regions for an example of an olivine Moon are as follows: crust, < 440 K; intermediate layer, 890 K; and core, 1240 K. The whole-moon relative permeability has been calculated from the measurements to be/ ₀ = 1.03 ± 0.13. Remanent magnetic fields at the landing sites are 38 ± 3 at Apollo 12, 43 ± 6 and 103 ± 5 at two Apollo 14 sites separated by 1.1 km, and 6 ± 4 at the Apollo 15 site. Measurements show that the 38 remanent field at the Apollo 12 site is compressed to 54 by a solar wind pressure increase of 7 × 10^–8 dynes/cm².National Research Council Postdoctoral Associate.     

A Razin-Tsytovich effect for bremsstrahlung

It is shown that bremsstrahlung from electrons with Lorentz factor 1 is suppressed for >_p in a plasma with plasma frequency _p compared with emission in vacuo. For _p the ratio of the power emitted per unit frequency in the plasma to that in vacuo varies as ².This suppression effect is analogous to the suppression of synchrotron radiation in a plasma (Razin-Tsytovich effect). It is argued that such suppression is a characteristic property of emission by relativistic particles in a plasma.     

The photometric solution of cc com by use of the

The contact binary system CC Com (=12^h09^m33^s.8, =+22°4339, (1950);V _max=11.31, (B-V)_max=1.24) is a W UMa-type system with the shortest known period. The photometric solution of CC Com is presented using the Wilson and Devinney method. The results show that the CC Com belongs to the late-type eclipsing binary with the spectral type K5V and K6V, low temperatureT ₁=4300 K,T ₂=4265 K, the mass ratioq=0.5873±0.0021, and the inclinationi=87°.719±1°.44. The best regions of the gravity darkening exponents , the bolomotric albedov, and the limb-darkening coefficients are tested. It is found that 0.1250.065, 0.1v0.5, =0.5 are better regions for CC Com. The third body ofl ₃ is not found to be significant. The results are combined with the spectroscopic results of Rucinski to provide an estimate of the absolute parameters.     

Alfvén instabilities in streaming plasmas with anisotropic pressures and their relevance for the solar wind

Low frequency or Alfvén waves in streaming plasmas can become unstable when the square of the Alfvén velocity is smaller than the mean square of the bulk motion in a co-moving reference frame, (u –u )², whereu stands for the bulk velocity of each species and u is the average bulk velocity of the plasma as a whole. For these new Alfvén instabilities the streaming effects can be enhanced by a suitable pressure anisotropy. Perpendicular pressure effects are stabilizing, parallel pressure effects are destabilizing, as in the usual firehose instability. The observed velocity differences between helium and the main (hydrogen) flow in the solar wind plasma are such that the Alfvén waves are getting close to marginal instability. These new Alfvén instabilities limit the velocity differences between helium and hydrogen and thus provide a possible mechanism for accelerating the helium particles up to the order of the main flow velocity.     

Detection of background gravitational radiation by Doppler tracking of spacecraft

Low-frequency gravitational radiation, with wavelengths reaching or exceeding interplanetary distances, and with a mean energy density of the order of the critical cosmological density _c , generates a frequency-shift of order/10^–15 h ₀(1/10⁸km)(/ _c )^1/2 in electromagnetic signals transponded by interplanetary spacecraft at a distancel from the Earth.     

Effects of metal abundances on the evolutionary period changes of classical Cepheids

Some peculiarities in the behaviour of a model self-gravitating system described by hydrodynamical equations and isothermal equation of state connected with the presence of thermodynamical fluctuations in real systems were investigated in numerical experiment. The values of density and velocity , , respectively, were computed by numerical code perturbed on each time-step and in each computational cell by random values , for modeling such fluctuations. Perturbed values _i = _i + _i ,v _i = _i + v _i were used to initiate the next step of computations. This procedure is equivalent to an introduction into original hydrodynamical equations of Langevin sources which are random functions. It is shown that these small fluctuations (= v =0,² =v ² = 10^–8) grow many times in marginally-stable state.     

Statistical survey of planetary nebulae: Distances,masses, and distribution in the galaxy

On the basis of empirical (D)-dependency at the frequency of 5 GHz constructed using 15 planetary nebulae with the independently measured distances (10^–171×10^–20 W m^–2 Hz^–1 ster^–1), we evaluated distances of 335 objects. Independent evidence of the correctness of the accepted scale are given. Then(D)-dependency is constructed and it is shown that atD<0.08 pc the mean electron density is higher than the one determined by the Seaton method. We showed that the filling factor diminishes with the increase of the PN diameter (1 atD0.08 pc and 0.2 atD0.4 pc). the ionized mass of 33 PNs is determined. With the diameter increase the ionized mass grows and atD0.4 pc reaches the valueM0.07M . We used the new distance scale when investigating the space distribution of PNs. The mean scale height =130±15 pc and the mean gradient of the change of surface densitym=0.37, which allowed us to estimate the total number of nebulae in the GalaxyN4×10⁴. We divided the PNs according to their velocities (withV _LSR>35 km s^–1 andV _LSR<35 km s^–1) and permitted us to confirm that the PN belong to different sub-systems of the Galaxy. The estimated local formation rate of PNs [=(4.6±2.2)×10^–12 pc^–3 yr^–1] is a little higher than the one of the white dwarfs. That can be explained by a large number of PNs having binary cores, which used in our sample. The statistical estimation of PN expansion velocity showed thatV _ex increases from 5–7 km s^–1 (atD0.03 pc) to 40–50 km s^–1 (atD0.8 pc).     

Spatial density fluctuations in the radiation era of the Universe

It is shown that in the radiation era of the Universe spatial temperature fluctuations (T/T)<10^–5 in the cosmic plasma lead to huge changes of the density up to (/)10⁴. This effect results from the fact that the cosmic plasma in the radiation era can be considered as a general relativistic Boltzmann gas which is found in the very vincinity of equilibrium.     

(Super) cosmological solution for the Kasner model

In the theory of supergravity (N=1), the supersymmetric version of general relativity, and for the Kasner cosmological model (Bianchi type I) we find a non-trivial solution (for the metric and spinor-vector) under the most simple assumption =₁₁ + ₂₂; ₁₂+₂₁=0 and for a special choosed gaugeN=1,N ^j=0, ₀=0. This method could be also applied to other cosmological metrics and extended to enlarged Grassmann basis.O. Obregón was partially supported by the Alexander von Humboldt Stiftung.     

Quantum effects in cyclotron plasma absorption

It is shown that X-ray radiation of neutron stars with magnetic fieldsB=10¹¹–10¹³ G near cyclotron resonances=s _B (s=1,2,...) is deeply affected by such quantum effects as electron-positron vacuum polarization (significant at V=3×10²⁸ n _e ^–1 (B/B _C ⁴)1, whereB _C =4.4×10¹³G), the quantizing character of the magnetic field (significant atV=3 x 10²⁸ n _e ^–1 (B/B _c)⁴1 whereB _c =4.4 x 10¹³G), the non-harmonic character of the Landau levels, and the quantum recoil of electrons. The latter two factors shift the resonances by the frequency –s ² _B (B/2B _c )sin², being the angle between the direction of radiation propagation and the magnetic field. IfVV ₀ (for 1,V ₀^–1=(mc ²/2T)^1/2), the normal mode (NM) polarizations, as well as the absorption coefficientk ₁ of the extraordinary NM in the Doppler core of the first resonance (|–| _B cos ), is only slightly affected by varyingb and/orV, whereas for the ordinary NM (at 1)k ₂k ₁ ²[b + (3 + tan²–2V)²]k ₁. For sufficiently largeb and/orV the quantum effects amplify resonant absorption of the ordinary NM at _B , with spin-flip transitions playing a major role atb1+V ². IfVV ₀, the coefficientsk ₁ andk ₂ in the Doppler core of the resonance are of the same order and acquire some peculiar features (shifts, intersections, etc.), with the NM polarizations depending sharply on and being strongly non-orthogonal. AtVV ₀,k ₂=k ₁(cos² +B/2B _C ) and the polarizations are almost linear. Near high resonances (s2), as a rule,k _1,2(1 + b) ^{s–1 2s–3} i.e., absorption increases withb due to replacement of the thermal energy of the transverse motion of electron,T, by the magnetic energy _B . The above effects should be taken into account for an interpretation of observational data on X-ray pulsars (e.g., Her X-1) and other X-ray sources associated with neutron stars.     

Compton scattering of relativistic electrons in compact X-ray sources

The problem of single Compton scattering is considered and the resulting spectrum, angular distribution and polarization of scattered photons in a general case are obtained. The inverse Compton scattering (ICS) for arbitrary energies of electronsE and photons ₀ is investigated in detail. In the case of isotropically-distributed initial photons and relativistic electrons, a strong rise of the scattered spectrum near the upper edge takes place, starting from the values of the characteristic parameterb4E ₀10 (in units of mc²=1). The energy-loss rate of relativistic electrons due to ICS is calculated. It is shown that the relativistic electrons of the energiesE100 MeV, when scattering on the X-rays with ₀~10KeV, transmit the dominant part of their energy to the photons which fall after scattering into the energy range of the electrons (100 MeV).The radiation spectrum of ICS, as well as the energy-losses of relativistic electrons distributed by power-lawE ^–, are calculated. The radiation spectrum reveals the power-law behaviour with the different indices in two limits: the dependence ^–(1)/2 at ₀1 gradually changes to ^–(+1) ln (₀) law for ₀1.     

B,V surface photometry of the UV continuum galaxy NGC 838

Surface photometry of the UV continuum galaxy NGC 838 has been carried out in theB, V system using photographic plates obtained with the 74 Kottamia telescope, Egypt. Isophotes, luminosity profiles, integrated photographic magnitudes, effective diameters and other photometric parameters are derived.The photoelectrically calibrated total apparent magnitudes areB _T =13.57 with maximum diameters 1.57×1.34 (at threshold _m =27.7 mag.//) andV _T =12.91 with maximum diameters 1.54×1.32 (at threshold _m =27.7 mag./). The integrated colour index(B–V) _T =0.66 and the effective surface brightness _e (B=19.0 mag./) and _e (V=19.7 mag./. The major axis is at position angle =85°±1°.The nucleus of NGC 838 is quite blue (integrated colour(B–V)=0.41 forr ^*<0.1) compared to normal galaxies while the colour becomes redder from the nucleus outwards. The UV excess, H emission and radio continuum emission previously observed from this galaxy by other investigators may be attributed to a recent burst of star formation in the nucleus of the galaxy of duration slightly greater than 2×10⁷ yr.     

Solar particle propagation from 1 to 5 AU

A statistical analysis of solar particle events, observed by the GSFC-UNH charged particle detector on board Pioneer 10 and Pioneer 11 from March 1972 to December 1974 (from 1 to 5 AU for each spacecraft), is carried out with the goal of experimentally determining the statistical average interplanetary propagation conditions from 3 to 30 MeV. A numerical propagation model is developed that includes diffusion with a diffusion coefficient of the form k _r =k _o r , convection, adiabatic deceleration, and a variable coronal injection profile. The statistical analysis is carried out by individually analyzing each of five parameters (t _max, (t_max), t ₅, ) that are uniquely defined in a solar particle event. Each of the five parameter data sets were analyzed in terms of both a spacecraft-solar flare connection longitude 50°, and a numerical model that employed a variable exponential decaying coronal injection profile.The five individual parameter analyses are combined with the results that the statistical average radial interplanetary diffusion coefficient from 1 to 5 AU is given by k _r = (1.2 ± 0.4) × 10²¹ cm² s^-1 with = 0.0± 0.3 for 3.4 to 5.2 MeV protons and k _r = (2.6 ± 0.6) × 10²¹ cm² s^-1 with () = 0.0± 0.3 for 24 to 30 MeV protons. Using the classical relationship for the radial scattering mean free path _r, i.e. k _r = _r/3, we obtain _r = 0.09 ± 0.03 AU and 0.075 ± 0.020 AU for the low and high energy data, respectively. These results show, from 1 to 5 AU and from 3 to 30 MeV, that _r is both independent of radial distance and approximately independent of rigidity (for _r~P , where P = rigidity, = -0.15 ± 0.20).The above diffusion coefficients are inconsistent With both the predictions of the diffusion coefficient from present theoretical transport models and with the diffusion coefficient used in modulation studies at low energies.