مجله پژوهش فیزیک ایران
سال نهم شماره 3 (پاییز 1388)

cosmic ray tracking telescope has been made for the measurement of cosmic rays from different directions, especially those received from the sun direction. Our observations by the telescope shows a noticeable deficiency in the detected number of cosmic rays entering the telescope when its axis was pointing to the sun compared to that entering the telescope with no sun in its field of view. The statistical significance of this deficit with the Li and Ma method stands near 2σ for all of our observations.

We investigate the influence of longitudinal structuring on the fast kink modes of the coronal loops oscillations. Using a simple longitudinal exponential density structure, an analytical dispersion relation is derived. The properties of oscillatory periods and mode profiles and their deviations for such stratified structure are compared with those of the homogeneous tubes. Also, the effects of negative scale heights and total mass column on oscillation and mode profiles of the loops are investigated. Here we confirmed that the shift of the antinodes and mode profiles and the ratio of the frequencies are potentially good tools to estimate the density scale heights of the solar atmosphere.

In this paper, we have considered that the strange-star consists of quark matter from its center to surface. For quark matter, we have used two models, the MIT bag model and string-flip like model. In the bag model, the energy of the system has been considered the kinetic energy of the particles of system in addition to a constant B. We have considered two states for B, one of them is constant and the other one is density dependent. The second state has been obtained from the recent Cern data from quark-geleon plasma formation. In string-flip like model, the energy of the particles of the system has been obtained from the Schrodinger equation, where the Hamiltonian has been considered the sum of kinetic and potential energies. The potential in Hamiltonian is the general potential which depends on density that is the block potential. In the String-flip like model, the block potential is linear or square functions of the relative distance between two quarks. We have also obtained the equation of state of quark matter for all considered cases. Finally, we have computed the structure of the quark star using our equations of state.

In this work, we carry out self –similar solutions of viscous-resistive accretion flows around a magnetized compact object. We consider an axi-symmetric, rotating, isothermal steady accretion flow, which contains a poloidal magnetic field of the central star. The dominant mechanism of energy dissipation is assumed to be the turbulence viscosity and magnetic diffusivity due to the magnetic field of the central star. We explore the effect of viscosity, magnetic diffusivity and advection on a rotating disk. We show that dynamical quantities of advection dominated accretion flows (ADAFs) are sensitive to the advection, viscosity and magnetic diffusivity parameters.

Celestial positioning has been used for navigation purposes for many years. Stars as the extra-terrestrial benchmarks provide unique opportunity in absolute point positioning. However, astronomical field data acquisition and data processing of the collected data is very time-consuming. The advent of the Global Positioning System (GPS) nearly made the celestial positioning system obsolete. The new satellite-based positioning system has been very popular since it is very efficient and convenient for many daily life applications. Nevertheless, the celestial positioning method is never replaced by satellite-based positioning in absolute point positioning sense. The invention of electro-optical devices at the beginning of the 21st century was really a rebirth in geodetic astronomy. Today, the digital cameras with relatively high geometric and radiometric accuracy has opened a new insight in satellite attitude determination and the study of the Earth's surface geometry and physics of its interior, i.e., computation of astronomical coordinates and the vertical deflection components. This method or the so-called astrogeodetic vision-based method help us to determine astronomical coordinates with an accuracy better than 0.1 arc second. The theoretical background, an innovative transformation approach and the preliminary numerical results are addressed in this paper.

The solutions of photometric BV light curves for the Algol like system UV Leo were obtained using Wilson-Devinney code. The physical and orbital parameters along with absolute dimensions of the system were determined. It has been found that to best fit the V light curve of the system, assumptions of three dark spots were necessary; two on the secondary and one on the primary. The absolute visual magnitudes (Mv) of the individual components i.e., primary and secondary were estimated to 4.41 and 4.43, respectively, through the color curve analysis. The period analysis of the system presented elsewhere, indicated a cyclic period change of 12 yr duration, which was attributed to magnetic activity cycle, as a main cause of period variation in the system, through the Applegate mechanism. To verify the Applegate model I preformed calculations of some related parameters barrowed from Apllegate and Kalimeris. Values of all the calculated parameters were in accordance to those obtained for similar systems by Applegate. The differential magnitudes Δ B and Δ V, along with corresponding values of Δ(B-V) color index. The cyclic variations in brightness are quite clear. There are three predictions of Applegate's theory concerning effects of cyclic magnetic changes on the period variations, which can be checked through the observations, these are as follows: I) The long term variations in mean brightness (at outside of eclipses) and cyclic changes of orbital period, vary with the same period. II) The active star gets bluer as it gets brightened and/or the brightness and color variations are to be in phase. III) Changes in luminosity due to changes in quadrupole moment should be of the order 0.1 mag. All the above mentioned predictions of Applegate’s theory are verified. These results combined with cyclic character of P(E) presented elsewhere and also consistency of parameters which are obtained in this paper, led me to conclude that one the main causes of period variability in UV Leo system is magnetic activity cycle (newly presented here. Since both components (G0&G2) of this system magnetically can be active, and separation of the components is relatively low (3.9Rs), the magnetic braking could also cause the period change. The magnetized star winds move outward from the star, but are twisted due to rapid rotation of star. Charged particles in the stars wind become trapped in the star's magnetic field and are dragged along the field lines. The result is angular momentum (AM) transfer from the star by magnetic field to the charged particles. As the winds leave the star surface they are dragged by the magnetic field which in turn slows down the star's rotation.

As double layers (DLs) are one of the most important acceleration mechanisms in space as well as in laboratory plasmas, they are studied from different points of view. In this paper, the emitted power and energy radiated from charged particles, accelerated in relativistic cosmic DLs are investigated. The effect of the presence of additional ions in a multi-species plasma, as a real example of astrophysical plasma, is also investigated. Considering the acceleration role of DLs, radiations from accelerated charged particles could be seen as a loss mechanism. These radiations are influenced directly by the additional ion species as well as their relative densities.

In this paper we have analyzed the photometric data of LS DEL eclipsing binary system, which was W UMa one, in UBV filters. To solve light curves we use Wilson program 2003. We have found the darkening coefficients of the side by using Klinglesmith and Sobieski (1970) Algorithm in Van Hamme program. The results show that the system was a contacted one, and both primary and secondary components fill their limiting Roche lobe. The spectrums of primary and secondary components are F8V and F5V, respectively.

In the present work, the origin of antiprotons observed in cosmic rays (above the atmosphere) is analyzed in details. We have considered the origin of the primaries, (which their interactions with the interstellar medium is one of the most important sources of antiprotons) is a supernova type II then used a diffusion model for their propagation. We have used the latest parameterization for antiproton production cross section in pp collisions (instead of well known parameterization introduced by Tan et al.) as well as our calculated residence time for primaries. The resulted intensity shows the secondary antiprotons produced in pp collisions in the galaxy, have a high population as one can not consider an excess for extragalactic antiprotons. Also there is a high degree of uncertainty in different parameters.

RZ Cas is an Algol-type partial eclipsing binary, the secondary component of which has filled its Roche lobe. Its visual magnitude is 6.18 and its period is 1.195 days. The most important characteristics of RZ Cas are period change (due to mass transfer) and anomalies in the primary minimum of its light curve (due to δ Scuti pulsations). In this paper, light curves of RZ Cas are obtained using the Johnson's U, B, V, and R filters at Isfahan University Observatory, and B and V filters at Biruni Observatory of Shiraz University. Continuous photometric measurements have also been made to detect δ Scuti type pulsations. A new ephemeris and period is obtained: Min.I =HJD2453620.5500 + 1d.1952639 E, and a mass transfer rate of 1.5×10 -7 M⊙ yr -1 is estimated. None of the observed primary minima is flat as found by some observers before. The residuals from the observed minus computed light curves of the system give the pulsation light curves of the primary component. The frequencies of δ Scuti pulsation are searched for using the Period04 program. It is found that the dominant frequency is 65.5-68.5 cycle/day, corresponding to a period of 21-22 min.

Using measured radial velocity data of five double-lined spectroscopic binary systems EQ Tau, V376 And, V776 Cas, V2377 Oph and V380 Cygni, we find corresponding orbital and spectroscopic elements via the method introduced by Karami & Teimoorinia and Karami & Mohebi. Our numerical results are in good agreement with those obtained by others using more traditional methods.

Dynamics of stationary axisymmetric configuration of the viscous accreting fluids surrounding a non-rotating compact object in final stages of accretion flow is presented here. For the special case of thin disk approximation, the relativistic fluid equations ignoring self-gravity of the disk are derived in Schwarzschild geometry. For two different state equations, two sets of self-consistent analytical solutions of fully relativistic fluid equations are obtained separately. The effect of bulk viscosity coefficient on the physical functions are investigated for each state equation, as well as the bounds that exert on the free parameters due to the condition of accretion flow in the last stages. The solutions found show that the radial and azimuthal velocities, density and pressure of the fluid increase inwards for both state equations. Also, viscosity has no effect on the velocities and density distributions in both state equations. Two state equations show different types of behavior with respect to the bulk viscosity coefficient. For p=K state equation, if there is no bulk viscosity, the pressure remains constant throughout the disk, whereas with increasing bulk viscosity the pressure falls off in the inner regions but soon stabilizes at an almost constant value. However, for p=ρc2 state equation, the pressure is never constant, even in the absence of bulk viscosity. The larger the value of ηb, the higher the value of pressure in the inner regions.