Yazar "Karafistan, A. I." seçeneğine göre listele

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    Öğe
    A magnetohydrodynamic model applied to the lower convective region in the Sun
    (Oxford Univ Press, 2007) Cavus, H.; Karafistan, A. I.
    We have investigated the effects of a toroidal-type magnetic field of 10 T (10(5) G), in the lower convective region of a standard solar model. From the numerical solution of the magnetohydrodynamic (MHD) equations, distributions of some physical variables are obtained in spherical coordinates for this layer. It is shown that the most important feature of this type of magnetic field is to break the spherical symmetric distribution of density and alter its compressibility with respect to latitude. This type of magnetic field does not change much the density of the reference model, and the resulting flux is also comparable to that found in other research. It is further shown that the MHD plasma acts as incompressible at the poles, in contrast to the perfect fluid behaviour at the equator. As a result we have estimated the limits and applicability of the anelastic and Boussinesq approximations for this layer. Thus our results might be useful, especially in simplifying the numerical integration schemes related to the lower convection zone in the Sun.
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    On the effect of magnetic field on the low-l solar p-mode oscillations
    (Elsevier Science Bv, 2010) Cavus, H.; Karafistan, A. I.
    One of the possible magnetic field effects on the stellar pulsations is known to be a splitting in the observed frequencies. Using this knowledge in the solar convection zone, there are two aims in this work Considering the Sun as an incompressible fluid, our first objective was to investigate the variation of the physical parameters in the 30% outermost convective solar layer, during a pulsation period. The second purpose was to calculate, by means of the spherical harmonics, the shifts on the low-l p-mode frequencies which could be caused by the presence of the magnetic field in the Sun. The first order perturbation approximation was used in order to calculate analytically the resulting frequency shifts and the small perturbations on the magnetic field, as well as the physical parameters, such as density, pressure and temperature, of a Standard Solar Model excluding both rotation and magnetic field (Christensen-Dalsgaard et al., 1996) in the unperturbed equilibrium case. (C) 2010 Published by Elsevier B.V.
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    On the Modelling of Rotational Effects in the Lower Convective Region of the Sun
    (Springer, 2010) Cavus, H.; Karafistan, A. I.
    The purpose of this work is to study effects of differential rotation in the lower convective region of the Sun. Similar to MHD case; the governing equations are separated in variables, allowing numerical integration in this layer. This algorithm facilitates solutions of more complicated systems, with less computing time. Two different known rotation profiles are used in order to fit the model. The fitting procedure is accomplished by making use of sphericity and density shape parameters related to the rotation profiles. It is also shown that the most important feature of rotation is to break the spherical symmetric distribution of density in this layer. As in the MHD effects found before, differential rotation changes considerably the density of the reference model for both cases.
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    Öğe
    Some MHD solutions for the bottom of the solar convective layer
    (Astronomical Soc Pacific, 2007) Cavus, H.; Karafistan, A. I.
    The magnetic field responsible for the solar activity is stored in the base of the convective zone. Applying this knowledge to the bottom of the convection zone in the Sun our objective was to investigate some magnetohydrodynamical (MHD) solutions. The first order perturbation approximation was used in order to calculate the small perturbations on the physical parameters of a Standard Solar Model (SSM) excluding both rotation and magnetic field (Christensen-Dalsgaard et al. 1996) in the unperturbed equilibrium case. The validity of each approximation is tested and examined from the SSM. The MHD results thus obtained are presented graphically and compared with those of the SSM.