مدولاسیون پریود مداری با فعالیت مغناطیسی در ستارگان کوتاه پریود RS CVn
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: فیزیک
PHYSICAL DESCRIPTION
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۱۱۴ص
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چاپی
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فاقداطلاعات کامل
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دکتری تخصصی Ph.D))
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فیزیک - اخترفیزیک
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۱۳۸۷/۰۶/۲۵
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تبریز
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Eclipsing variables are excellent laboratories for studying a wide variety of processes in stellar astrophysics. These objects offer probes of tidal dissipation, mass transfer or loss, angular momentum transfer or loss, magnetic activity, and stellar evolution. Clearly, their usefulness extends far beyond their text-book role in the determination of stellar masses and radii. This usefulness largely derives from the fact that precision measurements can be made. The careful timing of eclipses can reveal orbital period changes of order a part in ۱۰۵-۱۰۶ because deviations from an assumed ephemeris can build up over many orbits, and many systems have observational records spanning decades or more. These observational records reveal a surprising result: systems which show period changes of alternating sign (orbital period modulations) are common.he decade time scale and lack of strict periodicity of the orbital period modulations suggests that they might be a manifestation of magnetic activity. Orbital period modulations only occur in those systems which possess all of the ingredients of a dynamo. The magnetic fields of the Sun and other stars are thought to be the result of magnetic dynamo action occurring in their convective envelopes or at the interface between their convective envelopes and radiative cores. Magnetic activity results from the interplay between differential rotation and cyclonic convection. Orbital period modulation can be a powerful tool for studying stellar magnetic activity because the mechanism that produces the period change depends on the magnitude of the subsurface magnetic field. The observed amplitude and period of orbital period modulation can be used to determine the mean subsurface field strength. These measurements, not possible by any other technique, will provide important constraints on dynamo models of magnetic activity.The RS CVn short period eclipsing binaries (with orbital period less than one day) are chromosphericaly actives. Researches of these binaries in both photoelectric and spectroscopic data in different ranges of the spectrum indicate the coronal and chromospheric activity as general characteristic of these eclipsing binary systems. In the present study, the photoelectric data and times of minima of selected short period RS CVn systems have been presented. The (O-C) curves derived from these data, has been analyzed by Kalimeris method, and fast furier transform method to find the possible orbital modulations. Long-time luminosities and color indices variations of these eclipsing binaries have been derived. It has been shown that the Applegate mechanism (magnetic cycle) can explain the period changes of these systems with various period of modulations in the time range of decades.The appropriate selections are as follows:SV Cam, RT And, CG Cyg, XY Uma, WY Cnc, ER Vul, BH Vir, UV Psc and BX And