INFLUENCE OF THE TEMPERATURE PROFILE ON THE MAGNETOHYDRODYNAMIC MODESOF A PROMINENCE-CORONA SYSTEM

To explain the observational evidence gathered during recent years abo ut periodic oscillations in quiescent solar prominences, the modes of oscillation of some theoretical models for solar prominences have been studied. The main drawback of these models is the lack of a realistic temperature profile for the prominence-corona system, which should be obtained from the coupling between magnetostatics and energetics once the physical properties of the prominence and the prominence-corona t ransition region (PCTR) are known. However, this seems to be far from our present possibilities since there is a lack of knowledge about the physical processes occurring in both. To make further progress in the study of MHD waves in prominences, we have adopted an ''ad hoc'' temp erature profile that can be adjusted to give different runs of the tem perature, from prominence to coronal values. This profile allows us to modify the thickness of the PCTR while modifying the steepness of the temperature variation within it. Also, by including this profile in t he model proposed by Poland & Anzer, we are able to construct an equil ibrium model for the prominence-corona system and to study the linear, adiabatic MHD waves of such configuration. Among the results obtained we highlight that the presence of a PCTR does not eliminate the subdi vision of modes into hybrid, external, and internal and that its exist ence is linked to the presence of two temperature plateaus. A change i n the thickness of the PCTR produces a modification of the mode freque ncy and also affects the horizontal velocity component of internal mod es by diminishing its amplitude in the prominance region. For a thin P CTR, because of the velocity amplitude inside the prominence, the mode s likely to be detected in prominence oscillations are the internal an d hybrid ones, although as a consequence of the effect already pointed out, the existence of a thick PCTR could make difficult or even impos sible the detection of internal modes. In summary, our results point o ut the importance of the PCTR to the oscillations of quiescent solar p rominences and to the identification of modes through the amplitudes o f the eigenfunctions in the prominence. This indicates the strong need for accurate knowledge of the physical properties of this region, in order to be able to make accurate theoretical predictions about the am plitudes and frequencies of oscillations in quiescent prominences. Pro bably, that knowledge can be obtained in the near future by means of t he UV instruments of the SOHO spacecraft.