ილიას სახელმწიფო უნივერსიტეტი
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ილიას სახელმწიფო უნივერსიტეტი
დოქტორანტის სახელი და გვარი: ეკა გურგენაშვილი
ფაკულტეტი: საბუნებისმეტყველო მეცნიერებებისა და მედიცინის ფაკულტეტი
ხელმძღვანელი ილიაუნი: თეიმურაზ ზაქარაშვილი
ხელმძღვანელი გოტინგენი: ანსგარ რაინერსი
Besides the Schwabe 11year cycle, solar activity undergoes temporal variations of shorter and longer time scales. Short-term variations of 155-200 days known as Rieger-type periodicity occur in many indices of solar activity (Rieger et al. 1984, Oliver et al. 1998, Zaqarashvili et al. 2010a). Previous studies revealed that the Rieger-type periodicity appears/disappears in different solar cycles and has different value in various activity indices. Our recent analysis of long-term sunspot data showed that observed Rieger periods correlate with solar cycle strength: stronger cycles show shorter periods and this periodicity is smaller in more active hemisphere in each cycle (Gurgenashvili et al. 2016, 2017). Observed correlation of Rieger periodicity with the solar activity strength suggests that the periodicity is related to the dynamo layer in the solar interior. Several mechanisms have been proposed to explain the Rieger-type periodicity, but most promising explanation seems to be connected with Rossby waves.
Recent Kepler and CoRoT space missions collected huge amount of data about stellar activity, which gives an excellent basis to search for the Sun-like periodicities on other stars. Variation of magnetic activity of solar-like stars is known for a long time. Several stars showed shorter-term variations, which are in the range of Rieger periodicity on the Sun (Lanza et al. 2008, Bonomo and Lanza 2012). We aim to analyze the light curves of solar-type stars from Kepler and CoRoT missions in order to search the Rieger-type periodicity in activity.
Observed periodicities on solar-like stars with different rotational periods are very important to understand the development of dynamo activity over the stellar evolution. Magnetic field strength in the solar and stellar dynamo layers, where the magnetic field is generated, is crucial to understand which dynamo model is responsible for activity cycles. However, direct measurement of the magnetic field in solar/stellar interiors is impossible; therefore invoking of indirect methods is necessary to make some estimation. As the Rieger periodicity might correspond to magnetic Rossby waves in the dynamo layer then the observed periods can be used to probe the internal magnetic field. Then the observed and the theoretical periods can be combined to find the strength of dynamo magnetic field on the Sun and solar-like stars at different phase of evolution. Finally, the field strength will be used to test different dynamo models and follow the development of the dynamo process through the stellar evolution.
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