Study of stellar flares

Includes bibliographical references (pages 40-41)Kepler observations revealed that many sun-like stars produce flares that are much greater strength in terms of total luminosity visual wavelengths compared to solar flares. It is well known that energy released in solar flares is stored in the magnetic field structures which are anchored to sun through sunspots. Powerful flares that are produced at locations of greater energy storage that often manifest in more light output. As such, relation between the sunspot area and flare productivity have been observed since long. Since the flares occur at the locations of flux emergence, it is possible to relate the fluctuation in spot area with flare productivity. Assuming that the stellar flares occur due to similar processes as solar flares, we have investigated superflares data that are taken from the Kepler catalog in order to find relationship between the flare frequencies with spot activity. We measured the flare frequencies by counting the number of flares produced by the star during an observing quarter. The amplitude of the light curve is estimated by computing the contrast, which is due to the passage of star spot on stellar disk. Larger mean contrast would be produced by bigger star-spots, which is a measure of surface magnetic field. The standard deviation of mean contrast is used as a measure of fluctuating field resulting from flux emergence. We examine the relationship between the amplitude of the light curve and its change with the flare frequency. Our results show that the flare frequency of a star increase with the contrast of the light curve observed with Kepler instrument. This shows that the large stellar flares are produced at the locations of greater magnetic field reserve. Dependence of flux emergence in flare frequency is less obvious.\ud In the second part of our research, we investigated Kepler IDs pre- flare dips. We observed ten stellar flares with pre- flare dip on Kepler device. We found that the flare amplitude increase with the pre- flare dip flux, however, this is not a reliable result as relativity we do not have enough data