Yu-Hsiang Weng(Graduate institute of astronomy, National Central University); Wing-Huen Ip(Graduate institute of astronomy, National Central University;Graduate Institute of Space Science, National Central University;3Space Science Institute, Macau University of Science and Technology);Li-Ching Huang(Graduate institute of astronomy, National Central University);Chia-Lung Lin(Graduate institute of astronomy, National Central University)
An important finding of the Kepler space telescope is the discovery of super flares whose energy could exceed that of the largest solar flare (i.e., the Carrington event ~10**33 ergs) ever recorded by a factor of 10-100 in the case of M-dwarfs and up to a factor of 10**4 for Gtype stars (Maehara et al., APJ 2012). The coronal mass ejections (CMEs) are believed to be able to cause severe erosion of the planetary atmosphere effects, thus limiting the habitability of super-Earths in close orbital distances (Lammer et al. 2007 Astrobiology ; Tarter et al. 2007 Astrobiology). We follow the analytical treatment of Khodachenko et al. (2007 Astrobiology) in estimating the impact probability of coronal mass ejections of a number of habitable exoplanets identified in Armstrong et al. (MNRAS, 455, 3110, 2016). These include Kepler-442, Kepler-62, Kepler-186, Kepler-438, Kepler-452, Kepler-1229, Kepler-1638 and others. There are several steps. The first step is to examine their light curves from Kepler observations. The second step is to evaluate the corresponding flare frequency distributions according to the light curve data. For those stars without flares, an upper limit of the flare frequency distributions may be set by using the rotation-age-activity relation. The third step is to estimate the CME impact frequency of individual exoplanets according to geometrical consideration and morphological models of the stellar CMEs. As a final step, such a method will permit us not just to assess the present space weather conditions but also the possible evolutionary histories of the astrobiological environments of these habitable exoplanets. We revisited the flare activities of several habitable-exoplanet hosting stars identified in Armstrong et al. (MNRAS,455,3110,2016). These included the different spectral types from M-types to G-types. As we known, flares hit the exoplanets with the energy around 7.9E33 ergs which is 10 times powerful than the radiative energy of a Carrington-class solar flare. Due to the radius of the exoplanet surrounding by these seven stars are small, that is, the irradiation to the exoplanet must be large. So, we are curious about how much energy will received by exoplanet per year. In this study, we will find the flare frequency and scale the hitting energy with calculated hitting probability, and discuss whether the exoplanet is habitable or not by the gyro chronology relation.