Events in Physics
Monday, April 25, 2016
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Chloe Pugh & Petra KohutovaPS1282nd Year PhD student seminars Chloe Pugh: 'Kepler Observations of Quasi-periodic Pulsations in Stellar Flares' Abstract: Quasi-periodic pulsations (QPPs) in solar flares have been widely observed, and can be used as a coronal plasma diagnostics tool. More recently, QPPs have been observed in flares of other stars, many of which are thousands of times more powerful than anything observed on the Sun. Stellar flares have been identified in the short-cadence light curves of over 200 Kepler stars, and examined for evidence of QPPs. Those showing evidence of pulsations have been analysed using the autocorrelation and wavelet techniques. QPP-like signatures have been detected in 56 flares, and of these 11 have clear damped oscillations which could be modelled. A statistical analysis suggests that the QPPs found in these stellar flares are consistent with those found in solar flares. Petra Kohutova: 'Magnetohydrodynamic oscillations in solar coronal rain' Abstract: Coronal rain composed of cool plasma condensations falling from coronal heights is a phenomenon occurring in active region coronal loops as a result of thermal instability. Recent high resolution observations have shown that coronal rain is much more common than previously thought, suggesting its important role in the chromosphere-corona mass cycle. I address the observational evidence for the thermal instability in a coronal loop using observed evolution of the emission intensities in several SDO/AIA channels. The evolution of the temperature and density of the coronal loop plasma is recovered using inversion methods and forward modelling and suggests the coronal loop is going through a sequence of periodically repeating heating-condensation cycles. I further present the analysis of MHD oscillations and kinematics of the coronal rain using coordinated observations by IRIS, Hinode/SOT and SDO/AIA. The plasma condensations are found to move with accelerations largely below the free fall rate, with the likely reasons being pressure effects and the ponderomotive force resulting from the oscillations of the loop. The effect of both factors is investigated using LARE2D MHD simulations. |