D.B. Jess, 1 M. Mathioudakis, 1 D.S. Bloomfield, 1 V. Dhillon, 2 T. Marsh 3 1 Astrophysics and Planetary Science Division, Dept. of Physics and Astronomy, Queen’s University Belfast, Belfast, BT7 1NN Abstract We have carried out high time resolution photometry of EQ Pegasi and LHS 3966 for approximately 14 hr and detected seventy-five flare events. The flares exhibit a power law distribution with a scaling index, α, of 1.9 ± 0.2 for EQ Pegasi and 1.6 ± 0.4 for LHS A Fourier transform of the microflaring activity found on these objects exhibited a shot noise distribution, f -(0.9 ± 0.2), at low frequencies. Performing a Monte-Carlo simulation of microflaring activity, based on the value of α above, produced the same f -1 distribution. Two flares were found on LHS 3966 which exhibit oscillatory behaviour during their decay phases. Running the two lightcurves through wavelet analysis produced oscillation periods of 10s and 20s with a confidence greater than 99%. This corresponds to stellar magnetic loop lengths of (3.9 ± 2.2)% and (7.6 ± 3.5)% of the stellar radius. 1 - Introduction 2 - Instrumentation 3 - Observations 4 - Analysis 5 - Results ULTRACAM (Fig 1) is a triple-beam CCD camera Image acquisition cadence of 0.07 s Time stamped images with 0.1 ms accuracy Ability to monitor comparison and target WHT observing run 1 st – 5 th November 2003 Late M-type stars EQ Pegasi and LHS 3966 studied (Fig 2) Images acquired in u ’, g ’ and r ’ SDSS colour bands EQ Pegasi LHS 3966 Data primarily studied in u ’ band for deviations above quiescent flux (Fig 3) 75 flares detected during 14 hr observation period Individual flare energies established and plotted as cumulative distributions (Fig 4) Values of α calculated from gradients of cumulative Quiescent behaviour investigated using Fourier techniques Wavelet analysis applied to flare decays to search for oscillatory behaviour Stellar magnetic loop lengths calculated from derived properties using the relation (Nakariakov et al. 2004), with 0.3 arcsec/pixel resolution stars simultaneously Fourier power spectra of actual and simulated quiescent behaviour (Fig 5) revealed a shot noise distribution, f -1, below white noise frequencies Two flare decays on LHS 3966 indicated oscillatory behaviour showing separate periods of 10 s (Fig 6) and 20 s Assuming loop temperatures of 30–50 MK yields loop lengths of ± R  L = P√T 6.7 and ± R  for the 10 s and 20 s periods, respectively – similar to those for solar coronal loops References: - Nakariakov V.M., Tsiklauri D., Kelly A., Arber T.D., Aschwanden M.J., 2004, A&A, 414, L Krucker S., Benz A.O., 1999, Solar Physics, 191, Coronal heating paradox has always intrigued solar and stellar physicists Microflaring activity and/or wave motion may contribute to plasma heating mechanisms away from the photosphere M-type stars possess coronae just like the sun and due to increased flaring rates, compared with other spectral types, provide a perfect laboratory to test coronal heating mechanisms Flare energies are believed to follow a power law distribution of the form, dN(E) dE = CE -α where E is energy, N(E) is the number of flares in the interval E → δE, C is a constant and α is the power law scaling index (Krucker & Benz 1999) For low energy events to dominate the flare energy budget, a value of α > 2 is necessary Figure 1: ULTRACAM attached to WHT where L is loop length in Mm, P is oscillation period in s, and T is average loop temperature in MK Figure 3: u ’ band flare on LHS 3966 Figure 2: u ’ band target field of view energy distributions EQ Pegasi α = 1.9 ± 0.2 α = 1.6 ± 0.4 LHS 3966 Figure 4: Cumulative u ’ band flare energy distributions, i.e. number of flares above energy, E, as a function of E The values of α determined for EQ Pegasi and LHS 3966 (Fig 4) are inconclusive as to the significance of low energy events contributing to the total flare energy budget Figure 5: Log-Log Fourier power spectra of actual (left) and simulated (right) quiescent time series Figure 6: Detrended time series (upper) and wavelet power spectra (lower) for a u ’ band flare decay phase (10 s case) As can be clearly seen in Figure 6, the period of peak power varies during the flare – in accordance with the period-temperature interplay stated above in the Nakariakov et al. relation Application of solar coronal seismology to stars allows us to determine spatial dimensions of structures in their outer atmospheres 2 Astrophysics Division, Dept. of Physics and Astronomy, University of Sheffield, Sheffield, S3 7RH 3 Astronomy & Astrophysics Division, Dept. of Physics, University of Warwick, Coventry, CV4 7AL Flares & Waves of Fully Convective Stars Actual Simulated