Detection of transient high frequency optical oscillations of the flare star YZ CMin

摘要

In this paper we present the results of the analysis of the B -light curve for the flares of the red dwarf YZ CMin (dM4.5e), which were observed on February of 2002, with the help of the 30-inch Cassegrain telescope of the Stephanion Observatory, Greece. Discrete Fourier Transform analysis and the use of the Brownian Walk noise enable us to estimate the proper random noise and detect possible weak transient optical oscillations. Our results indicate that: (1) Transient high frequency oscillations occur during the flare event and during the quiet-star phase as well. (2) The observed frequencies range between 0.0083 Hz (period 2 min) and 0.3 Hz (period 3 s) is not rigorously bounded. The phenomenon is most pronounced during the flare state. (3) During the flare state: (a) Oscillations with period 2 to 1.5 min, 60 s, 11 s, 7.5 s, and 4 s appear around the maximum light state and persist during the whole flare state, (b) from the flare maximum phase on, a progressive increase of oscillations with periods 30 s, 20 s down to 4.0 s is markedly indicated, and (c) at the end of the flare only the oscillation of the pre-flare state do remain. Our observations are consistent with the phenomenology of impulsively exited oscillations on a coronal magnetic loop and subsequent chromospheric heating by electronic flux at the foot of the loop or/and by soft X-ray coronal emission. Our observation give evidence that more than one impulsive events may occur in the course of an observed flare (? 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)