Detection of high‐frequency optical oscillation during the flare phase of EV Lac in 1999

Abstract

Abstract.A program of Many-sites Multi Channel simultaneous observations of flare stars by a network of telescops was initiated in 1998. The purpose of this program is to investigate the fine structure of the flares light-curve in UBVRI, depressing atmospheric and instrumental noises. In this paper we present the results of the observations on the Flare star EV Lac in the B color, which were carried out at the Stephanion observatory during the campaign of 1999. Discrete Fourier Transform analysis of the B-light curve of the largest flares reveal the presence of high frequency small amplitude oscillations with periods ranging between 6.9 sec and 20 sec in around the flare maximum phase. The oscillation amplitude ranges from 1.4 to 2.6 % of the star brightness in accordance with the results of the campaign of 1998 (Zhilyaev et al. 2000). In addition there is a tendency the higher frequencies to persist in the late phases of the flare evolution. The observations are consistent with the phenomenology of the evolution of a fast mode magneto-acoustic wave generated at the impulsive phase of the flare and traveling through the magnetic loop.

Quasi-Periodic Pulsations in Solar and Stellar Flares: A Review of Underpinning Physical Mechanisms and Their Predicted Observational Signatures

“…It was found that transient high-frequency oscillations occurred during the flare event, and the observed frequencies (periods) ranged between 0.011 Hz (∼1.5 min) and 0.083 Hz (∼12 s). They found it in accordance with the results of the observation of transient optical oscillations on strong and medium flares (e.g Contadakis et al, 2004Contadakis et al, , 2012Contadakis, 2013,. and references cited there) Vida et al (2019b).…”

Fast colorimetry of the flare star EV Lacertae fromUBVRIobservations in 2004

“…The first application of the technique resulted in the discovery of HFO in brightness and colors of the detected flares (Zhilyaev et al 2000(Zhilyaev et al , 2003. Similar HFO of stellar flares were confirmed recently by Contadakis et al (2004). Here we present a complete colorimetric analysis of the two EV Lac flares detected during the multi-site monitoring in September 2004, processed with the digital filtering technique, analyzed with a set of the color-color diagrams, and considered in the network of a time-dependent phenomenological model of flares.…”

Retraction: [M. E. Contadakis, S. J. Avgoloupis, Ch. Papantoniou, Detection of starquakes on the flare star AD Leo, Astronomische Nachrichten 2017, 1–6, https://doi.org/10.1002/asna.201713307.]

“…We identify the potential frequencies of the star's brightness oscillations from the power spectrum. To do this, we use the H o hypothesis test (see Contadakis et al 2004a), in which 𝜎 BN is used. 4.…”

“…High-frequency, small-amplitude optical oscillations during a flare maximum of HII 2411 with a period of 14.4 s have been reported by Rodono (1974), while high-frequency optical oscillations of amplitude 10% in U and 2.5% in B and period 14.4 s on a flare of EV Lac around the flare maximum phase have been reported by Zhilyaev et al (2000). A multitude of high-frequency oscillations with amplitudes ranging between 1.4 and 2.6% and periods ranging between 6.9 and 20 s around maximum phase and the subsequent stages of the flare evolution of a flare on EV Lac have been reported by Contadakis et al (2004a). The resolution of the data was 1.2 s.…”

“…Nevertheless, a better understanding of such oscillations demands a unified analysis of the flare light curve for a wider time window covering the preflare, flare, and postflare state and a broader band of frequencies. Thus, in addition to the international campaign, the Stefanion Observatory group observed and analyzed single-color (B or U) observations of different red dwarfs: EV Lac (Contadakis et al 2004a(Contadakis et al , 2004b(Contadakis et al , 2006, AD Leo (Contadakis et al 2011a(Contadakis et al , 2011b, YZ CMin (Contadakis et al 2010;, UV Cet (Contadakis et al 2013a), as well as the red giant (G8) V 390 Aur, the flare activity of which was reported by Konstantinova-Antova et al (2005, Contadakis et al (2013), andContadakis (2013b), at every stage of their activity (quiescence, weak flares, strong flares). In this paper, we present the analysis of the quiet-state observations of the flare star AD Leo in order to confirm whether starquakes appear far apart from the observed flares, during the quiet state of the stars, as a result of the general magnetic activity of the star.…”