High-frequency variations of spectral lines in cromospherically active stars 61 cyg AB

Abstract

We report on the detection of rapid variability in subsecond mode in the Balmer lines of hydrogen, lines Ca II H,K, and b Mg I triplet in chromospherically active stars 61 Cyg A, B. The spectral observations of 61 Cyg A, B were performed with MMCS spectrograph in Cassegrain’s focus of the 2-m telescope at peak Terskol (R = 13000), with a grating spectrograph mounted on a 60-cm telescope at peak Terskol (R ≈ 100), and a 60-cm telescope of the Andrushivka Observatory (R ≈ 200). The observations were carried out in the framework of international campaign of observations of variable stars using the Synchronous Network of Telescopes. The high-resolution spectra were obtained with intervals of approximately 2 minutes. The low-resolution spectra were obtained with intervals from 2 to 3 seconds. Spectral monitoring lasted from 30 minutes to 2 hours. We found that chromospherically active dwarf stars 61 Cyg A, B, having extensional spots on their surfaces exhibit rapid variations in the hydrogen lines, lines CaII H, K of ionized calcium and chromospheric triplet b Mg I on a time scale from approximately 2 seconds to approximately 2 minutes. Variations in the intensity of lines range from 1.5% in the Balmer series of hydrogen to approximately 0.5% in the lines of b Mg I triplet. These variations are well described by the shot noise model in the form of random elementary pulses with the frequency of occurrence of a few fractions of events per second to a few events per second. Comparison of rapid variations in chromospheric lines with different time intervals demonstrates the transient nature of this activity both on short (subsecond) and long-time scales.