Optical flares and flaring oscillations on the M-type eclipsing binary CU Cnc

TL;DR

This study reports the detection of significant optical flares and oscillations on the M-type eclipsing binary CU Cnc, revealing high magnetic activity and its effects on stellar brightness and behavior.

Contribution

First detection of large optical flares and flaring oscillations on CU Cnc, providing insights into magnetic activity in fully convective M-dwarf binaries.

Findings

Largest R-band flare amplitude (~0.52 mag) observed in CU Cnc

Flare rate of about 0.05 flares per hour over 79.9 hours

Presence of quasi-periodic oscillations during and after flares

Abstract

We report here the discovery of an optical flare observed in R band from the red-dwarf eclipsing binary CU Cnc whose component stars are at the upper boundary of full convection (M1=0.43 and M2=0.4M0, M0 is the solar mass). The amplitude of the flare is the largest among those detected in R band (~0.52mag) and the duration time is about 73 minutes. As those observed on the Sun, quasi-periodic oscillations were seen during and after the flare. Three more R-band flares were found by follow up monitoring. In total, this binary was monitored photometrically by using R filter for 79.9 hours, which reveals a R-band flare rate about 0.05 flares per hour. These detections together with other strong chromospheric and coronal activities, i.e., very strong H_alpha and H_beta emission features and an EUV and X-ray source, indicate that it has very strong magnetic activity. Therefore, the apparent faintness (~1.4 magnitude in V) of CU Cnc compared with other single red dwarfs of the same mass can be plausibly explained by the high coverage of the dark spots.