Photospheric and chromospheric activity in V405 And: An M dwarf binary with components on the two sides of the full convection limit

TL;DR

This study examines the magnetic activity and flare phenomena in the fast-rotating M dwarf binary V405 And, providing insights into stellar dynamo processes in stars with different internal structures.

Contribution

It offers detailed observational analysis of activity in a unique binary system with components on either side of the full convection threshold, testing stellar dynamo models.

Findings

Detected three flare events, including post-flare eruptions from trans-equatorial magnetic loops.

Estimated system parameters from light and radial velocity curves.

Observed magnetic activity in a binary with components on both sides of the full convection limit.

Abstract

We investigate the fast-rotating (P_orb=P_rot=0.465d), active dwarf binary V405 And (M0V+M5V) using photometric BV(RI)_C and optical spectroscopic data. The light variation is caused by the combined effect of spottedness and binarity with a small eclipse. We estimate the system parameters from the available light and radial velocity curves. Three flare events occurred during the observations: two were found in the spectroscopic data and one was observed photometrically in BV(RI)_C colours. An interesting eruptive phenomenon emerged from the photometric measurements that can be interpreted as a series of post-flare eruptions lasting for at least 3 orbits (rotations) of the system, originating from trans-equatorial magnetic loops, which connect the active regions in the two hemispheres. The two components of V405 And have masses well over and below the theoretical limit of full convection. This rare property makes the binary an ideal target for observing and testing models for stellar dynamo action.