Investigating magnetic activity in very stable stellar magnetic fields: long-term photometric and spectroscopic study of the fully convective M4 dwarf V374 Peg

TL;DR

This study presents a long-term analysis of the magnetic activity of the fully convective M4 dwarf V374 Peg, revealing a remarkably stable magnetic topology, frequent flaring, and complex CMEs over 16 years.

Contribution

It provides the first comprehensive 16-year observational evidence of magnetic stability and activity patterns in a fully convective star, combining photometry and spectroscopy.

Findings

Magnetic topology remains stable over 16 years.

Frequent flaring observed, including a possible sympathetic flare.

CME rate is lower than solar flare-CME extrapolations suggest.

Abstract

The ultrafast-rotating ($P_\mathrm{rot}\approx0.44 d$) fully convective single M4 dwarf V374 Peg is a well-known laboratory for studying intense stellar activity in a stable magnetic topology. As an observable proxy for the stellar magnetic field, we study the stability of the light curve, and thus the spot configuration. We also measure the occurrence rate of flares and coronal mass ejections (CMEs). We analyse spectroscopic observations, $BV(RI)_C$ photometry covering 5 years, and additional $R_C$ photometry that expands the temporal base over 16 years. The light curve suggests an almost rigid-body rotation, and a spot configuration that is stable over about 16 years, confirming the previous indications of a very stable magnetic field. We observed small changes on a nightly timescale, and frequent flaring, including a possible sympathetic flare. The strongest flares seem to be more concentrated around the phase where the light curve indicates a smaller active region. Spectral data suggest a complex CME with falling-back and re-ejected material, with a maximal projected velocity of $\approx$675km/s. We observed a CME rate much lower than expected from extrapolations of the solar flare-CME relation to active stars.