Investigating magnetic activity in very stable stellar magnetic fields

Abstract

The ultrafast-rotating (P rot ≈ 0.44 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, hence the spot configuration. We also measure the occurrence rate of flares and coronal mass ejections (CMEs). We have analysed spectroscopic observations, BV(RI) C photometry covering 5 yrs, and additional R C photometry that expands the temporal base over 16 yr. The light curve suggests an almost rigid-body rotation and a spot configuration that is stable over about 16 yrs, 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 ∼675 km s −1 . We observed a CME rate that is much lower than expected from extrapolations of the solar flare-CME relation to active stars.

Coronal mass ejections and their sheath regions in interplanetary space

“…The stellar CME observed by Houdebine et al (1990), also using the optical spectra, had speed of about 5800 km s −1 . The estimated CME rate by Vida et al (2016) using the V374 Pegasus X-ray luminosity was 15-60 eruptions per day, considerably higher than for the Sun (0.5-10 CMEs per day depending on the solar cycle phase). The recent more extensive surveys have, however, reported much less stellar CMEs than expected (Korhonen 2016).…”

“…The dynamic H α spectra in Fig. 37 from Vida et al (2016) shows three distinct blue-wing enhancements that occurred in association with flares on a M4 dwarf V374 Pegasus. These blue-wings could hence signal the mass carried away from the star by a CME associated with a flare.…”

“…The upcoming James Webb telescope can yield important information of their atmospheric constituents, and hence, find proxies for possible life. However, the atmospheres of these planets may be Vida et al (2016), copyright by ESO significantly influenced due to erosion as response to stellar eruptions (e.g., Airapetian et al 2017).…”

“…In addition, in-situ observations of stellar ICMEs will remain impossible until unforeseeable future. Some possible detections of stellar CMEs have been made through long-term spectrophotometric observations of Doppler shifted emission in H α (e.g., Vida et al 2016, and references therein). The dynamic H α spectra in Fig.…”

Most Observations of Our Nearest Neighbor: Flares on Proxima Centauri

“…Proxima Cen is thus a high priority target for spectroscopic monitoring to study CME velocities and rates associated with flare events (see e.g. Vida et al 2016). …”