Search for indications of stellar mass ejections using FUV spectra

Abstract

Aims. We search for highly energetic activity phenomena in a small sample of late-type main-sequence stars in the far ultraviolet (FUV) using data from the Far Ultraviolet Spectroscopic Explorer (FUSE). Methods. Because FUSE allows a simultaneous photometric and spectroscopic analysis, we are able to analyze variations in the light curves (flares) and possible, activity-related signatures (line asymmetries, enhancements, and shifts) in the spectra. Furthermore, the computation of the well-known density-sensitive line ratio C iii(λ1176 Å)/C iii(λ977 Å) is also possible, and allows the investigation of its dependence on stellar activity. Results. Three late-type main-sequence stars found in the FUSE archive (HD 36705, HD 197481, and Gl 388) show flares in their light curves. We find no obvious Doppler shifts in the brightest lines of these stars, but the O vi(λ1032 Å) transition region line of AD Leo shows a blue wing enhancement one spectrum after a flare event. This emission feature is shifted by ∼-84 km s −1 from the line core. We can exclude that the spectral feature was caused by a gas cloud co-rotating with the star and favor an interpretation of a mass ejection. In addition we find an increase of the C iii(λ1176 Å)/C iii(λ977 Å) line ratio during all detected flares. We compare this finding to the Sun using solar full-disk spectra from the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) and SOlar Radiation and Climate Experiment (SORCE) missions, and find that powerful flare events also show an increased C iii(λ1176 Å)/C iii(λ977 Å) line ratio but this result is of low statistical significance. Owing to a lack of perfectly temporally coinciding TIMED/SORCE spectra and a low temporal resolution (∼15 spectra per day) it is not possible to distinguish clearly if this increase is caused by the flares or by the related mass ejections.

Mass Loss in Pre-Main-Sequence Stars via Coronal Mass Ejections and Implications for Angular Momentum Loss

“…Efforts have been made with EUV spectroscopy; Leitzinger et al (2011) point out a lack of simultaneous solar spectra during flare/CME events, creating great difficulty for the interpretation of stellar data. Additionally, managing to catch a stellar CME with the right set of parameters for observation (e.g., density and projection) requires sufficient observing time to increase the probability of detection.…”

“…While the faint scattered light of CMEs cannot yet be directly detected from most other stars, there have been recent observations of young stars with the FUSE satellite (Leitzinger et al 2011) and the detection of a large flare-associated mass ejection in the PMS star Z CMa (Stelzer et al 2009;Whelan et al 2010). More generally, CMEs are expected from lowmass stars by analogy to the Sun as well as from basic escape velocity considerations for the flaring material; indeed, CMEs are believed to have been detected on M and K dwarfs from balmer line asymmetries, transient spectral line absorption components, and EUV dimmings (cf., Leitzinger et al 2011, and references therein). In particular, the extreme X-ray flares observed on PMS stars are expected to have associated extreme CMEs (e.g., Aarnio et al 2011), the ramifications of which-for the evolution of the star, for the protoplanetary environment, and for the star's angular momentum evolution-depend on the resulting mass-loss rate and the evolution of that mass loss over the course of the star's PMS evolution.…”

Mass-loss Rates from Coronal Mass Ejections: A Predictive Theoretical Model for Solar-type Stars

“…However, observational evidence for intermittent mass loss is still elusive. There are multiple measurements of time-variable outflows from cool stars (Houdebine et al 1990;Cully et al 1994;Fuhrmeister & Schmitt 2004;Leitzinger et al 2011;Dupree et al 2014;Vida et al 2016;Korhonen et al 2017), but it is not yet clear whether these should be interpreted as magnetically driven events analogous to solar CMEs. It is possible that observing the extrasolar equivalents of Type II radio bursts (Crosley et al 2016) or the polarization signatures of off-limb prominences (Felipe et al 2017) could be promising avenues toward the goal of definitive exo-CME detection.…”

The Search for Signatures of Transient Mass Loss in Active Stars

“…They claimed, with high confidence, that they found radio emission originating from AD Leo that had a burst structure similar to solar type III bursts in the decameter range. A stellar analog of the solar type II burst has not been detected (Leitzinger et al 2011).…”