2020/06/16 by B. Fuhrmeister, S. Czesla, L. Hildebrandt +25 · 36 citations
Engineering · Physics and Astronomy · #Astronomy #Astronomy and Astrophysical Research #Astrophysics #Calibration and Measurement Techniques #Exoplanet #Flare #Line (geometry) #Physics #Spectral line #Spectrograph #Spectroscopy #Stars #Stellar classification #Stellar, planetary, and galactic studies #astro-ph.EP #astro-ph.SR
paper · pdf · doi:10.1051/0004-6361/202038279
published in Astronomy and Astrophysics 640, A52 (EDP Sciences) · 14 pages, 12 figures, accepted by A&A, full Table 2 only available electronically at CDS
arxiv created 2020/06/16 · openalex publication_date 2020/06/20 · arxiv updated 2020/08/12 · openalex created_date 2022/07/28 · openalex updated_date 2026/08/06
The He I infrared (IR) triplet at 10 830 Å is known as an activity indicator in solar-type stars and has become a primary diagnostic in exoplanetary transmission spectroscopy. He I IR lines are a tracer of the stellar extreme-ultraviolet irradiation from the transition region and corona. We study the variability of the He I triplet lines in a spectral time series of 319 M dwarf stars that was obtained with the CARMENES high-resolution optical and near-infrared spectrograph at Calar Alto. We detect He I IR line variability in 18% of our sample stars, all of which show H α in emission. Therefore, we find detectable He I variability in 78% of the sub-sample of stars with H α emission. Detectable variability is strongly concentrated in the latest spectral sub-types, where the He I lines during quiescence are typically weak. The fraction of stars with detectable He I variation remains lower than 10% for stars earlier than M3.0 V, while it exceeds 30% for the later spectral sub-types. Flares are accompanied by particularly pronounced line variations, including strongly broadened lines with red and blue asymmetries. However, we also find evidence for enhanced He I absorption, which is potentially associated with increased high-energy irradiation levels at flare onset. Generally, He I and H α line variations tend to be correlated, with H α being the most sensitive indicator in terms of pseudo-equivalent width variation. This makes the He I triplet a favourable target for planetary transmission spectroscopy.