The CARMENES search for exoplanets around M dwarfs. Variability of the He I line at 10 830 Å

Publication date: 
Main author: 
Fuhrmeister, B.
IAA authors: 
Amado, P. J.;Bauer, F. F.
Fuhrmeister, B.;Czesla, S.;Hildebrandt, L.;Nagel, E.;Schmitt, J. H. M. M.;Jeffers, S. V.;Caballero, J. A.;Hintz, D.;Johnson, E. N.;Schöfer, P.;Zechmeister, M.;Reiners, A.;Ribas, I.;Amado, P. J.;Quirrenbach, A.;Nortmann, L.;Bauer, F. F.;Béjar, V. J. S.;Cortés-Contreras, M.;Dreizler, S.;Galadí-Enríquez, D.;Hatzes, A. P.;Kaminski, A.;Kürster, M.;Lafarga, M.;Montes, D.
Astronomy and Astrophysics
Publication type: 
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 Hα in emission. Therefore, we find detectable He I variability in 78% of the sub-sample of stars with Hα 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 Hα line variations tend to be correlated, with Hα 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. <P />Full Table 2 is only available at the CDS via anonymous ftp to <A href=''></A> ( or via <A href=''></A>
ADS Bibcode: 
stars: activity;stars: chromospheres;stars: late-type;Astrophysics - Solar and Stellar Astrophysics;Astrophysics - Earth and Planetary Astrophysics