The CARMENES search for exoplanets around M dwarfs. The He I triplet at 10830 Å across the M dwarf sequence

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.;Hintz, D.;Johnson, E. N.;Sanz-Forcada, J.;Schöfer, P.;Jeffers, S. V.;Caballero, J. A.;Zechmeister, M.;Reiners, A.;Ribas, I.;Amado, P. J.;Quirrenbach, A.;Bauer, F. F.;Béjar, V. J. S.;Cortés-Contreras, M.;Díez-Alonso, E.;Dreizler, S.;Galadí-Enríquez, D.;Guenther, E. W.;Kaminski, A.;Kürster, M.;Lafarga, M.;Montes, D.
Astronomy and Astrophysics
Publication type: 
The He I infrared (IR) triplet at 10 830 Å is an important activity indicator for the Sun and in solar-type stars, however, it has rarely been studied in relation to M dwarfs to date. In this study, we use the time-averaged spectra of 319 single stars with spectral types ranging from M0.0 V to M9.0 V obtained with the CARMENES high resolution optical and near-infrared spectrograph at Calar Alto to study the properties of the He I IR triplet lines. In quiescence, we find the triplet in absorption with a decrease of the measured pseudo equivalent width (pEW) towards later sub-types. For stars later than M5.0 V, the He I triplet becomes undetectable in our study. This dependence on effective temperature may be related to a change in chromospheric conditions along the M dwarf sequence. When an emission in the triplet is observed, we attribute it to flaring. The absence of emission during quiescence is consistent with line formation by photo-ionisation and recombination, while flare emission may be caused by collisions within dense material. The He I triplet tends to increase in depth according to increasing activity levels, ultimately becoming filled in; however, we do not find a correlation between the pEW(He IR) and X-ray properties. This behaviour may be attributed to the absence of very inactive stars (L<SUB>X</SUB>/L<SUB>bol</SUB> &lt; -5.5) in our sample or to the complex behaviour with regard to increasing depth and filling in. <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