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

© ESO 2019Fuhrmeister, B.Czesla, S.Hildebrandt, L.Nagel, E.Schmitt, H. M. M.Hintz, D.Johnson, E. N.Sanz-Forcada, JorgeSchöfer, 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.Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737Centros de Excelencia Severo Ochoa, INSTITUTO DE ASTROFISICA DE ANDALUCIA (IAA), SEV-2017-0709Centros de Excelencia Severo Ochoa, INSTITUTO DE ASTROFÍSICA DE CANARIAS (IAC), SEV-2015-05482021-04-142021-04-142019-11-25Astronomy and Astrophysics 632: A24(2019)0004-6361https://www.aanda.org/articles/aa/full_html/2019/12/aa36193-19/aa36193-19.htmlhttp://hdl.handle.net/20.500.12666/334Full Table 2 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/632/A24The 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 (LX∕Lbol < −5.5) in our sample or to the complex behaviour with regard to increasing depth and filling in.engAttribution-NonCommercial-NoDerivatives 4.0 Internationalhttps://creativecommons.org/licenses/by-nc-nd/4.0/Stars: activityStars: chromospheresStars: late typeThe CARMENES search for exoplanets around M dwarfs The He I triplet at 10830 Å across the M dwarf sequenceinfo:eu-repo/semantics/articlehttps://doi.org/10.1051/0004-6361/2019361931432-0746info:eu-repo/semantics/openAccess