{
  "id": "2006.09372",
  "version": "v1",
  "published": "2020-06-16T11:10:17.000Z",
  "updated": "2020-06-16T11:10:17.000Z",
  "title": "The CARMENES search for exoplanets around M dwarfs. Variability of the He I line at 10830 Å",
  "authors": [
    "B. Fuhrmeister",
    "S. Czesla",
    "L. Hildebrandt",
    "E. Nagel",
    "J. H. M. M. Schmitt",
    "S. V. Jeffers",
    "J. A. Caballero",
    "D. Hintz",
    "E. N. Johnson",
    "P. Schöfer",
    "M. Zechmeister",
    "A. Reiners",
    "I. Ribas",
    "P. J. Amado",
    "A. Quirrenbach",
    "L. Nortmann",
    "F. F. Bauer",
    "V. J. S. Béjar",
    "M. Cortés-Contreras",
    "S. Dreizler",
    "D. Galadí-Enríquez",
    "A. P. Hatzes",
    "A. Kaminski",
    "M Kürster",
    "M. Lafarga",
    "D. Montes"
  ],
  "comment": "14 pages, 12 figures, accepted by A&A, full Table 2 only available electronically at CDS",
  "categories": [
    "astro-ph.SR",
    "astro-ph.EP"
  ],
  "abstract": "The He I infrared (IR) triplet at 10830 \\AA is known as an activity indicator in solar-type stars and has become a primary diagnostic in exoplanetary transmission spectroscopy. He I lines are a tracer of the stellar extreme-ultraviolet irradiation from the transition region and corona. We study the variability of the He I IR 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$\\alpha$ in emission. Therefore, we find detectable He I IR variability in 78% of the sub-sample of stars with H$\\alpha$ emission. Detectable variability is strongly concentrated in the latest spectral sub-types, where the He I IR lines during quiescence are typically weak. The fraction of stars with detectable He I IR 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 IR absorption, which is potentially associated with increased high-energy irradiation levels at flare onset. Generally, He I IR and H$\\alpha$ line variations tend to be correlated, with H$\\alpha$ being the most sensitive indicator in terms of pseudo-equivalent width variation. This makes the He I IR triplet a favourable target for planetary transmission spectroscopy.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2020-06-16T11:10:17.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "carmenes search",
      "ir variation remains lower",
      "exoplanets",
      "ir triplet",
      "pseudo-equivalent width variation"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 14,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}