{
  "id": "1803.02338",
  "version": "v1",
  "published": "2018-03-06T18:54:41.000Z",
  "updated": "2018-03-06T18:54:41.000Z",
  "title": "The CARMENES search for exoplanets around M dwarfs: Radial-velocity variations of active stars in visual-channel spectra",
  "authors": [
    "L. Tal-Or",
    "M. Zechmeister",
    "A. Reiners",
    "S. V. Jeffers",
    "P. Schöfer",
    "A. Quirrenbach",
    "P. J. Amado",
    "I. Ribas",
    "J. A. Caballero",
    "J. Aceituno",
    "F. F. Bauer",
    "V. J. S. Béjar",
    "S. Czesla",
    "S. Dreizler",
    "B. Fuhrmeister",
    "A. P. Hatzes",
    "E. N. Johnson",
    "M. Kürster",
    "M. Lafarga",
    "D. Montes",
    "J. C. Morales",
    "S. Reffert",
    "S. Sadegi",
    "W. Seifert",
    "D. Shulyak"
  ],
  "comment": "A&A accepted",
  "categories": [
    "astro-ph.SR",
    "astro-ph.EP"
  ],
  "abstract": "Previous simulations predicted the activity-induced radial-velocity (RV) variations of M dwarfs to range from $\\sim1$ cm/s to $\\sim1$ km/s, depending on various stellar and activity parameters. We investigate the observed relations between RVs, stellar activity, and stellar parameters of M dwarfs by analyzing CARMENES high-resolution visual-channel spectra ($0.5$$-$$1$$\\mu$m), which were taken within the CARMENES RV planet survey during its first $20$ months of operation. During this time, $287$ of the CARMENES-sample stars were observed at least five times. From each spectrum we derived a relative RV and a measure of chromospheric H$\\alpha$ emission. In addition, we estimated the chromatic index (CRX) of each spectrum, which is a measure of the RV wavelength dependence. Despite having a median number of only $11$ measurements per star, we show that the RV variations of the stars with RV scatter of $>10$ m/s and a projected rotation velocity $v \\sin{i}>2$ km/s are caused mainly by activity. We name these stars `active RV-loud stars' and find their occurrence to increase with spectral type: from $\\sim3\\%$ for early-type M dwarfs (M$0.0$$-$$2.5$V) through $\\sim30\\%$ for mid-type M dwarfs (M$3.0$$-$$5.5$V) to $>50\\%$ for late-type M dwarfs (M$6.0$$-$$9.0$V). Their RV-scatter amplitude is found to be correlated mainly with $v \\sin{i}$. For about half of the stars, we also find a linear RV$-$CRX anticorrelation, which indicates that their activity-induced RV scatter is lower at longer wavelengths. For most of them we can exclude a linear correlation between RV and H$\\alpha$ emission. Our results are in agreement with simulated activity-induced RV variations in M dwarfs. The RV variations of most active RV-loud M dwarfs are likely to be caused by dark spots on their surfaces, which move in and out of view as the stars rotate.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2018-03-06T18:54:41.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "carmenes search",
      "radial-velocity variations",
      "active stars",
      "exoplanets",
      "rv variations"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}