{
  "id": "2009.00876",
  "version": "v1",
  "published": "2020-09-02T07:55:02.000Z",
  "updated": "2020-09-02T07:55:02.000Z",
  "title": "The CARMENES search for exoplanets around M dwarfs: Rubidium abundances in nearby cool stars",
  "authors": [
    "C. Abia",
    "H. M. Tabernero",
    "S. A. Korotin",
    "D. Montes",
    "E. Marfil",
    "J. A. Caballero",
    "O. Straniero",
    "N. Prantzos",
    "I. Ribas",
    "A. Reiners",
    "A. Quirrenbach",
    "P. J. Amado",
    "V. J. S. Bejar",
    "M. Cortes-Contreras",
    "S. Dreizler",
    "Th. Henning",
    "S. V. Jeffers",
    "A. Kaminski",
    "M. Kürster",
    "M. Lafarga",
    "A. Lopez-Gallifa",
    "J. C. Morales",
    "E. Nagel",
    "V. M. Passegger",
    "S. Pedraz",
    "C. Rodriguez Lopez",
    "A. Schweitzer",
    "M. Zechmeister"
  ],
  "comment": "16 pag, 8 Figs, 1 table. Accepted in Astronomy & Astrophysics",
  "categories": [
    "astro-ph.SR"
  ],
  "abstract": "In this study, abundances of the neutron-capture elements Rb, Sr, and Zr are derived, for the first time, in a sample of nearby M dwarfs. We focus on stars in the metallicity range -0.5<[Fe/H]<+0.3, an interval poorly explored for Rb abundances in previous analyses. To do this we use high-resolution, high-signal-to-noise-ratio, optical and near-infrared spectra of 57 M dwarfs observed with CARMENES. The resulting [Sr/Fe] and [Zr/Fe] ratios for most M dwarfs are almost constant at about the solar value, and are identical to those found in GK dwarfs of the same metallicity. However, for Rb we find systematic underabundances ([Rb/Fe]<0.0) by a factor two on average. Furthermore, a tendency is found for Rb-but not for other heavy elements (Sr, Zr) -to increase with increasing metallicity such that [Rb/Fe]>0.0 is attained at metallicities higher than solar. These are surprising results, never seen for any other heavy element, and are difficult to understand within the formulation of the s- and r-processes, both contributing sources to the Galactic Rb abundance. We discuss the reliability of these findings for Rb in terms of non-LTE effects, stellar activity, or an anomalous Rb abundance in the Solar System, but no explanation is found. We then interpret the full observed [Rb/Fe] versus [Fe/H] trend within the framework of theoretical predictions from state-of-the-art chemical evolution models for heavy elements, but a simple interpretation is not found either. In particular, the possible secondary behaviour of the [Rb/Fe] ratio at super-solar metallicities would require a much larger production of Rb than currently predicted in AGB stars through the s-process without overproducing Sr and Zr.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2020-09-02T07:55:02.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "nearby cool stars",
      "rubidium abundances",
      "carmenes search",
      "exoplanets",
      "heavy element"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}