{
  "id": "1804.06417",
  "version": "v1",
  "published": "2018-04-17T18:00:37.000Z",
  "updated": "2018-04-17T18:00:37.000Z",
  "title": "The luminosities of cool supergiants in the Magellanic Clouds, and the Humphreys-Davidson limit revisited",
  "authors": [
    "Ben Davies",
    "Paul A. Crowther",
    "Emma R. Beasor"
  ],
  "comment": "11 pages, 6 figs. Accepted for publication in MNRAS",
  "categories": [
    "astro-ph.SR",
    "astro-ph.GA"
  ],
  "abstract": "The empirical upper luminosity boundary $L_{\\rm max}$ of cool supergiants, often referred to as the Humphreys-Davidson limit, is thought to encode information on the general mass-loss behaviour of massive stars. Further, it delineates the boundary at which single stars will end their lives stripped of their hydrogen-rich envelope, which in turn is a key factor in the relative rates of Type-II to Type-Ibc supernovae from single star channels. In this paper we have revisited the issue of $L_{\\rm max}$ by studying the luminosity distributions of cool supergiants (SGs) in the Large and Small Magellanic Clouds (LMC/SMC). We assemble samples of cool SGs in each galaxy which are highly-complete above $\\log L/L_{\\odot}$=5.0, and determine their spectral energy distributions from the optical to the mid-infrared using modern multi-wavelength survey data. We show that in both cases $L_{\\rm max}$ appears to be lower than previously quoted, and is in the region of $\\log L/L_{\\odot}$=5.5. There is no evidence for $L_{\\rm max}$ being higher in the SMC than in the LMC, as would be expected if metallicity-dependent winds were the dominant factor in the stripping of stellar envelopes. We also show that $L_{\\rm max}$ aligns with the lowest luminosity of single nitrogen-rich Wolf-Rayet stars, indicating of a change in evolutionary sequence for stars above a critical mass. From population synthesis analysis we show that the Geneva evolutionary models greatly over-predict the numbers of cool SGs in the SMC. We also argue that the trend of earlier average spectral types of cool SGs in lower metallicity environments represents a genuine shift to hotter temperatures. Finally, we use our new bolometric luminosity measurements to provide updated bolometric corrections for cool supergiants.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2018-04-17T18:00:37.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "cool supergiants",
      "magellanic clouds",
      "humphreys-davidson limit",
      "luminosity",
      "cool sgs"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 11,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}