{
  "id": "1305.1622",
  "version": "v1",
  "published": "2013-05-07T20:00:01.000Z",
  "updated": "2013-05-07T20:00:01.000Z",
  "title": "Core collapse and horizontal-branch morphology in galactic globular clusters",
  "authors": [
    "Mario Pasquato",
    "Gabriella Raimondo",
    "Enzo Brocato",
    "Chul Chung",
    "Anthony Moraghan",
    "Young-Wook Lee"
  ],
  "comment": "7 pages, 7 figures, A&A accepted",
  "categories": [
    "astro-ph.GA",
    "astro-ph.SR"
  ],
  "abstract": "Context. Stellar collision rates in globular clusters (GCs) do not appear to correlate with horizontal branch (HB) morphology, sug- gesting that dynamics does not play a role in the second-parameter problem. However, core densities and collision rates derived from surface-brightness may be significantly underestimated as the surface-brightness profile of GCs is not necessarily a good indicator of the dynamical state of GC cores. Core-collapse may go unnoticed if high central densities of dark remnants are present. Aims. We test whether GC HB morphology data supports a dynamical contribution to the so-called second-parameter effect. Methods. To remove first-parameter dependence we fitted the maximum effective temperature along the HB as a function of metal- licity in a sample of 54 Milky Way GCs. We plotted the residuals to the fit as a function of second-parameter candidates, namely dynamical age and total luminosity. We considered dynamical age (i.e. the ratio between age and half-light relaxation time) among possible second-parameters. We used a set of direct N-body simulations, including ones with dark remnants to illustrate how core density peaks, due to core collapse, in a dynamical-age range similar to that in which blue HBs are overabundant with respect to the metallicity expectation, especially for low-concentration initial conditions. Results. GC total luminosity shows nonlinear behavior compatible with the self-enrichment picture. However, the data are amenable to a different interpretation based on a dynamical origin of the second-parameter effect. Enhanced mass-stripping in the late red-giant- branch phase due to stellar interactions in collapsing cores is a viable candidate mechanism. In this picture, GCs with HBs bluer than expected based on metallicity are those undergoing core-collapse.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2013-05-07T20:00:01.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "galactic globular clusters",
      "core collapse",
      "horizontal-branch morphology",
      "gc hb morphology data supports",
      "core density"
    ],
    "tags": [
      "journal article"
    ],
    "publication": {
      "doi": "10.1051/0004-6361/201321361",
      "journal": "Astronomy and Astrophysics",
      "year": 2013,
      "month": "Jun",
      "volume": 554
    },
    "note": {
      "typesetting": "TeX",
      "pages": 7,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 1232326,
      "adsabs": "2013A&A...554A.129P"
    }
  }
}