{
  "id": "1011.4392",
  "version": "v1",
  "published": "2010-11-19T10:53:22.000Z",
  "updated": "2010-11-19T10:53:22.000Z",
  "title": "Search for p-mode oscillations in DA white dwarfs with VLT-ULTRACAM. I. Upper limits to the p-modes",
  "authors": [
    "Roberto Silvotti",
    "Gilles Fontaine",
    "Mike Pavlov",
    "Tom R. Marsh",
    "Vik S. Dhillon",
    "Stuart P. Littlefair",
    "Fedor Getman"
  ],
  "comment": "7 pages, 6 figures, Astronomy & Astrophysics in press",
  "categories": [
    "astro-ph.SR"
  ],
  "abstract": "The main goal of this project is to search for p-mode oscillations in a selected sample of DA white dwarfs near the blue edge of the DAV (g-mode) instability strip, where the p-modes should be excited following theoretical models. A set of high quality time-series data on nine targets has been obtained in 3 photometric bands (Sloan u', g', r') using ULTRACAM at the VLT with a typical time resolution of a few tens of ms. Such high resolution is required because theory predicts very short periods, of the order of a second, for the p-modes in white dwarfs. The data have been analyzed using Fourier transform and correlation analysis methods. Results: P-modes have not been detected in any of our targets. The upper limits obtained for the pulsation amplitude, typically less than 0.1%, are the smallest limits reported in the literature. The Nyquist frequencies are large enough to fully cover the frequency range of interest for the p-modes. For the brightest target of our sample, G 185-32, a p-mode oscillation with a relative amplitude of 5x10**(-4) would have been easily detected, as shown by a simple simulation. For G 185-32 we note an excess of power below ~2 Hz in all the three nights of observation, which might be due in principle to tens of low-amplitude close modes. However, neither correlation analysis nor Fourier transform of the amplitude spectrum show significant results. We also checked the possibility that the p-modes have a very short lifetime, shorter than the observing runs, by dividing each run in several subsets and analyzing these subsets independently. The amplitude spectra show only a few peaks with S/N ratio higher than 4 sigma but the same peaks are not detected in different subsets, as we would expect, and we do not see any indication of frequency spacing. As a secondary result of this project, ... (see the paper)",
  "revisions": [
    {
      "version": "v1",
      "updated": "2010-11-19T10:53:22.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "da white dwarfs",
      "p-mode oscillation",
      "upper limits",
      "vlt-ultracam",
      "amplitude spectrum"
    ],
    "tags": [
      "journal article"
    ],
    "publication": {
      "doi": "10.1051/0004-6361/201015334",
      "journal": "Astronomy and Astrophysics",
      "year": 2011,
      "month": "Jan",
      "volume": 525
    },
    "note": {
      "typesetting": "TeX",
      "pages": 7,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 878230,
      "adsabs": "2011A&A...525A..64S"
    }
  }
}