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Search for p-mode oscillations in DA white dwarfs with VLT-ULTRACAM I. Upper limits to the p-modes
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Silvotti, R., Fontaine, G., Pavlov, M., Marsh, T. R., Dhillon, V. S., Littlefair, S. P. and Getman, F. (2011) Search for p-mode oscillations in DA white dwarfs with VLT-ULTRACAM I. Upper limits to the p-modes. Astronomy & Astrophysics, Vol.525 . Article no. A64. doi:10.1051/0004-6361/201015334 ISSN 0004-6361.
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Official URL: http://dx.doi.org/10.1051/0004-6361/201015334
Abstract
Aims. 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.
Methods. 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 5 x 10(-4) would have been easily detected, as shown by a simple simulation. For G 185-32 we note an excess of power below similar to 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, the detection of a new g-mode DAV pulsator near the blue edge of the ZZ Ceti instability strip was claimed (Silvotti et al. 2006, MmSAI, 77, 486) and will be described in detail in a forthcoming paper (Silvotti et al., A&A, in prep. (Paper II)).
| Item Type: | Journal Article | ||||
|---|---|---|---|---|---|
| Subjects: | Q Science > QB Astronomy | ||||
| Divisions: | Faculty of Science, Engineering and Medicine > Science > Physics | ||||
| Journal or Publication Title: | Astronomy & Astrophysics | ||||
| Publisher: | EDP Sciences | ||||
| ISSN: | 0004-6361 | ||||
| Official Date: | January 2011 | ||||
| Dates: |
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| Volume: | Vol.525 | ||||
| Number of Pages: | 7 | ||||
| Page Range: | Article no. A64 | ||||
| DOI: | 10.1051/0004-6361/201015334 | ||||
| Status: | Peer Reviewed | ||||
| Publication Status: | Published | ||||
| Access rights to Published version: | Restricted or Subscription Access | ||||
| Funder: | STFC, RCUK | ||||
| Grant number: | PP/D002370/1, PP/E001777/1 (STFC) |
Data sourced from Thomson Reuters' Web of Knowledge
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