2011A&A...525A..64S


Query : 2011A&A...525A..64S

2011A&A...525A..64S - Astronomy and Astrophysics, volume 525A, 64-64 (2011/1-1)

Search for p-mode oscillations in DA white dwarfs with VLT-ULTRACAM. I. Upper limits to the p-modes.

SILVOTTI R., FONTAINE G., PAVLOV M., MARSH T.R., DHILLON V.S., LITTLEFAIR S.P. and GETMAN F.

Abstract (from CDS):

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. 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 ∼2Hz 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 4σ 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., 2006MmSAI..77..486S) and will be described in detail in a forthcoming paper (Silvotti et al., A&A, in prep. (Paper II)).

Abstract Copyright:

Journal keyword(s): white dwarfs - stars: oscillations

Simbad objects: 11

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Number of rows : 11
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024
#notes
1 EGGR 409 WD* 01 14 37.6538960064 +10 41 04.757053956   15.27 15.41 15.69   DB2.5 70 0
2 GD 127 WD* 11 05 15.3077601000 +00 16 26.175409392   15.43   15.3   DA3.5 41 0
3 GD 133 WD* 11 19 12.3988618680 +02 20 33.045927216   14.76 14.57 14.8   DA4.0 88 0
4 LP 734-74 WD* 12 06 56.2914581818 -13 53 53.037650505   15.72 15.53 15.6   DA4.4 33 0
5 HS 1253+1033 WD* 12 56 27.9832012704 +10 17 11.391150156   14.4       DA3.8 13 0
6 SDSS J133831.75-002328.0 WD* 13 38 31.7495135568 -00 23 27.996154224           DA4 23 0
7 V* MY Aps WD* 14 33 07.6366196272 -81 20 14.128475593   13.49 13.35 13.65   DA4.1 141 0
8 Ton 213 WD* 14 45 28.4732292408 +29 21 32.074698816   14.5       DA3.8 18 0
9 GD 358 WD* 16 47 18.3925183824 +32 28 32.862804384 12.511 13.530 13.653 13.752 13.852 DB2 350 0
10 EGGR 177 WD* 18 30 39.4327226184 -10 36 59.931584028   15.41 15.28 15.82   DA3.6 38 0
11 V* PY Vul WD* 19 37 13.7502269447 +27 43 18.733503670   13.14   12.7   DA4.0 130 0

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