Whole Earth Telescope observations of the hot helium atmosphere pulsating white dwarf EC 20058-5234

Abstract

We present the analysis of a total of 177h of high-quality optical time-series photometry of the helium atmosphere pulsating white dwarf (DBV) EC 20058-5234. The bulk of the observations (135h) were obtained during a WET campaign (XCOV15) in July 1997 that featured coordinated observing from 4 southern observatory sites over an 8-day period. The remaining data (42h) were obtained in June 2004 at Mt John Observatory in NZ over a one-week observing period. This work significantly extends the discovery observations of this low-amplitude (few percent) pulsator by increasing the number of detected frequencies from 8 to 18, and employs a simulation procedure to confirm the reality of these frequencies to a high level of significance (1 in 1000). The nature of the observed pulsation spectrum precludes identification of unique pulsation mode properties using any clearly discernable trends. However, we have used a global modelling procedure employing genetic algorithm techniques to identify the n, l values of 8 pulsation modes, and thereby obtain asteroseismic measurements of several model parameters, including the stellar mass (0.55 M_sun) and T_eff (~28200 K). These values are consistent with those derived from published spectral fitting: T_eff ~ 28400 K and log g ~ 7.86. We also present persuasive evidence from apparent rotational mode splitting for two of the modes that indicates this compact object is a relatively rapid rotator with a period of 2h. In direct analogy with the corresponding properties of the hydrogen (DAV) atmosphere pulsators, the stable low-amplitude pulsation behaviour of EC 20058 is entirely consistent with its inferred effective temperature, which indicates it is close to the blue edge of the DBV instability strip. (abridged)

arXiv comment19 pages, 8 figures, 5 tables, MNRAS accepted

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• New Pulsating DB White Dwarf Stars from the Sloan Digital Sky Survey
• Periodic Variations in the O-C Diagrams of Five Pulsation Frequencies of the DB White Dwarf EC 20058-5234
• Asteroseismology of the Kepler field DBV White Dwarf - It's a hot one!
• Asteroseismic constraints on diffusion in WD envelopes
• GD358: three decades of observations for the in-depth asteroseismology of a DBV star
• An Upper Bound to the Space Density of Interstellar Comets
• Time series photometry of the helium atmosphere pulsating white dwarf EC 04207-474
• Orbital Characteristics of the Subdwarf-B and F V Star Binary EC~20117-4014(=V4640 Sgr)
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• The Pulsating Helium-Atmosphere White Dwarfs I: New DBVs from the Sloan Digital Sky Survey
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• Anomalous Orbital Characteristics of the AQ Col (EC 05217-3914) System
• Simulating the photometric study of pulsating white dwarf stars in the physics laboratory