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Title:
Whole Earth Telescope observations of the hot helium atmosphere pulsating white dwarf EC20058-5234
Authors:
Sullivan, D. J.; Metcalfe, T. S.; O'Donoghue, D.; Winget, D. E.; Kilkenny, D.; van Wyk, F.; Kanaan, A.; Kepler, S. O.; Nitta, A.; Kawaler, S. D.; Montgomery, M. H.; Nather, R. E.; O'Brien, M. S.; Bischoff-Kim, A.; Wood, M.; Jiang, X. J.; Leibowitz, E. M.; Ibbetson, P.; Zola, S.; Krzesinski, J.; Pajdosz, G.; Vauclair, G.; Dolez, N.; Chevreton, M.
Affiliation:
AA(School of Chemical & Physical Sciences, Victoria University of Wellington, PO Box 600, Wellington, New Zealand), AB(Department of Astronomy and McDonald Observatory, University of Texas, Austin, TX 78712, USA; High Altitude Observatory, National Center for Atmospheric Research, PO Box 3000, Boulder, CO 80307, USA), AC(South African Astronomical Observatory, PO Box 9, Observatory 7935, South Africa), AD(Department of Astronomy and McDonald Observatory, University of Texas, Austin, TX 78712, USA), AE(South African Astronomical Observatory, PO Box 9, Observatory 7935, South Africa; Department of Physics, University of the Western Cape, Private Bag X17, Belville 7535, South Africa), AF(South African Astronomical Observatory, PO Box 9, Observatory 7935, South Africa), AG(Departamento de Física, UFSC, CP 476, 88040-900 Florianóplois, SC, Brazil), AH(Instituto de Física da UFRGS, 91501-900 Porto Alegre, RS, Brazil), AI(Department of Astronomy and McDonald Observatory, University of Texas, Austin, TX 78712, USA; Visiting Astronomer, Cerro Tololo Inter-American Observatory, Chile; Gemini Observatory, 670 N A'ohoku Pl., Hilo, HI 96720, USA), AJ(Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA), AK(Department of Astronomy and McDonald Observatory, University of Texas, Austin, TX 78712, USA), AL(Department of Astronomy and McDonald Observatory, University of Texas, Austin, TX 78712, USA), AM(Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA; Department of Astronomy, Yale University, PO Box 208101, New Haven, CT 06511, USA), AN(Department of Astronomy and McDonald Observatory, University of Texas, Austin, TX 78712, USA), AO(Department of Physics and Space Sciences and SARA Observatory, Florida Institute of Technology, Melbourne, FL 32901-6975, USA), AP(Beijing Astronomical Observatory, Chinese Academy of Sciences, 20 Datun Road, Chaoyang, Beijing 100012, China), AQ(Department of Physics and Astronomy and Wise Observatory, Tel Aviv University, Tel Aviv 69978, Israel), AR(Department of Physics and Astronomy and Wise Observatory, Tel Aviv University, Tel Aviv 69978, Israel), AS(Astronomical Observatory, Jagiellonian University, Ul. Orla 171, 30-244 Cracow, Poland; Mount Suhora Observatory, Pedagogical University, Ul. Podchoraazych 2, 30-024 Cracow, Poland), AT(Mount Suhora Observatory, Pedagogical University, Ul. Podchoraazych 2, 30-024 Cracow, Poland), AU(Mount Suhora Observatory, Pedagogical University, Ul. Podchoraazych 2, 30-024 Cracow, Poland), AV(Observatoire Midi-Pyrénées, Université Paul Sabatier, CNRS/UMR5572, 14 Avenue Edouard Belin, 31400 Toulouse, France), AW(Observatoire Midi-Pyrénées, Université Paul Sabatier, CNRS/UMR5572, 14 Avenue Edouard Belin, 31400 Toulouse, France), AX(Observatoire de Paris-Meudon, LESIA, 92195 Meudon, France)
Publication:
Monthly Notices of the Royal Astronomical Society, Volume 387, Issue 1, pp. 137-152. (MNRAS Homepage)
Publication Date:
06/2008
Origin:
MNRAS
Astronomy Keywords:
techniques: photometric , stars: individual: EC 20058-5234 , stars: interiors , stars: oscillations , white dwarfs
DOI:
10.1111/j.1365-2966.2008.13074.x
Bibliographic Code:
2008MNRAS.387..137S

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) EC20058-5234. The bulk of the observations (135h) were obtained during a WET campaign (XCOV15) in 1997 July that featured coordinated observing from four southern observatory sites over an 8-d period. The remaining data (42h) were obtained in 2004 June at Mt John Observatory in NZ over a one-week observing period. This work significantly extends the discovery observations of this low-amplitude (few per cent) 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 eight pulsation modes, and thereby obtain asteroseismic measurements of several model parameters, including the stellar mass (0.55 Msolar) and Teff (~28200K). These values are consistent with those derived from published spectral fitting: Teff ~ 28400K and logg ~ 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 EC20058 is entirely consistent with its inferred effective temperature, which indicates it is close to the blue edge of the DBV instability strip. Arguably, our most significant result from this work is the clear demonstration that EC20058 is a very stable pulsator with several dominant pulsation modes that can be monitored for their long-term stability.

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