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Preprint G/03

The everchanging pulsating white dwarf GD358

Kepler S.O. (1), Nather R.E. (2), Winget D.E. (2), Nitta A. (3) Kleinman S. (3), Metcalfe T. (2,4), Sekiguchi K. (5), Xiaojun J. (6), Sullivan D. (7), Sullivan T. (7), Janulis R. (8), Meistas E. (8),Kalytis R. (8), Krzesinski J. (9), Ogloza W. (9), Zola S. (10), O'Donogue D. (11), Romero-Colmenero E. (11), Martinez P. (11), Dreizler S. (12), Deetjen J. (12), Nagel T. (12), schuh, S.L. (12), Vauclair G. (13), Jian Ning F. (13), Chevereton M. (14), Solheim J.-E. (15), Gonzales Perez J. (15), Johannessen F. (15), Kanaan A. (16), Costa J.E. (1), Costa A.F.M. (1), Wood M.A. (17), Silvestri N. (17), Ahrens T.J. (17), Jones A.K. (18), Collins A.E. (19), Boyer M. (20), Shaw J.S. (21), Mukadam A. (2), Klumpe E.W. (22), Larrison J. (22), Kawaler S. (23), Riddle R. (23), Ulla A. (24), Bradley P. (25)

(1) Instituto de Fisica da UFRGS, Porto Alegre, RS-Brazil
(2) Department of Astronomy & Mc Donald Observatory, University of Texas, Austin, TX 78712, USA
(3) Sloan Digital Sky Survey, Apache Point Observatory, P.O. Box 59, Sunspot, NM 88349, USA
(4) Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
(5) Subaru National Astronomical Observatory of Japan
(6) Beijing Astronomical Observatory, Academy of sciences, Beijing 100080, China
(7) University of Victoria, Wellington, New Zealand
(8) Institute of Theoretical Physics and Astronomy, Gostouto 12, Vilnius 2600, Lithuania
(9) Mt. Suhora Observatory, Cracow Pedagogical University, Ul. Podchorazych 2, 30-084 Cracow, Poland
(10) Jagiellonian University, Krakow, Poland
(11) South African Astronomical observatory
(12) Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, D-72076 Tübingen, Germany
(13) Universite Paul Sabatier, Observatoire Midi-Pyrenees, CNRS/UMR5572, 14 av. E. Belin, 31400 Toulouse, France
(14) Observatoire de Paris-Meudon, DAEC, 92195 Meudon, France
(15) Institutt for fysikk, 9037 Tromsoe, Norway
(16) Departamento de Fisica, Universidade Federal de Santa Catarina, CP 476, CEP 88040-900, Florianopolis, Brazil
(17) Dept. of Physics and Space sciences & The SARA Observatory, Florida Institute of Technology, Melbourne, FL 32901
(18) University of Florida, 202 Nuclear Sciences Center Gainesville, FL 32611-8300
(19) Johnson Space Center, 2101 NASA road 1, Mail code GT2, Houston, TX 77058, USA
(20) University of Minnesota, Department of Physics & Astronomy, 116 Church St. S.E., Minneapolis, MN 55455
(21) University of Georgia at Athens, Department of Physics and Astronomy, Athens, GA 30602-2451, USA
(22) Middle Tennesse State University, Department of Physics and Astronomy, Murfreesboro, TN 37132, USA
(23) Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA
(24) Universidade de Vigo, Depto. de Fisica Aplicada, Facultade de ciencias, Campus Marcosende-Lagoas, 36200 Vigo (Pontevedra), Spain
(25) Los alamos National laboratory, X-2, MS T-085 Los Alamos, NM 87445, USA

A&A 401, 639 (2003)

Abstract. We report 323 hours nearly uninterrupted time series photometric observations of the DBV star GD 358 acquired with the Whole Earth Telescope (WET) during May 23rd to June 8th, 2000. We acquired more than 232000independent measurements. We also report on 48 hours of time-series photometric observations in aug 1996. We detected the non-radial g-modes consistent with degree l=1 and radial order 8 to 20 and their linear combinations up to 6th order. We also detect, for the first time, a high amplitude l=2 mode, with a period of 796 s. In the 2000 WET data, the largest amplitude modes are similar to those detected with the WET observations of 1990 and 1994, but the highest combination order previously detected was 4th order. At one point during the 1996 observations, most of the pulsation energy was transferred to the radial order k=8 mode, which displayed a sinusoidal pulse shape in spite of the large amplitude. the multiplet structure of the individual modes changes from year to year, and during the 200 observations only the k=9 mode dispalys clear normal triplet structure. Even though the pulsation amplitudes change on timescales of days and years, the eigenfrequencies remain essentially the same, showing the stellar structure is not changing on any dynamical time scale.

Key words: stars: white dwarfs - stars: variables: general - stars: oszillations - stars: individual: GD 358 - stars: evolution


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