The pulsation modes of the pre-white dwarf PG 1159-035^*

¹ Instituto de Física, Universidade Federal do Rio Grande do Sul, 91501-970 Porto Alegre, RS, Brazil e-mail: costajes@gmail.com
² Department of Astronomy & McDonald Observatory, University of Texas, Austin, TX 78712, USA
³ Department of Astronomy, Yale University, New Haven, Connecticut, CT 06851, USA e-mail: obrien@astro.yale.edu
⁴ Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA
⁵ Universidade de Caxias, Caxias do Sul, RS, Brazil
⁶ Departamento de Fíica, Universidade Federal de Santa Catarina, CP 476, CEP 88040-900, Florianópolis, SC, Brazil e-mail: kanaan@fsc.ufsc.br
⁷ Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195, USA e-mail: nms@astro.washington.edu
⁸ Gemini Observatory, Hilo, Hawaii, 96720, USA
⁹ Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA
¹⁰ Dept. of Physics and Space Sciences & The SARA Observatory, Florida Institute of Technology, Melbourne, FL 32901, USA
¹¹ Department of Physics and Astronomy, University of Arkansas at Little Rock, USA
¹² Department of Astronomy, The Ohio State University, 140 W. 18th Avenue, Columbus, OH 43210, USA e-mail: kilic@astronomy.ohio-state.edu
¹³ Los Alamos National Laboratory, X-2, MS T-085 Los Alamos, NM 87545, USA
¹⁴ Subaru National Astronomical Observatory of Japan, Mitaka, Tokyo 181, Japan e-mail: kaz@saburu.naoj.org
¹⁵ University of Hawaii, Hilo, Hawaii, USA
¹⁶ Beijing Astronomical Observatory, Academy of Sciences, Beijing 100080, PR China e-mail: jiang@astro.as.utexas.edu
¹⁷ University of Victoria, Wellington, New Zealand
¹⁸ University of North Carolina, Chapell Hill, NC 27599, USA
¹⁹ VU Institute of Theoretical Physics and Astronomy, Goštauto 12, 01108 Vilnius, Lithuania
²⁰ South African Astronomical Observatory
²¹ Mt. Suhora Observatory, Cracow Pedagogical University, UI. Podchorazych 2, 30-084 Cracow, Poland
²² INAF – Osservatorio Astronomico di Capodimonte, Napoli, Italy
²³ INAF – Osservatorio Astronomico di Bologna, Bologna, Italy
²⁴ Université Paul Sabatier, Observatoire Midi-Pyrénées, CNRS/UMR5572, 14 Av. E. Belin, 31400 Toulouse, France
²⁵ Observatoire de Paris-Meudon, DAEC, 92195 Meudon, France e-mail: chevreton@obspm.fr
²⁶ Institut für Astrophysik,Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
²⁷ Institut für Astronomie und Astrophysik Tübingen, Universitat Tübingen, Sand 1, 72076 Tübingen, Germany
²⁸ Institutt for Fysikk, Universitetet i Tromsø, 9037 Tromsø, Norway e-mail: j.e.solheim@astro.uio.no
²⁹ Institut for Teoretisk Astrofysikk, Universitetet i Oslo, pb 1029-Blindern, 0315 Oslo, Norway
³⁰ Instituto de Astrofisica, C/ via Lactea s/n, 38200 La Laguna, Tenerife, Spain
³¹ Universidade de Vigo, Depto. de Física Aplicada, Facultade de Ciencias do Mar, Campus Lagoas-Marcosende s/n, 36200 Vigo, Spain
³² Department of Physics and Astronomy, University of Leicester, UK
³³ High Altitude Observatory, National Center for Atmospheric Research, 3080 Center Green Dr (CG1/3164), USA e-mail: travis@hao.ucar.edu
³⁴ Korea Astronomy and Space Science Institute, Daejeon, 305-348, Korea
³⁵ Terskol Observatory, Ukraine
³⁶ Ege University Observatory, Bornova 35100, Izmir, Turkey
³⁷ Konkoly Observatory, PO Box 67, 1525 Budapest, Hungary
³⁸ Indian Space Research Organization, India
³⁹ Institut für Astronomie, Universität Wien, Turkenschanzstrasse 17, 1180 Wien, Austria
⁴⁰ Ege University Faculty of Science Astronomy and Space Sciences Department, Izmir, Turkey
⁴¹ Middle Tennessee State University, Department of Physics and Astronomy Murfreesboro, TN 37132, USA
⁴² Department of Astronomy, Beijing Normal University, Beijing, PR China
⁴³ Thirty Meter Telescope Project, 2632 E. Washington Blvd, Pasadena, CA 91107, USA e-mail: riddle@tmt.org
⁴⁴ Instituut voor Sterrenkunde, Celestijnenlaan 200B, 3001 Leuven, Belgium e-mail: Maja.Vuckovic@ster.kuleuven.be
⁴⁵ Astronomical Observatory, Jagiellonian University, ul. Orla 171, 30-244 Krakow, Poland e-mail: szola@oa.uj.edu.pl
⁴⁶ Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque S/N, (1900) La Plata, Argentina e-mail: [althaus;acorsico]@fcaglp.unlp.edu.ar
⁴⁷ Instituto de Astrofísica La Plata, IALP, CONICET-UNLP, Argentina

Received: 18 May 2005
Accepted: 31 October 2007

Abstract

Context.PG 1159-035, a pre-white dwarf with 140 000 K, is the prototype of both two classes: the PG 1159 spectroscopic class and the DOV pulsating class. Previous studies of PG 1159-035 photometric data obtained with the Whole Earth Telescope (WET) showed a rich frequency spectrum allowing the identification of 122 pulsation modes. Analyzing the periods of pulsation, it is possible to measure the stellar mass, the rotational period and the inclination of the rotation axis, to estimate an upper limit for the magnetic field, and even to obtain information about the inner stratification of the star.

Aims.We have three principal aims: to increase the number of detected and identified pulsation modes in PG 1159-035, study trapping of the star's pulsation modes, and to improve or constrain the determination of stellar parameters.

Methods.We used all available WET photometric data from 1983, 1985, 1989, 1993 and 2002 to identify the pulsation periods.

Results.We identified 76 additional pulsation modes, increasing to 198 the number of known pulsation modes in PG 1159-035, the largest number of modes detected in any star besides the Sun. From the period spacing we estimated a mass = 0.59 ± 0.02 for PG 1159-035, with the uncertainty dominated by the models, not the observation. Deviations in the regular period spacing suggest that some of the pulsation modes are trapped, even though the star is a pre-white dwarf and the gravitational settling is ongoing. The position of the transition zone that causes the mode trapping was calculated at = 0.83 ± 0.05. From the multiplet splitting, we calculated the rotational period P_rot = 1.3920 ± 0.0008 days and an upper limit for the magnetic field, G. The total power of the pulsation modes at the stellar surface changed less than 30% for = 1 modes and less than 50% for = 2 modes. We find no evidence of linear combinations between the 198 pulsation mode frequencies. PG 1159-035 models have not significative convection zones, supporting the hypothesis that nonlinearity arises in the convection zones in cooler pulsating white dwarf stars.