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1. Whole Earth telescope observations of the ZZ Ceti star HL Tau 76

Author

Waldemar Ogloza, P. Ibbetson, S. Zola, Matt A. Wood, M. S. O'Brien, Nicole M. Silvestri, R. E. Nather, Antonio Kanaan, E. W. Klumpe, Travis S. Metcalfe, S. Bernabei, G. Vauclair, Dong Xu, E. G. Meištas, Luciano Fraga, B. N. Ashoka, R. Kalytis, Ana Ulla, J. Krzesinski, N. Dolez, Michael D. Reed, Denis J. Sullivan, T. J. Ahrens, T. Sullivan, Rimvydas Janulis, Divas Sanwal, S. J. Kleinman, M. Chevreton, J. E. Solheim, Steven D. Kawaler, Pawel Moskalik, Roberto Silvotti, J. M. Gonzalez Perez, J. N. Fu, Xiao-Jun Jiang, Eran O. Ofek, Elia M. Leibowitz, D. Ališauskas, Anjum S. Mukadam, Gerald Handler, D. Kilkenny, Laboratoire Astrophysique de Toulouse-Tarbes (LATT), Centre National de la Recherche Scientifique (CNRS)-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées, Escola de Odontologia, UNIVALE, Unilever R&D, Brain imaging (LIAMA), Laboratoire Franco-Chinois d'Informatique, d'Automatique et de Mathématiques Appliquées (LIAMA), Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Institut National de la Recherche Agronomique (INRA)-Chinese Academy of Sciences [Changchun Branch] (CAS)-Institut National de Recherche en Informatique et en Automatique (Inria)-Institute of Automation - Chinese Academy of Sciences-Centre National de la Recherche Scientifique (CNRS)-Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Institut National de la Recherche Agronomique (INRA)-Chinese Academy of Sciences [Changchun Branch] (CAS)-Institut National de Recherche en Informatique et en Automatique (Inria)-Institute of Automation - Chinese Academy of Sciences-Centre National de la Recherche Scientifique (CNRS), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), and Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)

Subjects
Physics, Rotation period, 010308 nuclear & particles physics, stars: white dwarfs, Spectral density, Astronomy, White dwarf, Astronomy and Astrophysics, Astrophysics, stars: interiors, Star (graph theory), Rotation, 01 natural sciences, law.invention, [PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], Telescope, Space and Planetary Science, Duty cycle, law, 0103 physical sciences, stars: oscillations, Instability strip, 010303 astronomy & astrophysics, stars: individual: HL Tau 76
Abstract

International audience; This paper analyses the Whole Earth Telescope observations of HL Tau 76, the first discovered pulsating DA white dwarf. The star was observed during two Whole Earth Telescope campaigns. It was a second priority target during the XCOV13 campaign in 1996 and the first priority one during the XCOV18 campaign in 1999. The 1999 campaign reached 66.5% duty cycle. With a total duration of 18 days, the frequency resolution achieved is 0.68 ?Hz. With such a frequency resolution, we were able to find as many as 78 significant frequencies in the power spectrum, of which 34 are independent frequencies after removal of all linear combinations. In taking into account other frequencies present during the 1996 WET campaign and those present in earlier data, which do not show up in the 1999 data set, we find a total of 43 independent frequencies. This makes HL Tau 76 the richest ZZ Ceti star in terms of number of observed pulsation modes. We use those pulsation frequencies to determine as much as possible of the internal structure of HL Tau 76. The pulsations in HL Tau 76 cover a wide range of periods between 380 s and 1390 s. We propose an identification for 39 of those 43 frequencies in terms of ?=1 and ?=2 non-radial g-modes split by rotation. We derive an average rotation period of 2.2 days. The period distribution of HL Tau 76 is best reproduced if the star has a moderately "thick" hydrogen mass fraction log qH ? -7.0. The results presented in this paper constitute a starting point for a detailed comparison of the observed periods with the periods calculated for models as representative as possible of HL Tau 76.

Published
2006

2. Constraining the Evolution of ZZ Ceti

Author

N. Dolez, Pawel Moskalik, R. L. Riddle, Minia Manteiga, Gerald Handler, O. Suárez, Antonio Kanaan, W. Ogloza, J. E. Solheim, D. Kilkenny, B. N. Ashoka, Jaymie M. Matthews, Jian-Ning Fu, R. E. Nather, J. Krzesinski, M. S. O’Brien, T. J. Ahrens, Luciano Fraga, R. R. Shobbrook, Mukremin Kilic, Paul A. Bradley, Joyce A. Guzik, Eran O. Ofek, S. J. Kleinman, A. F. M. Costa, M. Müller, Nicole M. Silvestri, Elia M. Leibowitz, Margarida S. Cunha, T. K. Watson, R. Kalytis, Souza Oliveira Kepler, M. Chevreton, Fergal Mullally, O. Giovannini, Pierre Bergeron, Santosh Joshi, K. Sekiguchi, D. Ališauskas, Gilles Fontaine, E. G. Meištas, Atsuko Nitta, T. von Hippel, Divas Sanwal, Staszek Zola, D. J. Sullivan, R. Janulis, Anjum S. Mukadam, Donald E Winget, Xiao-Jun Jiang, D. W. Kurtz, Donal O'Donoghue, Roberto Silvotti, P. V. Birch, E. W. Klumpe, F. Johannessen, G. Vauclair, D. W. Xu, T. Sullivan, Matt A. Wood, P. Ibbetson, Ana Ulla, Michael D. Reed, T. S. Metcalfe, J. M. Gonzalez-Perez, S. Bernabei, Steven D. Kawaler, Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Pôle Astronomie du LESIA, and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris

Subjects
Proper motion, oscillations [Stars], evolution [Stars], Astrophysics, Asteroseismology, Movimento estelar, Pulsar, Modelos estelares, Astrophysics::Solar and Stellar Astrophysics, Stellar evolution, Physics, White dwarfs, Astronomy, White dwarf, Astronomy and Astrophysics, Espectros estelares, Atomic clock, Estrelas variaveis, variables: other [Stars], individual (ZZ Ceti, R548) [Stars], Pulsacoes estelares, Anãs brancas, Space and Planetary Science, Stochastic drift, Astrophysics::Earth and Planetary Astrophysics, Variable star, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract

We report our analysis of the stability of pulsation periods in the DAV star (pulsating hydrogen atmosphere white dwarf) ZZ Ceti, also called R548. On the basis of observations that span 31 years, we conclude that the period 213.13 s observed in ZZ Ceti drifts at a rate dP/dt 5 (5.5 plus or minus 1.9) x 10(exp -15) ss(sup -1), after correcting for proper motion. Our results are consistent with previous P values for this mode and an improvement over them because of the larger time base. The characteristic stability timescale implied for the pulsation period is |P||P(raised dot)|greater than or equal to 1.2 Gyr, comparable to the theoretical cooling timescale for the star. Our current stability limit for the period 213.13 s is only slightly less than the present measurement for another DAV, G117-B15A, for the period 215.2 s, establishing this mode in ZZ Ceti as the second most stable optical clock known, comparable to atomic clocks and more stable than most pulsars. Constraining the cooling rate of ZZ Ceti aids theoretical evolutionary models and white dwarf cosmochronology. The drift rate of this clock is small enough that we can set interesting limits on reflex motion due to planetary companions.

Published
2003

3. The temporal spectrum of the sdB pulsating star HS 2201+2610 at 2 ms resolution

Author

E. G. Meištas, O. Bärnbantner, U. Heber, O. Cordes, R. Kalytis, Stefan Dreizler, R. L. Riddle, J. Bochanski, S. Bernabei, Rimvydas Janulis, Sonja Schuh, Michael D. Reed, Stéphane Charpinet, D. Ališauskas, Roberto Silvotti, Roy Ostensen, Terry D. Oswalt, S. Marinoni, E. Goehler, Xiao-Jun Jiang, J. M. Gonzalez Perez, Nicole M. Silvestri, and G. Carlson

Subjects
Physics, Photometry (optics), Amplitude, Space and Planetary Science, Excited state, White dwarf, Astronomy and Astrophysics, Astrophysics, Effective temperature, Horizontal branch, Surface gravity, Secular variation
Abstract

In this article we present the results of more than 180 hours of time-series photometry on the low gravity (log g = 5.4, T e f f = 29 300 K, log He/H = -3.0 by number) sdB pulsating star HS 2201+2610, obtained between September 2000 and August 2001. The temporal spectrum is resolved and shows 5 close frequencies: three main signals at 2860.94, 2824.10 and 2880.69 μHz, with amplitudes of about 1%, 0.5% and 0.1% respectively, are detected from single run observations; two further peaks with very low amplitude (

Published
2002

4. The pulsation modes of the pre-white dwarf PG 1159-035

Author

J. E. S. Costa, W. Ogloza, R. Kalytis, T. J. Ahrens, Anjum S. Mukadam, Souza Oliveira Kepler, S. A. Good, J. Larrison, Albert D. Grauer, E. W. Klumpe, Gerald Handler, Donald E Winget, R. Rosen, H. Lee, P. Martinez, Encarni Romero-Colmenero, O. Giovannini, Matt A. Wood, F. Johannessen, M. C. Akan, R. Janulis, Brian Warner, G. Viraghalmy, X. J. Jiang, Michael H. Montgomery, M. Vuckovic, Leandro Gabriel Althaus, T. Sullivan, M. S. O'Brien, N. Dolez, J.-E. Solheim, Denis J. Sullivan, E. G. Meištas, Fergal Mullally, A. F. M. Costa, A. V. Sergeev, Andrzej S. Baran, M. Paparó, Stanisław Zoła, S. Seetha, Judith L. Provencal, Matthew R. Burleigh, J. C. Clemens, Paul A. Bradley, Antonio Kanaan, Travis S. Metcalfe, Stefan Dreizler, J. L. Deetjen, Jian-Ning Fu, Harry L. Shipman, R. E. Nather, T. Lawrence, Jurek Krzesinski, Steven D. Kawaler, J. M. Gonzalez Perez, A. Ulla, Kazuhiro Sekiguchi, Martin A. Barstow, B. N. Ashoka, S. L. Kim, Alejandro H. Córsico, Reed Riddle, Nicole M. Silvestri, Thorsten Nagel, S. Marinoni, Ö. Hürkal, Sonja Schuh, G. Vauclair, E. Pakštienė, Roberto Silvotti, D. O'Donoghue, M. Chevreton, R. Crowe, Atsuko Nitta, Scot Kleinman, Ömür Çakırlı, Mukremin Kilic, Centro de Fìsica Atòmica (CFA), Universidade de Lisboa (ULISBOA), Brain imaging (LIAMA), Laboratoire Franco-Chinois d'Informatique, d'Automatique et de Mathématiques Appliquées (LIAMA), Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Institut National de la Recherche Agronomique (INRA)-Chinese Academy of Sciences [Changchun Branch] (CAS)-Institut National de Recherche en Informatique et en Automatique (Inria)-Institute of Automation - Chinese Academy of Sciences-Centre National de la Recherche Scientifique (CNRS)-Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Institut National de la Recherche Agronomique (INRA)-Chinese Academy of Sciences [Changchun Branch] (CAS)-Institut National de Recherche en Informatique et en Automatique (Inria)-Institute of Automation - Chinese Academy of Sciences-Centre National de la Recherche Scientifique (CNRS), Department of Molecular Microbiology and Biotechnology, Tel Aviv University [Tel Aviv], Laboratoire Astrophysique de Toulouse-Tarbes (LATT), Centre National de la Recherche Scientifique (CNRS)-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées, Department of Electronic and Electrical Engineering, Pohang University of Science and Technology (POSTECH), Institute of Applied Physics of RAS, Russian Academy of Sciences [Moscow] (RAS), Department of Physics and Astronomy [Ames, Iowa], Iowa State University (ISU), University of Waterloo [Waterloo], Ege Üniversitesi, Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS), Universidade de Lisboa = University of Lisbon (ULISBOA), Tel Aviv University (TAU), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), and Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)

Subjects
Rotation period, Astrofísica, Ciencias Astronómicas, 010504 meteorology & atmospheric sciences, individual: PG 1159-035 [Stars], Ciencias Físicas, stars:evolution, stars:white dwarfs, Astrophysics, stars: interiors, 01 natural sciences, stars: individual: PG 1159-035, purl.org/becyt/ford/1 [https], Gravitation, stars:oscillations, asteroseismology: general, Astrophysics::Solar and Stellar Astrophysics, 010303 astronomy & astrophysics, Multiplet, Physics, Solar mass, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], stars: white dwarfs, Astrophysics (astro-ph), stars : white dwarfs, Radius, Magnetic field, Pulsacoes estelares, stars : interiors, Astrophysics::Earth and Planetary Astrophysics, stars: oscillations, CIENCIAS NATURALES Y EXACTAS, Convection, Oscillations, PG 1159-035 (estrella), oscillations [Stars], FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, stars : oscillations, white dwarfs [Stars], [PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], 0103 physical sciences, stars : individual : PG 1159-035, Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences, interiors [Stars], White dwarf, White dwarfs, Astronomy and Astrophysics, purl.org/becyt/ford/1.3 [https], VDP::Mathematics and natural science: 400::Physics: 430::Astrophysics, astronomy: 438, Astronomía, Interior stars, white dwarfs: individual( GD358), 13. Climate action, Space and Planetary Science, Oscilacoes, Anãs brancas, oscillations, stars: individual, PG 1159-035, stars: white dwarfs [stars], Interior estelar
Abstract

Context. PG 1159-035, a pre-white dwarf with Teff ≃ 140000 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 M/M⊙= 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 rc/R* = 0.83 ± 0.05. From the multiplet splitting, we calculated the rotational period Prot = 1.3920 ± 0.0008 days and an upper limit for the magnetic field, B < 2000 G. The total power of the pulsation modes at the stellar surface changed less than 30% for ℓ = 1 modes and less than 50% for ℓ = 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., La lista completa de autores que integran el documento puede consultarse en el archivo., Facultad de Ciencias Astronómicas y Geofísicas, Instituto de Astrofísica de La Plata

Published
2008

5. Whole Earth Telescope observations of BPM 37093: A seismological test of crystallization theory in white dwarfs

Author

A. Kanaan, A. Nitta, D. E. Winget, S. O. Kepler, M. H. Montgomery, T. S. Metcalfe, H. Oliveira, L. Fraga, A. F. M. da Costa, J. E. S. Costa, B. G. Castanheira, O. Giovannini, R. E. Nather, A. Mukadam, S. D. Kawaler, M. S. O'Brien, M. D. Reed, S. J. Kleinman, J. L. Provencal, T. K. Watson, D. Kilkenny, D. J. Sullivan, T. Sullivan, B. Shobbrook, X. J. Jiang, B. N. Ashoka, S. Seetha, E. Leibowitz, P. Ibbetson, H. Mendelson, E. G. Meištas, R. Kalytis, D. Ališauskas, D. O'Donoghue, D. Buckley, P. Martinez, F. van Wyk, R. Stobie, F. Marang, L. van Zyl, W. Ogloza, J. Krzesinski, S. Zola, P. Moskalik, M. Breger, A. Stankov, R. Silvotti, A. Piccioni, G. Vauclair, N. Dolez, M. Chevreton, J. Deetjen, S. Dreizler, S. Schuh, J. M. Gonzalez Perez, R. Østensen, A. Ulla, M. Manteiga, O. Suarez, M. R. Burleigh, M. A. Barstow, Departamento de Física (CFM), Universidade Federal de Santa Catarina, Apache Point Observatory, Department of Astronomy, University of Texas, Instituto de Física, Universidade Federal do Rio Grande do Sul, Institute of Astronomy, University of Cambridge (IoA), Harvard-Smithsonian Center for Astrophysics, Departamento de Física e Química, Universidade de Caxias do Sul, Department of Physics and Astronomy, Iowa State University, Department of Physics and Astronomy, University of Delaware, Southwestern University, South African Astronomical Observatory (SAAO), Victoria University of Wellington, Chatterton Astronomy Department, University of Sydney, Astronomical Observatory, Academy of Sciences, Indian Space Research Organization, Tel Aviv University (TAU), Institute of Theoretical Physics and Astronomy, Vilnius University, Vilnius University, Mount Suhora Observatory, Cracow Pedagogical University, Centrum Astronomiczne im. M. Kopernika, Warszawa (CAMK), Institut für Astronomie, Universität Wien (IfA), INAF-Osservatorio Astronomico di Capodimonte (INAF-OAC), Alma Mater Studiorum Università di Bologna [Bologna] (UNIBO), Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France, Observatoire de Paris, Université Paris sciences et lettres (PSL), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Pôle Astronomie du LESIA, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Eberhard Karls Universität Tübingen = Eberhard Karls University of Tuebingen, University of Tromsø, Isaac Newton Group of Telescopes, Universidade de Vigo, and University of Leicester

Subjects
010504 meteorology & atmospheric sciences, Stellar mass, oscillations [Stars], Hidrogênio, evolution [Stars], FOS: Physical sciences, Astrophysics, Trapping, Massa estelar, 01 natural sciences, law.invention, Telescope, law, Evolucao estelar, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, Crystallization, individual: BPM 37093 [Stars], 010303 astronomy & astrophysics, evolution, individual, BPM 37093, interiors, stars, oscillations, white dwarfs, 0105 earth and related environmental sciences, Physics, SIMPLE (dark matter experiment), Astrophysics (astro-ph), interiors [Stars], White dwarfs, White dwarf, Astronomy and Astrophysics, Estrelas variaveis, Core (optical fiber), Anãs brancas, Pulsacoes estelares, Space and Planetary Science, Astrophysics::Earth and Planetary Astrophysics, Interior estelar, Instability strip, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract

BPM 37093 is the only hydrogen-atmosphere white dwarf currently known which has sufficient mass (~ 1.1 M_sun) to theoretically crystallize while still inside the ZZ Ceti instability strip (T_eff ~ 12,000 K). As a consequence, this star represents our first opportunity to test crystallization theory directly. If the core is substantially crystallized, then the inner boundary for each pulsation mode will be located at the top of the solid core rather than at the center of the star, affecting mainly the average period spacing. This is distinct from the "mode trapping" caused by the stratified surface layers, which modifies the pulsation periods more selectively. In this paper we report on Whole Earth Telescope observations of BPM 37093 obtained in 1998 and 1999. Based on a simple analysis of the average period spacing we conclude that a large fraction of the total stellar mass is likely to be crystallized., Comment: 7 pages, 3 figures, 3 tables, accepted for Astronomy & Astrophysics

Published
2005

6. Amplitude and frequency variability of the pulsating DB white dwarf stars KUV 05134+2605 and PG 1654+160 observed with the Whole Earth Telescope

Author

G. Handler, D. O'Donoghue, M. Muller, J.- E. Solheim, J. M. Gonzalez-Perez, F. Johannessen, M. Paparo, B. Szeidl, G. Viraghalmy, R. Silvotti, G. Vauclair, N. Dolez, E. Pallier, M. Chevreton, D. W. Kurtz, G. E. Bromage, M. S. Cunha, R. Ostensen, L. Fraga, A. Kanaan, A. Amorim, O. Giovannini, S. O. Kepler, A. F. M. Da Costa, R. F. Anderson, M. A. Wood, N. Silvestri, E. W. Klumpe, R. F. Carlton, R. H. Miller, J. P. McFarland, A. D. Grauer, S. D. Kawaler, R. L. Riddle, M. D. Reed, R. E. Nather, D. E. Winget, J. A. Hill, T. S. Metcalfe, A. S. Mukadam, M. Kilic, T. K. Watson, S. J. Kleinman, A. Nitta, J. A. Guzik, P. A. Bradley, K. Sekiguchi, D. J. Sullivan, T. Sullivan, R. R. Shobbrook, X. Jiang, P. V. Birch, B. N. Ashoka, S. Seetha, V. Girish, S. Joshi, T. N. Dorokhova, N. I. Dorokhov, M. C. Akan, E. G. Meistas, R. Janulis, R. Kalytis, D. Alisauskas, S. K. Anguma, P. C. Kalebwe, P. Moskalik, W. Ogloza, G. Stachowski, G. Pajdosz, S. Zola, Ege Üniversitesi, Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Pôle Astronomie du LESIA, and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris

Subjects
010504 meteorology & atmospheric sciences, individual: KUV 05134+2605 [Stars], oscillations [Stars], FOS: Physical sciences, Fotometria estelar, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, stars : individual : KUV 05134+2605, 01 natural sciences, stars : oscillations, law.invention, Telescope, Photometry (optics), stars : individual : PG 1654+160, law, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, individual: PG 1654+160 [Stars], 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences, Physics, Astrophysics (astro-ph), White dwarf, Astronomy and Astrophysics, stars : variables : other, Estrelas variaveis, variables: other [Stars], Stars, Amplitude, [SDU]Sciences of the Universe [physics], Pulsacoes estelares, Anãs brancas, Space and Planetary Science, Mode coupling, Astrophysics::Earth and Planetary Astrophysics, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract

WOS: 000182039700036, We have acquired new time series photometry of the two pulsating DB white dwarf stars KUV 05134+2605 and PG 1654+160 with the Whole Earth Telescope. Additional single-site photometry is also presented. We use all these data plus all available archival measurements to study the temporal behaviour of the pulsational amplitudes and frequencies of these stars for the first time. We demonstrate that both KUV 05134+2605 and PG 1654+160 pulsate in many modes, the amplitudes of which are variable in time; some frequency variability of PG 1654+160 is also indicated. Beating of multiple pulsation modes cannot explain our observations; the amplitude variability must therefore be intrinsic. We cannot find stable modes to be used for determinations of the evolutionary period changes of the stars. Some of the modes of PG 1654+160 appear at the same periods whenever detected. The mean spacing of these periods (approximate to40 s) suggests that they are probably caused by non-radial gravity-mode pulsations of spherical degree l = 1. If so, PG 1654+160 has a mass around 0.6 M.. The time-scales of the amplitude variability of both stars (down to two weeks) are consistent with theoretical predictions of resonant mode coupling, a conclusion which might however be affected by the temporal distribution of our data.

Published
2003

7. The Everchanging Pulsating White Dwarf GD358

Author

Donald E Winget, Antonio Kanaan, Encarni Romero-Colmenero, Nicole M. Silvestri, J. E. Solheim, R. E. Nather, J. Larrison, Waldemar Ogloza, Jam Shaw, R. Kalytis, T. Sullivan, Paul A. Bradley, J. Xiaojun, Thorsten Nagel, Fu J. Ning, K. Sekiguchi, A. F. M. Costa, Souza Oliveira Kepler, M. Chevreton, Staszek Zola, E. W. Klumpe, D. Sullivan, F. Johannessen, Reed Riddle, J. L. Deetjen, Steven D. Kawaler, Martha L. Boyer, Matt A. Wood, G. Vauclair, T. S. Metcalfe, R. Janulis, J. Krzesinski, E. G. Meištas, P. Martinez, A. E. Collins, A. K. Jones, S. J. Kleinman, J. E. S. Costa, Ana Ulla, T. J. Ahrens, Anjum S. Mukadam, Donal O'Donoghue, J. M. Gonzalez Perez, Atsuko Nitta, S. Dreizler, Sonja Schuh, Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Pôle Astronomie du LESIA, and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris

Subjects
oscillations [Stars], FOS: Physical sciences, evolution [Stars], Fotometria estelar, Astrophysics, 01 natural sciences, law.invention, variables: general [Stars], Telescope, white dwarfs [Stars], law, 0103 physical sciences, Stellar structure, Linear combination, 010303 astronomy & astrophysics, Multiplet, Physics, 010308 nuclear & particles physics, Astrophysics (astro-ph), Mode (statistics), White dwarf, Astronomy and Astrophysics, Pulse (physics), Estrelas variaveis, Amplitude, [SDU]Sciences of the Universe [physics], 13. Climate action, Space and Planetary Science, Pulsacoes estelares, white dwarfs, stars: variables: general, stars: oscillations, stars: individual: GD 358, stars: evolution [stars], Astrophysics::Earth and Planetary Astrophysics, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], individual: GD 358 [Stars]
Abstract

We report 323 hours of 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 232 000 independent 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 796s. 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 into 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 2000 observations only the k=9 mode displays 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 timescale., 34 pages, 14 figures, WET data, accepted to A&A

Published
2003

8. Pulsation Period Stability in the SDBV Star HS 2201+2610

Author

Roberto Silvotti and R. Kalytis

Subjects
Physics, Astrophysics::High Energy Astrophysical Phenomena, Spectral window, Astrophysics::Solar and Stellar Astrophysics, White dwarf, Astrophysics, Stability (probability), Secular variation
Abstract

The stability of the pulsation periods of the sdB pulsator HS 2201+2610 is analyzed after 15 months of photometric monitoring. Although the time basis is not long enough to obtain a measurement of P, an upper limit of about 4×10-12 (in absolute value) is derived for the variation of the main pulsation period in time.

Published
2003

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