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1. Whole Earth Telescope observations and seismological analysis of the cool TIL Ceti star GD 154

Author

Chuck Claver, Judith L. Provencal, M. Chevreton, Martin A. Barstow, Tsevi Mazeh, J. A. Belmonte, J. R. Fremy, N. Dolez, Paul A. Bradley, Donald E Winget, S. J. Kleinman, O. Giovannini, Albert D. Grauer, T. K. Watson, J. S. Dixson, R. E. Nather, G. Vauclair, J. C. Clemens, Antonio Kanaan, Elia M. Leibowitz, B. Pfeiffer, F. Wesemael, Pierre Bergeron, Souza Oliveira Kepler, Pawel Moskalik, and Gilles Fontaine

Subjects
Rotation period, Physics, Hydrogen, Astronomy, Spectral density, chemistry.chemical_element, White dwarf, Astronomy and Astrophysics, QB1-991, Astrophysics, Star (graph theory), law.invention, Telescope, chemistry, Space and Planetary Science, law, Harmonics, Earth (classical element)
Abstract

This paper presents the results of high speed photo­ metric observations of the cool variable DA white dwarf (DAV) GD 154 obtained with the Whole Earth Telescope. GD 154 is one of the c;oolest pulsating DA white dwarfs and its study is important for understanding the red edge of the ZZ Ceti insta­ bility strip. Its power spectrum is dominated by three indepen­ dent modes (P 1 = 1186.5s, Pz = 1088.6s and P3 = 402.6s), and their harmonics and linear combinations. None of the half-integer harmonics reported in previous observations were present during the WET campaign. We propose that the ob­ served modes are trapped in the thin outer hydrogen layers. From the resulting identification of the pulsation modes, one derives an estimate of the rotation period (2.3 days) and of the mass ofthe outer hydrogen layer (2 X w-IO M *).

Published
1995

2. EMPIRICAL DETERMINATION OF CONVECTION PARAMETERS IN WHITE DWARFS. I. WHOLE EARTH TELESCOPE OBSERVATIONS OF EC14012-1446

Author

Zsofia Bognar, J. R. Fremy, M. Yang, Agnès Bischoff-Kim, Wen Ping Chen, Margit Paparo, Harry L. Shipman, A. V. Sergeev, J. L. Provencal, Scot Kleinman, Su Wang, A. Maksim, Stephane Vennes, Matt A. Wood, Péter Pápics, Thorsten Nagel, N. Loaring, Gerald Handler, B. Walter, Timothy M. Brown, Kiran S. Baliyan, Souza Oliveira Kepler, David A. H. Buckley, P. Henrique, David Kilkenny, D. Childers, R. Rosen, Atsuko Nitta, Chia-You Shih, Jérôme Perez, J. M. Almenara, R. Janulis, Michael H. Montgomery, D. Chandler, W. Ogloza, S. L. Kim, J. C. Clemens, Andrzej S. Baran, Stanisław Zoła, Antonio Kanaan, N. Dolez, A. Kniazev, Xiao-Jun Jiang, R. Sefako, Péter Németh, Barbara G. Castanheira, W. Strickland, T. K. Watson, Roberto Silvotti, J. Dalessio, Denis J. Sullivan, Susan E. Thompson, M. Winiarski, G. Vauclair, Luciano Fraga, Hari Om Vats, S. Galleti, Michael D. Reed, Centre Hospitalier Métropole Savoie [Chambéry], Copernicus Astronomical Center of the Polish Academy of Sciences (CAMK), Polish Academy of Sciences (PAN), Instituut voor Sterrenkunde [Leuven], Catholic University of Leuven - Katholieke Universiteit Leuven (KU Leuven), Department of Electrical Engineering [Yale University], Yale University [New Haven], London South Bank University (LSBU), Department of Electronic and Electrical Engineering, Pohang University of Science and Technology (POSTECH), Laboratory of Behavioral Neuroscience, National Institutes of Health [Bethesda] (NIH), Qingdao Institute of Marine Geology, China Geological Survey, Qingdao 266071, China, Université Paris Diderot - Paris 7 (UPD7), Institute of Applied Physics of RAS, Russian Academy of Sciences [Moscow] (RAS), Mt. Suhora Observatory, Pedagogical University, Astronomy Department, South African Astronomical Observatory (SAAO), Institut de recherche en astrophysique et planétologie (IRAP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-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)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), 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), Escola de Odontologia, UNIVALE, Université Toulouse III - Paul Sabatier (UT3), 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
oscillations [stars], Convection, FOS: Physical sciences, asteroseismology, Astrophysics, 01 natural sciences, law.invention, Photometry (optics), Telescope, symbols.namesake, law, 0103 physical sciences, 010303 astronomy & astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), ComputingMilieux_MISCELLANEOUS, white dwarfs, Physics, [PHYS]Physics [physics], 010308 nuclear & particles physics, White dwarf, Astronomy and Astrophysics, Light curve, Amplitude, Fourier transform, Astrophysics - Solar and Stellar Astrophysics, individual: EC14012-1446 [stars], 13. Climate action, Space and Planetary Science, evolution [stars], symbols, Instability strip, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract

We report on analysis of 308.3 hrs of high speed photometry targeting the pulsating DA white dwarf EC14012-1446. The data were acquired with the Whole Earth Telescope (WET) during the 2008 international observing run XCOV26. The Fourier transform of the light curve contains 19 independent frequencies and numerous combination frequencies. The dominant peaks are 1633.907, 1887.404, and 2504.897 microHz. Our analysis of the combination amplitudes reveals that the parent frequencies are consistent with modes of spherical degree l=1. The combination amplitudes also provide m identifications for the largest amplitude parent frequencies. Our seismology analysis, which includes 2004--2007 archival data, confirms these identifications, provides constraints on additional frequencies, and finds an average period spacing of 41 s. Building on this foundation, we present nonlinear fits to high signal-to-noise light curves from the SOAR 4.1m, McDonald 2.1m, and KPNO 2m telescopes. The fits indicate a time-averaged convective response timescale of 99.4 +/- 17 s, a temperature exponent 85 +/- 6.2 and an inclination angle of 32.9 +/- 3.2 degrees. We present our current empirical map of the convective response timescale across the DA instability strip., Comment: Accepted for publication in the Astrophysical Journal

Published
2012
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3. Preliminary XCOV26 results for EC14012-1446

Author

D. Chandler, Andrzej S. Baran, S. L. Kim, Zs. Bognár, S. Galleti, Souza Oliveira Kepler, David Kilkenny, M. Paparo, Michael D. Reed, J.M.G. Perez, Harry L. Shipman, R. Sefako, Rimvydas Janulis, Susan E. Thompson, A. Maksim, Gerald Handler, J. Dalessio, B. G. Castanheira, J. R. Fremy, Michael H. Montgomery, Waldemar Ogloza, N. Loaring, T. K. Watson, Chia-You Shih, Atsuko Nitta, Antonio Kanaan, Hari Om Vats, W. Strickland, B. Walter, Judith L. Provencal, Roberto Silvotti, Kiran S. Baliyan, Timothy M. Brown, C. Clemens, Stanisław Zoła, Denis J. Sullivan, Luciano Fraga, A. V. Sergeev, Wen Ping Chen, N. Dolez, Péter Pápics, Stephane Vennes, G. Vauclair, A. Kniazev, Thorsten Nagel, M. Winiarski, A. Kim, Xiao-Jun Jiang, Matt A. Wood, S. J. Kleinman, M. Yang, D. A. H. Buckley, R. Rosen, J. M. Almenara, P. Henrique, and D. Childers

Subjects
Physics, History, business.industry, White dwarf, Light curve, Computer Science Applications, Education, Computational physics, Photometry (optics), Nonlinear system, symbols.namesake, Optics, Fourier transform, Convection zone, Excited state, symbols, Astrophysics::Solar and Stellar Astrophysics, business, Multiplet
Abstract

EC14012-1446 is a hydrogen atmosphere (DA) white dwarf pulsator. Its rich pulsation spectrum displays a range of excited modes with complex multiplet structure, in addition to numerous combination frequencies. In April 2008, EC14012-1446 was the primary target of XCOV26. We obtained over 300 hrs of nearly continuous high speed photometry with the goal of using the nonlinear pulse shapes to empirically determine the parameters of the convection zone. The Fourier transform (FT) of the light curve contains power between 1000 to 4000 μHz, with the dominant peak at 1234 μHz. We find 13 independent frequencies distributed in 8 modes, as well as a myriad of combination frequencies. In the following, we present preliminary results and lay the groundwork for future investigation leading to light curve fitting of EC14012-1446.

Published
2009

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