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3. Optical determinations of the time delay in 0957+561

Author

Vanderriest, Christian, Schneider, Jean, Herpe, Georges, Chevreton, Michel, Wlérick, Gérard, Moles, Mariano, Araki, H., editor, Ehlers, J., editor, Hepp, K., editor, Kippenhahn, R., editor, Ruelle, D., editor, Weidenmüller, H. A., editor, Wess, J., editor, Zittartz, J., editor, Moran, J. M., editor, Hewitt, J. N., editor, and Lo, K. Y., editor

Published
1989
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4. The pulsations of PG 1351+489

Author

Redaelli, Maurício, Kepler, Souza Oliveira, Costa, Jose Eduardo da Silveira, Winget, Donald Earl, Handler, Gerald, Castanheira, Bárbara Garcia, Kanaan Neto, Antonio Nemer, Fraga, Luciano, Henrique, P., Giovannini Junior, Odilon, Provencal, Judith L., Shipman, Harry L., Dalessio, J., Thompson, S. E., Mullally, Fergal, Brewer, M. M., Childers, D., Oksala, M. E., Rosen, Rachel, Wood, Matthew A., Reed, M. D., Walter, B., Strickland, Willie, Chandler, Dean W., Watson, Todd K., Nather, R. Edward, Montgomery, Michael Houston, Bischoff-Kim, Agnès, Hansen, Carl J., Nitta, Atsuko, Kleinman, Scot James, Claver, C.F., Brown, Tim, Sullivan, Denis J., Kim, Seung-Lee, Chen, Wen-Ping, Yang, M., Shih, Chia-You, Zhang, X, Jiang, Xiaojun, Fu, Jianning Ning, Seetha, S., Ashoka, B.N., Marar, T.M. Krishnan, Baliyan, Kiran S., Vats, Hari Om, Chernyshev, A.V., Ibbetson, Peter A., Leibowitz, Elia M., Hemar, Shirley, Sergeev, A., Andreev, M., Janulis, Rimvydas, Meistas, Edmundas G., Moskalik, Pawel, Pajdosz, Gabriel, Baran, Andrzej, Winiarski, M., Zola, Staszek, Ogloza, Waldemar, Siwak, Michal, Bognár, Zsófia, Solheim, Jan-Eric, Sefako, R., Buckley, David A.H., O'Donoghue, Darragh, Nagel, Thorsten, Silvotti, Roberto, Bruni, I., Fremy, J. R., Vauclair, Gérard, Chevreton, Michel, Dolez, Noël, Pfeiffer, Ben, Barstow, Martin A., Creevey, o, Kawaler, Steven D., and Clemens, J. Christopher

Subjects
Anãs brancas, Oscilacoes, individual: PG 1351+489 [Stars], oscillations [Stars], Evolucao estelar, evolution [Stars], White dwarfs
Abstract

PG 1351+489 is one of the 20DBVs – pulsating helium-atmospherewhite dwarf stars – known and has the simplest power spectrum for this class of star, making it a good candidate to study cooling rates. We report accurate period determinations for the main peak at 489.334 48 s and two other normal modes using data from the Whole Earth Telescope (WET) observations of 1995 and 2009. In 2009, we detected a new pulsation mode and the main pulsation mode exhibited substantial change in its amplitude compared to all previous observations. We were able to estimate the star’s rotation period, of 8.9 h, and discuss a possible determination of the rate of period change of (2.0 ± 0.9) × 10−13 s s-ˡ, the first such estimate for a DBV.

Published
2011

5. The pulsations of PG 1351+489

Author

Redaelli, M., Kepler, S. O., Costa, José Eduardo, Winget, D. E., Handler, Gerald, Castanheira, B. G., Kanaan, A., Fraga, L., Henrique, P., Giovannini, O., Provençal, J. L., Shipman, H. L., Dalessio, J., Thompson, S. E., Mullally, Fergal, Brewer, M. M., Childers, D., Oksala, Mary E., Rosen, R., Wood, M. A., Reed, M. D., Walter, B., Strickland, W., Chandler, D., Watson, T. K., Nather, R. E., Montgomery, M. H., Bischoff-Kim, A., Hansen, Candice J., Nitta, A., Kleinman, S. J., Claver, C. F., Brown, Timothy M., Sullivan, D. J., Kim, S.-L., Chen, Wen-Ping, Yang, M., Shih, C.-Y., Zhang, X., Jiang, X., Fu, J.-N., Seetha, S., Ashoka, B. N., Marar, T. M. K., Baliyan, Kiran S., Vats, H. O., Chernyshev, A. V., Ibbetson, P., Leibowitz, E. M., Hemar, S., Sergeev, A. V., Andreev, M. V., Janulis, R., Meistas, E. G., Moskalik, P. A., Pajdosz, G., Baran, A., Winiarski, M., Zola, S., Ogloza, W., Siwak, M., Bognar, Zs., Solheim, J.-E., Sefako, R., Buckley, D., O'Donoghue, Darragh, Nagel, T., Silvotti, R., Bruni, I., Fremy, Jean-René, Vauclair, Gérard, Chevreton, Michel, Dolez, N., Pfeiffer, B., Barstow, Martin A., Creevey, Orlagh L., Kawaler, Steven D., Clemens, J. C., Instituto de Física, Universidade Federal do Rio Grande do Sul, Department of Astronomy and McDonald Observatory, University of Texas, Austin, Institut für Astronomie, Universität Wien (IfA), Departamento de Física, Universidade Federal de Santa Catarina, Southern Observatory for Astrophysical Research, Departamento de Física e Química, Universidade de Caxias do Sul, Department of Physics and Astronomy, University of Delaware, Delaware Asteroseismic Research Center, Mt Cuba Observatory, Greenville, SETI Institute, NASA Ames Research Center, Moffett Field, William Jewell College, Department of Math and Science, Delaware County Community College, Bartol Research Institute, University of Delaware, National Radio Astronomy Observatory, Green Bank (NRAO), Florida Institute of Technology, Department of Physics and Space Sciences, Melbourne, Baker Observatory, Missouri State University, Meyer Observatory and Central Texas Astronomical Society, Waco, Southwestern University, Department of Chemistry, Physics and Astronomy, Georgia College and State University, University of Colorado, Joint Institute for Laboratory Astrophysics (JILA), Gemini Observatory, Kitt Peak National Observatory, National Optical Astronomy Observatory, Tucson, Las Cumbres Observatory, Goleta, Victoria University of Wellington, Korea Astronomy and Space Science Institute (KASI), Lulin Observatory, National Astronomical Observatoires-CAS, Department of Astronomy, Beijing Normal University, Indian Space Research Organization, Physical Research Laboratory, Astronomy & Astrophysics Division, Astronomical Institute, Tel Aviv University (TAU), Main Astronomical Observatory, Academy of Sciences of Ukraine, Institute of Theoretical Physics and Astronomy, Vilnius University, Centrum Astronomiczne im. M. Kopernika, Warszawa (CAMK), Mount Suhora Observatory, Cracow Pedagogical University, Astronomical Observatory, Jagiellonia University, Konkoly Observatory, Research Center for Astronomy and Earth Sciences, University of Oslo (UiO), South African Astronomical Observatory (SAAO), Eberhard Karls Universität Tübingen = Eberhard Karls University of Tuebingen, INAF-Osservatorio Astrofisico di Torino (INAF-OATo), 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), Etoile, Laboratoire d'études spatiales et d'instrumentation en astrophysique = Laboratory of Space Studies and Instrumentation in Astrophysics (LESIA), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Ingénierie, 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, Laboratoire Astrophysique de Toulouse-Tarbes (LATT), 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), 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), Astronomy Department, Leicester University, Instituto de Astrofísica de Canarias (IAC), Department of Physics and Astronomy, Iowa State University, and Department of Physics and Astronomy, University of North Carolina

Subjects
oscillations [stars], [SDU]Sciences of the Universe [physics], evolution [stars], [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], individual: PG 1351+489 [stars], white dwarfs
Abstract

International audience; PG 1351+489 is one of the 20 DBVs - pulsating helium-atmosphere white dwarf stars - known and has the simplest power spectrum for this class of star, making it a good candidate to study cooling rates. We report accurate period determinations for the main peak at 489.334 48 s and two other normal modes using data from the Whole Earth Telescope (WET) observations of 1995 and 2009. In 2009, we detected a new pulsation mode and the main pulsation mode exhibited substantial change in its amplitude compared to all previous observations. We were able to estimate the star's rotation period, of 8.9 h, and discuss a possible determination of the rate of period change of (2.0 ± 0.9) × 10-13 s s -1, the first such estimate for a DBV.

Published
2011
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6. Abell 43 and PG 0122+200: a Look at the Beginning and at the End of the PG 1159 Instability Strip

Author

Vauclair, Gérard, Solheim, J.-E., Fu, J.-N., Chevreton, Michel, Dolez, N., O'Brien, M. S., Mukadam, Anjum S., Kim, S.-L., Park, B.-G., Handler, Gerald, Medupe, R., Wood, M., González Perez, J., Hashimoto, O., Kinugasa, K., Taguchi, H., Kambe, Eiji, Dobrovolskas, V., Provençal, J. L., Dreizler, Stefan, Schuh, S., Leibowitz, E. M., Lipkin, Y., Zhang, X.-B., Paparó, M., Szeidl, B., Viraghalmy, G., Zsuffa, D., 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
[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract

International audience

Published
2006

7. Whole earth telescope observations of the pulsating hot white dwarf PG 1707+427

Author

Kawaler, Steven D., Potter, E. M., Vuckovic, Maja, O'Toole, Simon, Clemens, J. Christopher, O'Brien, M. Sean, Grauer, Albert D., Nather, R. Edward, Moskalik, Pawel, Fontaine, Gilles, Wesemael, F., Bergeron, Pierre, Vauclair, Gérard, Dolez, Noël, Chevreton, Michel, Kleinman, Scot James, Watson, Todd K., Barstow, Martin A., Dind, Z. E., Sansom, A.E., Winget, Donald Earl, Kepler, Souza Oliveira, Kanaan Neto, Antonio Nemer, Bradley, Paul A., Dixson, James S., Provencal, Judith L., and Bedding, T. R.

Subjects
white dwarfs [Stars], Pulsacoes estelares, Anãs brancas, oscillations [Stars], Evolucao estelar, evolution [Stars], Fotometria estelar, Astrofisica estelar, Espectros estelares, individual: PG 1707+427 [Stars]
Abstract

We report on the analysis of multisite time-series photometry of the pulsating pre-white dwarf (GW Vir star) PG 1707+427, obtained by the Whole Earth Telescope collaboration. This is the last of the known GW Vir stars without surrounding nebulae to be resolved by multisite data. Successful resolution of the pulsation spectrum resulted from the combination of high signal-to-noise observations with a large telescope and wide coverage in longitude with smaller telescopes. We find a series of 8 pulsation frequencies (along with two nonlinear combination frequencies), and identify 7 of them as part of a sequence of l = 1 modes, with a common period spacing of 23.0 s. This spacing implies that the mass of PG 1707+427 is 0.57 Mѳ. Preliminary model fits suggest that the mass determined via asteroseismology is consistent with the mass determined from spectroscopy combined with evolutionary tracks.

Published
2004

10. Constraint on the Kuiper Belt Objects size distribution from Stellar Occultations

Author

Roques, Françoise, Chevreton, Michel, Colas, François, Fernandez, Andrée, Lecacheux, Jean, Moncuquet, Michel, 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, Ingénieurs, Techniciens et Administratifs, Physique des plasmas, Pôle Planétologie du LESIA, Laboratoire d'études spatiales et d'instrumentation en astrophysique = Laboratory of Space Studies and Instrumentation in Astrophysics (LESIA), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)

Subjects
[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract

International audience

Published
2003

11. Detection of small Kuiper Objects by stellar occultation method

Author

Roques, Françoise, Chevreton, Michel, Colas, François, Lecacheux, Jean, Moncuquet, Michel, Tozzi, Gian Paolo, Institut de Mécanique Céleste et de Calcul des Ephémérides (IMCCE), 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 de Lille-Centre National de la Recherche Scientifique (CNRS), Astronomie et systèmes dynamiques (ASD), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Lille-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, Groupe Astrométrie et Planétologie (GAP), F. Combes, D. Barret, and T. Contini

Subjects
[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract

International audience

Published
2003

12. WET Observations of GD 358 in 2000

Author

Kepler, S. O., Nather, R. E., Winget, D. E., Nitta, A., Kleinman, S. J., Metcalfe, Travis S., Sekiguchi, Kazuhiro, Xiaojun, Jiang, Sullivan, D., Sullivan, T., Janulis, R., Meistas, E. G., Kalytis, R., Krzesinski, J., Ogoza, W., Zola, S., O'Donoghue, Darragh, Romero-Colmenero, E., Martinez, Patrice, Dreizler, Stefan, Deetjen, J., Nagel, T., Schuh, S. L., Vauclair, Gérard, Fu, J.-N., Chevreton, Michel, Solheim, J.-E., Gonzalez Perez, J. M., Johannessen, F., Kanaan, A., Costa, José Eduardo, Murillo Costa, A. F., Wood, M. A., Silvestri, N., Ahrens, T. J., Jones, A. Kyle, Collins, A. E., Boyer, M., Shaw, J. S., Mukadam, Anjum S., Klumpe, E. W., Larrison, J., Kawaler, Steven D., Riddle, R. L., Ulla, A., Bradley, P., 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
[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract

International audience

Published
2003

13. The Everchanging Pulsating White Dwarf GD358

Author

Kepler, S.O., Solheim, Jan Erik, Nather, R. Edward, Gonzalez Perez, Jose M., Johannessen, Frank, Winget, Don E., Nitta, Atsuko, Kleinman, S. J., Metcalfe, Travis, Sekiguchi, Kazuhiro, Xiaojun, Jiang, Sullivan, Denis, Sullivan, Tiri, Janulis, Rimvydas, Meistas, Edmund, Kalytis, Romualdas, Krzesinski, Jurek, Ogloza, Waldemar, O’Donoghue, Darragh, Romero-Colmenero, Encarni, Martinez, Peter, Dreizler, Stefan, Deetjen, Jochen, Nagel, Thorsten, Schuh, Sonja L., Vauclair, Gerard, Ning, Fu Jian, Chevreton, Michel, Kanaan, Antonio, Costa, Jos´e Eduardo, Costa, Alex Fabiano Murillo, Wood, Matt A., Silvestri, Nicole, Ahrens, T.J., Jones, Aaron Kyle, Collins, Ansley E., Boyer, Martha, Mukadam, Anjum, Klumpe, Eric W., Larrison, Jesse, Kawaler, Steve, Riddle, Reed, Ulla, Ana, and Bradley, Paul

Subjects
VDP::Mathematics and natural science: 400::Physics: 430::Astrophysics, astronomy: 438, (Stars:) white dwarfs, Stars: oscillations, Stars: individual: GD 358, Stars: variables, general, Stars: evo- lution
Abstract

This is the authors' accepted version of the article. 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 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 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.

Published
2003

14. Research of small Kuiper Belt Objects by Stellar Occultations

Author

Roques, Françoise, Lavillonnière, N., Auvergne, Michel, Chevreton, Michel, Colas, François, Lecacheux, Jean, Moncuquet, Michel, Perrin, Jean-Marie, Observatoire de Paris, Université Paris sciences et lettres (PSL), Institut de Mécanique Céleste et de Calcul des Ephémérides (IMCCE), 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 de Lille-Centre National de la Recherche Scientifique (CNRS), Observatoire de Haute-Provence (OHP), Institut Pythéas (OSU PYTHEAS), and Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)

Subjects
[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract

International audience; Fast photometric observations of target stars in the ecliptic have been organised at the Pic du Midi Observatory (2-m TBL and T1M) and the Haute Provence Observatory (T193) in order to search for small Kuiper Belt Objects by stellar occultations. The target stars have been chosen in the Tycho catalog: 18-1201-1 (Vmag=12,4), 585-671-1 (Vmag=11.8), 4669-750-1 (Vmag=11.9 ), 548-592-1 (Vmag=10.9) and 583-907-1 (Vmag=12.8). They are O stars to optimize the brightness/apparent size ratio. The observation sampling was 20 Hz and we got good quality observation during 18 hours, 28 hours and 8 hours at TBL, T1M and T193, respectively. The r.m.s. signal fluctuations, which mainly varies with telescope diameter and star elevation, may be 0.014 for a 2-m telescope. Within such a signal, an event due to a 120 meters KBO diameter is detected at a 3 sigma r.m.s. level. A realistic size distribution in the KBO population leads to one such event for 27 hours observation (Roques and Moncuquet, Icarus, 147, 530, 2000). The observed events are presented and analyzed. This work was supported by the Programme National de Planetologie

Published
2001

15. Asteroseismology of a star cooled by neutrino emission : the pulsating pre-white dwarf PG 0122+200

Author

O'Brien, M. Sean, Vauclair, Gérard, Kawaler, Steven D., Watson, Todd K., Winget, Donald Earl, Nather, R. Edward, Montgomery, Michael Houston, Nitta, Atsuko, Kleinman, Scot James, Sullivan, Denis J., Jiang, Xiaojun, Marar, T.M. Krishnan, Seetha, S., Ashoka, B.N., Bhattacharya, J., Leibowitz, Elia M., Hemar, Shirley, Ibbetson, Peter A., Warner, B., Van Zyl, L., Moskalik, Pawel, Zola, Staszek, Pajdosz, Gabriel, Krzesinski, Jerzy, Dolez, Noël, Chevreton, Michel, Solheim, Jan-Eric, Thomassen, T., Kepler, Souza Oliveira, Giovannini Junior, Odilon, Provencal, Judith L., Wood, Matthew A., and Clemens, J. Christopher

Subjects
pulsars : general [Stars], interiors [Stars], Elementary particles, Fotometria estelar, Massa atômica, Rotação, individual (PG 0122+200) [Stars], Estrelas variaveis, Rotacao estelar, white dwarfs [Stars], Pulsacoes estelares, Anãs brancas, Luminosidade, Radiação estelar
Abstract

Observation of g-mode pulsations in the variable pre-white dwarf (GW Virginis) stars provides a unique means to probe their interiors and to study the late stages of stellar evolution. Multisite campaigns have in several cases proved highly successful in decoding preÈwhite dwarf light curves. Three previous attempts to untangle the pulsation spectrum of the coolest GW Virginis star, PG 0122+200, confirmed the existence of multiple g-modes but left the fundamental period spacing and therefore the star's mass and luminosity in doubt. We present an analysis based on new observations of PG 0122+200 obtained during a Whole Earth Telescope (WET) campaign conducted in the fall of 1996. Although our coverage was, because of bad weather, far poorer than in previous WET campaigns, we confirm the previous result that PG 0122+200 rotates once in 1.6±0.1 days. The most likely period spacing supported by the data implies a mass of 0.69±0.03 Mʘ. Based on the best seismology we can currently do, the cooling of PG 0122+200 is dominated by neutrino losses. This is not true for all pre-white dwarf stars and makes PG 0122+200 the prime candidate for learning useful physics. Constraints placed on the cooling rate of PG 0122+200 by future measurement of dII/dt could provide a unique test of the standard theory of lepton interactions in the (experimentally unexplored) region of phase-space appropriate to pre-white dwarf interiors.

Published
1998

16. Whole earth telescope observations of am canum venaticorum-discoseismology at last

Author

Solheim, Jan-Eric, Provencal, Judith L., Bradley, Paul A., Vauclair, Gérard, Barstow, Martin A., Kepler, Souza Oliveira, Fontaine, Gilles, Graver, A.D., Winget, Donald Earl, Marar, T.M. Krishnan, Leibowitz, Elia M., Enanvelsen, P.I., Chevreton, Michel, Dolez, Noël, Kanaan Neto, Antonio Nemer, Bergeron, Pierre, Claver, C.F., Clemens, J. Christopher, Kleinman, Scot James, Hine, B.P., Seetha, S., Shoka, B.N., Mazeh, Tsevi, Sansom, A.E., Tweedy, P.W., Meistas, Edmundas G., Bruvold, A., and Massacand, C.N.

Subjects
Estrelas binarias cataclismicas, Anãs brancas, Oscilacoes, Fotometria, Discos de acrecao, Astrofisica estelar, Estrelas magneticas
Abstract

We report the results of 143.2 hours of time-series photometry over a 12 day period for AM CVn (= HZ 29) as part of the Whole Earth Telescope (WET) project.ˡ This star is believed to be an ultra-short period cataclysmic binary. In the temporal spectrum of the light curve we find a series of 5 harmonically related frequency mo dulations, some with sidebands with a constant frequency spacing of 20.8 μHz always on the high-frequency side. The set of harmonics has a fundamental frequency of 951 μHz. No modulation is detected at this frequency in the light curve. In addition, modulations with frequencies 972.5 and 988.9 μHz are detected with low amplitudes. The structure of the dominant 1903 Hz modulation explains part of the “phase jitter” observed earlier. The amplitude of this peak is modulated with a period of 13.32 ± 0.05 hrs.

Published
1998

17. Whole Earth Telescope observations of the helium interacting binary PG 1346+082 (CR bootis)

Author

Provencal, Judith L., Winget, Donald Earl, Nather, R. Edward, Robinson, E.L., Clemens, J. Christopher, Bradley, Paul A., Claver, C.F., Kleinman, Scot James, Grauer, Albert D., Hine, B.P., Ferrario, Lilia, O'Donoghue, Darragh, Warner, B., Vauclair, Gérard, Chevreton, Michel, Kepler, Souza Oliveira, Wood, Matthew A., and Henry, G.W.

Subjects
Estrelas binarias cataclismicas, Anãs brancas, oscillations [Stars], individual (PG 1346+082) [Stars], White dwarfs, Fotometria estelar
Abstract

We present our analysis of 240 hr of white-light, high-speed photometry of the dwarf nova-like helium variable PG 1346+082 (CR Boo). We identify two frequencies in the low-state power spectrum, at 679.670±0.004 μHz and 669.887±0.008 μHz. The 679.670 μHz variation is coherent over at least a 2 week time span, the first demonstration of a phase-coherent photometric variation in any dwarf nova-like interacting binary white dwarf system. The high-state power spectrum contains a complex fundamental with a frequency similar, but not identical, to the low-state spectrum, and a series of harmonics not detected in low state. We also uncover an unexpected dependence of the high-frequency powerÏs amplitude and frequency structure on overall system magnitude. We discuss these Ðndings in light of the general AM CVn system model, particularly the implications of the high-order harmonics on future studies of disk structure, mass transfer, and disk viscosity.

Published
1997

18. New whole earth telescope observations of cd-247599 : steps towards delta scuti star seismology

Author

Handler, Gerald, Pikall, H., O'Donoghue, Darragh, Buckley, David A.H., Vauclair, Gérard, Chevreton, Michel, Giovannini Junior, Odilon, Kepler, Souza Oliveira, Goode, P.R., Provencal, Judith L., Wood, Matthew A., Clemens, J. Christopher, O'Brien, M. Sean, Nather, R. Edward, Winget, Donald Earl, Kleinman, Scot James, Kanaan Neto, Antonio Nemer, Watson, Todd K., Nitta, Atsuko, Montgomery, Michael Houston, Klumpe, Eric W., Bradley, Paul A., Sullivan, Denis J., Wu, K., Marar, T.M. Krishnan, Seetha, S., Ashoka, B.N., Mahra, H.S., Bhat, B.C., Babu, V.C., Leibowitz, Elia M., Hemar, Shirley, Ibbetson, Peter A., Mashal, E., Meistas, Edmundas G., Dziembowski, W.A., Pamyantnykh, A.A., Moskalik, Pawel, Zola, Staszek, Pajdosz, Gabriel, Krzesinski, Jerzy, Solheim, Jan-Eric, Bard, S., Massarand, C.M., Breger, M., Gelbmann, M.J., Paunzen, E., and North, P.

Subjects
oscillations [Stars], δ Scuti, photometric [Techniques], Astrofisica estelar, Fotometria : Padroes : Observacoes astronomicas [Estrelas], fundamental parameters [Stars], individual: CD-24 7599 [Stars]
Abstract

92 h of new Whole Earth Telescope observations have been acquired for the δ Scuti star CD -24 7599. All the seven pulsation modes reported by Handler et al. are confirmed. However, significant amplitude variations which are not caused by beating of closely spaced frequencies occurred within two years. Analysing the combined data of both WET runs, we detect six further pulsation modes, bringing the total number up to 13. We also examine our data for high-frequency pulsations similar to those exhibited by rapidly oscillating Ap stars, but we do not find convincing evidence for variability in this frequency domain. From new colour photometry and spectroscopy we infer that CD-24 7599 is a hot mainsequence δ Scuti star with approximately solar metallicity and ν sin i = 52 ± 2 km s -1. We cannot yet propose a definite pulsation mode identification, but we report the detection of a characteristic frequency spacing between the different modes. We ascribe it to the simultaneous presence of l = 1 and l = 2 modes of consecutive radial order. A comparison of this frequency spacing with frequencies of solar-metallicity models, as well as stability analysis, allows us to constrain tightly the evolutionary state of CD - 24 7599. It is in the first half of its main-sequence evolution, and has a mass of 1.85 ± 0.05 M̛ and a mean density of p = 0.246 ± 0.020 P̛. This yields a seismological distance of 650 ± 70 pc, which i~ as accurate as distance determinations for 0 Scuti stars observed in clusters. Most of the pulsation modes are pure p modes of radial order k = 4-6, but the gl mode of l = 2 is likely to be excited and observed as well. Since a significant contribution to this mode's kinetic energy comes from the outer part of the convective core, CD-247599 becomes particularly interesti1)g for testing convective overshooting theories.

Published
1997

19. Whole earth telescope observations and seismological analysis of the cool zz ceti star gd 154

Author

Pfeiffer, Ben, Vauclair, Gérard, Dolez, Noël, Chevreton, Michel, Fremy, J. R., Barstow, Martin A., Belmonte, J.A., Kepler, Souza Oliveira, Kanaan Neto, Antonio Nemer, Giovannini Junior, Odilon, Fontaine, Gilles, Bergeron, Pierre, Wesemael, F., Grauer, Albert D., Nather, R. Edward, Winget, Donald Earl, Provencal, Judith L., Clemens, J. Christopher, Bradley, Paul A., Dixson, James S., Kleinman, Scot James, Watson, Todd K., Claver, C.F., Matzeh, Tsevi, Leibowitz, Elia M., and Moskalik, Pawel

Subjects
Fotometria, oscillations [Stars], interiors [Stars], White dwarfs, individual (GD 154) [Stars], Astrofisica estelar, Oscilacoes [Estrelas]
Abstract

This paper presents the results of high speed photometric observations of the cool variable DA white dwarf (DAV) GD 154 obtained with the Whole Earth Telescope. GD 154 is one of the coolest pulsating DA white dwarfs and its study is important for understanding the red edge of the ZZ Ceti instability strip. Its power spectrum is dominated by three independent modes (P₁ = 1186.5s, P₂ = 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 observed 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 10ˉ¹° M*).

Published
1996

20. The unusual helium variable AM Canum Venaticorum

Author

Provencal, Judith L., Winget, Donald Earl, Nather, R. Edward, Robinson, E.L., Solheim, Jan-Eric, Clemens, J. Christopher, Bradley, Paul A., Kleinman, Scot James, Kanaan Neto, Antonio Nemer, Claver, C.F., Hansen, Carl J., Marar, T.M. Krishnan, Seetha, S., Ashoka, B.N., Leibowitz, Elia M., Meistas, Edmundas G., Bruvold, A., Vauclair, Gérard, Dolez, Noël, Chevreton, Michel, Barstow, Martin A., Sansom, A.E., Tweedy, R.W., Fontaine, Gilles, Bergeron, Pierre, Kepler, Souza Oliveira, Wood, Matthew A., and Grauer, Albert D.

Subjects
dose [Binaries], Estrelas binarias cataclismicas, Pulsacoes estelares, Anãs brancas, oscillations [Stars], individual (AM Canum Venaticorum) [Stars], Discos de acrecao, White dwarfs, Fotometria estelar, Accretion, accretion disks
Abstract

The unusual variable star AM CVn has puzzled astronomers for over 40 years. This object, both a photometric and spectroscopic variable, is believed to contain a pair of hydrogen-deficient white dwarfs of extreme mass ratio, transferring material via an accretion disk. We examine the photometric properties of AM CVn, analyzing 289 hours of high-speed photometric data spanning 1976 to 1992. The power spectrum displays significant peaks at 988.7, 1248.8, 1902.5, 2853.8, 3805.2, 4756.5, and 5707.8 μHz (1011.4, 800.8, 525.6, 350.4, 262.8, 210.2, and 175.2 s). We find no detectable power at 951.3 μHz (1051 s), the previously reported main frequency. The 1902.5, 2853.9, and 3805.2 μHz peaks are multiplets, with frequency splitting in each case of 20.77 ± 0.05 μHz. The 1902.5 μHz seasonal pulse shapes are identical, within measurement noise, and maintain the same amplitude and phase as a function of color. We have determined the dominant frequency to be 1902.509802 ± 0.00001 μHz, with p = + 1.71 (±0.04) X 10-11 s s-ˡ. We discuss the implications of these findings on a model forAM CVn.

Published
1995

21. Whole Earth Telescope observations of the DAV white dwarf G226-29

Author

Kepler, Souza Oliveira, Giovannini Junior, Odilon, Wood, Matthew A., Nather, R. Edward, Winget, Donald Earl, Kanaan Neto, Antonio Nemer, Kleinman, Scot James, Bradley, Paul A., Provencal, Judith L., Clemens, J. Christopher, Claver, C.F., Watson, Todd K., Yanagida, K., Krisciunas, K., Marar, T.M. Krishnan, Seetha, S., Ashoka, B.N., Leibowitz, Elia M., Mendelson, Haim, Mazeh, Tsevi, Moskalik, Pawel, Krzesinski, Jerzy, Pajdosz, Y., Zola, Staszek, Solheim, Jan-Eric, Emanuelsen, P.-I., Dolez, Noël, Vauclair, Gérard, Chevreton, Michel, Fremy, J. R., Barstow, Martin A., Sansom, A.E., Tweedy, R.W., Wickramasinghe, D.T., Ferrario, Lilia, Sullivan, Denis J., Peet, A.J. van der, Buckley, David A.H., and Chen, A.-L.

Subjects
rotation [Stars], Pulsacoes estelares, Anãs brancas, oscillations [Stars], White dwarfs, Astrofisica estelar, individual (G226-29) [Stars], Estrelas variaveis
Abstract

We observed G226-29 for 121 hr in 1992 February and confirm the presence of the three previously identified frequencies close to 109 s. We find no evidence of other pulsation periods down to our noise level of about 0.35 millimodulation amplitudes. The presence of only one triplet pulsation mode in G226-29 and its effective temperature near the blue edge of the instability strip identify the observed triplet of modes near 109 s as rotationally split components of the k = 1, l = 1 mode. With the mode identification, we derived a rotation period of 8.9 hr and an inclination of the pulsation axis of 70°-75° to our line of sight.

Published
1995

22. Whole Earth Telescope observations and seismological analysis of the pre-white dwarf pg 2131+066

Author

Kawaler, Steven D., O'Brien, M. Sean, Clemens, J. Christopher, Nather, R. Edward, Winget, Donald Earl, Watson, Todd K., Yanagida, K., Dixson, James S., Bradley, Paul A., Wood, Matthew A., Sullivan, Denis J., Kleinman, Scot James, Meistas, Edmundas G., Leibowitz, Elia M., Moskalik, Pawel, Zola, Staszek, Pajdosz, Y., Krzesinski, Jerzy, Solheim, Jan-Eric, Bruvold, A., O'Donoghue, Darragh, Katz, M., Vauclair, Gérard, Dolez, Noël, Chevreton, Michel, Barstow, Martin A., Kanaan Neto, Antonio Nemer, Kepler, Souza Oliveira, Giovannini Junior, Odilon, Provencal, Judith L., and Hansen, Carl J.

Subjects
individual (PG 2131 +066) [Stars], Pulsacoes estelares, Anãs brancas, oscillations [Stars], Radiação estelar, White dwarfs, Massa estelar, fundamental parameters [Stars], Estrelas variaveis
Abstract

As transition objects between the asymptotic giant branch (AGB) and cooling white dwarfs, the PG 1159 stars are key objects for understanding the late stages of stellar evolution. The pulsations exhibited by many members of the PG 1159 spectral class provide a mechanism for ferreting out this information. We present an analysis of the pulsation spectrum of the naked PG 1159 star PG 2131 +066, which we completely resolve using data from the Whole Earth Telescope (WET). The pulsation spectrum shows patterns that are expected from pulsation theory; comparison of these patterns with theoretical models indicate that PG 2131 has a mass of 0.61 ± 0.02 Mʘ, a luminosity of log (L/Lʘ) = 1.0 ± 0.2, and it lies ata distance of 470 +470 - 130pc. lt rotates with a period of 5.1 hr and shows evidence of a discontinuity in composition approximately 6 x 10- 3M* below the surface. Certain modes show complex structure in the power spectrum, while others show measur­ able frequency changes in 8 years. Fine structure in the prograde (m = -1) modes suggests the presence of nonlinear effects.

Published
1995

23. Whole Earth Telescope observations of the DBV white dwarf GD 358

Author

Winget, Donald Earl, Nather, R. Edward, Clemens, J. Christopher, Provencal, Judith L., Kleinman, Scot James, Bradley, Paul A., Claver, C.F., Dixson, James S., Montgomery, Michael Houston, Hansen, Carl J., Hine, B.P., Birch, P., Candy, M., Marar, T.M. Krishnan, Seetha, S., Ashoka, B.N., Leibowitz, Elia M., O'Donoghue, Darragh, Warner, B., Buckley, David A.H., Tripe, P., Vauclair, Gérard, Dolez, Noël, Chevreton, Michel, Serre, T., Garrido, R., Kepler, Souza Oliveira, Kanaan Neto, Antonio Nemer, Augusteijn, T., Wood, Matthew A., Bergeron, Pierre, and Grauer, Albert D.

Subjects
Pulsacoes estelares, Anãs brancas, oscillations [Stars], Observações astronômicas no visível, White dwarfs, Fotometria estelar, Astrofisica estelar, individual (GD 358) [Stars], Estrelas variaveis
Abstract

We report on the analysis of 154 hours of early continuous high-speed photometry on the pulsating DB white dwarf (DBV) GD 358, obtained during the Whole Earth Telescope (WET) run of 1990 May. The power spectrum of the light curve is dominated by power in the range from 1000 to 2400 μHz, with more than 180 significant peaks in the total spectrum. We identify ali of the triplet frequencies as degree l = 1, and from the details of their spacings we derive the total stellar mass as 0.61 ± 0.03 Mʘ , the mass of the outer helium envelope as 2.0 ± 1.0 x 10-6 M*, the absolute luminosity as 0.050 ± 0.012 Lʘ and the distance as 42 ± 3 pc. We find strong evidence for differential rotation in the radial direction−the outer envelope is rotating at least 1.8 times faster than the core−and we detect the presence of a weak magnetic field with a strength of 1300 ± 300 G. We also find a significant power at the sums and differences of the dominant frequencies, indi­ cating nonlinear processes are significant, but they have a richness and complexity that rules out resonant mode coupling as a major cause.

Published
1994

24. An observational limit to the evolutionary time scale of the 13,000 K white dwarf G117-B15A

Author

Kepler, Souza Oliveira, Vauclair, Gérard, Dolez, Noël, Chevreton, Michel, Barstow, Martin A., Nather, R. Edward, Winget, Donald Earl, Provencal, Judith L., Clemens, J. Christopher, and Fontaine, Gilles

Subjects
Pulsation-stars, Anãs brancas, Pulsacoes estelares, Evolution-stars, Evolucao estelar, Individual (Gll7-B15A)-stars, White dwarfs, Fotometria estelar, Stars, Estrelas variaveis
Abstract

Nature has provided us with a way of measuring the evolutionary time scale of some stars through aster­ oseismology, i.e., the study of stellar interiors through their intrinsic variations in brightness. By measuring the slow, secular change in one or more of its periodicities, we can measure the rate at which a luminosity­ variable white dwarf is cooling. Using 204 hr ofhigh-speed photometric observations ofthe DAV star G117-B15A during the last 14 yr, we have obtained an observational limit to the rate of period change for its dominant pulsation at 215.2 s of dPjdt = (8.3 ± 5.0) x 10-15 s s-ˡ. This rate of period change corresponds to an evolutionary time scale of r = (8.2 ± 5.0) x 108 yr, consistent with the change expected due to cooling of the white dwarf undergoing nonradial g-mode pulsations. The observed limit on the rate of period change makes G117-B15A the most accurate optical clock known, with a stability comparable to that of the atomic clocks used by the National Bureau of Standards, and exceeded only by a few ms radio pulsars. Since ali DA white dwarfs are thought to cool through the DAV instability strip, and there are no known differences between the properties of variables and nonvariable white dwarfs, the measurement of an evolu­ tionary time scale, suitably scaled by mass and surface temperature, should apply to ali DA white dwarfs.

Published
1990

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