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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. Wet Observations of GD 358 in 2000

Author

J. E. Solheim, T. Sullivan, Paul A. Bradley, J. M. Gonzalez Perez, E. G. Meištas, Encarni Romero-Colmenero, E. W. Klumpe, Thorsten Nagel, G. Vauclair, Stefan Dreizler, Waldemar Ogloza, J. Xiaojun, P. Martinez, F. Johannessen, M. Chevreton, Antonio Kanaan, Matt A. Wood, Sonja Schuh, Martha L. Boyer, Nicole M. Silvestri, J. N. Fu, A. Ulla, Donald E Winget, Kazuhiro Sekiguchi, Staszek Zola, Denis J. Sullivan, T. S. Metcalfe, Jam Shaw, R. L. Riddle, Atsuko Nitta, E. R. Nather, J. L. Deetjen, Donal O'Donoghue, Souza Oliveira Kepler, A. F. Murillo Costa, S. D. Kawaler, J. E. S. Costa, Anjum S. Mukadam, J. Larrison, T. J. Ahrens, A. Kyle Jones, J. KrzesiŃski, S. J. Kleinman, R. Kalytis, R. Janulis, and A. E. Collins

Subjects
Physics, stars, lcsh:QB1-991, Stars, Space and Planetary Science, lcsh:Astronomy, evolution, Astronomy, Astronomy and Astrophysics, individual, GD 358 - stars, Astrobiology
Abstract

We report on the 323 hours of nearly uninterrupted time series photometric observations of the DBV star GD 358 acquired with the Whole Earth Telescope (WET) during May 23 to June 8, 2000. We acquired more than 232 000 independent measurements and 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.

Published
2003

4. 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

5. The new series of the Vilnius-design classical WET photometer

Author

D. Ališauskas, R. Kalytis, J. Sperauskas, E. G. Meištas, Roberto Silvotti, Rimvydas Janulis, R. Skipitis, and E. Siauciunas

Subjects
Optics, Series (mathematics), Space and Planetary Science, law, business.industry, Astronomy, Environmental science, Astronomy and Astrophysics, QB1-991, Photometer, business, law.invention, Remote sensing
Published
2000

6. Preliminary Results from XCOV 17: PG 1336-018

Author

T. S. Metcalfe, Jérôme Perez, G. Vauclair, R. H. Østensen, E. G. Meištas, B. Shobbrook, B. N. Ashoka, H. Mendelson, Steven D. Kawaler, Matthew R. Burleigh, Stefan Dreizler, Waldemar Ogloza, Adalberto Piccioni, Denis J. Sullivan, F. van Wyk, R. Kalytis, Freddy Marang, J. Krzesinski, R. S. Stobie, O. Giovannini, J. L. Deetjen, Anjum S. Mukadam, A. Nitta-Kleinman, S. Seetha, T. K. Watson, S. J. Kleinman, P. Martinez, P. Mosaklik, Michael D. Reed, Sonja Schuh, Ana Ulla, D. O'Donoghue, M. Chevreton, Staszek Zola, D. Ališauskas, Antonio Kanaan, Martin A. Barstow, Judith L. Provencal, T. Sullivan, Roberto Silvotti, J. E. Solheim, Souza Oliveira Kepler, Olga Suarez, P. Ibbetson, J. Rene-Fremy, D. Kilkenny, Elia M. Leibowitz, Xiao-Jun Jiang, N. Dolez, and Minia Manteiga

Subjects
Physics, Space and Planetary Science, Astronomy, Astronomy and Astrophysics, QB1-991, Astrobiology
Published
2000

7. 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

8. 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

9. 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

10. 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

11. 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

12. A Whole Earth Telescope campaign on the pulsating subdwarf B binary system PG 1336-018 (NY Vir)

Author

P. Martinez, R. Kalytis, J. E. Solheim, Elia M. Leibowitz, T. K. Watson, M. Chevreton, B. N. Ashoka, T. Sullivan, R. S. Stobie, O. Giovannini, Xiao-Jun Jiang, Anjum S. Mukadam, S. J. Kleinman, Roberto Silvotti, Pawel Moskalik, Sonja Schuh, Ana Ulla, A. Nitta, J. L. Deetjen, Santosh Joshi, J. M. Gonzalez Perez, D. Ališauskas, D. Kilkenny, Olga Suarez, Matthew R. Burleigh, Stefan Dreizler, Waldemar Ogloza, Minia Manteiga, R. R. Shobbrook, Antonio Kanaan, Denis J. Sullivan, H. Mendelson, Steven D. Kawaler, Donal O'Donoghue, Judith L. Provencal, Souza Oliveira Kepler, Freddy Marang, Adalberto Piccioni, G. Vauclair, Michael D. Reed, E. G. Meištas, T. S. Metcalfe, R. H. Østensen, F. van Wyk, N. Dolez, S. Seetha, Staszek Zola, J. Krzesinski, P. Ibbetson, 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
Astrophysics::High Energy Astrophysical Phenomena, oscillations [Stars], Fotometria estelar, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Asteroseismology, law.invention, Telescope, law, Astrophysics::Solar and Stellar Astrophysics, Estrelas, Binary system, Astrophysics::Galaxy Astrophysics, Physics, Astronomy, Astronomy and Astrophysics, Subdwarf, individual: PG 1336−018 [Stars], variables: other [Stars], Fotometria astronômica, Space and Planetary Science, [SDU]Sciences of the Universe [physics], Pulsacoes estelares, Astrophysics::Earth and Planetary Astrophysics, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Earth (classical element)
Abstract

We present results from a multisite (‘Whole Earth Telescope’) photometric campaign on PG 1336−018, the close eclipsing binary system containing a pulsating subdwarf B (sdB) star. The main part of the campaign (1999 April) resulted in ~172 h of observations, representing a coverage of about 47 per cent, and additional data were obtained outside the core campaign. Periodogram analysis shows that the light variations are dominated by three frequencies near 5757, 5585 and 5369 μHz (~174, 179 and 186s, respectively), although many frequencies are present, particularly in the range 5000–6000 μHz (~200–170 s). We identify, with some confidence, 28 frequencies down to a semi-amplitude of 0.0005 in fractional intensity (equivalent to about 0.5 mmag). It is clear that the pulsation frequencies of PG 1336−018 have changed substantially since the 1996 discovery observations were made, and that amplitude changes occur, at least in the dominant three frequencies, on relatively short time-scales (of the order of a day). On the assumption that the pulsating star is phase-locked in the binary system, we have searched for rotational splitting of frequencies near the orbital and half of the orbital period, but the results are confused by aliasing at those frequencies (due to the data gaps caused by the eclipses). A preliminary model qualitatively matches the distribution of frequencies in PG 1336−018, with some good individual correspondences, but cannot be considered adequate because geometric cancellation should hide some of the modes which are apparently detected. Analysis of the pulsations during eclipse recovers three of the strongest modes, but the limited eclipse data – which can, at best, be only about 9 per cent of the total – do not allow mode identification at this stage. Simulations indicate that an overall coverage of about 80 per cent would be required for this to be viable. An attempt was made to determine phase shifts in the pulsation frequencies as a way of directly measuring the size of the binary orbit, but the uncertainties in the method are comparable to the light travel time across the orbit (probably less than a second).

Published
2003

14. The Wet Instrumentation: Five Years of the Vilnius Group Experience

Author

R. Kalytis

Subjects
Engineering, medicine.medical_specialty, Space and Planetary Science, business.industry, Group (periodic table), Astronomy, medicine, QB1-991, Astronomy and Astrophysics, Medical physics, Instrumentation (computer programming), business, Remote sensing
Published
1998

15. Photometric instrumentation for the Whole Earth Telescope and other projects

Author

R. Kalytis, D. Ališauskas, E. G. Meištas, V. Luja, and R. Skipitis

Subjects
Photometry (optics), Physics, Telescope, Stars, law, Astronomy, Photometer, Filter wheel, Remote sensing, law.invention
Abstract

Some components of the photometric equipment, designed and made to use in high speed multichannel stellarphotometry for the Whole Earth Telescope (WET) and other astronomical programs, are described. Despite this specialpurpose, the described equipment could also be used for any kind of stellar photometry, especially for observations ofvariable stars. Small size and weight of the equipment make it suitable for observations in expeditionary conditions. An original solution of the step-motor feeding for the filter wheel rotation is presented, and the filter selling system FD 306based on it is described and discussed.Keywords: instrumentation: photometers 1. INTRODUCTION1.1. Whole Earth Telescope project The Whole Earth Telescope. or WET1 .isan existing telescope, which comes into life one or two times every year. Itconsists2 of astronomers who travel to telescopes at selected longitudes around the Earth and observe the same stars withfunctionally equivalent instruments. making those separate instruments like one much more productive instrument. When

Published
1997

16. Components of photometric instrumentation

Author

E. G. Meištas, R. Skipitis, R. Kalytis, D. Ališauskas, and V. Luja

Subjects
Engineering, Space and Planetary Science, business.industry, Astronomy, QB1-991, Astronomy and Astrophysics, Instrumentation (computer programming), business, Astrobiology
Published
1996

17. Photometric equipment for WET

Author

R. Kalytis and E. G. Meistas

Subjects
Space and Planetary Science, Astronomy, QB1-991, Astronomy and Astrophysics
Published
1995

19. First results from the multisite time-series campaign on the sdBV star HS2201+2610

Author

Michael D. Reed, J. M. Gonzalez Perez, E. G. Meištas, O. Bärnbantner, Nicole M. Silvestri, R. L. Riddle, U. Heber, Rimvydas Janulis, Xiao-Jun Jiang, O. Cordes, Roberto Silvotti, R. Kalytis, Terry D. Oswalt, and D. Ališauskas

Subjects
Photometry (optics), Physics, Amplitude, Space and Planetary Science, Excited state, Astronomy, Astronomy and Astrophysics, Astrophysics, Low Gravity
Abstract

In this article we present the first results of about 95 hours of time-series photometry on the low gravity sdB pulsating star HS 2201+2610, obtained from a multi-site time-series campaign in September-October 2000. The temporal spectrum of HS 2201+2610 shows 3 close frequencies at 2860.9, 2824.1 and 2880.8 μHz with amplitudes of about 1 %, 0.4 % and 0.1 % respectively. Due to the small number of excited modes, a mode identification is possible in principle but not easy; no clear signatures of rotational splitting are seen.

Published
2001

20. Observations of the pulsating subdwarf B star Feige 48: Constraints on evolution and companions

Author

M. D. Reed, S. D. Kawaler, S. Zola, X. J. Jiang, S. Dreizler, S. L. Schuh, J. L. Deetjen, R. Kalytis, E. Meištas, R. Janulis, D. Ališauskas, J. Krzesiński, M. Vuckovic, P. Moskalik, W. Ogłoza, A. Baran, G. Stachowski, D. W. Kurtz, J. M. González Pérez, A. Mukadam, T. K. Watson, C. Koen, P. A. Bradley, M. S. Cunha, M. Kilic, E. W. Klumpe, R. F. Carlton, G. Handler, D. Kilkenny, R. Riddle, N. Dolez, G. Vauclair, M. Chevreton, M. A. Wood, A. Grauer, G. Bromage, J. E. Solheim, R. Østensen, A. Ulla, M. Burleigh, S. Good, Ö. Hürkal, R. Anderson, E. Pakstiene, Department of Physics, Astronomy, and Materials Science, Missouri State University, Department of Physics and Astronomy, Iowa State University, Astronomical Observatory, Jagiellonia University, National Astronomical Observatoires-CAS, Eberhard Karls Universität Tübingen = Eberhard Karls University of Tuebingen, Institute of Material Science and Applied Research of Vilnius University, Astronomical Observatory, Institute of Theoretical Physics and Astronomy, Astronomical Observatory, Mount Suhora Observatory, Cracow Pedagogical University, Centrum Astronomiczne im. M. Kopernika, Warszawa (CAMK), Centre for Astrophysics, University of Central Lancashire, Institutt for Fysikk, Universitetet i Tromsø, Department of Astronomy, University of Texas, Southwestern University, Los Alamos National Laboratory (LANL), Centro de Astrofisica da Universidade do Porto (CAUP), Department of Physics and Astronomy, Middle Tennessee State University, South African Astronomical Observatory (SAAO), 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, Departement d'Astrophysique Extragalactique et de Cosmologie (DAEC), Observatoire de Paris, Université Paris sciences et lettres (PSL)-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, Department of Physics and Space Sciences and SARA Observatory, Florida Institute of Technology, Melbourne, Department of Physics and Astronomy, University of Arkansas, Isaac Newton Group of Telescopes, Universidade de Vigo, Department of Physics and Astronomy, University of Leicester, Department of Astronomy and Space Sciences, Ege University, Department of Physics and Astronomy, University of North Carolina, and Ege Üniversitesi

Subjects
oscillations [stars], Subdwarf B star, stars : individual (Feige 48), FOS: Physical sciences, Astrophysics, Star (graph theory), 01 natural sciences, Stability (probability), stars : oscillations, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, 010303 astronomy & astrophysics, individual (Feige 48) [stars], Physics, 010308 nuclear & particles physics, variables: other [stars], Astrophysics (astro-ph), Mode (statistics), Astronomy and Astrophysics, Horizontal branch, Subdwarf, stars : variables : other, Stars, Amplitude, Space and Planetary Science, Astrophysics::Earth and Planetary Astrophysics, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract

Since pulsating subdwarf B (sdBV or EC14026) stars were first discovered (Kilkenny et al, 1997), observational efforts have tried to realize their potential for constraining the interior physics of extreme horizontal branch (EHB) stars. Difficulties encountered along the way include uncertain mode identifications and a lack of stable pulsation mode properties. Here we report on Feige 48, an sdBV star for which follow-up observations have been obtained spanning more than four years, which shows some stable pulsation modes. We resolve the temporal spectrum into five stable pulsation periods in the range 340 to 380 seconds with amplitudes less than 1%, and two additional periods that appear in one dataset each. The three largest amplitude periodicities are nearly equally spaced, and we explore the consequences of identifying them as a rotationally split l=1 triplet by consulting with a representative stellar model. The general stability of the pulsation amplitudes and phases allows us to use the pulsation phases to constrain the timescale of evolution for this sdBV star. Additionally, we are able to place interesting limits on any stellar or planetary companion to Feige 48., accepted for publication in MNRAS

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