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Your search keyword '"O'Brien M. S."' showing total 3 results
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3 results on '"O'Brien M. S."'

1. Constraining the Evolution of ZZ Ceti

Author

Mukadam A. S., Kepler S. O., Winget D. E., Nather R. E., Kilic M., Mullally F., Hippel T. von, Kleinman S. J., Nitta A., Guzik J. A., Bradley P. A., Matthews J., Sekiguchi K., Sullivan D. J., Shobbrook R. R., Birch P., Jiang X. J., Xu D. W., Joshi S., Ashoka B.N., Ibbetson P., Leibowitz E., Ofek E. O., Meištas E. G., Janulis R., Ališauskas D., Kalytis R., Handler G., Kilkenny D., O’Donoghue D., Kurtz D. W., Müller M., Moskalik P., Ogłoza W., Zoła S., Krzesiński J., Johannessen F., Gonzalez-Perez J. M., Solheim J-E., Silvotti R., Bernabei S., Vauclair G., Dolez N., Fu J. N., Chevreton M., Manteiga M., Súarez O., Ulla A., Cunha M. S., Metcalfe T. S., Kanaan A., Fraga L., Costa A. F. M., Giovannini O., Fontaine G., Bergeron P., O’Brien M. S., Sanwal D., Wood M. A., Ahrens T. J., Silvestri N., Klumpe E. W., Kawaler S. D., Riddle R., Reed M. D., and Watson T. K.

Subjects
stars, white dwarfs, individual, ZZ Cet, R548 - stars, pulsations, evolution, Astronomy, QB1-991
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. Based on observations that span 31 years, we conclude that the period 213.132605 s observed in ZZ Ceti drifts at a rate dP/dt≤(5.5±1.9)×10−15 s/s, after correcting for proper motion. Our results are consistent with previous Ṗ values for this mode and an improvement over them due to the larger time-base. The characteristic stability timescale implied for the pulsation period is |P/ Ṗ|≥1.2 Gyr, comparable to the theoretical cooling timescale for the star. Our current stability limit for the period 213.132605 s is only slightly less than the present measurement for G117-B15A for the period 215.2 s, another DAV, establishing this mode in ZZ Ceti as the second most stable optical clock known, more stable than atomic clocks and most pulsars.

Published
2003
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2. Whole Earth Telescope observations of the hot helium atmosphere pulsating white dwarf EC20058-5234

Author

WET Collaboration, Sullivan, D. J., Metcalfe, T. S., O'Donoghue, D., Winget, D. E., Kilkenny, D., van Wyk, F., Kanaan, A., Kepler, S. O., Nitta, A., Kawaler, S. D., Montgomery, M. H., Nather, R. E., O'Brien, M. S., Bischoff-Kim, A., Wood, M., Jiang, X. J., Leibowitz, E. M., Ibbetson, P., Zola, S., Krzesinski, J., Pajdosz, G., Vauclair, G., Dolez, N., Chevreton, M., 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), 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), 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), 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), and Université Fédérale Toulouse Midi-Pyrénées

Subjects
oscillations [stars], Stellar mass, FOS: Physical sciences, Astrophysics, Compact star, stars: interiors, 01 natural sciences, law.invention, Photometry (optics), Telescope, photometric [techniques], [PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], Análise asterosismológica, techniques: photometric, Observatory, law, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, 010303 astronomy & astrophysics, white dwarfs, Physics, interiors [stars], 010308 nuclear & particles physics, Estrelas ZZ Ceti, Astrophysics (astro-ph), White dwarf, Astronomy and Astrophysics, Effective temperature, stars: individual: EC 20058-5234, individual: EC 20058-5234 [stars], Fotometria astronômica, Anãs brancas, Pulsacoes estelares, 13. Climate action, Space and Planetary Science, stars: oscillations, Instability strip
Abstract

We present the analysis of a total of 177h of high-quality optical time-series photometry of the helium atmosphere pulsating white dwarf (DBV) EC 20058-5234. The bulk of the observations (135h) were obtained during a WET campaign (XCOV15) in July 1997 that featured coordinated observing from 4 southern observatory sites over an 8-day period. The remaining data (42h) were obtained in June 2004 at Mt John Observatory in NZ over a one-week observing period. This work significantly extends the discovery observations of this low-amplitude (few percent) pulsator by increasing the number of detected frequencies from 8 to 18, and employs a simulation procedure to confirm the reality of these frequencies to a high level of significance (1 in 1000). The nature of the observed pulsation spectrum precludes identification of unique pulsation mode properties using any clearly discernable trends. However, we have used a global modelling procedure employing genetic algorithm techniques to identify the n, l values of 8 pulsation modes, and thereby obtain asteroseismic measurements of several model parameters, including the stellar mass (0.55 M_sun) and T_eff (~28200 K). These values are consistent with those derived from published spectral fitting: T_eff ~ 28400 K and log g ~ 7.86. We also present persuasive evidence from apparent rotational mode splitting for two of the modes that indicates this compact object is a relatively rapid rotator with a period of 2h. In direct analogy with the corresponding properties of the hydrogen (DAV) atmosphere pulsators, the stable low-amplitude pulsation behaviour of EC 20058 is entirely consistent with its inferred effective temperature, which indicates it is close to the blue edge of the DBV instability strip. (abridged), 19 pages, 8 figures, 5 tables, MNRAS accepted

Published
2008

3. Whole Earth Telescope observations of the hot helium atmosphere pulsating white dwarf EC 20058−5234.

Author

Sullivan, D. J., Metcalfe, T. S., O'Donoghue, D., Winget, D. E., Kilkenny, D., van Wyk, F., Kanaan, A., Kepler, S. O., Nitta, A., Kawaler, S. D., Montgomery, M. H., Nather, R. E., O'Brien, M. S., Bischoff-Kim, A., Wood, M., Jiang, X. J., Leibowitz, E. M., Ibbetson, P., Zola, S., and Krzesinski, J.

Subjects
NOBLE gases, WHITE dwarf stars, ELECTROMAGNETIC measurements, SURFACE chemistry, COMBINATORIAL optimization, SURFACE tension
Abstract

We present the analysis of a total of 177 h of high-quality optical time-series photometry of the helium atmosphere pulsating white dwarf (DBV) EC 20058−5234. The bulk of the observations (135 h) were obtained during a WET campaign (XCOV15) in 1997 July that featured coordinated observing from four southern observatory sites over an 8-d period. The remaining data (42 h) were obtained in 2004 June at Mt John Observatory in NZ over a one-week observing period. This work significantly extends the discovery observations of this low-amplitude (few per cent) pulsator by increasing the number of detected frequencies from 8 to 18, and employs a simulation procedure to confirm the reality of these frequencies to a high level of significance (1 in 1000). The nature of the observed pulsation spectrum precludes identification of unique pulsation mode properties using any clearly discernable trends. However, we have used a global modelling procedure employing genetic algorithm techniques to identify the n, ℓ values of eight pulsation modes, and thereby obtain asteroseismic measurements of several model parameters, including the stellar mass and Teff (∼28 200 K). These values are consistent with those derived from published spectral fitting: and log g∼ 7.86. We also present persuasive evidence from apparent rotational mode splitting for two of the modes that indicates this compact object is a relatively rapid rotator with a period of 2 h. In direct analogy with the corresponding properties of the hydrogen (DAV) atmosphere pulsators, the stable low-amplitude pulsation behaviour of EC 20058 is entirely consistent with its inferred effective temperature, which indicates it is close to the blue edge of the DBV instability strip. Arguably, our most significant result from this work is the clear demonstration that EC 20058 is a very stable pulsator with several dominant pulsation modes that can be monitored for their long-term stability. [ABSTRACT FROM AUTHOR]

Published
2008
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