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TOPIC: HD 180642

Blobrana

L

Posts: 131433

Date: Mar 7 23:32 2013

RE: HD 180642	Permalink

Title: Chaos in large-amplitude pulsators: application to the beta Cep star HD180642 Authors: Pieter Degroote The CoRoT observations of the beta Cephei star HD180642 uncover an unexpectedly rich frequency spectrum, in addition to several heat-driven modes. So far, two processes have been proposed to explain this behaviour: the presence of stochastic oscillations, and the excitation of time-dependent frequencies by nonlinear resonance. I argue for a third explanation for the observations, in the form of chaos due to the nonlinear behaviour of the dominant radial mode. The long-term frequency stability of the dominant radial mode is studied using archival data spanning roughly 20 years. Nonlinear time series analysis techniques are applied to the CoRoT observations, and the observations are compared with simulations of a simple nonlinear oscillator. I show that chaos offers one single explanation for many of the observed features, such as the structure in the autocorrelation of the power spectrum, the long-term frequency shift, the power excess and the wide range of frequencies in the power spectrum. However, the mixture of opacity-driven linear oscillations and nonlinear oscillations complicate the nonlinear time series analysis techniques. Read more (1087kb, PDF) __________________

Blobrana

L

Posts: 131433

Date: Jul 6 06:21 2011

V1449 Aquilae	Permalink

Title: The strong magnetic field of the large-amplitude beta Cephei pulsator V1449 Aql Authors: S. Hubrig, I. Ilyin, M. Briquet, M. Schoeller, J.F. Gonzalez, N. Nunez, P. De Cat, T. Morel Only for very few beta Cephei stars has the behaviour of the magnetic field been studied over the rotation cycle. During the past two years we have obtained multi-epoch polarimetric spectra of the beta Cephei star V1449 Aql with SOFIN at the Nordic Optical Telescope to search for a rotation period and to constrain the geometry of the magnetic field. The mean longitudinal magnetic field is measured at 13 different epochs. The new measurements, together with the previous FORS1 measurements, have been used for the frequency analysis and the characterization of the magnetic field. V1449 Aql so far possesses the strongest longitudinal magnetic field of up to 700G among the beta Cephei stars. The resulting periodogram displays three dominant peaks with the highest peak at f=0.0720d^-1 corresponding to a period P=13.893d. The magnetic field geometry can likely be described by a centred dipole with a polar magnetic field strength B_d around 3kG and an inclination angle beta of the magnetic axis to the rotation axis of 76±4deg. As of today, the strongest longitudinal magnetic fields are detected in the beta Cephei stars V1449 Aql and xi^1 CMa with large radial velocity amplitudes. Their peak-to-peak amplitudes reach ~90km/s and ~33km/s, respectively. Concluding, we briefly discuss the position of the currently known eight magnetic beta Cephei and candidate beta Cephei stars in the Hertzsprung-Russell (H-R) diagram. Read more (657kb, PDF) __________________

Blobrana

L

Posts: 131433

Date: Jun 25 14:06 2009

V1449 Aquila	Permalink

Des oscillations de type solaire sont détectées sur une étoile massive par le satellite CoRoT Des oscillations, de même nature que celles du Soleil, dans une étoile massive déjà connue pour être un pulsateur classique, V1449 Aql (HD180642), viennent d'être découvertes grâce au satellite CoRoT. Ces oscillations vont permettre d'obtenir une meilleure connaissance des progéniteurs de supernovae, qui ont un impact important sur le milieu interstellaire ainsi que sur l'évolution galactique. La sismologie de ces étoiles permettra également une meilleure compréhension des processus hydrodynamiques dans des conditions extrêmes, le milieu stellaire étant très fortement stratifié et turbulent. Les résultats de cette découverte sont présentés dans la revue Science par des chercheurs français appartenant au Laboratoire d'Etudes Spatiales et d'Instrumentation en Astrophysique (INSU-CNRS, Observatoire de Paris) et à l'Institut d'Astrophysique Spatiale (INSU-CNRS, Université Paris-Sud 11), et à des laboratoires belges (Université de Liège, AGO) et québécois (Université de Montréal). Ce résultat est publié dans la revue Science du 19/00/09. Read more (French) __________________

Blobrana

L

Posts: 131433

Date: Jun 24 16:14 2009

V1449 Aql (HD180642)	Permalink

Title: Solar-Like Oscillations in a Massive Star Authors: Kévin Belkacem, Réza Samadi, Marie-Jo Goupil, Laure Lefèvre, Fréderic Baudin, Sébastien Deheuvels, Marc-Antoine Dupret, Thierry Appourchaux, Richard Scuflaire, Michel Auvergne, Claude Catala, Eric Michel, Andrea Miglio, Josefina Montalban, Anne Thoul, Suzanne Talon, Annie Baglin, Arlette Noels Seismology of stars provides insight into the physical mechanisms taking place in their interior, with modes of oscillation probing different layers. Low-amplitude acoustic oscillations excited by turbulent convection were detected four decades ago in the Sun and more recently in low-mass main-sequence stars. Using data gathered by the Convection Rotation and Planetary Transits mission, we report here on the detection of solar-like oscillations in a massive star, V1449 Aql, which is a known large-amplitude (beta Cephei) pulsator. Read more __________________

Blobrana

L

Posts: 131433

Date: Jun 22 12:48 2009

HD 180642	Permalink

Title: Ground-based observations of the beta Cephei CoRoT main target HD 180642: abundance analysis and mode identification Authors: M. Briquet, K. Uytterhoeven, T. Morel, C. Aerts, P. De Cat, P. Mathias, K. Lefever, A. Miglio, E. Poretti, S. Martin-Ruiz, M. Paparo, M. Rainer, F. Carrier, J. Gutierrez-Soto, J.C. Valtier, J.M. Benko, Zs. Bognar, E. Niemczura, P.J. Amado, J.C. Suarez, A. Moya, C. Rodriguez-Lopez, R. Garrido The known beta Cephei star HD 180642 was observed by the CoRoT satellite in 2007. From the very high-precision light curve, its pulsation frequency spectrum could be derived for the first time (Degroote and collaborators). In this paper, we obtain additional constraints for forthcoming asteroseismic modelling of the target. Our results are based on both extensive ground-based multicolour photometry and high-resolution spectroscopy. We determine T_eff = 24 500+-1000 K and log g = 3.45±0.15 dex from spectroscopy. The derived chemical abundances are consistent with those for B stars in the solar neighbourhood, except for a mild nitrogen excess. A metallicity Z = 0.0099+-0.0016 is obtained. Three modes are detected in photometry. The degree l is unambiguously identified for two of them: l = 0 and l = 3 for the frequencies 5.48694 1/d and 0.30818 1/d, respectively. The radial mode is non-linear and highly dominant with an amplitude in the U-filter about 15 times larger than the strongest of the other modes. For the third frequency of 7.36673 1/d found in photometry, two possibilities remain: l = 0 or 3. In the radial velocities, the dominant radial mode presents a so-called stillstand but no clear evidence of the existence of shocks is observed. Four low-amplitude modes are found in spectroscopy and one of them, with frequency 8.4079 1/d, is identified as (l,m)=(3,2). Based on this mode identification, we finally deduce an equatorial rotational velocity of 38±15 km/s. Read more (246kb, PDF) __________________

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