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Aims: We investigate how these observed splittings ... [more ▼]Context. Recent asteroseismic observations have led to the determination of rotational frequency splittings for ℓ = 1 mixed modes in red giants.
Aims: We investigate how these observed splittings can constrain the modelling of the physical processes transporting angular momentum in stellar interiors.
Methods: We first compare models including a comprehensive treatment of shellular rotation only, with the rotational splittings observed for the red giant KIC 8366239. We then study how these asteroseismic constraints can give us information about the efficiency of an additional mechanism for the internal transport of angular momentum. This is done by computing rotating models of KIC 8366239 that include a constant viscosity corresponding to this physical process, in addition to the treatment of shellular rotation.
Aims: We intend to improve the knowledge of the interior of α Centauri A by determining the nature of its core.
Methods: We combined the radial velocity time series obtained in May 2001 with three spectrographs in Chile and Australia: CORALIE, UVES, and UCLES. The resulting combined time series has a length of 12.45 days and contains over 10 000 data points and allows to greatly reduce the daily alias peaks in the power spectral window.
Results: We detected 44 frequencies that are in good overall agreement with previous studies, and found that 14 of these show possible rotational splittings. New values for the large (Δν) and small separations (δν[SUB]02[/SUB], δν[SUB]13[/SUB]) have been derived.
Conclusions: A comparison with stellar models indicates that the asteroseismic constraints determined in this study (namely r[SUB]10[/SUB] and δν[SUB]13[/SUB]) allows us to set an upper limit to the amount of convective-core overshooting needed to model stars of mass and metallicity similar to those of α Cen A. [less ▲]Detailed reference viewed: 7 (2 ULg) Effects of rotational mixing on the asteroseismic properties of solar-type starsEggenberger, P.; Meynet, G.; Maeder, A. et alin Astronomy and Astrophysics (2010), 519Context. Observations of solar-like oscillations obtained either from the ground or from space stimulated the study of the effects of various physical processes on the modelling of solar-type stars.
Aims: The influence of rotational mixing on the evolution and asteroseismic properties of solar-type stars is studied.
Methods: Global and asteroseismic properties of models of solar-type stars computed with and without a comprehensive treatment of shellular rotation are compared. The effects of internal magnetic fields are also discussed in the framework of the Tayler-Spruit dynamo.
Results: Rotational mixing changes the global properties of a solar-type star with a significant increase of the effective temperature resulting in a shift of the evolutionary track to the blue part of the HR diagram. These differences observed in the HR diagram are related to changes of the chemical composition, because rotational mixing counteracts the effects of atomic diffusion leading to larger helium surface abundances for rotating models than for non-rotating ones. Higher values of the large frequency separation are then found for rotating models than for non-rotating ones at the same evolutionary stage, because the increase of the effective temperature leads to a smaller radius and hence to an increase of the stellar mean density. In addition to changing the global properties of solar-type stars, rotational mixing also has a considerable impact on the structure and chemical composition of the central stellar layers by bringing fresh hydrogen fuel to the central stellar core, thereby enhancing the main-sequence lifetime. The increase of the central hydrogen abundance together with the change of the chemical profiles in the central layers result in a significant increase of the values of the small frequency separations and of the ratio of the small to large separations for models including shellular rotation. This increase is clearly seen for models with the same age sharing the same initial parameters except for the inclusion of rotation as well as for models with the same global stellar parameters and in particular the same location in the HR diagram. By computing rotating models of solar-type stars including the effects of a dynamo that possibly occurs in the radiative zone, we find that the efficiency of rotational mixing is strongly reduced when the effects of magnetic fields are taken into account, in contrast to what happens in massive stars. [less ▲]Detailed reference viewed: 7 (2 ULg) Gamma Dor and Gamma Dor - Delta Sct Hybrid Stars In The CoRoT LRa01Hareter, M.; Reegen, P.; Miglio, A. et alin ArXiv e-prints (2010), 1007A systematic search for gamma Dor and gamma Dor - delta Scuti hybrid pulsators was conducted on the CoRoT LRa01 Exo-archive yielding a total of 418 gamma Dor and 274 hybrid candidates. After an automatic ... [more ▼]A systematic search for gamma Dor and gamma Dor - delta Scuti hybrid pulsators was conducted on the CoRoT LRa01 Exo-archive yielding a total of 418 gamma Dor and 274 hybrid candidates. After an automatic jump correction 194 and 167 respectively, show no more obvious jumps and were investigated in more detail. For about 25\% of these candidates classification spectra from the Anglo-Australian Observatory (AAO) are available. The detailed frequency analysis and a check for combination frequencies together with spectroscopic information allowed us to identify I) 34 gamma Dor stars which show very different pulsation spectra where mostly two modes dominate. Furthermore, a search for regularities in their oscillation spectra allowed to derive recurrent period spacings for 5 of these gamma Dor stars. II) 25 clear hybrid pulsators showing frequencies in the gamma Dor and delta Sct domain and are of A-F spectral type. [less ▲]Detailed reference viewed: 13 (5 ULg) Testing the forward approach in modelling β Cephei pulsators: setting the stageMiglio, A.; Montalban Iglesias, Josefa ; Thoul, Anne in Communications in Asteroseismology (2009)The information on stellar parameters and on the stellar interior we can get by studying pulsating stars depends crucially on the available observational constraints: both seismic constraints (precision ... [more ▼]The information on stellar parameters and on the stellar interior we can get by studying pulsating stars depends crucially on the available observational constraints: both seismic constraints (precision and number of detected modes, identification, nature of the modes) and classical'' observations (photospheric abundances, effective temperature, luminosity, surface gravity). We consider the case of β Cephei pulsators and, with the aim of estimating quantitatively how the available observational constraints determine the type and precision of our inferences, we set the stage for Hare&Hound exercises. In this contribution we present preliminary results for one simple case, where we assume as observed'' frequencies a subset of frequencies of a model and then evaluate a seismic merit function on a dense and extensive grid of models of B-type stars. We also compare the behaviour of χ^2 surfaces obtained with and without mode identification. [less ▲]Detailed reference viewed: 16 (1 ULg) Solar-Like Oscillations in a Massive StarBelkacem, K.; Samadi, R.; Goupil, M.-J. et alin Science (2009), 324Seismology 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 ... [more ▼]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. [less ▲]Detailed reference viewed: 29 (14 ULg) Ground-based observations of the beta Cephei CoRoT main target HD 180642Briquet, Maryline ; Uytterhoeven, K.; Aerts, C. et alConference (2008, July)We present the preliminary results of a detailed study of ground-based photometric and spectroscopic observations dedicated to the β Cephei CoRoT main target HD 180642. Besides the non-linear dominant ... [more ▼]We present the preliminary results of a detailed study of ground-based photometric and spectroscopic observations dedicated to the β Cephei CoRoT main target HD 180642. Besides the non-linear dominant radial mode several low-amplitude modes are detected in both kinds of datasets. Our aim is to derive the wavenumbers (ℓ,m) of these modes, as additional constraints to the CoRoT pulsation frequencies, for forthcoming asteroseismic modelling of the star. [less ▲]Detailed reference viewed: 13 (3 ULg) 1