References of "Dupret, Marc-Antoine"
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See detailStochastic excitation of non-radial modes. I. High-angular-degree p modes
Belkacem, Kevin ULg; Samadi, R.; Goupil, Marie-José et al

in Astronomy and Astrophysics (2008), 478

Context: Turbulent motions in stellar convection zones generate acoustic energy, part of which is then supplied to normal modes of the star. Their amplitudes result from a balance between the efficiencies ... [more ▼]

Context: Turbulent motions in stellar convection zones generate acoustic energy, part of which is then supplied to normal modes of the star. Their amplitudes result from a balance between the efficiencies of excitation and damping processes in the convection zones. Aims: We develop a formalism that provides the excitation rates of non-radial global modes excited by turbulent convection. As a first application, we estimated the impact of non-radial effects on excitation rates and amplitudes of the high-angular-degree modes that are observed on the Sun. Methods: A model of stochastic excitation by turbulent convection was developed to compute the excitation rates and then successfully applied to solar radial modes. We generalise this approach to the case of non-radial global modes. This enables us to estimate the energy supplied to high-(l) acoustic modes. Qualitative arguments, as well as numerical calculations, are used to illustrate the results. Results: We find that non-radial effects for p modes are non-negligible: - For high-n modes (i.e. typically n > 3) and for high values of l, the power supplied to the oscillations depends on the mode inertia. - For low-n modes, independent of the value of l, the excitation is dominated by the non-radial components of the Reynolds stress term. Conclusions: Our numerical investigation of high-l p modes shows that the validity of the present formalism is limited to l < 500 due to the spatial separation of scale assumption. Thus, a model for very high-l p-mode excitation rates calls for further theoretical developments; however, the formalism is valid for solar g modes, which will be investigated in a paper in preparation. [less ▲]

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See detailA procedure for modelling asymptotic g-mode pulsators: The case of gamma Doradus stars
Moya, A.; Suárez, J. C.; Martín-Ruiz, S. et al

in Astronomische Nachrichten (2008), 329

Mode identification is one of the first and main problems we encounter in trying to develop the complete potential of asteroseismology. In the particular case of {g}-mode pulsators, this is still an ... [more ▼]

Mode identification is one of the first and main problems we encounter in trying to develop the complete potential of asteroseismology. In the particular case of {g}-mode pulsators, this is still an unsolved problem, from both the observational and theoretical points of view. Nevertheless, in recent years, some observational and theoretical efforts have been made to find a solution. In this work we use the latest theoretical and computational tools to understand asymptotic {g}-mode pulsators: 1) the Frequency Ratio Method, and 2) Time Dependent Convection. With these tools, a self-consistent procedure for mode identification and modelling of these {g}-mode pulsators can be constructed. This procedure is illustrated using observational information available for the gamma Doradus star 9 Aurigae. [less ▲]

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See detailImpact of the new solar abundances on the calibration of the PMS binary system RS Chamaeleontis
Alecian, E.; Lebreton, Y.; Goupil, Marie-José et al

in Astronomy and Astrophysics (2007), 473

Context: In a recent work, we tried to obtain a calibration of the two components of the pre-main sequence binary system RS Cha by means of theoretical stellar models. We found that the only way to ... [more ▼]

Context: In a recent work, we tried to obtain a calibration of the two components of the pre-main sequence binary system RS Cha by means of theoretical stellar models. We found that the only way to reproduce the observational parameters of RS Cha with standard stellar models is to decrease the initial abundances of carbon and nitrogen derived from the GN93 solar mixture of heavy elements by a few tenths of dex. Aims: In this work, we aim to reproduce the observational properties of the RS Cha stars with stellar evolution models based on the new AGS05 solar mixture recently derived from a three-dimensional solar model atmosphere. The AGS05 mixture is depleted in carbon, nitrogen and oxygen with respect to the GN93 mixture. Methods: We calculated new stellar models of the RS Cha components using the AGS05 mixture and appropriate opacity tables. We sought models that simultaneously satisfy the observations of the two components (masses, radii, luminosities, effective temperatures and metallicity). Results: We find that it is possible to reproduce the observational data of the RS Cha stars with AGS05 models based on standard input physics. From these models, the initial helium content of the system is YË 0.255 and its age is Ë 9.13 ± 0.12 Myr. [less ▲]

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See detailCalibration of the Pre-Main Sequence Binary System RS Cha: Impact of the Initial Chemical Mixture
Alecian, E.; Lebreton, Y.; Goupil, M*-J et al

in IAU Symposium (2007, August 01)

Accurate observational data are available for the eclipsing double-lined spectroscopic binary system RS Cha, composed of two stars in the pre-main sequence stage of evolution: masses, radii, luminosities ... [more ▼]

Accurate observational data are available for the eclipsing double-lined spectroscopic binary system RS Cha, composed of two stars in the pre-main sequence stage of evolution: masses, radii, luminosities and effective temperatures of each component and metallicity of the system. This allows to build pre-main sequence stellar models representing the components of RS Cha and to constrain them in terms of physical ingredients, initial chemical composition and age.We present stellar models we have calculated using the CESAM stellar evolution code for different sets of physical inputs (opacities, nuclear reaction rates, etc.) and different initial parameters (global metallicity, helium abundance, individual abundances of heavy elements). We discuss their ability to reproduce the observational constraints simultaneously for the two components. We focus on the impact on the models of the chemical mixture adopted and we propose a calibration for the RS Cha system providing an estimate of its age and initial helium abundance. [less ▲]

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See detailMultisite Observations of delta Scuti Stars 7 Aql and 8 Aql (a New delta Scuti Variable): The Twelfth STEPHI Campaign in 2003
Fox Machado, L.; Michel, Eric; Pérez Hernández, F. et al

in Astronomical Journal (The) (2007), 134

We present an analysis of the pulsation behavior of the delta Scuti stars 7 Aql (HD 174532) and 8 Aql (HD 174589), a new variable star, observed in the framework of the STEPHI XII campaign during 2003 ... [more ▼]

We present an analysis of the pulsation behavior of the delta Scuti stars 7 Aql (HD 174532) and 8 Aql (HD 174589), a new variable star, observed in the framework of the STEPHI XII campaign during 2003 June and July; 183 hr of high-precision photometry were acquired by using four-channel photometers at three sites on three continents during 21 days. The light curves and amplitude spectra were obtained following a classical scheme of multichannel photometry. Observations in different filters were also obtained and analyzed. Six and three frequencies have been unambiguously detected above a 99% confidence level in the range 190-300 muHz and 100-145 muHz in 7 Aql and 8 Aql, respectively. A comparison of observed and theoretical frequencies shows that 7 Aql and 8 Aql may oscillate with p-modes of low radial orders, typical among delta Scuti stars. In terms of radial oscillations the range of 8 Aql goes from n=1 to 3, while for 7 Aql the range spans from n=4 to 7. Nonradial oscillations have to be present in both stars as well. The expected range of excited modes according to a nonadiabatic analysis goes from n=1 to 6 in both stars. [less ▲]

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See detailEffect of convective outer layers modeling on non-adiabatic seismic observables of delta Scuti stars
Montalban Iglesias, Josefa ULg; Dupret, Marc-Antoine ULg

in Astronomy and Astrophysics (2007), 470

Context: The identification of pulsation modes in delta Scuti stars is mandatory for constraining the theoretical stellar models. The non-adiabatic observables used in the photometric identification ... [more ▼]

Context: The identification of pulsation modes in delta Scuti stars is mandatory for constraining the theoretical stellar models. The non-adiabatic observables used in the photometric identification methods depend, however, on convection modeling in the external layers. Aims: We determine how the treatment of convection in the atmospheric and sub-atmospheric layers affects the mode identification and what information about the thermal structure of the external layers can be obtained from amplitude ratios and phase lags in Strömgren photometric bands. Methods: We derive non-adiabatic parameters for delta Scuti stars by using, for the first time, stellar models with the same treatment of convection in the interior and in the atmosphere. We compute classical non-gray mixing length models, and as well non-gray ``full spectrum of turbulence'' (FST) models. Furthermore, we compute the photometric amplitudes and phases of pulsation by using the colors and the limb-darkening coefficients as derived from the same atmosphere models as used in the stellar modeling. Results: We show that the non-adiabatic phase-lag is mainly sensitive to the thermal gradients in the external layers, hence to the treatment of convection, and that this sensitivity is also clearly reflected in the multi-color photometric phase differences. [less ▲]

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See detailRevised instability domains of SPB and beta Cephei stars
Miglio, Andrea ULg; Montalban Iglesias, Josefa ULg; Dupret, Marc-Antoine ULg

in Communications in Asteroseismology (2007), 151

The excitation of pulsation modes in beta Cephei and Slowly Pulsating B stars is known to be very sensitive to opacity changes in the stellar interior where T Ë 2 × 10[SUP]5[/SUP] K. In this region ... [more ▼]

The excitation of pulsation modes in beta Cephei and Slowly Pulsating B stars is known to be very sensitive to opacity changes in the stellar interior where T Ë 2 × 10[SUP]5[/SUP] K. In this region differences in opacity up to Ë 50% can be induced by the choice between OPAL and OP opacity tables, and between two different metal mixtures (Grevesse & Noels 1993 and Asplund et al. 2005). We have extended the non-adiabatic computations presented in Miglio et al. (2007) towards models of higher mass and pulsation modes of degree l = 3, and we present here the instability domains in the HR- and log P-log Teff diagrams resulting from different choices of opacity tables, and for three different metallicities. [less ▲]

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See detailThe field high-amplitude SX Phoenicis variable BL Camelopardalis: results from a multisite photometric campaign. I. Pulsation
Rodríguez, E.; Fauvaud, S.; Farrell, J. A. et al

in Astronomy and Astrophysics (2007), 471

Context: BL Cam is an extreme metal-deficient field high-amplitude SX Phe-type variable where a very complex frequency spectrum is detected, with a number of independent nonradial modes excited, unusual ... [more ▼]

Context: BL Cam is an extreme metal-deficient field high-amplitude SX Phe-type variable where a very complex frequency spectrum is detected, with a number of independent nonradial modes excited, unusual among the high-amplitude pulsators in the Lower Classical Instability Strip. Aims: An extensive and detailed study has been carried out to investigate the pulsational content and properties of this object. Methods: The analysis is based on 283 h of CCD observations obtained in the Johnson V filter, during a long multisite photometric campaign carried out along the Northern autumn-winter of 2005-2006. Additionally, multicolour BI photometry was also collected to study the phase shifts and amplitude ratios, between light curves obtained in different filters, for modal discrimination of the main excited modes. Results: The detailed frequency analysis revealed a very rich and dense pulsational content consisting of 25 significant peaks, 22 of them corresponding to independent modes: one is the already known main periodicity f[SUB]0[/SUB] = 25.5765 cd[SUP]-1[/SUP] (Delta V = 153 mmag) and the other 21 are excited modes showing very small amplitudes. Some additional periodicities are probably still remaining in the residuals. This represents the most complex spectrum ever detected in a high-amplitude pulsator of this type. The majority of the secondary modes suspected from earlier works are confirmed here and, additionally, a large number of new peaks are detected. The amplitude of the main periodicity f[SUB]0[/SUB] seems to be stable during decades, but the majority of the secondary modes show strong amplitude changes from one epoch to another. The suspected fundamental radial nature of the main periodicity of BL Cam is confirmed, while the secondary peak f[SUB]1[/SUB] = 25.2523 cd[SUP]-1[/SUP] is identified as a nonradial mixed mode g[SUB]4[/SUB] with l = 1. The radial double-mode nature, claimed by some authors for the main two frequencies of BL Cam, is not confirmed. Nevertheless, the frequency f[SUB]6[/SUB] = 32.6464 cd[SUP]-1[/SUP] could correspond to the first radial overtone. [less ▲]

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See detailSeismic study of the Alpha Centauri binary system using the minimisation algorithm of Levenberg-Marquarth
Ozel, N.; Dupret, Marc-Antoine ULg; Baglin, A.

in SF2A-2007: Proceedings of the Annual meeting of the French Society of Astronomy and Astrophysics held in Grenoble, France, July 2-6, 2007, Eds.: J. Bouvier, A. Chalabaev, and C. Charbonnel, p.545 (2007, July 01)

Thanks to the CoRoT mission, we are going to get seismic data of very high precision for many stars. Throughout the method of asteroseismology these data will allow us to constrain the physical ... [more ▼]

Thanks to the CoRoT mission, we are going to get seismic data of very high precision for many stars. Throughout the method of asteroseismology these data will allow us to constrain the physical description of stellar interiors with unprecedented precision. In this context, we have developed a general tool which allows us to find stellar models fitting a set of seismic constraints (the oscillations frequencies) and non-seismic constraints (e.g. the luminosity, the effective temperature, ...). This tool follows the algorithm of Levenberg-Marquarth which seeks the fundamental parameters of the stellar model (e.g. the mass, the age, the helium abundance, the mixing-length parameter,ldots). We apply it to a specific case: the alpha Cen binary system. Taking into account all observational constraints available for this binary system, we succeed to find models entering between the one or two sigma error box of the observational constraints. [less ▲]

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See detailInstability strips of main sequence B stars: a parametric study of iron enhancement
Miglio, Andrea ULg; Bourge, P.-O.; Montalban Iglesias, Josefa ULg et al

in Communications in Asteroseismology (2007), 150

The discovery of beta Cephei stars in low metallicity environments, as well as the difficulty to theoretically explain the excitation of the pulsation modes observed in some beta Cephei and SPB stars ... [more ▼]

The discovery of beta Cephei stars in low metallicity environments, as well as the difficulty to theoretically explain the excitation of the pulsation modes observed in some beta Cephei and SPB stars, suggest that the iron opacity ``bump'' provided by standard models could be underestimated. We investigate, by means of a parametric study, the effect of a local iron enhancement on the location of the beta Cephei and SPB instability strips. [less ▲]

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See detailAn asteroseismic Main Sequence model for the delta Scuti star 44 Tau
Garrido, R.; Suárez, J. C.; Grigahcène, A. et al

in Communications in Asteroseismology (2007), 150

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See detailTwo-scale mass-flux closure models for turbulence: p-mode amplitudes in solar-like stars
Belkacem, Kevin ULg; Samadi, R.; Goupil, Marie-José et al

in Communications in Asteroseismology (2007), 150

A new closure model has been developed, which takes into account both the skewness of the velocity distribution induced by the presence of two flows in the convection zone, and the effects of turbulence ... [more ▼]

A new closure model has been developed, which takes into account both the skewness of the velocity distribution induced by the presence of two flows in the convection zone, and the effects of turbulence onto each flow (Belkacem et al. 2006a). Applied to the formalism of p-mode excitation, it has been possible to validate this theoretical model by a comparison with the observational excitation rates in the solar case using GOLF data (see Belkacem et al. 2006b). The next step is to consider alpha Cen A for which observations of the mode-damping rates are available. [less ▲]

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See detaillambda Boo stars among the gamma Dor-type pulsators: the cases of HD 218427 and HD 239276
Rodríguez, E.; Suárez, J. C.; Moya, A. et al

in Communications in Asteroseismology (2007), 150

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See detailAsteroseismology and mode driving of the Herbig Ae star HD 104237
Dupret, Marc-Antoine ULg; Théado, S.; Böhm, T. et al

in Communications in Asteroseismology (2007), 150

Eight pulsation frequencies were detected in the Herbig Ae star HD 104237 during two observational campaigns in 1999 -- 2000 (Böhm et al. 2004). Moreover, Böhm et al. (in preparation) detected recently in ... [more ▼]

Eight pulsation frequencies were detected in the Herbig Ae star HD 104237 during two observational campaigns in 1999 -- 2000 (Böhm et al. 2004). Moreover, Böhm et al. (in preparation) detected recently in their data two independent signatures of a signal at 95 hr that corresponds probably to rotational modulation. We present here a seismic study of this Pre-Main Sequence star based on these observations. Different possible interpretations of the pulsation spectrum are considered. The driving of the pulsation modes is not explained by standard models, the observed frequencies being too high for delta Scuti-type pulsations. We consider the effect of He accumulation in its partial ionization zones as a possible explanation for this driving. [less ▲]

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See detailSolar-like oscillation amplitudes and line-widths as a probe for turbulent convection in stars
Samadi, R.; Belkacem, Kevin ULg; Goupil, M*-J et al

in IAU Symposium (2007, May 01)

Excitation of solar-like oscillations is attributed to turbulent convection and takes place at the upper-most part of the outer convective zones. Amplitudes of these oscillations depend on the efficiency ... [more ▼]

Excitation of solar-like oscillations is attributed to turbulent convection and takes place at the upper-most part of the outer convective zones. Amplitudes of these oscillations depend on the efficiency of the excitation processes as well as on the properties of turbulent convection. We present past and recent improvements on the modeling of those processes. We show how the mode amplitudes and mode line-widths can bring information about the turbulence in the specific cases of the Sun and Alpha Cen A. [less ▲]

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See detailOscillating blue stragglers, gamma Doradus stars and eclipsing binaries in the open cluster NGC 2506
Arentoft, T.; De Ridder, J.; Grundahl, F. et al

in Astronomy and Astrophysics (2007), 465

Context: This is the first step in a project to combine studies of eclipsing binaries and oscillating stars to probe the interior of Blue Stragglers (BS). This may imply a way to discriminate ... [more ▼]

Context: This is the first step in a project to combine studies of eclipsing binaries and oscillating stars to probe the interior of Blue Stragglers (BS). This may imply a way to discriminate observationally between different birth mechanisms of BS stars. Aims: We study the open cluster NGC 2506 which contains oscillating BS stars and detached eclipsing binaries for which accurate parameters can be derived. This will tightly constrain the cluster isochrone and provide an absolute mass, radius and luminosity-scale for the cluster stars along with the cluster age, metallicity and distance. The present work focuses on obtaining the light curves of the binaries and determine their orbital periods, on obtaining power spectra of the oscillating BS stars to select targets for follow-up studies, and on searching for gamma Doradus type variables which are also expected to be present in the cluster. Methods: With a two-colour, dual-site photometric campaign we obtained 3120 CCD-images of NGC 2506 spread over four months. We analysed the BI time-series of the oscillating stars and used simulations to derive statistical uncertainties of the resulting frequencies, amplitudes and phases. A preliminary mode-identification was performed using frequency ratios for the oscillating BS stars, and amplitude ratios and phase differences for a population of newly detected gamma Doradus stars. Results: We quadrupled the number of known variables in NGC 2506 by discovering 3 new oscillating BS stars, 15 gamma Doradus stars and four new eclipsing binaries. The orbital periods of 2 known, detached eclipsing binaries were derived. We discovered a BS star with both p-mode and g-mode variability and we confronted our gamma Doradus observations with state-of-the-art seismic models, but found significant discrepancy between theory and observations. Conclusions: . NGC 2506 is an excellent target for asteroseismic tests of stellar models, as strong external constraints can be imposed on the models of a population of more than 20 oscillating stars of different types. Based on observations obtained at the Flemish Mercator telescope on La Palma, Spain, the Danish 1.5-m telescope at ESO, La Silla, Chile, and on observations collected at the European Southern Observatory, Paranal, Chile (ESO Programme 075.D-0206(B)). Catalog of individual photometry measurements for all variables is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/465/965 [less ▲]

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