References of "Dupret, Marc-Antoine"
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See detailPreliminary seismic study of the gamma Doradus COROT target HD 49434
Bouabid, M.-P.; Uytterhoeven, K.; Miglio, Andrea ULg et al

in Communications in Asteroseismology (2008), 157

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See detailThe driving mechanism of roAp stars
Dupret, Marc-Antoine ULg; Théado, S.; Noels-Grötsch, Arlette ULg

in Journal of Physics: Conference Series (2008), 118

We analyse in detail the driving mechanism of roAp stars and present the theoretical instability strip predicted by our models with solar metallicity. A particular attention is given to the interpretation ... [more ▼]

We analyse in detail the driving mechanism of roAp stars and present the theoretical instability strip predicted by our models with solar metallicity. A particular attention is given to the interpretation of the role played by the different eigenfunctions in the stabilization of the modes at the red edge of the instability strip. The gradient of temperature in the H[SUB]I[/SUB] opacity bump appears to play a major role in this context. We also consider the particular and complex role played by the shape of the eigenfunctions (location of the nodes, ...). [less ▲]

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See detailTime-dependent convection study of the driving mechanism in the DBV white dwarfs
Dupret, Marc-Antoine ULg; Quirion, P. O.; Fontaine, G. et al

in Journal of Physics: Conference Series (2008), 118

We apply for the first time time-dependent convection (TDC) models to the study of the driving mechanism of the Pulsating DB (V777 Herculis) white dwarfs. From the blue to the red edge of the instability ... [more ▼]

We apply for the first time time-dependent convection (TDC) models to the study of the driving mechanism of the Pulsating DB (V777 Herculis) white dwarfs. From the blue to the red edge of the instability strip of these stars, TDC appears to play a central role in the driving. Around the blue edge, the convection adapts quasi-instantaneously to the oscillations, so that TDC must be included in the models. For the first time, we show that the red edge of the DB instability strip is successfully obtained with a TDC treatment, especially thanks to the terms due to the turbulent pressure variations, while it is not reproduced with frozen convection models. [less ▲]

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See detailDriving and damping mechanisms in hybrid pressure-gravity modes pulsators
Dupret, Marc-Antoine ULg; Miglio, Andrea ULg; Montalban Iglesias, Josefa ULg et al

in Journal of Physics: Conference Series (2008), 118

We study the energetic aspects of hybrid pressure-gravity modes pulsations. The case of hybrid beta Cephei-SPB pulsators is considered with special attention. In addition to the already known sensitivity ... [more ▼]

We study the energetic aspects of hybrid pressure-gravity modes pulsations. The case of hybrid beta Cephei-SPB pulsators is considered with special attention. In addition to the already known sensitivity of the driving mechanism to the heavy elements mixture (mainly the iron abundance), we show that the characteristics of the propagation and evanescent regions play also a major role, determining the extension of the stable gap in the frequency domain between the unstable low order pressure and high order gravity modes. Finally, we consider the case of hybrid delta Sct-gamma Dor pulsators. [less ▲]

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See detailCoRoT Measures Solar-Like Oscillations and Granulation in Stars Hotter Than the Sun
Michel, Eric; Baglin, Annie; Auvergne, Michel et al

in Science (2008), 322

Oscillations of the Sun have been used to understand its interior structure. The extension of similar studies to more distant stars has raised many difficulties despite the strong efforts of the ... [more ▼]

Oscillations of the Sun have been used to understand its interior structure. The extension of similar studies to more distant stars has raised many difficulties despite the strong efforts of the international community over the past decades. The CoRoT (Convection Rotation and Planetary Transits) satellite, launched in December 2006, has now measured oscillations and the stellar granulation signature in three main sequence stars that are noticeably hotter than the sun. The oscillation amplitudes are about 1.5 times as large as those in the Sun; the stellar granulation is up to three times as high. The stellar amplitudes are about 25% below the theoretic values, providing a measurement of the nonadiabaticity of the process ruling the oscillations in the outer layers of the stars. [less ▲]

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See detailModeling the excitation of acoustic modes in alpha Centauri A
Samadi, R.; Belkacem, Kevin ULg; Goupil, M. J. et al

in Astronomy and Astrophysics (2008), 489

From different seismic observations we infer the energy supplied per unit of time by turbulent convection to the acoustic modes of alpha Centauri A (HD 128620), a star that is similar but not identical to ... [more ▼]

From different seismic observations we infer the energy supplied per unit of time by turbulent convection to the acoustic modes of alpha Centauri A (HD 128620), a star that is similar but not identical to the Sun. The inferred rates of energy supplied to the modes (i.e. mode excitation rates) are found to be significantly higher than in the Sun. They are compared with those computed with an excitation model that includes two sources of driving, the Reynolds stress contribution and the advection of entropy fluctuations. The model also uses a closure model, the Closure Model with Plumes (CMP hereafter), that takes the asymmetry between the up- and down-flows (i.e. the granules and plumes, respectively) into account. Different prescriptions for the eddy-time correlation function are also compared to observational data. Calculations based on a Gaussian eddy-time correlation underestimate excitation rates compared with the values derived from observations for alpha Centauri A. On the other hand, calculations based on a Lorentzian eddy-time correlation lie within the observational error bars. This confirms results in the solar case. Compared to the helioseismic data, those obtained for alpha Centauri A constitute an additional support for our model of excitation. We show that mode masses must be computed taking turbulent pressure into account. Finally, we emphasize the need for more accurate seismic measurements in order to distinguish between the CMP closure model and the quasi-normal approximation in the case of alpha Centauri A, as well as to confirm or not the need to include the excitation by the entropy fluctuations. [less ▲]

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See detailA seismic approach to testing different formation channels of subdwarf B stars
Hu, Haili; Dupret, Marc-Antoine ULg; Aerts, C. et al

in Astronomy and Astrophysics (2008), 490

Context: There are many unknowns in the formation of subdwarf B stars. Different formation channels are considered to be possible and to lead to a variety of helium-burning subdwarfs. All seismic models ... [more ▼]

Context: There are many unknowns in the formation of subdwarf B stars. Different formation channels are considered to be possible and to lead to a variety of helium-burning subdwarfs. All seismic models to date, however, assume that a subdwarf B star is a post-helium-flash-core surrounded by a thin inert layer of hydrogen. Aims: We examine an alternative formation channel, in which the subdwarf B star originates from a massive (>~2 M[SUB]o[/SUB]) red giant with a non-degenerate helium-core. Although these subdwarfs may evolve through the same region of the log g-T_eff diagram as the canonical post-flash subdwarfs, their interior structure is rather different. We examine how this difference affects their pulsation modes and whether it can be observed. Methods: Using detailed stellar evolution calculations we construct subdwarf B models from both formation channels. The iron accumulation in the driving region due to diffusion, which causes the excitation of the modes, is approximated by a Gaussian function. The pulsation modes and frequencies are calculated with a non-adiabatic pulsation code. Results: A detailed comparison of two subdwarf B models from different channels, but with the same log g and T_eff, shows that their mode excitation is different. The excited frequencies are lower for the post-flash than for the post-non-degenerate subdwarf B star. This is mainly due to the differing chemical composition of the stellar envelope. A more general comparison between two grids of models shows that the excited frequencies of most post-non-degenerate subdwarfs cannot be well-matched with the frequencies of post-flash subdwarfs. In the rare event that an acceptable seismic match is found, additional information, such as mode identification and log g and T_eff determinations, allows us to distinguish between the two formation channels. [less ▲]

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See detailHD 203608, a quiet asteroseismic target in the old galactic disk
Mosser, B.; Deheuvels, S.; Michel, Eric et al

in Astronomy and Astrophysics (2008), 488

Context: We conducted a 5-night observing run with the spectrometer harps at the ESO 3.6-m telescope in August 2006, to continue exploring the asteroseismic properties of F-type stars. In fact, Doppler ... [more ▼]

Context: We conducted a 5-night observing run with the spectrometer harps at the ESO 3.6-m telescope in August 2006, to continue exploring the asteroseismic properties of F-type stars. In fact, Doppler observations of F-type on the main sequence are demanding and remain currently limited to a single case (HD 49933). Comparison with photometric results obtained with the CoRoT space mission (Convection, Rotation and planetary Transits) on similar stars will be possible with an enhanced set of observations. Aims: We selected the 4th magnitude F8V star HD 203608 to investigate the oscillating properties of a low-metallicity star of the old galactic disk. Methods: We reduced the spectra with the on-line data reduction software provided by the instrument. We developed a new statistical approach for extracting the significant peaks in the Fourier domain. Results: The oscillation spectrum shows a significant excess power in the frequency range [1.5, 3.0 mHz]. It exhibits a large spacing of about 120.4 muHz at 2.5 mHz. Variations of the large spacing with frequency are clearly identified, which require an adapted asymptotic development. The modes identification is based on the unambiguous signature of 15 modes with l = 0 and 1. Conclusions: These observations show the potential diagnostic of asteroseismic constraints. Including them in the stellar modeling significantly enhances the precision on the physical parameters of HD 203608, resulting in a much more precise position in the HR diagram. The age of the star is now determined in the range 7.25±0.07 Gyr. Based on observations obtained with the harps échelle spectrometer mounted on the 3.6-m telescope at ESO-La Silla Observatory (Chile), programme 077.D-0720. Data corresponding to Figs. [see full textsee full textsee full text], [see full textsee full textsee full text], and Table [see full textsee full textsee full text] are 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/488/635 [less ▲]

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See detailHydrogen-Deficient Compact Pulsators: The GW Virginis Stars and the Variable DB White Dwarfs
Quirion, P*-O; Dupret, Marc-Antoine ULg; Fontaine, G. et al

in Hydrogen-Deficient Stars (2008, July 01)

We review briefly the basic properties of the GW Vir stars and of the V777 Her stars. We describe the classical kappa-mechanism operating in the GW Vir stars and the effects of the chemical composition ... [more ▼]

We review briefly the basic properties of the GW Vir stars and of the V777 Her stars. We describe the classical kappa-mechanism operating in the GW Vir stars and the effects of the chemical composition and of the interaction between diffusion and mass loss on the boundaries of the instability domain of these objects in the log g - T[SUB]eff[/SUB] diagram. Because of the presence of an extensive superficial convection zone in pulsating DB (V777 Her) white dwarfs, oscillation modes are not excited through a similar classical kappa-mechanism in those stars but, instead, involve pulsation-convection interactions. We describe the effects of a time-dependent convection (TDC) treatment on the driving mechanism of the V777 Her stars. We show how convection deeply affects the excitation of modes via the entropy transport mechanism or S-mechanism. Provisional blue and red edges are calculated for the V777 Her stars and are found at T[SUB]eff[/SUB] ~= 28,500 K and ~= 20,500 K, respectively, for a 0.6 M[SUB]o[/SUB] star under the assumption of ML2 convection. [less ▲]

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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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