References of "Dupret, Marc-Antoine"
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See detailSolar-like oscillations in massive main-sequence stars. I. Asteroseismic signatures of the driving and damping regions
Belkacem, Kevin ULg; Dupret, Marc-Antoine ULg; Noels-Grötsch, Arlette ULg

in Astronomy and Astrophysics (2010), 510

Motivated by the detection of stochastically excited modes in the massive star V1449 Aql, which is already known to be a β Cephei star, we theoretically investigate the driving by turbulent convection ... [more ▼]

Motivated by the detection of stochastically excited modes in the massive star V1449 Aql, which is already known to be a β Cephei star, we theoretically investigate the driving by turbulent convection. By using a full non-adiabatic computation of the damping rates, together with a computation of the energy injection rates, we provide an estimate of the amplitudes of modes excited by both the convective region induced by the iron opacity bump and the convective core. Despite the uncertainties in the dynamical properties of these convective regions, we demonstrate that both regions are able to efficiently excite p modes above the CoRoT observational threshold and the solar amplitudes. In addition, we emphasise the potential asteroseismic diagnostics provided by each convective region, which we hope will help us to identify the region responsible for solar-like oscillations, and to place constraints on this convective zone. A forthcoming work will be dedicated to an extended investigation of the likelihood of solar-like oscillations across the Hertzsprung-Russell diagram. [less ▲]

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See detailKepler observations: Light shed on the hybrid γ Doradus - δ Scuti pulsation phenomenon
Grigahcène, A.; Uytterhoeven, K.; Antoci, V. et al

in Astronomische Nachrichten (2010), 331

Through the observational study of stellar pulsations, the internal structure of stars can be probed and theoretical models can be tested. The main sequence γ Doradus (Dor) and δ Scuti (Sct) stars with ... [more ▼]

Through the observational study of stellar pulsations, the internal structure of stars can be probed and theoretical models can be tested. The main sequence γ Doradus (Dor) and δ Scuti (Sct) stars with masses 1.2-2.5 M[SUB]ȯ[/SUB] are particularly interesting for asteroseismic study. The γ Dor stars pulsate in high-order gravity (g) modes, with pulsational periods of order of one day. The δ Sct stars, on the other hand, show low-order g and pressure (p) modes with periods of order of 2 hours. Theory predicts the existence of `hybrid' stars, i.e. stars pulsating in both types of modes, in an overlap region between the instability strips of γ Dor and δ Sct stars in the Hertzsprung-Russell diagram. Hybrid stars are particularly interesting as the two types of modes probe different regions of the stellar interior and hence provide complementary model constraints. Before the advent of Kepler, only a few hybrid stars had been confirmed. The {{Kepler}} satellite is providing a true revolution in the study of and search for hybrid stars. Analysis of the first 50 days of {{Kepler}} data of hundreds of γ Dor and δ Sct candidates reveals extremely rich frequency spectra, with most stars showing frequencies in both the δ Sct and γ Dor frequency range. As these results show that there are practically no pure δ Sct or γ Dor pulsators, a new observational classification scheme is proposed by \cite{Grig10}. We present their results and characterize 234 stars in terms of δ Sct, γ Dor, δ Sct/γ Dor or γ Dor/δ Sct hybrids. [less ▲]

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See detailTheoretical study of γ Doradus pulsations in pre-main sequence stars
Bouabid, M*-P; Montalban Iglesias, Josefa ULg; Miglio, Andrea ULg et al

in Astronomische Nachrichten (2010), 331

The question of the existence of the pre-main sequence (PMS) γ Doradus (γ Dor) pulsators has been raised by observations of young clusters such as NGC 884 hosting γ Dor members. We have explored the ... [more ▼]

The question of the existence of the pre-main sequence (PMS) γ Doradus (γ Dor) pulsators has been raised by observations of young clusters such as NGC 884 hosting γ Dor members. We have explored the properties of γ Dor-type pulsations with a grid of PMS models covering the mass range {1.2 < M_*/M_ȯ < 2.5} and we derive the theoretical instability strip (IS) for the PMS γ Dor pulsators. We explore the possibility of distinguishing between PMS and MS γ Dor by the behaviour of the period spacing of their high order gravity modes (g-modes). [less ▲]

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See detailImpact of helium diffusion and helium-flash-induced carbon production on gravity-mode pulsations in subdwarf B stars
Hu, Haili; Nelemans, G.; Aerts, C. et al

in Astronomy and Astrophysics (2009), 508

Context: Realistic stellar models are essential to the forward modelling approach in asteroseismology. For practicality however, certain model assumptions are also required. For example, in the case of ... [more ▼]

Context: Realistic stellar models are essential to the forward modelling approach in asteroseismology. For practicality however, certain model assumptions are also required. For example, in the case of subdwarf B stars, one usually starts with zero-age horizontal branch structures without following the progenitor evolution. <BR /> Aims: We analyse the effects of common assumptions in subdwarf B models on the g-mode pulsational properties. We investigate if and how the pulsation periods are affected by the H-profile in the core-envelope transition zone. Furthermore, the effects of C-production and convective mixing during the core helium flash are evaluated. Finally, we reanalyse the effects of stellar opacities on the mode excitation in subdwarf B stars.<BR /> Methods: We computed detailed stellar evolutionary models of subdwarf B stars, and their non-adiabatic pulsational properties. Atomic diffusion of H and He is included consistently during the evolution calculations. The number fractions of Fe and Ni are gradually increased by up to a factor of 10 around log T = 5.3. This is necessary for mode excitation and to approximate the resulting effects of radiative levitation. We performed a pulsational stability analysis on a grid of subdwarf B models constructed with OPAL and OP opacities.<BR /> Results: We find that helium settling causes a shift in the theoretical blue edge of the g-mode instability domain to higher effective temperatures. This results in a closer match to the observed instability strip of long-period sdB pulsators, particularly for l â ¤ 3 modes. We show further that the g-mode spectrum is extremely sensitive to the H-profile in the core-envelope transition zone. If atomic diffusion is efficient, details of the initial shape of the profile become less important in the course of evolution. Diffusion broadens the chemical gradients, and results in less effective mode trapping and different pulsation periods. Furthermore, we report on the possible consequences of the He-flash for the g-modes. The outer edge of a flash-induced convective region introduces an additional chemical transition in the stellar models, and the corresponding spike in the Brünt-Väisälä frequency produces a complicated mode trapping signature in the period spacings. <BR /> [less ▲]

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See detailCollective pulsational velocity broadening due to gravity modes as a physical explanation for macroturbulence in hot massive stars
Aerts, C.; Puls, J.; Godart, Mélanie ULg et al

in Astronomy and Astrophysics (2009), 508

Aims. We aimed at finding a physical explanation for the occurrence of macroturbulence in the atmospheres of hot massive stars, a phenomenon found in observations for more than a decade but that remains ... [more ▼]

Aims. We aimed at finding a physical explanation for the occurrence of macroturbulence in the atmospheres of hot massive stars, a phenomenon found in observations for more than a decade but that remains unexplained.<BR /> Methods: We computed time series of line profiles for evolved massive stars broadened by rotation and by hundreds of low-amplitude nonradial gravity-mode pulsations which are predicted to be excited for evolved massive stars.<BR /> Results: In general, line profiles based on macrotubulent broadening can mimic those subject to pulsational broadening. In several cases, though, good fits require macroturbulent velocities that pass the speed of sound for realistic pulsation amplitudes. Moreover, we find that the rotation velocity can be seriously underestimated by using a simple parameter description for macroturbulence rather than an appropriate pulsational model description to fit the line profiles.<BR /> Conclusions: We conclude that macroturbulence is a likely signature of the collective effect of pulsations. We provide line diagnostics and their typical values to decide whether or not pulsational broadening is present in observed line profiles, as well as a procedure to avoid an inaccurate estimation of the rotation velocity. [less ▲]

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See detailOn posterior probability and significance level: application to the power spectrum of HD 49 933 observed by CoRoT
Appourchaux, T.; Samadi, R.; Dupret, Marc-Antoine ULg

in Astronomy and Astrophysics (2009), 506

Context: The CoRoT mission provides asteroseismic data of very high quality allowing one to adopt new statistical approaches for mode detection in power spectra, especially with respect to testing the ... [more ▼]

Context: The CoRoT mission provides asteroseismic data of very high quality allowing one to adopt new statistical approaches for mode detection in power spectra, especially with respect to testing the null hypothesis (H{0}, which assumes that what is observed is pure noise). Aims: We emphasize that the significance level when rejecting the null hypothesis can lead to the incorrect conclusion that the H{0} hypothesis is unlikely to occur at that significance level. We demonstrate that the significance level is unrelated to the posterior probability of H{0}, given the observed data set, and that this posterior probability is very much higher than implied by the significance level. Methods: We use Bayes theorem to derive the posterior probability of that H{0} is true assuming an alternative hypothesis H{1} that a mode is present, taking some prior for the mode height, mode amplitude and linewidth. Results: We compute the posterior probability of H{0} for the p modes detected on HD 49 933 by CoRoT. Conclusions: We conclude that the posterior probability of H{0} provide a much more conservative quantification of the mode detection than the significance level. This framework can be applied to any similar stellar power spectra obtained to complete asteroseismology. The CoRoT space mission, launched on 2006 December 27, was developed and is operated by the CNES, with participation of the Science Programs of ESA, ESA's RSSD, Austria, Belgium, Brazil, Germany and Spain. [less ▲]

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See detailTheoretical amplitudes and lifetimes of non-radial solar-like oscillations in red giants
Dupret, Marc-Antoine ULg; Belkacem, Kevin ULg; Samadi, Réza et al

in Astronomy and Astrophysics (2009), 506

Context: Solar-like oscillations have been observed in numerous red giants from ground and from space. An important question arises: could we expect to detect non-radial modes probing the internal ... [more ▼]

Context: Solar-like oscillations have been observed in numerous red giants from ground and from space. An important question arises: could we expect to detect non-radial modes probing the internal structure of these stars? <BR />Aims: We investigate under what physical circumstances non-radial modes could be observable in red giants; what would be their amplitudes, lifetimes and heights in the power spectrum (PS)? <BR />Methods: Using a non-radial non-adiabatic pulsation code including a non-local time-dependent treatment of convection, we compute the theoretical lifetimes of radial and non-radial modes in several red giant models. Next, using a stochastic excitation model, we compute the amplitudes of these modes and their heights in the PS. <BR />Results: Distinct cases appear. Case A corresponds to subgiants and stars at the bottom of the ascending giant branch. Our results show that the lifetimes of the modes are mainly proportional to the inertia I, which is modulated by the mode trapping. The predicted amplitudes are lower for non-radial modes. But the height of the peaks in the PS are of the same order for radial and non-radial modes as long as they can be resolved. The resulting frequency spectrum is complex. Case B corresponds to intermediate models in the red giant branch. In these models, the radiative damping becomes high enough to destroy the non-radial modes trapped in the core. Hence, only modes trapped in the envelope have significant heights in the PS and could be observed. The resulting frequency spectrum of detectable modes is regular for â =0 and 2, but a little more complex for â =1 modes because of less efficient trapping. Case C corresponds to models of even higher luminosity. In these models the radiative damping of non-radial modes is even larger than in the previous case and only radial and non-radial modes completely trapped in the envelope could be observed. The frequency pattern is very regular for these stars. The comparison between the predictions for radial and non-radial modes is very different if we consider the heights in the PS instead of the amplitudes. This is important as the heights (not the amplitudes) are used as detection criterion. CIFIST Marie Curie Excellence Team. [less ▲]

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See detailHybrid γ Doradus/δ Scuti Stars: Comparison Between Observations and Theory
Bouabid, M-P; Montalban Iglesias, Josefa ULg; Miglio, Andrea ULg et al

in AIP Conference Proceedings (2009), 1170

γ Doradus (γ Dor) are F-type stars pulsating with high order g-modes. Their instability strip (IS) overlaps the red edge of the δ Scuti δ Sct) one. This observation has led to search for objects in this ... [more ▼]

γ Doradus (γ Dor) are F-type stars pulsating with high order g-modes. Their instability strip (IS) overlaps the red edge of the δ Scuti δ Sct) one. This observation has led to search for objects in this region of the HR diagram showing p and g-modes simultaneously. The existence of such hybrid pulsators has recently been confirmed [10] and the number of candidates is increasing (e.g. [17]). From a theoretical point of view, non-adiabatic computations including a time-dependent treatment of convection (TDC) predict the existence of γ Dor/δ Sct hybrid pulsators ([5], [8]). Our aim is to confront the properties of the observed hybrid candidates with the theoretical predictions from non-adiabatic computations of non-radial pulsations including the convection-pulsation interaction. [less ▲]

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See detailThe Enigma of B-type Pulsators in the SMC
Salmon, Sébastien ULg; Montalban Iglesias, Josefa ULg; Miglio, Andrea ULg et al

in AIP Conference Proceedings (2009, September 01), 1170

Since the early nineties it is accepted that the excitation mechanism of B-type pulsators on the main sequence is due to the opacity peak in the iron-group elements at T~200,000 K. The Fe content plays ... [more ▼]

Since the early nineties it is accepted that the excitation mechanism of B-type pulsators on the main sequence is due to the opacity peak in the iron-group elements at T~200,000 K. The Fe content plays then a major role in the excitation of β Cep and SPB pulsations. While theoretical non-adiabatic computations predict no β Cep pulsators and only a small number of SPBs for low metallicity environments such as that of the Magellanic Clouds (MCs), recent variability surveys of B stars in the SMC have reported the detection of a significant number of SPB and β Cep candidates. Since the SMC is the metal poorest (Z~0001-0.004) of the MCs, it constitutes an interesting object for investigating the disagreement between theory and observations. We approach the problem by calling into question some of the hypotheses made in previous studies: given the different chemical evolution of the SMC compared with our local galactic environment, is it appropriate to describe the chemical composition of SMC B stars by scaling the solar mixture to lower Z? Is that composition uniform in space and time? In this paper we present the results of a stability analysis of B-type stellar models computed with a revised chemical composition and metallicity specific to the SMC. [less ▲]

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See detailUnveiling the internal structure of massive supergiants: HD 163899
Godart, Mélanie ULg; Dupret, Marc-Antoine ULg; Noels-Grötsch, Arlette ULg

in Communications in Asteroseismology (2009), 158

Supergiant massive stars are post-main sequence stars. During the H shell burning phase of evolution, they present a radiative core in which a strong damping prevents the pulsation modes from being ... [more ▼]

Supergiant massive stars are post-main sequence stars. During the H shell burning phase of evolution, they present a radiative core in which a strong damping prevents the pulsation modes from being excited. However Saio et al. (2006) have recently highlighted p and g pulsation modes in a post-main sequence star (HD 163899) observed by MOST. They suggest that the presence of an intermediate convective region (ICZ) at the top of the radiative core allows a partial or total reflexion of the mode. Through some numerical results achieved with CLES (Scuflaire et al. 2008) and MAD (Dupret et al. 2003) codes, we show that this scenario depends on the evolution stage of the star and on the considered mass loss rate and overshooting parameter. [less ▲]

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See detailLedoux's convection criterion in evolution and asteroseismology of massive stars
Lebreton, Yves; Montalban Iglesias, Josefa ULg; Godart, Mélanie ULg et al

in Communications in Asteroseismology (2009), 158

Saio et al. (2006) have shown that the presence of an intermediate convective zone (ICZ) in post-main sequence models could prevent the propagation of g-modes in the radiative interior and hence avoid the ... [more ▼]

Saio et al. (2006) have shown that the presence of an intermediate convective zone (ICZ) in post-main sequence models could prevent the propagation of g-modes in the radiative interior and hence avoid the corresponding radiative damping. The development of such a convective region highly depends on the structure of the star in the mu-gradient region surrounding the convective core during the main sequence phase. In particular,the development of this ICZ depends on physical processes such as mass loss, overshooting (Chiosi & Maeder 1986, Chiosi et al. 1992, see also Godart et al., 2009) and convective instability criterion (Schwarzschild's or Ledoux's criteria). In this paper we study the consequences of adopting the Ledoux's criterion on the evolution of the convective regions in massive stars (15 and 20 M_{o}), and on the pulsation spectrum of these new B-type variables (also called SPBsg). [less ▲]

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

in Communications in Asteroseismology (2009), 158

We have investigated the influence of a local metallicity enhancement on the excitation mechanism of roAp star pulsations. Our computations show that such accumulations poorly affect the position of the ... [more ▼]

We have investigated the influence of a local metallicity enhancement on the excitation mechanism of roAp star pulsations. Our computations show that such accumulations poorly affect the position of the theoretical roAp star instability strip although the opacity in the driving region of roAp modes is affected by metal accumulation. [less ▲]

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See detailCan mass loss and overshooting prevent the excitation of g-modes in blue supergiants?
Godart, Mélanie ULg; Noels-Grötsch, Arlette ULg; Dupret, Marc-Antoine ULg et al

in Monthly Notices of the Royal Astronomical Society (2009), 396

Thanks to their past history on the main-sequence phase, supergiant massive stars develop a convective shell around the helium core. This intermediate convective zone (ICZ) plays an essential role in ... [more ▼]

Thanks to their past history on the main-sequence phase, supergiant massive stars develop a convective shell around the helium core. This intermediate convective zone (ICZ) plays an essential role in governing which g-modes are excited. Indeed, a strong radiative damping occurs in the high-density radiative core but the ICZ acts as a barrier preventing the propagation of some g-modes into the core. These g-modes can thus be excited in supergiant stars by the kappa-mechanism in the superficial layers due to the opacity bump of iron, at logT = 5.2. However, massive stars are submitted to various complex phenomena such as rotation, magnetic fields, semiconvection, mass loss, overshooting. Each of these phenomena exerts a significant effect on the evolution and some of them could prevent the onset of the convective zone. We develop a numerical method which allows us to select the reflected, thus the potentially excited, modes only. We study different cases in order to show that mass loss and overshooting, in a large enough amount, reduce the extent of the ICZ and are unfavourable to the excitation of g-modes. [less ▲]

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See detailTheoretical amplitudes of solar-like oscillations in classical pulsators
Belkacem, Kevin ULg; Goupil, M. J.; Dupret, Marc-Antoine ULg et al

in Communications in Asteroseismology (2009), 158

Seismology based on oscillation mode amplitudes allows a different probing of turbulent convection zones than usual seismology based on frequencies as shown, for instance, by Belkacem et al. (2006) for ... [more ▼]

Seismology based on oscillation mode amplitudes allows a different probing of turbulent convection zones than usual seismology based on frequencies as shown, for instance, by Belkacem et al. (2006) for the Sun. Going a step further, we now turn to investigations of stochastic excitation of solar-like oscillations in superficial convective layers as well as in convective cores of stars more massive than the Sun. Issues are the frequency domain where solar-like oscillations can be excited, the expected magnitude of these oscillation amplitudes, and whether these amplitudes are detectable with the CoRoT mission. This is an important task since the detection of solar-like oscillations will provide strong seismic constraints on the dynamical properties of the convective layers. The detection of solar-like oscillations in stars such as beta Cephei or SPB stars will also help to determine their fundamental stellar parameters. [less ▲]

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See detailOn the origin of macroturbulence in hot stars
Aerts, C.; Puls, J.; Godart, Mélanie ULg et al

in Communications in Asteroseismology (2009), 158

Since the use of high-resolution high signal-to-noise spectroscopy in the study of massive stars, it became clear that an ad-hoc velocity field at the stellar surface, termed macroturbulence, is needed to ... [more ▼]

Since the use of high-resolution high signal-to-noise spectroscopy in the study of massive stars, it became clear that an ad-hoc velocity field at the stellar surface, termed macroturbulence, is needed to bring the observed shape of spectral lines into agreement with observations. We seek a physical explanation of this unknown broadening mechanism. We interprete the missing line broadening in terms of collective pulsational velocity broadening due to non-radial gravity-mode oscillations. We also point out that the rotational velocity can be seriously underestimated whenever the line profiles are fitted assuming a Gaussian macroturbulent velocity rather than an appropriate pulsational velocity expression. [less ▲]

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See detailDomain of validity of a 1D second order perturbative approach for the effects of rotation on stellar oscillations
Ouazzani, R*-M; Goupil, M*-J; Dupret, Marc-Antoine ULg et al

in Communications in Asteroseismology (2009), 158

At rotational velocities such as that of upper Main Sequence stars - between 50 to 200 km/s - the effects of rotation on oscillation frequencies must be included. Considering the accuracy reached by ... [more ▼]

At rotational velocities such as that of upper Main Sequence stars - between 50 to 200 km/s - the effects of rotation on oscillation frequencies must be included. Considering the accuracy reached by available ground-based and space observations, the aim of this study is to determine the limits - in terms of rotational velocity - of a perturbative approach to model the effects of rotation on oscillation frequencies. We thus compare the oscillation frequencies computed by 1D second order perturbative methods to the ones obtained in Reese et al. (2006) - direct integration of a 2D eigenvalue system. To do so, we use polytropic models (N=3) in uniform rotation, and we discuss the results for a beta Cephei star (8.2 M_{o}, 5.04 R_{o}). [less ▲]

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See detailRelative weights of the observational constraints on the determination of stellar parameters
Ozel, N.; Dupret, Marc-Antoine ULg; Baglin, A.

in Communications in Asteroseismology (2009), 158

We study the effect of using different observed quantities (oscillation frequencies, binarity, interferometric radius) and the impact of their accuracy on constraining the uncertainities of global free ... [more ▼]

We study the effect of using different observed quantities (oscillation frequencies, binarity, interferometric radius) and the impact of their accuracy on constraining the uncertainities of global free stellar parameters (i.e. the mass, the age etc.). We use the Singular Value Decomposition (SVD) formalism to analyse the behavior of the chi^2 fitting function around its minimum. This method relates the errors in observed quantities to the precision in the model parameters. We apply this tool to the alpha Cen A for which, seismic, binarity and interferometric properties are known with high accuracy. We determine how changes of the accuracy of the observable constraints affect the precision obtained on the global stellar parameters. [less ▲]

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See detailSignature of main sequence internal structure in post-main sequence stars
Dupret, Marc-Antoine ULg; Godart, Mélanie ULg; Noels-Grötsch, Arlette ULg et al

in Communications in Asteroseismology (2009), 158

Post Main Sequence (post MS) stars keep a trace of their past main sequence history. Typically, the presence or not of an Intermediate Convective Zone (ICZ) above the H-burning shell of massive stars ... [more ▼]

Post Main Sequence (post MS) stars keep a trace of their past main sequence history. Typically, the presence or not of an Intermediate Convective Zone (ICZ) above the H-burning shell of massive stars critically depends on the details of the Main Sequence (MS) phase modeling (convection criterion, mass loss,~...). We show here how the excitation of g-modes in blue supergiant stars is closely related to this ICZ, allowing to constrain different associated physical processes. [less ▲]

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See detailHelioseismic Spectral Diagnostics - An Update
Leibacher, John W; Baudin, F.; Belkacem, Kevin ULg et al

in AAS/Solar Physics Division Meeting (2009, May 01)

In order to test models of the excitation of p modes and their behavior in the visible atmosphere, we calculate time sequences of Fraunhofer absorption line profiles of the Ni, Fe, K, Na, and Ca lines ... [more ▼]

In order to test models of the excitation of p modes and their behavior in the visible atmosphere, we calculate time sequences of Fraunhofer absorption line profiles of the Ni, Fe, K, Na, and Ca lines used in helioseismology, focusing on Sun-as-a-star observations in this initial work. The atmospheric models, which give rise to the line profiles, are based on the VAL-C, perturbed by realistic p-mode eigenfunctions. The time sequences of line profiles are analyzed as for various instruments, to compare predicted and observed mode amplitudes as a function of temporal frequency [less ▲]

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See detailCoRot observations of active giants: preliminary results
Gondoin, P.; Fridlund, M.; Goupil, M. J. et al

in American Institute of Physics Conference Series (2009, February 01)

We have analysed rotation modulated light-curves of active giants observed with CoRot using spots model. Preliminary results suggest an increase of the surface spot coverage with decreasing rotation ... [more ▼]

We have analysed rotation modulated light-curves of active giants observed with CoRot using spots model. Preliminary results suggest an increase of the surface spot coverage with decreasing rotation period. A maximum of the surface spot coverage seems to occur on giants with effective temperature around 5100 K. Confirmation and interpretation of these preliminary results require groundbased follow-up observations to measure activity indicators, to identify binary systems, and to determine the stellar parameters and evolutionary status of the sample giants. [less ▲]

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