References of "Dupret, Marc-Antoine"
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See detailThe puzzling new class of variable stars in NGC 3766 : old friend pulsators?
Salmon, Sébastien ULg; Montalban Iglesias, Josefa ULg; Reese, Daniel et al

in Astronomy and Astrophysics (2014), 569

The recent variability survey of the NGC 3766 cluster revealed a considerable number of periodic variable stars in a region of the H-R diagram where no pulsation is expected. This region lies between the ... [more ▼]

The recent variability survey of the NGC 3766 cluster revealed a considerable number of periodic variable stars in a region of the H-R diagram where no pulsation is expected. This region lies between the instability strips of the delta Scuti and SPB stars. Moreover the periods of the new phenomenon, P~0.1-0.7 d, do not allow to associate it a priori to either of these two types of pulsations. Stars in the NGC 3766 cluster are known as fast rotators with rotational velocities typically larger than half of their critical velocity. Rotation can affect both the geometrical properties and period domain of pulsations. It also alters the apparent stellar luminosity through gravity darkening, effect seldom taken considered in theoretical studies of the rotation-pulsation interaction. We explore if both of these effects are able to deliver a consistent interpretation for the observed properties of the "new variables" in NGC 3766: explaining their presence outside the known instability strips and their variability periods. We carry out an instability analysis of SPB models within the framework of the Traditional Approximation of Rotation and study the visibility of modes according to the angle of view and rotation. We also check how gravity darkening affects the effective temperature and luminosity of stellar models for different angles of view and rotation velocities. At the red (cold) border of the instability strip, prograde sectoral modes are preferentially excited and their visibilities are maximum when seen equator-on. Furthermore low-mass SPB models seen equator-on can appear in the gap between non-rotating SPB and delta Scuti stars due to gravity darkening. In that case, periods of these most visible modes are shifted to the 0.2-0.5 d range due to the effects of the Coriolis force. We hence suggest that the new variable stars observed in NGC 3766 are actually fast rotating SPB pulsators. [less ▲]

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See detailAsteroseismology of evolved stars: from hot B subdwarfs to white dwarfs
Van Grootel, Valérie ULg; Fontaine, G.; Charpinet, S. et al

Conference (2014, September)

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See detailThe instability strip of ZZ Ceti white dwarfs
Van Grootel, Valérie ULg; Fontaine, G.; Brassard, P. et al

Conference (2014, August)

The determination of the location of the theoretical ZZ Ceti instability strip in the log g − Teff diagram has remained a challenge over the years, due to the lack of a suitable treatment for convection ... [more ▼]

The determination of the location of the theoretical ZZ Ceti instability strip in the log g − Teff diagram has remained a challenge over the years, due to the lack of a suitable treatment for convection in these stars. We report here a detailed stability survey over the whole ZZ Ceti regime, including the low and extremely low masses. We computed to this aim 29 evolutionary sequences of DA models with various masses, chemical layering, and core compositions. These models are characterized by the so- called ML2/α=1.0 convective efficiency and take into account the important feedback effect of convection on the atmospheric structure. We computed pulsation spectra for these models with the Liège nonadiabatic pulsation code MAD, which is the only one to conveniently incorporate a full time-dependent convection treatment and, thus, provides the best available description of the blue edge of the instability strip. On the other hand, given the failure of all nonadiabatic codes to account properly for the red edge of the strip, including MAD, we tested the idea that the red edge is due to energy leakage through the atmosphere. Using this approach, we found that our theoretical ZZ Ceti instability strip accounts remarkably well for the boundaries of the empirical strip. [less ▲]

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See detailA First Look at the Nonadiabatic Properties of Pulsating Accreting White Dwarfs of the GW Lib Type
Van Grootel, Valérie ULg; Fontaine, G.; Brassard, P. et al

Poster (2014, August)

We present results of a detailed stability survey of the pulsation properties of accreting white dwarfs of the GW Lib type. This is based on several state-of-the- art white dwarf evolutionary sequences ... [more ▼]

We present results of a detailed stability survey of the pulsation properties of accreting white dwarfs of the GW Lib type. This is based on several state-of-the- art white dwarf evolutionary sequences with varying envelope compositions, from pure hydrogen to pure helium. Using the same tools as in Van Grootel et al. (2013), where we have presented the first consistent view of the ZZ Ceti instability strip, we have mapped the GW Lib instability strip over the effective temperature-surface gravity plane, and as a function of envelope composition. We find that the location of the GW Lib instability domain is a strong and continuous function of the assumed envelope composition. We can accomodate all of the known GW Lib pulsators in various strips according to their atmospheric compositions. [less ▲]

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See detailPulsations in hot supergiants
Godart, Mélanie ULg; Grotsch-Noels, Arlette; Dupret, Marc-Antoine ULg et al

in Precision Asteroseismology, Proceedings of the International Astronomical Union, IAU Symposium, Volume 301 (2014, February 01)

Massive stars are the cosmic engines that shape and drive our Universe. Many issues such as their formation, their stability and the mass loss effects, are far from being completely understood. Recent ... [more ▼]

Massive stars are the cosmic engines that shape and drive our Universe. Many issues such as their formation, their stability and the mass loss effects, are far from being completely understood. Recent ground-based and space observations have shown pulsations in massive MS and post-MS stars, such as acoustic and gravity modes excited by the κ-mechanism and even solar-like oscillations. Theoretical studies emphasized the presence of strange modes in massive models, and recent theoretical analyses have shown that hot supergiants can pulsate in oscillatory convective modes. We review the instability domains of massive stars as well as their excitation mechanisms and present the latest results. [less ▲]

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See detailStellar acoustic radii and ages from seismic inversion techniques
Buldgen, Gaël ULg; Dupret, Marc-Antoine ULg; Reese, Daniel Roy et al

Poster (2014)

Context: Determining stellar characteristics such as the radius, mass or age is crucial for the study of stellar evolution, exoplanetary systems or the characterisation of stellar populations in the ... [more ▼]

Context: Determining stellar characteristics such as the radius, mass or age is crucial for the study of stellar evolution, exoplanetary systems or the characterisation of stellar populations in the Galaxy. Asteroseismology is currently the most promising tool to accurately determine these characteristics. However, a key question is how to reduce the model dependence of asteroseismic methods. Method: We extend the SOLA inversion technique to new global characteristics in addition to the mean density (see Reese et al. 2012). We apply our methodology to the acoustic radius and an age indicator based on the sound speed derivative. The results from SOLA inversions are compared with estimates based on the small and large frequency separations for several test cases, including differing mixing-lengths, and the presence or absence of non-adiabatic effects or turbulent pressure. Results: We show that SOLA inversions yield accurate results in all test cases, unlike the other techniques which are more sensitive to surface effects. We observe that the acoustic radius and mean density inversions are more robust than the age indicator inversions, which are limited to relatively young stars with radiative cores. [less ▲]

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See detailAsteroseismic inversions in the context of Plato
Buldgen, Gaël ULg; Dupret, Marc-Antoine ULg; Reese, Daniel Roy

Conference (2014)

The determination of stellar characteristics such as the mass, the age or the radius, is crucial when studying both stellar evolution and exoplanetary systems. In the context of the Plato mission, the ... [more ▼]

The determination of stellar characteristics such as the mass, the age or the radius, is crucial when studying both stellar evolution and exoplanetary systems. In the context of the Plato mission, the high quality data allows us to reach a new level of accuracy and model-independence for stellar characterization by using inversion techniques. In this study, we will use the SOLA method (F. Pijpers and M. J. Thompson 1994), known for its successes in helioseismology, and show how it can offer us new insights into the structure of observed stars. We will present results for the mean density, building on the approach of Reese et al. 2012, and other custom-made structural characteristics constraining the outer layers of stars and the chemical content of their cores. We will show that inversions can determine these characteristics within 0.5%, a significant improvement over the capabilities of the classical forward modelling process. Consequently, such inversions lead to better stellar models and help us obtain more accurate estimates of fundamental parameters such as the age, mass or radius. [less ▲]

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See detailNon-adiabatic study of the Kepler subgiant KIC 6442183
Grosjean, Mathieu ULg; Dupret, Marc-Antoine ULg; Belkacem, Kevin et al

Poster (2014)

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See detailEnergetical aspects of solar-like oscillations in red giants
Grosjean, Mathieu ULg; Dupret, Marc-Antoine ULg; Belkacem, Kevin et al

in Precision Asteroseismology, Proceedings of the International Astronomical Union, IAU Symposium, Volume 301 (2014)

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See detailDifferential Seismic Modeling of Stars
Ozel, N.; Mosser, B.; Dupret, Marc-Antoine ULg et al

in Astronomical Society of the Pacific Conference Series (2013, December 01)

CoRoT (Convection Rotation and planetary Transits) observations provide the opportunity to study a large sample of stars ranging from the Main Sequence (MS) to the Red Giant Branch. With the large ... [more ▼]

CoRoT (Convection Rotation and planetary Transits) observations provide the opportunity to study a large sample of stars ranging from the Main Sequence (MS) to the Red Giant Branch. With the large increase in the number of stars showing solar-like oscillations, we intend to extract as much information as possible from a low signal-to-noise ratio (SNR) oscillation spectrum, benefiting from comparison with a reference star having similar seismic and fundamental parameters. We propose a differential method to determine stellar properties of solar-like oscillations which we call “differential seismology of stellar twins”. [less ▲]

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See detailNon-Perturbative Effect of Rotation on Dipolar Mixed-Modes in Red Giants
Ouazzani, R.-M.; Goupil, M.-J.; Dupret, Marc-Antoine ULg et al

in Astronomical Society of the Pacific Conference Series (2013, December 01)

The space missions CoRoT (Convection Rotation and Planetary Transits) and Kepler provide high quality data that allows the transport of angular momentum in stars to be investigated by the seismic ... [more ▼]

The space missions CoRoT (Convection Rotation and Planetary Transits) and Kepler provide high quality data that allows the transport of angular momentum in stars to be investigated by the seismic determination of the internal rotation profile. In a former study (Ouazzani et al. 2013b) we test the validity of seismic diagnostics for red giant rotation that are based on a perturbative method. Our aim here is to investigate oscillation spectra when that validity no longer holds. We use a non-perturbative approach implemented in the Adiabatic Code of Oscillations including Rotation (ACOR code) (Ouazzani et al. 2012) that accounts for the eff [less ▲]

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See detailEnergetical aspects of solar-like oscillations in red giants
Grosjean, Mathieu ULg; Dupret, Marc-Antoine ULg; Belkacem, Kevin et al

Conference (2013, December)

CoRoT and Kepler observations of red giants reveal very rich spectra of non-radial solar- like oscillations allowing us to probe their internal structure. The study of energetic aspects of these ... [more ▼]

CoRoT and Kepler observations of red giants reveal very rich spectra of non-radial solar- like oscillations allowing us to probe their internal structure. The study of energetic aspects of these oscillations is of great importance to predict the peak parameters in the power spectrum. The theoretical determination of lifetimes (or equivalently width) of the modes require non- adiabatic computations. Next, combined with a stochastic excitation model, we can also predict the height of the mode and finally obtain theoretical power spectra. Comparison between our theoretical predictions with observations give important constraint on red-giants models. Lifetimes and amplitudes of modes trapped in the envelope (e.g. radial modes) constrain the characteristics of the convective envelope and its time-dependent interaction with oscillations. Lifetimes of mixed-modes (mainly dipolar modes) strongly depend on mode trapping, allowing us to probe the core of red-giants. I will discuss under which circumstances mixed modes are detectable for a large variety of red-giant stellar models, with emphasis on the effect of the evolutionary status of the star (along the red-giant branch and during the He-burning phase) for a wide range of stellar masses (from 0.7 to 4 Msun ) on theoretical power spectra. [less ▲]

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See detailEvolution of the theoretical power spectrum of solar-like oscillations along the ascending phase on the red giant branch.
Grosjean, Mathieu ULg; Dupret, Marc-Antoine ULg; Belkacem, Kevin et al

in Astronomical Society of the Pacific Conference Series (2013, December), 479

CoRoT and Kepler observations of red giants reveal rich spectra of non-radial solar-like oscillations allowing to probe their internal structure. An important question comes from the observation of mixed ... [more ▼]

CoRoT and Kepler observations of red giants reveal rich spectra of non-radial solar-like oscillations allowing to probe their internal structure. An important question comes from the observation of mixed modes : When during the star’s ascension on the RGB are mixed-modes more likely to be detectable ? We follow the evolution of a star on the RGB and investigate the effect of its ascension on theoretical power spectrum. Equilibrium models (computed with the code ATON) represent four different stages of a star on the RGB. The mass of the star (1.5M") is in the typical mass range of stars observed by CoRoT and Kepler. We used a non-radial non-adiabatic code to compute the theoretical solar-like oscillations of these models. An important output of these calculations is the theoretical lifetimes of the modes. Then we computed the oscillation amplitudes through a stochastic excitation model. These computations allow us to draw theoretical power spectrum and discuss the possibility to observe mixed-modes at different evolutionary stages on the RGB. We found that structure modifications in a star ascending the RGB have an important impact on theoretical power spectrum of solar-like oscillations. Efficiencies of trapping and lifetimes of mixed modes are indeed strongly affected by this evolution. [less ▲]

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See detailThe instability strip of ZZ Ceti white dwarfs and its extension to the extremely low mass pulsators
Van Grootel, Valérie ULg; Fontaine, Gilles; Brassard, Pierre et al

in Astronomical Society of the Pacific Conference Series (2013, December), 479

The determination of the location of the theoretical ZZ Ceti instability strip in the log g − Teff diagram has remained a challenge over the years, due to the lack of a suitable treatment for convection ... [more ▼]

The determination of the location of the theoretical ZZ Ceti instability strip in the log g − Teff diagram has remained a challenge over the years, due to the lack of a suitable treatment for convection in these stars. We report here a detailed stability survey over the whole ZZ Ceti regime, including the very low masses where three pulsators have recently been found. We computed to this aim 29 evolutionary sequences of DA models with various masses and chemical layering. These models are characterized by the so-called ML2/α=1.0 convective efficiency and take into account the important feedback effect of convection on the atmospheric structure. We pulsated these models with the Liege nonadiabatic pulsation code MAD, which is the only one to conveniently incorporate a full time-dependent convection treatment and, thus, provides the best available description of the blue edge of the instability strip. On the other hand, given the failure of all nonadiabatic codes to account properly for the red edge of the strip, including MAD, we tested the idea that the red edge is due to energy leakage through the atmosphere. Using this approach, we found that our theoretical ZZ Ceti instability strip accounts remarkably well for the boundaries of the empirical strip. [less ▲]

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See detailDifferential asteroseismic study of seismic twins observed by CoRoT. Comparison of HD 175272 with HD 181420
Ozel, N.; Mosser, B.; Dupret, Marc-Antoine ULg et al

in Astronomy and Astrophysics (2013), 558

Context. The CoRoT short asteroseismic runs give us the opportunity to observe a large variety of late-type stars through their solar-like oscillations. We report the observation and modeling of the F5V ... [more ▼]

Context. The CoRoT short asteroseismic runs give us the opportunity to observe a large variety of late-type stars through their solar-like oscillations. We report the observation and modeling of the F5V star HD 175272. <BR /> Aims: Our aim is to define a method for extracting as much information as possible from a noisy oscillation spectrum. <BR /> Methods: We followed a differential approach that consists of using a well-known star as a reference to characterize another star. We used classical tools such as the envelope autocorrelation function to derive the global seismic parameters of the star. We compared HD 175272 with HD 181420 through a linear approach, because they appear to be asteroseismic twins. <BR /> Results: The comparison with the reference star enables us to substantially enhance the scientific output for HD 175272. First, we determined its global characteristics through a detailed seismic analysis of HD 181420. Second, with our differential approach, we measured the difference of mass, radius and age between HD 175272 and HD 181420. <BR /> Conclusions: We have developed a general method able to derive asteroseismic constraints on a star even in case of low-quality data. This method can be applied to stars with interesting properties but low signal-to-noise ratio oscillation spectrum, such as stars hosting an exoplanet or members of a binary system. 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, ESAs RSSD, Austria, Belgium, Brazil, Germany and Spain. [less ▲]

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See detailEnergetical aspects of solar-like oscillations in red giants
Grosjean, Mathieu ULg; Dupret, Marc-Antoine ULg

Conference (2013, August 23)

CoRoT and Kepler observations of red giants reveal a large variety of spectra of non- radial solar- like oscillations. Up to now we understood pretty well the frequency patterns for the different global ... [more ▼]

CoRoT and Kepler observations of red giants reveal a large variety of spectra of non- radial solar- like oscillations. Up to now we understood pretty well the frequency patterns for the different global properties or different evolutionary stages of the stars. Here we are interested in the theoretical predictions for the two other components of a power spectra (the linewitdths and the heights). The study of energetic aspects of these oscillations is of great importance to predict the peak parameters in the power spectrum. I will discuss under which circumstances mixed modes are detectable for a large variety of red-giant stellar models, with emphasis on the effect of the evolutionary status of the star along the red-giant branch, for a wide range of stellar masses (from 1 to 2M⊙ ) on theoretical power spectra. [less ▲]

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See detailNon-perturbative effect of rotation on dipolar mixed modes in red giant stars
Ouazzani, R.-M.; Goupil, M. J.; Dupret, Marc-Antoine ULg et al

in Astronomy and Astrophysics (2013), 554

Context. The space missions CoRoT and Kepler provide high-quality data that allow us to test the transport of angular momentum in stars by the seismic determination of the internal rotation profile. <BR ... [more ▼]

Context. The space missions CoRoT and Kepler provide high-quality data that allow us to test the transport of angular momentum in stars by the seismic determination of the internal rotation profile. <BR /> Aims: Our aim is to test the validity of seismic diagnostics for red giant rotation that are based on a perturbative method and to investigate the oscillation spectra when the validity does not hold. <BR /> Methods: We use a non-perturbative approach implemented in the ACOR code that accounts for the effect of rotation on pulsations and solves the pulsation eigenproblem directly for dipolar oscillation modes. <BR /> Results: We find that the limit of the perturbation to first order can be expressed in terms of the rotational splitting compared to the frequency separation between consecutive dipolar modes. Above this limit, non-perturbative computations are necessary, but only one term in the spectral expansion of modes is sufficient as long as the core rotation rate remains significantly smaller than the pulsation frequencies. Each family of modes with different azimuthal symmetry, m, has to be considered separately. In particular, in case of rapid core rotation, the density of the spectrum differs significantly from one m-family of modes to another, so that the differences between the period spacings associated with each m-family can constitute a promising guideline toward a proper seismic diagnostic for rotation. [less ▲]

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See detailTesting Convective-core Overshooting Using Period Spacings of Dipole Modes in Red Giants
Montalbán, J.; Miglio, A.; Noels-Grötsch, Arlette ULg et al

in Astrophysical Journal (2013), 766

Uncertainties on central mixing in main-sequence (MS) and core He-burning (He-B) phases affect key predictions of stellar evolution such as late evolutionary phases, chemical enrichment, ages, etc. We ... [more ▼]

Uncertainties on central mixing in main-sequence (MS) and core He-burning (He-B) phases affect key predictions of stellar evolution such as late evolutionary phases, chemical enrichment, ages, etc. We propose a test of the extension of extra-mixing in two relevant evolutionary phases based on period spacing (ΔP) of solar-like oscillating giants. From stellar models and their corresponding adiabatic frequencies (respectively, computed with ATON and LOSC codes), we provide the first predictions of the observable ΔP for stars in the red giant branch and in the red clump (RC). We find (1) a clear correlation between ΔP and the mass of the helium core (M [SUB]He[/SUB]); the latter in intermediate-mass stars depends on the MS overshooting, and hence it can be used to set constraints on extra-mixing during MS when coupled with chemical composition; and (2) a linear dependence of the average value of the asymptotic period spacing (langΔPrang[SUB] a [/SUB]) on the size of the convective core during the He-B phase. A first comparison with the inferred asymptotic period spacing for Kepler RC stars also suggests the need for extra-mixing during this phase, as evinced from other observational facts. [less ▲]

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See detailNon-radial, non-adiabatic solar-like oscillations in RGB and HB stars
Grosjean, Mathieu ULg; Dupret, Marc-Antoine ULg; Belkacem, K. et al

in EPJ Web of Conferences (2013, March 01), 43

CoRoT and Kepler observations of red giants reveal rich spectra of non-radial solar-like oscillations allowing to probe their internal structure. We compare the theoretical spectrum of two red giants in ... [more ▼]

CoRoT and Kepler observations of red giants reveal rich spectra of non-radial solar-like oscillations allowing to probe their internal structure. We compare the theoretical spectrum of two red giants in the same region of the HR diagram but in different evolutionary phases. We present here our first results on the inertia, lifetimes and amplitudes of the oscillations and discuss the differences between the two stars. [less ▲]

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