References of "Dupret, Marc-Antoine"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailStellar acoustic radii, mean densities, and ages from seismic inversion techniques
Buldgen, Gaël ULg; Dupret, Marc-Antoine ULg; Reese, Daniel et al

in Astronomy and Astrophysics (2015), 574

Context. Determining stellar characteristics such as the radius, mass or age is crucial when studying stellar evolution or exoplanetary systems, or when characterising stellar populations in the Galaxy ... [more ▼]

Context. Determining stellar characteristics such as the radius, mass or age is crucial when studying stellar evolution or exoplanetary systems, or when characterising stellar populations in the Galaxy. Asteroseismology is the golden path to accurately obtain these characteristics. In this context, a key question is how to make these methods less model-dependent. Aims: Building on the previous work of Daniel Reese, we wish to extend the Substractive Optimally Localized Averages (SOLA) inversion technique to new stellar global characteristics beyond the mean density. The goal is to provide a general framework in which to estimate these characteristics as accurately as possible in low-mass main-sequence stars. Methods: First, we describe our framework and discuss the reliability of the inversion technique and possible sources of error. We then apply this methodology to the acoustic radius, an age indicator based on the sound speed derivative and the mean density, and compare it to estimates based on the average large and small frequency separations. These inversions are carried out for several test cases including various metallicities, different mixing-lengths, non-adiabatic effects, and turbulent pressure. Results: We observe that the SOLA method yields accurate results in all test cases whereas results based on the large and small frequency separations are less accurate and more sensitive to surface effects and structural differences in the models. If we include the surface corrections of Kjeldsen et al. (2008, ApJ, 683, L175), we obtain results of comparable accuracy for the mean density. Overall, the mean density and acoustic radius inversions are more robust than the inversions for the age indicator. Moreover, the current approach is limited to relatively young stars with radiative cores. Increasing the number of observed frequencies improves the reliability and accuracy of the method. [less ▲]

Detailed reference viewed: 16 (3 ULg)
Full Text
Peer Reviewed
See detailConstraining mixing processes in 16CygA using Kepler data and seismic inversion techniques
Buldgen, Gaël ULg; Dupret, Marc-Antoine ULg; Reese, Daniel Roy

Conference (2015)

Constraining additional mixing processes is a central problem in stellar physics. Indeed, their impact on determined stellar ages is non-negligible and thus strongly affects our studies of stellar ... [more ▼]

Constraining additional mixing processes is a central problem in stellar physics. Indeed, their impact on determined stellar ages is non-negligible and thus strongly affects our studies of stellar evolution, galactic history, and exoplanetary systems. However, the quality of the Kepler data allows us to use new seismic tools to constrain these processes. In this talk, we will show a particularly efficient method for constraining chemical mixing in stellar interiors using custom-made structural integrated quantities. These quantities are designed to probe particular regions of the stellar interior and are estimated via the SOLA inversion method (Pijpers and Thompson 1994). They help us determine the values of parameters describing extra mixing processes. Inversions of such quantities have been originally described for the mean density in Reese et al. (2012) and have been extended to the acoustic radius and a first indicator of core conditions in Buldgen et al. (2015). A more efficient indicator for core conditions has now been derived and successfully tested using test cases similar to the 16Cyg binary system (Buldgen et al. in prep.). In this talk, we will show how our technique applies to the system 16Cyg and constrains additional mixing processes using the above structural indicators. Additional indicators and further studies will lead to seismically constrained chemical profiles for stars observed by Kepler, thereby helping us to disentangle the problem of additional mixing processes and ultimately to provide better stellar ages. [less ▲]

Detailed reference viewed: 21 (1 ULg)
Full Text
See detailWhat can we learn from asteroseismology of β Cephei stars through forward approach modelling?
Salmon, Sébastien ULg; Montalban, J.; Miglio, A. et al

Poster (2014, December)

The beta Cephei pulsating stars present a unique opportunity to test and probe our knowledge on the interior of massive stars. The information we can obtain depends on the quality and number of ... [more ▼]

The beta Cephei pulsating stars present a unique opportunity to test and probe our knowledge on the interior of massive stars. The information we can obtain depends on the quality and number of observational constraints, both seismic and classical ones. The asteroseismology of beta Cephei stars proceeds by a forward approach, which often result in multiple solutions, without clear indication on the level of confidence. We seek a method to derive confidence intervals on stellar parameters obtained by forward approach and investigate how these latter behave depending the seismic data accessible to the observer. We realise forward modelling with help of a grid of pre-computed models and use Monte-Carlo simulations to build confidence intervals on the inferred stellar parameters. We apply and test this method in a series of hare and hound exercises on a subset of theoretical models simulating observed stars. Results show that a set of 5 frequencies (with knowledge of their associated angular degree) yields good seismic constraints. In particular, presence of mixed modes provides a strong diagnosis on the evolutionary state of the star. Significant errors on the determinination of the extent of the central mixed region appear when the theoretical models do not present the same chemical mixture as the observed star. [less ▲]

Detailed reference viewed: 18 (2 ULg)
Full Text
Peer Reviewed
See detailTheoretical power spectra of mixed modes in low-mass red giant stars
Grosjean, Mathieu ULg; Dupret, Marc-Antoine ULg; Belkacem, Kevin et al

in Astronomy and Astrophysics (2014), 572

CoRoT and Kepler observations of red giant stars revealed very rich spectra of non-radial solar-like oscillations. Of particular interest was the detection of mixed modes that exhibit significant ... [more ▼]

CoRoT and Kepler observations of red giant stars revealed very rich spectra of non-radial solar-like oscillations. Of particular interest was the detection of mixed modes that exhibit significant amplitude, both in the core and at the surface of the stars. It opens the possibility of probing the internal structure from their innermost layers up to their surface throughout their evolution on the red giant branch, as well as on the red clump. Our objective is primarily to provide physical insight into the mechanism responsible for mixed-mode amplitudes and lifetimes. Subsequently, we aim at understanding the evolution and structure of red-giant spectra along with their evolution. The study of energetic aspects of these oscillations is also important for predicting the mode parameters in the power spectrum. Non-adiabatic computations, including a time-dependent treatment of convection, are performed and provide the lifetimes of radial and non-radial mixed modes. We then combine these mode lifetimes and inertias with a stochastic excitation model that gives us their heights in the power spectra. For stars representative of CoRoT and Kepler observations, we show under which circumstances mixed modes have heights comparable to radial ones. We stress the importance of the radiative damping in determining the height of mixed modes. Finally, we derive an estimate for the height ratio between a g-type and a p-type mode. This can thus be used as a first estimate of the detectability of mixed modes. [less ▲]

Detailed reference viewed: 33 (5 ULg)
Full Text
Peer Reviewed
See detailThe blue-edge problem of the V1093 Herculis instability strip revisited using evolutionary models with atomic diffusion
Bloemen, S.; Hu, H.; Aerts, C. et al

in Astronomy and Astrophysics (2014), 569

We have computed a new grid of evolutionary subdwarf B star (sdB) models from the start of central He burning, taking into account atomic diffusion due to radiative levitation, gravitational settling ... [more ▼]

We have computed a new grid of evolutionary subdwarf B star (sdB) models from the start of central He burning, taking into account atomic diffusion due to radiative levitation, gravitational settling, concentration diffusion, and thermal diffusion. We have computed the non-adiabatic pulsation properties of the models and present the predicted p-mode and g-mode instability strips. In previous studies of the sdB instability strips, artificial abundance enhancements of Fe and Ni were introduced in the pulsation driving layers. In our models, the abundance enhancements of Fe and Ni occur naturally, eradicating the need to use artificial enhancements. We find that the abundance increases of Fe and Ni were previously underestimated and show that the instability strip predicted by our simulations solves the so-called blue edge problem of the subdwarf B star g-mode instability strip. The hottest known g-mode pulsator, KIC 10139564, now resides well within the instability strip even when only modes with low spherical degrees (l ≤ 2) are considered. Appendix A is available in electronic form at <A href="http://www.aanda.org/10.1051/0004-6361/201323309/olm">http://www.aanda.org</A> [less ▲]

Detailed reference viewed: 14 (1 ULg)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 27 (10 ULg)
Full Text
Peer Reviewed
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)

Detailed reference viewed: 13 (1 ULg)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 12 (0 ULg)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 29 (0 ULg)
Full Text
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 ▲]

Detailed reference viewed: 13 (3 ULg)
Full Text
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 ▲]

Detailed reference viewed: 16 (0 ULg)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 14 (0 ULg)
Full Text
See detailNon-adiabatic study of the Kepler subgiant KIC 6442183
Grosjean, Mathieu ULg; Dupret, Marc-Antoine ULg; Belkacem, Kevin et al

Poster (2014)

Detailed reference viewed: 14 (1 ULg)
Full Text
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)

Detailed reference viewed: 21 (3 ULg)
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 ▲]

Detailed reference viewed: 23 (0 ULg)
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 ▲]

Detailed reference viewed: 8 (0 ULg)
Full Text
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 ▲]

Detailed reference viewed: 13 (0 ULg)
Full Text
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 ▲]

Detailed reference viewed: 30 (2 ULg)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 28 (3 ULg)