Period spacings of γ Doradus pulsators in the Kepler field: detection methods and application to 22 slow rotators

In γ Doradus (γ Dor) stars, the g-mode period spacing shows an approximately linear relation with period. The slope is a new asteroseismic diagnostic, related to the rotation rate and the azimuthal order m. We report two automated methods, the ‘moving-window Fourier transform’ and the ‘cross-correlation’, to detect and measure the period spacings based on 4-yr light curves from the Kepler satellite. The results show that the cross-correlation method performs better at detecting the period spacings and their slopes. In this paper, we apply our method to 22 γ Dor stars with g-mode multiplets split by rotation. The rotation periods are similar to the g-mode period spacings, causing the multiplets to overlap. To clarify the overlapping patterns, we use the échelle diagram and introduce a ‘copy-shift’ diagram to discern and measure the splittings. The first observational relation between slopes and splittings is shown. The slope deviates from zero when the splitting increases, as the theory predicts. We found that what appears to be rotational splittings in two stars is in fact caused by two nearly identical overlapping patterns from binaries

A new asteroseismic diagnostic for internal rotation in γ Doradus stars

With four years of nearly continuous photometry from Kepler, we are finally in a good position to apply asteroseismology to γ Doradus stars. In particular, several analyses have demonstrated the possibility to detect non-uniform period spacings, which have been predicted to be directly related to rotation. In this paper, we define a new seismic diagnostic for rotation in γ Doradus stars which are too rapidly rotating to present rotational splittings. Based on the non-uniformity of their period spacings, we define the observable Σ as the slope of the period spacing when plotted as a function of period. We provide a one-to-one relation between this observable Σ and the internal rotation, which applies widely in the instability strip of γ Doradus stars. We apply the diagnostic to a handful of stars observed by Kepler. Thanks to g modes in γ Doradus stars, we are now able to determine the internal rotation of stars on the lower main sequence, which is still not possible for Sun-like stars

What CoRoT tells us about Scuti stars: Existence of a regular pattern and seismic indices to characterize stars

Inspired by the so appealing example of red giants, where going from a handful of stars to thousands revealed the structure of the eigenspectrum, we inspected a large homogeneous set of around 1860 {\delta} Scuti stars observed with CoRoT. This unique data set reveals a common regular pattern which appears to be in agreement with island modes featured by theoretical non-perturbative treatments of fast rotation. The comparison of these data with models and linear stability calculations suggests that spectra can be fruitfully characterized to first order by a few parameters which might play the role of seismic indices for {\delta} Scuti stars, as {\Delta \nu} and {\nu_{max}} do for red giants. The existence of this pattern offers an observational support for guiding further theoretical works on fast rotation. It also provides a framework for further investigation of the observational material collected by CoRoT and Kepler. Finally, it sketches out the perspective of using {\delta} Scuti stars pulsations for ensemble asteroseismology.The CoRoT space mission, launched on December 27th 2006, has been developed and is operated by the Centre Na- tional d’Etudes Spatiales (CNES), with contributions from Aus- tria, Belgium, Brazil, the European Space Agency (RSSD and Science Programme), Germany and Spain. We ac- knowledge the support from the EC Project SpaceInn (FP7- SPACE-2012-312844). EM, KB, RS and DR acknowledge the support from the Programme de Physique Stellaire (PNPS). AGH acknowledges support from Fundação para a Ciên- cia e a Tecnologia (FCT, Portugal) through the fellowship SFRH / BPD / 80619 / 2011. JCS acknowledges funding support from Spanish public funds for research under project ESP201 5- 65712-C5-5-R (MINECO / FEDER), and under Research Fellow- ship program “Ramón y Cajal” (MINECO / FEDER

The SAPP pipeline for the determination of stellar abundances and atmospheric parameters of stars in the core program of the PLATO mission

We introduce the SAPP (Stellar Abundances and atmospheric Parameters Pipeline), the prototype of the code that will be used to determine parameters of stars observed within the core program of the PLATO space mission. The pipeline is based on the Bayesian inference and provides effective temperature, surface gravity, metallicity, chemical abundances, and luminosity. The code in its more general version has a much wider range of potential applications. It can also provide masses, ages, and radii of stars and can be used with stellar types not targeted by the PLATO core program, such as red giants. We validate the code on a set of 27 benchmark stars that includes 19 FGK-type dwarfs, 6 GK-type subgiants, and 2 red giants. Our results suggest that combining various observables is the optimal approach, as this allows the degeneracies between different parameters to be broken and yields more accurate values of stellar parameters and more realistic uncertainties. For the PLATO core sample, we obtain a typical uncertainty of 27 (syst.) ± 37 (stat.) K for Teff, 0.00 ± 0.01 dex for log g, 0.02 ± 0.02 dex for metallicity [Fe/H], −0.01 ± 0.03 R⊙ for radii, −0.01 ± 0.05 M⊙ for stellar masses, and −0.14 ± 0.63 Gyr for ages. We also show that the best results are obtained by combining the νmax scaling relation with stellar spectra. This resolves the notorious problem of degeneracies, which is particularly important for F-type stars

Validity domain of a perturbative approach for rot. effects on asteroseismic data

International audienc

La rotation et son interaction avec les oscillations dans les étoiles

Stellar rotation plays a key role in the evolution of stars. It causes mixing of chemical elements and transport of angular momentum inside the star which will strongly determine the star’s history. Asteroseismology is the most efficient observational mean to get information about stellar interiors by measuring magnitude variability induced by seismic waves emerging at the stellar surface. But rotation also impacts these seismic pulsations : the centrifugal force distorts the resonant cavity while the Coriolis force modifies the fluid dynamics. Therefore, in order to get relevant information about the stellar structure from asteroseismology, one should reach a good understanding of the rotational effect on stellar pulsations. On the one hand, when rotation velocity is small, a perturbative approach gives satisfying results for the computations of the rotational impact on oscillations. Therefore, the first step of my work consisted in the determination of validity domains for such methods. Within the established validity domain, I showed that the perturbative method, up to the cubic order in terms of the rotation angular velocity Ω and accounting for near degeneracy corrections enables us to constrain stellar surface rotation from seismic observations.However, when the perturbative approach is no longer relevant, for rapid rotators, I built a non perturbative, two dimensional code which fully takes into account both centrifugal distorsion and Coriolis force. The numerical method is based on a spectral multi-domain method which expands the angular dependence of pulsation modes on spherical harmonics series, and which radial treatment is particularly well adapted to the behaviour of equilibrium quantities in evolved models at the interface of convective and radiative regions, and at the stellar surface. The radial differenciation is made by means of a sophisticated finite differences method which is accurate up to the fifth order in terms of the radial resolution. This code has been validated by comparison with the results of Reese et al. (2006) for polytropic models. The agreement between the two codes is found excellent. Finally, I used this newly developed tool in order to compute pulsations of anevolved centrifugally distorted model of star computed by Roxburgh (2006). I found a new type of oscillation modes which are the equivalent of low degree gravito-acoustic mixed modes for very rapid rotators. They show amplitude both in the core (in the μ gradient region) and in the envelop and angular geometry which varies from the center to the surface of the star. These modes represent a very interesting seismic tool for differential rotation in massive rapidly rotating stars.La rotation stellaire joue un rôle essentiel dans l’évolution des étoiles. Elle induit des phénomènes de mélange des éléments chimiques et de redistribution du moment cinétique qui vont déterminer l’histoire de la structure de l’étoile. Le moyen observationnel le plus efficace pour sonder les intérieurs stellaires est l’astérosismologie, l’étude des ondes sismiques s’y propageant. Mais la rotation agit également sur les oscillations par l’intermédiaire de la force centrifuge qui déforme la cavité résonnante des modes de pulsation et de la force de Coriolis qui agit sur la dynamique du fluide stellaire. Dans le but de comprendre toute l’information que peut nous apporter l’astérosismologie sur l’intérieur des étoiles, il faut alors se donner les moyens d’appréhender correctement l’effet de la rotation sur les oscillations stellaires.Dans le cas où la vitesse de rotation de l’étoile est faible, l’approche perturbative nous permet de calculer l’impact de la rotation sur les oscillations de manière suffisamment précise (la fréquence d’oscillation se décompose en série de la vitesse angulaire de rotation Ω, l’ordre zéro correspondant au cas sans rotation). Une première étape de ce travail de thèse a donc consisté à déterminer jusqu’à quelle vitesse de rotation les méthodes perturbatives sont valides pour une telle détermination.Dans la limite où elle est valide, la méthode perturbative poussée à l’ordre 3 en terme de vitesse de rotation m’a permis de montrer comment on pouvait contraindre la rotation de surface à partir des observations sismiques.Par ailleurs, dans le cas où elles ne sont pas valides, pour les rotateurs rapides, j’ai développé un outil non perturbatif bidimensionnel de calcul des oscillations stellaires capable de prendre en compte à la fois la distorsion centrifuge et l’effet de la force de Coriolis de manière complète. La méthode numérique repose sur une approche spectrale multidomaine, c’est-à-dire que la dépendance angulaire des solutions est développée sur une série tronquée d’harmoniques sphériques, et que le système de coordonnées mis au point permet de s’adapter parfaitement à la structure de l’étoile (que ce soit aux interfaces entre les régions convectives et radiatives ou à la surface stellaire). Ladifférenciation radiale des équations hydrodynamiques se fait au moyen d’une méthode particulièrement stable et précise jusqu’à l’ordre 5 en terme de la résolution radiale. Le code ainsi mis au point a été validé par comparaison avec les résultats issus du code développé dans Reese et al. (2006) pour des modèles polytropiques. L’accord entre les modes propres issus des deux calculs est excellent. Enfin, j’ai utilisé cet outil nouvellement développé afin de calculer les pulsations d’un modèle évolué d’étoile dont la déformation induite par la rotation est calculée a posteriori de manière autocohérente suivant la méthode développée par Roxburgh (2006). Ce type de modèle est chimiquement hétérogène et présente un cœur convectif entouré d’une enveloppe radiative, ce qui est particulièrement délicat à traiter étant donné les variations brusques des grandeurs de structure. Ceci m’a permis d’obtenir des modes d’oscillation alors jamais observés en rotation rapide : des modes mixtes (ayant de l’amplitude à la fois dans le cœur et dans l’enveloppe) de bas degré angulaire, qui représentent l’outil sismique de sondage de la rotation différentielle par excellence

Validity domain of a perturbative approach for rot. effects on asteroseismic data

International audienc

PLATO: PSF modelling using a micro-scanning technique

International audienc

La rotation et son interaction avec les oscillations dans les étoiles

La rotation stellaire joue un rôle essentiel dans l'évolution des étoiles. Le moyen observationnel de sonder ses effets est l'astérosismologie, l'étude des ondes sismiques se propageant dans l'intérieur stellaire. Mais la rotation agit également sur les oscillations sismiques, c'est l'objet d'étude de cette thèse. Selon les situations stellaires, on peut adopter différentes approches. Pour une rotation faible, l'approche perturbative permet de calculer l'impact de la rotation sur les oscillations de manière suffisamment précise. Après avoir déterminé la limite de validité de cette approche en terme de vitesse de rotation, j'ai montré comment la méthode perturbative nous permet de contraindre la rotation de surface à partir des observations sismiques. Par ailleurs, pour les rotateurs rapides, j'ai développé un programme non-perturbatif bi-dimensionnel de calcul des oscillations stellaires. J'ai utilisé cet outil afin de calculer les pulsations d'un modèle évolué d'étoile déformé. Ceci m'a permis d'obtenir des modes d'oscillations alors jamais observés en rotation rapide: des modes mixtes de bas degré angulaire, qui représentent l'outil sismique de sondage de la rotation différentielle par excellence.PARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF