References of "Salmon, Sébastien"
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See detailPeriod–luminosity relations of fast-rotating B-type stars in the young open cluster NGC 3766
Saio, H.; Ekström, S.; Mowlavi, N. et al

in Monthly Notices of the Royal Astronomical Society (2017), 467(4), 3864-3873

We study the pulsational properties of rapidly rotating main-sequence B-type stars using linear non-adiabatic analysis of non-radial low-frequency modes taking into account the effect of rotation. We ... [more ▼]

We study the pulsational properties of rapidly rotating main-sequence B-type stars using linear non-adiabatic analysis of non-radial low-frequency modes taking into account the effect of rotation. We compare the properties of prograde sectoral g and retrograde r modes excited by the κ mechanism at the Fe opacity peak with the newly discovered period–luminosity relation that is obeyed by a group of fast-rotating B-type stars in the young open cluster NGC 3766. The observed relation consists of two sequences in the period versus magnitude diagram, at periods shorter than 0.5 d. We find that this property is consistent with similar period–luminosity relations predicted for excited sectoral prograde g modes of azimuthal orders m = −1 and −2 in fast-rotating stars along an isochrone. We further show that some of the rapidly rotating stars that have photometric variability with periods longer than a day may be caused by r-mode pulsation predicted to be excited in these stars. One fast-rotating star, in particular, shows both short and long periods that can be explained by the simultaneous excitation of g- and r-mode pulsations in models of fast-rotating stars. [less ▲]

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See detailConstraining the efficiency of angular momentum transport with asteroseismology of red giants: the effect of stellar mass
Eggenberger, P.; Lagarde, N.; Miglio, A. et al

in Astronomy and Astrophysics (2017), 599

Context: Constraints on the internal rotation of red giants are now available thanks to asteroseismic observations. Preliminary comparisons with rotating stellar models indicate that an undetermined ... [more ▼]

Context: Constraints on the internal rotation of red giants are now available thanks to asteroseismic observations. Preliminary comparisons with rotating stellar models indicate that an undetermined additional process for the internal transport of angular momentum is required in addition to purely hydrodynamic processes. Aims: We investigate how asteroseismic measurements of red giants can help us characterize the additional transport mechanism. Methods: We first determine the efficiency of the missing transport mechanism for the low-mass red giant KIC 7341231 by computing rotating models that include an additional viscosity corresponding to this process. We then discuss the change in the efficiency of this transport of angular momentum with the mass, metallicity and evolutionary stage. Results: In the case of the low-mass red giant KIC 7341231, we find that the viscosity corresponding to the additional mechanism is constrained to the range 1 x 10^3 - 1.3 x 10^4 cm^2/s. This constraint on the efficiency of the unknown additional transport mechanism during the post-main sequence is obtained independently of any specific assumption about the modelling of rotational effects during the pre-main sequence and the main sequence (in particular, the braking of the surface by magnetized winds and the efficiency of the internal transport of angular momentum before the post-main-sequence phase). When we assume that the additional transport mechanism is at work during the whole evolution of the star together with a solar-calibrated braking of the surface by magnetized winds, the range of nu_add is reduced to 1 - 4 x 10^3 cm^2/s. In addition to being sensitive to the evolutionary stage of the star, we show that the efficiency of the unknown process for internal transport of angular momentum increases with the stellar mass. [less ▲]

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See detailA new asteroseismic diagnostic for internal rotation in γ Doradus stars
Ouazzani, Rhita-Maria; Salmon, Sébastien ULg; Antoci, V. et al

in Monthly Notices of the Royal Astronomical Society (2017), 465

With four years of nearly-continuous photometry from Kepler, we are finally in a good position to apply asteroseismology to $\gamma$ Doradus stars. In particular several analyses have demonstrated the ... [more ▼]

With four years of nearly-continuous photometry from Kepler, we are finally in a good position to apply asteroseismology to $\gamma$ 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 the present work, we define a new seismic diagnostic for rotation in $\gamma$ Doradus stars that are too rapidly rotating to present rotational splittings. Based on the non uniformity of their period spacings, we define the observable $\Sigma$ as the slope of the period spacing when plotted as a function of period. We provide a one-to-one relation between this observable $\Sigma$ and the internal rotation, which applies widely in the instability strip of $\gamma$ Doradus stars. We apply the diagnostic to a handful of stars observed by Kepler. Thanks to g-modes in $\gamma$ 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. [less ▲]

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See detailThe IACOB project. IV. New predictions for high-degree non-radial mode instability domains in massive stars and their connection with macroturbulent broadening
Godart, Mélanie ULg; Simón-Díaz, S.; Herrero, A. et al

in Astronomy and Astrophysics (2016), 597

Context. Asteroseismology is a powerful tool to access the internal structure of stars. Apart from the important impact of theoretical developments, progress in this field has been commonly associated ... [more ▼]

Context. Asteroseismology is a powerful tool to access the internal structure of stars. Apart from the important impact of theoretical developments, progress in this field has been commonly associated with the analysis of time-resolved observations. Recently, the so-called macroturbulent broadening has been proposed as a complementary and less expensive way - in terms of observational time - to investigate pulsations in massive stars. <BR /> Aims: We assess to what extent this ubiquitous non-rotational broadening component which shapes the line profiles of O stars and B supergiants is a spectroscopic signature of pulsation modes driven by a heat mechanism. <BR /> Methods: We compute stellar main-sequence and post-main-sequence models from 3 to 70 M[SUB]⊙[/SUB] with the ATON stellar evolution code, and determine the instability domains for heat-driven modes for degrees ℓ = 1-20 using the adiabatic and non-adiabatic codes LOSC and MAD. We use the observational material compiled in the framework of the IACOB project to investigate possible correlations between the single snapshot line-broadening properties of a sample of ≈260 O and B-type stars and their location inside or outside the various predicted instability domains. <BR /> Results: We present an homogeneous prediction for the non-radial instability domains of massive stars for degree ℓ up to 20. We provide a global picture of what to expect from an observational point of view in terms of the frequency range of excited modes, and we investigate the behavior of the instabilities with respect to stellar evolution and the degree of the mode. Furthermore, our pulsational stability analysis, once compared to the empirical results, indicates that stellar oscillations originated by a heat mechanism cannot explain alone the occurrence of the large non-rotational line-broadening component commonly detected in the O star and B supergiant domain. Based on observations made with the Nordic Optical Telescope, operated by NOTSA, and the Mercator Telescope, operated by the Flemish Community, both at the Observatorio del Roque de los Muchachos (La Palma, Spain) of the Instituto de Astrofísica de Canarias. [less ▲]

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See detailIn-depth study of 16CygB using inversion techniques
Buldgen, Gaël ULg; Salmon, Sébastien ULg; Reese, D. R. et al

in Astronomy and Astrophysics (2016), 596

Context. The 16Cyg binary system hosts the solar-like Kepler targets with the most stringent observational constraints. Indeed, we benefit from very high quality oscillation spectra, as well as ... [more ▼]

Context. The 16Cyg binary system hosts the solar-like Kepler targets with the most stringent observational constraints. Indeed, we benefit from very high quality oscillation spectra, as well as spectroscopic and interferometric observations. Moreover, this system is particularly interesting since both stars are very similar in mass but the A component is orbited by a red dwarf, whereas the B component is orbited by a Jovian planet and thus could have formed a more complex planetary system. In our previous study, we showed that seismic inversions of integrated quantities could be used to constrain microscopic diffusion in the A component. In this study, we analyse the B component in the light of a more regularised inversion. <BR /> Aims: We wish to analyse independently the B component of the 16Cyg binary system using the inversion of an indicator dedicated to analyse core conditions, denoted t[SUB]u[/SUB]. Using this independent determination, we wish to analyse any differences between both stars due to the potential influence of planetary formation on stellar structure and/or their respective evolution. <BR /> Methods: First, we recall the observational constraints for 16CygB and the method we used to generate reference stellar models of this star. We then describe how we improved the inversion and how this approach could be used for future targets with a sufficient number of observed frequencies. The inversion results were then used to analyse the differences between the A and B components. <BR /> Results: The inversion of the t[SUB]u[/SUB] indicator for 16CygB shows a disagreement with models including microscopic diffusion and sharing the chemical composition previously derived for 16CygA. We show that small changes in chemical composition are insufficient to solve the problem but that extra mixing can account for the differences seen between both stars. We use a parametric approach to analyse the impact of extra mixing in the form of turbulent diffusion on the behaviour of the t[SUB]u[/SUB] values. We conclude on the necessity of further investigations using models with a physically motivated implementation of extra mixing processes including additional constraints to further improve the accuracy with which the fundamental parameters of this system are determined. [less ▲]

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See detailModels of rotating stars constrained by asteroseismic measurements of red giants
Eggenberger, P.; Lagarde, N.; Miglio, A. et al

in Astronomische Nachrichten (2016, September 01), 337(8-9), 832-836

Solar-like oscillations have now been characterized for a large number of stars, thanks to asteroseismic data obtained recently by space missions. This has led to the determination of the global and ... [more ▼]

Solar-like oscillations have now been characterized for a large number of stars, thanks to asteroseismic data obtained recently by space missions. This has led to the determination of the global and internal properties of these stars. In particular, core rotation rates have been obtained for red-giant stars, which is of prime importance to progress in the modelling of the dynamical processes at work in stellar interiors. In this presentation, we discuss which constraints can be brought by these asteroseismic measurements on stellar models that include rotational effects. Similarly to the solar case, we show that an efficient mechanism is required for the transport of angular momentum in the radiative zones of red giants. The efficiency of this transport process can be determined by asteroseismic observations of red-giant stars. [less ▲]

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See detailAsteroseismic hare & hound exercises: the case of β Cephei stars
Salmon, Sébastien ULg; Montalbán, J.; Miglio, A. et al

in Martins, F.; Boissier, S.; Buat, V. (Eds.) et al SF2A-2015: Proceedings of the Annual meeting of the French Society of Astronomy and Astrophysics. Eds.: F. Martins, S. Boissier, V. Buat, L. Cambrésy, P. Petit, pp.423-428 (2015, December 01)

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

The β Cephei pulsating stars present a unique opportunity to test and probe our knowledge of the interior of massive stars. The information that we can get depends on the quality and number of observational constraints, both seismic and classical ones. The asteroseismology of β Cephei stars proceeds by a forward approach, which can result in multiple solutions, without clear indication on the level of confidence. We seek a method to derive confidence intervals on stellar parameters and investigate how these latter behave depending on the seismic data accessible to the observer. We realise forward modelling with the help of a grid of pre-computed models. We also 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 precise seismic constraints. Significant errors on the determination of the extent of the central mixed region may result when the theoretical models do not present the same chemical mixture as the observed star. [less ▲]

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See detailFirst New Solar Models With Opas Opacity Tables
Le Pennec, Maëlle; Turck-Chièze, Sylvaine; Salmon, Sébastien ULg et al

in Astrophysical Journal Letters (2015), 813(2), 42

Stellar seismology appears more and more as a powerful tool for a better determination of the fundamental properties of solar-type stars. However, the particular case of the Sun is still challenging. For ... [more ▼]

Stellar seismology appears more and more as a powerful tool for a better determination of the fundamental properties of solar-type stars. However, the particular case of the Sun is still challenging. For about a decade now, the helioseismic sound-speed determination has continued to disagree with the standard solar model (SSM) prediction, questioning the reliability of this model. One of the sources of uncertainty could be in the treatment of the transport of radiation from the solar core to the surface. In this Letter, we use the new OPAS opacity tables, recently available for solar modeling, to address this issue. We discuss first the peculiarities of these tables, then we quantify their impact on the solar sound-speed and density profiles using the reduced OPAS tables taken on the grids of the OPAL ones. We use the two evolution codes, Modules for Experiments in Stellar Astrophysics and Code Liégeois d'Evolution Stellaire, that led to similar conclusions in the solar radiative zone. In comparison to commonly used OPAL opacity tables, the new solar models are computed for the most recent photospheric composition with OPAS tables and present improvements to the location of the base of the convective zone and to the description of the solar radiative zone in comparison to the helioseismic observations, even if the differences in the Rosseland mean opacity do not exceed 6%. We finally carry out a comparison to a solar model computed with the OP opacity tables. [less ▲]

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See detailOpacities in the massive stellar envelopes
Le Pennec, Maëlle; TURCK-CHIEZE, Sylvaine; Salmon, Sébastien ULg et al

Conference (2015, August 01)

Helio and asteroseismology (SoHo, CoRoT, KEPLER...) have produced observed acoustic oscillations of thousands of stars. The characteristics of these oscillations are deeply linked to the transport of ... [more ▼]

Helio and asteroseismology (SoHo, CoRoT, KEPLER...) have produced observed acoustic oscillations of thousands of stars. The characteristics of these oscillations are deeply linked to the transport of radiation inside the stars. However, the comparisons of seismic data of Sun and stars with model predictions have led to significant discrepancies, which could be due to a bad knowledge of production and transport of energy.We will focus here on the case of β-Cephei.β-Cephei are pulsating stars, progenitor of supernovae and thus deeply linked to our understanding of stellar medium enrichment. Their study has shown some difficulty to predict the observed oscillation modes, which are directly linked to a bump of the opacity of the elements of the iron group (Cr, Fe, Ni) at log T=5.25 through their pulsating mechanism called the κ-mechanism. We will show that the different parameters of the stars (mass, age, metallicity) have a great influence on the amplitude of the bump, and then on the structure of the considered star.The mastery of the κ-mechanism that produces the pulsation of these stars supposes a fine determination of the peak opacity of the iron group in their envelope. We will present the final results of an experiment conducted at LULI 2000 in 2011 on Cr, Fe and Ni and compare them to OP and ATOMIC, SCO-RCG codes. We will show how to improve the opacity in the range of temperature around log T= 5.3. [less ▲]

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See detailTesting stellar opacities with laser facilities
Le Pennec, Maëlle; TURCK-CHIEZE, Sylvaine; RIBEYRE, Xavier et al

Conference (2015, August 01)

Helio and asteroseismology (SoHo, KEPLER...) have produced observed acoustic oscillations of thousands of stars which characteristics are deeply linked to the transport of radiation inside the stars ... [more ▼]

Helio and asteroseismology (SoHo, KEPLER...) have produced observed acoustic oscillations of thousands of stars which characteristics are deeply linked to the transport of radiation inside the stars. However, the comparisons of seismic data with model predictions have led to significant discrepancies, which could be due to a bad knowledge of production and transport of energy.β-Cephei are pulsating stars, progenitor of supernovae and thus deeply linked to our understanding of stellar medium enrichment. Their study has shown some difficulty to predict the observed oscillation modes, which are directly linked to an opacity bump of the elements of the iron group (Cr, Fe, Ni) at log T=5.25 (κ-mechanism). We will show that several parameters of the stars (mass, age, metallicity) have a great influence on the amplitude of the bump, which impact their structure. We will then present the final results of an experiment conducted at LULI 2000 in 2011 on Cr, Fe and Ni compared to several opacity codes. We will show how to improve the opacity in the range of temperature around log T= 5.3.The Sun is a privilege place to test and validate physics. Since the recent update of the solar composition, there is a well established large discrepancy (Turck-Chièze et al. 2001) between solar models and seismic data, visible on the solar sound speed profile comparison.An explanation could be that the calculations of energy transport are not correctly taken into account.Unfortunately, there are very few experiments to validate these calculations (Bailey et al. 2014). That's why we are proposing an opacity experiment on a high-energy laser like LMJ, in the conditions of the radiative zone. We are exploiting in that purpose an approach called the Double Ablation Front to reach these high temperatures and densities at LTE and validate or not plasma effects and line widths. We will show the principle of this technique and the results of our simulations on several elements.In the mean time, we are also exploiting new opacity calculations thanks to the OPAS code (Blancard et al. 2012) at the conditions of the solar radiative zone. We will show the impact of these calculations on the solar model. [less ▲]

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See detailWhat can we learn from asteroseismology of beta Cephei stars?
Salmon, Sébastien ULg; Montalban, J.; Miglio, A. et al

Poster (2015, June 01)

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See detailEx Parrot: The Aarhus-Sydney gamma Dor experiment on pulsations and rotation
Antoci, V.; Ouazzani, R.; Murphy, S. et al

Poster (2015, June 01)

γ Doradus stars, exhibiting pure gravity modes pulsations, occupy the region between the solar-like oscillators and the delta Sct stars in the HRD. The Kepler mission delivered data of unprecedented ... [more ▼]

γ Doradus stars, exhibiting pure gravity modes pulsations, occupy the region between the solar-like oscillators and the delta Sct stars in the HRD. The Kepler mission delivered data of unprecedented quality spanning up to 4 years, allowing to resolve closely spaced modes to measure, e.g., period spacings and to infer internal rotation profiles. Here we present an ensemble study of all γ Doradus stars observed with the Kepler mission. We investigate among others the range of excited modes, their amplitudes and the impact of rotation on these quantities. Our aim is to better understand the pulsation excitation as well as the mode selection mechanism in these stars. Our results may help to also explain the lack of solar-like oscillators exhibiting g-modes pulsations on the main sequence, although the instability domains of γ Doradus and solar-like stars overlap. [less ▲]

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See detailPLATO Simulator: Realistic simulations of expected observations
Marcos-Arenal, P.; Zima, W.; De Ridder, J. et al

Software (2015)

PLATO Simulator is an end-to-end simulation software tool designed for the performance of realistic simulations of the expected observations of the PLATO mission but easily adaptable to similar types of ... [more ▼]

PLATO Simulator is an end-to-end simulation software tool designed for the performance of realistic simulations of the expected observations of the PLATO mission but easily adaptable to similar types of missions. It models and simulates photometric time-series of CCD images by including models of the CCD and its electronics, the telescope optics, the stellar field, the jitter movements of the spacecraft, and all important natural noise sources. [less ▲]

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See detailAnalyser et contraindre les opacités stellaires via les pulsations des étoiles B de séquence
Salmon, Sébastien ULg; Truck-Chièze, S.; Le Pennec, M.

Conference (2015, June)

Les étoiles B de séquence principale, bien que peu nombreuses, présentent un intérêt particulier puisque les plus massives d'entre elles termineront leur évolution par un évènement de type effondrement du ... [more ▼]

Les étoiles B de séquence principale, bien que peu nombreuses, présentent un intérêt particulier puisque les plus massives d'entre elles termineront leur évolution par un évènement de type effondrement du coeur. Parmis les diverses étoiles pulsantes du diagramme d'Hertzsprung-Russell, nous avons la chance de trouver deux types de pulsation au sein des étoiles B de séquence : d'une part celles de type beta Cephei, correspondant à des modes de gravité et acoustiques d'ordres faibles, et d'autre part celles de type SPB (Slowly Pulsating B stars), correspondant à des modes de gravité d'ordres élevés. En étudiant ces pulsations, nous pouvons ainsi améliorer notre connaissance des processus physiques internes des étoiles B de séquence. Nous nous intéressons au cas récent de la détection d'étoiles B pulsantes au sein des Nuages de Magellan, galaxies de si faible métallicité que de telles pulsations n'y étaient pas attendues d'un point de vue théorique. Les pulsations de ces étoiles B sont en effet sensibles à la composition chimique car elles sont activées par le mécanisme kappa, lié à la présence d'un pic d'opacité des éléménts du groupe du fer à une température d'environ 200 000K. Dès lors nous étudions le rôle de la composition chimique et des opacités sur ces pulsations, et mettons en évidence une possible sous-estimation des opacités théoriques. Dans ce cadre, nous présentons les efforts récents du projet OPAC portant sur l'étude des opacités des éléments du groupe du fer, pour des conditions similaires aux enveloppes radiatives des étoiles B. [less ▲]

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See detailWhat can we learn about gamma Doradus star internal structure from Kepler?
Ouazzani, R-M.; Antoci, V.; Salmon, Sébastien ULg et al

Conference (2015, June)

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See detailAsteroseismology of Massive Stars: Some Words of Caution
Noels-Grötsch, Arlette ULg; Godart, M.; Salmon, Sébastien ULg et al

in Meynet, Georges; Georgy, Cyril; Groh, Jose (Eds.) et al Proceedings of the International Astronomical Union S307 (2015, January 01)

Although playing a key role in the understanding of the supernova phenomenon, the evolution of massive stars still suffers from uncertainties in their structure, even during their ``quiet'' main sequence ... [more ▼]

Although playing a key role in the understanding of the supernova phenomenon, the evolution of massive stars still suffers from uncertainties in their structure, even during their ``quiet'' main sequence phase and later on during their subgiant and helium burning phases. What is the extent of the mixed central region? In the local mixing length theory (LMLT) frame, are there structural differences using Schwarzschild or Ledoux convection criterion? Where are located the convective zone boundaries? Are there intermediate convection zones during MS and post-MS phase, and what is their extent and location? We discuss these points and show how asteroseismology could bring some light on these questions. [less ▲]

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See detailAre the stars of a new class of variability detected in NGC 3766 fast rotating SPB stars?
Salmon, Sébastien ULg; Montalbán, J.; Reese, D. R. et al

in Meynet, Georges; Georgy, Cyril; Groh, Jose (Eds.) et al Proceedings of the International Astronomical Union S307 (2015, January 01)

A recent photometric survey in the NGC 3766 cluster led to the detection of stars presenting an unexpected variability. They lie in a region of the Hertzsprung-Russell (HR) diagram where no pulsation are ... [more ▼]

A recent photometric survey in the NGC 3766 cluster led to the detection of stars presenting an unexpected variability. They lie in a region of the Hertzsprung-Russell (HR) diagram where no pulsation are theoretically expected, in between the δ Scuti and slowly pulsating B (SPB) star instability domains. Their variability periods, between ~0.1-0.7 d, are outside the expected domains of these well-known pulsators. The NCG 3766 cluster is known to host fast rotating stars. Rotation can significantly affect the pulsation properties of stars and alter their apparent luminosity through gravity darkening. Therefore we inspect if the new variable stars could correspond to fast rotating SPB stars. We carry out instability and visibility analysis of SPB pulsation modes within the frame of the traditional approximation. The effects of gravity darkening on typical SPB models are next studied. We find that at the red border of the SPB instability strip, prograde sectoral (PS) modes are preferentially excited, with periods shifted in the 0.2-0.5 d range due to the Coriolis effect. These modes are best seen when the star is seen equator-on. For such inclinations, low-mass SPB models can appear fainter due to gravity darkening and as if they were located between the δ Scuti and SPB instability strips. [less ▲]

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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 ▲]

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See detailThe PLATO 2.0 Mission
Rauer, H.; Catala, C.; Aerts, C. et al

in Experimental Astronomy (2014)

PLATO 2.0 has recently been selected for ESA’s M3 launch opportunity (2022/24). Providing accurate key planet parameters (radius, mass, density and age) in statistical numbers, it addresses fundamental ... [more ▼]

PLATO 2.0 has recently been selected for ESA’s M3 launch opportunity (2022/24). Providing accurate key planet parameters (radius, mass, density and age) in statistical numbers, it addresses fundamental questions such as: How do planetary systems form and evolve? Are there other systems with planets like ours, including potentially habitable planets? The PLATO 2.0 instrument consists of 34 small aperture telescopes (32 with 25 s readout cadence and 2 with 2.5 s candence) providing a wide field-of-view (2232 deg 2) and a large photometric magnitude range (4–16 mag). It focusses on bright (4–11 mag) stars in wide fields to detect and characterize planets down to Earth-size by photometric transits, whose masses can then be determined by ground-based radial-velocity follow-up measurements. Asteroseismology will be performed for these bright stars to obtain highly accurate stellar parameters, including masses and ages. The combination of bright targets and asteroseismology results in high accuracy for the bulk planet parameters: 2 %, 4–10 % and 10 % for planet radii, masses and ages, respectively. The planned baseline observing strategy includes two long pointings (2–3 years) to detect and bulk characterize planets reaching into the habitable zone (HZ) of solar-like stars and an additional step-and-stare phase to cover in total about 50 % of the sky. PLATO 2.0 will observe up to 1,000,000 stars and detect and characterize hundreds of small planets, and thousands of planets in the Neptune to gas giant regime out to the HZ. It will therefore provide the first large-scale catalogue of bulk characterized planets with accurate radii, masses, mean densities and ages. This catalogue will include terrestrial planets at intermediate orbital distances, where surface temperatures are moderate. Coverage of this parameter range with statistical numbers of bulk characterized planets is unique to PLATO 2.0. The PLATO 2.0 catalogue allows us to e.g.: - complete our knowledge of planet diversity for low-mass objects, - correlate the planet mean density-orbital distance distribution with predictions from planet formation theories,- constrain the influence of planet migration and scattering on the architecture of multiple systems, and - specify how planet and system parameters change with host star characteristics, such as type, metallicity and age. The catalogue will allow us to study planets and planetary systems at different evolutionary phases. It will further provide a census for small, low-mass planets. This will serve to identify objects which retained their primordial hydrogen atmosphere and in general the typical characteristics of planets in such low-mass, low-density range. Planets detected by PLATO 2.0 will orbit bright stars and many of them will be targets for future atmosphere spectroscopy exploring their atmosphere. Furthermore, the mission has the potential to detect exomoons, planetary rings, binary and Trojan planets. The planetary science possible with PLATO 2.0 is complemented by its impact on stellar and galactic science via asteroseismology as well as light curves of all kinds of variable stars, together with observations of stellar clusters of different ages. This will allow us to improve stellar models and study stellar activity. A large number of well-known ages from red giant stars will probe the structure and evolution of our Galaxy. Asteroseismic ages of bright stars for different phases of stellar evolution allow calibrating stellar age-rotation relationships. Together with the results of ESA’s Gaia mission, the results of PLATO 2.0 will provide a huge legacy to planetary, stellar and galactic science. [less ▲]

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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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