References of "Noels-Grötsch, Arlette"
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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 detailUncertainties in Models of Stellar Structure and Evolution
Noels-Grötsch, Arlette ULg; Bragaglia, Angela

in Astrophysics and Space Science Proceedings (2015), 39

Numerous physical aspects of stellar physics have been presented in Session 2 and the underlying uncertainties have been tentatively assessed. We try here to highlight some specific points raised after ... [more ▼]

Numerous physical aspects of stellar physics have been presented in Session 2 and the underlying uncertainties have been tentatively assessed. We try here to highlight some specific points raised after the talks and during the general discussion at the end of the session and eventually at the end of the workshop. A table of model uncertainties is then drawn with the help of the participants in order to give the state of the art in stellar modeling uncertainties as of July 2013. [less ▲]

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See detailMixed modes in red giants: a window on stellar evolution
Mosser, B.; Benomar, O.; Belkacem, K. et al

in Astronomy and Astrophysics (2014), 572

Context. The detection of oscillations with a mixed character in subgiants and red giants allows us to probe the physical conditions in their cores. <BR /> Aims: With these mixed modes, we aim at ... [more ▼]

Context. The detection of oscillations with a mixed character in subgiants and red giants allows us to probe the physical conditions in their cores. <BR /> Aims: With these mixed modes, we aim at determining seismic markers of stellar evolution. <BR /> Methods: Kepler asteroseismic data were selected to map various evolutionary stages and stellar masses. Seismic evolutionary tracks were then drawn with the combination of the frequency and period spacings. <BR /> Results: We measured the asymptotic period spacing for 1178 stars at various evolutionary stages. This allows us to monitor stellar evolution from the main sequence to the asymptotic giant branch and draw seismic evolutionary tracks. We present clear quantified asteroseismic definitions that characterize the change in the evolutionary stages, in particular the transition from the subgiant stage to the early red giant branch, and the end of the horizontal branch. <BR /> Conclusions: The seismic information is so precise that clear conclusions can be drawn independently of evolution models. The quantitative seismic information can now be used for stellar modeling, especially for studying the energy transport in the helium-burning core or for specifying the inner properties of stars entering the red or asymptotic giant branches. Modeling will also allow us to study stars that are identified to be in the helium-subflash stage, high-mass stars either arriving or quitting the secondary clump, or stars that could be in the blue-loop stage. Table 1 is only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/572/L5">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/572/L5</A> [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 detailVizieR Online Data Catalog: Mixed modes in red giants (Mosser+, 2014)
Mosser, B.; Benomar, O.; Belkacem, K. et al

in VizieR Online Data Catalog (2014), 357

Seismic global parameters of the stars listed in the paper. Each star is identified with its KIC number (Kepler Input Catalog). The asymptotic frequency and period spacing are derived from the fit of the ... [more ▼]

Seismic global parameters of the stars listed in the paper. Each star is identified with its KIC number (Kepler Input Catalog). The asymptotic frequency and period spacing are derived from the fit of the radial and dipole oscillation modes. The stellar mass is derived from the seismic scaling relations. The evolutionary status is derived according to the location of the star in the DPi1 - Dnu diagram (Fig. 1) (1 data file). [less ▲]

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See detailProper use of Schwarzschild Ledoux criteria in stellar evolution computations
Gabriel, Maurice; Noels-Grötsch, Arlette ULg; Montalbán, J. et al

in Astronomy and Astrophysics (2014), 569

The era of detailed asteroseismic analyses opened by space missions such as CoRoT and Kepler has highlighted the need for stellar models devoid of numerical inaccuracies, in order to be able to diagnose ... [more ▼]

The era of detailed asteroseismic analyses opened by space missions such as CoRoT and Kepler has highlighted the need for stellar models devoid of numerical inaccuracies, in order to be able to diagnose which physical aspects are being ignored or poorly treated in standard stellar modeling. We tackle here the important problem of fixing convective zone boundaries in the frame of the local mixing length theory. First we show that the only correct way to locate a convective zone boundary is to find, at each iteration step, through interpolations or extrapolations from points within the convective zone, the mass where the radiative luminosity is equal to the total luminosity. We then discuss two misuses of the boundary condition and the ways they affect stellar modeling and stellar evolution. The first consists in applying the neutrality condition for convective instability on the radiative side of the convective boundary. The second way of misusing the boundary condition comes from the process of fixing the convective boundary through the search for a change of sign of a possibly discontinuous function. We show that these misuses can lead to completely wrong estimates of convective core sizes with important consequences for the following evolutionary phases. We point out the advantages of using a double mesh point at each convective zone boundary. The specific problem of a convective shell is discussed and some remarks concerning overshooting are given. [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 detailDifferential population studies using asteroseismology: Solar-like oscillating giants in CoRoT fields LRc01 and LRa01
Miglio, A.; Chiappini, C.; Morel, Thierry ULg et al

in European Physical Journal Web of Conferences (2013, March 01)

Solar-like oscillating giants observed by the space-borne satellites CoRoT and Kepler can be used as key tracers of stellar populations in the Milky Way. When combined with additional photometric ... [more ▼]

Solar-like oscillating giants observed by the space-borne satellites CoRoT and Kepler can be used as key tracers of stellar populations in the Milky Way. When combined with additional photometric/spectroscopic constraints, the pulsation spectra of solar-like oscillating giant stars not only reveal their radii, and hence distances, but also provide well-constrained estimates of their masses, which can be used as proxies for the ages of these evolved stars. In this contribution we provide supplementary material to the comparison we presented in Miglio et al. (2013) between populations of giants observed by CoRoT in the fields designated LRc01 and LRa01. [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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See detailMode lifetime and associated scaling relations
Belkacem, K.; Appourchaux, T.; Baudin, F. et al

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

Thanks to the CoRoT and Kepler spacecrafts, scaling relations (linking seismic indices and global stellar parameters) are becoming the cornerstone of ensemble asteroseismology. Among them, the relation ... [more ▼]

Thanks to the CoRoT and Kepler spacecrafts, scaling relations (linking seismic indices and global stellar parameters) are becoming the cornerstone of ensemble asteroseismology. Among them, the relation between the cut-off frequency and the frequency of the maximum in the power spectrum of solar-like pulsators as well as the relation between mode lifetime and the effective temperature remain poorly understood. However, a solid theoretical background is essential to assess the accuracy of those relations and subsequently of the derived stellar parameters. We will thus present recent advances on the understanding of the underlying mechanisms governing those relations and show that the physics of mode lifetime (thus of mode damping) plays a major role. [less ▲]

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See detailEffects of the Coriolis force on high-order g modes in γ Doradus stars
Bouabid, M.-P.; Dupret, Marc-Antoine ULg; Salmon, Sébastien ULg et al

in Monthly Notices of the Royal Astronomical Society (2013), 429(3), 2500

γ Doradus stars pulsate with high-order gravity modes having typical frequencies which can be comparable to or higher than their rotation frequencies. Therefore, rotation has a non-negligible effect on ... [more ▼]

γ Doradus stars pulsate with high-order gravity modes having typical frequencies which can be comparable to or higher than their rotation frequencies. Therefore, rotation has a non-negligible effect on their oscillation properties. To explore the rotation-pulsation coupling in γ Dor stars, we perform a non-adiabatic study including the traditional approximation of rotation on a grid of spherical stellar models covering the mass range 1.4 < M[SUB]*[/SUB] < 2.1 M[SUB]&sun;[/SUB]. This approximation allows us to treat the effect of the Coriolis force on the frequencies and the stability of high-order g modes. The effect of the Coriolis force depends on the kind of mode considered (prograde sectoral or not) and increases with their periods. As a consequence, we first find that the period spacing between modes is no longer periodically oscillating around a constant value. Secondly, we show that the frequency gap (5-15 cycles day[SUP]-1[/SUP]) arising from stable modes between γ Dor-type high-order g modes and δ Scuti-type modes can be easily filled by g-mode frequencies shifted to higher values by the rotation. Thirdly, we analyse the combined effect of diffusive mixing and the Coriolis force on the period spacings. And finally, we predict a slight broadening of the γ Dor instability strip. [less ▲]

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See detailCoRoT Observations of O Stars: Diverse Origins of Variability
Blomme, R.; Briquet, Maryline ULg; Degroote, P. et al

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

Six O-type stars were observed continuously by the CoRoT satellite during a 34.3-day run. The unprecedented quality of the data allows us to detect even low-amplitude stellar pulsations in some of these ... [more ▼]

Six O-type stars were observed continuously by the CoRoT satellite during a 34.3-day run. The unprecedented quality of the data allows us to detect even low-amplitude stellar pulsations in some of these stars (HD 46202 and the binaries HD 46149 and Plaskett's star). These cover both opacity-driven modes and solar-like stochastic oscillations, both of importance to the asteroseismological modeling of O stars. Additional effects can be seen in the CoRoT light curves, such as binarity and rotational modulation. Some of the hottest O-type stars (HD 46223, HD 46150 and HD 46966) are dominated by the presence of red-noise: we speculate that this is related to a sub-surface convection zone. [less ▲]

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See detailTheoretical Instability Domains of Massive Stars
Godart, Mélanie ULg; Dupret, Marc-Antoine ULg; Noels-Grötsch, Arlette ULg et al

in ASP Conference Proceeding, Vol. 462, 27 (2012, September 01)

Massive stars are characterized by a large radiation over gas pressure ratio. With increasing stellar initial mass, they suffer stronger stellar winds, and the induced mass-loss affects the evolution and ... [more ▼]

Massive stars are characterized by a large radiation over gas pressure ratio. With increasing stellar initial mass, they suffer stronger stellar winds, and the induced mass-loss affects the evolution and internal structure on the main sequence and on the post-main sequence. Recent ground-based observations and space missions have shown the presence of pulsations in massive stars, such as acoustic and gravity modes excited by the κ-mechanism and even solar-like oscillations. Strange modes could also be excited in the most massive stars (Aerts et al. 2010). We computed evolutionary tracks and non-adiabatic frequencies for initial masses ranging from 15 to 70 M[SUB]&sun;[/SUB] on the main sequence and on the post-main sequence taking mass loss into account and we discuss in this paper the results for 25 M[SUB]&sun;[/SUB] models. [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, Kevin et al

Poster (2012, July)

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 (amplitudes and life ... [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 (amplitudes and life- times) of two red giants in the same region of the HR diagram but in different evolutionary phases. The lifetimes are obtained by computing theoretical non-adiabatic non-radial solar-like oscillations for mixed modes in the two models. Thanks to this, we have been able to compute the oscillation amplitudes through a stochastic excitation model. We present here our first results on the inertia, damping rates and amplitudes of the oscillations in the two stars and discuss the trapping, the visibilities and the am- plitudes of the different modes. The differences in the spectra of the two stars are also investigated. As already known, the period spacings in the two models are very different. Moreover, we find significant differences in amplitudes and lifetimes between the two models. [less ▲]

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See detailTesting the effects of opacity and the chemical mixture on the excitation of pulsations in B stars of the Magellanic Clouds
Salmon, Sébastien ULg; Montalban Iglesias, Josefa ULg; Morel, Thierry ULg et al

in Monthly Notices of the Royal Astronomical Society (2012), 422

The B-type pulsators known as β Cephei and slowly pulsating B (SPB) stars present pulsations driven by the κ mechanism, which operates thanks to an opacity bump due to the iron-group elements. In low ... [more ▼]

The B-type pulsators known as β Cephei and slowly pulsating B (SPB) stars present pulsations driven by the κ mechanism, which operates thanks to an opacity bump due to the iron-group elements. In low-metallicity environments such as the Magellanic Clouds, β Cep and SPB pulsations are not expected. Nevertheless, recent observations show evidence for the presence of B-type pulsator candidates in both galaxies. We seek an explanation for the excitation of β Cep and SPB modes in those galaxies by examining basic input physics in stellar modelling: (i) the specific metal mixture of B-type stars in the Magellanic Clouds and (ii) the role of a potential underestimation of stellar opacities. We first derive the present-day chemical mixtures of B-type stars in the Magellanic Clouds. Then, we compute stellar models for that metal mixture and perform a non-adiabatic analysis of these models. In the second approach, we simulate parametric enhancements of stellar opacities due to different iron-group elements. We then study their effects in models of B stars and their stability. We find that adopting a representative chemical mixture of B stars in the Small Magellanic Cloud cannot explain the presence of B-type pulsators there. An increase of the opacity in the region of the iron-group bump could drive B-type pulsations, but only if this increase occurs at the temperature corresponding to the maximum contribution of Ni to this opacity bump. We recommend an accurate computation of the Ni opacity to understand B-type pulsators in the Small Magellanic Cloud, as well as the frequency domain observed in some Galactic hybrid β Cep–SPB stars. [less ▲]

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See detailAsteroseismology of old open clusters with Kepler: direct estimate of the integrated red giant branch mass-loss in NGC 6791 and 6819
Miglio, A.; Brogaard, K.; Stello, D. et al

in Monthly Notices of the Royal Astronomical Society (2012), 419

Mass-loss of red giant branch (RGB) stars is still poorly determined, despite its crucial role in the chemical enrichment of galaxies. Thanks to the recent detection of solar-like oscillations in G-K ... [more ▼]

Mass-loss of red giant branch (RGB) stars is still poorly determined, despite its crucial role in the chemical enrichment of galaxies. Thanks to the recent detection of solar-like oscillations in G-K giants in open clusters with Kepler, we can now directly determine stellar masses for a statistically significant sample of stars in the old open clusters NGC 6791 and 6819. The aim of this work is to constrain the integrated RGB mass-loss by comparing the average mass of stars in the red clump (RC) with that of stars in the low-luminosity portion of the RGB [i.e. stars with L≲L(RC)]. Stellar masses were determined by combining the available seismic parameters ν[SUB]max[/SUB] and Δν with additional photometric constraints and with independent distance estimates. We measured the masses of 40 stars on the RGB and 19 in the RC of the old metal-rich cluster NGC 6791. We find that the difference between the average mass of RGB and RC stars is small, but significant [? (random) ±0.04 (systematic) M[SUB]&sun;[/SUB]]. Interestingly, such a small ? does not support scenarios of an extreme mass-loss for this metal-rich cluster. If we describe the mass-loss rate with Reimers prescription, a first comparison with isochrones suggests that the observed ? is compatible with a mass-loss efficiency parameter in the range 0.1 ≲η≲ 0.3. Less stringent constraints on the RGB mass-loss rate are set by the analysis of the ˜2 Gyr old NGC 6819, largely due to the lower mass-loss expected for this cluster, and to the lack of an independent and accurate distance determination. In the near future, additional constraints from frequencies of individual pulsation modes and spectroscopic effective temperatures will allow further stringent tests of the Δν and ν[SUB]max[/SUB] scaling relations, which provide a novel, and potentially very accurate, means of determining stellar radii and masses. [less ▲]

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See detailAdiabatic Solar-Like Oscillations in Red Giant Stars
Montalban Iglesias, Josefa ULg; Miglio, Andrea; Noels-Grötsch, Arlette ULg et al

in Red Giants as Probes of the Structure and Evolution of the Milky Way (2012)

Since the detection of non-radial solar-like oscillation modes in red giants with the CoRoT satellite, the interest in the asteroseismic properties of red giants and the link with their global properties ... [more ▼]

Since the detection of non-radial solar-like oscillation modes in red giants with the CoRoT satellite, the interest in the asteroseismic properties of red giants and the link with their global properties and internal structure is substantially increasing. Moreover, more and more precise data are being collected with the space-based telescopes CoRoT and Kepler. In this paper we present a survey of the most relevant theoretical and observational results obtained up to now concerning the potential of solar-like oscillations in red giants. [less ▲]

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See detailRed Giants as Probes of the Structure and Evolution of the Milky Way
Miglio, Andrea; Montalban Iglesias, Josefa ULg; Noels-Grötsch, Arlette ULg

in Red Giants as Probes of the Structure and Evolution of the Milky Way (2012)

Not Available

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See detailCoRoT's view on variable B8/9 stars: spots versus pulsations. Evidence for differential rotation in HD 174648
Degroote, P.; Acke, B.; Samadi, R. et al

in Astronomy and Astrophysics (2011), 536

Context. There exist few variability studies of stars in the region in the Hertzsprung-Russell diagram between the A and B-star pulsational instability strips. With the aid of the high precision ... [more ▼]

Context. There exist few variability studies of stars in the region in the Hertzsprung-Russell diagram between the A and B-star pulsational instability strips. With the aid of the high precision continuous measurements of the CoRoT space satellite, low amplitudes are more easily detected, making a study of this neglected region worthwhile. <BR /> Aims: We collected a small sample of B stars observed by CoRoT to determine the origin of the different types of variability observed. <BR /> Methods: We combine literature photometry and spectroscopy to measure the fundamental parameters of the stars in the sample, and compare asteroseismic modelling of the light curves with (differentially rotating) spotted star models. <BR /> Results: We found strong evidence for the existence of spots and differential rotation in HD 174648, and formulated hypotheses for their origin. We show that the distinction between pulsations and rotational modulation is difficult to make solely based on the light curve, especially in slowly rotating stars. The CoRoT space mission was developed and is operated by the French space agency CNES, with participation of ESA's RSSD and Science Programmes, Austria, Belgium, Brazil, Germany, and Spain.Based on observations made with the ESO telescopes at La Silla Observatory under the ESO Large Programme LP182.D-0356.Based on observations made with the Mercator Telescope, operated on the island of La Palma by the Flemish Community, at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.Appendix A is available in electronic form at <A href="http://www.aanda.org">http://www.aanda.org</A> [less ▲]

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