References of "Miglio, Andrea"
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See detailA seismic approach to testing different formation channels of subdwarf B stars
Hu, Haili; Dupret, Marc-Antoine ULg; Aerts, C. et al

in Astronomy and Astrophysics (2008), 490

Context: There are many unknowns in the formation of subdwarf B stars. Different formation channels are considered to be possible and to lead to a variety of helium-burning subdwarfs. All seismic models ... [more ▼]

Context: There are many unknowns in the formation of subdwarf B stars. Different formation channels are considered to be possible and to lead to a variety of helium-burning subdwarfs. All seismic models to date, however, assume that a subdwarf B star is a post-helium-flash-core surrounded by a thin inert layer of hydrogen. Aims: We examine an alternative formation channel, in which the subdwarf B star originates from a massive (>~2 M[SUB]o[/SUB]) red giant with a non-degenerate helium-core. Although these subdwarfs may evolve through the same region of the log g-T_eff diagram as the canonical post-flash subdwarfs, their interior structure is rather different. We examine how this difference affects their pulsation modes and whether it can be observed. Methods: Using detailed stellar evolution calculations we construct subdwarf B models from both formation channels. The iron accumulation in the driving region due to diffusion, which causes the excitation of the modes, is approximated by a Gaussian function. The pulsation modes and frequencies are calculated with a non-adiabatic pulsation code. Results: A detailed comparison of two subdwarf B models from different channels, but with the same log g and T_eff, shows that their mode excitation is different. The excited frequencies are lower for the post-flash than for the post-non-degenerate subdwarf B star. This is mainly due to the differing chemical composition of the stellar envelope. A more general comparison between two grids of models shows that the excited frequencies of most post-non-degenerate subdwarfs cannot be well-matched with the frequencies of post-flash subdwarfs. In the rare event that an acceptable seismic match is found, additional information, such as mode identification and log g and T_eff determinations, allows us to distinguish between the two formation channels. [less ▲]

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See detailCLÉS, Code Liégeois d'Évolution Stellaire
Scuflaire, Richard ULg; Théado, Sylvie; Montalban Iglesias, Josefa ULg et al

in Astrophysics & Space Science (2008), 316

CLÉS is an evolution code recently developed to produce stellar models meeting the specific requirements of studies in asteroseismology. It offers the users a lot of choices in the input physics they want ... [more ▼]

CLÉS is an evolution code recently developed to produce stellar models meeting the specific requirements of studies in asteroseismology. It offers the users a lot of choices in the input physics they want in their models and its versatility allows them to tailor the code to their needs and implement easily new features. We describe the features implemented in the current version of the code and the techniques used to solve the equations of stellar structure and evolution. A brief account is given of the use of the program and of a solar calibration realized with it. [less ▲]

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See detailThe Liège Oscillation code
Scuflaire, Richard ULg; Montalban Iglesias, Josefa ULg; Théado, S. et al

in Astrophysics & Space Science (2008), 316

The Liège Oscillation code can be used as a stand-alone program or as a library of subroutines that the user calls from a Fortran main program of his own to compute radial and nonradial adiabatic ... [more ▼]

The Liège Oscillation code can be used as a stand-alone program or as a library of subroutines that the user calls from a Fortran main program of his own to compute radial and nonradial adiabatic oscillations of stellar models. We describe the variables and the equations used by the program and the methods used to solve them. A brief account is given of the use and the output of the program. [less ▲]

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See detailProbing the properties of convective cores through g modes: high-order g modes in SPB and γ Doradus stars
Miglio, Andrea ULg; Montalban Iglesias, Josefa ULg; Noels-Grötsch, Arlette ULg et al

in Monthly Notices of the Royal Astronomical Society (2008), 386(3), 1487-1502

In main-sequence stars, the periods of high-order gravity modes are sensitive probes of stellar cores and, in particular, of the chemical composition gradient that develops near the outer edge of the ... [more ▼]

In main-sequence stars, the periods of high-order gravity modes are sensitive probes of stellar cores and, in particular, of the chemical composition gradient that develops near the outer edge of the convective core. We present an analytical approximation of high-order g modes that takes into account the effect of the μ gradient near the core. We show that in main-sequence models, similarly to the case of white dwarfs, the periods of high-order gravity modes are accurately described by a uniform period spacing superposed to an oscillatory component. The periodicity and amplitude of such component are related, respectively, to the location and sharpness of the μ gradient. We investigate the properties of high-order gravity modes for stellar models in a mass domain range between 1 and 10M[SUB]solar[/SUB], and the effects of the stellar mass, evolutionary state and extra-mixing processes on period spacing features. In particular, we show that for models of a typical Slowly Pulsating B (SPB) star, a chemical mixing that could likely be induced by the slow rotation observed in these stars is able to significantly change the g-mode spectra of the equilibrium model. Prospects and challenges for the asteroseismology of γ Doradus and SPB stars are also discussed. [less ▲]

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See detailThorough analysis of input physics in CESAM and CLÉS codes
Montalban Iglesias, Josefa ULg; Lebreton, Yveline; Miglio, Andrea ULg et al

in Astrophysics & Space Science (2008), 316(1-4), 219-229

This contribution is not about the quality of the agreement between stellar models computed by CESAM and CLÉS codes, but more interesting, on what ESTA-Task 1 run has taught us about these codes and about ... [more ▼]

This contribution is not about the quality of the agreement between stellar models computed by CESAM and CLÉS codes, but more interesting, on what ESTA-Task 1 run has taught us about these codes and about the input physics they use. We also quantify the effects of different implementations of the same physics on the seismic properties of the stellar models, that in fact is the main aim of ESTA experiments. [less ▲]

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See detailGravity modes and mixed modes as probes of stellar cores in main-sequence stars: From solar-like to β Cep stars
Miglio, Andrea ULg; Montalban Iglesias, Josefa ULg; Eggenberger, P. et al

in Astronomische Nachrichten (2008), 329

We investigate how the frequencies of gravity modes depend on the detailed properties of the chemical composition gradient that develops near the core of main-sequence stars and, therefore, on the ... [more ▼]

We investigate how the frequencies of gravity modes depend on the detailed properties of the chemical composition gradient that develops near the core of main-sequence stars and, therefore, on the transport processes that are able to modify the \mu profile in the central regions. We show that in main-sequence models, similarly to the case of white dwarfs, the periods of high-order gravity modes are accurately described by a uniform period spacing superposed to an oscillatory component. The periodicity and amplitude of such a component are related, respectively, to the location and sharpness of the \mu gradient. We briefly discuss and interpret, by means of this simple approximation, the effect of turbulent mixing near the core on the periods of both high-order and low-order g modes, as well as of modes of mixed pressure-gravity character. [less ▲]

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See detailThe effect of turbulent mixing on g-modes spectrum of MS stars
Montalban Iglesias, Josefa ULg; Miglio, Andrea ULg; Eggenberger, P. et al

in Astronomische Nachrichten (2008), 329

Understanding transport processes inside stars is one of the main goals of asteroseismology. Chemical turbulent mixing can affect the internal distribution of μ near the energy generating core, having an ... [more ▼]

Understanding transport processes inside stars is one of the main goals of asteroseismology. Chemical turbulent mixing can affect the internal distribution of μ near the energy generating core, having an effect on the evolutionary tracks similar to that of overshooting. This mixing leads to a smoother chemical composition profile near the edge of the convective core, which is reflected in the behavior of the buoyancy frequency and, therefore, in the frequencies of gravity modes. We describe the effects of convective overshooting and turbulent mixing on the frequencies of gravity modes in B-type main sequence stars. In particular, the cases of p-g mixed modes in β Cep stars and high-order modes in SPBs are considered. [less ▲]

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See detailAsteroseismic observations and modelling of 70 Ophiuchi AB
Eggenberger, P.; Miglio, Andrea ULg; Carrier, F. et al

in Journal of Physics Conference Series (2008), 118(1), 012053-

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See detailRevised instability domains of SPB and beta Cephei stars
Miglio, Andrea ULg; Montalban Iglesias, Josefa ULg; Dupret, Marc-Antoine ULg

in Communications in Asteroseismology (2007), 151

The excitation of pulsation modes in beta Cephei and Slowly Pulsating B stars is known to be very sensitive to opacity changes in the stellar interior where T Ë 2 × 10[SUP]5[/SUP] K. In this region ... [more ▼]

The excitation of pulsation modes in beta Cephei and Slowly Pulsating B stars is known to be very sensitive to opacity changes in the stellar interior where T Ë 2 × 10[SUP]5[/SUP] K. In this region differences in opacity up to Ë 50% can be induced by the choice between OPAL and OP opacity tables, and between two different metal mixtures (Grevesse & Noels 1993 and Asplund et al. 2005). We have extended the non-adiabatic computations presented in Miglio et al. (2007) towards models of higher mass and pulsation modes of degree l = 3, and we present here the instability domains in the HR- and log P-log Teff diagrams resulting from different choices of opacity tables, and for three different metallicities. [less ▲]

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See detailInstability strips of main sequence B stars: a parametric study of iron enhancement
Miglio, Andrea ULg; Bourge, P.-O.; Montalban Iglesias, Josefa ULg et al

in Communications in Asteroseismology (2007), 150

The discovery of beta Cephei stars in low metallicity environments, as well as the difficulty to theoretically explain the excitation of the pulsation modes observed in some beta Cephei and SPB stars ... [more ▼]

The discovery of beta Cephei stars in low metallicity environments, as well as the difficulty to theoretically explain the excitation of the pulsation modes observed in some beta Cephei and SPB stars, suggest that the iron opacity ``bump'' provided by standard models could be underestimated. We investigate, by means of a parametric study, the effect of a local iron enhancement on the location of the beta Cephei and SPB instability strips. [less ▲]

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See detailInstability strips of slowly pulsating B stars and beta Cephei stars: the effect of the updated OP opacities and of the metal mixture
Miglio, Andrea ULg; Montalban Iglesias, Josefa ULg; Dupret, Marc-Antoine ULg

in Monthly Notices of the Royal Astronomical Society (2007), 375

The discovery of beta Cephei stars in low-metallicity environments, as well as the difficulty in theoretically explaining the excitation of the pulsation modes observed in some beta Cephei and hybrid ... [more ▼]

The discovery of beta Cephei stars in low-metallicity environments, as well as the difficulty in theoretically explaining the excitation of the pulsation modes observed in some beta Cephei and hybrid slowly pulsating B-beta Cephei pulsators, suggest that the `iron opacity bump' provided by stellar models could be underestimated. We analyze the effect of uncertainties in the opacity computations and in the solar metal mixture on the excitation of pulsation modes in B-type stars. We carry out a pulsational stability analysis for four grids of main-sequence models with masses between 2.5 and 12M[SUB]solar[/SUB] computed with OPAL and OP opacity tables and two different metal mixtures. We find that in a typical beta Cephei model the OP opacity is 25 per cent larger than OPAL in the region where the driving of pulsation modes occurs. Furthermore, the difference in the Fe mass fraction between the two metal mixtures considered is of the order of 20 per cent. The implication on the excitation of pulsation modes is non-negligible: the blue border of the slowly pulsating B star (SPB) instability strip is displaced at higher effective temperatures, leading to a larger number of models being hybrid SPB-beta Cephei pulsators. Moreover, higher overtone p-modes are excited in beta Cephei models and unstable modes are found in a larger number of models for lower metallicities, in particular beta Cephei pulsations are also found in models with Z = 0.01. [less ▲]

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See detailAn asteroseismic study of the β cephei star θ ophiuchi : constraints on global stellar parameters and core overshooting
Briquet, Maryline ULg; Morel, Thierry ULg; Thoul, Anne ULg et al

in Monthly Notices of the Royal Astronomical Society (2007), 381(4), 1482-1488

We present a seismic study of the beta Cephei star theta Ophiuchi. Our analysis is based on the observation of one radial mode, one rotationally split l = 1 triplet and three components of a rotationally ... [more ▼]

We present a seismic study of the beta Cephei star theta Ophiuchi. Our analysis is based on the observation of one radial mode, one rotationally split l = 1 triplet and three components of a rotationally split l = 2 quintuplet for which the m values were well identified by spectroscopy. We identify the radial mode as fundamental, the triplet as p(1) and the quintuplet as g(1). Our non-local thermodynamic equilibrium abundance analysis results in a metallicity and CNO abundances in full agreement with the most recent updated solar values. With X epsilon [0.71, 0.7211] and Z epsilon [0.009, 0.015], and using the Asplund et al. mixture but with a Ne abundance about 0.3 dex larger, the matching of the three independent modes enables us to deduce constrained ranges for the mass (M = 8.2 +/- 0.3 M circle dot) and central hydrogen abundance (X-c = 0.38 +/- 0.02) of theta Oph and to prove the occurrence of core overshooting (alpha(ov) = 0.44 +/- 0.07). We also derive an equatorial rotation velocity of 29 +/- 7 km s(-1). Moreover, we show that the observed non-equidistance of the l = 1 triplet can be reproduced by the second-order effects of rotation. Finally, we show that the observed rotational splitting of two modes cannot rule out a rigid rotation model. [less ▲]

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See detailTheoretical aspects of g-mode pulsations in $\gamma$ Doradus stars
Dupret, Marc-Antoine ULg; Miglio, Andrea ULg; Grigahcène, A. et al

in Communications in Asteroseismology (2007), 150

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See detailThe new solar abundances - Part II: the crisis and possible solutions
Montalban Iglesias, Josefa ULg; Miglio, Andrea ULg; Theado, S. et al

in Communications in Asteroseismology (2006), 147

Recent 3D, NLTE analysis of the solar spectrum (Asplund et al. 2006, Part I; Asplund et al. 2005) have led to a significant reduction of the CNO and Ne abundances leading to a (Z/X) 30% smaller than the ... [more ▼]

Recent 3D, NLTE analysis of the solar spectrum (Asplund et al. 2006, Part I; Asplund et al. 2005) have led to a significant reduction of the CNO and Ne abundances leading to a (Z/X) 30% smaller than the previously recommended value. The corresponding decrease in opacity increases dramatically the discrepancies between the sound-speed derived from helioseismology and our new standard solar models (SSM). We present in this paper some numerical experiments trying to reduce this discrepancy. [less ▲]

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See detailEffects of extra-mixing processes on the periods of high-order gravity modes in main-sequence stars
Miglio, Andrea ULg; Montalban Iglesias, Josefa ULg; Noels-Grötsch, Arlette ULg

in Communications in Asteroseismology (2006), 147

In main-sequence stars, the chemical composition gradient that develops at the edge of the convective core is responsible for a non-uniform period spacing of high-order gravity modes. In this work we ... [more ▼]

In main-sequence stars, the chemical composition gradient that develops at the edge of the convective core is responsible for a non-uniform period spacing of high-order gravity modes. In this work we investigate, in the case of a 1.6 M(solar) star, the effects on the period-spacing of extra mixing processes in the core (such as diffusion and overshooting). [less ▲]

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See detailSolar Model with CNO Revised Abundances
Montalban Iglesias, Josefa ULg; Miglio, Andrea ULg; Noels-Grötsch, Arlette ULg et al

in Danesy, D. (Ed.) Proceedings of the SOHO 14 / GONG 2004 Workshop (ESA SP-559). "Helio- and Asteroseismology: Towards a Golden Future" (2004, October 01)

Recent three-dimensional, NLTE analyses of the solar spectrum have shown a significant reduction in the C, N, O and Ne abundances leading to a Z/X ratio of the order of 0.0177. We have computed solar ... [more ▼]

Recent three-dimensional, NLTE analyses of the solar spectrum have shown a significant reduction in the C, N, O and Ne abundances leading to a Z/X ratio of the order of 0.0177. We have computed solar models with this new mixture in the OPAL opacity tables. The present He abundance we find seems rather consistent with the helioseismic value. However, the convective envelope is too shallow, and diffusion, even if it reduces the discrepancy, is not able to give the current value. We present some numerical experiments consisting in changing the diffusion velocities and/or the value of opacity at the base of the convective envelope. [less ▲]

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