Driving and damping mechanisms in hybrid pressure-gravity modes pulsators

in Journal of Physics: Conference Series [=JPCS] (2008), 118

We study the energetic aspects of hybrid pressure-gravity modes pulsations. The case of hybrid beta Cephei-SPB pulsators is considered with special attention. In addition to the already known sensitivity ... [more ▼]

We study the energetic aspects of hybrid pressure-gravity modes pulsations. The case of hybrid beta Cephei-SPB pulsators is considered with special attention. In addition to the already known sensitivity of the driving mechanism to the heavy elements mixture (mainly the iron abundance), we show that the characteristics of the propagation and evanescent regions play also a major role, determining the extension of the stable gap in the frequency domain between the unstable low order pressure and high order gravity modes. Finally, we consider the case of hybrid delta Sct-gamma Dor pulsators. [less ▲]

CLÉS, Code Liégeois d'Évolution Stellaire

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 ▲]

Probing the properties of convective cores through g modes: high-order g modes in SPB and γ Doradus stars

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 ▲]

Gravity modes and mixed modes as probes of stellar cores in main-sequence stars: From solar-like to β Cep stars

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 ▲]

Asteroseismic observations and modelling of 70 Ophiuchi AB

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

Instability strips of main sequence B stars: a parametric study of iron enhancement

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 ▲]

An asteroseismic study of the β cephei star θ ophiuchi : constraints on global stellar parameters and core overshooting

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 ▲]

The new solar abundances - Part II: the crisis and possible solutions

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 ▲]

Solar Model with CNO Revised Abundances

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 ▲]