Hybrid gamma Doradus/delta Scuti Stars: Comparison Between Observations and Theory

Gamma Doradus are F-type stars pulsating with high order g-modes. Their instability strip (IS) overlaps the red edge of the delta Scuti one. This observation has led to search for objects in this region of the HR diagram showing p and g-modes simultaneously. The existence of such hybrid pulsators has recently been confirmed (Handler 2009) and the number of candidates is increasing (Matthews 2007). From a theoretical point of view, non-adiabatic computations including a time-dependent treatment of convection (TDC) predict the existence of gamma Dor/delta Sct hybrid pulsators (Dupret et al. 2004; Grigahcene et al. 2006). Our aim is to confront the properties of the observed hybrid candidates with the theoretical predictions from non-adiabatic computations of non-radial pulsations including the convection-pulsation interaction.Comment: 3 pages, 3 figures, Poster at "Stellar Pulsation: challenges for theory and observation", Santa Fe, June 200

The IACOB project. IV. New predictions for high-degree non-radial mode instability domains in massive stars and their connection with macroturbulent broadening

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. 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. 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. 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

An Improved Method of Photometric Mode Identification: Applications to Slowly Pulsating B, beta Cephei, delta Scuti and gamma Doradus Stars

peer reviewedWe present an improved version of the method of photometric mode identification based upon the inclusion of non-adiabatic eigenfunctions determined in the stellar atmosphere, according to the formalism recently proposed by Dupret et al. (2002). We apply our method to beta Cephei, Slowly Pulsating B, delta Scuti and gamma Doradus stars. Besides identifying the degree l of the pulsating stars, our method is also a tool for improving the knowledge of stellar interiors and atmospheres, by imposing constraints on the metallicity for beta Cephei and SPBs, the characteristics of the superficial convection zone for delta Scuti and gamma Doradus stars and the limb-darkening law

Stability Problems and Linear Driving

Much progress has been made through this half century in the search of driving mechanisms and selection of modes. After a short historical account tracing the steps already taken in the early days of stellar stability, quasi-adiabatic and non adiabatic oscillations are described with an emphasis on the physical meaning of the stability coefficient. A simplified picture is presented for the major driving mechanisms. Applications for the major classes of variables stars are reviewed with the problems encountered during this half century and some of the various remedies that have been proposed. At each step, a special care is given to Art CoxUs important contributions

Treatment of Opacities in Stellar Modeling and Asteroseismology

We have tested the effect of the new generation of OPAL opacities as well as a more sophisticated way of interpolating in the opacity data. New calibrated models have been computed for the binary system Alpha Centauri. Constraints given by asteroseismology are discussed

Stability of g+ Modes in a 30 M_solar Star

peer reviewe

Vibrational stability of G plus modes towards non-radial oscillations for solar models

peer reviewedThe vibrational stability of solar models towards g plus modes has been studied from the Zero Age Main Sequence (ZAMS) up to the age of 5 billion yr. The nuclear energy contribution to instability is calculated with the effective sensitivity of the reactions to change of temperature. The perturbation of convective terms is taken from an extension for nonradial oscillations of Unno's theory. The ZAMS model and the present sun are stable. However, for intermediate ages, models are unstable with respect to the lowest modes due to the effects of nuclear reactions. If, moreover, the mechanical effects of convection are taken into account, all models are unstable. However their theory is uncertain enough to require caution