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Context. Realistic stellar models are essential to the forward modelling approach in asteroseismology. For practicality however, certain model assumptions are also required. For example, in the case of subdwarf B stars, one usually starts with zero-age horizontal branch structures without following the progenitor evolution.

Context. The CoRoT mission provides asteroseismic data of very high quality allowing one to adopt new statistical approaches for mode detection in power spectra, especially with respect to testing the null hypothesis (H0, which assumes that what is observed is pure noise).

Context. Solar-like oscillations have been observed in numerous red giants from ground and from space. An important question arises: could we expect to detect non-radial modes probing the internal structure of these stars?

Context. Observations suggest that a relationship exists between the driving mechanism of roAp star pulsations and the heavy element distribution in these stars.

From different seismic observations we infer the energy supplied per unit of time by turbulent convection to the acoustic modes of αCentauri A (HD 128620), a star that is similar but not identical to the Sun. The inferred rates of energy supplied to the modes (i.e. mode excitation rates) are found to be significantly higher than in the Sun. They are compared with those computed with an excitation model that includes two sources of driving, the Reynolds stress contribution and the advection of entropy fluctuations. The model also uses a closure model, the Closure Model with Plumes (CMP hereafter), that takes the asymmetry between the up- and down-flows (i.e. the granules and plumes, respectively) into account. Different prescriptions for the eddy-time correlation function are also compared to observational data. Calculations based on a Gaussian eddy-time correlation underestimate excitation rates compared with the values derived from observations for αCentauri A. On the other hand, calculations based on a Lorentzian eddy-time correlation lie within the observational error bars. This confirms results in the solar case. Compared to the helioseismic data, those obtained for αCentauri A constitute an additional support for our model of excitation. We show that mode masses must be computed taking turbulent pressure into account. Finally, we emphasize the need for more accurate seismic measurements in order to distinguish between the CMP closure model and the quasi-normal approximation in the case of αCentauri A, as well as to confirm or not the need to include the excitation by the entropy fluctuations.

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.

Context. We conducted a 5-night observing run with the spectrometer harpsat the ESO 3.6-m telescope in August 2006, to continue exploring the asteroseismic properties of F-type stars. In fact, Doppler observations of F-type on the main sequence are demanding and remain currently limited to a single case (HD 49933). Comparison with photometric results obtained with the CoRoT space mission (Convection, Rotation and planetary Transits) on similar stars will be possible with an enhanced set of observations.

Context.In a recent work, we tried to obtain a calibration of the two components of the pre-main sequence binary system RS Cha by means of theoretical stellar models. We found that the only way to reproduce the observational parameters of RS Cha with standard stellar models is to decrease the initial abundances of carbon and nitrogen derived from the GN93 solar mixture of heavy elements by a few tenths of dex.

Context.BL Cam is an extreme metal-deficient field high-amplitude SX Phe-type variable where a very complex frequency spectrum is detected, with a number of independent nonradial modes excited, unusual among the high-amplitude pulsators in the Lower Classical Instability Strip.

Context.The identification of pulsation modes in δScuti  stars is mandatory for constraining the theoretical stellar models. The non-adiabatic observables used in the photometric identification methods depend, however, on convection modeling in the external layers.

Context.The calibration of binary systems with accurately known masses and/or radii provides powerful tools to test stellar structure and evolution theory and to determine the age and helium content of stars. We study the eclipsing double-lined spectroscopic binary system RS Cha, for which we have accurate observations of the parameters of both stars (masses, radii, luminosities, effective temperatures and metallicity).

Context.This is the first step in a project to combine studies of eclipsing binaries and oscillating stars to probe the interior of Blue Stragglers (BS). This may imply a way to discriminate observationally between different birth mechanisms of BS stars.

Aims.We selected a large sample of O-B stars that were considered as (candidate) slowly pulsating B, βCep, and Maia stars after the analysis of their hipparcosdata. We analysed our new seven passband genevadata collected for these stars during the first three years of scientific operations of the mercatortelescope. We performed a frequency analysis for 28 targets with more than 50 high-quality measurements to improve their variability classification. For the pulsating stars, we tried both to identify the modes and to search for rotationally split modes.

The variability of HD 239276 was suspected photometrically nearly twenty years ago, but was confirmed with new observations obtained in 2001 during a two-site photometric campaign carried out from Spain, in uvbyβStrömgren-Crawford photometry, and China, using the Johnson Vfilter. Two low-dispersion spectra were also collected. The results establish this star as a new multiperiodic γDor-type pulsator with deficiency in metallicity. Its possible λBoo nature is discussed. The frequency analysis shows three pulsational frequencies as significant, but some more are probably present among the residuals. The method based on phase shifts and amplitude ratios in multicolour photometry is used to identify the excited modes with non-adiabatic time-dependent convection models. A very good agreement between the theoretical and observed amplitude ratios is obtained and the two main modes are identified as $l=1$modes. Nevertheless, our results do not allow us to discriminate between a solar abundance and a metal deficient nature for this star. The frequency ratio method is further used for the identification of the modes. The results suggest low metallicity for this star, but a λBoo nature may be not ruled out.

Oscillations of γDor-type were discovered in the star HD 218427 through simultaneous uvbyphotometric observations carried out in the year 2003. A few H$_{\beta}$-Crawford measurements were also collected for calibration purposes and they locate this star well inside the γDor instability region. We find HD 218427 to be deficient in metals, similar to other well-defined γDor stars, and discuss the possibility that it has a λBoo nature. We carried out frequency analysis for different filters, including the combined “vby” filter, and five frequencies were found as significant with periods ranging between 0.3 and 0.8 days. The recently-developed frequency ratio method is used in order to identify the excited modes. The results are consistent with an $l=2$identification for all the modes and with high radial quantum numbers ($n\sim40$) for the three main observed periodicities. The possibility of multiplet structures is also discussed. However, no consistency is found when using the time-dependent convection treatment to discriminate modes. This disagreement can be due to the large rotation velocity taking place in HD 218427 and, consequently, the significant coupling between the modes.

We apply here the Time Dependent Convection (TDC) treatment presented in our earlier paper in this series to the study of δSct and γDor pulsating stars. Stabilization of the δSct p-modes at the red edge of the Instability Strip (IS) and the driving of the γDor g-modes are explained by our models. Theoretical IS obtained with different values of the Mixing Length (ML) parameter αare compared to observations and a good agreement is obtained for αbetween 1.8 and 2. The influence of each term of our TDC treatment (perturbation of convective flux, turbulent pressure, and turbulent kinetic energy dissipation) on the eigenfrequencies and on the driving and damping mechanisms is investigated. Finally, we show that our TDC models predict the likely existence of hybrid stars with both δSct p-modes and γDor g-modes oscillations.

We present in details a time-dependent convection treatment in the frame of the Mixing-Length Theory (MLT). Following the original ideas by Unno (1967, PASJ, 19, 140), this theory has been developed by Gabriel et al. (1974, Bull. Ac. Roy. Belgique, Classe des Sciences, 60, 866) and Gabriel (1996, Bull. Astron. Soc. India, 24, 233). In this paper, we present it in a united form, we detail the basic derivations and approximations and give final improvements. A new perturbation of the energy closure equation is proposed for the first time, making it possible to avoid the occurrence of short wavelength spatial oscillations of the thermal eigenfunctions. This theory accounts for the perturbation of the convective flux, the turbulent Reynolds stress and the turbulent kinetic energy dissipation. It has been numerically implemented in a non-radial non-adiabatic pulsation code and the first results published in a Letter by Dupret et al. (2004a, A&A, 414, L17) indicate that the theory predicts the observed red border of the lower end of the instability strip and the driving mechanism of the recently discovered γDor stars.

We present the results of the mode identification for a sample of 7 bright southern slowly pulsating B stars showing one pulsation frequency in the $\lambda\lambda$413 nm Si II profiles. We combined the results from (1) the method of photometric amplitudes; (2) the moment method; and (3) the amplitude and phase variation across the profile to search for the $\ell$and mvalues of the modes best fitting the data. It is the first time that the applicability of these techniques is tested to a sample of main-sequence g-mode pulsators. Combining the moment method with the amplitude and phase variations across the observed line profile gives an improvement in spectroscopic identification of low degree $\ell$g-mode pulsations. Using the variations of the higher order even moments ${\langle v^4\rangle}$and ${\langle v^6\rangle}$of the moment method solutions can also help. For HD 181558, HD 24587, HD 140873 and HD 177863, the photometric and spectroscopic results are compatible and point towards $(\ell,m)$= (1, +1) sectoral modes. For HD 215573, HD 53921 and HD 92287, the results are inconclusive. Our proposed methodology for mode identification is also applicable to γDoradus stars.

We gathered long-term multicolour Geneva $UB_1BB_2V_1VG$photometric and high-resolution ($R=40\,000$) spectroscopic data of the two $\gamma\,$Doradus stars HD 12901 and HD 48501. The photometry reveals three frequencies for each of the two stars: $f_1=1.21563$c d-1, $f_2=1.39594$c d-1and $f_3=2.18636$c d-1for HD 12901 and $f_1=1.09408$c d-1, $f_2=1.29054$c d-1and $f_3=1.19924$c d-1for HD 48501. The photometric amplitude is each time largest in the Geneva B1filter and the variations in all the different filters are perfectly in phase within the measurement errors. Mode identification points out that the six modes are all $\ell=1$modes and that the non-adiabatic temperature variations are extremely small, in contradiction to current theoretical predictions. Our spectra show that all the observed frequencies are intrinsic to the stars and cannot be due to binarity. We detect clear line-profile variations at low amplitude (${<}1\,$km s-1) due to the oscillations of both targets. The estimated $v\sin\,i$from the spectra are ${\sim}53\,$km s-1for HD 12901 and ${\sim}29\,$km s-1for HD 48501. It is at present unclear if the triplet-like structure for HD 48501 is the consequence of rotational splitting or of the large separation expected for high-order gravity modes in the asymptotic regime.

Phase differences and amplitude ratios at different colour photometric bands are currently being used to discriminate pulsation modes to facilitate mode identification of κ-driven non-radial pulsating stars. In addition to physical inputs (e.g., mass, Teff, etc.), these quantities depend on the non-adiabatic treatment of the atmosphere. This paper presents theoretical results concerning δScuti pulsating stars. The envelope of each of these stellar structures possesses a convection zone whose development is determined by various factors. An interacting pulsation-atmosphere physical treatment is introduced which supplies two basic non-adiabatic physical quantities: the relative effective temperature variation and the phase lag $\phi^{\rm T}$, defined as the angle between effective temperature variation and radial displacement. These quantities can be used to derive the phase differences and amplitude ratios. Numerical values for these quantities depend critically on the αMLT parameter used to calculate the convection in the envelope. The dependence on αwas analyzed and it was found that the use of colour observations may be of considerable importance in testing the MLT. Finally, examples are given of how αintroduces uncertainties in the theoretical predictions regarding phases and amplitudes of photometric variations in δScuti pulsating stars.

New theoretical instability strips for δSct and γDor stars are presented. These results have been obtained taking into account the perturbation of the convective flux following the treatment of Gabriel ([CITE]). For the first time, the red edge of the δSct instability strip for non-radial modes is obtained. The influence of this time-dependent convection (TDC) on the driving of the γDor gravity modes is investigated. The results obtained for different values of the mixing-length parameter αare compared for the γDor models. A good agreement with observations is found for models with αbetween 1.8 and 2.0.

We perform seismic modelling of the massive $\beta\,$Cep star EN Lacertae. The starting point of our analysis is the spectroscopic mode identification recently performed. To this, we add a new updated photometric mode identification based upon a non-adiabatic description of the eigenfunctions in the outer atmosphere. Both mode identifications agree and this allows us to fine-tune the stellar parameters of EN Lacertae with unprecedented precision. This is done by producing a huge amount of stellar models with different parameters and selecting those that fulfill the frequency values and the mode identification. Our study is the first one of its kind in which a reconcilation between observed pulsational characteristics and theoretical models can be achieved at a level that allows accurate determination of the basic stellar parameters of a massive oscillator. We derive a mass of $M=9.62\pm 0.11\,M_\odot$and an age of 15.7 million years if we assume that convective overshooting does not occur.

We present an improved version of the method of photometric mode identification of Heynderickx et al. ([CITE]). Our new version is based on the inclusion of precise non-adiabatic eigenfunctions determined in the outer stellar atmosphere according to the formalism recently proposed by Dupret et al. ([CITE]). Our improved photometric mode identification technique is therefore no longer dependent on ad hoc parameters for the non-adiabatic effects. It contains the complete physical conditions of the outer atmosphere of the star, provided that rotation does not play a key role. We apply our method to the two slowly pulsating B stars HD 74560 and HD 138764 and to the ßCephei star EN (16) Lac. Besides identifying the degree $\ell$of the pulsating stars, our method is also a tool for improving the knowledge of stellar interiors and atmospheres, by imposing constraints on parameters such as the metallicity and the mixing-length parameter a(a procedure we label non-adiabatic asteroseismology).

We perform for the first time spectroscopic mode identification in the eclipsing binary $\beta\,$Cephei star EN (16) Lac. This mode identification is based upon a time series of 942 line profiles of the He I $\lambda\lambda$6678 Å line in its spectrum. All three known frequencies $f_1, f_2, f_3$of the star are present in the line-profile variations, but we failed to find additional modes. Using different identification methods we find conclusive evidence for the radial nature of the main mode and for the $\ell=2, m=0$identification of the mode with frequency f2. A unique identification of the third mode is not possible from the spectra, but we do derive that $\ell_3<3$. Fits to the amplitude and phase variability of the modes imply a rotation frequency between 0.1 and 0.4 c d-1. The star's rotation axis is not aligned with the orbital axis.

In this study, we compute theoretical line profiles of a non-radially pulsating star, taking the non-adiabatic effects into account. These non-adiabatic effects are especially important in the atmosphere, where the spectral lines are formed, and must be accounted for. In this first paper of the series, we present a new treatment of the perturbed thermal and dynamical equations in the atmosphere of a pulsating star. We apply our formalism to the computation of non-adiabatic eigenfunctions in a typical βCephei star with low order p-modes and in a typical slowly pulsating B star with high-order g-modes.

We investigate to what extent non-adiabatic temperature variations at the surface of slowly rotating non-radially pulsating βCephei stars and slowly pulsating B stars affect silicon line profile variations. We use the non-adiabatic amplitudes of the effective temperature and gravity variation presented in Dupret et al. ([CITE]), together with a Kurucz intensity grid, to compute time series of line profile variations. Our simulations point out that the line shapes do not change significantly due to temperature variations. We find equivalent width variations of at most two percent of the mean equivalent width. We confront our results with observational equivalent width variations and with photometrically obtained effective temperature variations.

A new general method for the computation of nonradial nonadiabatic oscillations of a given stellar model is presented for a linear approximation. A simple and useful modelling of the atmosphere is included, allowing to obtain credible values for the eigenfunctions in the atmosphere. Some of the results obtained for a $10 M_{\odot}$model are shown as an illustration. Our study opens the way to different applications. Better theoretical line-profile variations could be obtained from our method, allowing a more detailed comparison with observations. More generally, our study is relevant for asteroseismology, giving a way for a better knowledge of stellar interiors.

Aims. We aimed at finding a physical explanation for the occurrence of macroturbulence in the atmospheres of hot massive stars, a phenomenon found in observations for more than a decade but that remains unexplained.Methods. We computed time series of line profiles for evolved massive stars broadened by rotation and by hundreds of low-amplitude nonradial gravity-mode pulsations which are predicted to be excited for evolved massive stars.Results. In general, line profiles based on macrotubulent broadening can mimic those subject to pulsational broadening. In several cases, though, good fits require macroturbulent velocities that pass the speed of sound for realistic pulsation amplitudes. Moreover, we find that the rotation velocity can be seriously underestimated by using a simple parameter description for macroturbulence rather than an appropriate pulsational model description to fit the line profiles.Conclusions. We conclude that macroturbulence is a likely signature of the collective effect of pulsations. We provide line diagnostics and their typical values to decide whether or not pulsational broadening is present in observed line profiles, as well as a procedure to avoid an inaccurate estimation of the rotation velocity.

Context. Detection of solar gravity modes remains a major challenge to our understanding of the inner parts of the Sun. Their frequencies would enable the derivation of constraints on the core physical properties, while their amplitudes can put severe constraints on the properties of the inner convective region.Aims. Our purpose is to determine accurate theoretical amplitudes of solar g?modes and estimate the SOHO observation duration for an unambiguous detection of individual modes. We also explain differences in theoretical amplitudes derived from previous works.Methods. We investigate the stochastic excitation of modes by turbulent convection, as well as their damping. Input from a 3D?global simulation of the solar convective zone is used for the kinetic turbulent energy spectrum. Damping is computed using a parametric description of the nonlocal, time-dependent, convection-pulsation interaction. We then provide a theoretical estimation of the intrinsic, as well as apparent, surface velocity.Results. Asymptotic g-mode velocity amplitudes are found to be orders of magnitude higher than previous works. Using a 3D?numerical simulation from the ASH code, we attribute this to the temporal-correlation between the modes and the turbulent eddies, which is found to follow a Lorentzian law rather than a Gaussian one, as previously used. We also find that damping rates of asymptotic gravity modes are dominated by radiative losses, with a typical life time of 3 ?105?years for the ?=1?mode at ?=60?Hz. The maximum velocity in the considered frequency range (10-100??Hz) is obtained for the ?=1 mode at ?=60?Hz and for the ?=2 at ?=100 ?Hz. Due to uncertainties in the modeling, amplitudes at maximum i.e. for ?=1 at?60??Hz can range from?3 to?6?mm?s-1. The upper limit is too high, as g?modes would have been easily detected with SOHO, the GOLF instrument, and this sets an upper constraint mainly on the convective velocity in the Sun.

Context. We conducted a 5-night observing run with the spectrometer harps?at the ESO 3.6-m telescope in August 2006, to continue exploring the asteroseismic properties of F-type stars. In fact, Doppler observations of F-type on the main sequence are demanding and remain currently limited to a single case (HD?49933). Comparison with photometric results obtained with the CoRoT space mission (Convection, Rotation and planetary Transits) on similar stars will be possible with an enhanced set of observations.Aims. We selected the 4th magnitude F8V star HD?203608 to investigate the oscillating properties of a low-metallicity star of the old galactic disk.Methods. We reduced the spectra with the on-line data reduction software provided by the instrument. We developed a new statistical approach for extracting the significant peaks in the Fourier domain.Results. The oscillation spectrum shows a significant excess power in the frequency range [1.5, 3.0?mHz]. It exhibits a large spacing of about 120.4??Hz at 2.5?mHz. Variations of the large spacing with frequency are clearly identified, which require an adapted asymptotic development. The modes identification is based on the unambiguous signature of 15 modes with ? = 0 and?1.Conclusions. These observations show the potential diagnostic of asteroseismic constraints. Including them in the stellar modeling significantly enhances the precision on the physical parameters of HD?203608, resulting in a much more precise position in the HR?diagram. The age of the star is now determined in the range 7.25?0.07?Gyr.

Context.Turbulent motions in stellar convection zones generate acoustic energy, part of which is then supplied to normal modes of the star. Their amplitudes result from a balance between the efficiencies of excitation and damping processes in the convection zones. Aims.We develop a formalism that provides the excitation rates of non-radial global modes excited by turbulent convection. As a first application, we estimated the impact of non-radial effects on excitation rates and amplitudes of the high-angular-degree modes that are observed on the Sun. Methods.A model of stochastic excitation by turbulent convection was developed to compute the excitation rates and then successfully applied to solar radial modes. We generalise this approach to the case of non-radial global modes. This enables us to estimate the energy supplied to high-(?) acoustic modes. Qualitative arguments, as well as numerical calculations, are used to illustrate the results. Results.We find that non-radial effects for p?modes are non-negligible: - For high-n modes (i.e. typically n > 3) and for high values of ?, the power supplied to the oscillations depends on the mode inertia. - For low-n?modes, independent of the value of ?, the excitation is dominated by the non-radial components of the Reynolds stress term. Conclusions.Our numerical investigation of high-? p?modes shows that the validity of the present formalism is limited to ? < 500 due to the spatial separation of scale assumption. Thus, a model for very high-? p-mode excitation rates calls for further theoretical developments; however, the formalism is valid for solar g?modes, which will be investigated in a paper in preparation.

Context.The CoRoT mission has provided thousands of red-giant light curves. The analysis of their solar-like oscillations allows us to characterize their stellar properties.

Context.Seismic parameters such as the large Δ0and small δ02frequency separations are now being measured in a very large number of stars and begin to be used to test the physics of stellar models.

Context.The late A and F-type γDoradus (γDor) stars pulsate with high-order gravity modes (g-modes). The existence of different evolutionary phases crossing the γDor instability strip raises the question whether pre-main sequence (PMS) γDor stars exist.

Asteroseismology of stars that exhibit solar-like oscillations are enjoying a growing interest with the wealth of observational results obtained with the CoRoT and Kepler missions. In this framework, scaling laws between asteroseismic quantities and stellar parameters are becoming essential tools to study a rich variety of stars. However, the physical underlying mechanisms of those scaling laws are still poorly known. Our objective is to provide a theoretical basis for the scaling between the frequency of the maximum in the power spectrum (νmax) of solar-like oscillations and the cut-off frequency (νc). Using the SoHO GOLF observations together with theoretical considerations, we first confirm that the maximum of the height in oscillation power spectrum is determined by the so-called plateau of the damping rates. The physical origin of the plateau can be traced to the destabilizing effect of the Lagrangian perturbation of entropy in the upper-most layers, which becomes important when the modal period and the local thermal relaxation time-scale are comparable. Based on this analysis, we then find a linear relation between νmaxand νc, with a coefficient that depends on the ratio of the Mach number of the exciting turbulence to the third power to the mixing-length parameter.