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 References of "Goupil, M. J"      in Complete repository Arts & humanities   Archaeology   Art & art history   Classical & oriental studies   History   Languages & linguistics   Literature   Performing arts   Philosophy & ethics   Religion & theology   Multidisciplinary, general & others Business & economic sciences   Accounting & auditing   Production, distribution & supply chain management   Finance   General management & organizational theory   Human resources management   Management information systems   Marketing   Strategy & innovation   Quantitative methods in economics & management   General economics & history of economic thought   International economics   Macroeconomics & monetary economics   Microeconomics   Economic systems & public economics   Social economics   Special economic topics (health, labor, transportation…)   Multidisciplinary, general & others Engineering, computing & technology   Aerospace & aeronautics engineering   Architecture   Chemical engineering   Civil engineering   Computer science   Electrical & electronics engineering   Energy   Geological, petroleum & mining engineering   Materials science & engineering   Mechanical engineering   Multidisciplinary, general & others Human health sciences   Alternative medicine   Anesthesia & intensive care   Cardiovascular & respiratory systems   Dentistry & oral medicine   Dermatology   Endocrinology, metabolism & nutrition   Forensic medicine   Gastroenterology & hepatology   General & internal medicine   Geriatrics   Hematology   Immunology & infectious disease   Laboratory medicine & medical technology   Neurology   Oncology   Ophthalmology   Orthopedics, rehabilitation & sports medicine   Otolaryngology   Pediatrics   Pharmacy, pharmacology & toxicology   Psychiatry   Public health, health care sciences & services   Radiology, nuclear medicine & imaging   Reproductive medicine (gynecology, andrology, obstetrics)   Rheumatology   Surgery   Urology & nephrology   Multidisciplinary, general & others Law, criminology & political science   Civil law   Criminal law & procedure   Criminology   Economic & commercial law   European & international law   Judicial law   Metalaw, Roman law, history of law & comparative law   Political science, public administration & international relations   Public law   Social law   Tax law   Multidisciplinary, general & others Life sciences   Agriculture & agronomy   Anatomy (cytology, histology, embryology...) & physiology   Animal production & animal husbandry   Aquatic sciences & oceanology   Biochemistry, biophysics & molecular biology   Biotechnology   Entomology & pest control   Environmental sciences & ecology   Food science   Genetics & genetic processes   Microbiology   Phytobiology (plant sciences, forestry, mycology...)   Veterinary medicine & animal health   Zoology   Multidisciplinary, general & others Physical, chemical, mathematical & earth Sciences   Chemistry   Earth sciences & physical geography   Mathematics   Physics   Space science, astronomy & astrophysics   Multidisciplinary, general & others Social & behavioral sciences, psychology   Animal psychology, ethology & psychobiology   Anthropology   Communication & mass media   Education & instruction   Human geography & demography   Library & information sciences   Neurosciences & behavior   Regional & inter-regional studies   Social work & social policy   Sociology & social sciences   Social, industrial & organizational psychology   Theoretical & cognitive psychology   Treatment & clinical psychology   Multidisciplinary, general & others     Showing results 1 to 20 of 21 1 2     Rotation Effects as Possible Responsible for the Surface Effects on the Sun and Solar-Type StarsSuárez, J. C.; Goupil, M. J.; Reese, Daniel et alin Suárez, Juan Carlos; Garrido, Rafael; Balona, Luis A. (Eds.) et al Stellar Pulsations (2013)One of the main sources of uncertainty in the asteroseismic models of the Sun and solar-like stars is the poor match between predicted oscillation frequencies and observed ones in the very high frequency ... [more ▼]One of the main sources of uncertainty in the asteroseismic models of the Sun and solar-like stars is the poor match between predicted oscillation frequencies and observed ones in the very high frequency domain. Today, effects of turbulence, diffusion, etc., i.e., the so-called "surface effects" are signaled as possible responsible for such a discrepancy. We show that the effect of the stellar deformation due to rotation is of the same order or even larger than these effects. We show that rotation effects, are important for the asteroseismic analysis of the Sun and solar-like stars and they cannot be neglected when modeling such stars. [less ▲]Detailed reference viewed: 12 (2 ULg) Seismic Evidence for a Rapidly Rotating Core in a Lower-giant-branch Star Observed with KeplerDeheuvels, S.; García, R. A.; Chaplin, W. J. et alin Astrophysical Journal (2012), 756Rotation is expected to have an important influence on the structure and the evolution of stars. However, the mechanisms of angular momentum transport in stars remain theoretically uncertain and very ... [more ▼]Rotation is expected to have an important influence on the structure and the evolution of stars. However, the mechanisms of angular momentum transport in stars remain theoretically uncertain and very complex to take into account in stellar models. To achieve a better understanding of these processes, we desperately need observational constraints on the internal rotation of stars, which until very recently was restricted to the Sun. In this paper, we report the detection of mixed modes—i.e., modes that behave both as g modes in the core and as p modes in the envelope—in the spectrum of the early red giant KIC 7341231, which was observed during one year with the Kepler spacecraft. By performing an analysis of the oscillation spectrum of the star, we show that its non-radial modes are clearly split by stellar rotation and we are able to determine precisely the rotational splittings of 18 modes. We then find a stellar model that reproduces very well the observed atmospheric and seismic properties of the star. We use this model to perform inversions of the internal rotation profile of the star, which enables us to show that the core of the star is rotating at least five times faster than the envelope. This will shed new light on the processes of transport of angular momentum in stars. In particular, this result can be used to place constraints on the angular momentum coupling between the core and the envelope of early red giants, which could help us discriminate between the theories that have been proposed over the last few decades. [less ▲]Detailed reference viewed: 19 (3 ULg) Estimating stellar mean density through seismic inversionsReese, Daniel ; Marques, J. P.; Goupil, M. J. et alin Astronomy and Astrophysics (2012), 539(A63), 18Determining the mass of stars is crucial both for improving stellar evolution theory and for characterising exoplanetary systems. Asteroseismology offers a promising way for estimating the stellar mean ... [more ▼]Determining the mass of stars is crucial both for improving stellar evolution theory and for characterising exoplanetary systems. Asteroseismology offers a promising way for estimating the stellar mean density. When combined with accurate radii determinations, such as are expected from GAIA, this yields accurate stellar masses. The main difficulty is finding the best way to extract the mean density of a star from a set of observed frequencies. We seek to establish a new method for estimating the stellar mean density, which combines the simplicity of a scaling law while providing the accuracy of an inversion technique. We provide a framework in which to construct and evaluate kernel-based linear inversions that directly yield the mean density of a star. We then describe three different inversion techniques (SOLA and two scaling laws) and apply them to the Sun, several test cases and three stars, alpha Cen B, HD 49933 and HD 49385, two of which are observed by CoRoT. The SOLA (subtractive optimally localised averages) approach and the scaling law based on the surface correcting technique described by Kjeldsen et al. (2008, ApJ, 683, L175) yield comparable results that can reach an accuracy of 0.5 % and are better than scaling the large frequency separation. The reason for this is that the averaging kernels from the two first methods are comparable in quality and are better than what is obtained with the large frequency separation. It is also shown that scaling the large frequency separation is more sensitive to near-surface effects, but is much less affected by an incorrect mode identification. As a result, one can identify pulsation modes by looking for an l and n assignment which provides the best agreement between the results from the large frequency separation and those from one of the two other methods. Non-linear effects are also discussed, as is the effects of mixed modes. In particular, we show that mixed modes bring little improvement to the mean density estimates because of their poorly adapted kernels. [less ▲]Detailed reference viewed: 31 (16 ULg) Modelling a high-mass red giant observed by CoRoTBaudin, F.; Barban, C.; Goupil, M. J. et alin Astronomy and Astrophysics (2012), 538Context. The advent of space-borne photometers such as CoRoT and Kepler has opened up new fields in asteroseismology. This is especially true for red giants as only a few of these stars were known to ... [more ▼]Context. The advent of space-borne photometers such as CoRoT and Kepler has opened up new fields in asteroseismology. This is especially true for red giants as only a few of these stars were known to oscillate with small amplitude, solar-like oscillations before the launch of CoRoT.
Aims: The G6 giant HR 2582 (HD 50890) was observed by CoRoT for approximately 55 days. We present here the analysis of its light curve and the characterisation of the star using different observables, such as its location in the Hertzsprung-Russell diagram and seismic observables.
Methods: Mode frequencies are extracted from the observed Fourier spectrum of the light curve. Numerical stellar models are then computed to determine the characteristics of the star (mass, age, etc.) from the comparison with observational constraints.
Results: We provide evidence for the presence of solar-like oscillations at low frequency, between 10 and 20 μHz, with a regular spacing of (1.7 ± 0.1) μHz between consecutive radial orders. Only radial modes are clearly visible. From the models compatible with the observational constraints used here, We find that HR 2582 (HD 50890) is a massive star with a mass in the range (3-5 M[SUB]&sun;[/SUB]), clearly above the red clump. It oscillates with rather low radial order (n = 5-12) modes. Its evolutionary stage cannot be determined with precision: the star could be on the ascending red giant branch (hydrogen shell burning) with an age of approximately 155 Myr or in a later phase (helium burning). In order to obtain a reasonable helium amount, the metallicity of the star must be quite subsolar. Our best models are obtained with a mixing length significantly smaller than that obtained for the Sun with the same physical description (except overshoot). The amount of core overshoot during the main-sequence phase is found to be mild, of the order of 0.1 H[SUB]p[/SUB].
Conclusions: HR 2582 (HD 50890) is an interesting case as only a few massive stars can be observed due to their rapid evolution compared to less massive red giants. HR 2582 (HD 50890) is also one of the few cases that can be used to validate the scaling relations for massive red giants stars and its sensitivity to the physics of the star. The CoRoT space mission, launched on 2006 December 27, was developed and is operated by the CNES with participation of the Science Programs of ESA; ESA's RSSD, Austria, Belgium, Brazil, Germany and Spain. [less ▲]Detailed reference viewed: 5 (0 ULg) Mixed modes in red-giant stars observed with CoRoTMosser, B.; Barban, C.; Montalban Iglesias, Josefa et alin Astronomy and Astrophysics (2011), 532Context. 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.
Aims: Up to now, the ... [more ▼]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.
Aims: Up to now, the global seismic parameters of the pressure modes have been unable to distinguish red-clump giants from members of the red-giant branch. As recently done with Kepler red giants, we intend to analyze and use the so-called mixed modes to determine the evolutionary status of the red giants observed with CoRoT. We also aim at deriving different seismic characteristics depending on evolution.
Methods: The complete identification of the pressure eigenmodes provided by the red-giant universal oscillation pattern allows us to aim at the mixed modes surrounding the ℓ = 1 expected eigenfrequencies. A dedicated method based on the envelope autocorrelation function is proposed to analyze their period separation.
Results: We have identified the mixed-mode signature separation thanks to their pattern that is compatible with the asymptotic law of gravity modes. We have shown that, independent of any modeling, the g-mode spacings help to distinguish the evolutionary status of a red-giant star. We then report the different seismic and fundamental properties of the stars, depending on their evolutionary status. In particular, we show that high-mass stars of the secondary clump present very specific seismic properties. We emphasize that stars belonging to the clump were affected by significant mass loss. We also note significant population and/or evolution differences in the different fields observed by CoRoT. The CoRoT space mission, launched 2006 December 27, was developed and is operated by the CNES, with participation of the Science Programs of ESA, ESAŠs RSSD, Austria, Belgium, Brazil, Germany, and Spain.Apeendix A is available in electronic form at http://www.aanda.org [less ▲]Detailed reference viewed: 6 (0 ULg) The underlying physical meaning of the νmax - νc relationBelkacem, K.; Goupil, M. J.; Dupret, Marc-Antoine et alin Astronomy and Astrophysics (2011), 530Asteroseismology 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 ... [more ▼]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 (ν[SUB]max[/SUB]) of solar-like oscillations and the cut-off frequency (ν[SUB]c[/SUB]). 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 ν[SUB]max[/SUB] and ν[SUB]c[/SUB], 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. [less ▲]Detailed reference viewed: 9 (2 ULg) Effect of stellar rotation on oscillation frequenciesOuazzani, R. M.; Goupil, M. J.; Dupret, Marc-Antoine et alin Astrophysics & Space Science (2010), 328We investigate whether the rotational splittings of Î² Cephei stars can give some clue about the existence of a differential rotation in latitude, and if they are contaminated by the cubic order effects ... [more ▼]We investigate whether the rotational splittings of Î² Cephei stars can give some clue about the existence of a differential rotation in latitude, and if they are contaminated by the cubic order effects of rotation on oscillation frequencies. We also study some properties of splitting asymmetries and axisymmetric mode frequencies which provide seismic constrains on the distortion of the star. We find that only non-perturbative methods are able to reproduce those two seismic characteristics within 0.01% error bars for stars when they rotate faster than 3.3% Î© [SUB] k [/SUB]. If error bars of 1% are acceptable, the threshold of validity of perturbative methods is extended to 10% Î© [SUB] k [/SUB]. [less ▲]Detailed reference viewed: 5 (1 ULg) Stochastic excitation of gravity modes in massive main-sequence starsSamadi, R.; Belkacem, Kevin ; Goupil, M. J. et alin Astrophysics & Space Science (2010), 328We investigate the possibility that gravity modes can be stochastically excited by turbulent convection in massive main-sequence (MS) stars. We build stellar models of MS stars with masses M=10 M [SUB]È¯ ... [more ▼]We investigate the possibility that gravity modes can be stochastically excited by turbulent convection in massive main-sequence (MS) stars. We build stellar models of MS stars with masses M=10 M [SUB]È¯[/SUB],15 M [SUB]È¯[/SUB], and 20 M [SUB]È¯[/SUB]. For each model, we then compute the power supplied to the modes by turbulent eddies in the convective core (CC) and the outer convective zones (OCZ). We found that, for asymptotic gravity modes, the major part of the driving occurs within the outer iron convective zone, while the excitation of low n order modes mainly occurs within the CC. We compute the mode lifetimes and deduce the expected mode amplitudes. We finally discuss the possibility of detecting such stochastically-excited gravity modes with the CoRoT space-based mission. [less ▲]Detailed reference viewed: 12 (4 ULg) Survival of a convective core in low-mass solar-like pulsator HD 203608Deheuvels, S.; Michel, Eric; Goupil, M. J. et alin Astronomy and Astrophysics (2010), 514Context. A 5-night asteroseismic observation of the F8V star HD 203608 was conducted in August 2006 with harps, followed by an analysis of the data, and a preliminary modeling of the star (Mosser et al ... [more ▼]Context. A 5-night asteroseismic observation of the F8V star HD 203608 was conducted in August 2006 with harps, followed by an analysis of the data, and a preliminary modeling of the star (Mosser et al. 2008). The stellar parameters were significantly constrained, but the behavior of one of the seismic indexes (the small spacing Î´Î½[SUB]01[/SUB]) could not be fitted with the observed one, even with the best considered models.
Aims: We study the possibility of improving the agreement between models and observations by changing the physical properties of the inner parts of the star (to which Î´Î½[SUB]01[/SUB] is sensitive).
Methods: We show that, in spite of its low mass, it is possible to produce models of HD 203608 with a convective core. No such model was considered in the preliminary modeling. In practice, we obtain these models here by assuming some extra mixing at the edge of the early convective core. We optimized the model parameters using the Levenberg-Marquardt algorithm.
Results: The agreement between the new best model with a convective core and the observations is much better than for the models without. All the observational parameters are fitted within 1-Ï observational error bars. This is the first observational evidence of a convective core in an old and low-mass star such as HD 203608. In standard models of low-mass stars, the core withdraws shortly after the ZAMS. The survival of the core until the present age of HD 203608 provides very strong constraints on the size of the mixed zone associated to the convective core. Using overshooting as a proxy to model the processes of transport at the edge of the core, we find that to reproduce both global and seismic observations, we must have Î±[SUB]{ov[/SUB]} = 0.17 Â± 0.03 H[SUB]p[/SUB] for HD 203608. We revisit the process of the extension of the core lifetime due to overshooting in the particular case of HD 203608. [less ▲]Detailed reference viewed: 5 (0 ULg) The Asteroseismic Potential of Kepler: First Results for Solar-Type StarsChaplin, W. J.; Appourchaux, T.; Elsworth, Y. et alin Astrophysical Journal Letters (2010), 713We present preliminary asteroseismic results from Kepler on three G-type stars. The observations, made at one-minute cadence during the first 33.5 days of science operations, reveal high signal-to-noise ... [more ▼]We present preliminary asteroseismic results from Kepler on three G-type stars. The observations, made at one-minute cadence during the first 33.5 days of science operations, reveal high signal-to-noise solar-like oscillation spectra in all three stars: about 20 modes of oscillation may be clearly distinguished in each star. We discuss the appearance of the oscillation spectra, use the frequencies and frequency separations to provide first results on the radii, masses, and ages of the stars, and comment in the light of these results on prospects for inference on other solar-type stars that Kepler will observe. [less ▲]Detailed reference viewed: 5 (0 ULg) 2D non-perturbative modeling of oscillations in rapidly rotating starsOuazzani, Rhita-Maria ; Dupret, Marc-Antoine ; Goupil, M. J. et alin Astronomical Notes (2010), 331We present and discuss results of a recently developped two dimensional non-perturbative method to compute accurate adiabatic oscillation modes of rapidly rotating stars . The 2D calculations fully take ... [more ▼]We present and discuss results of a recently developped two dimensional non-perturbative method to compute accurate adiabatic oscillation modes of rapidly rotating stars . The 2D calculations fully take into account the centrifugal distorsion of the star while the non-perturbative method includes the full influence of the Coriolis acceleration. These characteristics allows us to compute oscillation modes of rapid rotators - from high order p-modes in $\delta$Scuti stars, to low order p- and g-modes in $\beta$ Cephei or Be stars. [less ▲]Detailed reference viewed: 1 (0 ULg) The CoRoT target HD 49933 . II. Comparison of theoretical mode amplitudes with observationsSamadi, R.; Ludwig, H*-G; Belkacem, Kevin et alin Astronomy and Astrophysics (2010), 509Context. The seismic data obtained by CoRoT for the star HD 49933 enable us for the first time to measure directly the amplitudes and linewidths of solar-like oscillations for a star other than the Sun ... [more ▼]Context. The seismic data obtained by CoRoT for the star HD 49933 enable us for the first time to measure directly the amplitudes and linewidths of solar-like oscillations for a star other than the Sun. From those measurements it is possible, as was done for the Sun, to constrain models of the excitation of acoustic modes by turbulent convection.
Aims: We compare a stochastic excitation model described in Paper I with the asteroseismology data for HD 49933, a star that is rather metal poor and significantly hotter than the Sun.
Methods: Using the seismic determinations of the mode linewidths detected by CoRoT for HD 49933 and the theoretical mode excitation rates computed in Paper I for the specific case of HD 49933, we derive the expected surface velocity amplitudes of the acoustic modes detected in HD 49933. Using a calibrated quasi-adiabatic approximation relating the mode amplitudes in intensity to those in velocity, we derive the expected values of the mode amplitude in intensity.
Results: Except at rather high frequency, our amplitude calculations are within 1-Ï error bars of the mode surface velocity spectrum derived with the HARPS spectrograph. The same is found with respect to the mode amplitudes in intensity derived for HD 49933 from the CoRoT data. On the other hand, at high frequency (Î½ âª 1.9 mHz), our calculations depart significantly from the CoRoT and HARPS measurements. We show that assuming a solar metal abundance rather than the actual metal abundance of the star would result in a larger discrepancy with the seismic data. Furthermore, we present calculations which assume the â newâ solar chemical mixture to be in better agreement with the seismic data than those that assumed the â oldâ solar chemical mixture.
Conclusions: These results validate in the case of a star significantly hotter than the Sun and Î± Cen A the main assumptions in the model of stochastic excitation. However, the discrepancies seen at high frequency highlight some deficiencies of the modelling, whose origin remains to be understood. We also show that it is important to take the surface metal abundance of the solar-like pulsators into account. The CoRoT space mission, launched on December 27 2006, has been developped and is operated by CNES, with the contribution of Austria, Belgium, Brasil, ESA, Germany and Spain. [less ▲]Detailed reference viewed: 8 (1 ULg) The CoRoT target HD 49933 . I. Effect of the metal abundance on the mode excitation ratesSamadi, R.; Ludwig, H*-G; Belkacem, Kevin et alin Astronomy and Astrophysics (2010), 509Context. Solar-like oscillations are stochastically excited by turbulent convection at the surface layers of the stars.
Aims: We study the role of the surface metal abundance on the efficiency of ... [more ▼]Context. Solar-like oscillations are stochastically excited by turbulent convection at the surface layers of the stars.
Aims: We study the role of the surface metal abundance on the efficiency of the stochastic driving in the case of the CoRoT target HD 49933.
Methods: We compute two 3D hydrodynamical simulations representative - in effective temperature and gravity - of the surface layers of the CoRoT target HD 49933, a star that is rather metal poor and significantly hotter than the Sun. One 3D simulation has a solar metal abundance, and the other has a surface iron-to-hydrogen, [Fe/H], abundance ten times smaller. For each 3D simulation we match an associated global 1D model, and we compute the associated acoustic modes using a theoretical model of stochastic excitation validated in the case of the Sun and Î± Cen A.
Results: The rate at which energy is supplied per unit time into the acoustic modes associated with the 3D simulation with [Fe/H] = -1 is found to be about three times smaller than those associated with the 3D simulation with [Fe/H] = 0. As shown here, these differences are related to the fact that low metallicity implies surface layers with a higher mean density. In turn, a higher mean density favors smaller convective velocities and hence less efficient driving of the acoustic modes.
Conclusions: Our result shows the importance of taking the surface metal abundance into account in the modeling of the mode driving by turbulent convection. A comparison with observational data is presented in a companion paper using seismic data obtained for the CoRoT target HD 49933. The CoRoT space mission, launched on December 27, 2006, has been developped and is operated by CNES, with the contribution of Austria, Belgium, Brasil, ESA, Germany and Spain. [less ▲]Detailed reference viewed: 5 (0 ULg) Theoretical amplitudes of solar-like oscillations in classical pulsatorsBelkacem, Kevin ; Goupil, M. J.; Dupret, Marc-Antoine et alin Communications in Asteroseismology (2009), 158Seismology based on oscillation mode amplitudes allows a different probing of turbulent convection zones than usual seismology based on frequencies as shown, for instance, by Belkacem et al. (2006) for ... [more ▼]Seismology based on oscillation mode amplitudes allows a different probing of turbulent convection zones than usual seismology based on frequencies as shown, for instance, by Belkacem et al. (2006) for the Sun. Going a step further, we now turn to investigations of stochastic excitation of solar-like oscillations in superficial convective layers as well as in convective cores of stars more massive than the Sun. Issues are the frequency domain where solar-like oscillations can be excited, the expected magnitude of these oscillation amplitudes, and whether these amplitudes are detectable with the CoRoT mission. This is an important task since the detection of solar-like oscillations will provide strong seismic constraints on the dynamical properties of the convective layers. The detection of solar-like oscillations in stars such as beta Cephei or SPB stars will also help to determine their fundamental stellar parameters. [less ▲]Detailed reference viewed: 11 (2 ULg) CoRot observations of active giants: preliminary resultsGondoin, P.; Fridlund, M.; Goupil, M. J. et alin American Institute of Physics Conference Series (2009, February 01)We have analysed rotation modulated light-curves of active giants observed with CoRot using spots model. Preliminary results suggest an increase of the surface spot coverage with decreasing rotation ... [more ▼]We have analysed rotation modulated light-curves of active giants observed with CoRot using spots model. Preliminary results suggest an increase of the surface spot coverage with decreasing rotation period. A maximum of the surface spot coverage seems to occur on giants with effective temperature around 5100 K. Confirmation and interpretation of these preliminary results require groundbased follow-up observations to measure activity indicators, to identify binary systems, and to determine the stellar parameters and evolutionary status of the sample giants. [less ▲]Detailed reference viewed: 4 (1 ULg) Stochastic excitation of nonradial modes. II. Are solar asymptotic gravity modes detectable?Belkacem, Kevin ; Samadi, R.; Goupil, M. J. et alin Astronomy and Astrophysics (2009), 494Context: 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 ... [more ▼]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 × 10[SUP]5[/SUP] years for the ell=1 mode at nu=60 muHz. The maximum velocity in the considered frequency range (10-100 muHz) is obtained for the ell=1 mode at nu=60 muHz and for the ell=2 at nu=100 muHz. Due to uncertainties in the modeling, amplitudes at maximum i.e. for ell=1 at 60 muHz can range from 3 to 6 mm s[SUP]-1[/SUP]. 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. [less ▲]Detailed reference viewed: 3 (1 ULg) Modeling the excitation of acoustic modes in alpha Centauri ASamadi, R.; Belkacem, Kevin ; Goupil, M. J. et alin Astronomy and Astrophysics (2008), 489From different seismic observations we infer the energy supplied per unit of time by turbulent convection to the acoustic modes of alpha Centauri A (HD 128620), a star that is similar but not identical to ... [more ▼]From different seismic observations we infer the energy supplied per unit of time by turbulent convection to the acoustic modes of alpha Centauri 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 alpha Centauri 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 alpha Centauri 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 alpha Centauri A, as well as to confirm or not the need to include the excitation by the entropy fluctuations. [less ▲]Detailed reference viewed: 6 (1 ULg) HD 203608, a quiet asteroseismic target in the old galactic diskMosser, B.; Deheuvels, S.; Michel, Eric et alin Astronomy and Astrophysics (2008), 488Context: 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 ... [more ▼]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 muHz 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 l = 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. Based on observations obtained with the harps échelle spectrometer mounted on the 3.6-m telescope at ESO-La Silla Observatory (Chile), programme 077.D-0720. Data corresponding to Figs. [see full textsee full textsee full text], [see full textsee full textsee full text], and Table [see full textsee full textsee full text] are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/488/635 [less ▲]Detailed reference viewed: 4 (1 ULg) Impact of Transport and Dynamical Processes Upon Stellar Oscillation FrequenciesGoupil, M. J.; Dupret, Marc-Antoine in EAS Publications Series (2007)In order to prepare the theoretical interpretation of the oscillation frequencies detected by CoRoT, comparisons of results from standard stellar models by the ESTA group have proven to be very useful ... [more ▼]In order to prepare the theoretical interpretation of the oscillation frequencies detected by CoRoT, comparisons of results from standard stellar models by the ESTA group have proven to be very useful. The next issue which is briefly addressed here is what are the additional physical processes that must be included in stellar models computed with different evolutionary codes for the next comparison exercises?'' We therefore discuss the impact on oscillation frequencies of several physical processes which are still poorly understood and/or poorly modelled but cannot be fully discarded. [less ▲]Detailed reference viewed: 4 (1 ULg) Rotational Splittings with CoRoT, Expected Number of Detections and Measurement AccuracyGoupil, M. J.; Lochard, J.; Samadi, R. et alin ESA Special Publication (2006, November 01)One of the main goal of the CoRoT experiment is to determine the internal rotation of stars. A seismic measure of rotation requires the detection and an accurate measurement of rotational splittings. Our ... [more ▼]One of the main goal of the CoRoT experiment is to determine the internal rotation of stars. A seismic measure of rotation requires the detection and an accurate measurement of rotational splittings. Our ability to achieve this goal with CoRoT observations depends on the properties of the target star (in short: spectral type and distance) and will be discussed. [less ▲]Detailed reference viewed: 6 (1 ULg) 1 2