References of "Miglio, Andrea"
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See detailFast core rotation in red-giant stars as revealed by gravity-dominated mixed modes
Beck, Paul G; Montalban Iglesias, Josefa ULg; Kallinger, Thomas et al

in Nature (2012), 481

When the core hydrogen is exhausted during stellar evolution, the central region of a star contracts and the outer envelope expands and cools, giving rise to a red giant. Convection takes place over much ... [more ▼]

When the core hydrogen is exhausted during stellar evolution, the central region of a star contracts and the outer envelope expands and cools, giving rise to a red giant. Convection takes place over much of the star's radius. Conservation of angular momentum requires that the cores of these stars rotate faster than their envelopes; indirect evidence supports this. Information about the angular-momentum distribution is inaccessible to direct observations, but it can be extracted from the effect of rotation on oscillation modes that probe the stellar interior. Here we report an increasing rotation rate from the surface of the star to the stellar core in the interiors of red giants, obtained using the rotational frequency splitting of recently detected `mixed modes'. By comparison with theoretical stellar models, we conclude that the core must rotate at least ten times faster than the surface. This observational result confirms the theoretical prediction of a steep gradient in the rotation profile towards the deep stellar interior. [less ▲]

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See detailAssessing the accuracy of the surface gravity determination in late-type stars with solar-like pulsators
Morel, Thierry ULg; Miglio, Andrea ULg

in Monthly Notices of the Royal Astronomical Society (2012), 419

The frequency of maximum oscillation power measured in dwarfs and giants exhibiting solar-like pulsations provides a precise, and potentially accurate, inference of the stellar surface gravity. An ... [more ▼]

The frequency of maximum oscillation power measured in dwarfs and giants exhibiting solar-like pulsations provides a precise, and potentially accurate, inference of the stellar surface gravity. An extensive comparison for about 40 well-studied pulsating stars with gravities derived using classical methods (ionization balance, pressure-sensitive spectral features or location with respect to evolutionary tracks) supports the validity of this technique and reveals an overall remarkable agreement with mean differences not exceeding 0.05 dex (although with a dispersion of up to ˜0.2 dex). It is argued that interpolation in theoretical isochrones may be the most precise way of estimating the gravity by traditional means in nearby dwarfs. Attention is drawn to the usefulness of seismic targets as benchmarks in the context of large-scale surveys. [less ▲]

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See detailUsing seismic targets as benchmarks for spectroscopic analyses of cool stars
Morel, Thierry ULg; Miglio, Andrea ULg; Valentini, Marica ULg

in Journal of Physics: Conference Series (2011), 328

The frequency of maximum oscillation power measured in dwarfs and giants exhibiting solar-like pulsations provides a precise, and potentially accurate, inference of the stellar surface gravity. An ... [more ▼]

The frequency of maximum oscillation power measured in dwarfs and giants exhibiting solar-like pulsations provides a precise, and potentially accurate, inference of the stellar surface gravity. An extensive comparison for about 40 well-studied pulsating stars with gravities derived by traditional means (ionization balance, pressure-sensitive spectral features or location with respect to evolutionary tracks) supports the validity of this technique and reveals an overall remarkable agreement with mean differences not exceeding 0.05 dex (although with a dispersion of up to ~0.2 dex). It is argued that interpolation in theoretical isochrones may be the most precise way of estimating the gravity by traditional means in nearby dwarfs. The use of seismic targets as benchmarks in the context of forthcoming large-scale surveys (such as the follow up of the Gaia mission) is briefly discussed. [less ▲]

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See detailCoRoT's view on variable B8/9 stars: spots versus pulsations. Evidence for differential rotation in HD 174648
Degroote, P.; Acke, B.; Samadi, R. et al

in Astronomy and Astrophysics (2011), 536

Context. There exist few variability studies of stars in the region in the Hertzsprung-Russell diagram between the A and B-star pulsational instability strips. With the aid of the high precision ... [more ▼]

Context. There exist few variability studies of stars in the region in the Hertzsprung-Russell diagram between the A and B-star pulsational instability strips. With the aid of the high precision continuous measurements of the CoRoT space satellite, low amplitudes are more easily detected, making a study of this neglected region worthwhile. <BR /> Aims: We collected a small sample of B stars observed by CoRoT to determine the origin of the different types of variability observed. <BR /> Methods: We combine literature photometry and spectroscopy to measure the fundamental parameters of the stars in the sample, and compare asteroseismic modelling of the light curves with (differentially rotating) spotted star models. <BR /> Results: We found strong evidence for the existence of spots and differential rotation in HD 174648, and formulated hypotheses for their origin. We show that the distinction between pulsations and rotational modulation is difficult to make solely based on the light curve, especially in slowly rotating stars. The CoRoT space mission was developed and is operated by the French space agency CNES, with participation of ESA's RSSD and Science Programmes, Austria, Belgium, Brazil, Germany, and Spain.Based on observations made with the ESO telescopes at La Silla Observatory under the ESO Large Programme LP182.D-0356.Based on observations made with the Mercator Telescope, operated on the island of La Palma by the Flemish Community, at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.Appendix A is available in electronic form at <A href="http://www.aanda.org">http://www.aanda.org</A> [less ▲]

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See detailSolar-like oscillations from the depths of the red-giant star KIC 4351319 observed with Kepler
di Mauro, M. P.; Cardini, D.; Catanzaro, G. et al

in Monthly Notices of the Royal Astronomical Society (2011), 415

We present the results of the asteroseismic analysis of the red-giant star KIC 4351319 (TYC 3124-914-1), observed for 30 d in short-cadence mode with the Kepler satellite. The analysis has allowed us to ... [more ▼]

We present the results of the asteroseismic analysis of the red-giant star KIC 4351319 (TYC 3124-914-1), observed for 30 d in short-cadence mode with the Kepler satellite. The analysis has allowed us to determine the large and small frequency separations, ?Hz and ?Hz, respectively, and the frequency of maximum oscillation power, ?Hz. The high signal-to-noise ratio of the observations allowed us to identify 25 independent pulsation modes whose frequencies range approximately from 300 to ?Hz. The observed oscillation frequencies together with the accurate determination of the atmospheric parameters (effective temperature, gravity and metallicity), provided by additional ground-based spectroscopic observations, enabled us to theoretically interpret the observed oscillation spectrum. KIC 4351319 appears to oscillate with a well-defined solar-type p-mode pattern due to radial acoustic modes and non-radial nearly pure p modes. In addition, several non-radial mixed modes have been identified. Theoretical models well reproduce the observed oscillation frequencies and indicate that this star, located at the base of the ascending red-giant branch, is in the hydrogen-shell-burning phase, with a mass of ˜1.3 M[SUB]&sun;[/SUB], a radius of ? and an age of ˜5.6 Gyr. The main parameters of this star have been determined with an unprecedented level of precision for a red-giant star, with uncertainties of 2 per cent for mass, 7 per cent for age, 1 per cent for radius and 4 per cent for luminosity. [less ▲]

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See detailMixed modes in red-giant stars observed with CoRoT
Mosser, B.; Barban, C.; Montalban Iglesias, Josefa ULg et al

in Astronomy and Astrophysics (2011), 532

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. <BR /> 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. <BR /> 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. <BR /> 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. <BR /> 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 <A href="http://www.aanda.org">http://www.aanda.org</A> [less ▲]

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See detailTheoretical seismic properties of pre-main sequence γ Doradus pulsators
Bouabid, M*-P; Montalban Iglesias, Josefa ULg; Miglio, Andrea ULg et al

in Astronomy and Astrophysics (2011), 531

Context. The late A and F-type γ Doradus (γ Dor) stars pulsate with high-order gravity modes (g-modes). The existence of different evolutionary phases crossing the γ Dor instability strip raises the ... [more ▼]

Context. The late A and F-type γ Doradus (γ Dor) stars pulsate with high-order gravity modes (g-modes). The existence of different evolutionary phases crossing the γ Dor instability strip raises the question whether pre-main sequence (PMS) γ Dor stars exist. <BR /> Aims: We intend to study the differences between the asteroseismic behaviour of PMS and main sequence (MS) γ Dor pulsators as predicted by the current theory of stellar evolution and stability. <BR /> Methods: We explore the adiabatic and non-adiabatic properties of high-order g-modes in a grid of PMS and MS models covering the mass range 1.2 M[SUB]&sun;[/SUB] < M[SUB]∗[/SUB] < 2.5 M[SUB]&sun;[/SUB]. <BR /> Results: We have derived the theoretical instability strip (IS) for the PMS γ Dor pulsators. This IS covers the same effective temperature range as the MS γ Dor one. Nevertheless, the frequency domain of unstable modes in PMS models with a fully radiative core is greater than in MS models, even if they present the same number of unstable modes. Moreover, the differences between MS and PMS internal structures are reflected in the average values of the period spacing, as well as in the dependence of the period spacing on the radial order of the modes, opening the window to determination of the evolutionary phase of γ Dor stars from their pulsation spectra. [less ▲]

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See detailKepler Detected Gravity-Mode Period Spacings in a Red Giant Star
Beck, P. G.; Bedding, T. R.; Mosser, B. et al

in Science (2011), 332

Stellar interiors are inaccessible through direct observations. For this reason, helioseismologists made use of the Sun’s acoustic oscillation modes to tune models of its structure. The quest to detect ... [more ▼]

Stellar interiors are inaccessible through direct observations. For this reason, helioseismologists made use of the Sun’s acoustic oscillation modes to tune models of its structure. The quest to detect modes that probe the solar core has been ongoing for decades. We report the detection of mixed modes penetrating all the way to the core of an evolved star from 320 days of observations with the Kepler satellite. The period spacings of these mixed modes are directly dependent on the density gradient between the core region and the convective envelope. [less ▲]

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See detailGravity modes as a way to distinguish between hydrogen- and helium-burning red giant stars
Bedding, Timothy R; Mosser, Benoit; Huber, Daniel et al

in Nature (2011), 471

Red giants are evolved stars that have exhausted the supply of hydrogen in their cores and instead burn hydrogen in a surrounding shell. Once a red giant is sufficiently evolved, the helium in the core ... [more ▼]

Red giants are evolved stars that have exhausted the supply of hydrogen in their cores and instead burn hydrogen in a surrounding shell. Once a red giant is sufficiently evolved, the helium in the core also undergoes fusion. Outstanding issues in our understanding of red giants include uncertainties in the amount of mass lost at the surface before helium ignition and the amount of internal mixing from rotation and other processes. Progress is hampered by our inability to distinguish between red giants burning helium in the core and those still only burning hydrogen in a shell. Asteroseismology offers a way forward, being a powerful tool for probing the internal structures of stars using their natural oscillation frequencies. Here we report observations of gravity-mode period spacings in red giants that permit a distinction between evolutionary stages to be made. We use high-precision photometry obtained by the Kepler spacecraft over more than a year to measure oscillations in several hundred red giants. We find many stars whose dipole modes show sequences with approximately regular period spacings. These stars fall into two clear groups, allowing us to distinguish unambiguously between hydrogen-shell-burning stars (period spacing mostly ~50seconds) and those that are also burning helium (period spacing ~100 to 300 seconds). [less ▲]

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See detailInference from adiabatic analysis of solar-like oscillations in red giants
Montalban Iglesias, Josefa ULg; Miglio, Andrea ULg; Noels-Grötsch, Arlette ULg et al

in Astronomische Nachrichten (2010), 331

The clear detection with CoRoT and Kepler of radial and non-radial solar-like oscillations in many red giants paves the way to seismic inferences on the structure of such stars. We present an overview of ... [more ▼]

The clear detection with CoRoT and Kepler of radial and non-radial solar-like oscillations in many red giants paves the way to seismic inferences on the structure of such stars. We present an overview of the properties of the adiabatic frequencies and frequency separations of radial and non-radial oscillation modes, highlighting how their detection allows a deeper insight into the properties of the internal structure of red giants. In our study we consider models of red giants in different evolutionary stages, as well as of different masses and chemical composition. We describe how the large and small separations computed with radial modes and with non-radial modes mostly trapped in the envelope depend on the stellar global parameters and evolutionary state, and we compare our theoretical predictions and first Kepler data.Finally, we find that the properties of dipole modes constitute a promising seismic diagnostic of the evolutionary state of red-giant stars. [less ▲]

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See detailCan an underestimation of opacity explain B-type pulsators in the SMC?
Salmon, Sébastien ULg; Montalban Iglesias, Josefa ULg; Miglio, Andrea ULg et al

in Astronomische Nachrichten (2010, October 09), 331(9-10),

Slowly Pulsating B and ß Cephei are ĸ mechanism driven pulsating B stars. That ĸ mechanism works since a peak in the opacity due to a high number of atomic transitions from iron-group elements occurs in ... [more ▼]

Slowly Pulsating B and ß Cephei are ĸ mechanism driven pulsating B stars. That ĸ mechanism works since a peak in the opacity due to a high number of atomic transitions from iron-group elements occurs in the area of log T ~ 5.3. Theoretical results predict very few SPBs and no ß Cep to be encountered in low metallicity environments such as the Small Magellanic Cloud. However recent variability surveys of B stars in the SMC reported the detection of a significant number of SPB and ß Cep candidates. Though the iron content plays a major role in the excitation of ß Cep and SPB pulsations, the chemical mixture representative of the SMC B stars such as recently derived does not leave room for a significant increase of the iron abundance in these stars. Whilst abundance of iron-group elements seems reliable, is the opacity in the iron-group elements bump underestimated? We determine how the opacity profile in B-type stars should change to excite SPB and ß Cep pulsations in early-type stars of the SMC. [less ▲]

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See detailSeismic Diagnostics of Red Giants: First Comparison with Stellar Models
Montalban Iglesias, Josefa ULg; Miglio, Andrea ULg; Noels-Grötsch, Arlette ULg et al

in Astrophysical Journal Letters (2010), 721

The clear detection with CoRoT and KEPLER of radial and non-radial solar-like oscillations in many red giants paves the way for seismic inferences on the structure of such stars. We present an overview of ... [more ▼]

The clear detection with CoRoT and KEPLER of radial and non-radial solar-like oscillations in many red giants paves the way for seismic inferences on the structure of such stars. We present an overview of the properties of the adiabatic frequencies and frequency separations of radial and non-radial oscillation modes for an extended grid of models. We highlight how their detection allows a deeper insight into the internal structure and evolutionary state of red giants. In particular, we find that the properties of dipole modes constitute a promising seismic diagnostic tool of the evolutionary state of red giant stars. We compare our theoretical predictions with the first 34 days of KEPLER data and predict the frequency diagram expected for red giants in the CoRoT exofield in the galactic center direction. [less ▲]

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See detailEvidence for a sharp structure variation inside a red-giant star
Miglio, Andrea ULg; Montalban Iglesias, Josefa ULg; Carrier, F. et al

in Astronomy and Astrophysics (2010), 520

Context. The availability of precisely determined frequencies of radial and non-radial oscillation modes in red giants is finally paving the way for detailed studies of the internal structure of these ... [more ▼]

Context. The availability of precisely determined frequencies of radial and non-radial oscillation modes in red giants is finally paving the way for detailed studies of the internal structure of these stars. <BR /> Aims: We look for the seismic signature of regions of sharp structure variation in the internal structure of the CoRoT target HR 7349. <BR /> Methods: We analyse the frequency dependence of the large frequency separation and second frequency differences, as well as the behaviour of the large frequency separation obtained with the envelope auto-correlation function. <BR /> Results: We find evidence for a periodic component in the oscillation frequencies, i.e. the seismic signature of a sharp structure variation in HR 7349. In a comparison with stellar models we interpret this feature as caused by a local depression of the sound speed that occurs in the helium second-ionization region. Using solely seismic constraints this allows us to estimate the mass (M = 1.2[SUB]-0.4[/SUB][SUP]+0.6[/SUP] M_&sun;) and radius (R = 12.2[SUB]-1.8[/SUB][SUP]+2.1[/SUP] R_&sun;) of HR 7349, which agrees with the location of the star in an HR diagram. [less ▲]

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See detailOvershooting and semiconvection: structural changes and asteroseismic signatures
Noels-Grötsch, Arlette ULg; Montalban Iglesias, Josefa ULg; Miglio, Andrea ULg et al

in Astrophysics & Space Science (2010), 328

Overshooting and semiconvection are two poorly known mechanisms which affect the extent and the efficiency of chemical mixing outside classical convection zones in stars. We discuss the uncertainties and ... [more ▼]

Overshooting and semiconvection are two poorly known mechanisms which affect the extent and the efficiency of chemical mixing outside classical convection zones in stars. We discuss the uncertainties and the inferences of those processes in main sequence stars burning hydrogen in a convective core. We then focus on the asteroseismic signatures of partially or fully mixed zones surrounding the convective core, through the detailed shape of the induced chemical composition profile. We emphasize the potential power of asteroseismology to determine the internal structure of stars and thus to help us understand the physical processes at work inside the stars. [less ▲]

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See detailSolar-like Oscillations in Low-luminosity Red Giants: First Results from Kepler
Bedding, T. R.; Huber, D.; Stello, D. et al

in Astrophysical Journal (2010), 713

We have measured solar-like oscillations in red giants using time-series photometry from the first 34 days of science operations of the Kepler Mission. The light curves, obtained with 30 minute sampling ... [more ▼]

We have measured solar-like oscillations in red giants using time-series photometry from the first 34 days of science operations of the Kepler Mission. The light curves, obtained with 30 minute sampling, reveal clear oscillations in a large sample of G and K giants, extending in luminosity from the red clump down to the bottom of the giant branch. We confirm a strong correlation between the large separation of the oscillations (Πν) and the frequency of maximum power (ν[SUB]max[/SUB]). We focus on a sample of 50 low-luminosity stars (ν[SUB]max[/SUB] > 100 μHz, L <~ 30 L [SUB]sun[/SUB]) having high signal-to-noise ratios and showing the unambiguous signature of solar-like oscillations. These are H-shell-burning stars, whose oscillations should be valuable for testing models of stellar evolution and for constraining the star formation rate in the local disk. We use a new technique to compare stars on a single échelle diagram by scaling their frequencies and find well-defined ridges corresponding to radial and non-radial oscillations, including clear evidence for modes with angular degree l = 3. Measuring the small separation between l = 0 and l = 2 allows us to plot the so-called C-D diagram of δν[SUB]02[/SUB] versus Πν. The small separation δν[SUB]01[/SUB] of l = 1 from the midpoint of adjacent l = 0 modes is negative, contrary to the Sun and solar-type stars. The ridge for l = 1 is notably broadened, which we attribute to mixed modes, confirming theoretical predictions for low-luminosity giants. Overall, the results demonstrate the tremendous potential of Kepler data for asteroseismology of red giants. [less ▲]

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See detailDetection of Solar-like Oscillations from Kepler Photometry of the Open Cluster NGC 6819
Stello, Dennis; Basu, Sarbani; Bruntt, Hans et al

in Astrophysical Journal Letters (2010), 713

Asteroseismology of stars in clusters has been a long-sought goal because the assumption of a common age, distance, and initial chemical composition allows strong tests of the theory of stellar evolution ... [more ▼]

Asteroseismology of stars in clusters has been a long-sought goal because the assumption of a common age, distance, and initial chemical composition allows strong tests of the theory of stellar evolution. We report results from the first 34 days of science data from the Kepler Mission for the open cluster NGC 6819—one of the four clusters in the field of view. We obtain the first clear detections of solar-like oscillations in the cluster red giants and are able to measure the large frequency separation, Δν, and the frequency of maximum oscillation power, ν[SUB]max[/SUB]. We find that the asteroseismic parameters allow us to test cluster membership of the stars, and even with the limited seismic data in hand, we can already identify four possible non-members despite their having a better than 80% membership probability from radial velocity measurements. We are also able to determine the oscillation amplitudes for stars that span about 2 orders of magnitude in luminosity and find good agreement with the prediction that oscillation amplitudes scale as the luminosity to the power of 0.7. These early results demonstrate the unique potential of asteroseismology of the stellar clusters observed by Kepler. [less ▲]

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See detailThe Asteroseismic Potential of Kepler: First Results for Solar-Type Stars
Chaplin, W. J.; Appourchaux, T.; Elsworth, Y. et al

in Astrophysical Journal Letters (2010), 713

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 ... [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 ▲]

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See detailDeviations from a uniform period spacing of gravity modes in a massive star
Degroote, Pieter; Aerts, Conny; Baglin, Annie et al

in Nature (2010), 464

The life of a star is dominantly determined by the physical processes in the stellar interior. Unfortunately, we still have a poor understanding of how the stellar gas mixes near the stellar core ... [more ▼]

The life of a star is dominantly determined by the physical processes in the stellar interior. Unfortunately, we still have a poor understanding of how the stellar gas mixes near the stellar core, preventing precise predictions of stellar evolution. The unknown nature of the mixing processes as well as the extent of the central mixed region is particularly problematic for massive stars. Oscillations in stars with masses a few times that of the Sun offer a unique opportunity to disentangle the nature of various mixing processes, through the distinct signature they leave on period spacings in the gravity mode spectrum. Here we report the detection of numerous gravity modes in a young star with a mass of about seven solar masses. The mean period spacing allows us to estimate the extent of the convective core, and the clear periodic deviation from the mean constrains the location of the chemical transition zone to be at about 10 per cent of the radius and rules out a clear-cut profile. [less ▲]

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See detailNon-radial oscillations in the red giant HR 7349 measured by CoRoT
Carrier, F.; De Ridder, J.; Baudin, F. et al

in Astronomy and Astrophysics (2010), 509

Context. Convection in red giant stars excites resonant acoustic waves whose frequencies depend on the sound speed inside the star, which in turn depends on the properties of the stellar interior ... [more ▼]

Context. Convection in red giant stars excites resonant acoustic waves whose frequencies depend on the sound speed inside the star, which in turn depends on the properties of the stellar interior. Therefore, asteroseismology is the most robust available method for probing the internal structure of red giant stars. <BR /> Aims: Solar-like oscillations in the red giant HR 7349 are investigated. <BR /> Methods: Our study is based on a time series of 380 760 photometric measurements spread over 5 months obtained with the CoRoT satellite. Mode parameters were estimated using maximum likelihood estimation of the power spectrum. <BR /> Results: The power spectrum of the high-precision time series clearly exhibits several identifiable peaks between 19 and 40 μHz showing regularity with a mean large and small spacing of Πν = 3.47 ± 0.12 μHz and δν[SUB]02[/SUB] = 0.65 ± 0.10 μHz. Nineteen individual modes are identified with amplitudes in the range from 35 to 115 ppm. The mode damping time is estimated to be 14.7[SUP]+4.7[/SUP][SUB]-2.9[/SUB] days. The CoRoT space mission has been developed and is operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA, Germany and Spain. [less ▲]

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See detailEffects of rotation on the evolution and asteroseismic properties of red giants
Eggenberger, P.; Miglio, Andrea ULg; Montalban Iglesias, Josefa ULg et al

in Astronomy and Astrophysics (2010), 509

Context. The recent observations of solar-like oscillations in many red giant stars with the CoRoT satellite stimulated the theoretical study of the effects of various physical processes on the modelling ... [more ▼]

Context. The recent observations of solar-like oscillations in many red giant stars with the CoRoT satellite stimulated the theoretical study of the effects of various physical processes on the modelling of these stars. <BR /> Aims: The influence of rotation on the properties of red giants is studied in the context of the asteroseismic modelling of these stars. <BR /> Methods: The effects of rotation on the global and asteroseismic properties of red giant stars with a mass larger than the mass limit for degenerate He burning are investigated by comparing rotating models computed with a comprehensive treatment of shellular rotation to non-rotating ones. <BR /> Results: While red giants exhibit low surface rotational velocities, we find that the rotational history of the star has a large impact on its properties during the red giant phase. In particular, for stars massive enough to ignite He burning in non-degenerate conditions, rotational mixing induces a significant increase of the stellar luminosity and shifts the location of the core helium burning phase to a higher luminosity in the HR diagram. This of course results in a change of the seismic properties of red giants at the same evolutionary state. As a consequence the inclusion of rotation significantly changes the fundamental parameters of a red giant star as determined by performing an asteroseismic calibration. In particular rotation decreases the derived stellar mass and increases the age. Depending on the rotation law assumed in the convective envelope and on the initial velocity of the star, non-negligible values of rotational splitting can be reached, which may complicate the observation and identification of non-radial oscillation modes for red giants exhibiting moderate surface rotational velocities. By comparing the effects of rotation and overshooting, we find that the main-sequence widening and the increase of the H-burning lifetime induced by rotation (V[SUB]ini[/SUB]) = 150 km s[SUP]-1[/SUP]) are well reproduced by non-rotating models with an overshooting parameter of 0.1, while the increase of luminosity during the post-main sequence evolution is better reproduced by non-rotating models with overshooting parameters twice as large. This illustrates the fact that rotation not only increases the size of the convective core but also changes the chemical composition of the radiative zone. [less ▲]

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