References of "Mosser, B"
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See detailDifferential Seismic Modeling of Stars
Ozel, N.; Mosser, B.; Dupret, Marc-Antoine ULg et al

in Astronomical Society of the Pacific Conference Series (2013, December 01)

CoRoT (Convection Rotation and planetary Transits) observations provide the opportunity to study a large sample of stars ranging from the Main Sequence (MS) to the Red Giant Branch. With the large ... [more ▼]

CoRoT (Convection Rotation and planetary Transits) observations provide the opportunity to study a large sample of stars ranging from the Main Sequence (MS) to the Red Giant Branch. With the large increase in the number of stars showing solar-like oscillations, we intend to extract as much information as possible from a low signal-to-noise ratio (SNR) oscillation spectrum, benefiting from comparison with a reference star having similar seismic and fundamental parameters. We propose a differential method to determine stellar properties of solar-like oscillations which we call “differential seismology of stellar twins”. [less ▲]

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See detailObservations of Red Giants in the Cluster NGC 6633 by the CoRoT Space Mission and the HARPS and SOPHIE Spectrometers
Barban, C.; Baudin, F.; Poretti, E. et al

in Astronomical Society of the Pacific Conference Series (2013, December 01)

The CoRoT space mission and the HARPS and SOPHIE ground-based spectrometers have observed red giants belonging to the open cluster NGC 6633. Solar-like oscillations are detected in the CoRoT data obtained ... [more ▼]

The CoRoT space mission and the HARPS and SOPHIE ground-based spectrometers have observed red giants belonging to the open cluster NGC 6633. Solar-like oscillations are detected in the CoRoT data obtained for four red giants. Spectroscopic data questions the cluster membership of one of these stars. The combination of these photometric and spectroscopic data will be a unique opportunity to estimate their global parameters as well as to probe their internal structure. [less ▲]

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See detailDifferential asteroseismic study of seismic twins observed by CoRoT. Comparison of HD 175272 with HD 181420
Ozel, N.; Mosser, B.; Dupret, Marc-Antoine ULg et al

in Astronomy and Astrophysics (2013), 558

Context. The CoRoT short asteroseismic runs give us the opportunity to observe a large variety of late-type stars through their solar-like oscillations. We report the observation and modeling of the F5V ... [more ▼]

Context. The CoRoT short asteroseismic runs give us the opportunity to observe a large variety of late-type stars through their solar-like oscillations. We report the observation and modeling of the F5V star HD 175272. <BR /> Aims: Our aim is to define a method for extracting as much information as possible from a noisy oscillation spectrum. <BR /> Methods: We followed a differential approach that consists of using a well-known star as a reference to characterize another star. We used classical tools such as the envelope autocorrelation function to derive the global seismic parameters of the star. We compared HD 175272 with HD 181420 through a linear approach, because they appear to be asteroseismic twins. <BR /> Results: The comparison with the reference star enables us to substantially enhance the scientific output for HD 175272. First, we determined its global characteristics through a detailed seismic analysis of HD 181420. Second, with our differential approach, we measured the difference of mass, radius and age between HD 175272 and HD 181420. <BR /> Conclusions: We have developed a general method able to derive asteroseismic constraints on a star even in case of low-quality data. This method can be applied to stars with interesting properties but low signal-to-noise ratio oscillation spectrum, such as stars hosting an exoplanet or members of a binary system. 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, ESAs RSSD, Austria, Belgium, Brazil, Germany and Spain. [less ▲]

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See detailSolar-like oscillations in distant stars as seen by CoRoT : the special case of HD 42618, a solar sister
Barban, C.; Deheuvels, S.; Goupil, M. J. et al

in Journal of Physics: Conference Series (2013), 440

We report the observations of a main-sequence star, HD 42618 (T[SUB]eff[/SUB] = 5765 K, G3V) by the space telescope CoRoT. This is the closest star to the Sun ever observed by CoRoT in term of its ... [more ▼]

We report the observations of a main-sequence star, HD 42618 (T[SUB]eff[/SUB] = 5765 K, G3V) by the space telescope CoRoT. This is the closest star to the Sun ever observed by CoRoT in term of its fundamental parameters. Using a preliminary version of CoRoT light curves of HD 42618, p modes are detected around 3.2 mHz associated to l = 0, 1 and 2 modes with a large spacing of 142 μHz. Various methods are then used to derive the mass and radius of this star (scaling relations from solar values as well as comparison between theoretical and observationnal frequencies) giving values in the range of (0.80 - 1.02)M[SUB]solar[/SUB] and (0.91 - 1.01)R[SUB]solar[/SUB]. A preliminary analysis of l = 0 and 1 modes allows us also to study the amount of penetrative convection at the base of the convective envelope. [less ▲]

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See detailDifferential population studies using asteroseismology: Solar-like oscillating giants in CoRoT fields LRc01 and LRa01
Miglio, A.; Chiappini, C.; Morel, Thierry ULg et al

in European Physical Journal Web of Conferences (2013, March 01)

Solar-like oscillating giants observed by the space-borne satellites CoRoT and Kepler can be used as key tracers of stellar populations in the Milky Way. When combined with additional photometric ... [more ▼]

Solar-like oscillating giants observed by the space-borne satellites CoRoT and Kepler can be used as key tracers of stellar populations in the Milky Way. When combined with additional photometric/spectroscopic constraints, the pulsation spectra of solar-like oscillating giant stars not only reveal their radii, and hence distances, but also provide well-constrained estimates of their masses, which can be used as proxies for the ages of these evolved stars. In this contribution we provide supplementary material to the comparison we presented in Miglio et al. (2013) between populations of giants observed by CoRoT in the fields designated LRc01 and LRa01. [less ▲]

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See detailAn abundance study of the red giants in the seismology fields of the CoRoT satellite
Morel, Thierry ULg; Miglio, A.; Lagarde, N. et al

in European Physical Journal Web of Conferences (2013, March 01)

A precise characterisation of the red giants in the seismology fields of the CoRoT satellite is a prerequisite for further in-depth seismic modelling. The optical spectra obtained for 19 targets have been ... [more ▼]

A precise characterisation of the red giants in the seismology fields of the CoRoT satellite is a prerequisite for further in-depth seismic modelling. The optical spectra obtained for 19 targets have been used to accurately estimate their fundamental parameters and chemical composition. The extent of internal mixing is also investigated through the abundances of Li, CNO and Na (as well as [SUP]12[/SUP]C/[SUP]13[/SUP]C in a few cases). [less ▲]

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See detailGalactic archaeology: mapping and dating stellar populations with asteroseismology of red-giant stars
Miglio, A.; Chiappini, C.; Morel, Thierry ULg et al

in Monthly Notices of the Royal Astronomical Society (2013), 429

Our understanding of how the Galaxy was formed and evolves is severely hampered by the lack of precise constraints on basic stellar properties such as distances, masses and ages. Here, we show that solar ... [more ▼]

Our understanding of how the Galaxy was formed and evolves is severely hampered by the lack of precise constraints on basic stellar properties such as distances, masses and ages. Here, we show that solar-like pulsating red giants represent a well-populated class of accurate distance indicators, spanning a large age range, which can be used to map and date the Galactic disc in the regions probed by observations made by the CoRoT and Kepler space telescopes. When combined with photometric constraints, the pulsation spectra of such evolved stars not only reveal their radii, and hence distances, but also provide well-constrained estimates of their masses, which are reliable proxies for the ages of the stars. As a first application, we consider red giants observed by CoRoT in two different parts of the Milky Way, and determine precise distances for ˜2000 stars spread across nearly 15 000 pc of the Galactic disc, exploring regions which are a long way from the solar neighbourhood. We find significant differences in the mass distributions of these two samples which, by comparison with predictions of synthetic models of the Milky Way, we interpret as mainly due to the vertical gradient in the distribution of stellar masses (hence ages) in the disc. In the future, the availability of spectroscopic constraints for this sample of stars will not only improve the age determination, but also provide crucial constraints on age-velocity and age-metallicity relations at different Galactocentric radii and heights from the plane. [less ▲]

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See detailSeismic Evidence for a Rapidly Rotating Core in a Lower-giant-branch Star Observed with Kepler
Deheuvels, S.; García, R. A.; Chaplin, W. J. et al

in Astrophysical Journal (2012), 756

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 ... [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 ▲]

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See detailModelling a high-mass red giant observed by CoRoT
Baudin, F.; Barban, C.; Goupil, M. J. et al

in Astronomy and Astrophysics (2012), 538

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 ... [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. <BR /> 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. <BR /> 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. <BR /> 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]. <BR /> 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 ▲]

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See detailSolar-like pulsating stars as distance indicators: G-K giants in the CoRoT and Kepler fields
Miglio, A.; Morel, Thierry ULg; Barbieri, M. et al

in European Physical Journal Web of Conferences (2012, February 01)

The detection of radial and non-radial solar-like oscillations in thousands of G-K giants with CoRoT and Kepler is paving the road for detailed studies of stellar populations in the Galaxy. The available ... [more ▼]

The detection of radial and non-radial solar-like oscillations in thousands of G-K giants with CoRoT and Kepler is paving the road for detailed studies of stellar populations in the Galaxy. The available average seismic constraints allow a precise and largely model-independent determination of stellar radii (hence distances) and masses. We here briefly report on the distance determination of thousands of giants in the CoRoT and Kepler fields of view. [less ▲]

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See detailAsteroseismology of old open clusters with Kepler: direct estimate of the integrated red giant branch mass-loss in NGC 6791 and 6819
Miglio, A.; Brogaard, K.; Stello, D. et al

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

Mass-loss of red giant branch (RGB) stars is still poorly determined, despite its crucial role in the chemical enrichment of galaxies. Thanks to the recent detection of solar-like oscillations in G-K ... [more ▼]

Mass-loss of red giant branch (RGB) stars is still poorly determined, despite its crucial role in the chemical enrichment of galaxies. Thanks to the recent detection of solar-like oscillations in G-K giants in open clusters with Kepler, we can now directly determine stellar masses for a statistically significant sample of stars in the old open clusters NGC 6791 and 6819. The aim of this work is to constrain the integrated RGB mass-loss by comparing the average mass of stars in the red clump (RC) with that of stars in the low-luminosity portion of the RGB [i.e. stars with L≲L(RC)]. Stellar masses were determined by combining the available seismic parameters ν[SUB]max[/SUB] and Δν with additional photometric constraints and with independent distance estimates. We measured the masses of 40 stars on the RGB and 19 in the RC of the old metal-rich cluster NGC 6791. We find that the difference between the average mass of RGB and RC stars is small, but significant [? (random) ±0.04 (systematic) M[SUB]&sun;[/SUB]]. Interestingly, such a small ? does not support scenarios of an extreme mass-loss for this metal-rich cluster. If we describe the mass-loss rate with Reimers prescription, a first comparison with isochrones suggests that the observed ? is compatible with a mass-loss efficiency parameter in the range 0.1 ≲η≲ 0.3. Less stringent constraints on the RGB mass-loss rate are set by the analysis of the ˜2 Gyr old NGC 6819, largely due to the lower mass-loss expected for this cluster, and to the lack of an independent and accurate distance determination. In the near future, additional constraints from frequencies of individual pulsation modes and spectroscopic effective temperatures will allow further stringent tests of the Δν and ν[SUB]max[/SUB] scaling relations, which provide a novel, and potentially very accurate, means of determining stellar radii and masses. [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 detailThe underlying physical meaning of the νmax - νc relation
Belkacem, K.; Goupil, M. J.; Dupret, Marc-Antoine ULg et al

in Astronomy and Astrophysics (2011), 530

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 ... [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 ▲]

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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 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 detailSurvival of a convective core in low-mass solar-like pulsator HD 203608
Deheuvels, S.; Michel, Eric; Goupil, M. J. et al

in Astronomy and Astrophysics (2010), 514

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 ... [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 δν[SUB]01[/SUB]) could not be fitted with the observed one, even with the best considered models. <BR /> 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 δν[SUB]01[/SUB] is sensitive). <BR /> 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. <BR /> 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 α[SUB]{ov[/SUB]} = 0.17 ± 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 ▲]

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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 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 detailThe CoRoT target HD 49933 . II. Comparison of theoretical mode amplitudes with observations
Samadi, R.; Ludwig, H*-G; Belkacem, Kevin ULg et al

in Astronomy and Astrophysics (2010), 509

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 ... [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. <BR /> 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. <BR /> 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. <BR /> 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 (ν ⪠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. <BR /> Conclusions: These results validate in the case of a star significantly hotter than the Sun and α 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 ▲]

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