We present grids of stellar models and their associated oscillation frequencies that have been used by the
CoRoT
Seismology Working Group
during the scientific preparation of the
CoRoT
mission. The ...stellar models have been calculated with the
C
ESAM stellar internal structure and evolution code while the oscillation frequencies have been obtained from the
C
ESAM models by means of the
ADIPLS
adiabatic oscillation programme. The grids cover a range of masses, chemical compositions and evolutionary stages corresponding to those of the
CoRoT
primary targets. The stellar models and oscillation frequencies are available on line through the
Evolution and Seismic Tools Activity
(ESTA) web site.
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⊙), 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 Hp. 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.
During the last decade, the understanding of fine features of the structure
and evolution of stars has become possible as a result of enormous progress
made in the acquisition of high-quality ...observational and experimental data,
and of new developments and refinements in the theoretical description of
stellar plasmas. The confrontation of high-quality observations with
sophisticated stellar models has allowed many aspects of the theory to be
validated, and several characteristics of stars relevant to Galactic evolution
and cosmology to be inferred. This paper is a review of the results of recent
studies undertaken in the context of the Hipparcos mission, taking benefit of
the high-quality astrometric data it has provided. Successes are discussed, as
well as the problems that have arisen and suggestions proposed to solve them.
Future observational and theoretical developments expected and required in the
field are also presented.
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, νmax. 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.
In this erratum, we provide corrected sets of r 01,10,02 difference ratio values and associated uncertainties, which were overestimated in the original paper (as noted by Roxburgh 2017) due to a ...missing trimming in the post-processing of the Markov chain Monte Carlo (MCMC) chains for these values. The typical reduction in the ratio uncertainties from performing the trimming is a factor of 10 (see Figure 3). Other parameters optimized in the peak-bagging (for instance, individual mode frequencies) are unaffected, as the trimming was performed for these in the original work (Lund et al. 2017). We also provide updated values for the n D 2 values of l=3 modes. We note that the values presented here, as with those presented in the original work, are obtained from a single peak-bagging procedure (see Lund et al. 2017 for details) and have yet to be verified by independent analyses using the same input power spectra. Examples of the updated tables from the original paper are given in Tables 1-3. We note that tables with individual mode parameters (Table 2) have been added for completeness, but the parameters in these tables are unchanged compared to the original paper. In addition to the corrected values mentioned above, we provide covariance matrices for the mode frequencies, frequency difference ratios (r 01,10,02), and second differences (n D 2) for the LEGACY sample (Lund et al. 2017), which were not published with the original work. The values provided by this erratum will be available in the online version of the paper. Figure 1. Comparison between ratio distribution of = r n 01, 25 (n » m 3090 Hz) for KIC 9139151 from the full (green) and properly thinned MCMC chains (black). The dashed red line (on top of the black curve) shows the distribution obtained by sampling from the reported frequency values and corresponding uncertainties (assuming that these are normally distributed and uncorrelated). The central peak is captured by both distributions, but the wide background signal representing the ratio prior has disappeared from the thinned chains. Dotted lines indicate the distribution medians; dashed lines bound the corresponding 68% highest probability density intervals.
Using VLTI/VINCI angular diameter measurements, we constrain the evolutionary status of three asteroseismic targets: the stars δ Eri, ξ Hya, η Boo. Our predictions of the mean large frequency spacing ...of these stars are in agreement with published observational estimations. Looking without success for a companion of δ Eri, we doubt its classification as an RS CVn star.
We compare stellar models produced by different stellar evolution codes for the CoRoT/ESTA project, comparing their global quantities, their physical structure, and their oscillation properties. We ...discuss the differences between models and identify the underlying reasons for these differences. The stellar models are representative of potential CoRoT targets. Overall we find very good agreement between the five different codes, but with some significant deviations. We find noticeable discrepancies (though still at the per cent level) that result from the handling of the equation of state, of the opacities and of the convective boundaries. The results of our work will be helpful in interpreting future asteroseismology results from CoRoT.
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