Modelling a high-mass red giant observed by CoRoT

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 ▲]

Solar-like Oscillations in Low-luminosity Red Giants: First Results from Kepler

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 ▲]

Solar-like oscillations in cluster stars

in Astronomische Nachrichten (2010), 331

This article summaries a talk given at the HELAS IV international meeting We present a brief overview of the history of attempts to obtain a clear detection of solar-like oscillations in cluster stars ... [more ▼]

This article summaries a talk given at the HELAS IV international meeting We present a brief overview of the history of attempts to obtain a clear detection of solar-like oscillations in cluster stars, and discuss the results on the first clear detection, which was made by the Kepler Asteroseismic Science Consortium (KASC) Working Group 2. Data from Kepler. [less ▲]

Signature of main sequence internal structure in post-main sequence stars

in Communications in Asteroseismology (2009), 158

Post Main Sequence (post MS) stars keep a trace of their past main sequence history. Typically, the presence or not of an Intermediate Convective Zone (ICZ) above the H-burning shell of massive stars ... [more ▼]

Post Main Sequence (post MS) stars keep a trace of their past main sequence history. Typically, the presence or not of an Intermediate Convective Zone (ICZ) above the H-burning shell of massive stars critically depends on the details of the Main Sequence (MS) phase modeling (convection criterion, mass loss,~...). We show here how the excitation of g-modes in blue supergiant stars is closely related to this ICZ, allowing to constrain different associated physical processes. [less ▲]

First asteroseismic results from CoRoT

in Communications in Asteroseismology (2008), 156

About one year after the end of the first observational run and six months after the first CoRoT data delivery, we comment the data exploitation progress for different types of stars. We consider first ... [more ▼]

About one year after the end of the first observational run and six months after the first CoRoT data delivery, we comment the data exploitation progress for different types of stars. We consider first results to illustrate how these data of unprecedented quality shed a new light on the field of stellar seismology. [less ▲]

Calibration of the Pre-Main Sequence Binary System RS Cha: Impact of the Initial Chemical Mixture

in IAU Symposium (2007, August 01)

Accurate observational data are available for the eclipsing double-lined spectroscopic binary system RS Cha, composed of two stars in the pre-main sequence stage of evolution: masses, radii, luminosities ... [more ▼]

Accurate observational data are available for the eclipsing double-lined spectroscopic binary system RS Cha, composed of two stars in the pre-main sequence stage of evolution: masses, radii, luminosities and effective temperatures of each component and metallicity of the system. This allows to build pre-main sequence stellar models representing the components of RS Cha and to constrain them in terms of physical ingredients, initial chemical composition and age.We present stellar models we have calculated using the CESAM stellar evolution code for different sets of physical inputs (opacities, nuclear reaction rates, etc.) and different initial parameters (global metallicity, helium abundance, individual abundances of heavy elements). We discuss their ability to reproduce the observational constraints simultaneously for the two components. We focus on the impact on the models of the chemical mixture adopted and we propose a calibration for the RS Cha system providing an estimate of its age and initial helium abundance. [less ▲]

The Seismology Programme of CoRoT

in Proceedings of "The CoRoT Mission Pre-Launch Status - Stellar Seismology and Planet Finding (2006, November 01)

We introduce the main lines and specificities of the CoRoT Seismology Core Programme. The development and consolidation of this programme has been made in the framework of the CoRoT Seismology Working ... [more ▼]

We introduce the main lines and specificities of the CoRoT Seismology Core Programme. The development and consolidation of this programme has been made in the framework of the CoRoT Seismology Working Group. With a few illustrative examples, we show how CoRoT data will help to address various problems associated with present open questions of stellar structure and evolution. [less ▲]

RS Cha, a spectroscopic binary system as a test of stellar physics modeling during the pre-main sequence phase

in SF2A-2005: Semaine de l'Astrophysique Francaise (2005, December 01)

New spectra of the PMS eclipsing binary RS Cha obtained with the GIRAFFE spectrograph at the SAAO, allowed us to measure the metallicity and new masses of both components of RS Cha. The system is ... [more ▼]

New spectra of the PMS eclipsing binary RS Cha obtained with the GIRAFFE spectrograph at the SAAO, allowed us to measure the metallicity and new masses of both components of RS Cha. The system is therefore observationally well constrained, and modelling both stars (both with masses around 1.8 M[SUB]o[/SUB]) at the same (young) age is a severe challenge for stellar evolutionary codes. We find no evidence that our models are deficient. However accurate detection of modes and measurements of periods of the recently discovered pulsations in both components are required to constrain more severely the physical description of PMS stellar models. [less ▲]

ENEAS: the European Network of Excellence in AsteroSeismology

in Favata, F.; Aigrain, S.; Wilson, A. (Eds.) Second Eddington Workshop: Stellar structure and habitable planet finding, 9 - 11 April 2003, Palermo, Italy (2004, January 01)

Asteroseismology is one of the major important science topics in astrophysics in the coming decade. Several recent breakthroughs have indeed been made in Europe in this field. The observational data will ... [more ▼]

Asteroseismology is one of the major important science topics in astrophysics in the coming decade. Several recent breakthroughs have indeed been made in Europe in this field. The observational data will improve significantly in the near future, as upgraded ground-based instruments are being built and two European asteroseismic space missions are planned for launch between 2005 and 2008. They will provide us for the first time with ultra-high-accuracy, high-temporal resoluton data from space for stars other than the Sun. A successful asteroseismic study involves many different steps, from state-of-the-art raw data treatment to theoretical physical modelling of the oscillation frequencies. Our network is set up to meet the needs of combining and exchanging the different expertises of the participating institutes, of training PhD students and of both training and exchanging post-doctoral researchers. This will guarantee the most fruitful and efficient exploitation of the very substantial investments that are being made in Europe in future observations of stellar oscillations, strengthening Europe's leading position in this research field. Also, it will be a test-bed for the development of efficient procedures for collaboration across the internet, involving a vast range of procedures and skills, as well as extensive common use of a broad variety of data. Furthermore, procedures will be incorporated for the joint training of students, which is an essential part of our project. [less ▲]