References of "Lebreton, Y"
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See detailThe Gaia astrophysical parameters inference system (Apsis). Pre-launch description
Bailer-Jones, C. A. L.; Andrae, R.; Arcay, B. et al

in Astronomy and Astrophysics (2013), 559

The Gaia satellite will survey the entire celestial sphere down to 20th magnitude, obtaining astrometry, photometry, and low resolution spectrophotometry on one billion astronomical sources, plus radial ... [more ▼]

The Gaia satellite will survey the entire celestial sphere down to 20th magnitude, obtaining astrometry, photometry, and low resolution spectrophotometry on one billion astronomical sources, plus radial velocities for over one hundred million stars. Its main objective is to take a census of the stellar content of our Galaxy, with the goal of revealing its formation and evolution. Gaia's unique feature is the measurement of parallaxes and proper motions with hitherto unparalleled accuracy for many objects. As a survey, the physical properties of most of these objects are unknown. Here we describe the data analysis system put together by the Gaia consortium to classify these objects and to infer their astrophysical properties using the satellite's data. This system covers single stars, (unresolved) binary stars, quasars, and galaxies, all covering a wide parameter space. Multiple methods are used for many types of stars, producing multiple results for the end user according to different models and assumptions. Prior to its application to real Gaia data the accuracy of these methods cannot be assessed definitively. But as an example of the current performance, we can attain internal accuracies (RMS residuals) on F,G,K,M dwarfs and giants at G=15 (V=15-17) for a wide range of metallicites and interstellar extinctions of around 100K in effective temperature (Teff), 0.1mag in extinction (A0), 0.2dex in metallicity ([Fe/H]), and 0.25dex in surface gravity (logg). The accuracy is a strong function of the parameters themselves, varying by a factor of more than two up or down over this parameter range. After its launch in November 2013, Gaia will nominally observe for five years, during which the system we describe will continue to evolve in light of experience with the real data. [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 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 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 detailSolar-like oscillations in cluster stars
Stello, D.; Basu, S.; Bedding, T. R. et al

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 ▲]

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See detailCan mass loss and overshooting prevent the excitation of g-modes in blue supergiants?
Godart, Mélanie ULg; Noels-Grötsch, Arlette ULg; Dupret, Marc-Antoine ULg et al

in Monthly Notices of the Royal Astronomical Society (2009), 396

Thanks to their past history on the main-sequence phase, supergiant massive stars develop a convective shell around the helium core. This intermediate convective zone (ICZ) plays an essential role in ... [more ▼]

Thanks to their past history on the main-sequence phase, supergiant massive stars develop a convective shell around the helium core. This intermediate convective zone (ICZ) plays an essential role in governing which g-modes are excited. Indeed, a strong radiative damping occurs in the high-density radiative core but the ICZ acts as a barrier preventing the propagation of some g-modes into the core. These g-modes can thus be excited in supergiant stars by the kappa-mechanism in the superficial layers due to the opacity bump of iron, at logT = 5.2. However, massive stars are submitted to various complex phenomena such as rotation, magnetic fields, semiconvection, mass loss, overshooting. Each of these phenomena exerts a significant effect on the evolution and some of them could prevent the onset of the convective zone. We develop a numerical method which allows us to select the reflected, thus the potentially excited, modes only. We study different cases in order to show that mass loss and overshooting, in a large enough amount, reduce the extent of the ICZ and are unfavourable to the excitation of g-modes. [less ▲]

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See detailSignature of main sequence internal structure in post-main sequence stars
Dupret, Marc-Antoine ULg; Godart, Mélanie ULg; Noels-Grötsch, Arlette ULg et al

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 ▲]

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See detailCoRot observations of active giants: preliminary results
Gondoin, P.; Fridlund, M.; Goupil, M. J. et al

in 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 ▲]

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See detailFirst asteroseismic results from CoRoT
Michel, Eric; Baglin, A.; Weiss, W. W. et al

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 ▲]

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See detailImpact of the new solar abundances on the calibration of the PMS binary system RS Chamaeleontis
Alecian, E.; Lebreton, Y.; Goupil, Marie-José et al

in Astronomy and Astrophysics (2007), 473

Context: In a recent work, we tried to obtain a calibration of the two components of the pre-main sequence binary system RS Cha by means of theoretical stellar models. We found that the only way to ... [more ▼]

Context: In a recent work, we tried to obtain a calibration of the two components of the pre-main sequence binary system RS Cha by means of theoretical stellar models. We found that the only way to reproduce the observational parameters of RS Cha with standard stellar models is to decrease the initial abundances of carbon and nitrogen derived from the GN93 solar mixture of heavy elements by a few tenths of dex. Aims: In this work, we aim to reproduce the observational properties of the RS Cha stars with stellar evolution models based on the new AGS05 solar mixture recently derived from a three-dimensional solar model atmosphere. The AGS05 mixture is depleted in carbon, nitrogen and oxygen with respect to the GN93 mixture. Methods: We calculated new stellar models of the RS Cha components using the AGS05 mixture and appropriate opacity tables. We sought models that simultaneously satisfy the observations of the two components (masses, radii, luminosities, effective temperatures and metallicity). Results: We find that it is possible to reproduce the observational data of the RS Cha stars with AGS05 models based on standard input physics. From these models, the initial helium content of the system is YË 0.255 and its age is Ë 9.13 ± 0.12 Myr. [less ▲]

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See detailCalibration of the Pre-Main Sequence Binary System RS Cha: Impact of the Initial Chemical Mixture
Alecian, E.; Lebreton, Y.; Goupil, M*-J et al

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 ▲]

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See detailCalibration of the pre-main sequence RS Chamaleontis binary system
Alecian, E.; Goupil, Marie-José; Lebreton, Y. et al

in Astronomy and Astrophysics (2007), 465

Context: The calibration of binary systems with accurately known masses and/or radii provides powerful tools to test stellar structure and evolution theory and to determine the age and helium content of ... [more ▼]

Context: The calibration of binary systems with accurately known masses and/or radii provides powerful tools to test stellar structure and evolution theory and to determine the age and helium content of stars. We study the eclipsing double-lined spectroscopic binary system RS Cha, for which we have accurate observations of the parameters of both stars (masses, radii, luminosities, effective temperatures and metallicity). Aims: We have calculated several sets of stellar models for the components of the RS Cha system, with the aim of reproducing simultaneously the available observational constraints and to estimate the age and initial helium abundance of the system. Methods: Using the CESAM stellar evolution code, we model both components starting from the initial mass and metallicity and adjusting the input parameters and physics in order to satisfy the observational constraints. Results: We find that the observations cannot be reproduced if we assume that the abundance ratios are solar but they are satisfied if carbon and nitrogen are depleted in the RS Cha system with respect to the Sun. This is in accordance with the abundances observed in other young stars. The RS Cha system is in an evolutionary stage at the end of the PMS phase where models are not strongly sensitive to various physical uncertainties. However we show that the oscillations of these two stars, which have been detected, would be able to discriminate between different options in the physical description of this evolutionary phase. [less ▲]

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See detailThe Seismology Programme of CoRoT
Michel, Eric; Baglin, A.; Auvergne, M. et al

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 ▲]

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See detailRS Cha, a binary system suitable for testing stellar physics modeling during the pre-main sequence phase.
Alecian, E.; Catala, C.; Goupil, Marie-José et al

in Memorie della Società Astronomica Italiana : Journal of the Italian Astronomical Society (2006), 77

We use accurate spectroscopic data of the pre-main sequence eclipsing binary system RS Cha to redetermine masses and radii of both components and to measure the metallicity of the system. Knowing all ... [more ▼]

We use accurate spectroscopic data of the pre-main sequence eclipsing binary system RS Cha to redetermine masses and radii of both components and to measure the metallicity of the system. Knowing all fundamental parameters of both stars we are able to test stellar physics modeling during the PMS phase. We find no evidence that our models are deficient. 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 ▲]

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See detailRS Cha, a spectroscopic binary system as a test of stellar physics modeling during the pre-main sequence phase
Alecian, E.; Catala, C.; Goupil, Marie-José et al

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 ▲]

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See detailAsteroseismology of delta Scuti Stars: Problems and Prospects
Goupil, Marie-José; Dupret, Marc-Antoine ULg; Samadi, R. et al

in Journal of Astrophysics & Astronomy (2005), 26

We briefly outline the state-of-the-art seismology of delta Scuti stars from a theoretical point of view: why is it so difficult a task? The recent theoretical advances in the field that these ... [more ▼]

We briefly outline the state-of-the-art seismology of delta Scuti stars from a theoretical point of view: why is it so difficult a task? The recent theoretical advances in the field that these difficulties have influenced are also discussed. [less ▲]

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See detailENEAS: the European Network of Excellence in AsteroSeismology
Aerts, C.; Baglin, A.; Christensen-Dalsgaard, J. et al

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 ▲]

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See detailCalibration of the Alpha Centauri system - Metallicity and age
Noels-Grötsch, Arlette ULg; Grevesse, Nicolas ULg; Magain, Pierre ULg et al

in Astronomy and Astrophysics (1991), 247

The binary system Alpha Cen A and B, with its well known parallax, its high quality orbit and the reasonable hypothesis of a common origin and age for both components, is a useful test of stellar ... [more ▼]

The binary system Alpha Cen A and B, with its well known parallax, its high quality orbit and the reasonable hypothesis of a common origin and age for both components, is a useful test of stellar evolution models. Evolutionary sequences are computed for 1.085 and 0.9 solar masses with different values of Z, Y and alpha (= l/Hp). Adopting luminosities and effective temperatures as derived from the observations, Z = 0.04, Y = 0.32, alpha = 1.6 and t = 5 Gyr. The Z-value derived from evolutionary sequences is very sensitive to the difference in effective temperature between the two components. [less ▲]

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