Absolute Properties of the Eclipsing Binary System Aq Serpentis: A Stringent Test of Convective Core Overshooting in Stellar Evolution Models

Torres, Guillermo; Vaz, L. P. R.; Lacy, Claud H.; Claret, A.

doi:10.1088/0004-6256/147/2/36

Cited by 36 publications

(30 citation statements)

References 42 publications

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“…With the usual expression d ov = α ov H p for the distance travelled by convective cells above the boundary of the core, it is clear that d ov changes as a star evolves because H p does, but α ov could well vary independently in some fashion (as speculated, e.g. by Torres et al 2014). Our measurements allow a first look into this issue.…”

Section: Discussionmentioning

confidence: 82%

The dependence of convective core overshooting on stellar mass

Claret

Torres

2016

A&A

110

118

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Context. Convective core overshooting extends the main-sequence lifetime of a star. Evolutionary tracks computed with overshooting are very different from those that use the classical Schwarzschild criterion, which leads to rather different predictions for the stellar properties. Attempts over the last two decades to calibrate the degree of overshooting with stellar mass using detached double-lined eclipsing binaries have been largely inconclusive, mainly because of a lack of suitable observational data. Aims. We revisit the question of a possible mass dependence of overshooting with a more complete sample of binaries, and examine any additional relation there might be with evolutionary state or metal abundance Z. Methods. We used a carefully selected sample of 33 double-lined eclipsing binaries strategically positioned in the H-R diagram with accurate absolute dimensions and component masses ranging from 1.2 to 4.4 M . We compared their measured properties with stellar evolution calculations to infer semi-empirical values of the overshooting parameter α ov for each star. Our models use the common prescription for the overshoot distance d ov = α ov H p , where H p is the pressure scale height at the edge of the convective core as given by the Schwarzschild criterion, and α ov is a free parameter. Results. We find a relation between α ov and mass, which is defined much more clearly than in previous work, and indicates a significant rise up to about 2 M followed by little or no change beyond this mass. No appreciable dependence is seen with evolutionary state at a given mass, or with metallicity at a given mass although the stars in our sample span a range of a factor of ten in [Fe/H], from −1.01 to +0.01.

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Section: Discussionmentioning

confidence: 82%

The dependence of convective core overshooting on stellar mass

Claret

Torres

2016

A&A

110

118

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“…Claret 2003;Southworth & Clausen 2007;Southworth 2013;Torres et al 2014). A direct computation, by means of error propagation under normality assumption, on the data presented in the cited literature showed that the correlation of the two effective temperatures is reproduced well when assuming ρ = 0.95.…”

Section: Effect Of Correlationsmentioning

confidence: 97%

“…This sometimes leads to introducing and/or calibrating some physical processes in evolutionary codes, such as convective core overshooting, or to varying the external convection efficiency through the mixing-length parameter (see e.g. Andersen 1991;Pols et al 1997;Ribas et al 2000;Torres et al 2006Torres et al , 2010Torres et al , 2014Morales et al 2009;Clausen et al 2009Clausen et al , 2010, and references therein).…”

Section: Introductionmentioning

confidence: 99%

Grid-based estimates of stellar ages in binary systems

Valle

Dell’Omodarme

Moroni

et al. 2015

A&A

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Aims. We investigate the performance of grid-based techniques in estimating the age of stars in detached eclipsing binary systems. We evaluate the precision of the estimates due to the uncertainty in the observational constraints -masses, radii, effective temperatures, and [Fe/H] -and the systematic bias caused by the uncertainty in convective core overshooting, element diffusion, mixing-length value, and initial helium content. Methods. We adopted the SCEPtER grid, which includes stars with mass in the range [0.8; 1.6] M and evolutionary stages from the zero-age main sequence to the central hydrogen depletion. Age estimates have been obtained by a generalisation of the maximum likelihood technique described in our previous work. Results. We showed that the typical 1σ random error in age estimates -due only to the uncertainty affecting the observational constraints -is about ±7%, which is nearly independent of the masses of the two stars. However, such an error strongly depends on the evolutionary phase and becomes larger and asymmetric for stars near the zero-age main sequence where it ranges from about +90% to −25%. The systematic bias due to the including convective core overshooting -for mild and strong overshooting scenariosis about 50% and 120% of the error due to observational uncertainties. A variation of ±1 in the helium-to-metal enrichment ratio ΔY/ΔZ accounts for about ±150% of the random error. The neglect of microscopic diffusion accounts for a bias of about 60% of the error due to observational uncertainties. We also introduced a statistical test of the expected difference in the recovered age of two coeval stars in a binary system. We find that random fluctuations within the current observational uncertainties can lead genuine coeval binary components to appear to be non-coeval with a difference in age as high as 60%.

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“…This or a similar test is often applied to binaries in order to test stellar evolution and investigate convective core overshooting (see e.g. Andersen 1991;Schroder et al 1997;Pols et al 1997;Clausen et al 2010;Torres et al 2010Torres et al , 2014, and references therein).…”

Section: Description Of Our Testmentioning

confidence: 99%

Bonnsai: a Bayesian tool for comparing stars with stellar evolution models

Schneider

Langer

Koter

et al. 2014

A&A

153

155

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Powerful telescopes equipped with multi-fibre or integral field spectrographs combined with detailed models of stellar atmospheres and automated fitting techniques allow for the analysis of large number of stars. These datasets contain a wealth of information that require new analysis techniques to bridge the gap between observations and stellar evolution models. To that end, we develop B (BONN Stellar Astrophysics Interface), a Bayesian statistical method, that is capable of comparing all available observables simultaneously to stellar models while taking observed uncertainties and prior knowledge such as initial mass functions and distributions of stellar rotational velocities into account. B can be used to (1) determine probability distributions of fundamental stellar parameters such as initial masses and stellar ages from complex datasets; (2) predict stellar parameters that were not yet observationally determined; and (3) test stellar models to further advance our understanding of stellar evolution. An important aspect of B is that it singles out stars that cannot be reproduced by stellar models through χ 2 hypothesis tests and posterior predictive checks. B can be used with any set of stellar models and currently supports massive main-sequence single star models of Milky Way and Large and Small Magellanic Cloud composition. We apply our new method to mock stars to demonstrate its functionality and capabilities. In a first application, we use B to test the stellar models of Brott et al. (2011, A&A, 530, A115) by comparing the stellar ages inferred for the primary and secondary stars of eclipsing Milky Way binaries of which the components range in mass between 4.5 and 28 M . Ages are determined from dynamical masses and radii that are known to better than 3%. We show that the stellar models must include rotation because stellar radii can be increased by several percent via centrifugal forces. We find that the average age difference between the primary and secondary stars of the binaries is 0.9 ± 2.3 Myr (95% CI), i.e. that the stellar models reproduce the Milky Way binaries well. The predicted effective temperatures are in agreement for observed effective temperatures for stars cooler than 25 000 K. In hotter stars, i.e. stars earlier than B1-2V and more massive than about 10 M , we find that the observed effective temperatures are on average hotter by 1.1 ± 0.3 kK (95% CI) and the bolometric luminosities are consequently larger by 0.06 ± 0.02 dex (95% CI) than predicted by the stellar models.

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Absolute Properties of the Eclipsing Binary System Aq Serpentis: A Stringent Test of Convective Core Overshooting in Stellar Evolution Models

Cited by 36 publications

References 42 publications

The dependence of convective core overshooting on stellar mass

The dependence of convective core overshooting on stellar mass

Grid-based estimates of stellar ages in binary systems

Bonnsai: a Bayesian tool for comparing stars with stellar evolution models

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