New strong evidence for the importance of convective overshooting in intermediate-mass stars

Andersen, J.; Clausen, J. V.; Nordström, B.

doi:10.1086/185858

Cited by 92 publications

(80 citation statements)

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“…In the solar case (Roxburgh 1978(Roxburgh , 1989Anderson et al 1990;Spiegel & Zahn 1992), helio-seismological data suggest an OV extent of 0.05-0.1 H p Thompson et al 2003;Christensen-Dalsgaard et al 2010), while theoretical predictions from both models (Xiong 1986;Deng & Xiong 2008) and numerical simulations (Brummet et al 2002) yield results that are an order of magnitude greater. The similarity of the latter results may actually be coincidental since it is known that numerical simulations are still too viscous; for example, the Prandtl number is O(1) while the real value of O(10 −8 ) and thus the numerical simulations do not yet resolve the full spectrum of eddies, while theoretical models are based on the assumption of infinite Reynolds numbers and thus account for all the eddies (for recent review of both methods, see Kupka 2008).…”

Section: Formulation Of the Problemmentioning

confidence: 99%

Stellar mixing

Canuto

2011

A&A

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Helio-seismological data suggest an overshooting (OV) extent of 0.07 H p (H p is the pressure scale height), while theoretical predictions from both models and numerical simulations yield values that are an order of magnitude higher. The reason identified by the authors of numerical simulations is the limited range of physical parameters allowed by the numerical simulations compared to the true solar values; specifically, the simulations are still too viscous. In the case of theoretical models, we discuss limitations that at present cannot be solved. For these reasons, we propose and work out a different methodology, which has in principle the following advantages. First, there is no longer a need to model the flux of turbulent kinetic energy, which has been a stumbling block for many years and whose modeling has introduced uncertainties that are difficult to control. Second, we account for processes not included before: shear (differential rotation), meridional currents, gravitational energy, stable-unstable stratification, and double diffusion.

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Section: Formulation Of the Problemmentioning

confidence: 99%

Stellar mixing

Canuto

2011

A&A

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“…Already 20 years ago, such systems were found to provide strong evidence for convective core overshoot in intermediate mass (1.5-2.5 M ) stars (Andersen et al 1990). From a sample of 2-12 M systems, found a significantly increasing of the amount of overshoot with increasing stellar mass, whereas Claret (2007) found that it is less pronounced and more uncertain.…”

Section: Comparison With Other Binariesmentioning

confidence: 99%

Absolute dimensions of eclipsing binaries

Clausen¹,

Olsen²,

Helt³

et al. 2010

A&A

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Context. Double-lined, detached eclipsing binaries are our main source for accurate stellar masses and radii. This paper is the first in a series with focus on the upper half of the main-sequence band and tests of 1-2 M evolutionary models. Aims. We aim to determine absolute dimensions and abundances for the detached eclipsing binary V1130 Tau, and to perform a detailed comparison with results from recent stellar evolutionary models. Methods. uvby light curves and uvbyβ standard photometry have been obtained with the Strömgren Automatic Telescope, and high-resolution spectra have been acquired at the FEROS spectrograph; both are ESO, La Silla facilities. We have applied the Wilson-Devinney model for the photometric analysis, spectroscopic elements are based on radial velocities measured via broadening functions, and [Fe/H] abundances have been determined from synthetic spectra and uvby calibrations. Results. V1130 Tau is a bright (m V = 6.56), nearby (71 ± 2 pc) detached system with a circular orbit (P = 0. d 80). The components are deformed with filling factors above 0.9. Their masses and radii have been established to 0.6-0.7%. We derive a [Fe/H] abundance of −0.25 ± 0.10. The measured rotational velocities, 92.4 ± 1.1 (primary) and 104.7 ± 2.7 (secondary) km s −1 , are in fair agreement with synchronization. The larger 1.39 M secondary component has evolved to the middle of the main-sequence band and is slightly cooler than the 1.31 M primary. Yonsai-Yale, BaSTI, and Granada evolutionary models for the observed metal abundance and a "normal" He content of Y = 0.25−0.26, marginally reproduce the components at ages between 1.8 and 2.1 Gyr. All such models are, however, systematically about 200 K hotter than observed and predict ages for the more massive component, which are systematically higher than for the less massive component. These trends can not be removed by adjusting the amount of core overshoot or envelope convection level, or by including rotation in the model calculations. They may be due to proximity effects in V1130 Tau, but on the other hand, we find excellent agreement for 2.5-2.8 Gyr Granada models with a slightly lower Y of 0.23-0.24. Conclusions. V1130 Tau is a valuable addition to the very few well-studied 1-2 M binaries with component(s) in the upper half of the main-sequence band, or beyond. The stars are not evolved enough to provide new information on the dependence of core overshoot on mass (and abundance), but might -together with a larger sample of well-detached systems -be useful for further tuning of the helium enrichment law. Analyses of such systems are in progress.

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“…The deviations from the equidistant period spacing carry information on the details of the physical conditions in the stellar interior, which are otherwise inaccessible for observational testing. Observations of binaries and stellar clusters show that a mixed zone larger than what is imposed by the convection theory is required 23 . Such an additional mixing could be the result of convective overshooting, that is, the extension of convective motions above the boundary given by the local treatment of convection used in the stellar modelling (the mixing length theory).…”

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confidence: 99%

Deviations from a uniform period spacing of gravity modes in a massive star

Degroote

Aerts

Baglin

et al. 2010

Nature

168

211

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The life of a star is dominantly determined by the physical processes in the stellar interior. Unfortunately, we still have a poor understanding of how the stellar gas mixes near the stellar core, preventing precise predictions of stellar evolution 1 . The unknown nature of the mixing processes as well as the extent of the central mixed region is particularly problematic for massive stars 2 . Oscillations in stars with masses a few times that of the Sun offer a unique opportunity to disentangle the nature of various mixing processes, through the distinct signature they leave on period spacings in the gravity mode spectrum 3 . Here we report the detection of numerous gravity modes in a young star with a mass of about seven solar masses. The mean period spacing allows us to estimate the extent of the convective core, and the clear periodic deviation from the mean constrains the location of the chemical transition zone to be at about 10 per cent of the radius and rules out a clearcut profile.The young massive star HD 50230 is poorly studied, but it is known to have spectral type B3V and a visual magnitude of 8.95. HD 50230 is in its central nuclear-burning phase, just like the Sun, transforming hydrogen into helium in its core (the so-called main sequence phase). This important evolutionary phase covers about 90% of the life of the star, and the detailed internal structure of the star during this phase determines its ultimate fate 1,2 . This star is at the limiting mass of ending either as core-collapse supernova or as a white dwarf, enriching the interstellar medium with helium and heavy metals in the former case and carbon in the latter. A highquality continuous photometric light curve with 32-s sampling and with a span of 137 days has been obtained for the star by the Convection Rotation and Planetary Transits (CoRoT 4 ) satellite. A linear downward trend was removed from the data, after outliers were excluded from the light curve. The duty cycle of the final set of measurements analysed here is 88.6% and the noise has an amplitude of 1 mmag (Fig. 1). The light curve reveals the presence of numerous oscillation modes.Stellar oscillations have been found to occur at different stages of stellar life, for a range of stellar masses 5 . The best known case is that of the solar oscillations, which are acoustic modes with periods near 5 min (refs 6-9). The seismic interpretation of the detected solar oscillations led to a drastic improvement in the knowledge of the internal structure of the Sun 10,11 . Meanwhile, similar acoustic modes have been detected in various types of distant stars [12][13][14] . Gravity modes, on the other hand, probe much deeper layers inside stars and in principle allow the study of the core properties of stars far better than acoustic modes. Although such modes have been detected in massive stars similar to HD 50230 15,16 , where they have typical periods of half a day to a few days, their seismic potential could not be exploited because the number of detected modes in one star was far too lo...

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New strong evidence for the importance of convective overshooting in intermediate-mass stars

Cited by 92 publications

References 0 publications

Stellar mixing

Stellar mixing

Absolute dimensions of eclipsing binaries

Deviations from a uniform period spacing of gravity modes in a massive star

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