On the (non-)universality of the mixing length parameter

Pinheiro, F. J. G.; Fernandes, J.

doi:10.1093/mnras/stt910

Cited by 5 publications

(5 citation statements)

References 25 publications

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Section: Resultssupporting

confidence: 88%

“…6. Results based on stellar modelling by Pinheiro & Fernandes (2013) show an opposite dependence to that of the numerical simulations, e.g. the mixing length parameter increases with the effective temperature, being thus consistent with the findings of Houdek (1996) showed that the linewidth dip becomes more pronounced with decreasing surface density if the mixing-length parameter and anisotropy of the turbulent velocity field are kept constant in the model computations.…”

Section: Resultssupporting

confidence: 86%

See 1 more Smart Citation

Oscillation mode linewidths and heights of 23 main-sequence stars observed byKepler

Appourchaux

Antia

Benomar

et al. 2014

A&A

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Context. Solar-like oscillations have been observed by Kepler and CoRoT in many solar-type stars, thereby providing a way to probe the stars using asteroseismology. Aims. We provide the mode linewidths and mode heights of the oscillations of various stars as a function of frequency and of effective temperature. Methods. We used a time series of nearly two years of data for each star. The 23 stars observed belong to the simple or F-like category. The power spectra of the 23 main-sequence stars were analysed using both maximum likelihood estimators and Bayesian estimators, providing individual mode characteristics such as frequencies, linewidths, and mode heights. We study the source of systematic errors in the mode linewidths and mode heights, and we present a way to correct these errors with respect to a common reference fit. Results. Using the correction, we can explain all sources of systematic errors, which could be reduced to less than ±15% for mode linewidths and heights, and less than ±5% for amplitude, when compared to the reference fit. The effect of a different estimated stellar background and a different estimated splitting will provide frequency-dependent systematic errors that might affect the comparison with theoretical mode linewidth and mode height, therefore affecting the understanding of the physical nature of these parameters. All other sources of relative systematic errors are less dependent upon frequency. We also provide the dependence of the so-called linewidth dip in the middle of the observed frequency range as a function of effective temperature. We show that the depth of the dip decreases with increasing effective temperature. The dependence of the dip on effective temperature may imply that the mixing length parameter α or the convective flux may increase with effective temperature.

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Section: Resultssupporting

confidence: 88%

Section: Resultssupporting

confidence: 86%

Oscillation mode linewidths and heights of 23 main-sequence stars observed byKepler

Appourchaux

Antia

Benomar

et al. 2014

A&A

View full text Add to dashboard Cite

show abstract

“…We note that the interferometric radius measurements used in each run indirectly constrain the model mass. Moreover, α mlt is known to have a significant degree of correlation with the stellar mass and effective temperature (Pinheiro and Fernandes, 2013).…”

Section: Discussionmentioning

confidence: 99%

On the Nature of the Core of α Centauri A: The Impact of the Metallicity Mixture

Nsamba

Campante

Monteiro

et al. 2019

Front. Astron. Space Sci.

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Forward asteroseismic modelling plays an important role towards a complete understanding of the physics taking place in deep stellar interiors. With a dynamical mass in the range over which models develop convective cores while in the main sequence, the solar-like oscillator α Centauri A presents itself as an interesting case study. We address the impact of varying the metallicity mixture on the determination of the energy transport process at work in the core of α Centauri A. We find that 70% of models reproducing the revised dynamical mass of α Centauri A have convective cores, regardless of the metallicity mixture adopted. This is consistent with the findings of Nsamba et al., where nuclear reaction rates were varied instead. Given these results, we propose that α Centauri A be adopted in the calibration of stellar model parameters when modelling solar-like stars with convective cores.

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“…For convection zones the mixing length theory (MLT) by Böhm-Vitense (1958) is applied, where we adopted α ML = 1.0 unless stated otherwise. We note that the value of α ML is uncertain (Pinheiro & Fernandes 2013) and may differ for stars in different evolutionary stages and/or mass ranges. Nevertheless, a mixing length parameter of the order of unity is in agreement with observations (Ferraro et al 2006;Cox & Giuli 1968).…”

Section: Modelling Of Stellar Evolution and Mass Transfermentioning

confidence: 95%

Mass transfer on a nuclear timescale in models of supergiant and ultra-luminous X-ray binaries

Quast

Langer

Tauris

2019

A&A

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Context. The origin and number of the Galactic supergiant X-ray binaries is currently not well understood. They consist of an evolved massive star and a neutron star or black hole companion. X-rays are thought to be generated from the accretion of wind material donated by the supergiant, while mass-transfer due to Roche-lobe overflow is mostly disregarded, since the high mass ratios of these systems is thought to render this process unstable. Aims. We investigate how the proximity of supergiant donor stars to the Eddington-limit, and their advanced evolutionary stage, may influence the evolution of massive and ultra-luminous X-ray binaries with supergiant donor stars (SGXBs and ULXs). Methods. We construct models of massive stars with different internal hydrogen/helium gradients and different hydrogen-rich envelope masses, and expose them to slow mass loss to probe the response of the stellar radius. In addition, we compute the corresponding Roche-lobe overflow mass-transfer evolution with our detailed binary stellar evolution code, approximating the compact objects as point masses.Results. We find that a hydrogen/helium gradient in the layers beneath the surface, as it is likely present in the well-studied donor stars of observed SGBXs, can enable nuclear timescale mass-transfer in SGXBs with a BH or a NS accretor, even for mass ratios in excess of 20. In our binary evolution models, the donor stars rapidly decrease their thermal equilibrium radius and can therefore cope with the inevitably strong orbital contraction imposed by the high mass ratio. We find the orbital period derivatives of our models in good agreement with empirical values. We argue that the SGXB phase may be preceded by a common envelope evolution. The envelope inflation near the Eddington-limit makes this mechanism more likely to occur at high metallicity. Conclusions.Our results open a new perspective for understanding the large number of Galactic SGXBs, and their almost complete absence in the SMC. They may also offer a way to obtain more ULX systems, to find nuclear timescale mass-transfer in ULX systems even with neutron star accretors, and shed new light on the origin of the strong B-field in these neutron stars.

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On the (non-)universality of the mixing length parameter

Cited by 5 publications

References 25 publications

Oscillation mode linewidths and heights of 23 main-sequence stars observed byKepler

Oscillation mode linewidths and heights of 23 main-sequence stars observed byKepler

On the Nature of the Core of α Centauri A: The Impact of the Metallicity Mixture

Mass transfer on a nuclear timescale in models of supergiant and ultra-luminous X-ray binaries

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