scholarly journals Atomic diffusion in solar-like stars with MESA. Comparison with the Montreal/Montpellier and CESTAM stellar evolution codes

Author(s):  
B. Campilho ◽  
M. Deal ◽  
D. Bossini
2015 ◽  
Vol 11 (A29B) ◽  
pp. 600-607
Author(s):  
Richard J. Stancliffe

AbstractJust how good are modern stellar models? Providing a rigorous assessment of the uncertainties is difficult because of the multiplicity of input physics. Some of the ingredients are reasonably well-known (like reaction rates and opacities). Others are not so good, with convection standing out as a particularly obvious example. In some cases, it is not clear what the ingredients should be: what role do atomic diffusion, rotation, magnetic fields, etc. play in stellar evolution? All this is then compounded by computational method. In converting all this physics into something we can implement in a 1D evolution code, we are forced to make choices about the way the equations are solved, how we will treat mixing at convective boundaries, etc. All of this can impact the models one finally generates. In this review, I will attempt to assess the uncertainties associated with the ingredients and methods used by stellar evolution modellers, and what their impacts may be on the science that we wish to do.


2002 ◽  
Vol 12 ◽  
pp. 279-281
Author(s):  
Georges Michaud ◽  
Olivier Richard ◽  
Jacques Richer

AbstractThe availability of large atomic data bases has made it possible to calculate stellar evolution models taking into detailed account the abundance variations of all important contributors to opacity. In a first step, in addition to nuclear reactions, the atomic diffusion, radiative accelerations and opacity are continuously calculated during evolution taking the abundance changes of 28 species into account. This leads to the first self consistent main sequence stellar evolution models. In A and F stars (M≥ 1.5Mʘ) an iron peak convection zone is shown to appear at a temperature of 200000 K. The calculated surface abundance anomalies, that follow without any arbitrary parameter, are very similar to those observed in AmFm stars in open clusters except that they are larger by a factor of about 3. The second step, is then to introduce a competing hydrodynamical process. To reduce the calculated anomalies to the observed ones, turbulence has been introduced. It is found that the mixed zone must be about 5 times deeper than the iron convection zone. Detailed comparisons to a few AmFm stars have been carried out. The determination of the abundance anomalies of a large number of atomic species (20 to 30 are probably accessible) makes it possible to constrain stellar hydrodynamics. In clusters, the original abundances and age may be known and the accurate determination of surface abundances may constrain turbulence, mass loss and differential rotation when the required atomic data bases are available and used for the modeling of particle transport in stellar evolution.


2013 ◽  
Vol 63 ◽  
pp. 199-208 ◽  
Author(s):  
G. Michaud ◽  
J. Richer

2000 ◽  
Vol 198 ◽  
pp. 460-469
Author(s):  
Georges Michaud ◽  
Jacques Richer ◽  
Olivier Richard

The availability of large atomic data bases has made it possible to calculate stellar evolution models taking into detailed account the atomic diffusion of all important contributors to opacity. The radiative accelerations and the opacity are continuously calculated during evolution taking the abundance changes of 28 species into account. This leads to the first self-consistent stellar evolution models for A and F stars. In A and F stars an iron-peak convection zone appears.The calculated abundance anomalies are very similar to those observed in AmFm stars in open clusters except that they are larger by a factor of about 3. To reduce the calculated anomalies to the observed ones, an additional source of turbulence (or some other hydrodynamical process) must be introduced. The mixed zone must extend about 5 times deeper than the iron convection zone. Detailed comparisons to a few AmFm stars have been carried out.The LiBeB abundances observed in clusters give additional information. The abundances of the 28 species offer considerable constraints on the models. Various potential turbulence models have been introduced in a stellar evolution code and results of evolutionary calculations for Li gap stars are discussed in the light of the constraints offered by the abundances of LiBeB and metals. The radiative accelerations of LiBeB have also been recalculated taking the effect of changing metal abundances into account. This modifies the expected Li gap in the absence of turbulence.


Author(s):  
G. Alecian

The chemical composition measured in stellar atmospheres is not necessarily the same as in deeper layers (outside the core). Indeed, for a significant fraction of main-sequence G to B types stars the discrepancies between superficial and internal abundances go from a few percent (for the coldest of these stars) to huge factors (for hot chemically peculiar stars). This is due to atomic diffusion process, which may produces elements segregation at some stages of the stellar evolution.


2008 ◽  
Vol 4 (S252) ◽  
pp. 289-295
Author(s):  
M. Vick ◽  
G. Michaud ◽  
O. Richard

AbstractAlthough chemical separation is generally accepted as the main physical process responsible for the anomalous surface abundances of AmFm stars, its exact behavior within the interior of these stars is still uncertain. We will explore two hydrodynamical processes which could compete with atomic diffusion: mass loss and turbulence. We will also discuss the extent to which separation occurs immediately below the surface convection zone as well as the extent to which separation occurs below 200,000 K. To do so, self-consistent stellar models with mass loss and turbulence where calculated using the Montreal stellar evolution code and compared to observations of A and F stars. It is shown that to the precision of observations available for F stars, a mass loss rate of 2×10−14M⊙· yr−1, is compatible with observations and that no turbulence is then required.


1962 ◽  
Vol 11 (02) ◽  
pp. 137-143
Author(s):  
M. Schwarzschild

It is perhaps one of the most important characteristics of the past decade in astronomy that the evolution of some major classes of astronomical objects has become accessible to detailed research. The theory of the evolution of individual stars has developed into a substantial body of quantitative investigations. The evolution of galaxies, particularly of our own, has clearly become a subject for serious research. Even the history of the solar system, this close-by intriguing puzzle, may soon make the transition from being a subject of speculation to being a subject of detailed study in view of the fast flow of new data obtained with new techniques, including space-craft.


1925 ◽  
Vol 133 (4) ◽  
pp. 241-241 ◽  
Author(s):  
Henry Norris Russell
Keyword(s):  

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