Stellar structure and stellar evolution

1991 ◽  
pp. 2-95
Author(s):  
Camiel Bert de Loore
Keyword(s):  
Stellar Evolution ◽  
Stellar Structure

scholarly journals Physical mechanisms of mixing in stellar interiors

1984 ◽  
Vol 105 ◽  
pp. 491-512
Author(s):  
Evry Schatzman
Keyword(s):  
Diffusion Equation ◽  
Stellar Evolution ◽  
Turbulent Mixing ◽  
Nuclear Reactions ◽  
Chemical Elements ◽  
Solar Neutrinos ◽  
Stellar Structure ◽  
Physical Mechanisms ◽  
Nitrogen Abundance ◽  
Stellar Interiors

The different mechanisms by which mixing can take place in stellar interiors are considered : the classical Rayleigh-Benard instability with penetrative convection and over-shooting, semi-convection, gravitationnal and radiative settling, turbulent mixing. The latter mechanism is thoroughly described, from the driving force of turbulent mixing to its influence on stellar structure, stellar evolution and the analysis of the corresponding observationnal data.Turbulent mixing has to be considered each time the building up of a concentration gradient takes place, either by gravitationnal or radiative settling or by nuclear reactions. Turbulent mixing, as a first approximation, can be described by an isotropic diffusion coefficient. The process is then governed by a diffusion equation. The behaviour of the solution of the diffusion equation needs some explanation in order to be well understood.A number of examples concerning surface abundances of chemical elements are given (3He, 7Li, Be, 12C, 13C, 14N), as well as a discussion of the solar neutrinos problem.The building up of a µ-barrier, which stops the turbulence allows stellar evolution towards the giant branch and explains nitrogen abundance at the surface of giants of the first ascending branch.Turbulent mixing is also of some importance for the transfer of angular momentum and has to be taken into account for explaining the abundance of the elements in Wolf-Rayet stars.

scholarly journals ω Centauri – a Laboratory for Critical Tests of Stellar Structure and Evolution

2000 ◽  
Vol 176 ◽  
pp. 252-253
Author(s):  
L. M. Freyhammer ◽  
J. O. Petersen ◽  
M. I. Andersen
Keyword(s):  
Stellar Evolution ◽  
Monitoring Program ◽  
Light Curves ◽  
Stellar Structure ◽  
Preliminary Results ◽  
Test Models ◽  
Multi Mode

AbstractPreliminary results are reported for a monitoring program on ω Cen. We search for multi-mode SX Phe stars and changes in pulsation parameters of the cluster variables in order to test models of stellar evolution. With a periodogram for 10,000 light curves, we estimate that ω Cen hosts several hundred SX Phe stars.

scholarly journals Stellar models of rotating, pre-main sequence low-mass stars with magnetic fields

2013 ◽  
Vol 9 (S302) ◽  
pp. 112-113 ◽  
Author(s):  
Luiz T. S. Mendes ◽  
Natália R. Landin ◽  
Luiz P. R. Vaz
Keyword(s):  
Magnetic Fields ◽  
Stellar Evolution ◽  
Large Scale ◽  
Main Sequence ◽  
Stellar Structure ◽  
Low Mass Stars ◽  
Large Scale Magnetic Field ◽  
Low Mass ◽  
Structure Equations ◽  
Stellar Models

AbstractWe report our present efforts for introducing magnetic fields in the ATON stellar evolution code code, which now evolved to truly modifying the stellar structure equations so that they can incorporate the effects of an imposed, large-scale magnetic field. Preliminary results of such an approach, as applied to low-mass stellar models, are presented and discussed.

scholarly journals Pulsation Theory and Stellar Structure

1993 ◽  
Vol 137 ◽  
pp. 483-496 ◽  
Author(s):  
J. Christensen-Dalsgaard
Keyword(s):  
Stellar Evolution ◽  
Stellar Structure ◽  
Evolution Theory ◽  
Pulsating Stars ◽  
Scuti Stars

AbstractObserved periods of pulsating stars provide information about the properties of the stars. As examples I here consider double-mode pulsators, solar-like oscillations and δ Scuti stars. The ongoing expansion in the observational efforts in this area may be expected to lead to increasingly detailed tests of stellar evolution theory.

scholarly journals The Aarhus red giants challenge

2020 ◽  
Vol 635 ◽  
pp. A164 ◽  
Author(s):  
V. Silva Aguirre ◽  
J. Christensen-Dalsgaard ◽  
S. Cassisi ◽  
M. Miller Bertolami ◽  
A. Serenelli ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Energy Generation ◽  
Abundance Ratio ◽  
Solar Radius ◽  
Stellar Mass ◽  
Stellar Structure ◽  
Red Giants ◽  
Numerical Implementation ◽  
Red Giant

Context. With the advent of space-based asteroseismology, determining accurate properties of red-giant stars using their observed oscillations has become the focus of many investigations due to their implications in a variety of fields in astrophysics. Stellar models are fundamental in predicting quantities such as stellar age, and their reliability critically depends on the numerical implementation of the physics at play in this evolutionary phase. Aims. We introduce the Aarhus red giants challenge, a series of detailed comparisons between widely used stellar evolution and oscillation codes that aim to establish the minimum level of uncertainties in properties of red giants arising solely from numerical implementations. We present the first set of results focusing on stellar evolution tracks and structures in the red-giant-branch (RGB) phase. Methods. Using nine state-of-the-art stellar evolution codes, we defined a set of input physics and physical constants for our calculations and calibrated the convective efficiency to a specific point on the main sequence. We produced evolutionary tracks and stellar structure models at a fixed radius along the red-giant branch for masses of 1.0 M⊙, 1.5 M⊙, 2.0 M⊙, and 2.5 M⊙, and compared the predicted stellar properties. Results. Once models have been calibrated on the main sequence, we find a residual spread in the predicted effective temperatures across all codes of ∼20 K at solar radius and ∼30–40 K in the RGB regardless of the considered stellar mass. The predicted ages show variations of 2–5% (increasing with stellar mass), which we attribute to differences in the numerical implementation of energy generation. The luminosity of the RGB-bump shows a spread of about 10% for the considered codes, which translates into magnitude differences of ∼0.1 mag in the optical V-band. We also compare the predicted [C/N] abundance ratio and find a spread of 0.1 dex or more for all considered masses. Conclusions. Our comparisons show that differences at the level of a few percent still remain in evolutionary calculations of red giants branch stars despite the use of the same input physics. These are mostly due to differences in the energy generation routines and interpolation across opacities, and they call for further investigation on these matters in the context of using properties of red giants as benchmarks for astrophysical studies.

scholarly journals Surface magnetic fields across the HR Diagram

2014 ◽  
Vol 10 (S305) ◽  
pp. 12-21
Author(s):  
John D. Landstreet
Keyword(s):  
Magnetic Field ◽  
Stellar Evolution ◽  
Field Structure ◽  
Stellar Structure ◽  
Detailed Data ◽  
Magnetic Field Structure ◽  
The Past ◽  
Magnetic Stars ◽  
First Time ◽  
Broad Outline

AbstractThe past 20 years have seen remarkable advances in spectropolarimetric instrumentation that have allowed us, for the first time, to identify some magnetic stars in most major stages of stellar evolution. We are beginning to see the broad outline of how such fields change during stellar evolution, to confront theoretical hypotheses and models of magnetic field structure and evolution with detailed data, and to understand more of the ways in which the presence of a field in turn affects stellar structure and evolution.

scholarly journals Recent Advances in Convection Theory and Modelling

1995 ◽  
Vol 10 ◽  
pp. 433-434
Author(s):  
S. Sofia
Keyword(s):  
Stellar Evolution ◽  
Numerical Models ◽  
Spatial Scales ◽  
Stellar Structure ◽  
Wave Number ◽  
The Sun ◽  
Mixing Length ◽  
Number Range ◽  
Wide Range ◽  
Non Locality

This Joint Discussion (Number 13), took place on August 22, 1994 at The Hague, in connection with the XXII General Assembly of the IAU. At the one-day long meeting, there were presentations by 15 invited speakers and 15 posters.The Joint Discussions had been organized in response to the considerable progress made in this field of research during the previous decade. Although it had long been known that the prevailing mixing length theory (MLT), used extensively and very successfully in Astrophysics for several decades had become needlessly limited, until recently it was impractical to contemplate more realistic approaches. The situation has changed recently as a consequence of advances in numerical techniques and computational capabilities, and thus JD 13 was organized to discuss the advances, and perhaps to understand the strengths and weaknesses of each approach.There were two presentations which addressed the main issues in convection theory (E. Schatzman), and the astrophysical implications (P. Demarque). Several talks covered current numerical codes, which included deep convection in a rotating reference frame (K. Chan), convection in the presence of magnetic fields (P. Fox), and shallower solar convection simulations on a wide range of spatial scales (A. Nordlund). Although these approaches have enriched (and are continuing to enrich) our understanding of the physics of convective fluids, they are much too detailed (both in space and in time) to be integrated in the study of stellar evolution. To overcome this shortcoming, S. Sofia described a technique developed together with Lydon and Fox to use relationships between dynamical and thermodynamic properties of convective flows derived in numerical models to be applied in stellar structure and evolution codes by performing small modifications of the standard MLT formalism. The advantage of this technique is that it does not contain a mixing length or any other arbitrary parameter, and it was used successfully in modeling the evolution of the Sun and other solar analogues. V. Canuto also presented a formulation of convection both amenable to be used in stellar evolution studies, and not requiring an arbitrary mixing length-like parameter. His formulation uses the Reynolds stress method, which has the advantage of modeling the full eddy spectrum of the turbulence, rather than the narrow wave number range for energy containing eddies assumed in the MLT. Additionally, this technique can address the problems of non-locality and overshoot. M. Stix also addressed non-locality and overshoot by presenting results of a non-local mixing length model of the Sun derived from the Shaviv and Salpeter model.

scholarly journals Constraints on stellar evolution theory from precise eclipsing binary data

1984 ◽  
Vol 105 ◽  
pp. 391-394
Author(s):  
J. Andersen ◽  
J.V. Clausen ◽  
H.E. J⊘rgensen ◽  
B. Nordström
Keyword(s):  
Stellar Evolution ◽  
Binary Data ◽  
Main Sequence ◽  
Theoretical Models ◽  
Stellar Structure ◽  
Sequence Evolution ◽  
Evolution Theory ◽  
Eclipsing Binary ◽  
Standard Models ◽  
Structure Calculations

Previous attempts at a detailed confrontation of eclipsing binary data with theoretical models of main-sequence evolution were faced with the choice between data of inhomogeneous (mostly low) quality for many systems (Kriz, 1969; Lacy, 1979) or accurate values of mass, radius, and temperature (or luminosity) for very few systems only (Popper et al., 1970). In addition, more detailed and homogeneous stellar structure calculations for several compositions were needed. Since 1972, a coordinated photometric and spectroscopic programme at our institute contributes to building a sufficient observational basis for such a test. Among published standard models for the range 1–10 M⊙, Hejlesen's (1980) are the most extensive, agree well with other standard models, and are presented in a format suitable for comparison with binary data. Here we can only outline a few salient new results from this study.

scholarly journals Coupling 1D stellar evolution with 3D-hydrodynamical simulations on-the-fly II: stellar evolution and asteroseismic applications

2019 ◽  
Vol 491 (1) ◽  
pp. 1160-1173 ◽  
Author(s):  
Jakob Rørsted Mosumgaard ◽  
Andreas Christ Sølvsten Jørgensen ◽  
Achim Weiss ◽  
Víctor Silva Aguirre ◽  
Jørgen Christensen-Dalsgaard
Keyword(s):  
Stellar Evolution ◽  
Surface Effect ◽  
Stellar Structure ◽  
Red Giants ◽  
3D Simulations ◽  
Stellar Models ◽  
Red Giant ◽  
Hydrodynamical Simulations ◽  
Indispensable Tool ◽  
Oscillation Frequencies

ABSTRACT Models of stellar structure and evolution are an indispensable tool in astrophysics, yet they are known to incorrectly reproduce the outer convective layers of stars. In the first paper of this series, we presented a novel procedure to include the mean structure of 3D hydrodynamical simulations on-the-fly in stellar models, and found it to significantly improve the outer stratification and oscillation frequencies of a standard solar model. In this work, we extend the analysis of the method; specifically how the transition point between envelope and interior affects the models. We confirm the versatility of our method by successfully repeating the entire procedure for a different grid of 3D hydrosimulations. Furthermore, the applicability of the procedure was investigated across the HR diagram and an accuracy comparable to the solar case was found. Moreover, we explored the implications on stellar evolution and find that the red-giant branch is shifted about $40\, \mathrm{K}$ to higher effective temperatures. Finally, we present for the first time an asteroseismic analysis based on stellar models fully utilizing the stratification of 3D simulations on-the-fly. These new models significantly reduce the asteroseismic surface term for the two selected stars in the Kepler field. We extend the analysis to red giants and characterize the shape of the surface effect in this regime. Lastly, we stress that the interpolation required by our method would benefit from new 3D simulations, resulting in a finer sampling of the grid.

General calibration problems

1966 ◽  
Vol 24 ◽  
pp. 303
Author(s):  
R. M. Petrie
Keyword(s):  
Stellar Evolution ◽  
Absolute Magnitude ◽  
Stellar Atmosphere ◽  
Stellar Structure ◽  
Surface Gravity ◽  
Central Problem ◽  
Spectral Parameters ◽  
Stellar Interior ◽  
Radiation Passing

During this symposium we have already heard papers which have dealt with the calibration of certain spectral parameters. In this session we turn to the matter of calibrating luminosity criteria in terms of absolute magnitude. This is a central problem in studies of our Galaxy and it finds in this topic its widest application. At the same time we remind ourselves that the determination of absolute magnitude is necessary in studies of stellar structure and stellar evolution since this information tells us about the radiation passing through the stellar interior and the stellar atmosphere and of the amount of energy generated by the star. The luminosity also allows us to calculate the size of a star and to estimate its surface gravity.

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