The Equation of State of Stellar Matter

Kippenhahn, Rudolf; Weigert, Alfred

doi:10.1007/978-3-642-61523-8_16

Cited by 37 publications

(48 citation statements)

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“…For the calculation of the stellar models a descendant of the program by Kippenhahn et al (1967) in the latest version described in Schlattl (2001) is used. In particular the opacities tables of and the nuclear reaction rates given by Adelberger et al (1998) are employed.…”

Section: Stellar and Solar Modelsmentioning

confidence: 99%

Microscopic diffusion of partly ionized metals in the Sun and metal-poor stars

Schlattl

2002

A&A

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Abstract. An improved microscopic diffusion in stars is presented considering in detail the partly ionized stages of metals. Besides, the influence of degenerate electron-gas and of the contribution of radiation to the total pressure has been accounted for. The solution of the diffusion equations is then performed following the scheme of Thoul et al. (1994). By defining one mean charged ion per element very few modifications are necessary to solve the improved diffusion scheme. (A portable FORTRAN routine is provided.) The change in the sound-speed profile of a solar model obtained with the new diffusion description is at most about 25% at r = 0.6 R . The biggest effect on low-mass stars is expected near the turn off, where the convective envelope is shallowest. However, only a difference of at most 40 K in the effective temperature could be observed when assuming either fully or partly ionized metals in the diffusion equation. Nevertheless, the surface metal distribution is strongly altered.

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Section: Stellar and Solar Modelsmentioning

confidence: 99%

Microscopic diffusion of partly ionized metals in the Sun and metal-poor stars

Schlattl

2002

A&A

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“…Overshooting and mass loss were ignored. Our revised stellar evolution code was originally described by Kippenhahn et al (1967).…”

Section: Physical Assumptions and Computation Methodsmentioning

confidence: 99%

Blue loops of intermediate mass stars

2004

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Abstract. Based on the results of the blue loop formation for models of solar-like metallicity, we have explored the blue loop evolution of metal-poor stars. Three series of models with a wide range of metallicity and the initial helium abundance were calculated. An important parameter, η c , defined as the envelope convection mass divided by the total envelope mass at the bottom of the RGB, was introduced as a criterion to determine the formation of the blue loop. We have found that the low-Z models will develop extensive blue loops when η c is lower than a critical value η crit . The physical explanation for this result could be as follows. Lower Z reduces the envelope opacity and leads to a hotter stellar envelope and a bluer RGB. Thus the model will have a smaller η a at the top and an even smaller η c at the bottom of the RGB. When η c is lower than the critical value η crit , the envelope is radiation-dominated. Under this condition and the constraint of the virial theorem, the response of the star to the increase of the stellar luminosity is to contract to increase the thermal conductivity coefficient in the stellar envelope and to form a blue loop. Compared with the high-Z models, we have confirmed that the development of convection in the stellar envelope is a crucial factor to determine the formation of the blue loop, but the low-Z models reach low η c values in a different way from the high-Z models, in which the modulation of the nuclear reaction rates by higher 14 N abundance in the H-burning shell is responsible for the stars to get small η c values. It has been found that η crit depends not only on the stellar mass, but also on metallicity and the initial helium abundance. Our numerical results show that η crit decreases with Z while slowly increases with Y.

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“…The surface boundary condition use a triangulation method as described in Kippenhahn et al (1967). In order to specify the surface boundary condition, three inward envelope integrations are constructed.…”

Section: Computationmentioning

confidence: 99%

Asteroseismic study of helium and heavy element diffusion in solar-type stars

Gai¹,

Bi²,

Tang³

et al. 2009

A&A

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Aims. Element diffusion is a basic physical element transport mechanism which induces the redistribution of chemical elements. Using the asteroseismic method, we study the effects of helium and heavy element diffusion on the internal structure and stellar evolution of solar-type stars. We also provide asteroseismic parameters for a grid of models which would be useful for direct comparison with the Kepler mission observations. Methods. We construct a grid of solar-type stellar models with various masses (from 0.8 M to 1.2 M ) and metallicities (Z i = 0.03, 0.025, 0.02, 0.015, 0.01, 0.005) with and without helium and heavy element diffusion. We compute "second differences" and "small separations" of the solar-metallicity models (Z i = 0.02) to analyze the effects of diffusion on the convection zone, helium abundance and the evolutionary sequence of the star. In order to study the asteroseismic property of models with and without diffusion, we compute the p-mode oscillation frequencies of low-degree modes for a grid of models and construct the ( Δν 0 , d 02 ) asteroseismic diagram. Results. We find that the element diffusion could speed up the evolution of the star, especially in the main sequence. The results show that it could enlarge the convective core and change the base of the convection envelope. In addition, the helium and heavy element diffusion make the models evolve to lower large and small separations in the asteroseismic diagram. This effect is more efficient at lower metallicity.

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The Equation of State of Stellar Matter

Cited by 37 publications

References 0 publications

Microscopic diffusion of partly ionized metals in the Sun and metal-poor stars

Microscopic diffusion of partly ionized metals in the Sun and metal-poor stars

Blue loops of intermediate mass stars

Asteroseismic study of helium and heavy element diffusion in solar-type stars

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