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The Physical Mechanism for Super-Wind in the Thermally Pulsing AGB Phase

Author: HongYaFang
Tutor: JiangSuYun
School: Zhejiang Normal University
Course: Theoretical Physics
Keywords: stellar evolution TP-AGB HR diagram mass-loss turbulence compressible fluid
CLC: P144
Type: Master's thesis
Year: 2011
Downloads: 11
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Abstract

Although the turbulent pressure is omitted usually, the presence of convection region make it really exists. Stars with initial masses in the range 3≤M/M⊙≤10 have been evolved from the main-sequence phase through to the end of asymptotic giant branch (AGB). The evolution tracks in HR diagram are investigated.εHe, p and T given at maximumεHe in the helium-shell,stellar radius, and the ratio of luminosity at the upper border of helium-shell to that of the stellar surface also are analyzed, as functions of time. The consequence that the demarcation point in HR diagram from E-AGB (the early AGB phase) to TP-AGB (the thermally pulsing AGB phase) for intermediate-mass stars are proposed, which are in excellent agreement with millimetric observations of 119 carbonrich giants. To the aim of the formation of continuous superwind, the suggestion that the mass-loss function may need a parameter which is unaffected by the luminosity of stellar surface after that point is brought forth.Turbulent pressure has been taken into account with the mass-loss, structure and evolution of a star of 5M⊙. The affect of turbulent pressure cannot be overlooked in TP-AGB phase, in particular stellar mass-loss.To see into the impact of turbulence on the intermediate-mass stars, the pressure, mach number, gravitational acceleration and the outer mass at the maximum turbulence in the outer shell of 5Mo star, as functions of time. The compressible fluid is found in the convective region of the outer shell. And the influence can’t be overlooked. After the mechanism of compressible fluid is taken into account to the physical reasoning of mass-loss, a new formula for the mass-loss rate is brought forth.Stars with initial masses in the range 3≤M/M⊙≤5 have been evolved from the main-sequence phase through to the end of asymptotic giant branch (AGB). The mass-loss rates of the new formula are in excellent agreement with that of the classical mass-loss formula from the main-sequence phase through to the end of the stage of central helium burning. To the classical formula, the concussion of mass-loss rate has arisen at the end of AGB because of the effect of the surface luminosity. On the contrary, the continuous major mass-loss rate has obtained by the use of the new formula at the end of AGB. And then, the conclusion that the new mass-loss formula is more measure up to the actual observed value is obtained

The Physical Mechanism for Super-Wind in the Thermally Pulsing AGB Phase

Abstract

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