van Marle 2006 thesis 长伽玛暴的外部介质环境的数值模拟 4

主要内容:
博士论文，其实就是一个摘要加几篇文章，而且文章连格式都没怎么变。

数值模拟大质量恒星的演化，重点是外部介质环境的变化。以此来揭示伽玛暴的外部介质环境。

下一步是做出旋转的前身星的环境，将更实际，但将不是球对称的。

精彩摘抄:


文章信息:
title: Models for the Circumstellar Medium of Long Gamma-Ray Burst Progenitor Candidates
author: Allard Jan van Marle
Ph. D. Thesis Utrecht University, May 2006

In this thesis, we describe the effect of the evolution of a massive star on the surrounding medium. We will then explore the connection between massive stars and gamma-ray bursts by comparing our results for the circumstellar medium of massive stars with the observations and models of long gamma-ray bursts.

1. Chapter 2: The evolution of the CSM around a massive star that ends its life as a Red Supergiant is considered. We describe the results of 1D hydrodynamical simulation of the interstellar medium around a 25 M_sun star. This simulation includes the effect of the stellar wind as well as that of photo-ionization. We find that during the main sequence this star produces an HII region outside its wind bubble. During the red supergiant phase, the HII region disappears due to a lack of high energy photons from the central star

2. Chapter 3: Differences between 1D, 2D and 3D simulations of circumstellar shells
are worked out. We present the results of 1D, 2D and 3D simulations of the same hydrodynamical interaction: the formation of a shell, that is driven by a fast wind
and sweeps up a slow wind. From this example we describe the differences in results that occur, in case more dimensions are used for the same numerical simulation. The difference between 1D and 2D results is considerable, since the 2D
simulations show instabilities that are suppressed in 1D. A 3D simulation is usually unnecessary, since it follows the same general trend as the 2D simulation. However,
it is useful to note the (small) differences and to see how the 2D shape translates into a 3D structure

3. Chapters 4 and 5: The CSM around potential long gamma-ray burst progenitors and the way their surrounding media show up in the absorption spectrum of the gammaray burst afterglow is computed. We have made simulations of the circumstellar medium around a 40 M_sun and a 60 M_sun star. From the results we calculate the blueshifted column density profile that would be visible in the spectrum of a supernova or gamma-ray burst at the end of the life of such a star. We find that the time dependent column density features can be used to constrain the progenitor. The presence of intermediate (100..700 km s^-1) absorption features in gamma-ray burst GRB 021004 leads us to conclude that the progenitor star had only a short Wolf-Rayet phase. This means it was either a comparatively low mass (. 30 M_sun) star, or part of a binary, which went through a late mass transfer phase.

4. Chapter 6: Possible ways to obtain constant circumstellar medium density profile
around observed gamma-ray bursts are explored. A constant density profile close to
a star requires a small radius of the wind termination shock. We present numerical
simulations of the hydrodynamical interactions of the possible interactions that can
lead to this situation. All such probable scenarios require rather extreme conditions, either in the ISM or in the wind parameters. This makes it unlikely, that any single explanation can account for all instances of a constant density medium in a gammaray burst afterglow. The large number of possible scenarios, however, can explain why this is such a common occurrence. In all cases, a weak stellar wind is helpful. This means, that these gamma-ray bursts most likely had low metallicity progenitor stars.