YNAO OpenIR  > 大样本恒星演化研究组
alpha增丰对恒星演化的影响与寄主恒星周围的宜居带
郭建坡
学位类型博士
导师韩占文
2010-05-27
学位授予单位中国科学院研究生院(云南天文台)
学位授予地点北京
学位专业天体物理
关键词恒星演化 不透明度表 热亚矮星 宜居带
摘要我们用OPAL 高温不透明度表和Wichita State 新低温不透明度表,做出了与Eggleton's 恒星演化程序相匹配的不透明度表。我们用Eggleton's 恒星演化程序,系统的计算了标准太阳模型和alpha 增丰模型的正常恒星的演化。在我们的计算中,恒星的质量范围是0.25-80.0Msun,金属丰度Z 分别是~0.0001、0.0003、0.001、0.004、0.01、0.02、0.03、0.04、0.06、0.08 和~0.10。通过对比我们发现,alpha 增丰可以使恒星的有效温度升高上千度,使恒星的光度升高十几个百分点,使恒星的演化寿命缩短十几个百分点。 我们用中等质量恒星在红巨星阶段抛星风的方法来构建热亚矮星的初始演化模型。在我们的计算中,热亚矮星的金属丰度分别为0.001、0.004、0.02 和0.04,热亚矮星的核心质量分别为0.400、0.450、0.475、0.500 和0.550Msun,热亚矮星的壳层质量分别为0.001、0.005、0.010、0.015 和0.020Msun。通过计算和对比,我们发现alpha 增丰可以使热亚矮星的有效温度升高数千K,可以使热亚矮星的表面重力加速度升高数十个百分点,可以使热亚矮星的光度升高几个百分点,可以使热亚矮星的演化寿命缩短几个百分点。 金属丰度越高,alpha 增丰效应越明显;壳层越厚,alpha 增丰效应越明显。 我们计算了金属丰度为0.02、质量在0.08-4.00Msun 之间的恒星演化,并且重新拟合出恒星的光度和半径随恒星质量变化的函数关系式。我们计算出了0.08-4.00Msun 寄主恒星周围的宜居带。采用Ida 和Lin 在2005 年给出的行星半长轴和质量分布函数,我们进一步计算出了0.08-4.00Msun 寄主恒星周围居带内类地行星的概率分布。根据恒星初始质量分布函数,我们算出了在银河系中位于其寄主恒星宜居带内的类地行星的数量是398 亿颗,可能存在生命的类地行星的数量是37.4 亿颗。 采用Buccino 等人给出的紫外宜居带内外边界的紫外辐射流量表达式,我们算出了0.08-4.00Msun 寄主恒星周围的紫外宜居带。随着寄主恒星的演化,它会变的越来越亮,其周围的宜居带也会离它越来越远。一开始不在宜居带内的类地行星,到后来也可能进入它的寄主恒星的 宜居带内。我们计算了太阳在主序后各个阶段的宜居带,发现当太阳演化到水平分支阶段时,土星轨道恰好位于太阳的宜居带内,可以维持1.37 亿年。
其他摘要Using the OPAL high temperature opacities and the new Wichita State low temperature opacities, we constructed the opacities matching well with Eggleton's code. Using Eggleton's code, we systematically calculate the normal stellar evolution, for both scaled-solar metal mixture and alpha-enhanced metal mixtures. In our calculations, the masses of stars range from 0.25 to 80.0 MsunThe values of metallicities Z are respectively as 0.0001, 0.0003, 0.001, 0.004, 0.01, 0.02, 0.03, 0.04, 0.06, 0.08 and 0.10. Through comparison, we find that alpha-enhancement can raise stellar effective temperatures by several thousand K, raise stellar luminosities by more than ten percent and reduce the evolutionary lifetime by more than ten percent. We make intermediate mass stars sharply lose envelope masses during the red giant branch phase, to construct a series of initial evolutionary models of hot subdwarfs. In our calculation, the metallicities of hot subdwarfs are 0.001, 0.004, 0.02 and 0.04, respectively. The core masses of hot subdwarfs are 0.400, 0.450, 0.475, 0.500 and 0.550 Msun, respectively. And the envelope masses of hot subdwarfs are 0.001, 0.005, 0.010, 0.015 and 0.020 Msun, respectively. Through calculation and comparison, it is found that alpha-enhancement can raise the effective temperatures by several thousand K, raise the gravity on the surface by dozens of percent, raise the luminosities by several percent and reduce the evolutionary lifetime by several percent, for hot subdwarfs. The higher values their metallicities are, the more obvious the alpha-enhanced effects are; and the thicker their envelopes are, the more obvious the \alpha-enhancement effects are. Using Eggleton’s code, we calculate the evolution of stars with metallicity 0.02 and with masses from 0.08 to 4.00 Msun. Then we newly fit the formulae of stellar luminosity and radius, the variable is stellar mass. Using the the boundary flux of habitable zones given by Jones in 2006, we calculate the habitable zones of host stars with masses 0.08-4.00 Msun. Using the distribution of semimajor axis and mass of planets given by Ida and Lin in 2005, we further achieve the probability distribution of terrestrial planets in habitable zones around host stars with masses 0.08-4.00Msun. Using the initial mass function of stars, we obtain the number of terrestrial planets in habitable zones of host stars in the Milky Way, just as 39.8 billion. And the number of terrestrial planets with lives in the Milky Way is about 3.74 billion. Using the boundary ultraviolet radiation of ultraviolet habitable zone given by Buccino et al. in 2006, we calculate the ultraviolet habitable zones of host stars with masses 0.08-4.00 Msun. A star will become brighter and brighter with stellar evolution, and the distance of its habitable zone will become larger and larger. Some planets outside the habitable zone of a host star during the main sequence phase may enter the habitable zone of the host star during other evolutionary phases. We calculate the habitable zone of our Solar system after the main sequence phase. It is found that the orbit of Saturn will enter the habitable zone of Solar during the horizontal branch phase for 137 million years.
学科领域天文学
页数110
语种中文
文献类型学位论文
条目标识符http://ir.ynao.ac.cn/handle/114a53/4659
专题大样本恒星演化研究组
推荐引用方式
GB/T 7714
郭建坡. alpha增丰对恒星演化的影响与寄主恒星周围的宜居带[D]. 北京. 中国科学院研究生院(云南天文台),2010.
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