长周期变星的演化及振动

题名	长周期变星的演化及振动
作者	郭建恒
学位类别	硕士
答辩日期	2001
授予单位	中国科学院云南天文台
授予地点	昆明
导师	李焱
关键词	大质量星的演化金属丰度周期光度关系
学位专业	天体物理
中文摘要	长周期变星的演化和振动一直是引人入胜的课题。这不仅仅是因为在它们的变化过程中有丰富的物理内容，更重要的是可以用它们来做河外星系距离的定标者。在本文中详细的计算了在z = 0.005, z = 0.001, = 0.005, z = 0.01 和 z = 0.02这样一个大的金属丰度跨度下，质量为15M_⊙，20M_⊙和30_⊙恒星的演化和振动。在计算中采用了最新的不透明度，考虑了星风损失对大质量星的影响，对于每一个模型都从零年龄主序演化到了中心氦燃烧结束。在本文中仔细研讨了混合长参数以及中心对流核的对流超射对演化模型的影响，同时在中心氦燃烧阶段蓝超巨星和红超巨星的比值被用来限定模型的参数（尤其是混合长和对流超射）。尽管在本文中并滑得到和观测一致的结论即随着金属丰度的增加B/R增加。但是，通过在低金属丰度区采用对流超射，而在高金属丰度区放弃对流超射这一方法得到了与观测更相符合的比值。在新的演化模型的基础上，对于大质量星的振动进行了详细的计算。各项振动的性质用来和LMC，M33以及MW中的RSGs做比较。对于LMC和M33中长周期变星，理论的周周光关系和观测在基步振动模式下很好的符合；而对于MW中长周期变星，它们更可能在一阶模式下振动。最终，得到了金属丰度和周光关系的之间的联系，即随着金属丰度的增加，有周期增加、光度下降的趋势。一个近似的改正δM_(bol) ～ 0.831gZ对于决定河外星系的距离相信应该有所改善。
英文摘要	In this thesis we have calculated the evolution models and the pulsating property of 15M_⊙, 20M_⊙and 30M_⊙ stars under different metallicity, in order to understand the dependence of the period-luminosity relation on metallicity, Up-to-date opacities, overshooting from the convective core and mass loss through the stellar wind was included in our evolution models. In order to get better agreement with the observed blue-to-red ratio of supergiant numbers, we adopted 1.0 and 1.8 as the ratio of the mixing-length to local pressure scale height in the convection zone. We find that normal models without overshooting seems to produce too many blue supergiants while over shooting models seems to produce too many red supergiants, but neither of them can correctly predict the tendency of increasing the B/R ratios with increasing the metal abundance observed in many stellar systems. This result seems to indicate that the overshooting from the convective core is strong in extremely metal-poor stars and fades gradually away with the increase of the metal abundance. With a proper combination of model parameters we have constructed a series of stellar models with a = 1.0 that give theoretical B/R ratios in better agreement with the observations, and these models have been used to calculate the period-luminosity relation of the RSG long-period variables. We have compared the theoretical P-L relations with observed long-period variables in the LMC, M33 and our Milky Way. The observed LPVs are in good agreement with the P-L relations of the fundamental mode for the LMC and M33, but the LPVs in the MW seems to have shorter periods and more likely to be the first overtone pulsators. We have found that the period-luminosity relations under different metallicity show a tendency of decreasing the luminosity and increasing the period with the increase of the metal abundance, and the correction of the luminosity at a given period is δM_(bo1) ～ 0.831gZ.
语种	中文
学科主题	天文学
页码	67
内容类型	学位论文
源URL	[http://ir.ynao.ac.cn/handle/114a53/5313]
专题	云南天文台_恒星物理研究组
推荐引用方式 GB/T 7714	郭建恒. 长周期变星的演化及振动[D]. 昆明. 中国科学院云南天文台. 2001.