Evolution of massive AGB stars - II. model properties at non-solar metallicity and the fate of Super-AGB stars
Evolution of massive AGB stars - II. model properties at non-solar metallicity and the fate of Super-AGB stars
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DOI：
10.1051/0004-6361:20078132
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发表时间：
2007-12
影响因子：
6.5
通讯作者：
L. Siess
中科院分区：
文献类型：
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作者：
L. Siess
上下文。大质量AGB(以下简称超AGB或SAGB)恒星偏心地点燃碳，初始质量介于MUP和MMAS之间，MUP是碳点火的最小初始质量，MMAS是形成铁核塌缩超新星的最小质量。在这个质量区间内，比MN质量大的恒星将经历一次电子俘获超新星(EC-SN)。目标。我们研究了SAGB星的命运和选定的演化性质，直到碳燃烧阶段结束，作为金属丰度和核心超射的函数。方法：研究方法。该方法基于对覆盖质量范围为5−13M的一大组恒星模型的分析，并计算了Z=10−5和两次太阳之间的7种不同的金属丰度。当Z=10−4和0.02时，在两个子集中考虑了岩心过冲。这些模型可以在http://www-astro.ulb.ac.be/∼siess/database.html.上在线购买。通过一个参数模型研究了SAGB恒星的命运，该模型允许我们评估质量损失和第三次疏散的作用。结果。我们的主要结果概括如下：a)在C燃烧之前，SAGB星的演化与中等质量星非常相似，它们的亮度更高；b)SAGB星在第二次挖掘结束时受到大量的He丰度；c)极限质量MUP、MN和MMAS随Z呈现非线性行为，在Z=10−附近有一个极小值；d)当考虑核心过冲时，MUP、MN和MMAS的值减少了∼2 M；e)我们的模型预测了最小的氧霓虹白矮星质量∼1.05M�，F)Mn的测定高度依赖于质量损失和核心生长速率，g)EC-SN的演化通道仅限于<的很窄的质量范围；1SAGB1.5M的宽度，如果在质量损失率上应用一定的金属丰度标度因子，这个质量窗口可以进一步减小，h)−星的最终命运与第二次扬升有关，这一性质使我们能够精炼形成EC-SN的初始质量范围。我们发现，如果在碳燃烧后的演化过程中，质量损失率与核心增长率的平均比率ζ=uMoss/uMcore大于约70−90，
Context. Massive AGB (hereafter super-AGB or SAGB) stars ignite carbon off-center and have initial masses ranging between Mup, the minimum initial mass for carbon ignition, and Mmas the minimum mass for the formation of an iron core collapse supernova. In this mass interval, stars more massive than Mn will undergo an electron capture supernova (EC-SN). Aims. We study the fate and selected evolutionary properties of SAGB stars up to the end of the carbon burning phase as a function of metallicity and core overshooting. Methods. The method is based on the analysis of a large set of stellar models covering the mass range 5−13 Mand calculated for 7d ifferent metallicities between Z = 10 −5 and twice solar. Core overshooting was considered in two subsets for Z = 10 −4 and 0.02. The models are available online at http://www-astro.ulb.ac.be/∼siess/database.html. The fate of SAGB stars is investigated through a parametric model which allows us to assess the role of mass loss and of the third dredge-up. Results. Our main results can be summarized as follows: a) prior to C-burning, the evolution of SAGB stars is very similar to that of intermediate-mass stars, being more luminous, b) SAGB stars suffer a large He enrichment at the end of the second dredge-up, c) the limiting masses Mup, Mn and Mmas present a nonlinear behavior with Z, characterized by a minimum around Z = 10 −4 ,d ) the values of Mup, Mn and Mmas are decreased by ∼2 Mwhen core overshooting is considered, e) our models predict a minimum oxygen- neon white dwarf mass of ∼1.05 M� , f) the determination of Mn is highly dependent on the mass loss and core growth rates, g) the evolutionary channel for EC-SN is limited to a very narrow mass range of <1−1.5 Mwidth and this mass window can be further decreased if some metallicity scaling factor is applied to the mass loss rate, h) the final fate of SAGB stars is connected to the second dredge-up and this property allowed us to refine the initial mass range for the formation of EC-SN. We find that if the ratio of the mass loss rate to the core growth rate averaged over the post carbon-burning evolution ζ = u Mloss/ u Mcore is greater than about 70−90,