THE EFFECTS OF ROTATION ON THE MAIN-SEQUENCE TURNOFF OF INTERMEDIATE-AGE MASSIVE STAR CLUSTERS
THE EFFECTS OF ROTATION ON THE MAIN-SEQUENCE TURNOFF OF INTERMEDIATE-AGE MASSIVE STAR CLUSTERS
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DOI：
10.1088/0004-637x/776/2/112
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发表时间：
2013-04
期刊：
影响因子：
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通讯作者：
Wuming Yang;S. Bi;X. Meng;Zhie Liu
中科院分区：
文献类型：
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作者：
Wuming Yang;S. Bi;X. Meng;Zhie Liu
在大麦哲伦星云的中年龄大质量星团的彩色星等图（CMD）中，双主序关闭或扩展主序关闭（MSTOs）通常被解释为年龄差几百迈珥。然而，这种年龄差异在较年轻的群体（即40-300迈）中并不存在，这对这一解释提出了挑战。旋转对星团msto的影响在以往的研究中已经有过，但得到的结果相互矛盾。与以往的工作相比，我们考虑了旋转对恒星主序寿命的影响。我们的计算表明，相对于年龄在0.8到2.2 Gyr之间的非旋转模型，旋转模型的MSTO更暗、更红，但当年龄大于2.4 Gyr时，MSTO更亮、更蓝。典型轮调率造成的MSTO扩散相当于大约200迈尔的年龄扩散的影响。对于年龄在0.8 ~ 2.2 Gyr之间的星团，旋转可导致其CMD中出现双MSTOs或扩展MSTOs。然而，这种扩展并不显著，甚至在较年轻的星团中也不存在。如果混合效率足够高，混合效应会抵消演化后期离心支撑的影响，在中老年星团中，旋转诱导的扩展会消失，而年轻星团的MSTO会延长。此外，旋转的影响可能有助于理解球状星团中一些“多种群”的形成。
The double or extended main-sequence turnoffs (MSTOs) in the color–magnitude diagram (CMD) of intermediate-age massive star clusters in the Large Magellanic Cloud are generally interpreted as age spreads of a few hundred Myr. However, such age spreads do not exist in younger clusters (i.e., 40–300 Myr), which challenges this interpretation. The effects of rotation on the MSTOs of star clusters have been studied in previous works, but the results obtained are conflicting. Compared with previous works, we consider the effects of rotation on the main-sequence lifetime of stars. Our calculations show that rotating models have a fainter and redder MSTO with respect to non-rotating counterparts with ages between about 0.8 and 2.2 Gyr, but have a brighter and bluer MSTO when age is larger than 2.4 Gyr. The spread of the MSTO caused by a typical rotation rate is equivalent to the effect of an age spread of about 200 Myr. Rotation could lead to the double or extended MSTOs in the CMD of the star clusters with ages between about 0.8 and 2.2 Gyr. However, the extension is not significant, and it does not even exist in younger clusters. If the efficiency of the mixing were high enough, the effects of the mixing would counteract the effect of the centrifugal support in the late stage of evolution, and the rotationally induced extension would disappear in the old intermediate-age star clusters, but younger clusters would have an extended MSTO. Moreover, the effects of rotation might aid in understanding the formation of some “multiple populations” in globular clusters.