On the interpretation of sub-giant branch morphologies of intermediate-age star clusters with extended main sequence turnoffs
On the interpretation of sub-giant branch morphologies of intermediate-age star clusters with extended main sequence turnoffs
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DOI：
10.1093/mnras/stv700
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发表时间：
2015-03
影响因子：
4.8
通讯作者：
P. Goudfrooij;L. Girardi;P. Rosenfield;A. Bressan;P. Marigo;M. Correnti;Thomas H. Puzia STScI;P. O
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文献类型：
--
作者：
P. Goudfrooij;L. Girardi;P. Rosenfield;A. Bressan;P. Marigo;M. Correnti;Thomas H. Puzia STScI;P. O
最近对麦哲伦星云中年龄为1-2Gyr的许多星团进行的高质量光度测量显示，主序列转折(MSTO)比简单恒星群(SSP)所能解释的要宽得多。这种扩展的MSTO(EMSTO)通常被解释为几个108年的年龄分布，挑战了传统的认为星团是在单个恒星形成等值线中形成的观点。Li等人。巴斯蒂安和尼德霍夫最近研究了NGC1651、NGC1806和NGC1846的亚巨星分支(SGB)，这是大麦哲伦星云(LMC)中的三个星团，表现出eMSTO。他们认为，这些星团的SGB只能用SSP来解释。我们研究了LMC中的这些星团和另外两个类似的星团，使用了对SSP的大量模拟，包括未分辨的双星。我们发现，当星团的年龄分布被解释为年龄分布时，样本中所有星团的SGB交叉剖面的S形状实际上与MSTO的交叉剖面一致。结果表明，带有eMSTO的星团的SGB形态与模拟的SSP的SGB形态不一致。最后，我们从具有对流过冲水平网格和非常精细的恒星质量网格的轨迹创建了秒等时线。观测到的光度与这些等时线的比较表明，这些星团的红团(RC)的形态也与它们在年龄扩展情景下的MSTO所暗示的形态一致。我们的结论是，具有eMSTO的星团的SGB和RC形态与eMSTO由恒星年龄分布引起的情况是一致的。
Recent high-quality photometry of many star clusters in the Magellanic Clouds with ages of 1 ‐ 2 Gyr revealed main sequence turnoffs (MSTOs) that are significantly wider than can be accounted for by a simple stellar population (SSP). Such extended MSTOs (eMSTOs) are often interpreted in terms of an age spread of several 10 8 yr, challenging the traditional view of star clusters as being formed in a single star formation ep isode. Li et al. and Bastian & Niederhofer recently investigated the sub-giant branches (SGBs) of NGC 1651, NGC 1806, and NGC 1846, three star clusters in the Large Magellanic Cloud (LMC) that exhibit an eMSTO. They argued that the SGB of these star clusters can be explained only by a SSP. We study these and two other similar star clusters in the LMC, using extensive simulations of SSPs including unresolved binaries. We find that the shape s of the cross-SGB profiles of all star clusters in our sample are in fact consistent with th eir cross-MSTO profiles when the latter are interpreted as age distributions. Conversel y, SGB morphologies of star clusters with eMSTOs are found to be inconsistent with those of simulated SSPs. Finally, we create PARSEC isochrones from tracks featuring a grid of convective overshoot levels and a very fine grid of stellar masses. A comparison of the observed phot ometry with these isochrones shows that the morphology of the red clump (RC) of such star clusters is also consistent with that implied by their MSTO in the age spread scenario. We conclude that the SGB and RC morphologies of star clusters featuring eMSTOs are consistent with the scenario in which the eMSTOs are caused by a distribution of stellar ages.