THE RELATIONSHIP BETWEEN MONO-ABUNDANCE AND MONO-AGE STELLAR POPULATIONS IN THE MILKY WAY DISK
THE RELATIONSHIP BETWEEN MONO-ABUNDANCE AND MONO-AGE STELLAR POPULATIONS IN THE MILKY WAY DISK
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DOI：
10.3847/1538-4357/834/1/27
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发表时间：
2016-08
期刊：
影响因子：
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通讯作者：
I. Minchev;M. Steinmetz;C. Chiappini;M. Martig;F. Anders;G. Matijevič;R. D. Jong
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文献类型：
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作者：
I. Minchev;M. Steinmetz;C. Chiappini;M. Martig;F. Anders;G. Matijevič;R. D. Jong
利用[Fe/H]和[α/Fe]窄仓中的恒星研究银河系盘结构是最近提出的一种理解银河系厚盘和薄盘形成的有力方法。到目前为止，人们一直认为这些单丰度种群（MAP）也是同时代或单年龄种群。在这里，我们研究了银河系化学动力学模型的这种关系，并表明，MAPs和单年龄人口之间的等价性只存在于高-[α/Fe]尾，其中不同的银河系半径的化学演化曲线相距甚远。在较低的[α/Fe]-值下，即使对于小的观测不确定性和小的MAP箱尺寸，MAP也由具有一定年龄范围的恒星组成。由于星盘由内而外的形成，对于这些MAP来说，年轻的恒星通常位于更大的半径处，这导致负径向年龄梯度可能高达2 Gyr kpc-1。正的径向年龄梯度可以导致最低[α/Fe]和最高[Fe/H]端的MAP。这种年龄的变化使得无法对没有准确年龄的观测结果进行简单的解释。在我们的模型中，研究了恒星表面密度和尺度高度随半径的变化，我们发现，当1-4 Gyr老恒星占主导地位时（正如对RC所预期的那样），APOGEE红团（RC）样本的最新分析与最近的分析吻合得很好。我们的研究结果表明，APOGEE数据是一致的银河系模型的单年龄人口耀斑的所有年龄。我们建议对我们的预测的有效性进行观察测试，并认为使用准确的年龄测量（例如来自星震学的测量）对于限制银河系的形成和演化至关重要。
Studying the Milky Way disk structure using stars in narrow bins of [Fe/H] and [α/Fe] has recently been proposed as a powerful method to understand the Galactic thick and thin disk formation. It has been assumed so far that these mono-abundance populations (MAPs) are also coeval, or mono-age, populations. Here we study this relationship for a Milky Way chemodynamical model and show that equivalence between MAPs and mono-age populations exists only for the high-[α/Fe] tail, where the chemical evolution curves of different Galactic radii are far apart. At lower [α/Fe]-values an MAP is composed of stars with a range in ages, even for small observational uncertainties and a small MAP bin size. Due to the disk inside-out formation, for these MAPs younger stars are typically located at larger radii, which results in negative radial age gradients that can be as large as 2 Gyr kpc−1. Positive radial age gradients can result for MAPs at the lowest [α/Fe] and highest [Fe/H] end. Such variations with age prevent the simple interpretation of observations for which accurate ages are not available. Studying the variation with radius of the stellar surface density and scale height in our model, we find good agreement to recent analyses of the APOGEE red-clump (RC) sample when 1–4 Gyr old stars dominate (as expected for the RC). Our results suggest that the APOGEE data are consistent with a Milky Way model for which mono-age populations flare for all ages. We propose observational tests for the validity of our predictions and argue that using accurate age measurements, such as from asteroseismology, is crucial for putting constraints on Galactic formation and evolution.