Possible Evidence for Metal Accretion onto the Surfaces of Metal-Poor Main-Sequence Stars
Possible Evidence for Metal Accretion onto the Surfaces of Metal-Poor Main-Sequence Stars
复制标题
贫金属主序星表面金属吸积的可能证据
DOI：
10.1088/0004-637x/784/2/153
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
服部公平 ; 吉井譲 ; Timothy C. Beers ; Daniela Carollo ; Young Sun Lee
中科院分区：
文献类型：
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作者：
森田航;矢野航;長岡朋人;中務真人;服部公平 ; 吉井譲 ; Timothy C. Beers ; Daniela Carollo ; Young Sun Lee
银河系的整个演化，包括它的质量组装和恒星形成历史，都印在其成员恒星的化学动力学分布函数f（x，v，[X/H]）上，在由位置、速度和元素丰度比所跨越的多维相空间中。特别是，低质量恒星（如G型或K型矮星）的化学动力学分布函数是银河系形成最早阶段的宝贵示踪剂，因为它们的主序星寿命接近或超过宇宙的年龄。基本上所有以前的分析的一个基本原则是，恒星的金属丰度，通常参数化为[Fe/H]，对于主序星（至少是那些没有被污染，由于质量转移从联星）是保守的。如果这是真的，那么不同质量、有效温度或光谱类型的长寿主序星的金属丰度和运动学之间的任何相关性都必须严格相同，因为它们反映了相同的质量组装和恒星形成历史。通过分析取自斯隆数字巡天数据发布8的主序列上附近贫金属晕和厚盘星的样本，我们发现G型矮星的金属丰度中值系统地高于（约0.2 dex）具有相同的银河系中心旋转速度中值的K型矮星。如果这一发现得到证实，可能会推翻长期以来被接受的假设，即长寿恒星的大气金属丰度随时间而保持不变。
The entire evolution of the Milky Way, including its mass-assembly and star-formation history, is imprinted onto the chemo-dynamical distribution function of its member stars, f (x, v,[X/H]), in the multi-dimensional phase space spanned by position, velocity, and elemental abundance ratios. In particular, the chemo-dynamical distribution functions for low-mass stars (eg, G-or K-type dwarfs) are precious tracers of the earliest stages of the Milky Way's formation, since their main-sequence lifetimes approach or exceed the age of the universe. A basic tenet of essentially all previous analyses is that the stellar metallicity, usually parameterized as [Fe/H], is conserved over time for main-sequence stars (at least those that have not been polluted due to mass transfer from binary companions). If this holds true, any correlations between metallicity and kinematics for long-lived main-sequence stars of different masses, effective temperatures, or spectral types must strictly be the same, since they reflect the same mass-assembly and star-formation histories. By analyzing a sample of nearby metal-poor halo and thick-disk stars on the main sequence, taken from Data Release 8 of the Sloan Digital Sky Survey, we find that the median metallicity of G-type dwarfs is systematically higher (by about 0.2 dex) than that of K-type dwarfs having the same median rotational velocity about the Galactic center. If it can be confirmed, this finding may invalidate the long-accepted assumption that the atmospheric metallicities of long-lived stars are conserved over time.