银河系薄盘和厚盘恒星的金属丰度与运动学演化

发布时间：2018-07-04 19:55

  本文选题：银河系 + 银盘　； 参考：《河北师范大学》2010年硕士论文

【摘要】： 银盘恒星的金属丰度和运动学特征是区分薄盘和厚盘的重要依据,可以为银河系的结构和化学演化模型提供直接的观测约束。尤其是研究大样本恒星的运动学和金属丰度以及年龄的关系,对于准确解释银盘形成和演化的一些问题更具有重要意义。我们基于近年来两个大样本恒星的观测工作,从其共有的恒星样本中选取出恒星年龄比较一致(年龄差别在3 Gyr以内)的4004颗恒星样本,包括年龄(age17Gyr)、金属丰度(?1 [Fe/H] 0.5)、空间运动速度、径向及法向轨道半径等参数。用运动学标准区分恒星的星族成分,确定了3855颗薄盘星和146颗厚盘星,分别讨论了薄盘和厚盘恒星的运动学参数与金属丰度、年龄的关系;金属丰度[Fe/H]与轨道偏心率e、径向平均轨道半径Rm以及最大银盘法向距离Zmax的关系。结果发现,薄盘恒星和厚盘恒星确实在运动学性质上存在较大的差异。具体结果如下: (1)厚盘恒星和薄盘恒星在空间运动速度上可以区分开,并且厚盘恒星的空间运动速度弥散明显大于薄盘恒星。厚盘星的空间运动速度弥散度(σU,σV,σW)=(58±3,34±2,39±2)km/s,薄盘星的(σU,σV,σW)=(31±2,18±1,15±1)km/s。 (2)银盘恒星的速度弥散度都随着恒星年龄的增加而逐渐变大,而当年龄约大于10Gyr时速度弥散度突然成倍增加。在薄盘中,σU在恒星年龄约为8Gyr时达到饱和,σU≈41km/s;σV在恒星年龄约为8Gyr时达到饱和,σV≈22km/s;σW在恒星年龄约为6Gyr时达到饱和,σW≈21km/s。而厚盘恒星的空间速度弥散度与恒星年龄没有关系,并且厚盘恒星和薄盘恒星在W方向速度弥散度上存在间隙,薄盘星σW≤21km/s,厚盘星σW30km/s。 (3)银盘恒星的轨道偏心率随金属丰度的增加而逐渐变小,厚盘恒星的轨道偏心率(e0.25)明显大于薄盘恒星(e0.20),但当[Fe/H]?0.3以后银盘恒星的轨道偏心率几乎保持不变。 (4)沿银盘径向,薄盘总体上存在明显的金属丰度梯度,但这一丰度梯度分布由内到外是不连续的,内盘(Rm8kpc)丰度梯度接近于0,外盘(Rm≥8kpc)丰度梯度为?0.12dex/kpc。厚盘几乎不存在径向金属丰度梯度。 (5)沿银盘法向,厚盘和薄盘存在明显的金属丰度梯度,大小分别为?0.15 dex/kpc和?0.25dex/kpc,而且薄盘和厚盘的法向丰度梯度都表现出随银河系演化而逐渐变陡的趋势。我们的结果支持关于银盘形成和演化的坍缩机制。
[Abstract]:The metallic abundance and kinematic characteristics of silver disk stars are the important basis for distinguishing thin and thick disks, which can provide direct observation constraints for the structural and chemical evolution models of the Milky way galaxy. In particular, the study of the kinematics, the abundance of metals and the age relationship of large sample stars is of great significance for the accurate interpretation of some problems of silver disk formation and evolution. Based on the observations of two large stars in recent years, we have selected 4004 star samples of the same age (age difference within 3 Gyr) from their common star samples. These parameters include age (age17 Gyr), metal abundance (Fer 1 [Fe / H] 0.5), space velocity, radial and normal orbital radius and so on. 3855 thin disk stars and 146 thick disk stars are determined by using kinematics criterion to distinguish star family composition. The relationship between the kinematics parameters of thin disk star and thick disk star and the metal abundance and age are discussed respectively. The relationship between metal abundance [Fe / H] and orbit eccentricity (e), radial mean orbit radius (R _ m) and maximum silver disk normal distance Z _ (max). It is found that there is a great difference in kinematics between thin disk stars and thick disk stars. The results are as follows: (1) thick disk stars and thin disk stars can be distinguished in space motion velocity, and the space motion velocity of thick disk stars is obviously larger than that of thin disk stars. The velocity dispersion of thick disk stars (蟽 U, 蟽 V, 蟽 W) = (58 卤3) 34 卤2 39 卤2 km / s, (蟽 U, 蟽 V, 蟽 W) of thin disk stars = (31 卤2 18 卤1 1 卤15 卤1) km / s 路s. (2) the velocity dispersion of silver disk stars increases gradually with the increase of star age. In thin disk, 蟽 U reaches saturation at star age about 8 Gyr, 蟽 U 鈮，

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