标准宇宙学模型认为，目前的可观测宇宙始于137亿年前的大爆炸，大爆炸发生一分钟之后，通过原初的核合成，宇宙中开始形成氢、氦、以及极少量锂、铍、硼元素。尽管今天我们尚未发现任何的原初物质，但是我们可以通过研究现在宇宙中物质的丰度来估计宇宙的原初元素丰度。今天我们能观测到的不同恒星，其表面的化学组成记录了大量有关银河系不同阶段的化学演化历史。银河系演化过程中元素的再生进程构成了恒星形成过程中的核合成历史，而恒星表面包含的信息，则是核合成历史的累积。通过对不同年龄阶段的恒星表面大气丰度进行研究，可以探测恒星化学组成随时间的变化，进一步描绘银河系化学演化历史。将观测结果与理论模型进行比较，我们可以进一步探索初始质量函数、恒星形成率以及恒星系统的形成时标，这对我们深入了解银河系各个组成部分的形成及演化历史具有十分重要的意义。在借助恒星丰度研究银河系历史的过程中，我们必须首先假设：恒星表面的化学组成能够代表恒星形成时星际介质的化学组成，即恒星的表面化学组成不随恒星的演化而改变。因此，我们的研究对象必须是未经演化的恒星（矮星），并且这些恒星的对流区应当足够浅，使得恒星内部生成的物质无法与恒星表面的物质相混合，同时对流层也应当足够深，使得所受引力恰到好处，对流区的气体既不弥散也不被恒星内部吸积。依据上述的特征，小质量的、长寿命的矮星应该是追踪星际介质化学组成的理想天体。基于上述研究目的和Hipparcos数据的优势，同时依据以下两个准则：[1]视星等V < 7.3+1.1sin|b|；[2]绝对星等满足5.5 < Mv < 7.3，我们挑选出Hipparcos星表中的下主序星作为研究样本，并利用中国科学院国家天文台兴隆观测站的2.16米望远镜，对其中30颗晚型主序星进行了高分辨率、高信噪比光谱观测，得到了它们的高质量光谱。利用红外流量方法和三种不同测光系统给出的色指数，我们确定了30颗样本星的有效温度；利用精确的Hipparcos三角视差和Y2恒星演化轨迹，我们得到了样本星的表面重力；通过光谱综合方法，分别确定FeI和FeII线的丰度值，并将对非局部热动平衡效应不敏感的[FeII/H]作为恒星的金属丰度。采用MAFAGS模型计算得到的谱线覆盖的局部热动平衡模型大气，以及经过太阳丰度校正的振子强度值，我们对30颗样本星进行了详细的丰度分析，得到了O、Na、Mg、Al、K、Ca、Sc、Ti、V、Cr、Ni和Ba等元素的丰度，讨论了元素丰度与Fe元素的丰度比[X/Fe]随金属丰度[Fe/H]的分布趋势，并与F、G型矮星以及其他小质量矮星的已有结果进行了比较和讨论。此外，我们还研究了这30颗样本星的运动学参数并进行了分析和讨论。通过上述研究，我们得到了以下几个主要结论：1.我们的结果表明对于[FeI/H]和[FeII/H]，两者之间的差别不超过0.1dex。另外，两者之间的差△([FeII/H] - [FeI/H])与金属丰度有弱的依赖关系，但是不依赖于恒星的有效温度以及表面重力。2. 采用氧7771Å附近的三重线，我们确定了氧元素的丰度值，并且通过多维非线性插值对氧元素丰度进行了非局部热动平衡效应修正，发现对于我们恒星样本，氧元素丰度的non-LTE修正很小：△([O/Fe]NLTE - [O/Fe]LTE) ～ -0.04dex。无论修正前后，我们的结果表明在整个金属丰度范围内，[O/Fe]与恒星的金属丰度无关。3. 对于大多数的元素，它们与铁元素的丰度比[X/Fe]随金属丰度的分布趋势与薄盘中F和G型矮星以及其他小质量富金属矮星的丰度结果类似。4. 通过对样本的运动学参数进行分析，发现HD18702和HD222935这两颗样本星，具有厚盘恒星的运动学特征，即可能为厚盘星；但是由于它们的[α/Fe]接近于太阳的丰度值，因而其化学元素丰度特征又与薄盘恒星类似。

According to the so-called “Standard Model”, the Universe originated from a singularity about 15 billion years ago. At about one minute after the Big Bang, the protons and neutron initiated primordial nucleosynthesis and produced hydrogen, helium, and very small amounts of elements heavier than Li. Although we can not find any primordial matter today, it is possible to estimate the primordial abundances by studying the present matter. As the Galaxy was evolving dynamically and chemically, the chemical history was recorded in the surface composition of the surviving stars that we can observe today. The record is an accumulation of nucleosynthesis history in generations of stars by way of elemental recycling processes during the evolution of the Galaxy. By studying the stellar surface abundance in stars with different ages, we can track an observational chemical history of the Galaxy by exploring stellar chemical composition as a function of time. The comparison of the observed history with the theretical model gives a way to investigate the IMF, SFR, and the formation timescales of stellar systems, which is significant for us to understand the formation and evolution history of each part of the Galaxy.In the study of Galactic history from stellar abundances, there was an implied assumption: the stellar surface composition is a representative of the ISM’s composition at the time it was formed, i.e. the surface composition in these stars did not change during their evolution. To meet this assumption, stars must be unevolved (dwarfs), and their convection zones are shallow enough so that they do not mix up processed materical from deep layers to the surface layers and at the same time deep enough so that they are free from gravitational settling, diffusion and accretion. With all these features, long-lived dwarfs with low mass are ideal tracers of the chemical composition of the ISM at a given Galactic time.Based on these purposes and advantages of Hipparcos data, the low main sequence stars were selected from Hipparcos catalogue according to the two criteria: [1] visual magnitude: V < 7.3+1.1sin|b|; [2] absolute magnitude: 5.5 < Mv < 7.3. Using the 2.16 meter telescope at National Astronomical Observatories (Xinglong, China), thirty sample stars have been observed with efficiency and high resolution, high signal to ratio spectra. By using the infrared flux method and three different color indice given by different photometric system, we derived the effective temperature for these thirty program stars; based on the accurate parallax of Hipparcos and Y2 stellar evolution tracks, we determined the surface gravity of our program stars; abundances of FeI and FeII were derived using the spetral synthesis method and [FeII/H] are suggested as the metallicity of our program stars as FeII lines are not sensitive to the non-LTE effects. In our analysis, the line-blanketed local thermodynamic equilibrium models atmospheres which are computed with the MAFAGS code and the adjusted oscillator strength values by using the theoretical solar model atmosphere with Teff = 5780K, log g = 4.44 dex, and microturbulence ξ = 0.85 km s-1. Finally, abundances of O, Na, Mg, Al, K, Ca, Sc, Ti, V, Cr, Ni, and Ba are determined for the program stars and some comparisons and discussions are made together with the results from F and G dwarfs as well as other dwarfs. Also, kinematic parameters were calculated for our program stars.Our main results and conclusions derived are given below:1. Abundances of FeI and FeII were derive by using the spetral synthesis method and our results shows a much smaller difference between [FeI/H] and [FeII/H], which are less than 0.1dex. The discrepances △([FeII/H] - [FeI/H]) slightly depend on the iron abundances, while are independent of the effective temperature and surface gravity.2. Using the triplet at 7771Å, abundances of oxygen were derived and the non-LTE corrections for oxygen are calculated by multidimensional interpolation. The corrections are small (△([O/Fe]NLTE - [O/Fe]LTE) ～ -0.04dex) for all of our program stars. Our results show that the ratio of [O/Fe] is almost flat at the whole metallicity. 3. For most of the elements, the abundance patterns of our dwarfs are very similar to those of F, G, and other metal-rich dwarfs with low mass.4. Two of our program stars: HD18702, and HD222935, have a thick-disk-like kinematics, while their chemistries are identified clearly as a thin disk member, since their [α/Fe] are about solar.