The Chemical Evolution of the Dwarf Spheroidal Galaxies

AST98-03071 Zinn星系的化学演化中有许多复杂的过程交织在一起。其中包括星系形成前宇宙中的化学演化，大爆炸中的化学演化，以及可能是最早的恒星中的化学演化，这些恒星为星系的化学演化设定了初始条件。星系的化学成分随着时间的推移而演变，因为新的元素在恒星中产生，返回星际介质，并并入后续的恒星。星系的化学演化涉及恒星形成、恒星演化、核合成、恒星风和银河系风之间的复杂相互作用。此外，星系合并或星系吸积气体等随机事件可能对化学进化产生了深远的影响。这个循环过程极其复杂，涉及几个鲜为人知的过程和变量。这个复杂过程的最简单形式可能发生在最小、最不复杂的星系中，即矮球星系(DSph)。这些星系是非常低光度的星系，通常是本星系群的成员。银河系和仙女座菌株都是当地小组的成员。由于这种简单性，人们有希望分离和理解这些星系化学演化的最重要特征。一般来说，这些星系含有极少的高碘气体，如果有的话。有明确的证据表明，恒星是在很大的时间范围内形成的，或多或少是连续形成的，或者是在不同的时期形成的。津恩博士正在详细研究三个dSph星系：在德拉科、小熊座和雕像。他正在对这些星系中的红巨星进行光谱和光度测量，以确定它们的金属丰度分布。将这些分布相互比较，并与模型进行比较，可能会揭示控制低质量星系演化的最重要因素。***

AST 98-03071 Zinn There are many complex processes intertwined in the chemical evolution of galaxies. These include the chemical evolution in the universe before formation of galaxies, in the Big Bang, and possibly in the earliest stars which set the initial conditions for the chemical evolution in galaxies. The chemical compositions of galaxies evolve with time as new elements are created in stars, returned to the interstellar medium, and incorporated into subsequent generations of stars. A galaxy's chemical evolution involved a complicated interplay among star formation, stellar evolution, nucleosynthesis, stellar winds, and galactic winds. In addition, random events such as the merger of galaxies or the accretion of gas by a galaxy may have had a profound effect on chemical evolution. This cyclic process is exceedingly complex, and involves several poorly known processes and variables. Probably the simplest form of this complex process occurs in the smallest, least complicated of galaxies, the dwarf spheroidal (dSph) galaxies. These galaxies are very low luminosity galaxies usually members of the Local Group. Both the Milky Way and Andromeda are members of the Local Group. Because of this simplicity, there is hope that the most important features of the chemical evolution of these galaxies may be isolated and understood. In general, these galaxies contain very little, if any, H I gas. There is clear evidence that stars formed over a large range in time, either more or less continuously or at separate epochs. Dr. Zinn is studying in detail three dSph galaxies: in Draco, Ursa Minor and Sculptor. He is obtaining spectroscopy and photometry of red giant stars in these galaxies to determine their metallicity distributions. The comparison of these distributions with each other and with models may reveal the most important factors controlling the evolution of low mass galaxies. ***