The Chemical Evolution of the Dwarf Spheroidal Galaxies

矮球状星系的化学演化

• 批准号: 9803071
• 负责人: Robert Zinn
• 金额: $ 21.1万
• 依托单位: Yale University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-06-15 至 2002-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9803071&HistoricalAwards=false
• 关键词: Chemical; Evolution; Dwarf; Spheroidal; Galaxies

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. ***

在星系的化学演化中，有许多复杂的过程交织在一起。其中包括在星系形成之前宇宙中的化学演化，在大爆炸中，以及可能在最早的恒星中，这些恒星为星系中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，新元素在恒星中产生，返回到星际介质中，并被合并到后代的恒星中。星系的化学演化涉及恒星形成、恒星演化、核合成、恒星风和星系风之间复杂的相互作用。此外，星系合并或星系吸积气体等随机事件可能对化学演化产生深远影响。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——矮球状星系（dSph）中。这些星系光度很低，通常是本星系群的成员。银河系和仙女座星系都是本星系群的成员。由于这种简单性，这些星系的化学演化的最重要特征有可能被分离出来并被理解。一般来说，这些星系含有很少的氢离子气体，如果有的话。有明确的证据表明，恒星形成的时间跨度很大，或多或少是连续的，或在不同的时期形成的。Zinn博士正在详细研究三个dSph星系：天龙座星系、小熊座星系和雕刻家星系。他正在获得这些星系中红巨星的光谱学和光度学，以确定它们的金属丰度分布。这些分布之间的相互比较以及与模型的比较可能揭示控制低质量星系演化的最重要因素。＊＊＊