Calibrating Stellar Chromospheric Activity and the Galaxy's Dark Matter Content Using White Dwarf Cooling Times

佛罗里达理工学院的特里·奥斯瓦尔特博士将对宽双星星星对进行光谱研究，这些双星对包含正常的冷主序星和遥远的无相互作用的白色矮星伴星。 白色矮星是银河系中所有前几代恒星缓慢冷却的残余物。 宽双星样本包含白色矮星，它们的冷却年龄跨越了太阳系的整个历史（约100亿年）。 其中一些可能是银河系光环组成部分的成员。 Oswalt博士的研究有两个主要目标：（1）在太阳46亿年的年龄之外，低主序星的色球活动和年龄之间的强相关性延伸了多远？ 除了年龄（如质量、金属丰度）以外，还有哪些变量影响色球层的活动？ (2)冷白色矮星的空间密度是多少，它对银河系的暗物质含量有多大贡献？ 从白色矮星冷却时间得出的盘和/或晕的年龄是多少？几十年来，人们已经知道恒星色球层的活动强烈地依赖于太阳型恒星的恒星年龄。 最近，人们认识到，在质量小于太阳四分之一的冷M型恒星中，这种关系会破裂，或者至少取决于额外的变量。 然而，所有这些先前的工作都是使用附近几个星团中的恒星进行校准的，这些恒星的年龄是从恒星演化模型中估计出来的。 没有比太阳更老的了。 恒星年龄是确定恒星基本属性最困难的方法之一。 宽联星中白色矮星的冷却时间，经过对它们祖先的主序星寿命的修正，提供了相对可靠的主序星同伴年龄的估计。 在先前的研究过程中，奥斯瓦尔特博士已经确定了宽双星中几百颗白色矮星的冷却年龄。 当已知白色矮星的质量时，年龄的不确定性可以小到30 - 40亿年的10-20%。 最近发现的几个晕白色矮星引起了人们的强烈兴趣，因为它们是太阳系附近第一代恒星的残余，可能是银河系暗物质的主要组成部分。 广泛的二进制可能有助于解决目前关于迄今发现的候选人的人口成员资格的争议。 主序星伴星为确定质量（通过引力红移）、运动学（通过径向速度）和化学丰度（金属丰度）提供了一个独特的基准，而这些都是无法从单一白色矮星近乎无特征的光谱中获得的。***

AST 0206115Oswalt Dr. Terry Oswalt, at the Florida Institute of Technology, will carry out a spectroscopic study of wide binary star pairs that contain normal cool main sequence stars with distant non-interacting white dwarf companions. White dwarfs are the slowly cooling remnants of all previous generations of stars in the Galaxy. The wide binary sample contains white dwarfs whose cooling ages span the entire history of the Solar neighborhood (~10 billion years). Some may be members of the Galaxy's halo component. Dr. Oswalt's study has two main objectives: (1) How far beyond the Sun's age of ~4.6 billion years does the strong correlation between chromospheric activity and age in lower main sequence stars extend? What variables other than age (e.g. mass, metallicity) affect chromospheric activity? (2) What is the space density of cool white dwarfs stars, and how much does it contribute to the dark matter content of the Galaxy? What are the ages of the disk and/or halo derived from the white dwarf cooling times? For several decades it has been known that stellar chromospheric activity strongly depends upon stellar age in Solar-type stars. Recently, it has been recognized that this relationship breaks down, or at least depends on additional variables, in cool M-type stars less massive than about one fourth that of the Sun. However, all this prior work has been calibrated using stars in several nearby clusters whose ages were estimated from stellar evolutionary models. None are much older than the Sun. Stellar ages are among the most difficult to determine fundamental properties of stars. Cooling times for the white dwarfs in wide binaries, corrected for their progenitors' main sequence lifetimes, provide relatively robust estimates for the ages of their main sequence companions. In the course of a prior investigation Dr. Oswalt has determined cooling ages for several hundred white dwarfs in wide binaries. The uncertainty in age can be as small as 10-20% in pairs older than about 3-4 billion years, when the white dwarf mass is known. The recent discovery of a few halo white dwarfs has spurred intense interest because they are the remnants of the first generation of stars in the Solar neighborhood and may be a large component of the Galaxy's dark matter. Wide binaries may help to resolve the current dispute over the population membership of the candidates found to date. A main sequence companion provides a unique benchmark for the determination of the mass (via gravitational redshift), kinematics (via radial velocity) and chemical abundance (metallicity) that cannot be obtained from the near featureless spectra of single white dwarfs. ***