RUI: Coordinated Studies of Close Binary Stars as Tracers of Stellar Evolution

9417035颗Etzel Post主序星在耗尽了核心中的氢燃料后，经历了核心收缩、薄壳层中氢的热核点火和外层的膨胀。当这样一颗恒星处于接近的双星系统中时，演化膨胀导致它填满了所谓的罗氏表面，罗氏表面是一个泪滴形状的叶，尖端指向另一颗恒星。物质沿着这颗恒星(“失败者”)的表面流动，通过尖点(引力相等的地方)，并以一条向另一颗恒星(“获得者”)输送质量的小流进行准直。这种通过质量交换进行的演化发生在100万到1000万年的时间尺度上，比恒星处于恒星演化的主序列路径上时的演化速度快100到1000倍。大自然的努力使质量流动和吸积过程的细节尤其在大卫二类型的双星系统中可观察到。对这些系统的研究将提高我们对这些过程的物理理解。研究工作将集中在研究长周期的ALGOL系统，在该系统中，转移的质量提供一个围绕“增益器”旋转的扁平吸积盘。盘中的粘性耗散使物质螺旋向内，被“增益者”吸积，为该恒星提供质量和角动量。利用吸积盘中产生的氧的强氢-α波长发射线和红外波长吸收线，研究吸积盘的质量、结构、组成、粘性加热和不稳定性。将开发一种预测线型的诊断模型。双星系统的轨道几乎是从侧面观察的，因此这些恒星相互遮挡。“失败者”也会部分遮盖圆盘，而圆盘也会部分遮盖失败者，大大增加了观测到的图像的空间分辨率。恒星光变化的多色光度测量和恒星径向速度的光谱观测将为计算恒星质量和半径提供数据，这将确定吸积盘中的引力分层。来自圆盘的物质在赤道上吸积到“获得者”上，导致恒星快速自转。除非角动量传输到恒星是非常有效的，否则“获得者”的表面自转应该是有差别的。随着日食的继续和恒星表面的不同部分被遮盖或暴露，将通过观察光谱线形来探测差异自转。使用其他测量恒星包层平均自转的技术得出的结果，将与差分自转数据结合起来，阐明“获益者”对最终质量和角动量的同化。将对某些系统中的传质速率进行估算。这将有可能从光度学解决方案的批判性判断“失败者”是否真的填补了他们的罗氏表面。在相当多的案例中，罗氏的销量没有填满。因此，除了简单的叶溢流之外，还必须有某种机制来驱动这些系统中的传质和演化。我们将研究“失败者”表面的磁场活动，以及相关系统中的冷恒星。

9417035 Etzel Post main-sequence stars, having exhausted the hydrogen fuel in their core, undergo core contraction, thermonuclear ignition of hydrogen in a thin shell, and expansion of their outer layers. When such a star is in a close binary system, evolutionary expansion causes it to fill its so-called Roche surface, a tear-dropped shaped lobe with a cusp pointed at the other star. Matter flows along the surface of this star (the "loser"), through the cusp (where the gravitational forces are equal), and is collimated in a stream that sends mass to the other star (the "gainer"). This evolution by mass exchange occurs on a time scale of one million to ten million years, some 100 to 1000 times faster than the rate of evolution when the star is on the main sequence path of stellar evolution. Nature has conspired to make the details of mass flows and accretion processes especially observable in Algol-type binary star systems. Research on these systems will improve our physical understanding of these processes. The research effort will be concentrated on studying long-period Algol systems in which the transferred mass supplies a flattened accretion disk rotating around the "gainer". The viscous dissipation in the disk allows matter to spiral inward to be accreted by the "gainer", supplying mass and angular momentum to that star. The mass, structure, composition, viscous heating, and instabilities of accretion disks will be studied using the strong hydrogen-alpha wavelength emission lines and infrared wavelength absorption lines of oxygen produced in these disks. A diagnostic model to predict line profiles will be developed. The orbits of binary star systems are viewed nearly edge-on, so the stars eclipse each other. The "losers" also partially eclipse the disks, and the disks partially eclipse losers, adding greatly to the observed spatial resolution of the images. Multi-color photometry of the stellar light variations and spectroscopic observations of stellar radial velocities will provide data to calculate stellar masses and radii, which will set the gravitation stratification in the accretion disks. Equatorial accretion of matter from the disk onto the "gainer" leads to rapid rotation of that star. Unless the angular momentum transport to the star is very efficient, the surface rotation of the "gainer" should be differential. The detection of the differential rotation will be sought by observing spectral line profiles as eclipses of the gainer proceed and various portions of the stellar surface are eclipsed or exposed. Results from using other techniques that gauge the average rotation of the stellar envelope, will be combined with the differential rotation data to shed light on the ultimate mass and angular momentum assimilation by "gainers". Estimates of the rate of mass transfer in some systems will be made. It will be possible to judge critically from photometric solutions whether "losers" truly fill their Roche surfaces. In a significant number of cases, the Roche volumes are not filled. Some mechanism other than simple lobe overflow must therefore drive mass transfer and evolution in these systems. Magnetic activity on "loser" surfaces, and cool stars in related systems, will be studied.