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

9417035 埃策尔波斯特主序星耗尽了其核心的氢燃料后，经历了核心收缩、薄壳中氢的热核点火以及外层的膨胀。 当这样的一颗恒星处于一个封闭的双星系统中时，进化膨胀会导致它充满所谓的洛希表面，即一个泪滴状的裂片，其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，穿过尖点（引力相等），并在流中准直，将质量发送到另一颗恒星（“增益者”）。 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主序路径上时的演化速度快约100到1000倍。 大自然共同努力使质量流和吸积过程的细节在大陵五型双星系统中尤其容易观察到。 对这些系统的研究将提高我们对这些过程的物理理解。 研究工作将集中于研究长周期大陵五系统，其中转移的质量提供围绕“增益器”旋转的扁平吸积盘。 盘中的粘性耗散使得物质向内螺旋并被“增益者”吸积，为该恒星提供质量和角动量。 将利用吸积盘中产生的强氢-α波长发射线和氧的红外波长吸收线来研究吸积盘的质量、结构、成分、粘性加热和不稳定性。 将开发预测线路轮廓的诊断模型。 双星系统的轨道几乎是从边缘观察的，因此恒星会互相遮挡。 “失败者”也使圆盘部分黯然失色，而圆盘又使失败者部分黯然失色，从而大大增加了观察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，从而确定吸积盘中的引力分层。 物质从赤道吸积到“增益者”上导致该恒星快速旋转。除非向恒星的角动量传输非常有效，否则“增益器”的表面旋转应该是微分的。 随着增益星日食的进行以及恒星表面的各个部分被遮蔽或暴露，将通过观察谱线轮廓来寻求差分旋转的检测。 使用其他技术测量恒星包层平均旋转的结果将与微分旋转数据相结合，以揭示“增益者”的最终质量和角动量同化。 将对某些系统中的传质速率进行估计。 可以从光度解决方案中批判性地判断“失败者”是否真正填充了他们的罗氏表面。 在很多情况下，罗氏卷都没有被填满。 因此，除了简单的波瓣溢出之外，还必须有某种机制来驱动这些系统中的传质和演化。 将研究“失败者”表面的磁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.