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

9417035 Etzel Post主序星在耗尽其核心的氢燃料后，经历核心收缩、薄壳内氢的热核点火和外层膨胀。当这样一颗恒星处于一个紧密的双星系统中时，进化的膨胀使它充满了所谓的罗氏表面，这是一个泪滴状的叶状突起，尖端指向另一颗恒星。物质沿着这颗恒星（“输家”）的表面流动，通过尖端（引力相等的地方），并在一条流中对准，将质量送到另一颗恒星（“赢家”）。这种质量交换的演化发生在100万到1000万年的时间尺度上，比恒星在恒星演化的主序星路径上的演化速度快100到1000倍。大自然密谋使质量流动和吸积过程的细节在大耳座型双星系统中特别容易观察到。对这些系统的研究将提高我们对这些过程的物理理解。研究工作将集中在研究长周期Algol系统，其中转移的质量提供了一个围绕“增益”旋转的扁平吸积盘。圆盘内的粘性耗散使物质螺旋向内被“增益器”吸积，为那颗恒星提供质量和角动量。利用吸积盘中产生的氧的强氢α波长发射谱线和红外波长吸收谱线，研究吸积盘的质量、结构、组成、粘性加热和不稳定性。将开发一种诊断模型来预测线路轮廓。双星系统的轨道几乎是侧面的，所以恒星会互相遮挡。“输家”也部分地遮蔽了圆盘，而圆盘也部分地遮蔽了输家，这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定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，这将设置吸积盘中的引力分层。物质从圆盘向“增益星”的赤道吸积导致了恒星的快速旋转。除非角动量传输到恒星非常有效，否则“增益器”的表面旋转应该是微分的。当增益器的日食发生时，恒星表面的不同部分被日食或暴露时，将通过观察光谱线剖面来寻找微分旋转的探测。使用其他测量恒星包层平均旋转的技术得到的结果，将与差分旋转数据相结合，以阐明“增益者”的最终质量和角动量同化。对某些系统的传质速率进行估计。这将有可能从光度法溶液中批判性地判断“失败者”是否真的填满了它们的罗氏表面。在相当数量的病例中，罗氏卷没有填充。因此，在这些系统中，除了简单的叶溢出之外，一定有某种机制驱动着传质和进化。将研究“失败者”表面的磁活动，以及相关系统中的冷星。

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.