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

RUI：作为恒星演化示踪剂的近距离双星协调研究

• 批准号: 9417035
• 负责人: Paul Etzel
• 金额: $ 18.7万
• 依托单位: San Diego State University Foundation
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1995
• 资助国家: 美国
• 起止时间: 1995-05-01 至 2001-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9417035&HistoricalAwards=false
• 关键词: RUI; Coordinated; Studies; Close; Binary

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.

小行星9417035 后主序星在耗尽核心的氢燃料后，会经历核心收缩、薄壳中氢的热核点火以及外层膨胀。 当这样一颗星星处于一个近距离双星系统中时，演化膨胀使它充满了所谓的罗氏表面，这是一个泪滴状的叶瓣，尖端指向另一颗星星。 物质沿着这颗星星（“失败者”）的表面流动，通过尖点（引力相等的地方），并被准直成一股流，将质量送到另一颗星星（“获得者”）。 这种物质交换的演化发生在100万到1000万年的时间尺度上，比星星在恒星演化的主序星路径上的演化速度快100到1000倍。 大自然的阴谋使质量流和吸积过程的细节，特别是在大陵型双星星星系统观察。 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 长周期的大陵五系统，其中转移的质量提供了一个扁平的吸积盘旋转的“增益”。 圆盘中的粘性耗散使物质向内螺旋，被“增益者”吸积，为该星星提供质量和角动量。 质量，结构，成分，粘性加热，吸积盘的不稳定性将研究使用强氢-α波长的发射线和红外波长的吸收线的氧在这些磁盘中产生。 将开发一个预测线路轮廓的诊断模型。 双星星系统的轨道几乎是从侧面观察的，所以恒星会互相遮挡。“失败者”也部分地遮蔽了圆盘，而圆盘部分地遮蔽了失败者，大大增加了观测到的图像的空间分辨率。 恒星光变化的多色测光和恒星径向速度的分光观测将提供计算恒星质量和半径的数据，这将确定吸积盘中的引力分层。 物质从圆盘到“增益者”的赤道吸积导致该星星的快速旋转。除非到星星的角动量传输非常有效，否则“增益者”的表面旋转应该是微分的。 差分旋转的检测将寻求通过观察光谱线轮廓作为日食的增益进行和恒星表面的各个部分被遮蔽或暴露。 使用其他技术测量恒星包络的平均旋转的结果，将与差分旋转数据相结合，以揭示最终的质量和角动量同化的“增益”。 将对某些系统中的传质速率进行估算。 这将是可能的判断严格从光度解决方案是否“失败者”真正填补他们的罗氏表面。 在相当多的情况下，罗氏卷没有填满。 因此，在这些系统中，除了简单的叶瓣溢流之外的一些机制必须驱动质量传递和演化。 将研究“失败者”表面的磁活动以及相关系统中的冷星。