POWRE: Direct Impact Accretion in Interacting Binary Star Systems

恒星中的直接碰撞吸积发生在相互作用的双星系统中，这类双星被称为Algol型双星。这些系统包含一颗B-A型主序列星和一颗填充其罗氏叶的冷型F-K型巨星或亚巨星伴星。在短周期的参宿四恒星中，来自冷成分的气流与伴星的表面直接接触。这种影响不会发生在长周期的ALGOL中，因为与双星中恒星的分离相比，它们更宽，质量获得者的半径相对较小。直接撞击产生的吸积结构范围从恒星表面的热点到称为吸积环的几乎稳定的吸积盘。对这些双星的多普勒层析观测数据显示，有证据表明氢-阿尔法沿着预测的质量转移流的引力路径发生了吸积。这种截然不同的图像在整个相互作用的双星中是独一无二的，因为阿尔戈尔星系处于质量转移的缓慢阶段，因此提供了一个捕捉实际质量转移过程的机会。一些短周期算法具有稳定的吸积结构，而另一些算法则变化很大，它们在一个轨道周期内从流状分布转变为类似经典吸积盘的分布。理查兹博士通过氢-阿尔法(H-阿尔法)波长和紫外光谱观测、多普勒层析成像和流体动力学模拟，研究了这些吸积结构。最近，理查兹博士完成了对18个大卫一类型恒星系统的H-α光谱形态的重大研究。理查兹博士将从弗吉尼亚大学休学术假，前往高级研究院进行休假访问。理查兹博士将能够在休假期间，通过使用紫外线光谱的类似研究的数据以及在光学和紫外线波长产生的多普勒断层图像的比较，来加强先前研究的结果。该项目由天文学司和数学和物理科学局的多学科活动办公室资助。

AST-0074586RichardsDirect impact accretion in stars occurs in the class of interacting binary star systems known as the Algol-type binary stars. These systems contain a type B-A main sequence star and a cool type F-K giant star or subgiant companion that fills its Roche lobe. In the short-period Algol stars, the gas flow from the cool component makes contact with the surface of the companion in a direct impact. This impact does not occur in the long-period Algols because they are wider and the radius of the mass gainer is relatively small when compared to the separation of the stars in the binary. The accretion structures produced by the direct impact range from a hot spot on the surface of the star to nearly stable accretion disks called accretion annuli. Data using Doppler tomogram observations of these binaries show evidence of Hydrogen-alpha accretion along the predicted gravitational path of the mass transfer stream. Such distinct images are unique among the entire class of interacting binaries because the Algols are in the slow phase of mass transfer and hence provide an opportunity to capture the process of mass transfer in action. Some short-period Algols have stable accretion structures while others are quite variable and they change within an orbital cycle from a stream-like distribution to one which resembles a classical accretion disk. Dr. Richards has studied these accretion structures by means of Hydrogen-alpha (H-alpha) wavelength and ultraviolet spectroscopy observations, Doppler tomography, and hydrodynamic simulations. Recently, Dr. Richards completed a major study of the H-alpha spectroscopic morphologies of 18 Algol-type star systems. Dr. Richards will take academic leave from the University of Virginia to go to the Institute of Advanced Studies for a sabbatical visit. Dr. Richards will be able to work on enhancing the results from the previous research, during the sabbatical period, by using data from similar studies of ultraviolet spectra and the comparison of Doppler tomograms generated at both optical and ultraviolet wavelengths.This project is funded by the Division of Astronomical Sciences and the Office of Multidisciplinary Activities in the Mathematical and Physical Sciences Directorate.***