High Sensitivity Array Studies of Stellar Radio Coronae

该奖项是根据2009年《美国复苏和再投资法案》(公法111-5)资助的。爱荷华大学的罗伯特·L·穆特尔和他的学生将开展一项研究计划，以前所未有的灵敏度、角度分辨率和位置精度拍摄几颗活跃的晚型双星在多个历元的射电日冕图像。这些系统将使用高灵敏度阵列(HSA)进行成像，HSA是世界上最强大的无线电成像长基线阵列。该计划将把HSA的成像能力与优化位置精度的观测策略结合起来，允许以大约一个恒星半径的绝对精度在射电地图上登记分量星的位置。这些图像将首次揭示扩展射电日冕和母星系统之间的关系：射电辐射是起源于一颗恒星还是产生于双星间区域，是否存在大规模的冕环，以及射电耀斑是否出现在恒星表面附近或环顶。除了恒星天体物理结果外，还将确定基本参数，如距离、自行和双轨方向，其精度将明显好于目前的地面或空间光学测量。多历元HSA射电地图将首次详细、系统地确定晚型活动恒星的射电日冕形态。这对于测试现有的恒星日冕模型至关重要，这些模型主要基于综合射电和/或X射线日冕的光谱测量，几乎没有空间信息。一项关键的测试将是解决射电日冕几何的相互竞争的假设，如极地模型、偶极陷阱和吸积盘驱动的双星间发射区。另一个将是确定大尺度磁环或其他结构是否是活动星冕的共同特征，如果是的话，确定它们的大小和时间演化。高保真射电地图，结合准确的覆盖恒星位置，将显著指导在统一理论框架内结合X射线、光学和紫外线观测的星冕综合模型的发展。此外，由于目标恒星都是光学明亮的，高精度测量恒星射电位置的能力将非常有用，可以将光学和射电坐标框架以亚毫秒精度联系在一起。这是一个对许多天体物理学科至关重要的长期目标，包括未来的天体测量空间任务，如Gaia和PlanetQuest。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Dr. Robert L. Mutel of the University of Iowa and his students will undertake a research program to image the radio coronae of several active late-type binary stars at multiple epochs with unprecedented sensitivity, angular resolution, and positional accuracy. The systems will be imaged using the High Sensitivity Array (HSA), the world's most powerful radio imaging long-baseline array. The program will combine the imaging power of the HSA with observational strategies that optimize positional accuracy, allowing registration of the component star positions on the radio maps with an absolute accuracy approximately one stellar radius. These images will reveal, for the first time, the relationship between extended radio coronae and the parent star system: Whether the radio emission originates on a single star or is generated in the inter-binary region, whether large-scale coronal loops exist, and if radio flares arise near the stellar surface or perhaps at the top of loops. In addition to stellar astrophysical results, fundamental parameters such as distance, proper motion, and binary orbital orientation will be determined with an accuracy significantly better than current ground- or space-based optical surveys. The multi-epoch HSA radio maps will allow the first detailed, systematic determination of the morphology of the radio coronae of late-type active stars. This is vital in testing existing models of stellar coronae, which are largely based on spectral measurements of the integrated radio and/or x-ray corona, with little or no spatial information. One key test will be to resolve competing hypotheses of radio coronal geometry, such as polar models, dipole traps, and accretion disk-driven inter-binary emission regions. Another will be to establish whether large-scale magnetic loops or other structures are a common feature in active stellar coronae, and if so, to establish their sizes and temporal evolution.High-fidelity radio maps, combined with accurate overlaid stellar positions, will significantly guide development of comprehensive models of stellar coronae which incorporate x-ray, optical, and UV observations in a unified theoretical framework. Also, since the target stars are all optically bright, the ability to measure stellar radio positions with high accuracy will be very useful in tying the optical and radio coordinate frames together with sub-milliarcsecond precision. This is a long-standing goal vital to many astrophysical disciplines, including future astrometric space missions such as Gaia and PlanetQuest.