High Sensitivity Array Studies of Stellar Radio Coronae

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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.