This proposal on "The Magnetic Structure of Stellar Atmospheres" between Drs. Jeffrey L. Linsky, James E. Neff, and Steven H. Saar of the University of Colorado at Boulder and Dr. Ilkka Vilhelmi Tuominen of the University of Helsinki, is jointly approved by NSF and the Academy of Finland under the U.S.-Finland Cooperative Science Program. The emission from outer atmospheres of late-type stars arises not homogeneously (as most current models assume), but from discrete, magnetically confined regions. Attempts to probe this structure on the most active, most rapidly-rotating start with spectral ("Doppler") imaging techniques yield a picture of the magnetic field morphology but no information about the field strength. Measurements of field strengths on slowly rotating, relatively inactive stars, provide the mean field strength but no information about the field morphology. However, simultaneous measurements of broad-band linear polarization (BLP) can help interpret the results of each program, as BLP provides some magnetic flux information for rapid rotators and some field morphology information for slow rotators. The researchers propose to exploit the potential of BLP observations by bringing together the unique magnetic field and spectral imaging data sets of the University of Colorado at Boulder with the best available BLP data, that of the University of Helsinki Observatory. The American researchers will obtain new observations using the University of Helsinki photopolarimeters and high- resolution spectrographs at the Crimean Astrophysical Observatory and at the Nordic Optical Telescope with their other observing programs.
