Abstract
White-light images are presently the primary source of information on physical conditions in the solar corona at distances greater than a few tenths of a solar radius above the limb. As a consequence, we still only have an incomplete description of structures extending beyond the solar limb. In particular, streamers, although observed for decades, represent a poorly known phenomenon. SOHO, to be launched in 1995, will be able to make long-term observations of these features up to heights of a fewR⊙, both in white light and UV. In this paper we present simulations of Lα intensity in coronal streamers, based on the two-dimensional (2-D) model developed by Wanget al. (1992, 1993) via a time-dependent numerical relaxation approach. Because the model is 2-D, we make ana priori hypothesis about the extension of streamers in the third dimension. Lα data, obtained from a rocket (Kohlet al., 1983), allowed us to identify a shape which fits the observations. We consider streamers with different magnetic field configurations and at different position angles with respect to the plane of the sky to illustrate how different regions along the line of sight contribute to the emergent intensity. Our purpose is twofold: to provide guidelines for UVCS observational operations and to explore the parameter space in order to understand the role of geometric factors and of the physical state of the corona in determining the overall streamer brightness. We conclude by showing how the results guide the future development of streamer models.
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Noci, G., Poletto, G., Suess, S.T. et al. Lα intensity in coronal streamers. Sol Phys 147, 73–96 (1993). https://doi.org/10.1007/BF00675488
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DOI: https://doi.org/10.1007/BF00675488