Solar Coronal Plumes

Polar plumes are thin long ray-like structures that project beyond the limb of the Sun polar regions, maintaining their identity over distances of several solar radii. Plumes have been first observed in white-light (WL) images of the Sun, but, with the advent of the space era, they have been identified also in X-ray and UV wavelengths (XUV) and, possibly, even in in situ data. This review traces the history of plumes, from the time they have been first imaged, to the complex means by which nowadays we attempt to reconstruct their 3-D structure. Spectroscopic techniques allowed us also to infer the physical parameters of plumes and estimate their electron and kinetic temperatures and their densities. However, perhaps the most interesting problem we need to solve is the role they cover in the solar wind origin and acceleration: Does the solar wind emanate from plumes or from the ambient coronal hole wherein they are embedded? Do plumes have a role in solar wind acceleration and mass loading? Answers to these questions are still somewhat ambiguous and theoretical modeling does not provide definite answers either. Recent data, with an unprecedented high spatial and temporal resolution, provide new information on the fine structure of plumes, their temporal evolution and relationship with other transient phenomena that may shed further light on these elusive features

BUSCA: Simultaneous imaging in 4 optical bands.

The "Bonn University Simultaneous CAmera" (BUSCA) is a CCD camera system for the CA 2.2.m telescope which allows simultaneous direct imaging of the same area in four colors. It is based on three dichroic beam splitters and four large area detectors (6x6 cm^2). The field of view at the 2.2 m telescope is 12'x12'. BUSCA offers new perspectives for multicolor photometry: i) Color indices in the optical can be determined with high reliability even in non-photometric atmospheric conditions. ii) Precious observing time is used very efficiently. iii) With the large field of view extended objects are covered in a single exposure. iv) Each exposure results in a complete dataset. The dichroics --- plane-parallel glass plates operating at an angle of 45 degrees --- split the optical wavelength range such that standard intermediate-band filter systems (e.g. Stroemgren) can be used. During the commissioning phase the instrument is equipped with four 2k x 2k LORAL CCDs. Three devices will be replaced by (thick) monolithic 4k x 4k, 15\mu CCDs from Lockheed Martin Fairchild Systems. The UV channel will be upgraded to a single thinned 4k x 4k or two thinned 2k x 4k devices depending on availability and funding