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Coordinated Observations with UVCS and LASCO

 

We consider coordinated observations of coronal structures with LASCO, to determine the directions of their magnetic fields, and with UVCS, to measure their thermodynamical parameters.

LASCO can measure the polarization degree and direction of the coronal [Fe XIV] ``green'' line ( 5303). The interpretation of the linear polarization of this line in terms of the resonance scattering/Hanle effect allows determination of the direction of the magnetic field in the observed coronal structure. Coordinated observations with UVCS can provide the ion outflow velocities, the electron density, and the proton and electron temperatures of the same structure. The combination of these data provides the most complete set of observational constraints to empirical models of coronal structures.

Interesting coordinated observations can be done with LASCO of the green line polarization brightness, pI, and with UVCS of the visible polarized radiance, . For radial magnetic fields (e.g., in the cusp of an helmet streamer), the green line depolarization by the Hanle effect is negligible. In this case, the ratio depends only on the abundance of the ion Fe, and therefore provides a method for measuring the coronal abundance of this ion. This method has the advantage of being independent of collisions.

The ion Fe abundance can also be compared to the ion Fe abundance obtained by UVCS observations of the [Fe XII] 1242 line. The knowledge of two ionization stages of the same element yields a better determination of the ionization temperature.

Coordinated Observations with UVCS and LASCO for Coronal Magnetic Field Direction Determination



Peter Smith
Fri Jan 17 12:11:15 EST 1997