Using a New Infrared Si x Coronal Emission Line for Discriminating between Magnetohydrodynamic Models of the Solar Corona During the 2006 Solar Eclipse

Abstract

Abstract During the 2006 March 29 total solar eclipse, coronal spectropolarimetric measurements were obtained over a 6 × 6 R ☉ field of view with a 1–2 μm spectral range. The data yielded linearly polarized measurements of the Fe xiii 1.075 μm, He i 1.083 μm, and for the first time, of the Si x 1.430 μm emission lines. To interpret the measurements, we used forward-integrated synthetic emission from two magnetohydrodynamic models for the same Carrington rotation with different heating functions and magnetic boundary conditions. Observations of the Fe xiii 1.075/Si x 1.430 line ratio allowed us to discriminate between two models of the corona, with the observations strongly favoring the warmer model. The observed polarized amplitudes for the Si x 1.430 μm line are around 7%, which is three times higher than the predicted values from available atomic models for the line. This discrepancy indicates a need for a closer look at some of the model assumptions for the collisional coefficients, as well as new polarized observations of the line to rule out any unknown systematic effect in the present data. All but two near-limb fibers show correlated bright He i 1.083 μm and H i 1.282 μm emission, which likely indicates cool prominence emission that is non-localized by the strongly defocused optics. One of the distant fibers located at 1.5 R ☉ detected a weak He i 1.083 μm intensity signal consistent with previous eclipse measurements around 3 × 10−7 B ☉ . However, given the limitations of these observations, it is not possible to completely remove contamination that is due to emission from prominence material that is not obscured by the lunar limb.