A. Asensio Ramos, M. J. Martinez Gonzalez, E. Khomenko, V. Martinez Pillet
Full Stokes filter-polarimeters are key instruments for investigating the
rapid evolution of magnetic structures on the solar surface. To this end, the
image quality is routinely improved using a-posteriori image reconstruction
methods. We analyze the robustness of circular polarization asymmetries to
phase-diversity image reconstruction techniques. We use snapshots of
magneto-hydrodynamical simulations carried out with different initial
conditions to synthesize spectra of the magnetically sensitive Fe I line at
5250.2 A. We degrade the synthetic profiles spatially and spectrally to
simulate observations with the IMaX full Stokes filter-polarimeter. We also
simulate the focused/defocused pairs of images used by the phase-diversity
algorithm for reconstruction and the polarimetric modulation scheme. We assume
that standard optimization methods are able to infer the projection of the
wavefront on the Zernike polynomials with 10% precision. We also consider the
less favorable case of 25% precision. We obtain reconstructed monochromatic
modulated images that are later demodulated and compared with the original
maps. Although asymmetries are often difficult to define in the quiet Sun due
to the complexity of the Stokes V profiles, we show how asymmetries are
degraded with spatial and spectral smearing. The results indicate that,
although image reconstruction techniques reduce the spatial smearing, they can
modify the asymmetries of the profiles, mainly caused by the appearance of
spatially-correlated noise.
View original:
http://arxiv.org/abs/1111.2496
No comments:
Post a Comment