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R. Casini, A. Lopez Ariste, S. Tomczyk, B. Lites (HAO/NCAR)
We present relatively new diagnostics of ``weak" magnetic fields in the solar atmosphere.
The first diagnostic is suggested by recent advances in the inversion of Stokes profiles of lines formed by resonance scattering in the weakly magnetized plasma of prominences (Hanle effect and level-crossing; 0 to 100 G). Use of pattern recognition techniques (PCA) in this field has marked a sensible progress with respect to previous diagnostic procedures.
The second diagnostic is the modelling of hyperfine structured (HFS) lines that can be observed in the spectrum of the quiet photosphere. This allows to investigate relatively weak photospheric fields (200 G to 1000 G), in which regime the HFS induces peculiar signatures in the Stokes profiles, including the appearance of subcomponents and net circular polarization.
The third diagnostic is suggested by interesting polarization properties of the Na I D1 line formed by resonance scattering: the atomic polarization in the upper level of D1, which is responsible of a characteristic antisymmetric (i.e., V-like) signature in the core of Stokes Q, is rapidly suppressed for B > 10 G, irrespective of the magnetic field direction.
A common denominator of these three diagnostics is their sensitivity to the actual strength of the magnetic field, instead of the magnetic flux within the resolution element. Another common aspect is that all require (or would profit from) high polarization sensitivity, which will be one of the strengths of ATST. For the diagnostics of prominence magnetic fields, the possibility of multiline spectropolarimetry could be decisive. Simultaneous observations of He I D3 (5876A) and 10830A, or of He I D3 and the Na I D lines (all within a 20A spectral range!), would increase the inversion accuracy of PCA. The high spatial resolution capabilities of ATST would be advantageous mostly to diagnose weak photospheric fields, already at the present time. Because of the complexity of radiative transfer in complicated structures like prominences, high spatial resolution in these structures is not the highest priority. However, we hope that when ATST will become operative, this complicated problem will have been attacked succesfully.
The author(s) of this abstract have provided an email address for comments about the abstract: casini@hao.ucar.edu
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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.