Bibcode
Lites, B. W.; Martinez Pillet, V.; Skumanich, A.
Referencia bibliográfica
Solar Physics (ISSN 0038-0938), vol. 155, no.1, p. 1-27
Fecha de publicación:
11
1994
Número de citas
56
Número de citas referidas
46
Descripción
We make a quantitative comparison between spectral vs filter measurement
and analysis techniques for extraction of solar vector magnetic fields
from polarimetric data using as a basis the accurately calibrated, high
angular resolution. Stokes profile data from the Advanced Stokes
Polarimeter. It is shown that filter-based measurements deliver
qualitative images of the field alignment for sunspots that are visually
similar to images derived from the more detailed analysis of the Stokes
profiles. However, quantitative comparison with least-squares fits to
the full Stokes profiles show that both the strength of the field
predicted by the filter-based analysis and its orientation contain
substantial errors. These errors are largest for plage regions outside
of sunspots, where the field strengths are inferred to be only a
fraction of their true values, and errors in the orientation of 40-50
deg are common. Within sunspots, errors of 20 deg are commonplace. The
greatest source of these errors is the inability of the filter-based
measurements to account for the small fill fraction of magnetic fields,
or, equivalently, scattered light in the instrument, which reduce the
degree of polarization. The uncertainties of the full profile fitting
methods are also discussed, along with the errors introduced by coarser
wavelength sampling of the observed Stokes profiles. The least-squares
fitting procedure operates best when the profiles are sampled at least
as frequently as one Doppler width of the line.