Solar Spectral Lines w/ Special Polarization Properties for the Calibration of Instrument Polarization

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Tuesday, May 9, 2017

We investigate atomic transitions that have previously been identified as having zero polarization from the Zeeman effect. Our goal is to identify spectral lines that can be used for the calibration of instrumental polarization of large astronomical and solar telescopes, such as the Daniel K. Inouye Solar Telescope, which is currently under construction on Haleakala.

Stokes profiles of the Fe I transition image
Stokes profiles of the Fe I transition $\rm ^5F^o_1$--$\rm ^5F_1$ at 7389.398\,\AA under different magnetic fields and Lande' factors.

We use a numerical model that takes into account the generation of scattering polarization and its modification by the presence of a magnetic field (Hanle effect, Zeeman effect, and incomplete Paschen-Back effect). We adopt values for the Land\'e factors from spectroscopic measurements or semi-empirical results, thus relaxing the common assumption of LS-coupling previously used in the literature. The mechanisms dominating the polarization of particular transitions are identified, and we summarize groups of various spectral lines useful for the polarization calibration of spectro-polarimetric instruments, classified according to their polarization properties.

Submitted to the Astrophysical Journal in April 2017.