Atomic Physics and Modern Solar Spectro-Polarimetry

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Tuesday, August 8, 2017

Observational solar physics is entering a new era with the advent of new 1.5 m class telescopes with adaptive optics, as well as the Daniel K. Inouye 4 m telescope which will become operational in 2019. Major outstanding problems in solar physics all relate to the solar magnetic field.

7090-eps-converted image
Minimally processed Stokes spectra are shown for the 709.0 nm region, obtained 21st August 2014 at the Dunn Solar Telescope using the SPINOR spectro-polarimeter. Standard cal- ibration procedures were applied with no attempts to ”massage” these data. The abscissa is wavelength in̊ A, the ordinate position along the spectrograph slit (arc seconds). The middle dark portion is the umbra (darkest region) of a small sunspot in NOAA active region 12147. The 709.04 nm transition of Fe I (5s 5 F1 → 4p 5 DO0 , both with the 3p63d7(4F) core), shows zero polarization at the sensitivity levels achieved in these observations. The Q, U panels are color scaled between ±0.02I, V is shown between ±0.1I

Spectropolarimetry offers the best, and sometimes only, method for accurate measurements of the magnetic field. In this paper we highlight how certain atomic transitions can help us provide both calibration data, as well as diagnostic information on solar magnetic fields, in the presence of residual image distortions through the atmosphere close to, but not at the diffraction limits of large and polarizing telescopes. Particularly useful are spectral lines of neutrals and singly charged ions of iron and other complex atoms. As a proof-of-concept, we explore atomic transitions that might be used to study magnetic fields without the need for an explicit calibration sequence, offering practical solutions to the difficult challenges of calibrating the next generation of solar spectropolarimetric telescopes. Suggestions for additional work on atomic theory and measurements, particularly at infrared wavelengths, are given. There is some promise for continued symbiotic advances between solar physics and atomic physics.

Publication Name: Can J. Phys