We present the first solar vector magnetogram constructed from measurements of infra-red Mg I 12.32-μm line spectra. Observations were made at the McMath-Pierce Telescope using the Celeste spectrometer/polarimeter. Zeeman-split Stokes line spectra were fitted with Seares profiles to obtain the magnetic field parameters. Maps of absolute field strength, line-of-sight angle, and azimuth are presented. Analysis shows that the variation in field strength within a spatial resolution element, 2 arcseconds, is greatest in the sunspot penumbra and that this is most likely caused by vertical field strength gradients, rather than horizontal image smearing. Widths of the Zeeman-split σ components, assuming a formation layer thickness of 200 km, indicate that vertical field strength gradients can be as large as 6.5 G/km in a penumbra.
Moran, T. G., Jennings, D. E., Deming, L. D., McCabe, G. H., Sada, P. V., & Boyle, R. J. (2007). Solar Magnetograms at 12 μm Using the Celeste Spectrograph. Solar Physics, 241(2), 213-222. https://doi.org/10.1007/s11207-007-0271-1