Observation of the Molecular Zeeman Effect in the G Band

Here we report on the first observational investigation of the Zeeman effectin the G band around 4305 A. Our spectropolarimetric observations of sunspotswith the Zurich Imaging Polarimeter at the IRSOL facility confirm our previoustheoretical prediction that the molecular Zeeman effect produces measurablecircular polarization signatures in several CH lines that are not overlappedwith atomic transitions. We also find both circular and linear polarizationsignals produced by atomic lines whose wavelengths lie in the G band spectralregion. Together, such molecular and atomic lines are potentially important forempirical investigations on solar and stellar magnetism. For instance, acomparison between observed and calculated Stokes profiles suggests that thethermodynamical and/or magnetic properties of the photospheric regions ofsunspot umbrae are horizontally structured with a component that might beassociated with umbral dots.Comment: 11 pages, 4 figures, accepted for publication in ApJ Letter