Characterization of the umbra–penumbra boundary by the vertical component of the magnetic field - Analysis of ground-based data from the GREGOR Infrared SpectrographP. Lindner, R. Schlichenmaier and N. Bello GonzálezA&A, 638 (2020) A25DOI: https://doi.org/10.1051/0004-6361/202037716
