Abstract
The near infrared presents several new and powerful advantages in the diagnostics of sunspot atmospheres: (1) increased magnetic sensitivity in Zeeman-split lines, (2) increased sensitivity of umbral brightness to temperature, and (3) reduced scattered light and seeing disturbances due to atmospheric turbulence. This has revealed a strong and consistent relationship between sunspot brightness and magnetic field strength.We have made spatial/spectral observations of sunspots in the highly sensitive (g = 3) Fe I line at λ = 1.5649 μm to compare field strengths with continuum intensities. We find a characteristic but nonlinear relationship between magnetic field strength, B, and brightness temperature, Tb, in sunspots. In umbrae there is an approximately linear relation between B2 and Tb.
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