The structure of sunspots

Magnetic field strengths in small umbrae and pores are measured using the line Ti i 6064.6 Å, which is formed purely in umbrae. We find field strengths between 1900 and 2600 G in the darkest parts of small umbrae and of well established pores; the spread is partly intrinsic. The field strength in diffuse transient protopores amounts to 1500 ± 250 G.We demonstrate that usage ofthe well-known magnetic line 6173.3 Å and other Fe i lines yield systematically smaller magnetic field strengths than Ti i 6064.6 Å. This is due to blending ofthe components with the central component due to photospheric stray light and the component. Routine measurements are therefore unreliable for small spots 251-01Based on observations at Sacramento Peak Observatory, Sunspot, New Mexico, U.S.A.