INFRARED LINES AS PROBES OF SOLAR MAGNETIC FEATURES .11. STRUCTURE OFA SUNSPOT UMBRA WITH A LIGHT BRIDGE

We investigate the magnetic structure of an umbra and the light bridge it contains using spectra at 1.56 mu m. The magnetic field strength i n the umbra reaches over 3500 G on the first day of observation and 32 00 G on the second and third days, while the field strength in the lig ht bridge is reduced by 1000-1400 G relative to the nearby umbra. The magnetic vector is also found to be much more horizontal in the light bridge. There is evidence that the boundary between the strong and wea k magnetic field is less than 1 '' wide, implying the presence of larg e currents there. At some locations a downflow of up to 1.5 km s(-1) i s seen in the light bridge relative to the umbral material. Finally, w e discuss the blending of the 1.5648 mu m line in sunspots and develop the depth of the OH 15650.7 Angstrom line as a diagnostic of umbral t emperatures.