STOKES PROFILE ANALYSIS AND VECTOR MAGNETIC-FIELDS .6. FINE-SCALE STRUCTURE OF A SUNSPOT

The vector magnetic field structure of a small, symmetric sunspot obse rved very close to disk center has been explored using data from the H igh Altitude Observatory/National Solar Observatory Advanced Stokes Po larimeter (ASP). This instrument provides, for the first time, quantit ative information on sunspot photospheric vector magnetic fields with high angular resolution, as derived from full Stokes profiles of the Z eeman-sensitive Fe I line pair at 630 nm. We find the following. (1) T he penumbra contains narrow, radial ''spines'' of more intense magneti c field more vertically oriented than their surroundings; (2) the magn etic field diverges azimuthally away from the spine axes, as it should for a more intense intrusion of field embedded in a gravitational str atified atmosphere; (3) there are dark protrusions out from the umbra which traverse much of the penumbra and which are characterized by mor e vertical magnetic field; (4) the observed structure of the magnetic field in both the umbra and penumbra is stable over the 30 minute dura tion of our observing sequence; (5) we do not find a tight correlation of field inclination with intensity in the penumbra; (6) at the outer edge of the penumbra, the field penetrates the photosphere at an aver age angle of about 70-degrees from the vertical; (7) outside of the pe numbra the sunspot field forms a canopy which is directly observed by our technique; (8) outside of, but close to the sunspot, there are sma ll magnetic features of mixed polarity that are rather highly inclined to the vertical, presumably as influenced by the sunspot canopy; (9) away from the sunspot, the isolated magnetic elements have nearly vert ical orientation. These observations suggest that magnetic buoyancy, i n addition to thermal buoyancy, plays an important role in maintaining the observed structure in sunspot penumbra.