THE VECTOR MAGNETIC-FIELD, EVERSHED FLOW, AND INTENSITY IN A SUNSPOT

We present results of simultaneous observations of the vector magnetic field, Evershed how, and intensity pattern in a nearly axisymmetric s unspot, made with the Advanced Stokes Polarimeter at the Vacuum Tower Telescope at NSO (Sacramento Peak). The vector magnetic held is determ ined from the Stokes profiles of the magnetically sensitive lines Fe I 630.15 and 630.25 nm, and Doppler velocities and intensities are meas ured in several lines including the weak C I 538.03 nm line, formed in the deepest layers of the atmosphere. The strength of the magnetic he ld decreases with increasing zenith angle (angle of inclination to the local vertical), and this decrease is nearly linear over most of the range of values in the sunspot. Magnetic field strength and continuum intensity are inversely related in the sunspot in a manner similar to the characteristic nonlinear relationship found by Kopp & Rabin in the infrared line Fe I 1564.9 Mn. A different relationship is found betwe en magnetic held strength and core intensity (in Fe I 630.25 nm), howe ver, with the curve doubling back to give two distinct values of field strength at the same core intensity in the penumbra-the higher and lo wer held strengths corresponding to the inner and outer penumbra, resp ectively. In the penumbra the magnetic held pattern consists of spokel ike extensions of stronger, more vertical magnetic held separated by r egions of weaker, nearly horizontal magnetic held, as found by Degenha rdt & Wiehr and Lites et al. The penumbral magnetic held extends outwa rd beyond the outer continuum boundary of the sunspot, forming a canop y at the height of formation of Fe I 630.25 nm. Our results for the Ev ershed flow confirm the discovery by Rimmele that this how is generall y confined to narrow, elevated channels in the penumbra. In the Fe I 6 30.25 nm line and other strong photospheric lines we see isolated, rad ially elongated channels of Evershed flow crossing the outer penumbra. These flow channels lie in regions of the penumbra where the magnetic held is very nearly horizontal. In the weak C I 538.03 nm line (forme d at a height h = 40 km) the flow pattern shows small, isolated patche s of upflow, lying at the inner end of the Fe I how channels where the magnetic held is more inclined to the horizontal. These patches presu mably correspond to the upstream footpoints of the arched magnetic flu x tubes carrying the Evershed flow. For some of the how channels we fi nd isolated patches of strong downflow in the C I line just outside th e penumbra that might correspond to the downstream footpoints of these flux tubes. There is a weak association between the Evershed flow cha nnels and the dark filaments seen in continuum intensity in the penumb ra, but a much stronger association between the how and the dark filam ents seen in core intensity measured in the same spectral line.