High-resolution spectroscopy of active regions

Abstract

We describe an observing program designed to obtain spectra of sunspots, pores, and other features in active regions using the Vacuum Tower Telescope and Echelle Spectrograph at Sacramento Peak Observatory. The spectral lines used in this study have been especially chosen to allow pointed studies of fine structure in the intensity distribution, and in the velocity and magnetic fields in the photospheric levels of active regions, and to relate this structure to chromospheric observations made in the Caii H line. We demonstrate the capacities of the observing program by two examples: umbral fine structure, and an emerging active region. Although the umbral spectrograms resolve the brightness structure down to less than one arc sec we do not find clear-cut relations in the spatial variations of brightness, magnetic field strength and line-of-sight velocity across the umbral structure. In the emerging active region several processes are observed in their relationship: the rising and draining of an arch-filament system, the convective collapse of flux tubes, and the growth of a sunspot pore by coalescing fluxtubes.