Tunable h-alpha Lyot filter with advanced servo system and image processing: instrument design and new scientific results with the Dutch Open Telescope

The Dutch Open Telescope (DOT; http://dot.astro.uu.nl) on La Palma is a revolutionary open solar telescope, on an excellent site, on top of a transparent tower of steel framework, and uses natural air flow to minimize local seeing. The DOT is a high-resolution multi-wavelength imager capable of long-duration time series aiming at magnetic fine structure, topology and dynamics in the photosphere and low- and high chromosphere. In this paper we describe the latest addition to the multi-wavelength imaging system: a Lyot H-alpha camera channel operating at a wavelength of 656.3 nm, being of major interest for high-chromospheric phenomena. The channel is operated strictly synchronous with the other channels and all data are speckle reconstructed. The channel permits profile sampling and delivers Dopplergrams in a 15 second time cadence, up to several hours long and adding up to a total data amount of 1.6 Terabyte/day. A dedicated computer (DSP, DOT Speckle Processor) has been built for processing the data overnight.