Real-Time Frame Selector and its Application to Observations of the Horizontal Velocity Field in the Solar Photosphere

A real-time frame selector (RTFS), a new observational system, was developed at the Domeless Solar Telescope of Hida Observatory, Kyoto University. Our RTFS allows us to automatically select out a video frame with the highest spatial resolution in a series of live video images during a prescribed time span, and stores the selected one in digital format to a hard disk file. We applied the RTFS to observations of solar granulation in the G-band wavelength (λ 4308 Å, passband 20 Å) and obtained a time series of data with a step of 15 seconds. By the method of local-correlation tracking, we derived the horizontal velocity field with the granulation pattern as tracers. In a quiet photosphere, we found the so-called mesogranulation flow field, clearly. Supergranular flow patterns were also detected and identified from a comparison with an Hα wing image. On the other hand, in a sunspot area, we found new evidence of horizontal inflow from penumbral areas to umbral areas as well as the presence of another circumferential inflow from the surrounding photosphere to the penumbral outer edge.