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Paper: 3-D Structure of Sunspots Using Imaging Spectroscopy
Volume: 354, Solar MHD Theory and Observations: A High Spatial Resolution Perspective
Page: 237
Authors: Balasubramaniam, K.S.; Gary, G.A.; Reardon, K.
Abstract: We use the Interferometric BIdimensional Spectrometer (IBIS) of the INAF/Arcetri Astrophysical Observatory and installed at the National Solar Observatory (NSO) Dunn Solar Telescope, to understand the structure of sunspots. Using the spectral lines Fe I 6301.5 Å, Fe II 7224.4 Å, and Ca II 8542.6 Å, we examine the spectroscopic variation of sunspot penumbral and umbral structures at the heights of formation of these lines. These high resolution observations were acquired on 2004 July 30 – 31, of active region NOAA 10654, using the high order NSO adaptive optics system. We map the spatio-temporal variation of Doppler signatures in these spectral lines, from the photosphere to the chromosphere. From a 70-minute temporal average of individual 32-second cadence Doppler observations we find that the averaged velocities decrease with height. They are about 3.5 times larger in the deeper photosphere (Fe II 7224.4 Å; height-of-formation ≈ 50 km) than in the upper photosphere Fe I 6301.5 Å; height-of-formation ≈ 350 km), There is a remarkable coherence of Doppler signals over the height difference of 300 km. From a high-speed animation of the Doppler sequence we find evidence for what appears to be ejection of high speed gas concentrations from edges of penumbral filaments into the surrounding granular photosphere. The Evershed flow persists a few arcseconds beyond the traditionally demarcated penumbra-granulation boundary. We present these and other results and discuss the implications of these measurements for sunspot models.
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