Unusual Light Structure in the NOAA 12109 Sunspot Umbra: Observations and Preliminary Results

Abstract

On July 12, 2014, an unusual light structure was observed in the NOAA 12109 sunspot umbra at the Horizontal Solar Telescope of the Sayan Observatory. It differed from traditional light bridges in that it was entirely within the umbra without any apparent connection with the penumbra or the photosphere. The observed light structure more closely resembles a light “island” in outward appearance. A scan was performed in two spectral ranges: ultraviolet (3930–3975 Å ) and infrared (8490–8560 Å ). Images were constructed from the spectrograms in both continua, two Са II lines (8498 and 3933.6 Å ) and four weak lines (Cr I 3963.7 Å, Fe I 3969.3 Å, Fe I 8514.1 Å, Si I 8556.8 Å). The contrast of the structure has been found to depend on the spectral range and to decrease with height. Within the light structure we have detected upflow line-of-sight velocities of ~500 m s⁻¹ from the infrared lines and up to 3000 m s⁻¹ from the ultraviolet lines relative to the sunspot umbra, in which, in turn, downflows (up to 1000 m s−1) relative to the quiet Sun areas that surrounded the sunspot were observed.