Transition region bright dots in active regions observed by the interface region imaging spectrograph

Abstract

The Interface Region Imaging Spectrograph (IRIS) reveals numerous small-scale (sub-arcsecond) brightenings that appear as bright dots sparkling the solar transition region in active regions. Here, we report a statistical study on these transition-region bright dots. We use an automatic approach to identify 2742 dots in a Si IV raster image. We find that the average spatial size of the dots is 0.8 arcsec<SUP>2</SUP> and most of them are located in the faculae area. Their Doppler velocities obtained from the Si IV 1394 Å line range from -20 to 20 km s<SUP>-1</SUP>. Among these 2742 dots, 1224 are predominantly blue-shifted and 1518 are red-shifted. Their non-thermal velocities range from 4 to 50 km s<SUP>-1</SUP> with an average of 24 km s<SUP>-1</SUP>. We speculate that the bright dots studied here are small-scale impulsive energetic events that can heat the active region corona.