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 arcsec2 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−1. 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−1 with an average of 24 km s−1. We speculate that the bright dots studied here are small-scale impulsive energetic events that can heat the active region corona.