On the formation of a helmet streamer on January 24, 1992 at the south-west limb

Abstract

We have analysed the soft X-ray images of the sun obtained with the YOHKOH satellite, white light coronal images observed at Mauna Loa and H-alpha pictures of the sun taken at Mitaka and Kodaikanal to study helmet streamers. We find that heating of a filament and subsequent brightening in X-rays, and eruption in the region lead to the formation of the helmet streamer on January 24, 1992. In another event of February 24, 1993, only the brightening and eruption-like expansion of the brightening in soft X-rays lead to the formation of the streamer. No H-alpha filament was seen in this region before and after the event of brightening in soft X-rays and formation of streamer on February 24, 1993. We, therefore, postulate that the plasma in the streamer comes from the solar surface during the X-ray eruption, and magnetic field of the region perhaps helps in containing the plasma and the formation of the streamer.