A rising cool column associated with formation of prominence and coronal cavity

A prominence consists of relatively cool chromospheric plasma found above the solar limb at coronal heights where the temperature and density are typically two order of magnitude higher and lower, respectively. Prominences are frequently associated with larger coronal structures known as coronal cavities. There are numerous observational studies on prominences with multi-wavelength and with high-spatial resolution and also on the relationship between cavities and coronal mass ejections, while less analyses on activities inside coronal cavities. Continuous observations were performed of a quiescent prominence with the Hinode satellite on 2006 December 23 and 24. In the Ca II H-line channel of the Solar Optical Telescope we observed a peculiar slowly-rising column of cool material from the lower atmosphere. The apparent ascent speed of the column is 2 km/s, while the fine structures of the column exhibit much faster motion of up to 20 km/s. The column eventually becomes a faint low-lying prominence. An overlying coronal cavity associated with the appearance of the column seen in the X-ray and EUV moves upward at 5 km/s. We discuss the relationship between these episodes and suggest that they are due to the emergence of a helical flux rope that undergoes reconnection with lower coronal fields, possibly carrying material into the coronal cavity. Under the assumption of the emerging flux scenario, the lower velocity of 2 km/s and the higher one of 20 km/s in the column are attributed to the rising motion of the emerging flux and to the outflow driven by magnetic reconnection between the emerging flux and the pre-existing coronal field, respectively. Our presentation gives a coherent explanation of the enigmatic phenomenon of the rising column with the emergence of the helical rope and its effect on the corona.