What is inside a prominence bubble?

Prominence bubble, termed to a cavity-like feature located at the base of the prominence, is believed to be the active location for mass supply into the prominence. Thanks to the high-resolution observations obtained from HINODE mission, detailed characterization of prominence bubble became possible only in the last decade. However, physical mechanisms responsible for the formation and uplifting of prominence bubbles are not clearly known. In this regard, we investigate the dynamical activities of the material inside a bubble, observed in the Hα line center and in ±0.4 Å wings by the 1-m NVST telescope of Yunnan, China. Flow map along with the Doppler map synthesized from the wing observations revealed a circular motion of the material inside the cavity; comprised sequentially of the blue-wing mass (towards the observer) to be exhibiting dominant upward motion, while the red-wing mass to be showing a downward motion. This enabled us to infer that the magnetic field structure of the investigated prominence bubble conforms well with a kinked flux-rope morphology. In view of no discernable signature of the brightening inside the cavity in the AIA EUV observation, we further propose that the prominence bubble is the site of the emerging flux rope.