Prominence fine structures in weakly twisted and highly twisted magnetic flux ropes

Context. Many prominences are supported by magnetic flux ropes. One important question is how we can determine whether the flux rope is weakly twisted or highly twisted. Aims. In this paper, we attempt to decipher whether prominences supported by weakly twisted and highly twisted flux ropes can manifest different features so that we might distinguish the two types of magnetic structures based on their appearance. Methods. We performed pseudo three-dimensional simulations of two magnetic flux ropes with different twists. Results. We find that the resulting two prominences differ in many aspects. The prominence supported by a weakly twisted flux rope is composed mainly of transient threads (similar to 82.8%), forming high-speed flows inside the prominence, and its horns are evident. Conversely, the prominence supported by a highly twisted flux rope consists mainly of stable quasi-stationary threads (similar to 60.6%), including longer independently trapped threads and shorter magnetically connected threads. Our simulations also reveal that the prominence spine deviates from the flux rope axis in the vertical direction and from the photospheric polarity inversion line projected on the solar surface, especially for the weakly twisted magnetic flux rope. Conclusions. The two types of prominences differ significantly in appearance. Our results also suggest that a piling-up of short threads in highly twisted flux ropes might account for the vertical-like threads in some prominences.