  The physical connection among and formation mechanisms of various components
of the prominence-horn cavity system remain elusive. Here we present
observations of such a system, focusing on a section of the prominence that
rises and separates gradually from the main body. This forms a configuration
sufficiently simple to yield clues to the above issues. It is characterized by
embedding horns, oscillations, and a gradual disappearance of the separated
material. The prominence-horn structure exhibits a large amplitude longitudinal
oscillation with a period of ~150 minutes and an amplitude of ~30 Mm along the
trajectory defined by the concave horn structure. The horns also experience a
simultaneous transverse oscillation with a much smaller amplitude (~3 Mm) and
shorter period (~10-15 minutes), likely representative of a global mode of the
large-scale magnetic structure. The gradual disappearance of the structure
indicates that the horn, an observational manifestation of the field-aligned
transition region separating the cool and dense prominence from the hot and
tenuous corona, is formed due to the heating and diluting process of the
central prominence mass, while most previous studies suggest that it is the
opposite process, i.e., the cooling and condensation of coronal plasmas, to
form the horn. This study also demonstrates how the prominence transports
magnetic flux to the upper corona, a process essential for the gradual build-up
of pre-eruption magnetic energy.
