A NARROW STREAMER-PUFF CORONAL MASS EJECTION FROM THE NONRADIAL ERUPTION OF AN ACTIVE-REGION FILAMENT

Abstract

So-called streamer-puff coronal mass ejections (CMEs) were recently identified by Bemporad et al. as a new variety of CME. They originate from nonradial ejecta from compact ejective flares occurring in the outskirts of the base of a streamer and travel out along it, during which the streamer is transiently inflated by the puff but is not disrupted. Moore & Sterling further indicated that streamer-puff CMEs are a particular subclass of a broad class of CMEs, called "over-and-out" CMEs, which come from flare-producing magnetic explosions of various sizes and are laterally far offset from the flare. In this paper, we present observations of a streamer-puff CME that resulted from the spectacular eruption of an active-region filament inside a single helmet streamer consisting of a double-arcade system, occurring in AR 10792 on 2005 July 29. The filament was covered by a smaller arcade in the outer flank of the streamer base, with a nearby quiescent prominence below another larger arcade. In the inner corona the filament eruption underwent nonradial motion, while in the outer corona the CME had a radial path along the streamer that was laterally offset from the original site of the filament. The CME was narrow with an angular width of only 15° and clearly showed a typical three-part structure below 1.38 R☉. In this eruption, the prominence remained nearly unchanged, but in other stronger eruptions of a homologous sequence from the same AR in the following days, it exhibited obvious oscillations. These observations can be explained by the magnetic-arch-blowout scenario for streamer-puff and over-and-out CMEs, in which the streamer arcade can act on the erupting filament, laterally deflecting and channeling its motion. The prominence oscillations probably indicate an interplay or interaction between the twin arcades that could affect but not destroy the overall field configuration supporting the prominence.