The Three-part Structure of a Filament-unrelated Solar Coronal Mass Ejection

Abstract

Coronal mass ejections (CMEs) often exhibit the typical three-part structure in the corona when observed with white-light coronagraphs, i.e., the bright leading front, dark cavity, and bright core, corresponding to a high-low-high density sequence. As CMEs result from eruptions of magnetic flux ropes (MFRs), which can possess either lower (e.g., coronal-cavity MFRs) or higher (e.g., hot-channel MFRs) density compared to their surroundings in the corona, the traditional opinion regards the three-part structure as the manifestations of coronal plasma pileup (high density), coronal-cavity MFR (low density), and filament (high density) contained in the trailing part of MFR, respectively. In this paper, we demonstrate that filament-unrelated CMEs can also exhibit the classical three-part structure. The observations were made from different perspectives through an event that occurred on 2011 October 4. The CME cavity corresponds to the low-density zone between the leading front and the high-density core, and it is obvious in the low corona and gradually becomes fuzzy when propagating outward. The bright core corresponds to a high-density structure that is suggested to be an erupting MFR. The MFR is recorded from both edge-on and face-on perspectives, exhibiting different morphologies that are due to projection effects. We stress that the zone (MFR) with lower (higher) density in comparison to the surroundings can appear as the dark cavity (bright core) when observed through white-light coronagraphs, which is not necessarily the coronal-cavity MFR (erupted filament).