The magnetic nature of wide EUV filament channels and their role in the mass loading of CMEs

Abstract

Previous works have shown that dark and wide EUV lament channels observed at <912 A are due to absorption of EUV lines in cool plasma condensations that are not observed in H. We extend this interpretation and we address the issue of the possible injection of their mass into CMEs, through the magneto-hydrostatic modeling in 3D of one lament observed both in H and in EUV. The model parameters are xed so as to match the H observations only. Further comparison of the model with the EUV observations reveal the magnetic nature of the absorbing plasma condensations. They are formed in magnetic dips, as for the lament itself. Opacity ratios and the hydrostatic condition imply that the dips must be lled by cool material up to 1700 km, which increases the lament mass by 50% as compared to H estimations. Far from the lament, the absorbing condensations are located below 4 Mm in altitude above the photosphere, on the edge of weak photospheric parasitic polarities, within the lower parts of long eld lines overlaying the lament. By physical analogy with H lament feet, we redened these extended regions as EUV feet. The broadening of the EUV lament channel is dominated by EUV feet, while the larger lling of dips plays a non-negligible but minor role. Further implications from this work are discussed, on the visibility and the geometry of the condensations, on the existence of EUV lament channels in the absence of laments, on the loading of cool material into lament feet through bald patch reconnection and on the complex geometry of the upper prominence-corona transition region. The magnetic topology implies that during the lament eruption, the mass of its wide EUV feet will not contribute to the CME, whereas the extra mass provided by the large lling of dips in the lament flux tube will be loaded into the CME.