First high-resolution spectroscopic observations of an erupting prominence within a coronal mass ejection by the Interface Region Imaging Spectrograph (IRIS)

Liu, Wei, De Pontieu, Bart, Vial, Jean-Claude, Title, Alan M., Carlsson, Mats, Uitenbroek, Han, Okamoto, Takenori J., Berger, Thomas E. and Antolin, Patrick (2015) First high-resolution spectroscopic observations of an erupting prominence within a coronal mass ejection by the Interface Region Imaging Spectrograph (IRIS). The Astrophysical Journal, 803 (2). p. 85. ISSN 0004-637X

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Abstract

Spectroscopic observations of prominence eruptions associated with coronal mass ejections (CMEs), although relatively rare, can provide valuable plasma and three-dimensional geometry diagnostics. We report the first observations by the Interface Region Imaging Spectrograph mission of a spectacular fast CME/prominence eruption associated with an equivalent X1.6 flare on 2014 May 9. The maximum plane-of-sky and Doppler velocities of the eruption are 1200 and 460 km s−1, respectively. There are two eruption components separated by ~200 km s−1 in Doppler velocity: a primary, bright component and a secondary, faint component, suggesting a hollow, rather than solid, cone-shaped distribution of material. The eruption involves a left-handed helical structure undergoing counterclockwise (viewed top-down) unwinding motion. There is a temporal evolution from upward eruption to downward fallback with less-than-free-fall speeds and decreasing nonthermal line widths. We find a wide range of Mg ii k/h line intensity ratios (less than ~2 expected for optically-thin thermal emission): the lowest ever reported median value of 1.17 found in the fallback material, a comparably high value of 1.63 in nearby coronal rain, and intermediate values of 1.53 and 1.41 in the two eruption components. The fallback material exhibits a strong (>5α ) linear correlation between the k/h ratio and the Doppler velocity as well as the line intensity. We demonstrate that Doppler dimming of scattered chromospheric emission by the erupted material can potentially explain such characteristics.

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