First High-resolution Spectroscopic Observations of an Erupting Prominence Within a Coronal Mass Ejection by the Interface Region Imaging Spectrograph (IRIS)

Abstract

Spectroscopic observations of prominence eruptions associated with coronal mass ejections (CMEs), although relatively rare, can provide valuable plasma and 3D geometry diagnostics. We report the first observations by the Interface Region Imaging Spectrograph (IRIS) 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, respectively. There are two eruption components separated by ~200 km/s 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 counter-clockwise (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 and 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 ($>5\sigma$) 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.

12 pages, 6 figures, accepted by ApJ (Feb 15, 2015)

References in corpus (5)

• Advances in Observing Various Coronal EUV Waves in the SDO Era and Their Seismological Applications (Invited Review)
• Double Coronal Hard and Soft X-ray Source Observed by RHESSI: Evidence for Magnetic Reconnection and Particle Acceleration in Solar Flares
• Open questions on prominences from coordinated observations by IRIS, Hinode, SDO/AIA, THEMIS, and the Meudon/MSDP
• Soft X-ray Fluxes of Major Flares Far Behind the Limb as Estimated Using STEREO EUV Images
• Effect of motions in prominences on the helium resonance lines in the extreme ultraviolet

Cited by in corpus (15)

• Transition Region and Chromospheric Signatures of Impulsive Heating Events. I. Observations
• Stellar coronal mass ejections II. Constraints from spectroscopic observations
• Helical motions of fine-structure prominence threads observed by Hinode and IRIS
• Solar prominence diagnostics from non-LTE modelling of Mgii h&k line profiles
• Modelling of Mg II lines in solar prominences
• Two-dimensional simulations of coronal rain dynamics. I. Model with vertical magnetic field and an unbounded atmosphere
• Relation of coronal rain originating from coronal condensations to interchange magnetic reconnection
• Comparing UV/EUV line parameters and magnetic field in a quiescent prominence with tornadoes
• Rapid Rotation of an Erupting Prominence and the Associated Coronal Mass Ejection on 13 May 2013
• Three-dimensional velocity fields of the solar filament eruptions detected by CHASE
• Revisiting the formation mechanism for coronal rain from previous studies
• Fast Magnetosonic Waves and Flows in a Solar Prominence Foot: Observations and Modeling
• From eruption to post-flare rain: a 2.5D MHD model
• Spectral evolution of an eruptive polar crown prominence with IRIS observations
• A new view of the solar interface region from the Interface Region Imaging Spectrograph (IRIS)