First High-resolution Spectroscopic Observations by IRIS of a Fast, Helical Prominence Eruption Associated with a Coronal Mass Ejection

Monday, 15 December 2014: 8:45 AM
Wei Liu1, Bart De Pontieu2, Takenori J. Okamoto3, Jean-Claude Vial4, Alan M Title2, Patrick Antolin5, Thomas E. Berger6 and Han Uitenbroek7, (1)Stanford University, Stanford, CA, United States, (2)Lockheed Martin Solar and Astrophysics Laboratory, Palo Alto, CA, United States, (3)Japan Aerospace Exploration Agency, Institute of Space and Astronautical Science, Yoshinodai, Sagamihara, Japan, (4)IAS Institut d'Astrophysique Spatiale, Orsay Cedex, France, (5)NAOJ National Astronomical Observatory of Japan, Tokyo, Japan, (6)NOAA Space Weather Prediction Center, Boulder, CO, United States, (7)National Solar Observatory, Sunspot, New Mexico, United States, United States
High-resolution spectroscopic observations of prominence eruptions and associated coronal mass ejections (CMEs) are rare but can provide valuable plasma and energy diagnostics. New opportunities have recently become available with the advent of the Interface Region Imaging Spectrograph (IRIS) mission equipped with high resolution of 0.33-0.4 arcsec in space and 1 km/s in velocity, together with the Hinode Solar Optical Telescope of 0.2 arcsec spatial resolution. We report the first result of joint IRIS-Hinode observations of a spectacular prominence eruption occurring on 2014-May-09. IRIS detected a maximum redshift of 450 km/s, which, combined with the plane-of-sky speed of 800 km/s, gives a large velocity vector of 920 km/s at 30 degrees from the sky plane. This direction agrees with the source location at 30 degrees behind the limb observed by STEREO-A and indicates a nearly vertical ejection. We found two branches of redshifts separated by 200 km/s appearing in all strong lines at chromospheric to transition-region temperatures, including Mg II k/h, C II, and Si IV, suggesting a hollow, rather than solid, cone in the velocity space of the ejected material. Opposite blue- and redshifts on the two sides of the prominence exhibit corkscrew variations both in space and time, suggestive of unwinding rotations of a left-handed helical flux rope. Some erupted material returns as nearly streamline flows, exhibiting distinctly narrow line widths (~10 km/s), about 50% of those of the nearby coronal rain at the apexes of coronal loops, where the rain material is initially formed out of cooling condensation. We estimate the mass and kinetic energy of the ejected and returning material and compare them with those of the associated CME. We will discuss the implications of these observations for CME initiation mechanisms.