What can we learn about coronal mass ejections through spectroscopic observations Hui Tian High Altitude Observatory, National Center for Atmospheric Research ASP research review 2011/10/5

Observation of the corona Habbal et al. 2010, ApJ Fe X 174 Å, imager Fe X 6374 Å, solar eclipse Lower corona, coronagraphExtended corona, coronagraph SOHO LASCO-2  White light  Ground & space  Eclipse  Coronagraph  UV & X-ray  Space  Imager  Coronagraph  Spectrograph/sp ectrometer

Coronal mass ejections (CMEs) Credit: STEREO Science Center  Occurring frequency  Solar maximum: 3-5 per day  Solar minimum: 1 every 3-5 days  Mass: 2 × g  Speed: km/s  Sometimes dimmings in EUV & X-ray

Credit: STEREO Science Center Space weather Credit: SwRI Credit: SOHO Daily MPEG  Earth-directed CMEs are potentially dangerous to our high-tech systems  Satellite anomalies, orbit changes, health of astronauts  Disruption of GPS & other spacecraft signals, radio signals  Damage of electric power grids & pipelines  Imaging observations at the Earth orbit can not observe the evolution of Earth-directed CMEs

EUV spectroscopy Curdt et al. 2001, A&A

Combine imaging & spectroscopic observations

Line profiles in the ejecta  Two well-separated components  A nearly stationary background  A high-speed components (~200 km/s) representing the emission of the ejecta  Calculate the real speed: v=Sqrt(v pos 2 +v los 2 )

Spectroscopic observations of coronal dimmings Attrill et al. 2010, Sol. Phys. McIntosh, ApJ, 2009  ~20 km/s Blue shift: outflows refilling the corona  Enhanced line width: growth of wave amplitude

Blueward asymmetry of line profiles in dimming regions

Two emission components in dimming regions  Two emission components  A nearly stationary background  A weak high-speed (~100 km/s) components representing outflows  Blue shift of ~ 20 km/s and enhanced line width are caused by the superposition of the two components  Only a small portion of the materials in the dimming region are flowing outward  The outflow speed is around 100 km/s

Conclusion  Spectroscopic observations can provide valuable information on the kinematics of CMEs  3-D CME evolutions can be obtained by simultaneous imaging and spectroscopic observations  The outflow speed in the dimming region is of the order of 100 km/s, not ~20 km/s