In June 1998, the UVCS, LASCO, and EIT instruments aboard SOHO
detected a very fast CME.  The CME shock crossed the UVCS
spectrograph slit at 1.75 solar radii during the time Type II
radio emission was seen, permitting the first study of a coronal
shock with UV emission line diagnostics, and providing a check on
the interpretation of the radio data.

Rapid opening of the magnetic loops was seen in emission lines formed
at 1.5 to 2.0 million K.  Comparison of sequential images indicates
a speed of 1200 km/s.

The green image (EIT) is Fe XII emission at 1.5 million K.
The red/orange image (LASCO C1) is [Fe XIV] emission at 2 million K.
The blue image (LASCO C2) is white light emission, and the blue/white
rectangle is the UVCS slit, sampling H I Lyman alpha line intensity.

The SOHO data provide a solid empirical basis for the shock
acceleration model of CMEs, and add the information that ions of
different species do not equilibrate to the same temperature in
the shock front.  When the shock arrives at the spectrograph slit,
the H I Lyman alpha intensity drops by about 10 percent, the O VI
line intensities increase by about 25 percent, and the Si XII
line intensity doubles.  These changes are consistent with
shock compression and some collisional ionization.  The O VI lines
(shown at upper left) develop 900 km/s broad wings (redshifted by
about 250 km/s).  This is consistent with randomization of the oxygen
ion speeds with no sharing of energy between oxygen ions and protons.

(Raymond et al. 2000, Geophys. Res. Letters, 27, 1493)