  We report quadrature observations of an extreme-ultraviolet (EUV) wave event
on 2011 January 27 obtained by the Extreme Ultraviolet Imager (EUVI) onboard
\emph{Solar Terrestrial Relations Observatory} (\emph{STEREO}), and the
Atmospheric Imaging Assembly (AIA) onboard the \emph{Solar Dynamics
Observatory} (\emph{SDO}). Two components are revealed in the EUV wave event. A
primary front is launched with an initial speed of $\sim$440 km s$^{-1}$. It
appears significant emission enhancement in the hotter channel but deep
emission reduction in the cooler channel. When the primary front encounters a
large coronal loop system and slows down, a secondary much fainter front
emanates from the primary front with a relatively higher starting speed of
$\sim$550 km s$^{-1}$. Afterwards the two fronts propagate independently with
increasing separation. The primary front finally stops at a magnetic
separatrix, while the secondary front travels farther before it fades out. In
addition, upon the arrival of the secondary front, transverse oscillations of a
prominence are triggered. We suggest that the two components are of different
natures. The primary front belongs to a non-wave coronal mass ejection (CME)
component, which can be reasonably explained with the field-line stretching
model. The multi-temperature behavior may be caused by considerable heating due
to the nonlinear adiabatic compression on the CME frontal loop. For the
secondary front, most probably it is a linear fast-mode magnetohydrodynamic
(MHD) wave that propagates through a medium of the typical coronal temperature.
X-ray and radio data provide us with complementary evidence in support of the
above scenario.
