  The most characteristic high-energy phenomena in the Galactic center (GC)
region is the presence of strong K-shell emission lines from highly ionized Si,
S, Ar, Ca, Fe and Ni, which form the Galactic Center X-ray Emission (GCXE).
These multiple lines suggest that the GCXE is composed of at least two plasmas
with temperatures of ~1 and ~7 keV. The GCXE also exhibits the K-shell lines
from neutral Si, S, Ar, Ca, Fe and Ni atoms. A debatable issue is the origin of
the GCXE plasma; whether it is a diffuse plasma or integrated emission of many
unresolved point sources such as cataclysmic variables and active binaries.
Detailed spectroscopy for these lines may provide a reliable picture of the
GCXE plasma. The origin of the K-shell lines from neutral atoms is most likely
the fluorescence by X-rays from a putative past flare of Sgr A*. Therefore
ASTRO-H may provide unprecedented data for the past light curve of Sgr A*. All
these lines may provide key information for the dynamics of the GCXE, using
possible Doppler shift and/or line broadening. This paper overviews these line
features and the previous interpretation of their origin. We propose extended
or revised science with the ASTRO-H observations of some select objects in the
GC region.
