  We report the discovery of a broad emission feature at ~0.7 keV in the
spectra of the ultra-compact X-ray binary 4U 1543-624, obtained with the
high-resolution spectrographs of the XMM-Newton and Chandra satellites. We
confirm the presence of the feature in the broad band MOS2 spectrum of the
source. As suggested before in the literature, the donor star in this source is
a CO or ONe white dwarf, which transfers oxygen-rich material to the accretor,
conceivably a neutron star. The X-rays reprocessed in this oxygen-rich
accretion disc could give a reflection spectrum with O VIII Ly alpha as the
most prominent emission line. Apart from the feature at ~0.7 keV we confirm the
possible presence of a weak emission feature at ~6.6 keV, which was reported in
the literature for this data set. We interpret the feature at ~0.7 keV and ~6.6
keV as O VIII Ly alpha and Fe K alpha emission respectively, caused by X-rays
reflected off the accretion disc in the strong gravitational field close to the
accretor.
