X-ray spectroscopy of the hot has in the M31 bulge
  We present an X-ray spectroscopic study of the nuclear region of the M31
bulge, based on observations of the Xmm-Newton Reflection Grating
Spectrometers. The obtained high-resolution grating spectra clearly show
individual emission lines of highly-ionized iron and oxygen, which
unambiguously confirm the presence of diffuse hot gas in the bulge, as
indicated from previous X-ray CCD imaging studies. We model the spectra with
detailed Monte-Carlo simulations, which provide a robust spectroscopic estimate
of the hot gas temperature $\sim0.29$ keV and the O/Fe ratio $\sim0.3$ solar.
The results indicate that iron ejecta of type Ia supernovae are partly-mixed
with the hot gas. The observed spectra show an intensity excess at the OVII
triplet, which most likely represents emission from charge exchanges at the
interface between the hot gas and a known cool gas spiral in the same nuclear
region.
