Detection of optical coronal emission from 10^6 K gas in the core of the
  Centaurus cluster
  We report a detection (3.5x10^37 \pm 5.6x10^36 ergps) of the optical coronal
emission line [Fe X]6374 and upper limits of four other coronal lines using
high resolution VIMOS spectra centred on NGC 4696, the brightest cluster galaxy
in the Centaurus cluster. Emission from these lines is indicative of gas at
temperatures between 1 and 5 million K so traces the interstellar gas in NGC
4696. The rate of cooling derived from the upper limits is consistent with the
cooling rate from X-ray observations (~10 solar masses per year) however we
detect twice the luminosity expected for [Fe X]6374 emission, at 1 million K,
our lowest temperature probe. We suggest this emission is due to the gas being
heated rather than cooling out of the intracluster medium. We detect no coronal
lines from [Ca XV], which are expected from the 5 million K gas seen near the
centre in X-rays with Chandra. Calcium is however likely to be depleted from
the gas phase onto dust grains in the central regions of NGC 4696.
