Suzaku Reveals Helium-burning Products in the X-ray Emitting Planetary   Nebula BD+303639
  BD+303639, the brightest planetary nebula at X-ray energies, was observed with Suzaku, an X-ray observatory launched on 2005 July 10. Using the X-ray Imaging Spectrometer, the K-lines from C VI, O VII, and O VIII were resolved for the first time, and C/O, N/O, and Ne/O abundance ratios determined. The C/O and Ne/O abundance ratios exceed the solar value by a factor of at least 30 and 5, respectively. These results indicate that the X-rays are emitted mainly by helium shell-burning products. 
M. Murashima (1), M. Kokubun (1), K. Makishima (1 and 2), J. Kotoku   (3), H. Murakami (4), K. Matsushita (5), K.Hayashida (...