FUV and X-ray grating spectra of novae and supersoft X-ray sources

I review recent FUV and X-ray observations of classical and recurrent novae and supersoft X-ray sources, among them potential type la supernova progenitors. FUSE spectra show emission lines of O VI, which appear to be produced very close to the white dwarf of the binary system. In one case, these lines have allowed a measurement of the white dwarf and secondary mass. X-ray grating spectra of post-novae and other non-nova supersoft X-ray sources fall into two classes: in some systems we observe X-ray emission in a wind, or diffuse circumstellar material; in others we detect the white dwarf atmosphere. "Composite" spectra, which show a superposition of the two sources of X-ray emission, are also observed. When the white dwarf atmosphere is observed, atmospheric models show promising preliminary results. In two objects, very anomalous abundances are found. One of them is a very bright classical nova, V4743 Sgr, observed 6-18 months after the outburst. The absorption lines appear to be blue-shifted, which may be attributed to a still expanding atmosphere. Carbon is strongly depleted with respect to the solar value, indicating CNO processed material, expected if the nova has not ejected all accreted material, and the white dwarf mass is growing during the secular evolution. In principle, such a nova may be a type la SN progenitor. X-ray grating observations can also be used for studying classical novae in quiescence, if they are sufficiently bright. The Chandra HETG spectra of Nova V603 Aq1 indicate a range of chemical abundances in the accreted material, as well as a range of plasma temperature, and the mass transfer rate in the accretion disk. (c) 2006 Published by Elsevier Ltd on behalf of COSPAR.