Observations of the wind of the old nova V 603 Aquilae with the HST - GHRS ?

High resolution spectra of the old nova V 603 Aql (1918) were taken in the regions of the C iv, Nv and Si iv resonance doublets, using the G160M grating of the GHRS on board the Hubble Space Telescope. No sign of sharp absorption components due to the envelope ejected in 1918 is present. If spherical symmetry is assumed, the estimated upper limits to the column densities indicate a maximum envelope mass near 6p× 10−4M , where p=C+3/C is on the order of 0.1. Fairly wide emission and blue shifted absorption components were however visible. Si iv was in emission unlike in other low inclination high mass transfer rate cataclysmic systems, Nv in pure absorption, while C iv showed both emission and absorption. The C iv absorption blue edge was at a velocity of about −2500 km s−1, the value being only of about −1500 km s−1 for Nv. The observations suggest a model in which a substantial proportion of the Si iv and C iv emission arises from an optically thick chromosphere-corona-like region which surrounds the accretion disk and corotates with it, leading to the observed broad and nearly symmetric emission profiles. The absorption components of the C iv and Nv lines are instead formed in a conical wind which flows out from near the centre of the disk and/or the boundary layer (if the latter exists) and whose axis is nearly aligned with the rotation axis of the accretion disk and the rotation axis of the system. The degree of ionization in the wind decreases outward and this suggests that the ionization source is energetic radiation (EUV-soft-X-ray) coming from a hot compact region near the white dwarf. The emission and the absorption lines show significant variations on a time scale of the order of ten minutes, which are probably due to variations in the flux of the ionizing radiation. Variations of the UV continuum flux of about 10% to 30% are also seen, but apparently these are not correlated with the variations in the line profiles. Send offprint requests to: P. Selvelli ? Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract 5-26555. A wide Lyα absorption strongly affects the observed continuum between 1218 and 1250 Å. We attribute most of this absorption to a stellar/circumstellar component, a minor component only being of interstellar origin.