2003A&A...401..297S

This new UV study of the ex-nova HR Del is based on all of the data obtained with the International Ultraviolet Explorer (IUE) satellite, and includes the important series of spectra taken in 1988 and 1992 that have not been analyzed so far. This has allowed us to make a detailed study of both the long-timescale and the short-timescale UV variations, after the return of the nova, around 1981-1982, to the pre-outburst optical magnitude. After the correction for the reddening (E_B–V=0.16), adopting a distance d =850 pc we have derived a mean UV luminosity close to L_UV∼56 L_☉, the highest value among classical novae in ``quiescence". Also the ``average" optical absolute magnitude (M_v=+2.30) is indicative of a bright object. The UV continuum luminosity, the HeII 1640Å emission line luminosity, and the optical absolute magnitude all give a mass accretion rate {dot}(M) very close to 1.4x10^–7M_☉/yr, if one assumes that the luminosity of the old nova is due to a non-irradiated accretion disk. The UV continuum has declined by a factor less than 1.2 over the 13 years of the IUE observations, while the UV emission lines have faded by larger factors. The continuum distribution is well fitted with either a black body of 33900 K, or a power-law F_λ ~λ^–2.20. A comparison with the grid of models of Wade & Hubeny (1998ApJ...509..350W) indicates a low M₁ value and a relatively high {dot}(M) but the best fittings to the continuum and the line spectrum come from different models. We show that the ``quiescent" optical magnitude at m<sub>v</sub>∼12 comes from the hot component and not from the companion star. Since most IUE observations correspond to the ``quiescent" magnitude at m_v∼12, the same as in the pre-eruption stage, we infer that the pre-nova, for at least 70 years prior to eruption, was also very bright at near the same L_UV, M_v, {dot}(M), and T values as derived in the present study for the ex-nova. The wind components in the P Cyg profiles of the CIV 1550Å and NV 1240Å resonance lines are strong and variable on short timescales, with v_edge up to -5000km/s, a remarkably high value. The phenomenology of the short-time variations of the wind indicates the presence of an inhomogeneous outflow. We discuss the nature of the strong UV continuum and wind features and the implications of the presence of a ``bright" state a long time before and after outburst on our present knowledge of the pre-nova and post-nova behavior.