The active quiescence of HR Del (Nova Del 1967)

This new UV study of the ex-nova HR Del is based on all of the data obtained with the International Ultraviolet Explorer (IUE), 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}$$\sim$ 56 $L_{\odot}$, the highest value among classical novae in "quiescence". Also the optical absolute magnitude ($M_{V}= +1.35$) is indicative of a bright object. From the observed UV and optical luminosities we might estimate a mass accretion rate $\dot{M}$ on the order of 1.4$\times$10$^{-7}$$ M_{\odot}$ yr$^{-1}$. 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 33,900 K, or a power-law $F_{\lambda}$$\sim$$\lambda$$^{-2.20}$. A comparison with the grid of models of Wade and Hubeny (1998) indicates a low $M_{1}$ value and a relatively high $\dot{M}$ but the best fittings to the continuum and the line spectrum come from different models. We show that the "quiescent" optical magnitude at $m_{v}$$\sim$12 comes from the hot component and not from the companion star. Since most IUE observations correspond to the "quiescent" magnitude at $m_{v}$$\sim$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 1550 \AA~ and NV 1240 \AA~ resonance lines are strong and variable on short timescales, with $v_{edge} $ up to -5000 km s$^{-1}$, a remarkably high value. The phenomenology in 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.