A brief history is given of the clues that led to the establishment, in the period c. 1950 to 1965, of a universal binary model for novae and related cataclysmic variables. The observational facts, established early in this period by A. H. Joy and R. F. Sanford (selected binary orbits), J. L. Greenstein (spectroscopy) and M. Walker (photometry) are reviewed, as are the theoretical ideas that formed the basis for the early models, viz., those of G. Kuiper (restricted 3–body problem), A. Sandage and M. Schwarzschild (stellar evolution), J. Crawford (“dog-eat-dog” hypothesis), F. Hoyle and H. Bondi (accretion), S.-S. Huang (angular momentum losses), and S. Chandrasekhar (gravitational radiation). Some comparisons are made between “what we knew then and what we know now.” With apologies to all, the speaker will recall some anecdotes of an earlier time and comment on developments of the past score of years from a very personal perspective.

Quiescent novae are more stable against mass transfer rate than dwarf novae. They may however show cyclical variations of their quiescent magnitudes on time scales of years, probably caused by solar–type cycles of activity of the secondary. The probability density function of the periods of the cycles observed in CVs is similar to that for single stars. Sometimes, periodic or quasi periodic light variations on time scales of tens to hundreds of days are also observed. Although the magnitudes of prenovae and postnovae are essentially the same, the definition of the magnitude of a quiescent nova is still uncertain. At present, the hibernation theory for old novae seems to be supported only by the observations of two very old novae.

With the recent publication of Classical Novae, edited by Bode and Evans, there is no need for me to give a list of novae or their overall characteristics. Furthermore, probably the most interesting developments in the past few years in studies of novae during quiescence have been in those areas (magnetic systems, long term brightness variations) which are reviewed separately at this conference. So that leaves me with the task of making some general comments about recent trends in the more mundane aspects of quiescent novae. However, what may at first sight seem mundane often has importance to theoretical interpretation.

The observed rate and spatial distribution of galactic novae can be explained with the concept of two nova populations, the disc novae of faster outburst development, and the slower bulge novae. Similar populations seem to exist in nearby galaxies. The space density of galactic novae depends strongly on the recurrence time, which is unknown and may lie between 500 and 20 000 years. If the recurrence time is long, the population of quiescent novae must be identified; the hibernation scenario may or may not be a solution.

My main goal in giving this review is NOT to induce hibernation in the audience. Rather, it is to survey the known cases of erupting classical novae in open and globular clusters, and galaxies external to the Milkey Way. More important, I want to emphasize what these novae in stellar systems can teach us about nova eruptions. In my conclusions I will make a few brief remarks about what we might hope to know about classical novae by the time IAU Symposium #222 occurs (by then Space Telescope will hopefully have been in orbit and producing scientific results for many years!). References to older works may be found in the reviews of Trimble (1980) and Webbink (1980).

The discovery of variable circular polarization in V1500 Cygni (the remnant of Nova Cygni 1975) is the strongest evidence for the presence of highly magnetic white dwarfs in nova systems. If interpreted in terms of diluted cyclotron emission from a hot accretion shock, the recent observations of Schmidt and Stockman (1990 preprint, Ap. J. 1991) of the color dependence of the circular polarization can provide a empirical lower-limit to the primary’s magnetic field strength of B > 25 × 106 gauss. Such a field strength is comparable to those observed in other magnetic variables, thus providing support for the general picture of the current and pre-nova system and the explanation for the observed search-light and period changes following the eruption. Schmidt and Stockman have also measured lengthening of the polarimetric period indicating that the system will be resynchronized within a few centuries and well before the next nova eruption. This is an independent confirmation of a significant magnetic moment for the white dwarf primary.

In this paper we present the statistical analysis of historical light curves of 8 old novae, performed through a Fourier analysis on ~ 1600 no-equispaced (in the time) observations published by Steavenson between 1921 and 1953. The results seems to support the existence of a semiregular variability on typical timescales of 50d ÷ 100d and amplitude of ~ 0.3 ± 0.1 magnitudes.

At present the largest body of data concerning the photometric behaviour of novae at minimum, is due to the pioneering works by Steavenson (1920→1950) and also to Robinson’s compilation (1975) of 33 preeruption lightcurves of novae.

Besides testing the evolutionary models, such as the Hibernation Scenario (Shara et al. 1986), the importance of very long term observations of novae at minimum, has been recently pointed out by Bianchini (1987) and Warner (1988) in close connection to the possible detection of solar-type cycles of activity of the secondary. In spite of these considerations an interesting body of ~ 1000 homogenous observations of 5 posteruption lightcurves provided by Steavenson between 1920 to 1950 (published on M.N.R.A.S) has been neglected and only recently recovered (Delia Valle 1988).

The aim of our analysis is:

1. a) to verify possible presence of Dwarf Nova activity

2. b) to confirm on the basis of a larger sample of objects, the existence of semiregular variability as observed in Q Cyg 1876 (Shugarov 1983) and v841 Oph (Della Valle and Rosino 1987).

In this contribute we present only the preliminary results of our Fourier’s analysis, performed by adopting the procedure suggested by Deeming (1975) to analyse data taken at unequally spaced time intervals, whereas a more complete analysis will be presented in a forthcoming paper.

An investigation of the rotation period variation of the white dwarf in FO Aqr/H2215-086 is presented. A cubic ephemeris is derived for the arrival times of maxima of the pulse light curve which is associated with the white dwarf rotation. Potential problems, resulting from variations of the pulse arrival time as function of orbital phase, and from the change with wavelength of the pulse light curve shape, are investigated. A possible explanation is given for the second effect, being caused by a variable contribution of a modulation at the beat period (of the pulse and orbital periods) as a function of orbital phase.

The recently estabilished values of M31 and M33 nova rate, rM31 = 29 ± 4 novae yr−1 (Capaccioli et al.,1989), rM33 = 4 ± 2 novae yr−1 (Della Valle, 1988), seems to be at variance with the present estimates for the galactic nova rate, r = 260 novae yr−1 (Sharov,1972) and r = 73 ± 24 novae yr−1 (Liller and Meyer,1987), if we take into account the luminosity class and the Hubble type of the Galaxy. Assuming the nova production per unit of B–luminosity about constant for spiral galaxies and adopting the derived values of the nova rate of M31, M33 and LMC as calibrators, we estimate a galactic nova rate of rGal = 15 ± 5 novae yr−1.

During a spectroscopic survey of IRAS sources with infrared colours similar to those in planetary nebulae, IRAS 06518-1041 revealed itself as a possible nova-like object. The spectrum of IRAS 06518 – 1041, which is shown in Figure 1, presents strong and broad hydrogen Balmer lines together with broad permitted lines of He and C. This spectrum also shows a much weaker narrow nebular component, with forbidden lines of [OIII] and narrow Hα. The mean velocity associated to the observed line widths is about 800 km s−1. The observed emission lines correspond well to typical post-novae objects in the quiescent phase (Warner, 1989). Another argument which supports the idea of this object being a nova-like star is that there are some indications of the binarity of the source if we attend to the asymmetries observed both in the Hβ and Hα profiles. The high resolution spectrum at Hα shows the presence of a sharp double-peaked central emission from a low expanding envelope at a velocity of 35±5 km s−1, together with a much broader emission with velocities of several hundred kilometers. The displacement between both components is about 130 km s−1. This broad component could be due to the presence of an accretion disk around the system with hydrogen-rich material falling onto the compact companion. This is supported by the fact that the broad emission looks like the combination of different velocity components giving rise to a complex and asymmetric line profile. From this high resolution spectrum we derive a VLSR = 57 km s−1, which points to a distance of 5.5 kpc if we adopt the model rotation curve of the Galaxy given by Pottasch (1984) and a distance of 9 kpc from the Sun to the galactic center. The large infrared excess detected by the IRAS satellite is probably the result of the formation of dust grains in the outer parts of the common envelope at a temperature of about 160 K, as can be derived from the infrared data. This infrared excess is also present in other nova-like objects and is specially important in old and slow novae (Callus et al, 1987) where the continuous ejection of mass produces dust shells which are strong emitters in the infrared.

A U-B search to 21st magnitude in a 1°×1° region centered on the best position for the Korean nova of 1437 has revealed no unique candidate. Instead, we find 7 faint UV-bright stars with CV-like emission lines. The implied space density is two orders of magnitude higher than the classical space density for CV’s.

In an earlier paper [1], we demonstrated that the declining ultraviolet flux, observed long after optical quiescence was reached in three dwarf novae, most likely represents the cooling of a white dwarf whose outer layers have been heated by the accretion event. If the observed change in temperature is due to the cooling of the white dwarf surface layers following the intense heating produced in the outburst, then a thermal timescale of the heated portion of the white dwarf is implied, which could yield a rough estimate of the depth of heating into the white dwarf envelope. The thermal timescale is essentially given by the ratio of the internal energy in the affected layers to their luminosity, L.

New spectroscopic observations of the old nova CP Pup suggest most probable orbital period of 0.061375 days. First systematic monitoring of the very old nova V841 Oph reveals orbital motion with a most probable period of about 0.6 days. A slightly eccentric solution at P = 0.3755 days is less probable.

As first pointed out by Warner (1985), the overall properties of CP Pup and V1500 Cyg are very similar: both were very fast, very large amplitude novae with ~ 0.3 mag photometric humps at roughly the orbital period. Neither variation is strictly periodic (Patterson 1979; Warner 1985). Variable circular polarization (with period slightly different from the orbital period) has been found in V1500 Cyg showing that its white dwarf is strongly magnetic and has broken synchronism with the secondary star (Stockman, Schmidt & Lamb 1988). In contrast, no circular polarization has been found in CP Pup. Nonetheless, does the slight difference between the photometric and spectroscopic periods indicate it is also a magnetic system (Warner 1985; Bianchini et al. 1985a)?

New photometric and spectroscopic data for CP Pup are reported which resolve the aliases and confusion in the periods found by Bianchini et al. (1985a,b), Warner (1985) and Duerbeck et al. (1987) and allow an examination of the evidence for its magnetic nature.

About 16 old novae are accessible to IUE, but only five (RR Pic, V 603 Aql, HR Del, DQ Her, and GK Per) have been observed in the ultraviolet and studied in any detail. Considering that, because of selection effects, only few and the brightest objects have been observed, it not possible to draw general conclusions on the UV luminosity LUV and mass accretion rates Ṁacc of old novae. We plan to improve the rather poor statistic by observing in the near future all objects falling above the IUE detection limit of m(V) ≃ 15 (i.e. X Ser, DK Lac, DN Gem, and HR Lyr). In the following we present preliminary results for 7 old novae observed with the IUE satellite whitin our observing programmes or obtained from the IUE archive.

Regular photometric observations of V1500 Gyg (Nova Cygni 1975) have been carried out at the Crimean Astrophysical Observatory of the USSR Academy of Sciences from 1975 till now. The 0.5 m telescope equipped with a TV system is used to estimate the star brightness in V.

The decline of the mean brightness is presented in Figure 1. The solid lines (1) and (2) show the changes of the V brightness according to Patterson (1979) and Arkhipova and Zaitseva (1978), respectively. The dotted line is drawn according to our data (Pavlenko 1988). The arrows indicate the amplitudes of the light and colour variations.

We derive the distance modulus of the Large Magellanic Cloud (LMC) by applying the new calibrated relationship between maximum magnitude and rate of decline (MMRD). The result, , is in close agreement with the most recent determinations based on RR Lyrae and Cepheids. We also discuss the properties of the MMRD of M31 and of the LMC.

Our photometry revealed that the old nova V603 Aql has four different coherent periods, including a period present in X-rays and so it is quite unique among all novae. Thus we classify V603 Aql as an intermediate polar (IP) system. Some time ago Hefner and Metz (1985) found that the period of the sinusoidal light variations of V603 Aql is 3.5 hour and thus it is longer by about 5 percent than the spectroscopic orbital period of 3.3 hour. Our observations covering over 30 hours and spanning 30 days confirm their result. However, we discovered also another coherent oscilation with a small amplitude of 0.02 mag and period of 61 min (Udalski and Schwarzenberg-Czerny, 1989). Our analysis of the X-ray observations by Drechsel et al. (1983) revealed 25 percent modulation with the same period and thus confirmed our discovery (Fig. 1). Additionaly we found in our light curves evidence of the 2.5 day beat period of the 3.3 and 3.5 hour periods.

A nova is followed optically from preoutburst to postoutburst appearance. Photospheric and atmospheric observational data are explained qualitatively through the energy budget, apparent in super-Eddington, Eddington, and sub-Eddington states, and the particle fluxes, according to their role in Grotrian’s model. In some instances, interpretations connected with Grotrian’s model are compared to results based on hydrostatic atmosphere models, for which quantitative versions exist. It is hoped that the physically and observationally sound ‘Ansatz’ of Grotrian may find followers to formulate an updated and extended theory.