An evolutionary scenario for classical novae is proposed, which is intended to solve the discrepancies that exist between theory and observations: the space densities of classical novae deduced from surveys in the solar neighbourhood are lower by about two orders of magnitude than those predicted theoretically, and the mass transfer rates in nova binaries, as estimated from observed luminosities in quiescence, are higher than those allowed by the thermonuclear runaway model for nova outbursts. These discrepancies disappear if mass transfer (at a high rate) takes place for only a few hundred years before and a few hundred years after an eruption, but declines afterwards and remains off for most of the time between outbursts. We show that such a behavior is to be expected if one takes into account the variation of binary separation, due to mass ejection on the one hand and angular momentum losses on the other hand.

One of the aspects of this scenario, on which we report in more detail, is the possibility of enhanced Roche-lobe overflow of the secondary, due to its expansion that results from irradiation by the high nova luminosity. We followed the evolution of a 0.5M⊙ main sequence star illuminated by a changing flux, typical of a classical nova. The numerical results indicate that, in spite of the slight binary separation that may occur after eruption, mass loss from the irradiated and thus bloated secondary should continue for a few hundred years. Other aspects of the variable Ṁ scenario are briefly summarized.

A classical nova model was evolved through a complete cycle, i.e. accretion leading to outburst, mass loss and again accretion, ending in another outburst, by means of an implicit Lagrangian hydrodynamic code, which included diffusion (concentration, pressure and thermal terms), as well as an extensive nuclear reactions network between 28 isotopes of C, N, O, F, Ne, Na, Mg and Al. The initial model was a 1.25 M⊙ C-O white dwarf (WD) and the accretion rate assumed was 10−11 M⊙/yr. For more details of this calculation, see Prialnik (l986).

We consider the possibility that dust grains in novae could nucleate on ions. We examine how different ejected masses and different elemental abundances effect the availability of nucleation centres, and we show how this model could explain why only novae of intermediate speed classes form dust.

We consider the possibility that carbon, in the form of the allotrope carbyne, might form in the atmosphere of the white dwarf in a cataclysmic variable system, and be expelled from the system by radiation pressure. It seems that, under some circumstances, cataclysmic variable systems may indeed have carbon dust in their vicinity.

Recent statistics indicate that each year an average of 3.5 novae or nova-like objects are discovered in the Galaxy. With reasonable assumptions about the completeness of the surveys, we arrive at an overall galactic production rate of 76 ± 38 y−1. When recurrent novae are omitted, this rate drops to 60 + 30 y−1. Hence, it seems that our Galaxy is more prolific than M31 in nova production. The total amount of material released into galactic space by novae each year is about one-tenth that ejected by supernovae.

The period-amplitude relation and the period-energy relation for dwarf novae and novae are discussed. The total outbursts energy is shown to be a more suitable characteristic of the outburst than its amplitude.

Decelerations of the shells around the novae V603 Aql, V476 Cyg, DQ Her and GK Per were determined from photographs and recent CCD observations. The deceleration is larger for higher expansion velocities, the mean half-lifetime, after which the expansion velocity has dropped to half its initial value, is 75 years.

Exnovae and nova shells are generally faint and difficult to observe. Only a few have been studied, and even less of them in sufficient detail. We give a progress report on our survey of exnovae and nova shells, especially on the results of a spectral survey of novae in the southern Milky Way. The three-dimensional structure in the light of Hα derived for the nebula of GK Per is displayed.

Nova Vul 1984 n°2 has been again observed at Observatoire de Haute-Provence in the autumn of 1985, i.e. 270–295 days after maximum. It was then in the nebular phase. The spectra cover the blue-violet and the near infrared regions. Over 50 lines and blends have been identified and are given in Table 2. No clear pattern is observed in the emission bands of a width of about 1450 km/sec. The most conspicuous features observed are the forbidden NeIII and NeV lines. The infrared region is dominated by a very strong He I 1083nm emission.

We present optical spectroscopic data on the nova LW Serpentis 1978, covering its diffuse-enhanced phase until the onset of [OI] flash. The spectra, cover a range of 4000–8700 A, at dispersions ranging from 83–675 A mm−1.

During the August 1983 outburst of the old nova GK Persei observations with EXOSAT showed for the first time a 351 second periodicity in X-rays.

Our fast photometry (U(B)V with 25 sec time resolution) was made at the end of the outburst in the nights of September 29 , and October 1–3 , using the 2.2 meter telescope at Calar Alto (Spain).

Optical variations up to 10% in U and 4% in V with periodicities in the range 350 to 360 seconds were found, lasting only for few cycles.

A comparison with the extrapolated prediction of the X-ray maxima did not show a coincidence, but rather an anticoincidence in several cases. This supports a model of reprocessed X-rays at the inner edge of an accretion disk.

UBV photometry and spectroscopy of the symbiotic nova PU Vul support the suggestion that the system consists of a mass-losing M-giant massive component and a C-O dwarf accreting hydrogen-rich matter, mimicing in outer appearance an F-supergiant.

The observational properties and outburst histories of each member of the small class of recurrent novae are reviewed, with the objective of identifying the outburst mechanisms for these systems. Examples are found of both accretion-powered outbursts (T CrB and RS Oph) and thermonuclear-powered outbursts (T Pyx and U Sco). Outburst properties which might be used in future to distinguish between these mechanisms are identified. Many erstwhile recurrent novae (VY Aqr, RZ Leo, V616 Mon, V1195 Oph, V529 Ori, WZ Sge, and V1017 Sgr) appear to be misclassified examples of other types of cataclysmic variables.

Observed characteristics of outbursts of eight dwarf novae are compared with those predicted for the two types of outbursts by the disk instability theory. OY Car, U Gem, VW Hyi, and WX Hyi are identified as Type A, while RX and, SS Cyg, AH Her, and CN Ori - as Type B.

Two outbursts and a minimum phase of the dwarf nova CN Orionis have been observed spectroscopically. One outburst was covered almost completely. The outburst spectra show periodic variations of the absorption lines which are interpreted with the formation of an elliptic disc during outburst stage. During decline from outburst a narrow emission line appears in the core of the broad H« absorption line. The balmer decrement in the outburst phase is much steeper than in the minimum phase. This implies that during the outburst the emission line region is located more outward in the disk. The semi amplitude of the radial velocity curve was determined to Kl = 152 km/s ± 10 km/s. Using the photometric orbital period and an assumption about the inclination angle the approximate system parameters could be derived.

Some recent photometric and spectroscopic results for this “ultrashort” period system are summarized, and several straightforward consequences of these results for our understanding of the evolution of cataclysmic binaries are pointed out: The space motion of Z Cha is characteristic of the old disk population. The white dwarf cannot be composed primarily of He, unless it grew by accretion by at least 20%. The inferred masses of the component stars, combined with the usual gravitational quadrupole formula, probably do not suffice to explain the inferred rate of mass transfer, even in quiescence. The secondary star does not lie on the computed evolutionary tracks in the period - mass diagram of Paczynski and Sienkiewicz.

More than a third of all cataclysmic variables (CV’s) with established binary periods contain strongly magnetic degenerate dwarfs (Ritter 1985). The history of the manner in which the magnetic character of these systems was established suggests that many more CV’s—perhaps most—are magnetic. By comparison, only ≈ 2% of isolated degenerate dwarfs are magnetic (Angel, Borra, and Landstreet 1981; Schmidt and Liebert 1986). The magnetic CV’s divide naturally into two subclasses: the DQ Herculis stars (recently reviewed by Warner 1983, 1985) and the AM Herculis stars (recently reviewed by Liebert and Stockman 1985). Each subclass currently has about a dozen members.

Comparison of the period distributions of various classes of CVs confirms an extreme bias of the synchronous AM Her systems toward short orbital periods, while the DQ Her systems do not differ significantly from the distribution of non-magnetic systems. This suggests either strong selection effects or enhanced evolution of the AM Her systems. There is as yet no obvious bimodality in either the magnetic field distributions of isolated white dwarfs or of CV primaries. However, clear differences between the two exist: the strongest being that magnetic primaries are overrepresented among short period CVs by more than an order of magnitude in comparison to the field white dwarfs.

The recently discovered phenomena in polars - Magnetic Close Binary Stars (MCBS), are discussed. Asynchronous MCBS are on the ‘propeller stage’ (which is analogous to the investigated one for neutron stars), and are synchronizing during ts ≲ 103 yr, being during this stage rapidly evolving, mass ejecting systems. The accretion rate is largest when the angle θ between the magnetic axis and the line of centers is near zero. If θ ≈ 90°, then the magnetic field prevents the plasma flow, and the ‘magnetic valve’ becomes closed. Near this position the oscillations of the orientation of the white dwarf’s magnetic axis may be excited. This model of a ‘swinging dipole’ has such observational properties: (a) the system’s luminosity changes with characteristical times of some years; (b) the phase curves of light, polarization and radial velocities must be cyclically changing with a few year cycle; (c) one would observe the correlation between the phase shift of these curves, and the system’s luminosity. The observational data on polars are briefly discussed. All these phenomena are observed in AM Herculis and some other polars, but subsequent studies are needed to investigate the orientation changes of the magnetic axis, and so the structure and evolution of this exotic class of our Galaxy population.

The intensity and polarisation properties of magnetic accretion columns are discussed in the regime where electron scattering is important. It is shown that the circular polarisation standstills observed in some AM Herculis type systems are inconsistent with cyclotron emission from scattering dominated regions.