Variation mechanisms in symbiotic nova V1329 Cygni

U, B, V light curves of symbiotic nova V1329 Cygni (=HBV 475) are modelled in terms of combined wind and chromospheric fluorescence, with eclipses and shadowing of fluorescent regions, eccentric orbit effects, and conversion of far-ultraviolet energy into the optical bands. Observational evidence re garding fluorescent brightness variation mechanisms is provided by waveform s and amplitudes and their changes from bandpass to bandpass. The combined set of U, B, V variations cannot be satisfied with a wind-only or chromosph ere-only model. Contrary to arguments in the literature, chromospheric fluo rescence can be comparable to wind fluorescence in brightness and can be fa r stronger than photospheric emission from a red giant. We show why there i s no conflict between the existence of strong chromospheric fluorescence an d symbiotic binary energetics, at least in this example. Ultraviolet and op tical radial velocities are also discussed and fitted. Some parts of the fl uorescent binary model omitted from the original paper by Wilson for lack o f space are given here. Fitting was done both subjectively and by different ial corrections (least-squares criterion), thus providing insight into the interplay of wind and chromospheric effects. The large bandpass-dependent w aveform and amplitude changes are accounted for by differing relative amoun ts of wind and chromosphere fluorescence, with the chromosphere relatively bright in U and the wind relatively bright in B and V A strong test of the model is provided by the way the amplitude and waveform change together-lar ger amplitude must go with wider minima, as observed. The differential corr ections solutions fit the light curves rather well. Because they were done in JD rather than in phase, the solutions were also able to find ephemeris parameters. Potentially interesting is an enormous period change of dP/dt a pproximate to -0.0020 +/-0.0004 s.d. which, if confirmed, means that the ap proximate to 955 d period is dropping by 2 d each cycle. Parameter results are tabulated, but our emphasis is on identification of variation mechanism s rather than specific numbers. Observational selection favours discovery o f periodic fluorescent variation for arguments of periastron near omega = p i /2 because wind and chromospheric fluorescence then combine to give maxim um amplitude. The possibility of pre-outburst drops in brightness being ecl ipses is examined. We urge spectroscopic observers to gather infrared radia l velocities of the red giant and to search for subtle evidence of eclipses of the hot object. Infrared light curves also would be helpful if reasonab ly large numbers of data points could be accumulated.