Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001mnras.326..437c&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Volume 326, Issue 2, pp. 437-452.
Astronomy and Astrophysics
Astronomy
5
Binaries: Symbiotic, Stars: Individual: V1329 Cyg, Novae, Cataclysmic Variables
Scientific paper
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 regarding fluorescent brightness variation mechanisms is provided by waveforms 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 chromosphere-only model. Contrary to arguments in the literature, chromospheric fluorescence can be comparable to wind fluorescence in brightness and can be far stronger than photospheric emission from a red giant. We show why there is no conflict between the existence of strong chromospheric fluorescence and symbiotic binary energetics, at least in this example. Ultraviolet and optical radial velocities are also discussed and fitted. Some parts of the fluorescent binary model omitted from the original paper by Wilson for lack of space are given here. Fitting was done both subjectively and by differential corrections (least-squares criterion), thus providing insight into the interplay of wind and chromospheric effects. The large bandpass-dependent waveform and amplitude changes are accounted for by differing relative amounts 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 - larger amplitude must go with wider minima, as observed. The differential corrections 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~-0.0020+/-0.0004 s.d. which, if confirmed, means that the ~955d period is dropping by 2d each cycle. Parameter results are tabulated, but our emphasis is on identification of variation mechanisms rather than specific numbers. Observational selection favours discovery of periodic fluorescent variation for arguments of periastron near ω=π/2 because wind and chromospheric fluorescence then combine to give maximum amplitude. The possibility of pre-outburst drops in brightness being eclipses is examined. We urge spectroscopic observers to gather infrared radial 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 reasonably large numbers of data points could be accumulated.
Chochol Drahomir
Wilson Robert E.
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