Fluorescence Model for AG Draconis

Abstract

AbstractA fluorescent light curve model (ionization-bounded wind and chromosphere with scale height) that previously found most fluorescent variation in symbiotic nova V1329 Cygni to be chromospheric, is applied to AG Draconis, where the strong wind of a well-detached red giant is illuminated by ultraviolet radiation from an accreting white dwarf. Bandpass dependence of light curve amplitude is even more striking than in V1329 Cyg and eliminates thermal re-radiation from the red star photosphere as a principal variation mechanism, since thermal re-radiation cannot change by large factors from U to B to V. Spectra show strong continuum and line emission, so both light curves and spectra show the importance of fluorescence. A small secular decay was included by fitting in time rather than phase, with dTwd/dt as a parameter. There is a 3σ indication of a large negative dP/dt. Chromospheric fluorescence accounts for the entire U variation, while B and V variations are too small for wind and chromosphere to be distinguished. We confirm a previously identified 355-day radial velocity period that is consistent with red star pulsation.