Variability of the post-AGB star HR 4049 : dust obscuration in a binary system

The variability of the peculiar post-AGB star HR 4049 is investigated. The data are 250 photometric observations in the Geneva system, most of which were taken during seven subsequent seasons, near-infrared photometry taken during one season, a few IUE spectra, and some spectrocopic data that are randomly distributed in time. The optical photometry reveals a period of 434 days, the amplitude is inversely proportional to the wavelength. The 434-day period is also distinctly present in the 20 radial velocities recorded for this star. The length of the period and the amplitude of the velocity variations lead to the interpretation that HR 4049 is a binary.