Observational survey of the puzzling star HD 179821: Photometric variations and period analysis

From new photometric observations ( UBVRI), we present the characteristic features of the light variations of the evolved star HD 179821 (= SAO 124414 = IRAS 19114+0002). Our data, collected through 1999 and 2000, have been combined together with previous photometric measurements available in the literature. Thus, a long term V-light curve (gathering more than 10 years of observations for HD 179821) has been composed. We have analysed it with the Fourier transform method. Two main frequencies are present in the resulting power spectrum, reflecting a dominant bimodal pulsator behavior. A long term phenomenon is also found, but it is not possible to decide whether it is periodic. The Fourier analysis has also been applied on two other filters ( U and B) and confirms the detected frequencies. On the basis of our period analysis, we discuss the nature of HD 179821: low-mass post-AGB star or high-mass star.