BS LYRAE - A DOUBLE-MODE MIRA STAR WITH A DOMINANT FIRST OVERTONE MODE

The frequency analysis of the photographic B light curve of the Mira s tar BS Lyr reveals besides the dominant period (P-1 = 304.7d) the unam biguous presence of a second one with P-2 = 272.3d. The analysis shows also the presence of the non-linear coupling terms between the two pe riodicities (1/P-1 + 1/P-2 and 1/P-2 - 1/P-1). The ratio between the t wo periods P-1/P-2 = 1.119 +/- 0.005 indicates that the two modes are the first (P-1) and the second (P-2) radial overtones. A third periodi city with P = 179d could be also present, even if it is only marginall y significant. It could correspond to the third overtone mode.