Modulations in multi-periodic blue variables in the large magellanic cloud

As shown by Mennickent et al., a subset of the blue variable stars in the Large Magellanic Cloud exhibit brightness variability of small amplitude in the period range 2.4-16 days as well as larger amplitude variability with periods of ̃ 140 to 600 days, with a remarkably tight relation between the long and the short periods. Our re-examination of these objects has led to the discovery of additional variability. The Fourier spectra of 11 of their 30 objects have three or four peaks above the noise level and a linear relation of the form f_a = 2(f_b - f_L ) among three of the frequencies. An explanation of this relation requires an interplay between the binary motion and that of a third object. The two frequency relations together with the Fourier amplitude ratios pose a challenging modeling problem.