Coupled long-term photometric and V/R variations in Be stars: evidence for prograde global one-armed disk oscillations

We review theoretical work on global oscillations of Be star disks and summarize possible observational tests. In addition, we analyze existing records on photometric data andV/R ratio for a sample of 6 V/R variable Be stars. Five stars showed coupled long-term photometric-V/R variations. In all cases the photometric extrema coincided with times of V = R transits, the fainter state being followed by a V < R phase. V 1294 Aql, 48 Lib and MXPup showed anticorrelated c1 and b − y colors during light cycles, the stars being redder in b − y when brightest. 48 Lib shows a complex color behaviour, exhibiting two minima during a V/R cycle and a pronounced b − y drop just at maximum light. In addition, this star shows enigmatic, non-periodic, eclipse-like features in its light curve. In general, the V/R-photometric observations can be grouped in three main groups, depending on the degree of correlation exhibited by the V/R ratio and the photometric fluxes and the rate of change of the u flux. These groups are compatible with prograde global disk oscillations observed under different system inclinations.