Periodic Light Curve Changes for Beta Lyrae

We apply a variety of classical and recently developed periodicity analyses to light curves of β Lyrae in 9 eras that extend over a range of about 150 years. Some new data are tabulated. Most periodic variations that have been reported in the literature do not pass standard significance tests, according to our adopted criteria. Certain other periods do pass the tests, although most do so only for one, or at most two, data sets. Our main findings are that a period of about 9 months is present in all data sets and that it connects extremely well in phase from era to era, all the way back to Baxendell's observations of 1840- 1877. The semiamplitude is small but reasonably consistent, averaging about 2% of the flux in the light curve maxima. Any substantially larger excursions that occur are nonperiodic. Phase coherence of the 9 month period is fairly good, even with a linear ephemeris, and becomes excellent if one allows for a slow sinusoidal variation of the 9 month periodicity. There is some evidence for a monotonic decrease in the amplitude of the 9 month periodicity with increasing wavelength.