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The period of beta Lyrae

Tony Markham

According to the GCVS, Beta Lyrae has a period of 12.913834 days. The light curves below cover the whole period of variation of Beta Lyrae, with both primary and secondary eclipses being visible. The phases were calculated using the GCVS elements. If the eclipses were occuring as predicted by the GCVS elements, then the primary eclipse would be centred on phase 0. However, in the 1995 light curve it is occuring over a day late and the discrepancy has increased markedly by 1998. Clearly there is a problem with the GCVS elements.

Alternative elements are given in SAC 65 (Supplemento ad Annuarrio Cracoviense no 65). These quote a longer period of 12.93804 days. The third light curve shows the 1998 observations replotted using the SAC 65 elements. There is now much better agreement between predictions and observations, with primary eclipse now occuring much closer to phase 0.

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