MACHO Project photometry of 45 LMC FO/SO beat Cepheids which pulsate in the first and second overtone ( FO and SO , respectively ) has been analysed to determine the lightcurve characteristics for the SO mode of Cepheid pulsation .
We predict that singly-periodic SO Cepheids will have nearly sinusoidal lightcurves ; that we will only be able to discern SO Cepheids from fundamental ( F ) and ( FO ) Cepheids for P \lesssim 1.4 days ; and that the SO distribution will overlap the short-period edge of the LMC FO Cepheid period-luminosity relation ( when both are plotted as a function of photometric period ) .

We also report the discovery of one SO Cepheid candidate , MACHO*05:03:39.6 - 70:04:32 , with a photometric period of 0.775961 \pm 0.000019 days and an instrumental amplitude of 0.047 \pm 0.009 mag in V .