Abstract
ABSTRACTObservations of the light curve for the 3.7 day Cepheid RT Aur both before and since 1980 indicate that the variable is undergoing an overall period increase, amounting to +0.082 ± 0.012 s yr−1, rather than a period decrease, as implied by all observations prior to 1980. Superposed on the star’s O - C variations is a sinusoidal trend that cannot be attributed to random fluctuations in pulsation period. Rather, it appears to arise from light travel time effects in a binary system. The derived orbital period for the system is P = 26,429 ± 89 days (72.36 ± 0.24 yr). The inferred orbital parameters from the O - C residuals differ from those indicated by existing radial velocity data. The latter imply the most reasonable results, namely a1 sin i = 9.09(± 1.81) × 108 km and a minimum secondary mass of M2 = 1.15 ± 0.25 M⊙. Continued monitoring of the brightness and radial velocity changes in the Cepheid are necessary to confirm the long‐term trend and to provide data for a proper spectroscopic solution to the orbit.
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