The orbital period of the Be/neutron star binary RX J0812.4-3114

We present the results of Rossi X-Ray Timing Explorer (RXTE) observations o f the Be star X-ray binary system RX J0812.4-3114. A light curve obtained w ith the RXTE All-Sky Monitor (ASM) shows that the source is currently in an active state with outbursts occurring at approximately 80 day intervals. T he source underwent a transition from an inactive state to this regular out burst state early in 1998. An observation of RX J0812.4-3114 was obtained w ith the RXTE Proportional Counter Array (PCA) dose to the time of a predict ed maximum in 1999 March, and strong pulsations were detected at a period o f 31.88 s. This confirms the result of an earlier PCA observation by Reig & Roche that was also obtained serendipitously near the predicted maximum fl ux of the 80 day period and also near the start of the current active state . We interpret the periodicity in the ASM light curve as indicating the orb ital period of RX J0812.4-3114 with outbursts occurring around periastron p assage.