Light curve of AKO 9 in 47 Tucanae

In this diagramme are shown the light curves (change of light intensity with time) for the binary system AKO 9 (o) and two other stars (x) with constant brightness in the southern globular cluster 47 Tucanae.

The ultraviolet magnitude of AKO 9 was U ~ 18 at the time of the first observation. The subsequent rise was very fast: 2.1 magnitudes in 1 hour. It then remained constant for about 2 hours before increasing by another 0.5 mag.

The observations ended with the system in this bright state. It is not known if and when it reverted to its normal state. At the end of these observations, AKO 9 was the brightest ultraviolet source in the core of the cluster.