Unexplained brightening of AKO 9 in 47 Tucanae

This is a reproduction of two images obtained in late 1996 with the Hubble Space Telescope (HST) , showing the field of the variable star AKO 9 at the centre of the southern globular cluster 47 Tucanae .


This star brightened by more than 2 magnitudes (a factor of seven) in less than 1 hour. Left: the first frame; right: the last frame in a series of 15 exposures, obtained during a period of just over 4 hours.


Yhe field of each image measures 3.9 arcsec x 3.9 arcsec. North is up and East is to the left.
No other star among the > 30,000 studied was found to have such a large amplitude.