Variation in the Surface Brightness Fluctuations of M32

The radial behavior of B and I-band surface brightness uctuations in M32 has been measured. We identify a systematic variation in the surface brightness uctuations of M32, which is seen as a local minimum in the uctuations at a distance of R 20 00 from the center. The systematic variation amounts to 0:2 mag around the average value m I = 22:78 0:04, and 0:3 mag around m B = 26:78 0:03. A possible population of asymptotic giant branch stars and associated post asymptotic giant branch stars likely concentrated towards the center may cause the observed increase in the luminosity uctuations for R < 20 00. The increase in luminosity uctuations outward may be attributed to a possible decrease in the mean metallicity of the underlying stellar population. A comparison of the present B-band luminosity uctuations with stellar population models having diierent horizontal branch morphologies indicates that a red clump horizontal branch cannot account for the observed \blue" uctuations. During the reduction procedure the main source of contamination turned out to be a not insigniicant contribution from M31's disk population. Based on the present observations and on simple simulations of the eld we argue that the mere recovery of added stars does not necessarily guarantee that the derived stellar photometry represents the true photometric properties of the stellar population. Realistic simulations of the crowded eld are essential in order to select a criterion that will eliminate spurious sources due to the surface brightness uctuations. Simulations show that our ground-based images with 1: 00 0 seeing do not have the spatial resolution that will allow us to supplement the uctuation measurement with stellar photometry of the most luminous stars.