Variation in the surface brightness fluctuations of M32

The radial behavior of B- and I-band surface brightness fluctuations in M32 has been measured. We identify a systematic variation in the surface brightness fluctuations of M32, which is seen as a local minimum in the fluctuations at a distance of R similar to 20 '' from the center. The systematic variation amounts to similar to 0.2 mag around the average value (m) over bar(l) = 22.78 +/- 0.04, and similar to 0.3 mag around (m) over bar(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 fluctuations for R < 20 ''. The increase in luminosity fluctuations 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 fluctuations with stellar population models having different horizontal branch morphologies indicates that a red clump horizontal branch cannot account for the observed ''blue'' fluctuations. During the reduction procedure the main source of contamination turned out to be a not insignificant contribution from M31's disk population. Based on the present observations and on simple simulations of the field 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 field are essential in order to select a criterion that will eliminate spurious sources due to the surface brightness fluctuations. Simulations show that our ground-based images with similar to 1.'' 0 seeing do not have the spatial resolution that will allow us to supplement the fluctuation measurement with stellar photometry of the most luminous stars. (C) 1996 American Astronomical Society.