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We observed two fields near M32 with the Advanced Camera for Surveys/HighResolution Channel (ACS/HRC) on board the Hubble Space Telescope (HST). Themain field, F1, is 1.8 arcmin from the center of M32; the second field, F2,constrains the M31 background, and is 5.4 arcmin distant. Each field wasobserved for 16-orbits in each of the F435W (narrow B) and F555W (narrow V)filters. The duration of the observations allowed RR Lyrae stars and othershort-period variables to be detected. A population of RR Lyrae starsdetermined to belong to M32 would prove the existence of an ancient populationin that galaxy, a subject of some debate. We detected 17 RR Lyrae variables inF1 and 14 in F2. A 1-sigma upper limit of 6 RR Lyrae variables belonging to M32is inferred from these two fields alone. Use of our two ACS/WFC parallel fieldsprovides better constraints on the M31 background, however, and implies that$7_{-3}^{+4}$ (68 % confidence interval) RR Lyrae variables in F1 belong toM32. We have therefore found evidence for an ancient population in M32. Itseems to be nearly indistinguishable from the ancient population of M31. The RRLyrae stars in the F1 and F2 fields have indistinguishable mean V-bandmagnitudes, mean periods, distributions in the Bailey diagram and ratios of RRcto RR(tot) types. However, the color distributions in the two fields aredifferent, with a population of red RRab variables in F1 not seen in F2. Wesuggest that these might be identified with the detected M32 RR Lyraepopulation, but the small number of stars rules out a definitive claim.

RR Lyrae variables in M32 and the disk of M31