The ancient stellar population of M32: RR Lyr Variable stars confirmed
  Using archival multi--epoch ACS/WFC images in the F606W and F814W filters of
a resolved stellar field in Local Group dwarf elliptical galaxy M32 we have
made an accurate Colour-Magnitude Diagram and a careful search for RR Lyr
variable stars. We identified 416 bona fide RR Lyr stars over our field of
view, and their spatial distribution shows a rising number density towards the
centre of M32. These new observations clearly confirm the tentative result of
Fiorentino et al. (2010), on a much smaller field of view, associating an
ancient population of RR Lyr variables to M32. We associate at least 83 RR Lyr
stars in our field to M32. In addition the detection of 4 Anomalous Cepheids
with masses in the range 1.2-1.9 Mo indicates the presence of relatively young,
1-4 Gyr old, stars in this field. They are most likely associated to the
presence of the blue plume in the Colour-Magnitude Diagram. However these young
stars are unlikely to be associated with M32 because the radial distribution of
the blue plume does not follow the M32 density profile, and thus they are more
likely to belong to the underlying M31 stellar population. Finally the
detection of 3 Population II Cepheids in this field gives an independent
measurement of the distance modulus in good agreement with that obtained from
the RRLyr, mu0=24.33 +- 0.21 mag.
