Astronomy and Astrophysics, volume 539A, 138-138 (2012/3-1)
The ancient stellar population of M 32: RR Lyrae variable stars confirmed.
FIORENTINO G., CONTRERAS RAMOS R., TOLSTOY E., CLEMENTINI G. and SAHA A.
Abstract (from CDS):
Using archival multi-epoch ACS/WFC images in the F606W and F814W filters of a resolved stellar field in Local Group dwarf elliptical galaxy M 32 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 M 32. These new observations clearly confirm the tentative result of Fiorentino et al. (2010ApJ...708..817F), on a much smaller field of view, associating an ancient population of RR Lyr variables to M 32. We associate at least 83 RR Lyr stars in our field to M 32. In addition the detection of 4 anomalous Cepheids with masses in the range 1.2-1.9M☉ indicates the presence of relatively young, 1-4Gyr 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 M 32 because the radial distribution of the blue plume does not follow the M 32 density profile, and thus they are more likely to belong to the underlying M 31 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 RR Lyr, µ0=24.33±0.21mag.
Local Group - stars: variables: RR Lyrae - galaxies: individual: M 31 - stars: horizontal-branch - galaxies: individual: M 32