2007A&A...473..783R

Using Chandra observations, we study the X-ray emission of the stellar population in the compact dwarf elliptical galaxy M32. The proximity of M32 allows one to resolve all bright point sources with luminosities higher than 8x10³³erg/s in the 0.5-7keV band. The remaining (unresolved) emission closely follows the galaxy's optical light and is characterized by an emissivity per unit stellar mass of ∼4.3x10²⁷erg/s/M_☉ in the 2-10keV energy band. The spectrum of the unresolved emission above a few keV smoothly joins the X-ray spectrum of the Milky Way's ridge measured with RXTE and INTEGRAL. These results strongly suggest that weak discrete X-ray sources (accreting white dwarfs and active binary stars) provide the bulk of the ``diffuse'' emission of this gas-poor galaxy. Within the uncertainties, the average X-ray properties of the M32 stars are consistent with those of the old stellar population in the Milky Way. The inferred cumulative soft X-ray (0.5-2keV) emissivity is however smaller than is measured in the immediate Solar vicinity in our Galaxy. This difference is probably linked to the contribution of young (age ≪1Gyr) stars, which are abundant in the Solar neighborhood but practically absent in M32. Combining Chandra, RXTE and INTEGRAL data, we obtain a broad-band (0.5-60keV) X-ray spectrum of the old stellar population in galaxies.