2006A&A...450..117S

We assessed the contribution to the X-ray (above 2keV) luminosity of the Milky Way by different classes of low-mass binary systems and single stars. We began by using the RXTE Slew Survey of the sky at |b|>10° to construct an X-ray luminosity function (XLF) of nearby X-ray sources in the range 10³⁰erg/s<L_x<10³⁴erg/s (where L_x is the luminosity over 2-10keV), occupied by coronally active binaries (ABs) and cataclysmic variables (CVs). We then extended this XLF down to L_x∼10^27.5erg/s using the Rosat All-Sky Survey in soft X-rays and available information on the 0.1-10keV spectra of typical sources. We found that the local cumulative X-ray (2-10keV) emissivities (per unit stellar mass) of ABs and CVs are (2.0±0.8)x10²⁷ and (1.1±0.3)x10²⁷erg/s/M_☉, respectively. In addition to ABs and CVs representing old stellar populations, young stars locally emit (1.5±0.4)x10²⁷erg/s/M_☉. Finally to the XLF of ABs and CVs we attached a high luminosity branch (up to ∼10³⁹erg/s) composed of neutron-star and black-hole low-mass X-ray binaries (LMXBs), derived in previous work. The combined XLF covers ∼12 orders of magnitude in luminosity. The estimated combined contribution of ABs and CVs to the 2-10keV luminosity of the Milky Way is ∼2x10³⁸erg/s, or ∼3% of the integral luminosity of LMXBs averaged over nearby galaxies. The XLF obtained in this work is used elsewhere to assess the contribution of point sources to the Galactic ridge X-ray emission.