The dependence of the soft X-ray properties of low-mass X-ray binaries on the metallicity of their environment

We determine the X-ray spectral properties of a sample of low-mass X-ray bi naries (LMXBs) that reside in globular clusters of M31 as well as five LMXB s in Galactic globular clusters and in the Large Magellanic Cloud using the ROSAT Position Sensitive Proportional Counter. We find a trend in the X-ra y properties of the LMXBs as a function of globular cluster metallicity. Th e spectra of LMXBs become progressively softer as the metallicity of their environment increases. The one M31 globular cluster LMXB in our sample that has a metallicity greater than solar has spectral properties similar to th ose of LMXBs in the bulge of M31 bur markedly different from those that res ide in low-metallicity globular clusters, both in M31 and the Galaxy. The s pectral properties of this high-metallicity LMXB are also similar to those of X-ray-faint, early-type galaxies. This lends support to the claim that a majority of the X-ray emission from these X-ray-faint, early-type galaxies results from LMXBs and not hot gas, as is the case in their X-ray-bright c ounterparts.