X-RAY OBSERVATIONS OF X2127+119 AC-211 IN THE METAL-POOR GLOBULAR-CLUSTER M15 - AN X-RAY MEASURE OF METALLICITY/

We present results from observations of the 17.1 hr low-mass X-ray bin ary X2127+119 (AC 211) in M15 obtained with the broadband X-ray telesc ope (BBXRT) in 1990 December and observations obtained with the solid state spectrometer (SSS) together with the monitor proportional counte r (MPG) on the Einstein Observatory in 1978 and 1979. The continuum ca n be well described with the two-component model of a blackbody (kT si milar to 1 keV) and a power law that was found to fit the EXOSAT mediu m-energy data. Short-term variability observed by the SSS and MPC was related to changes in the intensities of both components in this descr iption. The SSS and MPC observed factor of 10 differences in column de nsity in observations separated by a few binary orbits. These observat ions confirm correlations between the steepness of the spectrum and th e column density, and column density with phase. The percentage contri bution of the blackbody is anticorrelated with the factor of 4 variati ons in the apparent luminosity, but other correlations are weak. A 100 0 s observation by BBXRT at photometric phase 0.9 provides an upper li mit of similar to 150 eV to narrow Fe K line emission. BBXRT spectra a re generally inconsistent with the overall cluster metallicity of 1% o f solar, although complex spectral models can be more consistent with the cluster metallicity. A model separating the absorption of H and He from the metals gives 1.25(-0.2)(+0.03) x 10(18) cm(-2) for the colum n density of metals in the absorbing gas associated with the binary sy stem. The noted correlations between spectral parameters, luminosity, and their relation to orbital phase are consistent with a disk plus mo derate-sized corona interpretation.