X-ray Observations of X2127+119 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 Binary X2127+119 (AC211) in M15 obtained with the Broad Band X-ray Telescope (BBXRT) in December 1990 and observations obtained with the Solid State Spectrometer (SSS) together with the Monitor Proportional Counter (MPC) on the Einstein Observatory in 1978 and 1979. The continuum can be well described with the two component model of a blackbody (kT ~ 1 keV) and a power-law that was found to fit the EXOSAT ME data. Short term variability observed by the SSS and MPC was related to changes in the intensities of both components in this description. Longer timescale changes were larger. The SSS and MPC observed factor of 10 differences in column density in observations separated by a few binary orbits. These observations confirm correlation between the steepness of the spectrum and the column density, and column density with phase. The percentage contribution of the blackbody is anticorrelated with the factor of 4 variations in the apparent luminosity, but other correlations are weak. A 1000 second observation by BBXRT at photometric phase 0.9 provides an upper limit of ~ 150 eV to narrow Fe K line emission. BBXRT spectra are inconsistent with the known cluster metallicity of 1/100th of solar. A model separating the absorption of H and He and the metals gives 3.4(+0.09}_{-0.52) x10(21) cm(-2) for the column density of metals in the absorbing gas associated with the binary system. Interpretation of changes in spectral parameters and their relation to orbital phase and longer timescale variations will be discussed.