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   PR # 11036
    We propose to investigate the circumbinary regions around and the
    interstellar medium to the massive, eclipsing, and pulsing X-ray
    binaries LMC X-4, 4U1907+097, and 4U1538-52. We will use fluorescence
    lines, the rotating X-ray beam pattern, and pulse phase spectroscopy
    including the 6.7 keV iron line to determine the structure and
    abundance of the circumbinary region, including the stellar winds.
    Since these sources cover a luminosity range from 4 x 10^36 to
    6x10^38 erg/s, this study may reveal the dependence of the photo-
    ionization region on X-ray luminosity.In addition, during eclipse, we
    may be able to observe interstellar dustscattering of the X-rays.


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