A POSSIBLE SPECTRAL SIGNATURE OF ULTRACOMPACT LOW MASS X-RAY BINARIES

ASCA and BeppoSAX observations of a number of ultracompact (P<1hr)Xray binaries have revealed two possible spectral differences comparedto other LMXRB systems. These are (1) the presence of a discrete feature near0.7 keV (attributed to Ne) and (2) their bestfit parameter values when fit with a diskblackbody and Comptonized continuum. We wish to clarify and extend the emerging picture of a spectral signature for the ultracompact systems using XMMNewton. The proposed observations will allow a clear confirmation of such a signature which will, in turn, allow the nature of a LMXRB to be determined from its spectral characteristics. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]