[S2003] CS 22892-052 A , the SIMBAD biblio

A paper by Qian & Wasserburg suggests the optical absorption lines of uranium observed in the spectra of ultra-metal-poor stars (defined as [Fe/H]←3) arise from contamination from a supernova in a binary star system. Assuming the binary survived the explosion, a collapsed compact object may be present and implies potential accretion processes with accompanying X-ray emission. Upper limits on X-ray emission from an accreting compact object are described here.