Upper limits on the X-ray emission of "uranium" stars

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.