Multiwavelength Observations of Exo 0748–676 – Ii. Emission Line Behavior

We present optical and ultraviolet spectra, lightcurves, and Doppler tomograms of the low-mass X-ray binary EXO 0748–676. Using an extensive set of 15 emission line tomograms, we show that, along with the usual emission from the stream and “hot spot”, there is extended non-axisymmetric emission from the disk rim. Some of the emission and Hα and β absorption features lend weight to the hypothesis that part of the stream overflows the disk rim and forms a two phase medium. The data are consistent with a 1.35M⊙ neutron star with a main sequence companion and hence a mass ratio q ≈ 0.34. Subject headings: accretion, accretion disks—binaries: close – stars: individual: UY Vol