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We present here X-ray spectra of the HMXB SMC X-1 obtained in an observationwith the XMM observatory beginning before eclipse and ending near the end ofeclipse. With the Reflection Grating Spectrometers (RGS) on board XMM, weobserve emission lines from hydrogen-like and helium-like ions of nitrogen,oxygen, neon, magnesium, and silicon. Though the resolution of the RGS issufficient to resolve the helium-like n=2->1 emission into three linecomponents, only one of these components, the intercombination line, isdetected in our data. The lack of flux in the forbidden lines of thehelium-like triplets is explained by pumping by ultraviolet photons from the B0star and, from this, we set an upper limit on the distance of the emitting ionsfrom the star. The lack of observable flux in the resonance lines of thehelium-like triplets indicate a lack of enhancement due to resonance linescattering and, from this, we derive a new observational constraint on thedistribution of the wind in SMC X-1 in velocity and coordinate space. We findthat the solid angle subtended by the volume containing the helium-like ions atthe neutron star multiplied by the velocity dispersion of the helium-like ionsmust be less than 4pi steradians km/s. This constraint will be satisfied if thehelium-like ions are located primarily in clumps distributed throughout thewind or in a thin layer along the surface of the B0 star.

Constraints on the Velocity and Spatial Distribution of Helium-like Ions in the Wind of SMC X-1 from Observations with XMM-Newton/RGS