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Spectro-interferometric observations of interacting massive stars with VEGA/CHARA

We obtained spectro-interferometric observations in the visible of $β$ Lyrae and $\upsilon$ Sgr using the instrument VEGA of the CHARA interferometric array. For $β$ Lyrae, the dispersed fringe visibilities and differential phases were obtained in spectral regions containing the H$α$ and HeI 6678 lines and the H$β$ and HeI 4921 lines. Whereas the source is unresolved in the continuum, the source of the emission lines is resolved and the photocenter of the bulk of the H$α$ emission exhibits offsets correlated with the orbital phase. For $\upsilon$ Sgr, both the continuum and H$α$ sources are resolved, but no clear binary signal is detected. The differential phase shift across the line reveals that the bulk of the H$α$ emission is clearly offset from the primary.