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New opportunities with spectro-interferometry and spectro-astrometry

Latest-generation spectro-interferometric instruments combine a milliarcsecond angular resolution with spectral capabilities, resulting in an immensely increased information content. Here, I present methodological work and results that illustrate the fundamentally new scientific insights provided by spectro-interferometry with very high spectral dispersion or in multiple line transitions (Brackett and Pfund lines). In addition, I discuss some pitfalls in the interpretation of spectro-interferometric data. In the context of our recent studies on the classical Be stars β CMi and ζ Tau, I present the first position-velocity diagram obtained with optical interferometry and provide a physical interpretation for a phase inversion, which has in the meantime been observed for several classical Be-stars. In the course of our study on the Herbig B[e] star V921 Sco, we combined, for the first time, spectro-interferometry and spectro-astrometry, providing a powerful and resource-efficient way to constrain the spatial distribution as well as the kinematics of the circumstellar gas with an unprecedented velocity resolution up to R = λ/Δλ = 100,000. Finally, I discuss our phase sign calibration procedure, which has allowed us to calibrate AMBER differential phases and closure phases for all spectral modes, and derive from the gained experience science-driven requirements for future instrumentation projects.