We present VLTI-MIDI (Mid-Infrared Interferometric Instrument) observations of MWC349A, which are a prime example of the power of combined spatial and spectral resolution for addressing complex astrophysical phenomena.
Previous observations of the peculiar emission line star MWC349A suggest that it is a young massive star in the short-lived phase of already having dissipated its parent cloud, but still being surrounded by the accretion disk, which is seen nearly edge-on. It is believed that the unique hydrogen recombination line maser / laser activity of MWC349A from mm to infrared wavelengths is also a consequence of this viewing angle.
We have taken 13 measurements with MIDI at the VLTI (Very Large Telescope Interferometer) in the GRISM mode covering the N band (8 to 13 microns) at a spectral resolution R=230. The wavelength dependence of the continuum visibility agrees with model calculations for circumstellar dust disks. In addition, the signatures of at least a dozen emission lines have been identified in the interferometric data.
We will present the analysis of visibility amplitudes as well as of differential phase data, and discuss the correction of the phases for instrumental effects and dispersion. The differential phases show changes at the position of emission lines, clearly indicative of an asymmetry between the emission line region and the region emitting the continuum flux. As one can measure these relative phases to an accuracy of a few degrees, we obtain information on spacial scales of order 100 microarcseconds, which corresponds to a fraction of an AU at the distance of MWC349A.