VLTI/AMBER spectro-interferometry of the Herbig Be star MWC 297 with spectral resolution 12 000

Context. Circumstellar disks and outflows play a fundamental role in star formation. Infrared spectro-interferometry allows the inner accretion-ejection region to be resolved. Aims. We study the disk and Br gamma-emitting region of MWC 297 with high spatial and spectral resolution and compare our observations with disk-wind models. Methods. We measured interferometric visibilities, wavelength-differential phases, and closure phases of MWC 297 with a spectral resolution of 12 000. To interpret our MWC 297 observations, we employed disk-wind models. Results. The measured continuum visibilities confirm previous results that the continuum-emitting region of MWC 297 is remarkably compact. We derive a continuum ring-fit radius of similar to 2.2 mas (similar to 0.56 AU at a distance of 250 pc), which is similar to 5.4 times smaller than the 3 AU dust sublimation radius expected for silicate grains (in the absence of radiation-shielding material). The strongly wavelength-dependent and asymmetric Br gamma-emitting region is more extended (similar to 2.7 times) than the continuum-emitting region. At the center of the Br gamma line, we derive a Gaussian fit radius of similar to 6.3 mas HWHM (similar to 1.6 AU). To interpret the observations, we employ a magneto-centrifugally driven disk-wind model consisting of an accretion disk, which emits the observed continuum radiation, and a disk wind, which emits the Br gamma line. The calculated wavelength-dependent model intensity distributions and Br gamma line profiles are compared with the observations (i.e., K-band spectrum, visibilities, differential phases, and closure phases). The closest fitting model predicts a continuum-emitting disk with an inner radius of similar to 0.3 AU and a disk wind ejection region with an inner radius of similar to 0.5 AU (similar to 17.5 stellar radii). We obtain a disk-wind half-opening angle (the angle between the rotation axis and the innermost streamline of the disk wind) of similar to 80 degrees, which is larger than in T Tau models, and a disk inclination angle of similar to 20 degrees (i.e., almost pole-on). Conclusions. Our observations with a spectral resolution of 12 000 allow us to study the AU-scale environment of MWC 297 in similar to 10 different spectral channels across the Br gamma emission line. We show that the K-band flux, visibilities, and remarkably strong phases can be explained by the employed magneto-centrifugally driven disk wind model.