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

摘要

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 Brγ-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 ?~2.2?mas (~0.56?AU at a distance of 250?pc), which is ?~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 Brγ-emitting region is more extended (~2.7?times) than the continuum-emitting region. At the center of the Brγ line, we derive a Gaussian fit radius of ?~6.3?mas HWHM (~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 Brγ?line. The calculated wavelength-dependent model intensity distributions and Brγ?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 ?~0.3?AU and a disk wind ejection region with an inner radius of ?~?0.5?AU (~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 ?~80°, which is larger than in T Tau models, and a disk inclination angle of ?~20° (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 ?~10 different spectral channels across the Brγ 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.