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 wavelengthdependent 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 magnetocentrifugally 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.

Context. High angular and spectral resolution observations can provide us with fundamental clues to the complex circumstellar structure of young stellar objects (YSOs) and to the physical processes taking place close to these sources. Aims. We analyse the main physical parameters and the circumstellar environment of the young Herbig Be star HD 98922. Methods. We present AMBER/VLTI high spectral resolution (R = 12 000) interferometric observations across the Brγ line, accompanied by UVES high-resolution spectroscopy and SINFONI-AO assisted near-infrared (NIR) integral field spectroscopic data. To interpret our observations, we develop a magneto-centrifugally driven disc-wind model. Results. Our analysis of the UVES spectrum shows that HD 98922 is a young (∼5 × 10 5 yr) Herbig Be star (SpT = B9V), located at a distance of 440± 60 50 pc, with a mass accretion rate (Ṁ acc ) of ∼(9 ± 3) × 10 −7 M yr −1 . SINFONI K-band AO-assisted imaging shows a spatially resolved circumstellar disc-like region (∼140 AU in diameter) with asymmetric brightness distribution. Our AMBER/VLTI UT observations indicate that the Brγ emitting region (ring-fit radius ∼0.31 ± 0.04 AU) is smaller than the continuum emitting region (inner dust radius ∼0.7 ± 0.2 AU), showing significant non-zero V-shaped differential phases (i.e. non S-shaped, as expected for a rotating disc). The value of the continuum-corrected pure Brγ line visibility at the longest baseline (89 m) is ∼0.8 ± 0.1, i.e. the Brγ emitting region is partially resolved. Our modelling suggests that the observed Brγ line-emitting region mainly originates from a disc wind with a half opening angle of 30• , and with a mass-loss rate (Ṁ w ) of ∼2 × 10 −7 M yr −1 . The observed V-shaped differential phases are reliably reproduced by combining a simple asymmetric continuum disc model with our Brγ disc-wind model. Conclusions. In conclusion, the Brγ emission of HD 98922 can be modelled with a disc wind that is able to approximately reproduce all interferometric observations if we assume that the intensity distribution of the dust continuum disc is asymmetric.

This paper presents observations of an episode of accretion activity in the preÈmain-sequence star UX Ori. High-velocity, redshifted absorption is seen in several lines of H, Ca II, Na I, and Fe II during an interval of eight nights in the fall of 1996 with similar velocity and time evolution. A non-LTE analysis of the line optical depths shows that the infalling gas cannot be heavily hydrogen-depleted, as would be expected if it was produced by the evaporation of a solid body of chemical composition similar to solar system comets. On the contrary, the observations are consistent with gas of solar chemical composition at temperature D6000È7000 K.

Infrared interferometric observations with high spatial and spectral resolution and their quantitative modeling provide us with a unique opportunity to improve our understanding of the circumstellar environment of young stars and the accretion-ejection process. The goal of this paper is to investigate various models of the emitting regions in young Herbig Ae/Be stars that consist of (i) a compact rotating magnetosphere; (ii) an X-wind; and (iii) a disk wind. These models can be used, for example, to quantitatively interpret line profile measurements and infrared interferometric observations with the AMBER instrument of the Very Large Telescope Interferometer (VLTI) in the high spectral resolution mode (R = 12 000). VLTI/AMBER observations allow us to resolve the disk wind region and study the flux contribution of the unresolved magnetosphere and X-wind region to the total line flux. Analyzing the results of our non-LTE calculations, we conclude that the mechanisms of the different broadening of emission lines of different series include (1) the kinematic expansion due to the motion of the outflowing, accelerating gas in the magneto-centrifugal disk wind; (2) the Stark effect; and (3) the rotation of the magnetosphere. We also investigated extinction effects that can influence the shape of the line profiles. We considered the obscuration of the outer disk wind by an opaque dust and gas disk, the obscuration of the disk wind by a flared disk or by dust in the disk wind itself, and absorption of the star and disk continuum radiation in the disk wind along the line of sight. We show that due to extinction effects, the line profiles can change from double-peaked to single-peaked and P Cygni profiles. We studied the contribution of the different components of the stellar environment to different hydrogen emission lines and investigated how this contribution is dependent on the model parameters. The results of this study can be used for the detailed modeling of the emitting regions of individual young stars.