Hydrogen lines as a diagnostic tool for studying multicomponent emitting regions in hot young stars: magnetosphere, X-wind, and disk wind

Abstract

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 nonLTE 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.