Spatially resolving the inhomogeneous structure of the dynamical atmosphere of Betelgeuse with VLTI/AMBER

摘要

We present spatially resolved high-spectral resolution K-band observations ofthe red supergiant Betelgeuse (alpha Ori) using AMBER at the Very LargeTelescope Interferometer (VLTI). Betelgeuse was observed between 2.28 and 2.31micron using baselines of 16, 32, and 48m with spectral resolutions of 4800 --12000. Spectrally dispersed interferograms have been obtained in the 2nd, 3rd,and 5th lobes, which represents the highest spatial resolution (9 mas) achievedfor Betelgeuse, corresponding to 5 resolution elements over its stellar disk.The AMBER data in the continuum can be reasonably fitted by a uniform disk witha diameter of 43.19+/-0.03 mas or a limb-darkening disk with 43.56+/-0.06 mas.The K-band interferometric data taken at various epochs suggest that Betelgeuseseen in the continuum shows much smaller deviations from the aboveuniform/limb-darkened disk than predicted by 3-D convection simulations. On theother hand, our AMBER data in the CO lines reveal that the blue and red wingsof the CO lines originate in spatially distinct regions over the stellar disk,indicating an inhomogeneous velocity field. Our AMBER data in the CO lines canbe roughly explained by a simple model, in which a patch of CO gas is movingoutward or inward at velocities of 10--15 km s^-1, while the CO gas in theremaining region in the atmosphere is moving in the opposite direction at thesame velocities. The AMBER data are also consistent with the presence of warmmolecular layers at ~1.4--1.5 Rstar with a CO column density of ~1 x 10^20cm^-2. Our AMBER observations of Betelgeuse are the first spatially resolvedstudy of the so-called macroturbulence in a stellar atmosphere other than theSun. The spatially resolved CO gas motion is likely to be related to convectivemotion or intermittent mass ejections in clumps or arcs.