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Paper: 1-D Imaging of the Dynamical Atmosphere of the Red Supergiant Betelgeuse in the CO First Overtone Lines with VLTI/AMBER
Volume: 487, Resolving The Future Of Astronomy With Long-Baseline Interferometry
Page: 171
Authors: Ohnaka, K.
Abstract: We present high-spatial and high-spectral resolution observations of the red supergiant Betelgeuse in the CO first overtone lines near 2.3μm with the AMBER instrument at the Very Large Telescope Interferometer (VLTI). Our AMBER observations in 2008 spatially resolved the gas motions in a stellar atmosphere (photosphere and extended molecular outer atmosphere) for the first time other than the Sun. From our second observations one year later, we have reconstructed 1-D images in the individual CO lines with an angular resolution of 9.8 mas and a spectral resolution of 6000 by applying the self-calibration technique to restore the Fourier phase from the differential phase measurements. The reconstructed 1-D images reveal that the star appears different in the blue and red wing of the individual CO lines. In the blue wing, the star shows a pronounced, asymmetrically extended component at least up to 1.3 R, while such a component does not appear in the red wing 1-D image. This can be explained by a model in which the CO gas patch (or clump) more than half as large as the star is moving slightly outward with 0–5 km s-1, while the gas in the remaining region is infalling fast with 20–30 km s-1. Comparison between the CO line data taken in 2008 and 2009 shows a significant time variation in the dynamics of the photosphere and outer atmosphere. However, the 1-D images in the continuum show only a slight deviation from a limb-darkened disk with an angular diameter of 42.49±0.06 mas, which leads to an effective temperature of 3690± 54 K. Moreover, the continuum data taken in 2008 and 2009 reveal no or only marginal time variations, much smaller than the maximum variation predicted by the current 3-D convection simulation. The derived continuum diameter also shows that the near-IR size of Betelgeuse has been nearly constant over the last 18 years, in marked contrast to the recently reported noticeable decrease in the mid-IR size.
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