||1-D Imaging of the Dynamical Atmosphere of the Red Supergiant Betelgeuse in the CO First Overtone Lines with VLTI/AMBER
||487, Resolving The Future Of Astronomy With Long-Baseline Interferometry
||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.
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