2018A&A...620A..23O -
Astronomy and Astrophysics, volume 620A, 23-23 (2018/12-1)
Spatially resolving the thermally inhomogeneous outer atmosphere of the red giant Arcturus in the 2.3 µm CO lines.
OHNAKA K. and MORALES MARIN C.A.L.
Abstract (from CDS):
Aim. The outer atmosphere of K giants shows thermally inhomogeneous structures consisting of the hot chromospheric gas and the cool molecular gas. We present spectro-interferometric observations of the multicomponent outer atmosphere of the well-studied K1.5 giant Arcturus (α Boo) in the CO first overtone lines near 2.3µm.
Methods. We observed Arcturus with the AMBER instrument at the Very Large Telescope Interferometer (VLTI) at 2.28-2.31µm with a spectral resolution of 12 000 and at projected baselines of 7.3, 14.6, and 21.8m.
Results. The high spectral resolution of the VLTI/AMBER instrument allowed us to spatially resolve Arcturus in the individual CO lines. Comparison of the observed interferometric data with the MARCS photospheric model shows that the star appears to be significantly larger than predicted by the model. It indicates the presence of an extended component that is not accounted for by the current photospheric models for this well-studied star. We found out that the observed AMBER data can be explained by a model with two additional CO layers above the photosphere. The inner CO layer is located just above the photosphere, at 1.04±0.02R*, with a temperature of 1600±400K and a CO column density of 1020±0.3cm–2. On the other hand, the outer CO layer is found to be as extended as to 2.6±0.2R* with a temperature of 1800±100K and a CO column density of 1019±0.15cm–2.
Conclusions. The properties of the inner CO layer are in broad agreement with those previously inferred from the spatially unresolved spectroscopic analyses. However, our AMBER observations have revealed that the quasi-static cool molecular component extends out to 2-3R*, within which region the chromospheric wind steeply accelerates.
Abstract Copyright:
© ESO 2018
Journal keyword(s):
infrared: stars - techniques: interferometric - stars: late-type - stars: mass-loss - stars: atmospheres - stars: individual: Arcturus
Simbad objects:
6
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