Spatially resolving the thermally inhomogeneous outer atmosphere of the red giant Arcturus in the 2.3 micron CO lines

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 (alpha Boo) in the CO first overtone lines near 2.3 micron. We observed Arcturus with the AMBER instrument at the Very Large Telescope Interferometer (VLTI) at 2.28--2.31 micron with a spectral resolution of 12000 and at projected baselines of 7.3, 14.6, and 21.8 m. 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 +/- 0.02 stellar radii, with a temperature of 1600 +/- 400 K and a CO column density of 10^{20 +/- 0.3} cm^-2. On the other hand, the outer CO layer is found to be as extended as to 2.6 +/- 0.2 stellar radii with a temperature of 1800 +/- 100 K and a CO column density of 10^{19 +/- 0.15} cm^-2. 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--3 stellar radii, within which region the chromospheric wind steeply accelerates.Comment: 10 pages, 9 figures, accepted for publication in Astronomy and Astrophysic

A combination of SEM and EDX studies on a clay-based natural composite with animal fibre and its mechanical implications

A variety of natural fibres are nowadays being utilized as soil reinforcement. Test results demonstrate the positive effects of adding natural fibres to soils, in that they decrease shrinkage, reduce curing time and enhance compressive, flexural and shear strength if an optimum reinforcement ratio can be utilised. This paper describes a study which uses a Scanning Electron Microscope (SEM) and an Energy Diffraction Analysis of X-rays (EDX) technique on clay-based composites stabilized with natural polymer and fibres. Different dosages of fibres and several types of soils have been used in this study with the aim of determining advantageous properties for building material applications. SEM and EDX test results reveal the degree of bonding between the particles of soil and the natural fibers. This has enabled a better understanding of the micro-morphology of the natural fibers and their effect on the overall composite material structure. Microscopic analysis was combined with mechanical tests to establish the different strength characteristics of every soil