20,230 research outputs found
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
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