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Your search keyword '"Graauw, T."' showing total 179 results
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179 results on '"Graauw, T."'

167. Resolving Disks in Ysos

Author

Natta, A., Butner, H., Eiroa, C., editor, Alberdi, A., editor, Thronson, H., editor, De Graauw, T., editor, and Schalinski, C. J., editor

Published
1997
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175. <atl>Remote sounding of the Martian dust from ISO spectroscopy in the <f>2.7 μm CO2</f> bands

Author

Fedorova, A.A., Lellouch, E., Titov, D.V., de Graauw, T., and Feuchtgruber, H.

Subjects
*MARS (Planet), *AEROSOLS, *REMOTE sensing
Abstract

This paper presents a study of Martian aerosols based on the spectral observations near 2.7 μm. Simulations by Titov et al. [Planet. Space Sci. 48 (2000) 67] showed that the depth and the shape of saturated 2.7 μm band of atmospheric CO2 are sensitive to the presence of aerosols. This allows one to determine the aerosol optical depth, the scale height, and optical properties from the spectral measurements in the band. For the first time this method is applied to two disk-averaged spectra of Mars recorded by the Infrared Space Observatory (ISO). The analysis implies existence of sharp absorption band in the dust spectrum between 2.7 and 2.8 μm that probably indicates the presence of phyllosilicates (for instance, montmorillonite) in the dust. The best fit to the ISO spectra is obtained in the model with column optical depth of 0.33±0.13. This value is in good agreement with simultaneous Mars Pathfinder and Hubble Space Telescope observations. [Copyright &y& Elsevier]

Published
2002
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177. Low-temperature crystallization of silicate dust in circumstellar disks.

Author

Molster FJ, Yamamura I, Waters LB, Tielens AG, de Graauw T, de Jong T, de Koter A, Malfait K, van den Ancker ME, van Winckel H, Voors RH, and Waelkens C

Subjects
Cold Temperature, Crystallization, Cosmic Dust, Extraterrestrial Environment, Silicates chemistry
Abstract

Silicate dust in the interstellar medium is observed to be amorphous, yet silicate dust in comets and interplanetary dust particles is sometimes partially crystalline. The dust in disks that are thought to be forming planets around some young stars also appears to be partially crystalline. These observations suggest that as the dust goes from the precursor clouds to a planetary system, it must undergo some processing, but the nature and extent of this processing remain unknown. Here we report observations of highly crystalline silicate dust in the disks surrounding binary red-giant stars. The dust was created in amorphous form in the outer atmospheres of the red giants, and therefore must be processed in the disks to become crystalline. The temperatures in these disks are too low for the grains to anneal; therefore, some low-temperature process must be responsible. As the physical properties of the disks around young stars and red giants are similar, our results suggest that low-temperature crystallization of silicate grains also can occur in protoplanetary systems.

Published
1999
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179. Pseudo-random binary sequences for multiplex codes.

Author

Graauw T and Veltman BP

Abstract

A multiplex technique is described that can be used in photoelectric observations of dispersed spectra. The encoding pattern is a set of pseudo-random binary sequences. The data processing requires a minimum possible number of operations. A special purpose device could give the spectral intensity distribution on-line. An application at the solar eclipse (Mexico, 1970) is described.

Published
1970
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