Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004phdt........11p&link_type=abstract
PhD Dissertation, Max-Planck Institute of Astronomy, Heidelberg
Astronomy and Astrophysics
Astronomy
7
T Tauri, Infrared, N-Band, Spectra
Scientific paper
Observations in the mid-infrared spectral regime around lambda = 10 micron (N-band) allow a selective study of the properties of circumstellar dust around young stellar objects. In this thesis, such observations are presented. The first part deals with the analysis of a sample of N-band spectra obtained from 31 T Tauri stars. The prominent characteristic of N-band spectra of these stars is the silicate feature, which appears in emission as well as in absorption. The shape of this feature depends primarily on the chemical composition and the size of the dust grains. The detailed analysis of the emission spectra reveals a continous transition from spectra showing strong emission and a triangular shape to those with weak emission and a plateau-like shape. Comparing the spectra with theoretical ones of different chemical compositions and grain sizes indicates that the observed transition can be explained by an increase of the dust particle size. This suggests an effect of dust evolution by coagulation of dust grains. The second part of the thesis introduces MIDI, the Mid-Infrared Interferometric Instrument for the VLTI. The instrument offers the possibility of observations with very high angular resolution in the mid-infrared spectral regime. Technical aspects of the optical alignment and its influence on the quality of the measurements are explained and a description of the reduction process of typical interferometric data is given. The analysis of data from the young stellar binary system Z CMa yields an estimate of the size of mid-infrared radiation emitting dust around each component of about 15 mas. Furthermore, spectrally dispersed data of the two components of VV CrA are reduced. The increasing size of the intensity distribution with wavelength is determined for both components. It turns out that the SW-component of the binary is about 2 mas larger than the NE-component over the whole N-band.
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