Physics – Optics
Scientific paper
Nov 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993phdt.......108t&link_type=abstract
PhD Thesis, Laboratoire d'Astrophysique de l'Observatoire de Grenoble, Université Joseph Fourier / CNRS, Grenoble, France, and D
Physics
Optics
3
Scientific paper
Atmospheric turbulence limits the angular resolution of a telescope to about one arcsecond. Speckle interferometry is a diffraction-limited imaging technique, which gives access to the full resolution of the telescope (which is a function of its diameter). The implementation of a speckle mode on an infrared camera (CIRCUS) used at the focus of a 3.6 meter telescope (TCFH) is described; in the thermal near infrared, we obtain a resolution of 0.2 arcseconds. Since the array detector that equipped the camera has a high readout noise but a large storage capacity, speckle interferometry observations have been done at the wavelengths where the thermal emission noise is dominant, i.e., beyond 3 microns. For example, the limiting magnitude in the L band (3.8 microns) is ranging from 6 to 8 depending on turbulence conditions. I developed a user-friendly interface in order for the observer to control the acquisition and to get in real time either shift-and-add images or the power spectrum and the visibility of the source. I made available a data post-processing package (under IRAF) to build the complex visibility of the observed source. The modulus is computed from image power spectra using the method proposed by Labeyrie (1970) with seeing calibrations. A Gauss-Newton and gradient-conjugate algorithm is used to extract the phase from several sub-planes of the images cross-spectra. The shift-and-add method is also available. Image reconstruction is obtained by CLEAN and Lucy methods. Speckle observations of T Tauri stars carried out to detect infrared companions are presented. As a first result, there seems to be no systematic correlation between an infrared excess and the presence of an infrared companion among T Tauri stars. For example, RY Tau, which is the archetype of T tauri star with a flat IR spectrum has not revealed any companion. The binarity nature of DD Tau is established, both components have a strong IR excess. Z CMa binarity is confirmed on our data in the M band but the disk observed in adaptative optics in L and M is not seen down to a level of 5%. Other stars are carefully examined. Two other astrophysical programs currently using speckle data are shown.
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