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First results of AMBER stability tests (20 March 2004)
Saturday 20 March 2004, by Fabien Malbet

- During the period (17-19 March 2004) where the VLTI global alignment and the star acquisition are being tested, AMBER has continued its reproducibility and stability tests. We have cycled the instrument with constrast calibration of the all 7 spectral configurations (low spectral resolution JHK band, medium spectral resolution in each J, H and K band and idem with the high spectral resolution). Below the contrasts obtained these last days are displayed (left panel) with a magnification on the data from last night. The reproducibility is improving as the instrument goes less disturbed. We seem to be already in the range of better than 1% repeatability of the P2VM after several configuration changes.

- We have compared the contrast evolution with the temperature evolution at different locations in the instrument and in the laboratory. Below the evolution of the contrast of the 1-2 baseline in medium spectral resolution in the middle of the K band is displayed (top panels) together with the evolution of the temperature in 4 different locations in the instrument: at the calibration unit (red markers) , at the entrance (green ones) and output (blue ones) of the fibers, and at the entrance of the spectrograph (black ones). We see clearly a correlation between temperatures and contrast, probably through the influence of temperature on the quality of output beam superposition. However, when temperature variations approach the specified 0.1, the effect on the instrumental contrasts seems to go well below 1%.

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