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First Observational Results from ALFA with Natural and Laser Guide Stars

R. I. Davies·W. Hackenberg·T. Ott·A. Eckart·S. Rabien·S. Anders·S. Hippler·M. Kaspar
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Abstract

The sodium laser guide star adaptive optics system ALFA, which is installed at the Calar Alto 3.5-m telescope, has been undergoing an intensive optimisation phase. Observations using natural guide stars that are presented in this paper, show that for bright stars (V~<8) it is now possible to reach K-band Strehl ratios in excess of 60% and to easily resolve binaries at the diffraction limit of the telescope. In more typical usage Strehl ratios in the range 10-15% can be achieved over a wide field (~2'); and the limiting magnitude is currently V~<12.5. We also present some of the first spectroscopy at diffraction limited scales, showing we are able to distinguish spectra of binary stars with a separation of only 0.26''. Our last set of results are on Abell galaxy clusters, including a correction on a galaxy using the laser guide star as the reference. There are still a number of difficulties associated with the laser, but our best result to date is of the galaxy UGC 1347 in Abell 262. Correcting tip-tilt on a star 41'' away and higher orders on the laser, we achieved in increase in peak intensity of 2.5, and a reduction in FWHM from 1.07'' to 0.40''. It is expected that further significant advances will be made in the next 6 months and beyond.

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R. I. Davies, W. Hackenberg, T. Ott, A. Eckart, S. Rabien, S. Anders, S. Hippler, M. Kaspar. 1998-10-09. First Observational Results from ALFA with Natural and Laser Guide Stars. https://arxiv.org/abs/astro-ph/9810157

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