The science potential of ALFA: Adaptive optics with natural and laser guide stars

Abstract

Abstract. Adaptive optics with laser guide stars is mandatory in order to make use of the full capabilities of 8-m class telescopes. However, progress has been slow in two particular areas: techniques for spectroscopy at diffraction limited resolution and wavefront sensing on laser guide stars. ALFA -currently the only European laser guide star adaptive optics system, and the only one in the world open to guest observers -has made significant advances in both of these. In this paper we report on our first results from summer 1998, representing significant improvements over previous performance. We report on observations using natural guide stars which demonstrate that for bright stars (m V ∼ < 8) ALFA can now reach K-band Strehl ratios in excess of 60% and easily resolve binaries at the diffraction limit of the telescope. We then present some of the first integral field spectroscopy at diffraction limited scales, showing we are able to distinguish spectra of binary stars with a separation of only 0.26 . We also discuss results from a wide field image, which indicate that useful correction (allowing binary stars and circumstellar dust shells to be resolved) can be achieved from a relatively faint star to a radius of at least 1 . Our last set of results include a correction on a galaxy using the laser guide star as the reference. The 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 an increase in peak intensity of 2.5, and a reduction in FWHM from 1.07 to 0.40 .

Shock Excitation in Interacting Galaxies: Markarian 266

“…6. Clearly the system is far from trivial, and it would be useful to analyse all the line ratios with high spatial resolution, something which may be possible with adaptive optics and integral field spectroscopy in the (near) future (eg see Davies et al 1999). Here we present an analysis of the detailed integrated spectra together with some spatial information from both spectra and images.…”

Adaptive Optics for Extremely Large Telescopes

“…First laser guide star (LGS) assisted AO systems, which were installed during the 1990s on smaller telescopes, can be seen in retrospect as prototypes, even though few scienti¯c results have been published (Davies et al, 1999;Hackenberg et al, 2000).…”

Adaptive-optics performance of Antarctic telescopes

“…This error increases for smaller separation angles because brighter stars are more difficult to find. Techniques to reduce these errors include the use of multiple guide stars, the use of laser guide stars or beacons, 4 and the use of multiple deformable mirrors matched to separate atmospheric layers ͑multiconjugate adaptive optics 5 ͒. There are, however, disadvantages to each of these techniques.…”