Jerry E. Nelson

Performance of the W.M. Keck telescope active mirror control system

The active mirror control system of the W.M. Keck telescope maintains the optical figure of the segmented primary mirror under the changing influences of gravity and temperature. The ultimate performance of the system depends on the size of the calibration errors and on its stability. The design error budget calls for the calibrated mirror control system to contribute an image blur less than 0.1 arc seconds (80% enclosed energy) over the full range of operating conditions.

W.M. Keck Telescope phasing camera system

The segmented design of the W. M. Keck Telescope primary mirror places several unique demands upon the alignment and adjustment of the telescope optics. These include: (1) careful determination of the optical figures of individual segments (to provide input data for warping harness adjustment), (2) control of the two tilt degrees of freedom for each of the thirty-six primary mirror segments, and (3) phasing or control of the piston degree of freedom for each of these segments. In addition, (4) the proper alignment of the secondary with respect to the primary, although it is a requirement common to monolithic and segmented telescopes alike, is a more subtle and complicated task for the latter because the optic axis of the primary is not readily defined. These four tasks are performed at Keck by the Phasing Camera System.

Phasing the mirror segments of the W.M. Keck Telescope

We present data which illuminates the method and also discuss details of the operation of the Phasing Camera.

Optical quality of the W.M. Keck Telescope

Astronomical observations are now taking place on the Keck I telescope on a regular basis. We summarize here the status of the Keck I and II optics, and the current wavefront and image quality of the Keck I telescope as measured by in-telescope optical tests. Shack-Hartmann measurements of the individual primary mirror segments yield 80% encircled energy diameters that vary from 0.31 to 0.60 arc seconds. Full width at half maximum measurements of direct segment images obtained on a night of excellent seeing varied from 0.32 to 0.51 arcsec, and the combined image was 0.42 arcsec.

Pointing and tracking performance of the W.M. Keck Telescope

The achieved pointing and tracking performance of the telescope is presented and compared with the Keck goals. The implications of the current performance on observing are discussed, and planned remedies for deficiencies in pointing and tracking are proposed.

High-speed seeing measurements at the Keck Telescope

We have installed a high-speed camera system at the Keck Telescope, to be used for studying and monitoring atmospheric seeing as well as for telescope diagnostic purposes. This instrument, which consists of a Dalsa camera with a 64 X 64 pixel CCD, a 4 Megabyte Epix frame grabber, and a 486 computer, records sequences of 1248 frames at 181 Hz and 0.2 arcsecond resolution. We note that the Keck Telescope, by virtue of its 10 meter baseline as well as its ability to separate images formed by any or all of its 36 primary mirror segments, is ideally suited to seeing studies, in particular to those involving relatively long baselines and aperture-aperture correlations of wavefront aberrations. We present power spectra for atmospheric wavefront tilts for the primary mirror segments. In general they show the power law frequency dependance expected on theoretical grounds. However the measured segment-to-segment correlations are systematically smaller than theory predicts by a significant factor. It is possible that this effect is a manifestation of a finite outer scale of turbulence.

W.M. Keck Observatory adaptive optics program

The status and plans for a multi-phase program to build adaptive optics (AO) user facilities for one of the Keck telescopes is presented. The planned facilities include (1) fast tip/tilt correction, (2) near infrared AO with natural stars, and potentially (3) a near infrared AO facility with a single laser beacon. Description of these facilities and their implementation on the telescope are described. In addition, descriptions of the current and future suite of scientific instruments that would take advantage of adaptive optics are provided. Problems and concerns associated with implementing adaptive optics facilities at Keck (e.g., a segmented primary, a 10 meter baseline, rotation of a non-symmetric pupil, etc.) are discussed.