Instrumentation, Technical Services, and Meteorite Curation

CORBALLY continued to maintain the World Wide Web site of the Vatican Observatory (http://clavius.as.arizona.edu/vo/). For the first time, he posted the Annual Report (1998) on the site. He also changed the hit counter from a commercial one to a local SSI (server-side includes) counter, which shows that the average of 150 visits per day was sustained throughout the year as well as last year.

CROMWELL continued as project scientist for the Vatican Advanced Technology Telescope (VATT) and its instrumentation. In that capacity he provided scientific, technical, and managerial guidance in the activities reported below. NELSON, as on-site assistant staff scientist, and McKENNA, who was hired as senior engineer in December 1998, took the lead in many of the developments. The following personnel from the Steward Observatory Technical Division, directed by DERIGNE, made considerable contributions: WILSON, SCHALLER, BRAR, CORDOVA, DAVISON, LANUM, and HARVEY. The collaboration of Vatican Observatory scientists BOYLE and CORBALLY and of SWIFT and others of the Mt. Graham International Observatory staff, directed by RATJE, was indispensable. In December 1998 the Vatican Observatory Foundation was awarded a Science Initiative Grant by The Kresge Foundation (described in "From the Director") to improve the performance of the VATT. This award contributed significantly to the ongoing technical improvements being made to the telescope.

The VATT was regularly scheduled during the past year for astronomical observations. Long-exposure direct imaging was considerably improved as a result of the advances described below. Image quality was typically better than 1.5 arcsec fwhm, and under the best conditions it was on average 0.7 arcsec. Better performance and efficiency is expected when the following tasks are completed: dome thermal environment control, rebuilding the secondary mirror mechanical support hub, and refinement of auto focus and auto collimation systems.

Telescope positioning and setup at the beginning of the night have been simplified by the repair of an absolute encoder for the elevation axis and by the addition of calibration indexes to the azimuth and derotator axes. Guiding during long exposures was greatly improved with the addition of guide-star catalogs and auto guide-star finding software. New interface software has improved secondary mirror control: tip, tilt, and decenter and focus, which are all referenced to optical center zeros. Auto focus and auto collimation as a function of temperature and elevation have been implemented through empirical auto secondary-control algorithms. The secondary mirror control electronics were completely rebuilt; they now provide good stability, good noise immunity, electronic fail-safe limit checking, and the elimination of earlier heat sources from motors in the secondary mirror volume. The offset guider positioning and mirror drives were sped up by a critical factor of 5-10 to increase the efficiency in moving from one guide star to another. WEST, using his wave front sensor, determined that the previous alignment of the optics had been set up on a local null, giving the wrong impression from earlier optical tests that the alignment was correct. When the optics were correctly aligned, the unsymmetrical off-axis astigmatism, previously experienced, vanished. Evidence now exists that a faulty mechanical secondary-mirror support is giving rise to some residual field-independent astigmatism. This will be eliminated with a new mechanical support hub.