Stephen Shectman

During the past year, Stephen Shectman spent five months in residence at the Las Campanas Observatory working on the control system for the Magellan I telescope. This work was conducted in collaboration with many members of the Magellan Project staff, particularly Joe Asa, Greg Bredthauer, Dave Carr, Emilio Cerda, Charlie Hull, Matt Johns, and Frank Perez.

There are several highlights from the control system work. For instance, the precision optical tape encoders were installed; they provide accurate information about the position of the telescope axes. The servomotor drives and amplifiers were brought into reliable operation, and accurate servo control of the telescope mount was implemented. When the telescope is tracking the position of a star, the telescope's motion is controlled to an accuracy of a few hundredths of an arcsecond. In order to achieve this precision, the positions of the large structural components of the telescope mount must be maintained to within about 1 micron.

An accurate time-base, using signals from the Global Positioning System, was also installed in the system. A small telescope and TV camera were attached to the side of the mount, and a map of pointing corrections was derived by measuring more than 100 star positions around the sky. These corrections were needed for the manufacturing tolerances and mechanical flexure of the telescope structure, which are many times greater than the allowable uncertainties in the telescope's positioning. The computer control system uses the pointing corrections to set the telescope to within a few arcseconds of any position on the sky. The telescope mount and its control system are now reliable enough and safe enough to allow the primary mirror and cell to be installed.

Shectman has also been working with Hubble Fellow Rebecca Bernstein on the construction of MIKE, the high-resolution optical spectrograph for Magellan. This spectrograph features separate optical paths for the red and blue parts of the spectrum. These permit the optical design, dispersing elements, antireflection coatings, and detectors to be optimized separately for the red and the blue. The spectrograph will be able to measure the entire optical spectrum of an object between 3,300 and 10,000 angstroms in a single observation, with a resolution of a few tenths of an angstrom.

During the past year, Shectman and Bernstein finalized the optical design of the spectrograph, ordered and received all of the optical glass, and sent the first components to the optical contractor for polishing. They also worked with consulting engineer Steve Gunnels to define the mechanical structure of the device.

Working with engineers from L&F Industries, Shectman also conducted a design study for a major modification of the 2.5-m du Pont telescope at Las Campanas. This modification would add a Newtonian focus and corrector to the top end of the telescope, where a mosaic CCD camera could be used to image a one-square-degree-area of the sky. This area is more than six times larger than can be observed with a comparable mosaic camera at the present Cassegrain focus. Such a wide-field camera would be particularly interesting for conducting wide-area photometric surveys as well as real-time searches for distant supernovae, gravitational lens events, and variable stars. These examples require massive computational power, which has only recently become available and affordable.