C. F. Claver, WTTM Project Scientist, for the entire WTTM Team
The 3.5-m WIYN telescope is the facility of choice on Kitt Peak for high-resolution imaging. In an effort to further enhance this capability over a moderate field, a tip/tilt imager is being constructed for WIYN. The WIYN Tip/Tilt Module (WTTM) is an all-reflecting, visible near-IR re-imaging system that implements fast tip/tilt compensation and includes real-time focus sensing. The project has moved into the fabrication phase, with shared-risk observing projected for 2001B.
The field of view for the WTTM is 4' x 4' arcminutes with a plate scale of 0.12" per 15 Ám pixel. The WTTM will become an integral part of the WIYN Instrument Adapter System and provide a "second" imaging port, in addition to the 10 x 10 arcminute FOV MiniMosaic 4K x 4K imager. Fast change (e.g., less than 5 minutes) between these two imagers to accommodate changing atmospheric conditions is facilitated by moving a single pick-off mirror.
To date, the bulk of the fabrication progress has been made in the WTTM's optics. In early July 1999 the WTTM project let a contract with Contour Metrological Manufacturing (CMM) of Troy, MI, for the diamond- turned off-axis mirrors. The WTTM project worked with CMM to refine the fabrication process of these optics. In the end, each mirror was made in axially symmetric pairs with a "dummy" surface of the on-axis parent surrounding them. This allows these optics to be treated as normal on-axis while being post-polished and tested. During January 2000, D. Vaughnn (WTTM Project Engineer) visited CMM for two days and conducted final acceptance testing of the three mirrors. All three diamond-turned assemblies have been delivered to NOAO. The off-axis spheres, the pupil re-imaging mirror, and the second camera mirror are ready for post-polishing in the NOAO optics shop. The first mirror in the camera, an off-axis asphere, was post-polished by CMM and awaits final inspection and testing at NOAO. The NOAO optics shop has been busy fabricating some of the optics for the WTTM error sensor.
At the heart of the WTTM is a fast tip/tilt stage manufactured by Physik Instrumente. This stage, its interface, and servo amplifiers were delivered to the project in mid-January. Initial testing is underway in the NOAO Electronics Lab.
The WTTM CCD imager uses the central 2K x 2K portion of a SITe 2K x 4K CCD. This device was originally designated engineering grade. It does have a cosmetically very good central region. Initial lab tests of this CCD have been completed successfully in the NOAO Detector Lab. Further tests await integration with the WTTM module later this year.
After careful evaluation, the WTTM software system is being implemented under real-time LINUX with LabVIEW acting as a supervisory GUI and post-detection analysis suite. So that neither side is affected adversely by the other, a dual Pentium architecture is being deployed. The purchase of a 2 x 500MHz Pentium III machine with 256 Mb RAM to provide a large, shared-memory buffer was made in November 1999; and the system has been delivered, installed, and used in active development of the software simulation system. The detection of counts from the avalanche-photodiodes is being handled by two DUAL16CT counter/timer cards (two channels per card), and the transmission of values and receipt of status signals from the mirror electronics is carried out by a DIO316I digital i/o card. All three cards are actually `Industry Pack' modules that attach to a single PCI-slot motherboard. The drivers for the PCI devices will likely be written in-house, and the high-level library software delivered with the modules has already been ported to LINUX.
With this activity, the WTTM is presently on schedule to begin commissioning during second quarter 2001 and is expected to have shared-risk observing in 2000B. To meet this schedule we will have the WIYN IAS in the Tucson Instrument Shop beginning 8 January 2001. During the eight weeks the IAS is "downtown," the WTTM project will make the necessary modifications and upgrades to the IAS for integration with the WTTM. During this time, the WIYN facility will be without wide-field imaging from the MiniMosaic. The January date is being driven by the Project's goal of not impacting prime North Galactic Pole time beginning with March dark-time through May, yet getting the WTTM on the telescope as soon as possible. The IAS will return to WIYN during March bright-time and undergo a brief recommissioning to ready it for the beginning of dark-time in March 2001.