Tom Barnes, University of Texas and McDonald Observatory
The Hobby-Eberly Telescope has reached the end of its Commissioning phase and has entered `Early Operations'. The Early Operations phase emphasizes research operation of the HET 50% of each lunation, with instrument commissioning and facility improvements occupying the remainder of the time. Observing time is approximately centered on the date of the new moon. Early Operations will continue at least until June 2000 and may continue into the period of first public access.
In October 1999 the HET is operating at or near specification in pointing, sidereal tracking, autoguiding, and all other essential electromechanical functions. The primary mirror is in operation with a full array of 91 segments (9.2-m aperture on axis). The array is aligned using the Center of Curvature Alignment System (CCAS, a shearing interferometer) in about 15 minutes to a median-delivered primary mirror quality better than 1.1" (50% encircled energy, EE50). An intensive program to improve primary mirror quality to specification, EE(50) = 0.6", is continuing.
In the presence of typical seeing and immediately after a mirror alignment, the image quality is currently about EE50 = 1.8". During the course of typical on-object tracks, the primary mirror stack degrades as a function of the ambient thermal gradient. The typical degradation in image quality leads to a delivered image quality for 30 minute tracks between 2.0" and 2.5". Imaging performance is expected to improve modestly before June 2000, but major improvement is not expected until installation of the Segment Alignment and Maintenance System (SAMS) on the primary mirror array (an edge-sensor system). The SAMS will provide closed-loop control of the 91 segments and their global radius of curvature. We expect SAMS to reduce the need to align the segments using the CCAS from hourly to twice monthly. With SAMS, we expect the HET to be seeing-limited most of the time. The nominal schedule for SAMS calls for completion in January 2001 and for minimal impact upon research operation during installation.
The community will be kept informed of the status of the HET through frequent updates of the NOAO web site: http://www.noao.edu/gateway/het/.