First light with SpeX was successfully accomplished on the first night of the May 16-18 engineering run. During this and the May 24-26 engineering SpeX was tested in most of its observing modes and performed extremely well. The average throughput (removing slit losses) of the spectrograph in cross-dispersed mode was about 15%, with a peak throughput at the grating blaze angle of about 25%. Throughput was even higher in the prism and single order modes. The throughput of the infrared guider/imager was about 25%. With multiple reads the spectrograph array readnoise was 15 electrons RMS and the dark current less than 0.3 electrons per sec. The only significant performance issue was a significant fall in throughput below 0.9 microns. This was traced to a problem with the anti-reflection coatings on the ZnS lenses and ZnSe prism. (These components were repolished and recoated during scheduled downtime in August.) Following the two engineering runs, SpeX was used for shared-risk science runs by Hammel, Bendo, Rayner, Gaffey, Vacca, Spencer and Brooke during June and July. The functional performace was virtually flawless during these runs (mechanisms, electronics etc.), with only four hours lost to a disk crash in the motor-controller pc. The Graphical User Interface worked well from the start.
The only software which required sinificant development during commissioning was control for the infrared guider. This was to be expected since IR guiding is new to IRTF. The basic guider algorithm worked well but the user control of the guider was updated as we learnt how best to use it. By the end of July the guider was working well in all its modes. The magnitude limit for guiding on spill-over from the slit is about J=15 for auto-guiding and about J=18 for manual guiding.
This quarter's photo directories:
2000-05-09-preprm-to-cass - Spex in the summit prep room and being mounted on the telescope.
2000-05-16.1st-engineering - Spex 1st Light on the IRTF.