Third Quarter 1999

During this quarter the detailed drafting of the grating and prism mounts was completed and the mounts fabricated in the IfA machine shop. By the end of the quarter all prisms and gratings had been mounted and optically aligned relative to their mounts. All the drafting of the instrument telescope mount and calibration box had been completed by the end of the quarter and fabrication of the components was underway in the IfA machine.

In July all the cryogenic mechanisms (dichroic turret, order sorter wheel, rotator, slit wheel, guider filter wheel, grating turret and focus stage) and hall effect sensors were installed into the cryostat. The spectrograph and guider/slit-viewer detector assemblies were also installed. Following warm tests, the cryostat was cooled down for the third time for a series of cold mechanism tests and detector temperature control tests. All mechanisms and sensors worked well with the exception of the rotator. A loose coupling on its vacuum feedthrough prevented the rotator from being turned. The detector assemblies cooled down as predicted, reaching a nominal operating temperature of 30K in about 10 hrs, and the temperature successfully controlled to 30.00 +/- 0.01K.

After the cryostat was warmed up the cold structure was removed and the vacuum jacket modified to allow for better access to the grating turret. Once the cold structure and mechanisms were re-installed work started on installing and aligning all the optics. Laser alignment of the mirrors and lenses was successfully completed by mid-September. Small shims were required at the fore-optics collimator and spectrograph off-axis parabola.

After installation and alignment of the optics tests of the fully assembled cold structure were conducted to search for light leaks. This was done by placing small xenon flashlights at key locations inside the (nominally) sealed light-path and inspecting the cold structure inside a darkroom using image-intensified goggles. Light leaks were spotted at several locations and fixed.

Evaluation of the four Raytheon 512x512 Aladdin 2 InSb arrays for NASA and the PAIDAI project was completed. Two of the arrays are infested with dead pixel features known as 'snail trails' and are of engineering grade. The other two arrays are suitable for use as good imaging arrays. SCA49825 has a 3Hz readnoise of 56e RMS and a dark current of 0.4e/sec (measured over 120 sec). SCA46509 has a 3Hz readnoise of 58e RMS and a dark current of 1.5e/sec. Both arrays are cosmetically good with few defects (SCA 49825 is best), but with strong odd/even row effects (SCA46509 is best). These measurements were made at 30.0K. (At 35K readnoise is typically about 20% lower but dark current is an order of magnitude higher.) We will chose between SCA49825 and SCA46509 for the SpeX guider/slit-viewer.

As of August 1999 PAIDAI had hybridised and tested 12 1024x1024 InSb arrays, the initial 8 on Aladdin 2 (152) multiplexers and the last 4 on improved Aladdin 3 (206) multiplexers. The final two Aladdin 3 hybridisations are in question due to budget problems at Raytheon/SBRC. The best of the Aladdin 2 arrays is SCA47672: 44e RMS readnoise, 0.24e/sec median dark current, full well 145k electrons at 0.4V bias and very good cosmetics. The best of the Aladdin 3 arrays is SCA411779: 35e readnoise, 1.65e/sec median dark current, full well 168k electrons at 0.4V bias and very good cosmetics. With these performance numbers SCA47672 is clearly the better device and is 0.5 magnitudes more sensitive than SCA411779 in the 0.8-2.5 micron wavelength region at SpeX resolving powers. The reason we are considering SCA411779 is because of the reduced (but not eliminated) odd/even row effect in Aladdin 3 devices.

In software developments this quarter all the motif code was ported to GTK++. The move to GTK++ allowed for improvements in the SpeX instrument control graphical user interface. The SpeX guider slow-guide mode was implemented and tested on a simple 'moving star' simulator. Much progress was also made on the IDL-based quick-look spectral extraction software package. The software can now robustly fit and extract spectra from cross-dispersed formats. An online SpeX signal-to-noise calculator was made available to IRTF observers in time for the October 1 observing deadline for the six-month observing semester beginning February 1 2000. SpeX was offered in shared-risk mode from June 1 2000.