In March of this year we took the best of the first batch of ALADDIN arrays to the 2.1-m telescope to evaluate its astronomical performance. Our USNO colleagues have particular interest in astrometry, and were simultaneously observing many of the same fields from their Flagstaff observatory. The observing team consisted of Fred Vrba and Arne Henden (USNO), and Al Fowler and Ian Gatley (NOAO). The IR camera was a modification of the retired CTIO IR Imager, which was originally designed for the 58 x 62 InSb array. This dewar looks a lot like IRIM, and is very small compared to more modern instruments. Because of these space limitations in the dewar we were obliged to use 1:1 reimaging optics, giving 0.2"/pixel, thus oversampling the seeing, and restricting the field of view. However, the much larger array format still gave a field of view similar to that of SQIID. The resultant improvement in spatial resolution is dramatically obvious in Figure 1, which compares SQIID and ALADDIN images of the interacting galaxy pair NGC 4038/9.
Even though the weather was mediocre we were able to image several fields at three wavelengths (JHK), and so make color images demonstrating the power of this new generation of infrared detectors. As is always the case when making the initial tests of a system with radically improved capabilities, the excitement level in the dome was very high both for the observing team and for the many and frequent visitors who dropped in to join the fun.
Figures 2 and 3 show two of the more striking new images of well-known infrared targets, Mon R2 and GGD27, which serve to illustrate the kind of detail that future users can anticipate. Both Mon R2 and GGD27 are young and dusty, and so are invisible at optical wavelengths because of extinction. The color versions of these images are available on the NOAO homepage; they are far more impressive than these black and white versions, and we encourage you to browse them.
NOAO has already installed an ALADDIN array in the Phoenix high
resolution spectrometer, greatly extending its capability beyond the
256 x 256 InSb array for which it was originally designed. The ALADDIN
pixels are 27 
m, only slightly smaller than the 30 
m of the older
array, which translates into almost a factor of four increase in
spectral coverage over the original design. The next use of an ALADDIN
array at KPNO will be in an Ohio State imager, expected to be available
to users in the spring of 1997, as described elsewhere in this Newsletter.
Al Fowler