After many trials and tribulations, we are pleased to announce that a significant milestone in our project to upgrade the DIS detectors has been achieved. DIS is now ready for on-sky science observations with the new detectors, although there are still some problems. Although there is still work to be done to realize the full performance potential of the DIS detectors upgrade, the present performance of DIS now appears to be better than it was with the old chips. We intend to let scheduled science users try to use DIS in its current state on a shared-risk basis over the next few weeks. Also during this time, scheduled engineering and open time will be used to both finish fixing the remaining known problems, and systematically characterize the new performance parameters. A preliminary technical description of the new DIS detectors is given at http://galileo.apo.nmsu.edu/~hastings/Manual/instrumentinfo/dis/main.html. This page describes the basics, and will soon be linked to new data characterizing actual performance. The major changes in the detector upgrade are smaller pixels, lower read noise, and a larger detector format than we had with the old DIS CCDs. The new electronics also allow for simultaneous readout, which saves about 40 seconds of observing overhead per exposure. As we understand it, the current status is: o The DIS red camera is well-focused and aligned, has good throughput, and has low read noise when the camera is read serially (i.e., not in parallel with the blue camera). o The DIS blue camera is almost focused, but needs a dewar modification to get the last ~10% tweak in focus and focal plane tilt. Due to an inadvertent specification error, the AR coating on the new blue camera field flattener lens is defective, which reduces the throughput of the camera by about 30 to 40% below about 4600 Angstroms. This lens will be replaced in April to recover the throughput. The blue camera has low read noise when the camera is read serially (i.e., not in parallel with the red camera). o In parallel read mode, there is electronic noise in the data for both cameras of about 20 ADUs, similar to the read noise levels in the old DIS cameras. This seems to be largely eliminated when the cameras are read out serially. o The DIS controls in the Remark remote interface appear to work well. For tonight, the software cannot be changed to enable serial reads of the cameras, so the noise level in tonight's data will be similar to that of the old chips unless the users choose to just read one camera in an exposure. By tomorrow night, we hope to be able to implement the software changes to make serial reads of the camera the default. Over the next weeks, tests will be run to determine a way to read the two cameras simultaneously without the noise penalty. We are attempting to contact the PIs of the DIS programs for tonight and this weekend's observing, and more information will be posted as it develops. We encourage the PIs of the DIS programs over the next few weeks to use the instrument in its current and evolving condition; this will help us debug and characterize the new instrument, and hopefully obtain useful science data. If you feel that the current DIS performance limitations seriously impact your science programs, you should consider using an alternative instrument for a different approved science program, or contact me for other alternatives. You should also contact your Observing Specialist well in advance to determine which gratings are to be mounted for your observations. Due to the new chip format, the entire spectral range is available with the medium dispersion gratings and a much greater coverage is possible with high dispersion. On-chip rebinning makes it possible to reduce resolution in order to gain sensitivity without going to low resolution chips. Kudos to the DIS upgrade installation team, including Jeff Morgan, Peter Doherty, and Russ Owen (UWashington) plus Mark Klaene, Craig Loomis, Dave Woods, Russet McMillan, Camron Hastings, Jack Dembicky, Jon Davis and John Barentine at APO. APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 89 in the apo35-dis archive. You can find APO the archive on http://www.astro.princeton.edu/APO/apo35-dis/INDEX.html APO To join/leave the list, send mail to apo35-request@astro.princeton.edu APO To post a message, mail it to apo35-dis@astro.princeton.edu APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO