4/21/99-Dirt on 1.5-pixel Slit

After the surgery to fix the NIRC slit mechanisms it was noticed that the narrowest slit (slt1; the 1.5-pixel slit) has some dirt on it below center of the image. This should be taken into account when selecting a slit or setting up dither patterns with that particular slit.

9/25/98-NIRC Performance, Post-Surgery

Tests done after NIRC was fixed, reassembled, and cooled down again indicate that the slit mechanism is working fine now. Repeatability (without going to the home position) was better than 1/10 pixel.

The detector appears to have an elevated dark current; 200-300 DN/minute rather than 50. The sensitivity is the same as measured in June in JHK (and presumably all other) filters.

9/14/98-NIRC Open-Dewar Surgery

NIRC has been opened up in order to fix the broken slit mechanism (see next entry). We found that four teeth on a gear in the mechanism were broken; this is likely the cause of the failure we saw in late August. Other parts in the same gear train may have sustained damage as a result, so we will be replacing much of that mechanism.

We also found a bad bearing in the other mechanism, the one that runs the mask. A great deal of play in the shaft led us to suspect a bad bearing, and indeed one of the bearings fell part when it was removed. It was only a matter of time before the mask would have started failing. We will replace that part of the mechanism as well.

We may also take this opportunity to clean off the NIRC collimator, which was probably contaminated by the same (unknown) source as the dewar window. The window was replaced a year ago, and was more critical in that it was producing flat field artifacts, most noticeable in the high f/ratio speckle data. The collimator was not cleaned at that time because of the much greater complication of doing so.

9/3/98-Broken Slit Mechanism

In late August the NIRC slit slide stopped working properly. To fix it will require close to two weeks or more, hence to prevent it from becoming stuck partway in the beam, making NIRC useless for not just spectroscopy but imaging as well, it has been disabled. All facility NIRC commands that move the slit have been disabled or removed. The homemot script only turns on the power to that motor (in order to provide a holding torque).

Repairs will be undertaken as soon as the current science run ends.