NICMOS Synthetic Dark Request Form

WARNING: This tool creates darks for data taken BEFORE January 4, 1999! These darks will not properly calibrate any data taken during Cycle 11 and beyond!

This page has been set up to facilitate the making of dark reference files corresponding to a specific temperature. The shading is a temperature dependent component of the detector bias. This means having a temperature sensitive dark reference file is critical to the calibration process.

Right now this form only accomodates multiaccum data. At some later time we hope to have the models for accum mode data as well. For now, you should choose the camera with which the observations were made, the multiaccum readout sequence which was used, and the temperature at which the observations were made.

(The keyword NDWTMP11 (for cameras 1 and 2) or NDWTMP13 (for camera 3), in the headers of the _spt file corresponding to the dataset should be a good first estimate of the effective temperature. There is a separate temperature reading in the _spt file for each non-destructive readout in a multiaccum sequence.)

You should first try temperatures precise to 0.05 degrees K, and only more precise than that if further examination of the data warrants it, as the temperature fluctuates on the order of a tenth of a degree during the timespan of any exposure. After you fill in the form and submit it, a page should appear with a direct link to your new reference file. Remember, this form actually creates a 7 megabyte file in real time. The process can take up to 5 minutes. Do NOT impatiently hit the 'stop' button on your browser!

Help

Q: I still don't know where to find my observed temperature.

A: When you received your data, it should have been accompanied by data files with the same rootname as your science data, but with a "_spt.fits" extension in the filename. These files contain engineering and support data for the observation, including the temperature. To access the temperature information, do the following from the iraf prompt:

cl> hedit n45z21ayq_spt.fits[1] ndwtmp11 .

The output should look something like this:

n45z21ayq_spt.fits[1],NDWTMP11 = 61.8732

If you try this on another extension, you will get a different temperature:

cl> hedit n45z21ayq_spt.fits[12] ndwtmp11 .
n45z21ayq_spt.fits[12],NDWTMP11 = 61.9024

The temperatures for any one dataset should be within approximately 0.1 degrees K from each other, and the absolute range should be somewhere between 60 and 63 K.

Q: My observations were taken before 22 August 1997. Can I use these new darks?

A: No. These models only apply to science data taken after the on-board software fix on this date.

Q: After using these new darks, my quadrants have still have a DC offset from one another, or have a 'pedestal' effect that wasn't present when they were calibrated using the old darks. What's going on?

A: You might be experiencing a limitation of the models, which is ultimately a result of the pedestal problem. However, you should be able to fix any problems you might see with the new pedsky IRAF task.