Atmospheric lines for wavelength calibration at longer wavelengths.

Graham Harper asked me about what depth atmospheric line we need for wavelength calibration.  His project at 26.00 microns will have a few very strong lines and a 4-5% line.

I looked at this by fitting Gaussian absorption lines using CLICKFIT.PRO to black-sky from the 17 micron H2 setting on Jupiter during flight 1.  I should probably do other wavelengths and actually use the pipeline, but this was how I started.

The black-sky looks like this:

I used CLICKFIT to test how well we can fit a Gaussian to various lines.  The lines that I used (and the derived centroids) can be seen in this version with crosses on the lines.

The model atmosphere for this region (not ATRAN, but my AT version) is below.  The white is for 10 microns PWV and the red is for 40 microns PWV.  The green line is at 95% transmission.  The CO2 band near the bottom of the images above is near the right edge of the atmo plot.  The two strong lines are near the middle order and in the second order.  In the images above, wavenumber increases to the right and down, like a book.  In the atmo plot, wavenumber increases to the right.

The upshot is that most of the lines I used are ~10% and one of them is around 5% (just to right of strong line at 585.7 cm-1 in the second order from top).  Since the pipeline will sum along the slit and can combine multiple black-sky images, I think we are probably safe with 5% features at wavelengths where the sky emits well.  This probably includes 13 microns, although should check to be sure.  At 7 microns and shorter, I'm pretty certain we need stronger features.  Have to see how bright they should be....