I looked at a series of sky frames with different slits from the last flight. The central wavenumber is around 746 cm-1. The pair I eventually chose are at 749.4 cm-1 and separated by 5.4 km/s. The weaker line is actually a double (strength 2.5:1, separation 1 km/s), but I chose to ignore that.
If perfect on an unresolved line, our resolving power should be 1.5, 2, 2.67, 3.5, 4.5, and 6 km/s. Measuring the FWHM of Gaussian fits to the lines and trying to correct for the slit angle relative to rows/columns, I found values of 3.1, 3.1, 3.6, 4.0, 4.3, and 5.4 km/s. Not certain if diffraction, or intrinsic line width, or errors in our optics are the cause for not reaching slit limits. Note that we repeated the first setting, Slit 4, at the end of the series as we were climbing. It was slightly narrower at higher altitude, suggesting there could be some altitude effect.
Will add something on the gas cells later. They should be definitely unresolved. Titan may be able to help, too.
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| Sky frame with slit 4. Pair of ozone lines used for further analysis in box. Line cut for fits at row 150. |
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| zoom on the two 03 lines used for fits. Lines are 5.4 km/s apart. Right hand line is actually a pair with strength ratio of 2.5:1 and 1 km/s separation. |
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| 2 Gaussian fits to the cross cuts of each slit width. Note that we repeated the first setting (slit 4 - not shown) twice and I found that the second time (lower left) narrower. Looking at lower right, where the Gaussian FWHM equals the line separation, I'd say the FWHM does pretty well - the lines are just barely resolved at that point. |
