The setting is requested again for Cycle 4 by N.Indriolo, so I looked at 1485cm-1 at 6th and 8th order to check for any issues. We already used N07053 on sky to get ~1490cm-1 at order 3 for the IRC +10216 / VY CMa spectral maps, so that it works is no surprise.
Here's the side-by-side comparison of ~1485cm-1 in 6th order, Left: BP6600+MgF2. Result: 1500 counts in 136 sec. Right: N07053+CaF2. Result: 1500 in 30s.
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| Left: Apr 10 commissioning flight. 1500 counts in 136 seconds. Right: 1500 cts in 30 sec. |
Using the grating at intermediate angles (36 deg for 1485cm-1 in 6th order) incurs a penalty in thoughput due to groove shadowing. If we take 1485cm-1 in 8th order, the highest available, we get the same flux in about 15 seconds. Pictured below. Unfortunately, the slit is about 10.5" and maybe not suited for on-source nodding. So we may opt to go for coverage and a lower order. We were able to get 2500+ counts from the blackbody in 14 sec at 3rd order. However, the decker was only 7-pix.
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| N07053, 1485cm-1 at 8th order. ~1500 counts in 15 seconds on blackbody |
1 comment:
I think we'll go with N07053 in 8th order. There will be enough lines in the multiple settings, so S/N is probably more important than coverage.
The fringing pattern interests me. In the side-by-side in 6th order, we have 2 different filters and very similar fringing pattern. That seems a little surprising. For the next cooldown, can we try doing a series of room spectra with the filter moved a bit between each one? A filter isn't 100% uniform, I would suspect, so maybe we'd see differences at different locations. The detector, however, is always in the same place.
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