LhiresIII Image Response Curves

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LhiresIII Image Response Curves

Postby James Foster » Fri Sep 28, 2018 9:21 pm

Here is a graph showing the IR curves I got on Vega over a span of about a month at various elevations with my LhiresIII with a 1800 l/mm grating and
35 micron slit using the CDK17 inch scope at F/10.5 around the H-Alpha line. I was wondering if they seem fairly typical to what other folks here get.
The elevations (from the MaximDL fits header) are shown in the box on the right. My effective altitude above sea level is 148 meters.

The curves were made from the A0V spectra in the Elodie database, cropped and normalized in Bassproject V1.98, and processed with Isis V5.1.92 on the calibrated Vega spectra using the four (4) neon emission lines shown in the graph. Let me know if you need any other processing details.

James Foster
Lhires III (2400/1800/600 ln/mm Grat) Spectroscope,
LISA IR/Visual Spectroscope (IR Configured Presently)
Alpy 600 with Guide/Calibration modules and Photometric slit
Star Analyzer 200
James Foster
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Joined: Sun Jan 24, 2016 7:14 am

Re: LhiresIII Image Response Curves

Postby Robin Leadbeater » Sat Sep 29, 2018 3:01 pm

Hi James,

Interesting that you should be looking at this. I have just returned to high resolution with my LHIRES after tuning up the spectrograph on the bench over the summer. Here are some recent instrument responses at Halpha with the 2400 grating. To be honest, looking at the low levels of variability in these I am wondering if it is actually useful to use a new instrument response every time when working at H alpha over such a narrow wavelength range unless the air mass is very high. I am not convinced the differences are real at this level and I may actually be introducing variability.

I would even go further and argue that, although it is not the BeSS standard, rectified spectra would be just as useful and we could forget about instrument response and continuum shape all together ! (In any case, I suspect that the first thing professionals do when using our high resolution H alpha spectra is rectify them to get rid of continuum differences between different observers)

LHIRES_2400_instresp.png (7.42 KiB) Viewed 1101 times
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
Robin Leadbeater
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Re: LhiresIII Image Response Curves

Postby Peter Somogyi » Sat Sep 29, 2018 4:04 pm

Note sure if you have the same problem, but in ISIS I ofter have to correct he last few pixels in ISIS -> 5. Profile -> Edit tab (of course, just for response - for real spectra, I'm cut them).
The last 1-2 pixels always very bad, exactly causing to drive away the curvature at the right edge (very rarely seeing on the other side, too - e.g. when summing spectra with tiny shift).
But in general, seeing this also for 1 single exposure, possibly a rotation / deskew in 2D -> 1D might be introducing this artifact.

Examining the first and last pixels in ISIS -> Edit tab has became a standard procedure for me (up to ISIS - v5.7.0 - newer versions don't bring any advantage for me by release note, so not upgrading to avoid surprises).

- Peter
Peter Somogyi
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