search

Keck-DataReductionPipelines / KCWI_DRP

KCWI python DRP
BSD 3-Clause "New" or "Revised" License
8 stars 12 forks source link

Datacubes taken on different dates have different Wavelength zero point. Is it normal? #112

Open geoffcfchen opened 2 years ago

geoffcfchen commented 2 years ago

Hi, I found that the datacubes taken on different dates with the same observational setup have different Wavelength zero point even when I use the same data reduction procedure. For example, one datacube that I took in August has Wavelength zero point=3328.5A, while another datacube that I took in Nov has Wavelength zero point=3329.5A. Is this normal? I just feel that it is a bit weird given the same observation setup and same data reduction procedure, so I would like to check it with you. Thanks!

MNBrod commented 2 years ago

I will double check with the rest of the team, but so long as the overall wavelength solution is still correct (e.g. Hα is correctly identified as 656 nm in both observing runs), this might just be the instrument imperfectly recreating a setup (especially with a discrepancy as small as the one above). If the spectral lines are all offset by ~1Å, then it's a DRP problem. Can you check that for me?

Another thing to look for is if the arcs themselves are offset from each other. Again, if the arcs aren't perfectly overlapping each other, then the wavelength zero point should be different.