Update various NIRCam coronagraph reference data

spacetelescope / webbpsf

James Webb Space Telescope PSF simulation tool

https://webbpsf.readthedocs.io

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Update various NIRCam coronagraph reference data #115

Open mperrin opened 6 years ago

mperrin commented 6 years ago

Issue by mperrin Thursday Apr 28, 2016 at 05:04 GMT Originally opened as https://github.com/mperrin/webbpsf/issues/115

Per various emails from Stansberry:

The ND squares are not actually truly neutral, they definitely have some color to them. We could add the appropriate relative spectral response.
From https://confluence.stsci.edu/pages/viewpage.action?pageId=52920601: "The wedge element in the SW pupil wheel has chromatic effects which impact PSF shape for wide-bandpass filters, so PSF subtraction will be particularly tricky unless target and PSF reference star are very similar in color.” That’s an effect that is totally neglected in WebbPSF right now.

mperrin commented 6 years ago

Comment by mperrin Friday Apr 29, 2016 at 18:13 GMT

Coronagraph wedges info.

From NIRCam Engineering Memorandum NIR-EM_0424 "Coronagraph Wedge Angle Tolerance Effect on Focal Plane Image Position" (provided by Stansberry):

SW wedge is BaF_2, angle is 5 degrees
LW wedge is fused silicon, angle is 0.5 degrees.
- pupil stop diameter is 42 mm
- note also the pupil wheel mechanical repeatability was estimated to result in up to 2 pixels of PSF shifts in the direction parallel to the axis of the bar occulter. But that was a circa-2007 estimate and is thus not the most up to date numbers.

From "NIRCam wedge dispersion trade_Si-BaF2-CaF2-Fused Silica.ppt" for the BaF2 prism

JarronL commented 5 years ago

With respect to the wavelength dependence brought on by the Lyot wedges, would it be a process similar to the one we performed for the defocus Zernike component? That is, we would calculate how tip/tilt changes with wavelength using the Zemax data, then modify the OPD map for a given wavelength using the tip/tilt offset values?

mperrin commented 5 years ago

Yes, that would be the way to do it. Conceptually identical, except for modifying a different coefficient.

mperrin commented 3 months ago

@JarronL here is a very old webbpsf issue about improving some reference data, in particular adding the wavelength dependence of the Zernike wedges. I think there is no longer any benefit to keeping this issue open; do you agree? The wavelength dependence of the wedge you implemented a while ago. And the wavelength dependence of the ND filters I don't think we care about enough to add to webbpsf, do we?

JarronL commented 3 months ago

This all sounds fine. As long as a Lyot wedge is in place in the pupil_mask, then webbpsf should perform the dispersion. So, this should also occur automatically for the ND square observations.