Known Issues (Pending Validation)

Below is a list of known issues with STIPS that are pending validation. Items will be removed from this list as they are addressed in future STIPS updates.

  • The orientation of the image is non-standard, with east pointing to the right of the image. The relative position of sources is not affected.

  • There exists a function to place extended sources given a set of Sersic parameters, but its validity and functionality have not been tested.

  • The flux measurements of sources are only validated in the absence of noise/background. As such, the net flux of the image may be inaccurate.

  • STIPS interpolates nine PSFs generated by WebbPSF across the detector to the location of the source being placed. However, there is currently a known offset of 20 pixels (in both the X and Y directions) between the location at which the PSF is interpolated, and the location at which the target is displayed.

    Note

    This does not affect the target position or center on the detector. It only means that, if a point source is created with a position of (x, y), it will be placed at location (x, y) but the interpolated PSF shape will be the shape of the PSF at location (x+20, y+20). Because the WFI PSF shape does not vary strongly over this distance, the effect is minimal and should not be a concern for most science cases. If ultra-precise PSF models are required, the user should generate them directly with WebbPSF at the desired pixel location.

  • Bright sources will have large diffraction spikes that are visible beyond 22 pixels away from the center of the source. A psf_bright_limit and psf_xbright_limit (extra-bright limit) magnitude can be specified –– objects brighter than this threshold will be computed out to a radius of 44 (bright) and 88 (extra-bright) pixels, respectively. Note that, because point source flux is computed for every pixel, bright targets will take roughly four times as long (and extra-bright sources 16 times as long) to compute as standard sources, so these limits should only be set when it matters.

  • The STIPS star generation sub-module (stips.star_generator) depends on the esutil Python module. This module can currently be installed as part of a Conda environment, but can’t be installed in a working state from a pip/setup environment. As such, if you are installing STIPS without using Conda, and you need to use the star generation sub-module, you will have to make an additional step. After installing STIPS, but before using it, install esutil using pip without using a local cache (i.e. run pip install esutil --no-cache-dir).

If you encounter any issues not listed here, please see the help page.