Caveats of using STIPS for Roman
This page contains a description of known limitations and issues when using the Space Telescope Imaging Product Simulator (STIPS) software for the Nancy Grace Roman Space Telescope with relevant advice for users.
This documentation is written for STIPS version 2.2.2 (released on December 16, 2024).
Limitations
The limitations of STIPS are given below. These are fundamental to the scope of the software design and are not expected to change with future development.
Instrumental Effects and Output Images
STIPS directly creates the equivalent of Roman Level 2 (L2) data products in order to allow for fast simulations of the Roman Wide Field Instrument (WFI) outputs. Generating Level 1 (L1) data products, as required for a full forward-modeled simulation, would slow down the computation significantly. This capability is out of scope for STIPS , but the user is referred to Roman I-Sim for such simulations (including Level 1 (L1) data products).
Bright Sources
The point spread function (PSF) model radius in STIPS is forced to be 22 WFI pixels, meaning that the PSF is not modeled beyond this radius limit (note that the PSF is sampled at four times the resolution of the detector). Brighter sources may have long diffraction spikes that place significant signal beyond the default radius. Users requiring simulations beyond the default limit may use two keywords: psf_bright_limit or psf_xbright_limit (i.e., extra-bright limit) to indicate magnitude thresholds for simulating the PSF to larger PSF radii (44 WFI pixels and 88 WFI pixels, respectively). A summary of the PSF radius specifications is given in Table of STIPS PSF Radius. An image cut out from the M13 star cluster simulation shown in the STIPS landing page article is displayed in Figure of M13 Cut Out Example; this simulation required use of the three PSF radii available in STIPS .
The computation for bright targets will take about four times as long as standard sources because the point source flux is computed for every pixel, and the extra-bright sources will take about 16 times as long. Given the long computation times, users are cautioned to only use these options if a high level of detail is required.
Table of STIPS PSF Radius
| PSF Keyword | Description | Simulated PSF Radius | |
|---|---|---|---|
WFI Pixels | Arcsec | ||
default | default PSF radius applied to all sources in the input catalog regardless of their magnitude | 22 | 2.42 |
psf_bright_limit | stars brighter than the magnitude limit specified by this keyword will be computed to a large radius | 44 | 4.84 |
psf_xbright_limit | stars brighter than the magnitude limit specified by this keyword will be computed to an extra-large radius | 88 | 9.68 |
PSF Radius used in STIPS settings. The Radius is given in both pixels on the WFI detector and converted to arcsec assuming a pixel scale of 0.11 arcsec per pixel.
Figure of M13 Cut Out Example
Issues
A list of STIPS known development issues is maintained on the readthedocs documentation. These are items that may be resolved in future releases.
For additional questions not answered in this article, please contact the Roman Help Desk at STScI.
References
In addition to this documentation, STIPS is described in the following references. Users are encouraged to cite this publication:
- STIPS Development Team et al 2024, "STIPS: The Nancy Grace Roman Space Telescope Imaging Product Simulator", PASP 136 124502