JWST NIRCam ETC and Simulator
Project description
A JWST NIRCam ETC and Simulator
Authors: Jarron Leisenring (U. of Arizona, Steward Observatory)
Contributors: Everett Schlawin, Jonathan Fraine, Jonathan Aguilar
pyNRC is a set of Python-based tools for planning observations with JWST NIRCam, such as an ETC, a simple slope image simulator, and an enhanced data simulator compatible with the JWST pipeline.
While special attention has been placed on NIRCam coronagraphic modes, this package also works for a variety of NIRCam observing modes including:
direct imaging
coronagraphic imaging
weak lens imaging
slitless grism spectroscopy
DHS observations (TBI)
All PSFs are generated by WebbPSF as implemented by the WebbPSF Extensions package to reproduce realistic JWST images and spectra.
Documentation can be found at https://pynrc.readthedocs.io.
Similar to some of its dependencies, pyNRC requires input data files in order to generate simulations. Due to the size of these files, they are not included with this source distribution. Please see the documentation for instructions on how to to download the required data files.
Simulating PSFs
Simulating PSFs with WebbPSF can become computationally expensive if generating new ones on the fly, especially considering JWST PSFs vary with respect to wavelength, field position, and time-dependent wavefront error drift. In an effort to speed up this process, pyNRC uses WebbPSF to generate a series of monochromatic PSF simulations, then produces polynomial fits to each oversampled pixel. Storing the coefficients rather than a library of PSFS allows for quick creation (via matrix multiplication) of PSF images for an arbitrary number of wavelengths (subject to hardware memory limitations, of course). The applications range from quickly creating PSFs for many different stellar types over wide bandpasses to generating a large number of monochromatic PSFs for spectral dispersion.
In addition, each science instrument PSF is dependent on the detector position due to field-dependent wavefront errors. Such changes are tracked in WebbPSF, but it becomes burdensome to generate new PSFs from scratch at each location, especially for large starfields. Instead, these changes can be stored by the fitting the residuals of the PSF coefficients across an instrument’s field of view, then interpolating for an arbitrary location. A similar scheme can be achieved for coronagraphic occulters, where the PSF changes as the source position moves with respect to the mask.
JWST’s thermal evolution (e.g., changing the angle of the sunshield after slewing to a new target) causes small but significant distortions to the telescope backplane. WebbPSF has tools to modify OPDs, but high-fidelity simulations take time to calculate. Since the change to the PSF coefficients varies smoothly with respect to WFE drift components, it’s simple to parameterize the coefficient residuals in a fashion similar to the field-dependence.
Revision History
v1.0.1 (Dec 14, 2021)
Default OPD JWST_OTE_OPD_RevAA_prelaunch_predicted.fits
v1.0.0 (Nov 22, 2021)
Updates to work with WebbPSF v1 release candidate
Move PSF generation to new webbpsf_ext package (https://github.com/JarronL/webbpsf_ext)
Create DMS-like level1b FITS files using pipeline data models for imaging and coronagraphy
PSF coefficients now use Legendre polynomials by default
Create calibration files for each SCA (darks, IPC, noise, flats, linearity, etc)
Background roll-off at grism edges
SIAF-aware locations
v0.9.0beta (no release)
Updates to work with WebbPSF 0.9.0.
Start working on commissioning and DMS-like data
Add more advanced time-dependent detector effects
BEX model isochrones for low-mass companions from Linder et al (2019)
There was a pandemic…
v0.8.0beta (no release)
Updates to work with WebbPSF 0.8.0.
Phasing out support for Python 2
Add info on saturation limits in terms of surface brightness
Include option to create grism 2nd order
Detector pixel timing bugs
Field-dependent WFE extrapolated beyond FoV for better sampling diversity
Included field-dependent WFE for coronagraphy
Added wavelength dispersion of LW coronagraphic PSF
v0.7.0 (Jun 2018)
Did not make it out of development before WebbPSF 0.8.0 release.
Works with WebbPSF 0.7.0.
Field-dependent WFE
Image plane distortions
Implemented jwst_backgrounds (not required)
v0.6.5 (Mar 2018)
Fixed a critical bug where the off-axis PSF size was incorrect when performing WFE drift calculations.
v0.6.4 (Mar 2018)
Off-axis PSFs now get drifted in the same way as their on-axis counterparts.
Created an intermediate nrc_hci class to enable offsets of WFE drifted PSFs.
v0.6.3 (Mar 2018)
First PyPI release.
Effectively the same as 0.6.2, but better documentation of packaging and distributing.
v0.6.2 (Mar 2018)
Implemented coronagraphic wedges, including arbitrary offsets along bar
Renamed obs_coronagraphy to ~pynrc.obs_hci
Faster modeling of off-axis PSFs
Include coronagraphic features (e.g.: ND squares) in slope images
Roll subtracted images include option to use Roll1-Roll2
Fixed bug that was slowing down PSF convolution of disks
Can now generate docs directly from Jupyter notebooks using nbsphinx extension
Coronagraphic tutorials for docs
Create the source_spectrum class to fit spectra to observed photometry.
v0.6.0 (Dec 2017)
Support for Python 3 (mostly map, dict, and index fixes)
Updated code comments for sphinx and readthedocs documentation
Create setup.py install file
Modify grism PSF shapes due to aperture shape
Detector frames times based on ASIC microcode build 10
Headers for DMS data
Three major changes to PSF coefficients
coefficients based on module (SWA, SWB, LWA, LWB), rather than filter
WFE drift coefficient relations
field-dependent coefficient relation
v0.5.0 (Feb 2017)
Initial GitHub release
Match version numbering to WebbPSF equivalent
ND Acquisition mode
Ramp settings optimizer
Can now simulate ramps with detector noise
Query Euclid’s IPAC server for time/position-dependent Zodiacal emission
Added example Jupyter notebooks
v0.1.2 (Jan 2017)
Observations subclass for coronagraphs and direct imaging
v0.1.1 (Sep 2016)
Add support for LW slitless grism
Add support for extended sources
v0.1.0 (Aug 2016)
Rewrite of SimNRC and rename pynrc
Object oriented multiaccum, DetectorOps, and NIRCam classes
Create separate detector instances in NIRCam class
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