Notes on using aXeSIM to simulate JWST NIRCam grism images and spectra Tom Greene Feb 23, 2017
This package contains configuration files for simulating JWST NIRCam LW grism data. Results have the scale, dispersion, signal, noise, and orientation (in x, y detector coordinates) expected for actual LWA R grism data. Simulated images and extracted point source spectra are produced. Data values are in units of electrons per second.
CHANGES:
Created configuration files to allow simulation of spectra with F277w (m=1 & m=2), F410M (m=1) and F480M (m=1) filters. New files:
./CONF/ NIRCam_LWAR_F277W.conf NIRCam_LWAR_F410M.conf NIRCam_LWAR_F480M.conf
./SIMDATA/ F277W_passband.dat F410M_passband.dat F480M_passband.dat
Make new catalog files to reference correct filters and PSFs (last col): ./SAVE/ catalog_MOS_LWA_277W_PSF.lis catalog_MOS_LWA_410M_PSF.lis catalog_MOS_LWA_480M_PSF.lis
Make new demo files: axesim_nircam_F277W_demo.py axesim_nircam_F410M_demo.py axesim_nircam_F480M_demo.py
Also used the released JWST ETC to calculate medium backgrounds in the new filters and updated values in the axesim_nircam_*demo.py files:
Use these as bck_flux_disp values for each filter:
F277W 0.40
F322W2 0.56
F356W 0.34
F410M 0.30
F430M 0.17
F444W 0.96
F460M 0.23
F480M 0.28
PREVIOUS CHANGES January 5, 2017:
- Updated the expected medium background levels in the files:
axesim_nircam_F430M_demo.py
axesim_nircam_F460M_demo.py
axesim_nircam_demo.py - Create a new demo file for F356W: axesim_nircam_F356W_demo.py (mostly a copy of axesim_nircam_demo.py)
PREVIOUS CHANGES May 2016
- Updated the sensitivity files with more accurate throughputs from STScI for NIRCam ModA (March 2016 versions). Values changed by ~10%, a bit more at lambda > 4.5 microns: ./CONF/NIRCam.A.1st.sensitivity.fits ./CONF/NIRCam.A.2nd.sensitivity.fits
PREVIOUS CHANGES March 2016:
-
Updated the sensitivity files with more accurate throughputs from STScI for NIRCam ModA (Feb. 2016 versions): ./CONF/NIRCam.A.1st.sensitivity.fits ./CONF/NIRCam.A.2nd.sensitivity.fits
-
Updated the read noise in the configuration files for each filter. All now have READNOISE = 10 e- . Impacted files (these were 20.0): ./CONF/NIRCam_LWAR_F322W2.conf ./CONF/NIRCam_LWAR_F356W.conf ./CONF/NIRCam_LWAR_F444W.conf
-
Updated zodi backgrounds using values from J Leisenring. ZODI BACKGROUNDS HAVE INCREASED BY ~2x over the old ones computed from the STScI prototype ETC. Use these bck_flux_disp and bck_flux_dir values for these filters: [NOTE THESE ARE OBSOLETE IN 2017 - see more recent values above] Filter zodi (e-/s/pxl) F277W 0.30 F356W 0.90
F444W 3.00
F322W2 1.25 F430M 0.65
F460M 0.86
Files impacted: axesim_nircam_F430M_demo.py axesim_nircam_F460M_demo.py axesim_nircam_demo.py
PREVIOUS CHANGES Sep 2015:
- Created configuration files, passband files, object lists, and demo scripts for use with F430M and F460M filters: ./axesim_nircam_F430M_demo.py ./axesim_nircam_F460M_demo.py ./CONF/NIRCam_LWAR_F430M.conf ./CONF/NIRCam_LWAR_F460M.conf ./SAVE/catalog_MOS_LWA_430M_PSF.lis ./SAVE/catalog_MOS_LWA_460M_PSF.lis ./SIMDATA/F430M_passband.dat ./SIMDATA/F460M_passband.dat
PREVIOUS CHANGES Aug 2015:
- Copied missing F322W2 PSF flies to ./SIMDATA
- Edited ./SAVE/catalog_MOS_LWA_PSF.lis master catalog input file to set objects to use F356W PSF (MODIMAGE = 6)
- Edited README to list correct output file names (now LWAR)
PREVIOUS CHANGES May 2015:
- Updated CONF/NIRCam.A.*sensitivity.fits files with more realistic optics transmission and QE values
- Replaced CV2 point PSFs with ones created by WebbPSF centered on a pixel center (in SIMDATA directory)
- Updated imaging passband PCE files (SIMDATA/F*_passband.dat)
- Slight update to wavelength range in CONF/NIRCam_LWAR_F444W.conf file (other .conf files unchanged from April 2015)
**** USING aXWSIM to simulate JWST NIRCam LW grism data ****
- Start pyraf, load aXeSIM
This assumes that you are running aXeSIM from STSDAS. See the HST WFC3 aXeSIM README file if you want to install aXeSIM as an external pyraf package (as taxesim and use it that way - included below too). It may be best to install pyraf (including aXeSIM) as part of one of your python environments, as assumed below. Note that pyraf requires python 2.7 (or perhaps 2.x), not 3.x.
Do in terminal, assuming that you have installed pyraf in the astroconda python environment. Just change the name if you have pyraf in a different environment:
$ source activate astroconda
$ pyraf setting terminal type to xgterm...
--> stsdas --> slitless --> axesim
The aXeSIM software package 1.4 was developed by the Slitless Spectroscopy Group of the ST-ECF. Maintenance is provided by the Space Telescope Science Institute. Further information is available at: http://www.stsci.edu/resources/software_hardware/stsdas/axe
Any questions regarding this software can be directed to: help@stsci.edu
axesim/: prepimages prepspectra simdata simdirim simdispim
-->
$ cd aXeSIM_NC_2016Mar (the untarred directory)
- aXeSIM/taxesim14
aXeSIM and taxesim14 have the identical five commands that are listed whenthe package is loaded. However, in 'taxesim14' all commands have the letter 't' as a prefix (aXeSIM: simdata <--> taxesim14: tsimdata)
See the DOCUMENTATION directory for the aXeSIM manual
There exist a brief online-help for all commands (use e.g. "--> help simdata").
- Testing aXeSIM
There is the script 'axesim_nircam_demo.py' (need to edit for taxesim), which runs a simulation for the NIRCam LWA R grism + F356W filter. The simulations (results named 'WFC3_templ__*.fits') use a spectral template spectrum and a template PSF image while producing both, a simulated slitless and direct image. Also a default extraction is performed on the slitless image. To run the script in PyRAF, type on the command line for aXeSIM: --> pyexecute('axesim_nircam_demo.py')
The output images and spectra land in the ./OUTSIM directory: NIRCam_LWAR_F356W_direct.fits - Simulated direct image NIRCam_LWAR_F356W_images.fits - I think a single image made from the PSF file NIRCam_LWAR_F356W_slitless.fits - Simulated grism image NIRCam_LWAR_F356W_slitless_2.SPC.fits - Extracted 1-D spectra, 1 per object NIRCam_LWAR_F356W_slitless_2.STP.fits - 2D grism spectrum template? NIRCam_LWAR_F356W_spectra.fits - Input 1-D spectra, 1 for each object
Note that only 1 order (m = 1) is created or extracted for each object. The F356W filter will always only have 1 order, but F322W2 can have 2 orders (m=1 and m=2) depending on the object location in the image.
NOTE: It is also very instructive to do this interactively via:
--> epar simdata
*** NOTE that the aXeSIM output images have data units of electrons per second! They must be multiplied by the integration time to get the correct absolute signal, noise, and background levels. However, S/N can be measured from the output files as the are ***
=====================================================================
NOTES How to start aXeSIM as external pyraf package: In case that you have downloaded and installed aXeSIM as the external IRAF/PyRAF package 'taxesim14', you must make its location available to IRAF/PyRAF. To do this, put the following lines into the IRAF file "login.cl" (in "$HOME/iraf"; replace with the location of your aXeSIM installation):
reset taxesim14 = /taxe/iraf/ task taxesim14.pkg = taxesim14$taxesim14.cl reset helpdb = (envget("helpdb") //",taxesim14$lib/helpdb.mip")
(Then add a 't' in front of all axesim commands above... becomes 'taxesim') Would also need to edit the axesim_nircam_demo.py script file