Pandeia: The JWST Exposure Time Calculator The JWST Exposure Time Calculator. 2 Current version: 1.0...
Transcript of Pandeia: The JWST Exposure Time Calculator The JWST Exposure Time Calculator. 2 Current version: 1.0...
Klaus Pontoppidan, on behalf of the STScI ETC teamJWST @ STScI
Proposal Planning Workshop, May 15, 2017
Pandeia: The JWST Exposure Time Calculator
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Current version: 1.0 (January 2017)
jwst.etc.stsci.edu
for DD-ERS/GTO/GO Cycle 1
Fun fact: When an update occurs, your old workbooks will be saved as read-only
Planned update releases (version 1.1 ~June 1, including target acq + numerous updates, bug fixes and enhancements)
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SOME HISTORY
• Originally, it was envisioned that the JWST ETC would be similar to the HST ETC.
• It became clear that using the HST ETC as a basic design was not viable.
• Works ok for imaging, but not for most of the advanced JWST modes, JWST detector noise and to support modern user interaction and collaborations
• Something more modern/complex was needed. This was ~2012.
• Imaging • NIRCam SW+LW • NIRISS • MIRI • NIRSpec TA (through MSA mesh)
• Slit spectroscopy • NIRSpec FS • MIRI LRS
• IFU spectroscopy • NIRSpec IFU • MIRI MRS
• Multi-object spectroscopy • NIRSpec MSA
• Slitless spectroscopy • NIRISS WFSS • NIRISS SOSS • MIRI LRS
• Coronagraphy • NIRCam spots + wedges • MIRI Lyot • MIRI FQPMs
• Sparse Aperture Masking Interferometry • NIRISS AMI
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SOME HISTORY, CONT’D2012 Pandeia prototype2013 Recommendations to satisfy the ETC requirements
within a feasible framework.
1. The ETC should use a three-dimensional (two spatial and one spectral) framework.
2. The ETC should use a PSF library, for instance as generated by the WebbPSF tool.
3. The noise propagation should include correlated noise.
4. Post-observation additions of multiple exposures, subtraction of backgrounds, extraction of photometry and spectroscopy […] should be explicitly modeled under the unifying concept of “observing strategy”.
5. The ETC engine should have a stable API supporting different clients, including APT, a user web form and a standalone application.
6. ETC calculations should be sufficiently fast to support efficient comparative parameter studies, as well as inverse problems.
7. The ETC should be template-based for all three main inputs (instrument configuration, target design, observing strategy).
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ETC enginePython library
JWST reference database
Separate from other JWST reference data
Throughputs noise properties
PSFs
Web application @
jwst.etc.stsci.edu
User interface relevant for most users of the ETC
Collaborative functionality
JWST Background Model
Currently only available through the web
application
THE PANDEIA PROJECT
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Workbooks: Organize and save your ETC calculations
Build your own sources and scenes library
Analyze and compare different instruments and modes
Share your work with your team
WEB APPLICATION: A COLLABORATIVE WORK ENVIRONMENT
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• JWST code project called “Pandeia”
• Under the hood: 3D sensitivity engine
• Includes PSFs, correlated noise other detector effects, effects of background subtraction and extraction.
• Pointing+time dependent JWST background model.
• 100% data driven
ETC ENGINE
Reference: Pontoppidan, Pickering, et al. 2016, SPIE
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Python module
More functionality than available in the web application
Advanced scripting
pip install pandeia.engine
http://ssb.stsci.edu/pandeia/engine/1.0/
examples at https://github.com/spacetelescope/JWSTUserTraining2016
ETC ENGINE CODE AVAILABLE
Fun fact: The engine is a compact, general code, currently only ~12,500 lines, excluding standard libraries.
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ENGINE ALGORITHM: SCENE PROJECTIONSImage projection
Slit spectroscopy projection
Slitless spectroscopy projection
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Flux rate in pixel iTotal flux rate in measurement
scalar weight of pixel iVariance of measurement
covariance matrix of pixels (1,2,...,N)
ETC Strategies: Extracting signal and propagating noise
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Strategy example: Aperture photometry
Aperture correctionPixel flux rate in aperture
A = extraction region/aperture
B = sky region
Pixel flux rate in background
Pixel weights
Negative because the background is subtracted
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PSF LIBRARY•Uses WebbPSF to calculate theoretical point spread functions, including realistic wavefront errors. (M. Perrin, https://pythonhosted.org/webbpsf/).
•Almost 3000 individual monochromatic PSFs.
•Subsampled by integer factor of pixel size.
•Fun fact: The observed PSF depends on the color of the astronomical source.
NIRCam SW imaging PSFs
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PANDEIA REFERENCE DATAPandeia_data Observatory (JWST)
Extinction
SED (template spectra)
Normalization (external bandpasses)
Various defaults
MIRI
NIRCam
NIRISS
NIRSpec
Telescope
Detectors(IPC+correlation)
config.json
Spectral efficiency
Dispersion
Filters
Optical efficiency
Detector QE+QY
PSFs
Fun fact: The ETC reference data is a ~1.5 GB tarball. Almost all of that are PSF libraries.
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SATURATION
Two types of saturation:1. Partial saturation — the ramp saturates before it finishes, but more than the minimum reads are unsaturated
2. Full saturation — the ramp saturates before the minimum number of reads is reached
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Zodiacal and Galactic backgrounds
• JWST uses a dynamic “background model generator” (BMG).
• Zodi+ISM heritage from Spitzer’s operational system (IPAC).
• Data are from COBE/DIRBE.
• ISM “cirrus” uses fixed spectrum, including PAHs. Intensity set by Schlegel et al. extinction maps, which were fits to IRAS + DIRBE/COBE data.
• Wainscoat et al.1998 star counts model.
• The Zodi and Galactic emission is calculated for a given RA & DEC, in one of 2 ways:
1. for a given RA, DEC, date: “Dated background”
2. as a percentile of the backgrounds for those coordinates, over the visibility. “Dateless background”
• Fun fact: Benchmark sensitivities computed for (J2000, 17:26:44 -73:19:56) on June 19, 2019. — “minzodi*1.2”
• Fun fact: If using the ETC engine “stand-alone”, you should still use the web app to create a background.
Zodiacal
ISM
Stars
A. Noriega-Crespo
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Stray light• The background model calculates the
stray light for a given position and date, following Lightsey 2016 SPIE.
• Radiance Transfer Functions (RTFs) from Lightsey, at 0.7, 1, 2, 3, 5, 10, 15 micron.
• Sky map from Galactic + Zody engine (for that position, for that date)
• Interpolate RTFs at other wavelengths.
(Lightsey 2016 SPIE)
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Thermal self-emission
• Thermal emission from JWST itself is the dominant background at ~>15um.
• Sum of 20 blackbodies (P. Lightsey, J. Rigby).
• Produces backgrounds of 0.74 and 174 MJy/SR at 10 and 20 micron. (Reqs. are 3.9 and 200 MJy/SR). Temperatures are as expected: T(SS)=89K, T(PM)=54K (hottest segments).
• Blackbody model agrees with Lightsey calculations at 15, 25 micron to within 0.5%. Thermal-only curve (black line) + Glasse et al. 2015
SPIE (red and blue solid lines.) Zodiacal model of Glasse (dashed lines.) Figure from J. Rigby
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Fun fact: You can download all the ETC inputs/outputs in a convenient format from the downloads tab
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NIRCam F250M/F335M/F460M
MIRI F560W/F770W/F1000WFun fact: You can also use the ETC python module to script
complex, large scenes
USING THE ETC: IMAGING
Red bulge with star-forming knots at z=0.5
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MIRI F560W/F770W/F1000W
Fun fact 1: In spectroscopic modes extraction apertures are one wavelength pixel wide.
USING THE ETC: SPECTROSCOPIC MODESMIRI LRS
NIRSpec MSA
Fun fact 2: You can upload your own spectra, and add lines.
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ETC calculation of a MIRI MRS observation of a protoplanetary disk model.
12 individual calculations (one for each MRS channel+sub-band)
Fun fact 1: The ETC will slow down for more finely sampled input spectra (improved in v1.1).
Fun fact 2: All IFU calculations (NIRSpec+MIRI) will perform a dither to subtract background (pick in-field or off). (simplified in v1.1)
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BENCHMARKING THE ETCETC requirement: 10% in signal-to-noise ratio for 90% of calculations
Compared limiting sensitivities (10 sigma in 10,000 s) for all major instrument modes to independent calculations provided by the JWST instrument teams.
In comparing a 3D calculation with 1D calculations 10% is a reasonable threshold.
Using the same data and same assumptions, get within 10%.
Algorithms are appropriate and accurate Dashed curves are the benchmarks
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MIRI
NIRISS
NIRSpec
NIRCam
VALIDATION COMPARISON
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REAL LIFE ETC RESULTS VERSUS STANDARD SENSITIVITIES
There are many parameters affecting ETC sensitivities
That’s the point of having a versatile tool! Comes with some responsibility.
• Think about your background subtraction • Think about what extraction aperture is optimal (point or extended sources) • Is your background correct for your target? • Different read-out patterns change read noise • The ETC does cut some corners: No distortion
for instance (except for NIRISS SOSS).
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HOW TO GET HELPThe ETC is powerful = a lot of parameters
Documentation: jwst-docs.stsci.edu Known issues: Check the ETC help menu JWST help desk: jwsthelp.stsci.edu Have patience with us - the team is working hard (400+ open tasks)
…more to come