1. JWST NIRCam Time Series Observations
Tom Greene (NASA Ames)
E. Schlawin (UA)
& UA / STScI NIRCam team:
D. Kelly, J. Stansberry,
J. Leisenring, J. Fraine, et al.
ETEO w/JWST
July 10, 2017
July 10, 2017
NIRCam TSOs

2. NIRCam Intro (from STScI Jdox)
Focus of this talk
From
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NIRCam TSOs

3. NIRCam Fields of View (from STScI Jdox)
Time series spectra
Time series imaging
From
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NIRCam TSOs

4. NIRCam modes: selectable with wheels
From
OTE
0.6 – 2.4 mm
2,4 – 5 mm
No Short Wavelength Spectroscopic Capabilities in Cycle 1
2 LW grisms in each module provide R~1500 slitless spectroscopy:
Chose dispersion orientation and filters to suit your science
Simultaneous SW imaging is possible!
(LW)
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NIRCam TSOs

5. NIRCam LW Grism Spectra
Increasing l
2.’2
Right: Extracted spectrum. The continuum decreases toward longer wavelengths due to low fiber transmittance, and the broad feature near 4.27 mm is due to CO2 absorption. These are artifacts of the test equipment and not NIRCam itself.
Left: NIRCam spectral image of the OSIM super-continuum lamp point source taken with the LWA R grism and F444W filter during JWST instrument testing.
* NIRCam FOV is 2.’2 x 2.’2 with dispersion of 10 Å per 0.”065 x 0.”065 LW pixel
27 September 2016
NIRCam time series spectroscopy

6. NIRCam Spectral Coverage & Resolution
NOTE: Total spectroscopic throughput is the product of Grism curve and selected filter!
F322W2
F444W
Greene+ 2016b & 2017
NIRCam grisms were designed for wavefront sensing but are useful for science
27 September 2016
NIRCam time series spectroscopy

7. Module A (TSO) Spectral Saturation Values
NIRCam can observe
bright stars!
Greene+ JATIS 2017
c: K-band Vega magnitudes for saturation (80% full well or 65,000 electrons) for 0.68 s integrations (2 reads) of 2048 x 64 pixel regions in stripe mode (4 outputs).
See Greene+ (2017) JATIS article for more Module A & B saturations and sensitivity values
27 September 2016
NIRCam time series spectroscopy

8. Time-series imaging is also possible
l < 2.4 mm TSO imaging can be done simultaneously with either l > 2.4 mm imaging or spectroscopy
SW observations can be done with weak lenses that spread light over many pixels
better bright limits and potentially higher precision photometry
HAT-P-18 b use case is coming to Jdox soon
July 10, 2017
NIRCam TSOs

9. The NIRCam Niche: When to use NIRCam?
Ideal for TSO imaging:
Simultaneous SW & LW, weak lenses illuminate many pixels, good spatial sampling, good bright limits
l = 2.4 – 5 mm spectroscopy when:
Simultaneous SW imaging is required (& maybe spectroscopy in Cycle 2+)
Want true slitless, good spatial sampling or good bright limits needed
Needed wavelengths are covered by a single NIRCam filter or you have enough time to use 2 filters (2 transits or eclipses)
July 10, 2017
NIRCam TSOs

10. Setting TSO parameters
Determine how much dwell time for each object
Set subarrays and exposure parameters
Set SW filter: simultaneous l < 2.4 mm imaging
Consider target acquisition
STScI is working on acquiring on bright targets for Cycle 1
Visibility, position angles, and spectral overlaps
Enter values into APT
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NIRCam TSOs

11. NIRCam grism time series options (APT)
Can choose from 64, 128, 256, & 2048 x 2048 subarrays
1 or 4 outputs (4 for very bright stars)
Simultaneous short wavelength imaging with weak lens to spread the light over many pixels is possible
No dithering
Flexible detector MULTIACCUM exposure & readout parameters
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NIRCam TSOs

12. Is mag > bright limit + 1.5?
Select Subarray Size
mag > bright limit ?
2048 x 64
4 Outputs N Y
Want > 128 subarray?
2048 x 128
1 or 4 Outputs
Is mag > bright limit + 1.5?
2048 x 256
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NIRCam TSOs

13. Select Detector Readout Parameters
RAPID exceeds data limit?
RAPID N Y
RAPID Ngroups > limit?
BRIGHT1 > limits?
BRIGHT1
BRIGHT2 > limits?
BRIGHT2
Data limit is ~7 – 10 hr RAPID for 3 SCAs
Set #groups from:
host star brightness
mode saturation limit
subarray size
# of outputs
Set # Ints to fill dwell time
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NIRCam TSOs

14. Set SW Filter: Simultaneous l < 2.4 mm Imaging
Subarray > 64 tall?
CLEAR + WLP4 N Y
Favorite filter saturated?
Favorite Filter + WLP8
Another Filter+ WLP8
Currently Available SW Filters:
CLEAR + WLP4
WLP M
WLP M
WLP N
WLP N
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NIRCam TSOs

15. Check spectral overlap of nearby objects
Dispersion
Dispersion l l
We are working on an automated tool for this (NIRCam + MIRI LRS)
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NIRCam TSOs

16. Check spectral overlap of nearby objects
Lots of contamination, but the Visibility windows have PA ~190 – 260° & 137 – 69° - OK!
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NIRCam TSOs

17. The End
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NIRCam TSOs

18. Target Acquisition Note
In Cycle 1, grism time series target acquisition is done with F335M filter, 32 x 32 subarray, and Ngroups ≥ 3
Saturation limit is K = 7.0 mag
Stars with K < 7.0 may require offset target acquisition
Offset from nearby fainter star with known coordinates
Using a narrow-band acquisition filter would allow acquiring on K < ~4.5 mag stars (likely Cycle 2 and later)
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NIRCam TSOs

19. APT Example: WASP-80 b F322W2
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NIRCam TSOs

20. NIRCam uses the JWST time-series data pipeline
• Users can download & re-run the pipeline with different options, additions, or removals
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NIRCam time series spectroscopy

21. Future Possible Simultaneous 1 – 2 mm Spectra
• DHS elements
disperse ~40%
JWST’s light onto 2 NIRCam SW detectors with a small gap in-between
Dispersed Hartmann Sensor (DHS) elements in the SW channel of NIRCam provide 1 – 2 mm spectra using 10 sub-apertures of the JWST pupil, potentially allowing simultaneous spectra of bright stars during LW grism observations
This is not an approved science mode for Cycle 1; it may be approved for later cycles. There may be limitations on spectra.
See Schlawin+ (2017) PASP
27 September 2016
NIRCam time series spectroscopy