NIRCam Readout Pattern Considerations For readout patterns with the same Nframes+Nskip (e.g. Bright1 and Bright2), the pattern with the smaller number of Nframes provides better cosmic ray rejection The pattern with the small number of Nskip provides better readout performance and therefore more sensitivity For more information, see Robberto 2010 JWST-STScI-2128 “NIRCam Point Source SNR vs. Filter, Source Brightness and Readout Combinations”

“Highest SNR” NIRCam Readout Pattern From Robberto 2010 JWST-STScI-2100 “NIRCam Optimal Readout II: General Case (Including Photon Noise)”

NIRISS Readout Patterns NISRAPID Nskip = 0 Nframe = 1 tframe = 10.73 sec Min(Ngroup) = 1* Max(Ngroup) = 30 NIS Nframe = 4 Max(Ngroup) = 200 *not recommended

MIRI Readout Patterns FASTMODE Nskip = 0 Nframe = Ngroup tframe = 2.775 sec SLOWMODE* tframe = 23.89 sec *not recommended for imaging and not allowed for subarrays The MIRI team recommends a minimum of 5 groups per integration for good calibration

NIRCam Subarrays Full Field uses 4 amplifiers, Subarray uses 1 Subarrays are only taken on module B For imaging subarrays, only SCA B3 for SW Subarrays have same size in pixels on SW and LW SW and LW subarrays have the same center on the sky There are Point Source subarrays Extended Source subarray All point source subarrays will be on B3 B3 is the fundamental detector for flux calibration, extend to other detectors using LMC From M. Robberto

NIRCam Subarrays The subarrays are designed to provide for sources that are 2, 4, 6 magnitudes brighter than allowed by the full array

DIRBE All-Sky Maps

JWST Backgrounds A – Zodiacal Light Scattered (5500 K) B – Zodiacal Light Emission (270 K) C – Observatory Straylight (133.8 K) D – Observatory Straylight (71.0 K) E – Observatory Straylight (62.0 K) F – Observatory Straylight (51.7 K) Glasse et al. (2015)

Gain in bright source limit MIRI Subarrays Enables observations of bright sources. For example, observations of the telescope background at F2550W will saturate the imager in one FULL frame time Subarray Frame time [sec] Gain in bright source limit FULL 2.775 1.00 BRIGHTSKY 0.865 3.21 SUB256 0.300 9.25 SUB128 0.119 23.32 SUB64 0.085 32.65 MASKLYOT 0.324 8.56 MASK1550 0.240 11.56 MASK1140 MASK1065 SLITLESSPRISM 0.159 17.45 From A. Glasse

NIRCam Point Source Sensitivity Extra-wide, wide, medium, and narrow filters are labeled in normal, bold, and italic text, respectively each with progressively thicker bars. Calculated assuming 1000 sec exposures, a flat source spectra in nJy, and zodiacal light at 1.2 times the minimum. More precise sensitivity estimates may obtained using acquired from the Exposure Time Calculator (ETC).

NIRCam Saturation Limits Saturation, in magnitudes, in Vega K-band for a solar type G2V star in 21.4 sec (based on 2 readouts of the full detector), filling pixel wells to 80% capacity. Brighter saturation limits may be achieved by using subarrays to reduce the exposure time, and/or using time series observations with the weak lenses or grism.

NIRCam and NIRISS Sensitivities S/N = 10 in 10 ks NIRISS Filter nJy m(Vega) F090W 11.28 28.28 F115W 11.22 28.06 F140M 14.80 27.43 F150W 9.19 27.83 F158M 12.88 27.39 F200W 7.81 27.54 F277W 6.63 27.09 F356W 6.89 26.56 F380M 18.74 24.34 F430M 28.32 24.65 F444W 12.29 25.49 F480M 36.85 24.14 NIRCam SW advantages: (1) lower read noise (2) smaller pixels for resolving background for zodiacal light Filter widths are shown as horizontal bars. NIRISS advantages (1) All reflective optics (NIRCam dichroic absorbs) (2) Better Quantum Yield effects NIRCam F115W  13.2 nJy NIRISS   F150W  11.2 nJy

MIRI Sensitivity and Saturation Limits These sensitivity limits (below) apply to faint sources observed with the FULL imager field of view. They assume a photometric aperture of radius, rphot = 0.42 (l / 10 mm) (Note: The full width at half maximum intensity (FWHM) of the point spread function (PSF) is dFWHM = 0.32 (l / 10 mm). Filter Name Wave-length Band-width Sensitivity S/N = 10 in 10,000 second on-chip integration. Saturation Limit (Fbright) Point Source Extended Source Extended Source* µm microJansky microJansky arcsec-2 milliJansky milliJansky arcsec-2 F560W 5.6 1.2 0.16 0.89 13 140 F770W 7.7 2.2 0.25 0.77 7 75 F1000W 10.0 2.0 0.54 0.99 15 103 F1130W 11.3 0.7 1.35 1.89 68 366 F1280W 12.8 2.4 0.84 0.88 27 113 F1500W 15.0 3.0 1.39 1.11 36 110 F1800W 18.0 3.46 1.9 65 138 F2100W 21.0 5.0 7.09 2.9 66 F2550W 25.5 4.0 26.2 7.3 195 206 From A. Glasse

Observing Overheads Offset times (within mosaics or dither patterns) will depend on the size of the offset with larger offsets requiring more time Offsets larger than 20”-80”, depending on ecliptic latitude, will require a guide star acquisition. Guide star acquisitions are longer than simple offsets. Mosaics and the NIRCam FULL dither patterns will require guide star acquisitions. APT will be used to estimate overheads. The version of APT to be released in Fall 2017 will include accurate Cycle 1 overheads times. APT has a grayed out box that will give the exact visiting splitting distance for an observation

Mosaicking versus Dithering Mosaic patterns (for any instrument) are intended for covering larger areas of the sky than a single field of view. Fundamental operational difference between Dither and Mosaic: Dithers: all spatial positions in a pattern are imaged through the same filter before making a filter change. Mosaics: all filters in an observation (and all dithers) are executed before moving to the next mosaic point. Thus, dithers with large patterns and large step sizes can incur significant overheads due to spacecraft maneuvers. This must be balanced against lifetime limitations on filter wheel rotations. From G. Kriss

From M. Perrin

Example: NIRCam Mosaic Orion bar is broken up into 3 parts to improve the schedulability Long rectangles constrain the orientation of the telescope tighly Since there is typically +/-5 degree flexibility in orient at a time, breaking up into square pieces helps In cycle 2, may have a tool that designs mosaick intellgently based on when the target is observed From M. Robberto

Observability Constraints Snapshot from the schedulability tool from Chris Stark showing that in this configuration the orion bar observations can be made over the entire visibility window From M. Robberto

Coordinated Parallels Available Cycle 1: NIRCam Imaging and MIRI Imaging NIRCam Imaging and NIRISS WFSS MIRI Imaging and NIRISS WFSS NIRCam Imaging and NIRISS Imaging

Coordinated Parallel Dither Patterns: NIRCam + MIRI Have to deal with differences in SI-to-SI orientations and pixel scales E.g.: MIRI is offset by 4.756 degrees w.r.t. NIRCam (as of CV3) Dither patterns generally keep pixel phases “ideal” to within 0.05 pixel for parallel SI Exception: MIRI at λ > 12 μm (well-sampled anyway) Dither patterns involving MIRI customized for each filter, with offsets >= 3 × (FWHMPSF) Otherwise typically “Small”, “Medium”, and “Large” dither offsets being offered From P. Goudfrooij

NIRCam Detector Performance CDS noise CDS noise Effective noise Effective noise NIRCam readout noise performance generally better than requirements Noise levels at long times a little higher than expected because of 1/f noise NIRCam team working on how to remove 1/f noise From M. Robberto

MIRI Detector Performance The MIRIM detector has great cosmetics (<300 dead, hot or noisy pixels in the science field). MIRI’s PSF is well described at long wavelengths by the JWST’s diffraction profile. At short wavelengths (F560W, F770W filters) a cruciform pattern appears, at a level comparable to the telescope diffraction spikes. Identified with scattering in the detector. A model has been developed using PSF and out-of-field straylight test data which predicts that 22% of the point source light at F560W is scattered into the cross (11% for F770W). CV2 F560W image of OSIM IR LED Model JWST diffraction limited PSF Model MIRI PSF, including scattering. From A. Glasse