Imaging with the James Webb Space Telescope Christine Chen (STScI) JWST Deputy Project Scientist Based on work by many people across the JWST project Time change for next semester First in a series of practical talks about various instrument modes Introduce self – former miri instrument scientist

Contributions from ESAC Workshop Presenters… Conference presentations posted on the web at the following url: http://www.cosmos.esa.int/web/jwst-2016-esac

Wavelength Coverage From G. Kriss The long and short of it---long wavelengths, use MIRI; short wavelengths, use NIRCam. From G. Kriss

Imaging Instruments in the JWST Focal Plane Approximately 9’x18’ 133” NIRISS From G. Kriss

Imaging Fields of View Comparison 65 mas pixels 110 mas pixels Short Wavelength Camera 32 mas pixels Long Wavelength Camera 65 mas pixels From G. Kriss

Outline Instrument Overviews Dither Patterns Readout Patterns Sensitivities and Saturation Limits Subarrays Parallel Observations

The Near-Infrared Camera (NIRCam) Pocket Guide https://jwst.stsci.edu/files/live/sites/jwst/files/home/instrumentation/nircam/technical%20documents/NIRCam-pocket-guide.pdf Short Wavelength Channel: Field of View: 2x2.2’x2.2’ Plate Scale: 32 mas pix-1 Nyquist Sampled at 2 μm Long Wavelength Channel: Plate Scale: 65 mas pix-1 Nyquist Sampled at 4 μm

The Near-Infrared Imager and Slitless Spectrograph (NIRISS) Field of View: 2.2’x2.2’ Plate Scale: 65 mas pix-1 Nyquist Sampled at 4 μm Provides a powerful “parallel” capability Matched NIRCam filters; comparable sensitivity Increases areal coverage of the sky when paired with NIRCam Provides near-IR imaging at lower data rate than NIRCam Pocket Guide https://jwst.stsci.edu/files/live/sites/jwst/files/home/instrumentation/niriss/technical%20documents/NIRISS-pocket-guide.pdf

The Mid-Infrared Instrument (MIRI) 4QPM Coronagraphs 10.65µm 11.4µm 15.5µm 24 x 24 arcsec. Low Resolution Spectrometer Slit 5 x 0.6 arcsec Imager 75 x 113 arcsec Medium Resolution Spectrometer > 3.5 x 3.5 arcsec Lyot Coronagraph Mask 23mm 30” x 30” (arcminutes on sky) Field of View: 74”x113” Plate Scale: 110 mas pix-1 Nyquist Sampled at 7 μm Pocket Guide https://jwst.stsci.edu/files/live/sites/jwst/files/home/instrumentation/miri/technical%20documents/miri-pocket-guide.pdf Encyclopedia http://ircamera.as.arizona.edu/MIRI/encyclopedia.htm

NIRCam Primary Dithers Purpose: Provide even spatial coverage across module and detector gaps Available Patterns: (1) FULL – Large fields without gaps, including mosaics (tiled pointings of larger areas), 3:18% - 2:71% - 1:11%

NIRCam Primary Dithers 28:1% 29: 6% 30: 23% 31: 38% 32: 25% 33: 7% 34: 1%

NIRCam Primary Dithers (2) INTRAMODULE – Objects smaller than the individual modules (<110”),

NIRCam Primary Dithers (3) INTRASCA – Objects smaller than the individual SCA detectors (<50” or <100”) when optimizing for short or long wavelength observations, respectively Dither Size Science Target Size LWC SWC Large <25% <16” <32” Medium <50% <33” <66” Small <75% <50” <100” Confusing “Small” dither for large targets The primary use for this is improving the flat field

NIRCam: Secondary Dithers Purpose: (1) Provide sub-pixel sampling to improve image reconstruction and (2) mitigate the effect of bad pixels Available Patterns: Even sampling using a specified number of secondary dithers (Ns=1-64). If Ns<10, the all of the offsets will fit within a 10 pixel x10 pixel box. Instrument Requirement: Distortion at the edge of the field <2% that of the center

NIRISS Dithering The NIRISS Imaging template is intended to support pure or coordinated parallels only, since NIRCam is the better choice for all general imaging applications (e.g. bigger field of view, simultaneous blue/red channels, better PSF sampling) Template does not support the use of subarrays NIRISS will necessarily follow dither pattern / mosaic strategy of “primary” instrument

MIRI: Reuleaux Triangle Based on IRAC Dither pattern Designed for unresolved or barely resolved sources Dither Positions Recommended Pattern Sizes

MIRI: Two- and Four-Point Dither Patterns Optimized for sub-pixel sampling at the shortest wavelengths and dithering along the long direction of the imager FOV 1) Small point source pattern optimized for F560W and F770W 2) Small extended source pattern optimized for F560W and F770W 3) Subarray (SUB64) pattern

MIRI: Cycling Pattern Designed to be flexible Based on IRAC Cycling Pattern (positions drawn randomly from Gaussian distribution) Observers may choose starting position in table (of 311 position) and the number of positions desired. The pattern wraps for numbers of positions >311. Includes 0.5 pixel subsampling Will provide a limited-access “sparse cycling” option to select table positions

Maximum Data Rate Instrument ndetectors nx ny tframe (sec) JWST can downlink 229 Gbits of data in a nominal 4 hour contact with the Deep Space Network. Current plans allow for two 4-hour contacts per day. If the requested data rate exceeds the downlink capability then the program will be more difficult to schedule and runs the risk of being delayed but for good scientific cause a locally high data rate is possible Instrument ndetectors nx ny tframe (sec) Data in 12 hrs (Gbits) NIRCam SW RAPID 8 2048 10.74 2160. NIRCam LW RAPID 2 540. NIRISS NISRAPID 1 270. MIRI FASTMODE (1032+258 reference outputs) 1024 2.775 330. Hope to report in APT how data rate in the program compares with nominal downlink rate (really on a visit basis)

NIRCam Exposure Specification Nframe is the number of frames averaged in a group Nskip is the number of frames skipped in a group Ngroup is the number of groups in an integration Nint is the number of integrations in an exposure

NIRCam Readout Patterns Readout patterns consist of groups with 1, 2, 5, 10 or 20 frames On-board electronics can average 2, 4, or 8 frames within a group Deep8 may have an advantage in fewer cosmic rays compared with Medium8

NIRCam Readout Patterns Highlight that the number of groups for DEEP2 AND DEEP8 actually goes to n=20 even though it’s not shown on the table