NIRCam Apertures

JWST apertures define target reference positions on the detectors and the and nominal extent of the field of view. For NIRCam they depend on the APT observing template in use, module selected (e.g. A, B, or ALL), subarray selected, and in some cases other APT template parameters, for all observations and for target acquistion.

Apertures define targetable areas and their extents in the JWST field of view. These definitions are stored in the Science Instrument Aperture File (SIAF).

Each aperture has a reference position which will generally coincide with the observed target at the first dither position, and  coordinates defining the field of view for the given instrument configuration. Detector specific apertures define the reference position and subarray field of view for each detector. Compound apertures represent in a simplified way the overall field of view when multiple detectors are collecting data.  Nearly all NIRCam science observations involve data collection on multiple detectors, and in those cases the reference position on one detector is defined as the reference position for the entire observation. APT uses the relevant apertures to support visualization of observations in the Aladin tool.

Representative entries are given below for the NIRCam apertures corresponding the the FULL subarrays on all 10 detectors and the subarrays used for coronagraphy on Module A.  (The coronagraphic field of view is projected onto the detectors when in use.)

Words in bold italics are buttons 
or parameters in GUI tools. Bold 
style represents GUI menus/
panels & data software packages.

The ALL aperture is used for full frame observations with both modules. It defines the full extent displayed in APT Aladin as well as the default size for each tile in a mosaic. Full frame observations with module B alone use the "Bs" aperture. "Bs" spans the full extent of the short wavelength detectors in module B.

The aperture coordinates may change slightly based on calibration measurements obtained in flight.

All NIRCam apertures are nearly aligned (to ~1° of rotation) with both the JWST coordinate system (V2, V3) and all detector rows and columns.

Figure 1. Prominent NIRCam apertures

Target reference positions ("X") and and aperture vertices (outlines) for the NIRCam detectors and subarrays assigned to the coronagraphic masks in JWST (V2, V3) coordinates. Each detector is labeled (A1–B5). Blue and red correspond to the short and long wavelength channels, respectively. The smaller squares at the top are coronagraphic apertures with mask names labeled below. The larger ALL and Bs apertures are drawn in black dashed and gray dotted lines, respectively. Coordinates for all of these apertures are given in the tables below.

Table 1. NIRCam apertures for all ten detectors and FULL subarrays, and compound apertures for module=ALL and module=B.


Scroll right to view the full table.

Table 1 shows the target reference positions ("Ref") and aperture vertices (1–4) for the NIRCam detectors (SCAs) in JWST (V2, V3) coordinates in arcseconds. The penultimate row marked "ALL" is invoked when observing with both modules and defines the nominal tile spacing for mosaics. The final row "Bs" is used for full frame observations with module B alone. 

Table 2. NIRCam subarray apertures for coronagraphic occulting masks.


Scroll right to view the full table. 

Table 2 shows the nominal target reference positions ("Ref") and aperture vertices (1–4) for the coronagraphic occulting masks in JWST (V2, V3) coordinates in arcseconds. Bar occulters (with names ending in "B") have multiple reference positions (not shown here), one for each allowed filter. Note that only module A will be used for coronagraphy.

Latest updates

  • corrected aperture B3 vertex coordinates V2_1, V2_2, V2_3, V2_4
Originally published