NIRCam Apertures

A JWST aperture consists of a unique targetable fiducial point and its associated region, used in support of JWST science operations. Aperture definitions are stored in the Science Instrument Aperture File (SIAF, see Cox & Lallo, 2017).

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.  While in some cases apertures coincide with physical entities in the field of view (e.g. a detector and its center, or a slit and its location), this is not always the case. Apertures can sometimes be defined to represent convenience regions. 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. This is for example the case of the NIRCam ALL aperture. This aperture encompasses the entire NIRCam FoV, and its reference position is at the nominal center of the FoV, in the intra-modules gap, where no data are collected. In addition to their positions and extents, the SIAF appropriately defines several systems of coordinates for each aperture. These coordinates describe the field of view geometry for the given instrument configuration (see Cox & Lallo, 2017). Some types of apertures may not have all available coordinates systems defined. E.g. compound apertures, not physically bound to a single detector, do not have "det" or "sci" (detector or science) coordinates attached.

For NIRCam — for all observations and for target acquisition — the apertures in use depend on the APT observing template, module selected (e.g. A, B, or ALL), subarray selected, and in some cases, other APT template parameters (e.g. filter). 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. Separate tables are used for the corresponding coronagraphic entries on module A. The coronagraphic field of view is in fact different from e.g. the imaging one, and it is projected onto the detectors when the coronographic pupil elements are in use.

Words in bold are GUI menus/
panels or data software packages; 
bold italics are buttons in GUI
tools or package parameters.

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 another compound aperture, the "Bs" aperture (aka BSHORT). "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 as well as for the 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 accordingly. Note that from Cycle 2 NIRCam Coronagraphic Imaging is offered simultaneously on the SW and LW channels, but for simplicity we display only the aperture on the channel naturally associated with each mask. For example for the MASK 210R, optimized for 2.1 microns, the natural aperture is on the SW channel. 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.

Tables 1-3 show the target reference positions ("_ref") and aperture vertices (_1–4) for the NIRCam detectors (SCAs). Table 1 reports the values in JWST (V2, V3) coordinates and Tables 2, 3 in NIRCam ideal reference systems (XIdl, YIdl) in arcseconds. Note that while the (V2, V3) system is an absolute reference system, tied to the JWST focal plane, the ideal systems are each tied to a specific aperture. An ideal system is a distortion-removed frame, given in the SIAF in units of arc-seconds. Ideal frame coordinates can be treated as a location in a tangent plane projection. The tangent point (i.e. XY Idl origin) is defined at the given aperture's fiducial/reference position.


Table 1. NIRCam apertures, center and four corners, for all 10 detectors in the JWST (V2, V3) coordinate system. The ALL and the BS (aka BSHORT) apertures are compound apertures that correspond to all 10 modules A+B or just 5 module B detectors. These 2 apertures are used for defining the telescope pointing when MODULE=ALL or MODULE=B is selected in APT. Note that not being tied to a physical detector, compound apertures do not have vertices defined in the (V2,V3) focal plane system. Also note that the BS aperture has its reference point located within the footprint of the B4 SCA (see also Figure 1). Values are in arcseconds.

SCA*

V2_ref

V3_ref

V2_1

V2_2

V2_3

V2_4

V3_1

V3_2

V3_3

V3_4

A1

120.62

-527.54

153.10

88.84

88.67

152.03

-559.41

-560.04

-495.77

-495.30

A2

119.79

-459.83

151.59

88.28

88.40

151.04

-491.22

-491.59

-428.34

-428.11

A3

51.99

-527.96

84.04

19.49

20.27

83.93

-560.21

-560.35

-495.71

-495.92

A4

52.41

-459.94

84.10

20.50

20.95

83.87

-491.60

-491.70

-428.09

-428.32

A5

85.94

-493.51

151.24

20.71

22.13

149.59

-558.03

-558.84

-428.75

-428.90

B1

-122.38

-457.73

-90.98

-154.24

-153.52

-90.94

-489.54

-489.01

-425.97

-426.36

B2

-122.64

-525.44

-91.06

-155.25

-153.86

-90.55

-558.07

-557.11

-493.08

-493.87

B3

-54.56

-457.73

-22.50

-86.02

-86.17

-23.34

-489.26

-489.55

-426.35

-425.73

B4

-54.34

-525.66

-21.86

-86.33

-86.26

-22.68

-557.98

-557.90

-493.69

-493.43

B5

-89.39

-491.35

-24.02

-154.78

-153.16

-25.52

-556.76

-556.03

-426.71

-426.46

ALL

-1.90

-492.93









BS

-83.58

-496.00










Table 2. NIRCam apertures, center and four corners for all 10 NIRCam detectors in the NIRCam ideal coordinate system tied to the NRCALL aperture. This system is used e.g. by APT to specify the (X,Y) offset special requirement when Module=ALL. Note that while the ALL compound aperture does not have (V2,V3) vertices associated (see Table 1), it does have vertices defined in the Ideal system. Values are in arcseconds.

SCA*

XIdl_ref

YIdl_ref

XIdl_1

XIdl_2

XIdl_3

XIdl_4

YIdl_1

YIdl_2

YIdl_3

YIdl_4

A1

-122.47

-34.77

-154.91

-90.66

-90.56

-153.93

-66.67

-67.22

-2.95

-2.56

A2

-121.73

32.95

-153.49

-90.18

-90.38

-153.01

1.51

1.22

64.47

64.62

A3

-53.84

-35.10

-85.85

-21.30

-22.17

-85.82

-67.39

-67.45

-2.81

-3.10

A4

-54.35

32.92

-86.00

-22.40

-22.93

-85.85

1.22

1.20

64.81

64.50

A5

-87.84

-0.69

-153.06

-22.53

-24.11

-151.56

-65.29

-65.94

64.15

63.84

B1

120.44

35.35

89.08

152.34

151.54

88.96

3.49

4.11

67.14

66.67

B2

120.78

-32.37

89.24

153.43

151.96

88.66

-65.03

-64.00

0.04

-0.83

B3

52.62

35.26

20.59

84.12

84.19

21.36

3.69

3.48

66.68

67.22

B4

52.48

-32.67

20.04

84.52

84.37

20.79

-65.03

-64.87

-0.65

-0.47

B5

87.49

1.68

22.20

152.96

151.18

23.54

-63.80

-62.91

66.41

66.50

ALL

0.00

0.00

-154.91

153.43

151.54

-153.01

-66.67

-64.00

67.14

64.62


Table 3. NIRCam apertures, center and four corners for the 5 module B detectors in the NIRCam ideal coordinate systems tied  to the either the NRCBS or the NRCB5 aperture. These system are used e.g. by APT to specify the (X,Y) offset special requirement when Module = B, and subarray = FULL (BS) or subarray = 160/320/640 (B5). Note that while the BS compound aperture does not have (V2,V3) vertices associated, it does have vertices defined in the Ideal system. Also note that the BS aperture has its reference point located within the footprint of the B4 SCA. On the contrary, the B5 reference point resides in the intra-SCA gap of the 4 SW module B SCAs (see also Figure 1). Therefore, when using MODULE=B and subarray=160/320/640, the target is placed within the gap. This approach was chosen to maximize the area of overlap between the SW and LW channels. When using the SUB160/320/640 subarrays, the placement in the gap might not be problematic for extended sources, but for point sources the users will need to specify an offset special requirement in order to place the target within a physical detector on the SW channel as well, or alternatively use the "point source subarrays" provided in APT and located in the upper left corner of the B module (see NIRCam Detector Subarrays) .  Values are in arcseconds.

Subarray

SCA

XIdl_ref

YIdl_ref

XIdl_1

XIdl_2

XIdl_3

XIdl_4

YIdl_1

YIdl_2

YIdl_3

YIdl_4

FULL

B1

38.83

38.23

7.40

70.66

70.00

7.43

6.45

6.93

69.96

69.63


B2

39.02

-29.48

7.42

71.61

70.28

6.97

-62.07

-61.18

2.86

2.13


B3

-28.99

38.30

-61.08

2.44

2.66

-60.18

6.81

6.45

69.65

70.33


B4

-29.27

-29.63

-61.78

2.69

2.68

-60.90

-61.91

-61.90

2.31

2.64


B5

5.81

4.65

-59.62

71.14

69.65

-57.99

-60.70

-60.09

69.23

69.60


BS

0.00

0.00

-61.78

71.61

70.00

-60.18

-61.91

-61.18

69.96

70.33

SUB160/320/640

B1

33.01

33.60

1.60

64.85

64.17

1.59

1.81

2.31

65.34

64.99


B2

33.23

-34.11

1.64

65.83

64.47

1.16

-66.72

-65.80

-1.76

-2.52


B3

-34.81

33.64

-66.89

-3.36

-3.18

-66.02

2.13

1.81

65.00

65.65


B4

-35.06

-34.29

-67.56

-3.09

-3.13

-66.70

-66.59

-66.55

-2.33

-2.04


B5

0.00

0.00

-65.40

65.36

63.81

-63.83

-65.37

-64.71

64.61

64.93

* Sensor chip assembly



Table 4. NIRCam subarray apertures for coronagraphy in the JWST V2-V3 coordinate system. Starting in Cycle 2, NIRCam coronagraphic imaging is offered simultaneously on the SW and LW channel. Note that the SW and LW apertures have the same pixels size, but have angular sizes in a 1:2 ratio. When the natural channel for a mask is the SW channel, the apertures correspond to a 640x640 pixels subarray, with angular sizes of ~20" and ~40" on the SW and LW channel respectively. When the natural channel for a mask is the LW channel, the apertures correspond to a 320x320 pixels subarray, with angular sizes of ~10" and ~20" on the SW and LW channel respectively. The natural channel is the channel corresponding to the wavelength for which the mask is optimized, for example SW for the 210R mask, optimized at 2.1 microns, or LW for the 430R mask, optimized at 4.3 microns.

MASK

SCA*

V2_ref

V3_ref

V2_1

V2_2

V2_3

V2_4

V3_1

V3_2

V3_3

V3_4

210R


A2

127.34

-405.20

137.15

117.57

117.62

137.15

-415.31

-415.45

-395.71

-395.58

A5

127.34

-405.20

147.15

107.34

107.37

146.98

-425.05

-425.44

-385.17

-384.80

335R


A2

107.31

-405.15

112.17

102.39

102.43

112.20

-410.09

-410.10

-400.23

-400.22

A5

107.31

-405.15

116.59

96.72

96.76

116.59

-416.02

-416.10

-395.96

-395.90

430R


A2

87.29

-405.11

96.28

86.50

86.55

96.32

-410.10

-410.07

-400.18

-400.22

A5

87.29

-405.10

96.59

76.70

76.80

96.64

-416.10

-416.07

-395.91

-395.96

SWB


A4

67.16

-405.06

76.94

57.31

57.29

76.87

-415.44

-415.44

-395.63

-395.67

A5

67.16

-405.07

86.95

47.06

47.41

87.10

-425.29

-425.06

-384.63

-385.00

LWB


A4

43.29

-404.91

49.42

37.12

37.14

49.43

-408.93

-408.84

-400.90

-401.00

A5

43.29

-404.91

55.31

30.31

30.47

55.43

-414.17

-413.84

-397.64

-398.02


Scroll right to view the full table. 

* Sensor chip assembly

SCA used for Target Acquisition with this mask

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.



References

Cox C. & Lallo M., 2017, JWST-STScI-001550
Description and Use of the JWST Science Instrument Aperture File





Latest updates

  • Added coronagraphic apertures for Cycle 2. Several clarifications in the text. Added tables in Idl coordinates.

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