The following patterns use the new syntax but have been constructed to duplicate the earlier pattern forms (if applicable). Their nomenclature is meant to be obvious; for example, "STIS-CCD-BOX" means the former "box" pattern for the STIS CCD. After each description we show what the information would look like.
A specific entry for a parameter (such as 4 for Number_of_Points with STIS-CCD-BOX) means that value may not be changed and doing so will cause an error. An indicated range (such as 0.0275-2.75 for Point_Spacing in STIS-MAMA-BOX) means you may select from within that range, and a "?" means any numeric value may be entered.
As noted above, you may also nest patterns, but not all combinations make sense. In the first place, if you use both a Primary_Pattern and a Sub-Pattern (or Secondary_Pattern in the Text Proposal File), they should be for the same instrument or at least one should be generic. Do not mix instrument-specific patterns. We have shown below which other patterns may validly be used as a Sub-Pattern when the indicated one is the Primary_Pattern. When both a Primary_Pattern and a Sub-Pattern are shown for a given Pattern_Type, both must be used.
To see an illustration of the STIS POS-TARG reference frame, go to Section 9.9 .
This is normally used with a spectroscopic slit. It produces a scan along the POS TARG X-axis of the aperture; this is used to map a two-dimensional region of the sky (see Chapter 11 of the STIS Instrument Handbook). The target is moved perpendicular to the slit along the AXIS1 (dispersion) direction.
Permitted Sub-Pattern (Secondary_Pattern) values: STIS-ALONG-SLIT, LINE.
This is also normally used with a spectroscopic slit. It produces a scan along the POS TARG Y-axis of the aperture; this is used to step a target along the long slit to dither bad pixels or improve spatial resolution (see the STIS Instrument Handbook). The target is moved along the slit in the AXIS2 (cross-dispersion or spatial) direction.
Permitted Sub-Pattern (Secondary_Pattern) values: none.
To see an illustration of the STIS POS-TARG reference frame, go to Section 9.9 .
This will produce a four-point parallelogram scan designed for dithering across the CCD pixels. With the default Point_Spacing of 0.567, the four points of the parallelogram will be obtained at the following POS TARG (X,Y) offsets relative to the default aperture position:
(0.0", 0.0") (0.5070", 0.2535") (0.7605", 0.7605") (0.2535", 0.5070")
This default produces a parallelogram pattern (see diagram) with projected offsets from the starting point of 5n integer pixels in each coordinate, so that the above arcsec values correspond to pixel values of (0, 0), (10, 5), (15, 15), and (5, 10). With these integer-pixel offsets, the pattern is optimized to simultaneously compensate for hot pixels and small-scale detector non-uniformities. The pattern can be rescaled (e.g., by a factor of 0.5) to achieve shifts of N+half pixels for resolution enhancement by changing the Point_Spacing.
Permitted Sub-Pattern (Secondary_Pattern) values: none.
To see an illustration of the STIS POS-TARG reference frame, go to Section 9.9 .
This will produce a four-point parallelogram scan designed for dithering across the MAMA pixels. With the default Point_Spacing of 0.275, the four points of the parallelogram will be obtained at the following POS TARG (X,Y) offsets relative to the default aperture position:
(0.0", 0.0") (0.246", 0.123") (0.369", 0.369") (0.123", 0.246")
This default produces a parallelogram pattern (see diagram) with projected offsets from the starting point of 5n integer pixels in each coordinate, so that the above arcsec values correspond to pixel values of (0, 0), (10, 5), (15, 15), and (5, 10). With these integer-pixel offsets, the pattern is optimized to simultaneously compensate for hot pixels and small-scale detector non-uniformities. The pattern can be rescaled (e.g., by a factor of 0.5) to achieve shifts of N+half pixels for resolution enhancement by changing the Point_Spacing.
Permitted Sub-Pattern (Secondary_Pattern) values: none.
This produces a spiral dither pattern, starting at the center and moving outward counterclockwise. Note that a STIS-SPIRAL-DITH with four points yields a square pattern, but the optimum pattern for detector dithering to enhance resolution is either STIS-CCD-BOX or STIS-MAMA-BOX.
Permitted Sub-Pattern values: none.
To see an illustration of the STIS POS-TARG reference frame, go to Section 9.9 .
For general information on ACS pointing, and a library of carefully designed dither and mosaic pointing patterns (ready for use in a Phase II proposal), see the following Web page:
http://www.stsci.edu/hst/acs/proposing/dither
In addition to the default patterns provided below, many non-default variations are included in the pattern library (e.g., for hot pixel rejection, sub-pixel dithering, etc.) and parameters are updated using the latest distortion solution. Helpful diagrams and descriptions are provided along with Phase II pattern parameters.
General WFC dither line pattern. The default for this pattern shifts the image by 5 pixels in x and 60 in y in order to span the gap between the two WFC detectors.
Permitted Sub_Pattern (Secondary_Pattern) values: any other ACS/WFC patterns, LINE, BOX, SPIRAL
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Note: All ACS/WFC (and HRC) users are encouraged to use some form of dithering to allow for correction of hot pixels during data processing. The standard CR-SPLIT approach does not eliminate hot pixels (See Section 11.2.4). Users who would normally have taken that approach in the past are now encouraged to define and use instead the pattern: |
This is the default WFC box pattern. It is a 4-point pattern with relative pixel coordinates (0, 0), (5.0, 1.5), (2.5, 4.5), (-2.5, 3.0)-a parallelogram pattern with a combination of integer and sub-pixel shifts, which is relatively compressed in one dimension compared to its WFPC2 and STIS counterparts. This minimizes the effect of scale variation across the detector.
Permitted Sub_Pattern (Secondary_Pattern) values: any other ACS/WFC patterns, LINE, BOX, SPIRAL
General WFC mosaic line pattern. The default shift is in the y direction by 47% of the detector dimension, resulting in a field-of-view that is about 200x300 arcsec. This is a compromise which allows the 2-point WFC mosaic to be performed with one set of guide stars and to cover the inter chip gap as well.
Permitted Sub_Pattern (Secondary_Pattern) values: any other ACS/WFC patterns, LINE, BOX, SPIRAL
This is a 4-point box pattern for creating a WFC mosaic roughly 400x300 arc seconds. This pattern strikes a compromise with a y-shift that covers the inter chip gap (with one set of guide stars) and the maximum x-shift to expand the field of view. So another set of guide stars would be needed only for the x shifts, which are 95% of the detector x dimension (~193 arcsec).
Another useful WFC mosaic box pattern would maximize the field of view (~400x400 arcseconds). For this pattern, both the x and y shifts are ~95% of the detector dimensions, and would require multiple guide stars.
This pattern is also not supported in the ground system, but may be set up by hand using the following POS TARG offsets:
General HRC dither line pattern. The default for this pattern shifts the image by 5 pixels in x and 5 in y (i.e., on the diagonal) and is useful for removing WFC artifacts.
Permitted Sub_Pattern (Secondary_Pattern) values: any other ACS/HRC patterns, LINE, BOX, SPIRAL
Same as ACS-WFC-DITHER-BOX, but for the HRC detector.
Permitted Sub_Pattern (Secondary_Pattern) values: any other ACS/HRC patterns, LINE, BOX, SPIRAL
General HRC mosaic line pattern. The default creates a mosaic that shifts the images by 95% of its size in y to roughly double the FOV.
Permitted Sub_Pattern (Secondary_Pattern) values: any other ACS/HRC patterns, LINE, BOX, SPIRAL
This is a large 4-point box pattern for creating a mosaic roughly 4 times the HRC field-of-view, or ~52x52 arcsec. The shifts are 95% of the detector dimensions (~973 pixels or ~27.5 arcsec) along both the x and y axes of the detector. Center_Pattern defaults to YES so the target will be at the center of the pattern.
Permitted Sub_Pattern (Secondary_Pattern) values: any other ACS/HRC patterns, LINE, BOX, SPIRAL
General SBC dither line pattern. This pattern shifts the image on the diagonal (10 pixels in x and y).
Permitted Sub_Pattern (Secondary_Pattern) values: any other ACS/SBC patterns, LINE, BOX, SPIRAL
Same as ACS-WFC-DITHER-BOX, but for the SBC detector.
Permitted Sub_Pattern (Secondary_Pattern) values: any other ACS/SBC patterns, LINE, BOX, SPIRAL
General SBC mosaic line pattern. This pattern shifts the image by 95% in y to roughly double the FOV.
Permitted Sub_Pattern (Secondary_Pattern) values: any other ACS/SBC patterns, LINE, BOX, SPIRAL
This is a large 4-point box pattern for creating a mosaic roughly 4 times the SBC field-of-view, or ~64x64 arcsec. The shifts are 95% of the detector dimensions (~973 pixels or ~32 arcsec) along both the x and y axes of the detector.
Permitted Sub_Pattern (Secondary_Pattern) values: any other ACS/SBC patterns, LINE, BOX, SPIRAL
See the NICMOS Instrument Handbook for a full discussion of how and why to use patterns and for complete illustrations of their geometries.
This specifies a linear pattern of offsets in the POS TARG +X direction.
Permitted Sub-Pattern (Secondary_Pattern) values: NIC-YSTRIP-DITH, NIC-SPIRAL-DITH, NIC-SPIRAL-MAP, NIC-SQUARE-WAVE-DITH, LINE, SPIRAL.
This specifies a linear pattern of offsets in the POS TARG +Y direction.
Permitted Sub-Pattern (Secondary_Pattern) values: NIC-XSTRIP-DITH, NIC-SPIRAL-DITH, NIC-SPIRAL-MAP, NIC-SQUARE-WAVE-DITH, LINE, SPIRAL.
This specifies a spiral dither pattern.
Permitted Sub-Pattern (Secondary_Pattern) values: NIC-XSTRIP-DITH, NIC-YSTRIP-DITH, NIC-SPIRAL-MAP, NIC-SQUARE-WAVE-DITH, LINE, SPIRAL.
This specifies a spiral mosaic pattern.
Permitted Sub-Pattern (Secondary_Pattern) values: NIC-XSTRIP-DITH, NIC-YSTRIP-DITH, NIC-SPIRAL-DITH, NIC-SQUARE-WAVE-DITH, LINE, SPIRAL.
This specifies a square-wave pattern with the "amplitude" of the square wave along the POS TARG +Y axis and the main direction of motion along the POS TARG +X axis.
Permitted Sub-Pattern (Secondary_Pattern) values: NIC-XSTRIP-DITH, NIC-YSTRIP-DITH, NIC-SPIRAL-DITH, NIC-SPIRAL-MAP, LINE, SPIRAL.
This requires two pattern definitions. It specifies a repeated "chop" back and forth along the POS TARG +X axis.
Other permitted Sub-Pattern (Secondary_Pattern) values: none.
This requires two pattern definitions. It specifies a repeated "chop" along the POS TARG +X axis, similar to NIC-ONE-CHOP, but using four points instead of two.
Other permitted Sub-Pattern (Secondary_Pattern) values: none.
This requires two pattern definitions. It specifies a combination of a line pattern and a two-point line at right angles (the "chop").
Other permitted Sub-Pattern (Secondary_Pattern) values: none.
This requires two pattern definitions. It specifies a combination of a line pattern and a two-point line at right angles (the "chop").
Other permitted Sub-Pattern (Secondary_Pattern) values: none.
This requires two pattern definitions. It specifies a combination of a spiral pattern and a two-point line (the "chop").
Other permitted Sub-Pattern (Secondary_Pattern) values: none.
This specifies a linear mosaic pattern oriented on the sky.
Other permitted Sub-Pattern (Secondary_Pattern) values: none.
This requires two pattern definitions. It specifies a pattern similar to NIC-ONE-CHOP, except that it is oriented on the sky.
Other permitted Sub-Pattern (Secondary_Pattern) values: none.
This requires two pattern definitions. It specifies a pattern similar to NIC-TWO-CHOP, except that it is oriented on the sky.
Other permitted Sub-Pattern (Secondary_Pattern) values: none.
This requires two pattern definitions. It specifies a combination of a spiral pattern and a two-point line (the "chop"), similar to NIC-SPIRAL-DITH-CHOP except that the pattern is oriented on the sky.
Other permitted Sub-Pattern (Secondary_Pattern) values: none.
Please see Appendix C3 of the WFC3 Instrument Handbook for general information on WFC3 patterns, and Appendix B for information on geometric distortion. The step sizes in pixels specified below apply to the central regions of the detectors. For smaller steps, the steps in pixels are accurate over a larger region of the detectors.
This pattern dithers the UVIS aperture by (2.5, 2.5) pixels to sample the point spread function with fractional pixel steps.
This pattern for WFC3/UVIS samples the point spread function with fractional pixel steps and produces spacings of more than one column to move hot columns. The relative steps in pixels are (0, 0), (4.0, 1.5), (2.5, 4.0), and (-1.5, 2.5).
The primary pattern dithers over the gap between the two chips of the UVIS detector with relative steps of (-4.5,-60.25), (0, 0), and (4.5, 60.25) pixels. The secondary pattern adds a dither of (2.5, 1.5) pixels to the primary pattern.
This pattern produces a UVIS mosaic that can be executed with a single set of guide stars. It dithers the gap between the chips so that no region lies in the gap more than once. The relative steps in pixels are approximately (-1000, -997), (1000, -1001), (1000, 997), and (-1000,1001).
This pattern is designed for observations using the full WFC3/UVIS detector for primary exposures and the full ACS/WFC detector for parallel exposures. It dithers over the interchip gap on both detectors. The relative steps on the WFC3/UVIS detector are (0, 0) and (36.5, 71.5) pixels.
This pattern for WFC3/IR takes steps large enough for photometric accuracy and samples the point spread function with fractional pixel steps. The relative steps in pixels are (0, 0) and (3.5, 3.5).
This pattern for WFC3/IR takes steps just large enough for photometric accuracy and samples the point spread function with fractional pixel steps. The relative steps in pixels are (0, 0), (4.0, 1.5), (2.5, 4.0), and (-1.5, 2.5).
This is a four-point box pattern that produces an IR mosaic covering the same area as the UVIS detector. The IR imaging is intended to be accompanied by a UVIS exposure (or small dither pattern) using the aperture UVIS or UVIS-FIX or UVIS-CENTER (when implemented). If UVIS or UVIS-FIX is used, the UVIS exposures should use the Target Position Requirement, POS TARG Y = -12 arcsec, to achieve the same centering of the target in the UVIS exposures and the IR mosaic.
There are no predefined patterns for COS.
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