Phase 2 Proposal Instructions for Cycle 10
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Phase 2 Proposal Instructions for Cycle 10 | |||
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8.4 Convenience Patterns
To minimize confusion, the following patterns use the new syntax but have been constructed to duplicate the earlier pattern forms. Their nomenclature is meant to be obvious, so that ÒWFPC2-LINEÓ means the former ÒLINEÓ pattern for WFPC2, for example. After each description we show what the RPS2 entries would look like.
A specific entry for a parameter (such as 0.559 for Point_Spacing with WFPC2-BOX) means that value may not be changed and doing so will cause an error. An indicated range (such as 2-10 for Number_of_Points in WFPC2-LINE) means you may select from within that range, and a Ò?Ó 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 Secondary_Pattern, 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 Secondary_Pattern when the indicated one is the Primary_Pattern. When both a Primary_Pattern and a Secondary_Pattern are shown for a given Pattern_Type, both must be used.
8.4.1 WFPC2 Patterns
Note that these new patterns move HST in the opposite direction to the previously-provided WFPC2 patterns. Consult the WFPC2 Instrument Handbook for more information.
To see an illustration of the WFPC2 POS-TARG reference frame, go to 9.4WFPC2 Aperture Coordinate System.
Pattern_Type: WFPC2-LINE
This produces a single-line scan, with its default orientation along a 45-degree diagonal with respect to the pixels of the primary camera. The default and strongly recommended single-line dither scan is a two-point scan with a spacing of 0.3535 arcsec between points. This yields an offset of (2.5, 2.5) pixels in the WFC CCDs and (5.5, 5.5) pixels in the PC. This default offset is optimized for resolution enhancement.
If these defaults are not acceptable, the Number_Of_Points, Point_Spacing, and Pattern_Orient parameters may be used to vary the spacing and number of points along the line, and to change the orientation of the line. For example, observers interested only in removing CCD artifacts may prefer to use an integral-pixel offset, as this will simplify the data analysis. An example of an integral-pixel line dither is Point_Spacing: 0.707, which provides offsets of (5,5) pixels in the WFC CCDs and (11,11) pixels in the PC. Please discuss the use of these parameters with your Contact Scientist.
Number_of_Points:2-10 (default 2)
Point_Spacing:0.01-3.0 (default 0.3535)
Permitted Secondary_Pattern values: LINE, SPIRAL.
Pattern_Type: WFPC2-BOX
This will produce a four-point parallelogram scan. 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") (0.5", 0.25") (0.75", 0.75") (0.25", 0.5")
This default box pattern produces offsets on 0.25 arcsec centers, which represent 2.5 WFC pixels and 5.5 PC pixels. These offsets are optimized for resolution enhancement. If a box-type pattern other than this recommended parallelogram is desired, the POSition TARget special requirement may be used; see POSition TARGet <X-value>, <Y-value>.
The Pattern_Purpose for WFPC2-BOX is DITHER. The Number_Of_Points is 4. The Point_Spacing is 0.559 arcsec. The Coordinate_Frame is POS-TARG. The Pattern_Orient is fixed at 26.565 degrees.
Permitted Secondary_Pattern values: LINE, SPIRAL.
To see an illustration of the WFPC2 POS-TARG reference frame, go to 9.4WFPC2 Aperture Coordinate System.
8.4.2 STIS Patterns
To see an illustration of the STIS POS-TARG reference frame, go to 10.9STIS Coordinate System.
Pattern_Type: STIS-PERP-TO-SLIT
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.
Pattern_Type:STIS-PERP-TO-SLIT
Permitted Secondary_Pattern values: STIS-ALONG-SLIT, LINE.
Pattern_Type: STIS-ALONG-SLIT
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) direction.
Permitted Secondary_Pattern values: none.
To see an illustration of the STIS POS-TARG reference frame, go to 10.9STIS Coordinate System.
Pattern_Type: STIS-CCD-BOX
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.
Point_Spacing:0.0567-5.67 (default 0.567)
Pattern_Orient:? (default 26.6)
Permitted Secondary_Pattern values: none.
To see an illustration of the STIS POS-TARG reference frame, go to 10.9STIS Coordinate System.
Pattern_Type: STIS-MAMA-BOX
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.
Point_Spacing:0.0275-2.75 (default 0.275)
Pattern_Orient:? (default 26.6)
Permitted Secondary_Pattern values: none.
Pattern_Type: STIS-SPIRAL-DITH
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 Secondary_Pattern values: none.
To see an illustration of the STIS POS-TARG reference frame, go to 10.9STIS Coordinate System.
For general information on ACS patterns, please see the Instrument Science Report titled ÒACS Dither and Mosaic Pointing Patterns,Ó to be found at
That document also includes information on modifying these patterns, so they may be used for sub-pixel dithering, for example.
Pattern_Type: ACS-WFC-DITHER-LINE
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.
Pattern_Type: ACS-WFC-DITHER-LINE
Number_Of_Points: 2-9 (default 2)
Point_Spacing: 0.01 - 10.0 (default 3.011)
Pattern_Orient: ? (default 85.28)
Center_Pattern: ? (default NO)
Pattern_Type: ACS-WFC-DITHER-BOX
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)Ña 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.
Pattern_Type: ACS-WFC-DITHER-BOX
Center_Pattern: ? (default NO)
Pattern_Type: ACS-WFC-MOSAIC-LINE
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 adn to cover the interchip gap as well.
Pattern_Type: ACS-WFC-MOSAIC-LINE
Number_Of_Points: 2-9 (default 2)
Point_Spacing: 10.0 - 130.0 (default 96.816)
Pattern_Orient: ? (default 90.0)
Center_Pattern: ? (default YES)
Pattern_Type: ACS-WFC-MOSAIC-BOX
This is a 4-point box pattern for creating a WFC mosaic roughly 400x300 arcseconds. This pattern strikes a compromise with a y-shift that covers the interchip 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:
Pattern_Type: ACS-HRC-DITHER-LINE
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.
Pattern_Type: ACS-HRC-DITHER-LINE
Number_Of_Points: 2-9 (default 2)
Point_Spacing: 0.01 - 10.0 (default 0.198)
Pattern_Orient: ? (default 44.28)
Center_Pattern: ? (default NO)
Pattern_Type: ACS-HRC-DITHER-BOX
Same as ACS-WFC-DITHER-BOX, but for the HRC detector.
Pattern_Type: ACS-HRC-DITHER-BOX
Center_Pattern: ? (default NO)
Pattern_Type: ACS-HRC-MOSAIC-LINE
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.
Pattern_Type: ACS-HRC-MOSAIC-LINE
Number_Of_Points: 2-9 (default 2)
Point_Spacing: 10.0 - 130.0 (default 24.130)
Pattern_Orient: ? (default 90.0)
Center_Pattern: ? (default YES)
Pattern_Type: ACS-HRC-MOSAIC-BOX
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.
Pattern_Type: ACS-HRC-MOSAIC-BOX
Center_Pattern: ? (default YES)
Pattern_Type: ACS-SBC-DITHER-LINE
General SBC dither line pattern. This pattern shifts the image on the diagonal (10 pixels in x and y).
Pattern_Type: ACS-SBC-DITHER-LINE
Number_Of_Points: 2-9 (default 2)
Point_Spacing: 0.01 - 10.0 (default 0.472)
Pattern_Orient: ? (default 44.40)
Center_Pattern: ? (default NO)
Pattern_Type: ACS-SBC-DITHER-BOX
Same as ACS-WFC-DITHER-BOX, but for the SBC detector.
Pattern_Type: ACS-SBC-DITHER-BOX
Center_Pattern: ? (default NO)
Pattern_Type: ACS-SBC-MOSAIC-LINE
General SBC mosaic line pattern. This pattern shifts the image by 95% in y to roughly double the FOV.
Pattern_Type: ACS-SBC-MOSAIC-LINE
Number_Of_Points: 2-9 (default 2)
Point_Spacing: 10.0 - 130.0 (default 28.801)
Pattern_Orient: ? (default 90.0)
Center_Pattern: ? (default YES)
Pattern_Type: ACS-SBC-MOSAIC-BOX
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.
Pattern_Type: ACS-SBC-MOSAIC-BOX
Center_Pattern: ? (default YES)
8.4.3 NICMOS Patterns
See the NICMOS Instrument Handbook for a full discussion of how and why to use patterns and for complete illustrations of their geometries.
Pattern_Type: NIC-XSTRIP-DITH
This specifies a linear pattern of offsets in the POS TARG +X direction.
Permitted Secondary_Pattern values: NIC-YSTRIP-DITH, NIC-SPIRAL-DITH, NIC-SPIRAL-MAP, NIC-SQUARE-WAVE-DITH, LINE, SPIRAL.
Pattern_Type: NIC-YSTRIP-DITH
This specifies a linear pattern of offsets in the POS TARG +Y direction.
Permitted Secondary_Pattern values: NIC-XSTRIP-DITH, NIC-SPIRAL-DITH, NIC-SPIRAL-MAP, NIC-SQUARE-WAVE-DITH, LINE, SPIRAL.
Pattern_Type: NIC-SPIRAL-DITH
This specifies a spiral dither pattern.
Permitted Secondary_Pattern values: NIC-XSTRIP-DITH, NIC-YSTRIP-DITH, NIC-SPIRAL-MAP, NIC-SQUARE-WAVE-DITH, LINE, SPIRAL.
Pattern_Type: NIC-SPIRAL-MAP
This specifies a spiral mosaic pattern.
Permitted Secondary_Pattern values: NIC-XSTRIP-DITH, NIC-YSTRIP-DITH, NIC-SPIRAL-DITH, NIC-SQUARE-WAVE-DITH, LINE, SPIRAL.
Pattern_Type: NIC-SQUARE-WAVE-DITH
This specifies a square-wave pattern with the ÒamplitudeÓ of the square wave along the POS TARG +Y axis and the main direction of motion along the POS TARG +X axis.
Pattern_Type:NIC-SQUARE-WAVE-DITH
Line_Spacing:Equal to Point_Spacing
Permitted Secondary_Pattern values: NIC-XSTRIP-DITH, NIC-YSTRIP-DITH, NIC-SPIRAL-DITH, NIC-SPIRAL-MAP, LINE, SPIRAL.
Pattern_Type: NIC-ONE-CHOP
This requires two pattern definitions. It specifies a repeated ÒchopÓ back and forth along the POS TARG +X axis.
Other permitted Secondary_Pattern values: none.
Pattern_Type: NIC-TWO-CHOP
This requires two pattern definitions. It specifies a repeated ÒchopÓ along the POS TARG +X axis, similar to NIC-ONE-CHOP, but using four points instead of two.
Line_Spacing:Equal to Point_Spacing
Other permitted Secondary_Pattern values: none.
Pattern_Type: NIC-SPIRAL-DITH-CHOP
This requires two pattern definitions. It specifies a combination of a spiral pattern and a two-point line (the ÒchopÓ).
Pattern_Type:NIC-SPIRAL-DITH-CHOP
Pattern_Type:NIC-SPIRAL-DITH-CHOP
Pattern_Orient: Equal to <Primary_Pattern value>
Other permitted Secondary_Pattern values: none.
Pattern_Type: NIC-MAP
This specifies a linear mosaic pattern oriented on the sky.
Other permitted Secondary_Pattern values: none.
Pattern_Type: NIC-SKY-ONE-CHOP
This requires two pattern definitions. It specifies a pattern similar to NIC-ONE-CHOP, except that it is oriented on the sky.
Other permitted Secondary_Pattern values: none.
Pattern_Type: NIC-SKY-TWO-CHOP
This requires two pattern definitions. It specifies a pattern similar to NIC-TWO-CHOP, except that it is oriented on the sky.
Line_Spacing:Equal to Point_Spacing
Other permitted Secondary_Pattern values: none.
Pattern_Type: NIC-SKY-SPIRAL-DITH-CHOP
This requires two pattern definitions. It specifies a combination of a spiral pattern and a two-point line (the ÒchopÓ), similar to NIC-SPIRAL-DITH-CHOP except that the pattern is oriented on the sky.
Pattern_Type:NIC-SKY-SPIRAL-DITH-CHOP
Pattern_Type:NIC-SKY-SPIRAL-DITH-CHOP
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