WFPC2 Mosaic Patterns

This webpage contains large-scale WFPC2 mosaic patterns designed to increase the field-of-view for large targets. See the WFPC2 dither pattern webpage for patterns designed to improve the rejection of detector artifacts, and/or create sub-sampled data. See the pointing patterns top page for general information about WFPC2 pointing. See diagrams of these mosaic patterns projected onto the sky below. Send your pointing questions to the STScI Help Desk (help@stsci.edu).

MOSAIC LINE patterns

These two mosaic LINE patterns produce large mosaic shifts when using all chips (pattern 21) and just the WF2-WF3 chips (pattern 22). They leave about 5% overlap. See Figures 1 and 2, below.

     Pattern_Number: 21
       Pattern_Type: LINE
    Pattern_Purpose: MOSAIC
   Number_Of_Points: 2
      Point_Spacing: 99.599
   Coordinate_Frame: POS-TARG
     Pattern_Orient: 45.00
     Center_Pattern: NO

POS TARG equivalent:  0.000,  0.000
                     70.427, 70.427

     Pattern_Number: 22
       Pattern_Type: LINE
    Pattern_Purpose: MOSAIC
   Number_Of_Points: 2
      Point_Spacing: 74.7
   Coordinate_Frame: POS-TARG
     Pattern_Orient: 180.00
     Center_Pattern: NO

POS TARG equivalent:   0.000,  0.000
                     -74.700,  0.000

Note that as shifts approach 100 arcsec, it becomes more difficult to find guide stars. So the 100 arcsec shift in patern 21 can be reduced a bit to improve scheduleability, but pattern 22 is probably a better alternative, especially due to the WF4 bias problems.

MOSAIC BOX patterns

This mosaic BOX pattern is about as large as you can hope to conduct in one visit (with one guide star pair), since the shifts add up to a diagonal shift approaching 100 arcsec. This pattern could be compressed a bit (keep reducing the spacings until you have guide stars), or it may have to be split into two visits (iterations of pattern 22). See Figure 3 below.

     Pattern_Number: 23
       Pattern_Type: BOX
    Pattern_Purpose: MOSAIC
   Number_Of_Points: 4
      Point_Spacing: 74.700
       Line_Spacing: 74.700
   Coordinate_Frame: POS-TARG
     Pattern_Orient: 90.00
Angle_Between_Sides: 270.00
     Center_Pattern: NO

POS TARG equivalent:  0.000,  0.000
                      0.000, 74.700
                     74.700, 74.700
                     74.700,  0.000

A special note about large long-term observing programs

For very large programs, it is impossible to obtain all the observations at the same ORIENT, and more complicated pointing strategies are required. The User Information Report available below describes how Large programs can affect the overall schedule of HST and how observers can optimize their scientific return while minimizing difficulties in scheduling their program: www.stsci.edu/hst/proposing/docs/LargePrograms/.

Figure 1: WFPC2 mosaic LINE pattern 21 Figure 2: WFPC2 mosaic LINE pattern 22 Figure 3: WFPC2 mosaic BOX pattern 23