This tool is an aid to the community for determining if an object of interest will be in the Kepler field-of-view (FOV). The figure above provides a graphical representation of the layout of the CCDs, the location of the 84 channels, and row/column directions. The coordinates in the graphic are probably good to within about 1 arc minute. Each square module in the figure is composed of two rectangular CCDs with a small gap between the CCDs.
This tool will provide the precise values for the data channel, and the CCD row and column of the center of the point spread function of the object. The CCD data channels are numbered 1 to 84. Each channel has 1024 rows and 1100 columns. The 0,0 for each channel is in the corner of the module. Row 1024 is at the gap between two CCDs on a module. Column 1100 is where the two channels on a CCD meet in the middle of the CCD chip. A single pixel is 3.98 arcsec on a side.
If a row or column is less than 0 or a row is greater than 1024, the object is just off the CCD by a small amount. Objects that are off by large amounts will not have a calculated value, only a flag and message to indicate as much.
There are a number of caveats:
- This is based on the current design, which may change. The CCDs and optics are already being made so they won't change. The pointing on the sky may change.
- The precise CCD locations in the focal plane will have an uncertainty of a few pixels and will not be known until after launch
- Objects near the edges of the CCDs may be of marginal quality, since the psf for a point source is on the order of 2.5 to 5 pixels in size (95% encircled energy) and part of the psf may be off the edge of the CCD.
- The location of bad pixels is unknown at this time.
- Due to the very large FOV spanning nearly 15 degrees. differential velocity abberation causes the FOV to expand and contract by about 6 arcsec on an annual basis as the spacecraft orbits the Sun. This means that an object near the edge of the FOV will move by about 3/4 of a pixel. This is built into the automated target aperture definition (TAD) program used in the Science Operation Center at Ames.
The spacecraft will be rotated 90 degrees every 3 months to keep the Sun on the solar array and the radiator pointed to deep space to cool the CCDs. The layout of the focal plane is four-fold symmetric so that to within a few pixels the same stars are imaged onto active silicon independent of the rotation. Thus the CCD data channel changes with the season and the exact pixel location will move slightly.
So one needs to first pick the "season" and then enter the coordinates.