MOS background sources are assigned lower left source position #8459
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7 tasks
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Comment by Howard Bushouse on JIRA: Fixed by #8461 |
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Christian Hayes Can you please take a look at this for the NIRSpec team and close it out? |
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Comment by Christian Hayes on JIRA: The change looks good to me, closing this ticket. |
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Issue JP-3612 was created on JIRA by Melanie Clarke:
In assign_wcs for NIRSpec MOS observations, for background-only slits, any input x and y position for the source is ignored ('estimated_source_in_shutter_x', 'estimated_source_in_shutter_y' in the MSA file). The 'source_xpos' and 'source_ypos' values for the slit are set to 0.0 (line 665-666, jwst/assign_wcs/nirspec.py). However, these values are later corrected by -0.5, to account for the difference between the MSA coordinate origin and the model coordinate origin (line 724-725, jwst/assign_wcs/nirspec.py). This puts the background source location at -0.5, -0.5, which is the lower left corner of the slit.
I think it was probably intended to put the source position for the background at the center of the slit, not the lower left corner. Line 665-666 should be corrected to set the background slit source position to 0.5, 0.5. This will impact the point source pathloss correction, computed and stored by default for every slit, but should not otherwise impact processing for background slits, since they are always treated as uniform sources.
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