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NIRSpec and MIRI IFU master background subtraction: nodded backgrounds #5

Open eslavichjgbot opened 5 years ago

eslavichjgbot commented 5 years ago

Issue JP-521 was created on JIRA by Howard Bushouse:

Spectroscopic master background subtraction for the NIRSpec IFU and MIRI MRS modes can use exposures that nod a small source to different locations in the FOV, leaving enough area from which to sample the background and form the master background spectrum, which is then subtracted from the nodded 2-D exposures.

It is likely that the existing calspec x1d products for these exposures will not be useful (at least not easily) for creating the master background spectrum, because those spectra will be dominated by the source. Unique extractions within the IFU cubes (s3d products) of each exposures will likely be necessary in order to sample only the background regions of the cube data.

eslavichjgbot commented 5 years ago

Comment by Howard Bushouse on JIRA:

Nodded NIRSpec IFU exposures can be identified via the "2-POINT-NOD" and "4-POINT-NOD" values for the dither pattern type selected by the user in the APT.

eslavichjgbot commented 5 years ago

Comment by Howard Bushouse on JIRA:

Similary, MIRI MRS exposures to be treated as nodded are identified by the user APT selections of Dither Type = "2-Point" or "4-Point", with the dither Optimized For = "POINT SOURCE". It's not known at this time exactly which science product header keywords will contain these selections from the APT.

The 4-point nod pattern produces the same large-ish nod positions as the 2-point pattern, with a small sub-pixel dither added to each of the 2 main pattern positions.