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Q: How do I observe extended source objects?
A: Similar to point sources (see question above), but you must dither your object ON and OFF the slit. A quad would look like ON-OFF-OFF-ON, similar to an ABBA quad but with ~1/√2 times the S/B since you are not getting signal during OFF exposures. The pipeline will subtract the OFF frames from the ON frames to subtract the sky, dark, and bias.
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(S/N)corr = [ (S/N)sci-2 + (S/N)std-2]-1/2
where (S/N)sci is the S/N for your science target and (S/N)std is the S/N for your A0 telluric standard. It is clear that the smallest S/N will dominate the sum of (S/N)sci-2 + (S/N)std-2, thus would dominate (S/N)corr. Go to this page to estimate A0 star S/N or use the ETC.
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- ~5-10 minutes to acquire a new target withe telescope with telescope, make sure your pointing is good, and begin properly guiding. It is usually a good idea to have a finder chart ready ahead of time to speed this process up, especially for dimmer targets (see Kyle's IGRINS Observability program).
- ~1 minute between each exposure for readout, and dithering between AB or ON-OFF positions. Allow an extra minute 1-2 minutes when dithering between ON-OFF to reacquire guiding (~5 minutes per quad).
- ~20 minutes for an A0 telluric standard (depending on the star's magnitude, see this page for estimating S/N for telluric stds.)
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