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desihub / desispec

DESI spectral pipeline
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negative sky flux #981

Open sbailey opened 4 years ago

sbailey commented 4 years ago

As reported by @dkirkby, 60 second exposures often have negative sky models <4400 A, e.g. image This does not seem to be an issue for longer exposures, e.g. the previous spectroscopic exposure on the same night. image

20200225/52081 is a case of a 300 sec exposure where the sky model dips negative: image

The overall structure looks like an underlying CCD calibration problem (darks, biases) so start by inspecting the raw and pre-processed images. This is related to #978 (update master bias, dark).

dkirkby commented 4 years ago

For completeness, here is the list of all Andes exposures with EXPTIME >= 300s where SKY * IVAR < 0 in at least one wlen bin:

52081 52082 52083 52084 52085 52086 52087 52088 52089 52309