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my-ccd-guide.md

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Preface

Understanding an astronomical CCD image

Counts, photons and electrons

Burp

Not all counts are light

Your detector is not ideal

Construction of an artificial (but realistic) image

Calibration overview

Image combination

Calibration choices you need to make

Handling overscan, trimming, and bias subtraction

Inspect your images and make a choice about next steps

Subtract overscan, if desired

Trim, if needed

Combine bias images to make master

Dark current and hot pixels

The ideal case: your dark frames measure dark current, which scales linearly with time

Reality: most of your dark frame is noise and not all of the time dependent artifacts are dark current

Identifying hot pixels

Make a choice about next steps for darks

Subtract bias, if necessary

Interlude: Image masking

Identifying bad pixels

Creating a mask

incorporating the mask in reduction

Flat corrections

There are no perfect flats

Make a choice about next steps for flats

Calibrating the flats

Subtract overscan and trim, if necessary

Subtract bias, if necessary

Subtract dark current, scaling if necessary (scale down when possible)

Combining flats

Reducing science images

Initial reduction

Subtract overscan and trim, if necessary

Subtract bias, if necessary

Subtract dark current, scaling if necessary (scale down when possible)

Flat correct

Cosmic ray removal

Combining images

Combine without aligning to create a sky flat

Combination with alignment via WCS

Combination with alignment based on star positions in the image