dark

dark averages dark frames into a master dark.

With -bias, the bias is subtracted first, so the master holds the dark current alone and flat and phcorr can scale it to other exposure times (see Typical calibration sequence). Dark current depends strongly on chip temperature, so take darks at the temperature of your science frames.

By default each pixel is a mean clipped by the expected noise, which rejects cosmic rays and hot outliers while staying accurate for very weak darks.

Usage

munipack dark [-bias file] [--arith | --hampel] [options] file(s)

Options

Option	Default	Description
-bias	—	Master bias subtracted from every dark frame.
--arith	off	Plain arithmetic mean, no rejection.
--hampel	off	Robust (Hampel) mean, the old default; underestimates weak darks. Not with --arith.
-o, --output	dark.fits	Output file.
-st, --saturate	header SATURATE	Upper limit of raw values used [ADU].
-th, --threshold	1	Lower limit of raw values used [ADU].
-bitmask	—	Mask frame (0 = skip pixel).
-B, --bitpix	−32	Output type; keep −32 for a bias-subtracted dark, whose values can be below zero.
--verbose	off	Print the noise model, mean level, exposure time and temperature.
-h, --help	—	Show the help.

Output

The master dark, with a STDERR extension holding the error of each pixel. Give it to flat and phcorr with -dark.

Examples

# dark of the science exposure time, bias left in
munipack dark -o dark120.fits dark120_*.fits

# bias-subtracted dark, to be scaled to any exposure time
munipack dark -bias bias.fits -o dark300.fits dark300_*.fits

Notes

• Do not scale a dark that still contains the bias: the bias would be scaled too. Use such a dark only for frames of its own exposure time.

• Pixel rejection, masks, header checks and input lists work as for all masters: see Common to bias, dark and flat.