lickbase.cl

NAME

USAGE

lickbase input output

PARAMETERS

input

Images to be bias subtracted. The images may not contain image sections.

output

Output bias subtracted images. An output image may be the same as its matching input image.

rdnoise

If this value is >= 0., a RDNOISE card will be inserted with the value. This applies to readouts which are not denoted 'Fast' by the CLKSPEED card.

rdnoisef

If this value is >= 0., a RDNOISE card will be inserted with the value. This applies to readouts which are denoted 'Fast' by the CLKSPEED card.

gain

If this value is > 0., a GAIN card will be inserted with the value. This applies to readouts which are not denoted 'Fast' by the CLKSPEED card.

gainf

If this value is > 0., a GAIN card will be inserted with the value. This applies to readouts which are denoted 'Fast' by the CLKSPEED card.

gainb

If this value is > 0., a GAIN card will be inserted with the value. This applies to readouts which are not denoted 'Fast' by the CLKSPEED card, and which are binned in either dimension.

gainbf

If this value is > 0., a GAIN card will be inserted with the value. This applies to readouts which are denoted 'Fast' by the CLKSPEED card, and which are binned in either dimension.

pixtrim

An image section which will be inserted as an IRAF TRIMSEC card. This image section is expressed in a 1-based system (as in all IRAF and WCS usage), but in the coordinate system of the original, unbinned pixels on the silicon of the CCD. This permits a trim section to be specified and used on images which had different binning.

dispaxis

If this value is > 0, a DISPAXIS card will be inserted with the value.

observat

If this value is not null, an OBSERVAT card will be inserted with the value.

DESCRIPTION

For each input image in the input image list the last column is assumed to be a baseline column as would be produced by the Lick Data Acquisition Systems on Mt. Hamilton. The appropriate manipulations of the image are made, and then the colbias task is called to perform the bias fitting.

It is required that the IRAF parameters for the colbias task have already been set before running lickbase. Specifically, the user will wish to ensure that the "function", "order", "*_reject", and especially the "interactive" parameters are correctly set.

As the image is output, the OVERSCAN card and several other cards which are useful for the ccdproc task are inserted with suitable values. Images which already contain an OVERSCAN card will be flagged and not modified by this task. Thus, it should be safe to run this task twice over the same images without causing any harm. The image is not trimmed, but the TRIMSEC card is inserted so that ccdproc will be instructed to trim off the last column.

The parameters rdnoise, gain, dispaxis, and observat are for convenience. The Lick data-taking system does not insert these cards, but several IRAF tasks make use of them.

Note carefully that, as far as ccdproc is concerned, a binned detector is a different detector than the same detector with unit binning. The value of the RDNOISE card should be different for a binned detector. The value of GAIN can also vary depending on fast/slow readout modes and over time. Furthermore, when any kind of binning is requested on a Lick CCD, the gain of the amplifier is automatically reduced by a factor of 4.

If rdnoise is specified, it should be given in electrons (i.e., photons), NOT in DN. If gain is specified, it should be given as the number of electrons (photons) per DN. See, e.g., combine, imcombine, apphot.datapars, and apall for discussion of the use of RDNOISE and GAIN.

DISPAXIS is used by many of the spectral extraction tasks. OBSERVAT is used to set the position of your telescope for airmass, position angle, and other such calculations (see observatory).

N.B.: lickbase places temporary files in the directory specified by the IRAF cl variable "tmp". It is advised that you "reset tmp = /a/big/local/disk" in your loginuser.cl file.

SEE ALSO