coincor: Correct spectra for detector count rates

Package: iids

Usage

coincor input records

Parameters

input: The root file name of the input spectra.

records: The range of spectra. The names of the spectra will be formed by appending the range elements to the input root name.

output: This is the root file name for the corrected spectra. If no root name is specified (specified with the null string "") then the operation is done in place.

start_rec = 1: The starting record number to be appended to the root name of the created spectra.

ccmode = )_.ccmode

The mode used to model the detector count rate corrections. In the following C(obs) is the observed count rate and C(cor) is the corrected count rate.

"photo": Photoelectric photometer with discriminator mode. The count rate correction is C(cor) = C(obs) * exp (C(obs) * deadtime) where the parameter deadtime is the representative deadtime in seconds.

"iids": IIDS correction given by C(cor) = (-ln(1-C(obs)*deadtime)/deadtime)**power where deadtime is a parameter related to the sweep time used to correct for coincidence losses and power is a power law coefficient.

deadtime = )_.deadtime: For the "photo" mode this parameter is the period, in seconds, during which no counts can be registered by the detector. Note that this is based on a per pixel basis. So if the discriminator dead period is of order 50 nanoseconds and 2000 pixels are observed per readout, the effective deadtime is about 10E-4 seconds. For the "iids" mode this parameter defines the sweep time correction and has a value of 1.424E-3 seconds.

power = )_.power: The IIDS power law coefficient. The standard value is 0.975.

Description

The input spectra are corrected for detector count rate errors. If no output root name is given then the operation is done in place. The type of correction is specified by the parameter ccmode. The available modes are for a general photomultiplier with discriminator coincidence correction, and the NOAO IIDS. The parameters for these modes are deadtime and power. The exposure time, in seconds, is a required image header parameter (keyword = EXPOSURE).

The default mode is for the NOAO IIDS. The IIDS correction includes a power law correction for a nonlinear effect in the IIDS image tube chain which is not included by the mountain reduction software at the telescope. If the spectra have been coincidence corrected at the telescope then only the nonlinear power law correction is applied.

The coincidence correction flag may take the values -1 for no correction, 0 for the IIDS correction with power = 1 (the correction applied by the mountain reduction software), 1 for the full IIDS correction, and 2 for the photomuliplier mode correction.

Examples

The following example corrects a series of IIDS spectra:

cl> coincor nite1 1-250 output=nite1cc start_rec=1

The following example corrects a series of spectra from the Lick ITS:

cl> coincor its 1-250 output=itscc start=1 ccmode=photo \
>>> deadtime=2.4E-4 power=1

Time requirements

Coincor requires approximately 1 second per spectrum of length 1024.