specrectify

Name

specrectify– Correct images for wavelength dispersion

Usage

specrectify images solfile outimages outpref (caltype) (function) (order) (inttype) (w1) (w2) (dw) (nw) (blank) (clobber) (logfile) (verbose)

Parameters

images

String. List of FITS images to prepare. Data can be provided as a comma-separated list, or a string with a wildcard (e.g. ‘images=S20061210*.fits’), or a foreign file containing an ascii list of image filenames. For the ascii list option, the filename containing the list must be provided preceded by a ‘@’ character, e.g. 'images=@listoffiles.lis‘. The list can contain data files from multiple SALT instruments.

solfile

String. File or list of files with wavelength solution for each solution. The solfile should be the output from specidentify based on the measured wavelength calibration from an arc lamp. It does not need to be supplied if the caltype=’rss’.

outimage

String. A list of images. Data can be provided as a comma-separated list, or a string with a wildcard (e.g. ‘outimages=rS20061210*.fits’), or a foreign file containing an ascii list of image filenames. For ascii list option, the filename containing the list must be provided preceded by a ‘@’ character, e.g. 'outimages=@listoffiles.lis‘. This list must be of the same size as the images argument list.

outpref

String. If the outpref string is non-zero in length and contains characters other than a blank space, it will override any value of the outimages argument. Output file names will use the name list provided in the images argument, but adding a prefix to each output file defined by outpref. An absolute or relative directory path can be included in the prefix, e.g. ‘outpref=/Volumes/data/p’.

(caltype)

String. The type of wavelength calibration to be done. If ‘lines’ the task will assume that a wavelength solution was provided in the solfile. If ‘rss’ the task will use the RSS model to correct the data.

(function)

String. Functional form for the fit to the model. It is only needed if calytpe=’rss’.

(order)

Int. Order for the fit to the model. It is only needed if caltype=’rss’.

(inttype)

String. Interpolation type for the flux transformation. When transforming the flux from the calibrated to uncalibrated data, it is the interpolation type to use in the calculation. It can either be ‘linear’ or ‘spline’.

(w1)

Real. The starting wavelength for the output data. If it is not specified, it is the minimum wavelength value of the central row of the input data.

(w2)

Real. The end wavelength for the output data. If it is not specified, it is the maximum wavelength value of the central row fo the input data.

(dw)

Reale. The dispersion for the output data. It is given in terms of angstroms per pixels. If it is not specificied, it is calculated based on the input data.

(nw)

Int. Number of pixel in the output data in the dispersion direction. If this is set to None, it will default to the number of pixels in the input data in the wavelength direction.

(blank)

Real. The value to use for regions in the output data that do not correspond to regions in the input data.

(clobber)

Hidden boolean. If set to ‘yes’ files contained within the outpath directory will be overwritten by newly created files of the same name.

(logfile)

String. Name of an ascii file for storing log and error messages from the tool. The file may be new, or messages can also be appended to a pre-existing file.

(verbose)

Hidden Boolean. If verbose=n, log messages will be suppressed.

Description

Specrectify will wavelength calibrate a spectroscopic image based either on a solution from an arc lamp or based on the model of the spectrograph. Given an uncalibrated science frame, spectrectify returns a image where the x-axis has been transfered onto a scale with linear spacing. For the image, all of the appropriate information has been updated in the image header.

If caltype is ‘line’, the task will assume that the wavelength solution will be provided in solfile. This file is the output produced from specidentify and may contain multiple different wavelength solutions for different arc lamps and instrument setups. The task will find the calibration using the same instrument setup that is closest in time and use that calibration to correct the data.

If caltype is ‘rss’, the task will use the model parameters for RSS to wavelength calibrate the data.

In either case, the output will be a wavelength calibrated data set. If w1, w2, dw, or nw are set, it will use these parameters to determine the boundaries of the output data. Otherwise, it will calculate these paramters based on the data set by determine the maximum and minimum wavelength at the central row and maintining the same number of pixels in the output data. Currently, all spacing is assumed to be linear in wavelength space.

The user can specify the type of interpolation for the flux measurements with inttype. It can either be linear sampling or spline. With blank, the user can specify a constant value for the flux in regions in the final data that would not appear on the original data.

If the input file contains variance and bad pixel frames, it will produce those in the output files as well. If there are multiple science frames in the image, it will wavelength calibrate each of the science frames in the data along with the corresponding variance and bad pixel frames. It will not use the same calibration for each science frame, but it will recalculate the

Finally, the task will update the WCS keywords such that the data will transform between pixel and wavelength space. The default units for the wavelength axis are Angstroms.

EXAMPLES 1. To calibrate science FITS files with specrectify using solutions based on an arc lamp:

--> specrectify images='pmbxpP*.fits' solfile='dbsol'
outimages= outpref='r' caltype='lines' logfile='salt.log'

Time and disk requirements

Individual unbinned raw full-frame RSS files can be 112MB in size. It is recommended to use workstations with a minimum of 512MB RAM. On a linux machine with 2.8 Ghz processor and 2 Gb of RAM, one 2051x2051 image in 0.15 sec.

Bugs and limitations

Currently, the wavelengths are specified for air and not vacuum. The sampling type is fixed to linear.

Send feedback and bug reports to salthelp@saao.ac.za

See also

specidentify