specslit– Extract slits from a MOS image


specslit images outimages outpref exttype (slitfile) (outputslitfile) (regprefix) (sections) (width) (sigma) (thres) (order) (padding) (yoffset) (inter) (clobber) (logfile) (verbose)


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.
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.
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’.
String. Method for the extraction. The options are RSMT, FITS, ASCII, AUTO, DS9. The RSMT method uses the XML created by the slitmask tool. The FITS method uses another FITS file, ASCII uses the output from specslit for another file, AUTO uses the image itself to extract the output, and DS9 uses a ds9 region file.
String. For ASCII extraction type, this is the slitfile that contains the definition of each slit to be extracted.
String. If specified, an ascii list of slits to be extracted are written to this file
String. Prefix for optional DS9 region file to be created based on extracted slits. The full name will be given by appending this prefix onto the image file and adding the suffix ‘.reg’
Int. Additional pixels to add to the extracted slit
Real. For RSMT method, this is a constant offset applied between the expected y-position of the slits and the y-position in the image.
Hidden boolean. If set to ‘yes’ files contained within the outpath directory will be overwritten by newly created files of the same name.
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.
Hidden Boolean. If verbose=n, log messages will be suppressed.


SPECSLIT is a task to extract slits from an RSS MOS image. The task currently will use one of three methods to extract each slit from a MOS image: (1) from an XML file produced by the RSMT (which can be downloaded from the Web Manager), (2) based on an ascii file produced by specslit for the extraction from another file, or (3) based on a ds9 region file. After extracting the slits, it will produce a MEF file with a slit image in each extension.

The recommended method is to use the XML file used to cut the slit mask. The XML file can be downloaded from the Webmanager for the observed block or can be the one submitted by the user and created by either PySlitMask or the RSMT. The code will apply the RSS distortions to the on-sky slit positions to predict the slit positions in the image. The user can adjust the parameter y-offset to adjust the position of the slits. To see how well the process extracted the slits, the user can display the extracted slit regions on the original image by using the ds9 region file created if regprefix is specified. The process may need to be interated in order to determine the best central offset.

However, if the RSMT method does not produce a satisfactory method, then the output DS9 region file produced by specifying regprefix can be used to create the extracted slits. The user can adjust the slits in the image and then save the region file. When the region file is saved, it should be saved in ‘ds9’ format with ‘image’ set for the coordinate system. Then, specslit can be run using this file and exttype=’DS9’. This will produce an MEF with the regions saved in the ds9 file extracted. Likewise, the user can create their own region file but the regions must be specified as ‘box’ in order to be extracted.

If a satisfactory slit mask has already been extracted, the user can use the outputslitfile as the input for another image and by setting exttype=’ASCII’. The same slits will be extracted. Likewise, the output MEF file can also be used here if the exttype=’FITS’.

The output for the task is a multi-extension fits file. It will have a primary header and then one extenstion corresponding to each slit. The final extension will be a table containing information about each extracted slit. The extracted ymin and ymax from the original image will be included in the header for each extension. If exttype=’RSMT’, additinally information including the slitname, RA, and DEC will be included in the extension header.

EXAMPLES 1. To extract slits from files with specslit using an XML file produced by RSMT:

--> specslit  image=mfxgbpP201302010032.fits outimage= outpref=t exttype=rsmt
slitfile=P000832N03.xml outputslitfile='' regprefix='' padding=5 yoffset=-12.0
clobber=yes logfile=salt.log verbose=yes

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

No other guess types are currently accepted. If the user wants to change the function form or order and apply it to all data, they will have to restart the task.

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

See also

Table Of Contents

Previous topic


Next topic


This Page