1 Introduction

SPECX is a general mm and sub-mm wavelength data reduction system written by Rachael Padman at MRAO. At the time of writing the latest formally released version on the VAX is 6.2. However, pre-release copies of Version 6.3 are widely used. Branching off from the 6.3 VMS version, SPECX was ported to UNIX by Horst Meyerdierks of the Starlink Project and Rachael Padman. Remo Tilanus at JACH supplied the core routines to read GSD files and Tim Jenness at the JAC took over development for Version 6.7. The software version count on UNIX increased rather rapidly. 6.4 was the initial UNIX port of 6.3, but it existed only in beta-test versions. The first released version was 6.5, but it lacked the commands to read GSD files. Version 6.6 added support for GSD files. The current version on UNIX is 6.7 which added support for a new HDS map format (V4.2) and routines to aid the reduction of raster maps. Version 6.7 is currently supported by the Joint Astronomy Centre and distributed by Starlink.

Although SPECX may be used to process spectra obtained from many different instruments, Starlink users will find it particularly useful for the reduction of data obtained with the James Clerk Maxwell Telescope. SPECX has it’s own command line interpreter, and manipulates spectra on a pop-down stack. The package is designed to work on a variety of graphics terminals but is mainly used from within an X windows environment. Hardcopy may be output on a number of printers for which GKS drivers are provided by Starlink. In the UNIX version these are mainly different PostScript printers.

Some of the major features of SPECX are:

• The ability to process up to eight spectra (quadrants) simultaneously: these may have the same or different centre frequencies, resolutions, etc. This allows users to operate on different filter-banks, or dual polarisation data for example, in parallel.
• The ability to automatically save the current status of the system after each command is executed. This means that if SPECX is stopped (unintentionally or otherwise), when restarted it will ‘remember’ the previous state of the program.
• Commands for the listing and display of spectra on a graphics terminal, with hardcopy on a variety of printers.
• Single and multiple scan arithmetic, scan averaging, etc.
• Commands to store and retrieve intermediate spectra in storage registers.
• Commands to perform the fitting and removal of polynomial, harmonic and Gaussian baselines.
• Commands for filtering and editing spectra.
• Commands to determine important line parameters (peak intensity, width, etc.).
• The ability to perform Fourier transform and power spectrum calculations.
• Procedures for the calibration of data.
• The ability to assemble a number of reduced individual spectra into a map file, and contour or greyscale any plane or planes of the resulting cube.
• The ability to write indirect command files.

A thorough description of the package is given in the “SPECX Users’ Manual” which has been distributed as a Starlink Miscellaneous User Document (MUD/70). At the time of writing this MUD is available from Starlink for Version 6.3. No document has been prepared yet for the UNIX version, and the document on 6.3 is the closest approximation for UNIX users.

SPECX is intended primarily for the analysis of JCMT data and can read such data directly from the GSD files produced at the telescope. In the VMS version there are also facilities for reading data from a range of other important mm-wave telescopes, e.g. Onsala, FCRAO, UMASS CO survey, IRAM-FITS, JCMT RxG, NRAO 8-beam (see the SPECX user manual for details). Spectra and maps can be output as FITS files, Starlink NDFs, or ASCII files for reading into other packages.

This document concerns itself with the unix version of SPECX and will no longer discuss the VMS Version 6.2.