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ARC command interface

When ARC is entered, the prompt changes to:

OPTION - ARC fitting option - HE for help >

There is a much smaller set of commands available within ARC. These are summarised here:

• EX - exit from the routine and return to the LEXT prompt.
• LA - list arcline wavelengths in current ARCL list in Å.
• LF - For a specified spectrum, lists the lines which have been individually identified with particular arc-lines. This information should be contained in the current LIPOS list, in the form of pixel coordinate of the line centre versus given wavelength of line.
• RA - Removes a specified arc-line from the current list (ARCL), and also removes any fits to this arc-line which have been made, from the LIPOS list. The arc-line is identified by its wavelength, in Å, as contained in the appropriate entry in the ARCL list.

  This will not effect any scrunch coefficients which may have been derived using this line. In order to revise these, the fitting procedure must be explicitly repeated using FI or FA.

• AL - Adds the user given wavelength of an arc-line to the current ARCL list.
• CU - Begin interactive session of identifying lines in an arc spectrum. The arc image should be displayed on the current graphics device. The options are selected by depressing keyboard keys.
  • D - displays the selected cursor position.
  • W - Allows the user to directly insert a wavelength into the arc-line (ARCL) list. This option cannot be used to directly identify a particular arc-line for insertion into the LIPOS list.
  • <1551>>F - This is the main option. With it the cursor is used to indicate the approximate position of the line, on the displayed image. A precise position for the line is derived by fitting a gaussian cross-section ridge within a user-defined window around the cursor hit. This fit is indicated graphically, and can be then accepted or rejected. If accepted, the user is prompted for the wavelength to associate with the line.
• HE - Displays brief help information on the available ARC commands.
• FI - Fits a polynomial of given order to the (pixel,wavelength) pairs for a specified spectrum, from the information stored in the LIPOS list. The fit details are reported to the user, who is then asked whether firstly to store the full information for this fit in its own RESL list slot, and secondly whether to store the scrunch coefficients in the COEFS list slot for the field.
• FA - Uses the line positions identified for a given spectrum as a template, and attempts to automatically identify the same lines for each spectrum in the image, and hence produce scrunch coefficients. The line fitting follows the same procedure as the interactive option, CU, by fitting a ridge within a given window around the predicted line position.

  The scrunch coefficients are derived in the same way as for the single spectrum option FI, and stored in the current COEFS list slot. The user is required to specify a maximum value for fitting residuals in order to be acceptable.

  Since the information generated by this routine has not been scrutinised interactively, it is not used to update the current LIPOS list, nor are any RESL lists produced. Instead it is recorded in a FITL list.

  The progress of this routine is reported to the user and the image display is also updated showing the calculated line positions. It is advisable to note possible failures, so that these spectra can be subsequently re-worked individually.

• AR - Automatically refine the scrunch fits to each spectrum by searching for fainter lines which are listed in the ARCL list, but haven't been identified in the LIPOS list. This procedure is meant to provide a second order improvement to the fit once an initial attempt has reached the level where the positions of the faint lines can be searched for with confidence.

  The procedure followed is similar to that for FA.

• CP - allows setting of several parameters and criteria governing the fitting of arc spectral lines.

Details of standard arc-lines can be found from various sources, for example, in files such as FIGARO_PROG_S:*.ARC

The wavelengths of these can be added manually to the current list using the command AL.