EMLT-Fits gaussians to the strongest lines in a spectrum

Description:

Analyses an emission line spectrum (typically an arc), and produces a list of the strongest lines, giving their widths and strengths. Can also produce a synthetic spectrum from the positions, widths and strengths of the fitted lines.

Parameters:

SPECTRUM

Specifies the spectrum whose strongest emission lines are to be fitted. If the data is more than one- dimensional, the analysis is repeated for each cross- section (i.e. spectrum) in the data.

XSTART

Specifies the X-value (wavelength for calibrated data, or pixel number for uncalibrated data) at which the analysis is to start.

XEND

Specifies the X-value (wavelength for calibrated data, or pixel number for uncalibrated data) at which the analysis is to end.

LINES

If LINES is non-zero, it specifies that only the indicated number of strongest lines are to be included in the analysis. If zero, all lines for which a reasonable fit can be obtained are included.

FWHM

If FWHM is zero, the fits performed are unconstrained; that is, the fit determines full width at half maximum for each line independently. If FWHM is non-zero, it specifies a fullwidth at half maximum (in pixels) for each line in the spectrum, and the fit is constrained accordingly.

MOMENTS

If MOMENTS is set, a center of moment analysis is performed (in addition to the gaussian fit) for each line and the results included in the output. This analysis is performed for each line found, not just the LINES strongest lines.

SYNTH

If SYNTH is set, a synthetic spectrum based on the fitted positions, strengths and widths of the lines is generated.

OUTPUT

The name of the resulting synthetic spectrum, if one is to be created.

Source comments:

 E M L T

 Figaro version of the original SDRSYS routine EMLT, which analyses
 emission lines in a spectrum, fitting gaussians to the strongest
 lines and logging their positions, widths and centers.  Optionally,
 it will also give line centers using a centre of moment analysis,
 and can also produce a synthetic spectrum generated from the
 positions and widths of the located lines.  Note: Figaro and SDRSYS
 differ in their pixel numbering, Figaro counting from 1 and SDRSYS
 counting from 0, so there will be a discrepancy of 1 between the
 output from the two versions for any pixel number values; wavelength
 values produced by the two should be the same.

 Parameters -

 SPECTRUM    (Character) The name of the spectrum to be analysed.
 XSTART      (Numeric) The first X-value to be used for the analysis.
 XEND        (Numeric) The last X-value to be used for the analysis.
 LINES       (Numeric) If LINES is zero, all lines that can be
             fitted are listed.  Otherwise, it gives the number of
             lines to be included in the analysis, starting with the
             strongest and cutting off the weaker lines.
 FWHM        (Numeric) If non-zero, all lines fitted are constrained
             to a full width at half maximum of this value - in pixels.
 OUTPUT      (Character) The name of any synthetic spectrum to be
             generated.

 Keywords -

 MOMENTS     If set, a center of moment analysis is also performed
             on all lines found.
 SYNTH       If set, a synthetic spectrum is generated.

 User variables -  (">" input, "<" output)

 (<) EMLT_LINES    (Real) Number of lines found.
 (<) EMLT_BIN      (Real array) List of line centres (pixels).
 (<) EMLT_POS      (Real array) List of line centres (wavelength units).
 (<) EMLT_FWHM_BIN (Real array) List of FWHM (pixels).
 (<) EMLT_FWHM_ANG (Real array) List of FWHM (wavelength units).
 (<) EMLT_STREN    (Real array) List of line strengths.
 (<) EMLT_PEAK     (Real array) List of peak heights.

                                              KS / AAO  4th March 1988