ECH_LINLOC

Summary

This option is used to locate arc-line features for later identification.

It consists of two steps:

    9.1  Determine the average arc-line FWHM.
         A typical interactive plot appears below.

         

    9.2  Locate all possible arc lines.

The FWHM is evaluated by co-adding all possible line features in the arc frame, and then averaging the resulting profile, and calculating its FWHM. The value is used to scale the Gaussians which are fitted to each arc line in order to obtain an estimate of its centre position in X.

Possible arc lines are denoted by any region of an order in which 5 consecutive pixels (P1-5) obey the following relation:

    P1 less than P2 less than P3 greater than P4 greater than P5

and are amenable to a Gaussian fit with the FWHM calculated.

This ensures that even very faint features are put forward for possible identification (useful when there are no bright lines in an entire order).