ecreidentify: Automatically identify features in spectra

Package: echelle

Usage

ecreidentify images reference

Parameters

images

Echelle images in which the features in the reference image are to be reidentified and a new dispersion function fit.

reference

Echelle image with previously identified features and dispersion function.

shift = 0.

Shift in user coordinates to be added to the reference features before centering. If INDEF then a shift is determined by correlating the reference features to features automatically identified in the image to be reidentified.

cradius = 5.

Centering radius in pixels. If a reidentified feature falls further than this distance from the reference position (after shifting) it is not reidentified.

threshold = 10.

In order for a feature center to be determined the range of pixel intensities around the feature must exceed this threshold.

refit = yes

Refit the dispersion function? If yes and there are more than 4 features in more than one order and a dispersion function was defined in the reference image then a new dispersion function of the same type and order offset as in the reference image is fit using the new pixel positions. Otherwise only a zero point shift is determined from the revised fitted coordinates without changing the form of the dispersion function.

database = "database"

Database containing the feature data for the reference image and in which the features for the reidentified images are recorded.

logfiles = "STDOUT,logfile"

List of file in which to keep a processing log. If a null file, "", is given then no log is kept. If the log file is "STDOUT" then the log is written to the terminal.

Description

Emission or absorption features in a reference echelle spectrum are reidentified in other echelle spectra. The features for the reference image and those determined for reidentified images are recorded in the specified database.

The first step in transferring identifications from the reference spectrum to another spectrum is to add a shift (in wavelength) to each feature in the reference image. The shift is specified by the parameter shift. This shift is for the fundamental order (order number 1) which is then applied to each order by dividing by the order number. If the shift is specified as INDEF then a shift is determined by finding the peaks in the input spectrum and correlating these peaks against the feature in the reference spectrum. This is the 'x' algorithm described in ecidentify.

After the shift has been added to move the reference features to near the input spectrum features these positions are adjusted by centering on the features using the center1d algorithm. The parameters cradius and threshold are used in this operation. If the centering fails to find the feature within the centering radius (cradius) that feature is eliminated from the feature list.

If the parameter refit has the value "no" then the average shift in the feature positions is recorded as a zero point wavelength offset for the fundamental order without changing the shape of the dispersion function. If the parameter has the value "yes" then the new feature positions are used to refit the dispersion function (of the same function type and orders). The order offset is also maintained.

Log information is written to the specified log files. To log this to the terminal, called the standard output, use STDOUT. The log information includes reference spectrum, the spectrum being reidentified, the number of initial features and the number actually reidentified, the average shift in pixels, the average shift in wavelength (in terms of the fundamental order), the average fractional shift in wavelength (which can be scaled to a radial velocity), and the RMS of the features wavelengths given by the dispersion function to the user specified true wavelengths.

Examples

The features in the spectrum f033.ec were identified previously with the task ecidentify. The features positions in f043.ec are are reidentified with and without refitting the dispersion function as follows:

ec> ecreidentify f043.ec f033.ec

ECREIDENTIFY: NOAO/IRAF V2.7 seaman@puppis Mon 09:03:51 27-Jun-88
  Reference image = f033.ec, Refit = yes
               Image    Found  Pix Shift  User Shift  Z Shift      RMS
             f043.ec  561/561       0.11       -1.07  -1.9E-6   0.0117

ec> ecreidentify f043.ec f033.ec refit=no

ECREIDENTIFY: NOAO/IRAF V2.7 seaman@puppis Mon 09:15:21 27-Jun-88
  Reference image = f033.ec, Refit = no
               Image    Found  Pix Shift  User Shift  Z Shift      RMS
             f043.ec  561/561       0.11       -1.07  -1.9E-6   0.0131

See also

center1d, ecidentify