esorex fors_trace_flat [OPTIONS] FILE.sof


This recipe is used to trace the edges of MOS/MXU flat field slit spectra and determine the spectral curvature solution. The input master flat field image, product of the recipe fors_flat, is expected to be oriented with horizontal dispersion direction and red wavelengths on the right side.

The input slits location table should be the product of the recipe fors_detect_spectra.

The input master flat image is shifted one pixel down and is subtracted from the original image. The result is a vertical gradient map. Next, the negative values are forced positive, to obtain an absolute gradient map. The map is passed with a horizontal median filter, and after that the gradient peaks are traced starting from the slits positions listed in the input slits location table. The number of pixels to the left and to the right of the reference pixel is trivially derived from the specified spectral range and spectral dispersion.

The output spectral curvature table contains the coefficients of the polynomial fitting of the found traces, while the output trace table contains the traced spectral edges positions in CCD (Y) coordinates for each spectrum, and their comparison with their modeling. A spatial map is also created, where to each CCD pixel is assigned the value of the spatial coordinate along the slit (in pixel). For more details please refer to the FORS Pipeline User\'s Manual.

Note that specifying an input GRISM_TABLE will set some of the recipe configuration parameters to default values valid for a particular grism.

Again, see the pipeline manual for more details.

In the table below the MXU acronym can be alternatively read as MOS.

Input files:

  DO category:               Type:       Explanation:         Required:
  MASTER_SCREEN_FLAT_MXU     Calib       Master flat frame       Y
  SLIT_LOCATION_DETECT_MXU   Calib       Slits location          Y
  GRISM_TABLE                Calib       Grism table             .

Output files:

  DO category:               Data type:  Explanation:
  CURV_TRACES_MXU            FITS table  Flat field tracings
  CURV_COEFF_MXU             FITS table  Spectral curvature table
  SPATIAL_MAP_MXU            FITS image  Map of spatial coordinate


--dispersion <float>

Expected spectral dispersion (Angstrom/pixel) (float; default: 0.0). The full name of this option for the EsoRex configuration file is fors.fors_trace_flat.dispersion [default = 0.0].

--startwavelength <float>

Start wavelength in spectral extraction (float; default: 0.0). The full name of this option for the EsoRex configuration file is fors.fors_trace_flat.startwavelength [default = 0.0].

--endwavelength <float>

End wavelength in spectral extraction (float; default: 0.0). The full name of this option for the EsoRex configuration file is fors.fors_trace_flat.endwavelength [default = 0.0].

--cdegree <long>

Degree of spectral curvature polynomial (long; default: 0). The full name of this option for the EsoRex configuration file is fors.fors_trace_flat.cdegree [default = 0].

--cmode <long>

Interpolation mode of curvature solution applicable to MOS-like data (0 = no interpolation, 1 = fill gaps, 2 = global model) (long; default: 1). The full name of this option for the EsoRex configuration file is fors.fors_trace_flat.cmode [default = 1].

Note that it is possible to create a configuration file containing these options, along with suitable default values. Please refer to the details provided by the 'esorex --help' command.

RELATED TO fors_trace_flat…

The full documentation for the fors pipeline can be downloaded as a PDF file using the following URL:


An overview over the existing ESO pipelines can be found on the web page

Basic documentation about the EsoRex program can be found at the esorex (1) man page.

It is possible to call the pipelines from python using the python-cpl package. See for further information.

The other recipes of the fors pipeline are fors_wave_calib_lss(7), fors_img_sky_flat(7), fors_resample(7), fors_config(7), fors_extract_objects(7), fors_calib(7), fors_wave_calib(7), fors_detect_objects(7), fors_pmos_science(7), fors_extract_slits(7), test_hough(7), fors_img_screen_flat(7), fors_extract(7), fors_remove_bias(7), fors_subtract_sky(7), fors_normalise_flat(7), montecarlo(7), fors_photometry(7), fors_zeropoint(7), fors_dark(7), fors_subtract_sky_lss(7), fors_flatfield(7), fors_img_science(7), fors_detect_spectra(7), fors_sumflux(7), fors_pmos_extract(7), fors_align_sky_lss(7), fors_bias(7), fors_align_sky(7), fors_pmos_calib(7), fors_spec_mflat(7), fors_science(7)


fors_trace_flat 5.0.0


Carlo Izzo <[email protected]>


Please report any problems to [email protected] Alternatively, you may send a report to the ESO User Support Department <[email protected]>.


This file is currently part of the FORS Instrument Pipeline Copyright (C) 2002-2010 European Southern Observatory

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