Determine spectral curvature model
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.
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 .
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
Create an object for the recipe fors_trace_flat.
import cpl
fors_trace_flat = cpl.Recipe("fors_trace_flat")
Expected spectral dispersion (Angstrom/pixel) (float; default: 0.0) [default=0.0].
Start wavelength in spectral extraction (float; default: 0.0) [default=0.0].
End wavelength in spectral extraction (float; default: 0.0) [default=0.0].
Degree of spectral curvature polynomial (long; default: 0) [default=0].
Interpolation mode of curvature solution applicable to MOS-like data (0 = no interpolation, 1 = fill gaps, 2 = global model) (long; default: 1) [default=1].
The following code snippet shows the default settings for the available parameters.
import cpl
fors_trace_flat = cpl.Recipe("fors_trace_flat")
fors_trace_flat.param.dispersion = 0.0
fors_trace_flat.param.startwavelength = 0.0
fors_trace_flat.param.endwavelength = 0.0
fors_trace_flat.param.cdegree = 0
fors_trace_flat.param.cmode = 1
You may also set or overwrite some or all parameters by the recipe parameter param, as shown in the following example:
import cpl
fors_trace_flat = cpl.Recipe("fors_trace_flat")
[...]
res = fors_trace_flat( ..., param = {"dispersion":0.0, "startwavelength":0.0})
See also
cpl.Recipe for more information about the recipe object.
Please report any problems to Carlo Izzo. Alternatively, you may send a report to the ESO User Support Department.
This file is currently part of the FORS Instrument Pipeline Copyright (C) 2002-2010 European Southern Observatory
This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
Code author: Carlo Izzo <usd-help@eso.org>