fors_detect_spectra7

Usage

Overview

This recipe is used to detect and locate MOS/MXU slit spectra on the CCD, applying a pattern-matching algorithm. The input spectral exposure must contain spectra with the dispersion direction approximately horizontal, with blue on the left and red on the right. Use recipe fors_wave_calib_lss for LSS data, or for MOS/MXU data where all slits have the same offset.

The rows of the input spectral exposure are processed separately, one by one. First, the background continuum is removed. Second, a list of positions of reference lines candidates is created. Only peaks above a given threshold (specified by the parameter --peakdetection) are selected.

Third, the pattern-matching task selects from the found peaks the ones corresponding to the reference lines, listed in the input line catalog, associating them to the appropriate wavelengths. The ensuing polynomial fit is used to locate the central wavelength of the applied grism along each image row. The contributions from all rows form an image of the location of all spectra, that can be used as a starting point for the proper modeling of the optical and spectral distortions. For more details on this reduction strategy 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:
LAMP_UNBIAS_MXU Calib Bias subtracted arc Y
MASTER_LINECAT Calib Line catalog Y
GRISM_TABLE Calib Grism table .

Output files:

DO category: Data type: Explanation:
SLIT_MAP_MXU FITS image Map of central wavelength on CCD
SLIT_LOCATION_DETECT_MXU FITS table Slits positions on CCD
SPECTRA_DETECTION_MXU FITS image Check of preliminary detection

Options

--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_detect_spectra.dispersion [default = 0.0].

--peakdetection <float>

Initial peak detection threshold (ADU) (float; default: 0.0). The full name of this option for the EsoRex configuration file is fors.fors_detect_spectra.peakdetection [default = 0.0].

--wdegree <int>

Degree of wavelength calibration polynomial (int; default: 0). The full name of this option for the EsoRex configuration file is fors.fors_detect_spectra.wdegree [default = 0].

--wradius <int>

Search radius if iterating pattern-matching with first-guess method (int; default: 4). The full name of this option for the EsoRex configuration file is fors.fors_detect_spectra.wradius [default = 4].

--wreject <float>

Rejection threshold in dispersion relation fit (pixel) (float; default: 0.7). The full name of this option for the EsoRex configuration file is fors.fors_detect_spectra.wreject [default = 0.7].

--wcolumn <str>

Name of line catalog table column with wavelengths (str; default: ´WLEN´). The full name of this option for the EsoRex configuration file is fors.fors_detect_spectra.wcolumn [default = WLEN].

--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_detect_spectra.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_detect_spectra.endwavelength [default = 0.0].

--slit_ident <bool>

Attempt slit identification for MOS or MXU (bool; default: True). The full name of this option for the EsoRex configuration file is fors.fors_detect_spectra.slit_ident [default = True].

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.

Version

fors_detect_spectra 5.5.6