FORS_DETECT_SPECTRA(7)

📦 version 5.5.7, in ubuntu jammy, ubuntu noble

💖 fors_detect_spectra — FORS_DETECT_SPECTRA(7) 💖

okay bestie, sit down, hydrate, and let me tell you about a little recipe called fors_detect_spectra from the FORS pipeline. she's giving ✨detective✨ energy and she is so good at her job 🕵️♀️💅

🌸 NAME 🌸

fors_detect_spectra — detect MOS/MXU spectra on CCD. no cap, that's literally the whole vibe: finding spectra. 🔍

✨ SYNOPSIS ✨

esorex fors_detect_spectra [OPTIONS] FILE.sof

🦋 DESCRIPTION 🦋

so this recipe's whole thing is detecting and locating MOS/MXU slit spectra on the CCD, using a pattern-matching algorithm. iykyk. 🧠✨

your input spectral exposure has to contain spectra with the dispersion direction approximately horizontal, with blue on the left and red on the right. not negotiable, bestie, that's just how she rolls. 🌈

use recipe fors_wave_calib_lss for LSS data, or for MOS/MXU data where all slits have the same offset. 👑

here's how the processing goes, one step at a time:

the rows of the input spectral exposure are processed separately, one by one. so:

first, the background continuum is removed.
second, a list of positions of reference line candidates is created. only peaks above a given threshold (specified by the parameter --peakdetection) are selected. so if it's too faint? not invited. 🙅♀️
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. (the way she just knows what defaults you need… iconic.) 💅

again, see the pipeline manual for more details. 🙈

in the table below the MXU acronym can be alternatively read as MOS. cute, flexible, bilingual.

Input files: 📥

DO category: LAMP_UNBIAS_MXU — Type: Calib — Explanation: Bias subtracted arc — Required: Y
DO category: MASTER_LINECAT — Type: Calib — Explanation: Line catalog — Required: Y
DO category: GRISM_TABLE — Type: Calib — Explanation: Grism table — Required: .

Output files: 📤

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

💅 OPTIONS 💅

okay here come the knobs and dials. every single one, no skipping, we don't do that here. 🎀

--dispersion <float> — expected spectral dispersion, in Angstrom/pixel. it's a float, and the default is 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, in 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 the 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 the 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 the dispersion relation fit, in pixels. 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 the 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. 👀

🌈 SEE ALSO 🌈

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

ftp://ftp.eso.org/pub/dfs/pipelines/fors/fors-pipeline-manual-4.9.pdf

an overview over the existing ESO pipelines can be found on the web page https://www.eso.org/sci/software/pipelines/. 🌐

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 https://packages.python.org/python-cpl/index.html for further information. 🐍

the other recipes of the fors pipeline are: fors_align_sky(7), fors_align_sky_lss(7), fors_bias(7), fors_calib(7), fors_config(7), fors_dark(7), fors_detect_objects(7), fors_extract(7), fors_extract_objects(7), fors_extract_slits(7), fors_flatfield(7), fors_img_science(7), fors_img_screen_flat(7), fors_img_sky_flat(7), fors_normalise_flat(7), fors_photometry(7), fors_pmos_calib(7), fors_pmos_extract(7), fors_pmos_science(7), fors_remove_bias(7), fors_resample(7), fors_science(7), fors_spec_mflat(7), fors_subtract_sky(7), fors_subtract_sky_lss(7), fors_sumflux(7), fors_trace_flat(7), fors_wave_calib(7), fors_wave_calib_lss(7), fors_zeropoint(7) ✨ (the whole friend group, fr fr)

⭐ VERSION ⭐

fors_detect_spectra 5.5.7 — she's on version 5.5.7 and she's thriving. 👑

🎀 AUTHOR 🎀

Carlo Izzo <usd-help@eso.org> — thank you for your service, king 🫡💖

😭 BUG REPORTS 😭

please report any problems to usd-help@eso.org. alternatively, you may send a report to the ESO User Support Department usd-help@eso.org. (yes, same address twice, they really want to hear from you, bestie 📬)

💜 LICENSE 💜

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.

🫶 and that's the whole page!! that was fors_detect_spectra, version 5.5.7, manual page FORS_DETECT_SPECTRA(7) — go detect some spectra, you absolute main character. slay. periodt. 💖✨🎀🦋🌸

📦 where this page comes from

ubuntu jammy: cpl-plugin-fors-doc 5.5.7+dfsg-2build1 · GPL-v2+
ubuntu noble: cpl-plugin-fors-doc 5.5.7+dfsg-2build1 · GPL-v2+
💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash on 2026-10-18: a language model's rewrite of the original, under its terms