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ALFOSC Sequencer Command Documentation

Go to the SEQUENCER Reference Manual Main Page.

Instrument : ALFOSC
Observing Mode: ANY IMA SPEC POL
Command Type: ANY DATA DET DISP INST TEL
Usage: BASIC GENERAL STAFF
Description: SHORT LONG

SystemCommandArgumentsDescriptionType
alfosc acquisition [-c] [-q] [-nofo] <slit> <tt>

Script for ALFOSC-spectroscopy target acquisition. Supported modes:
  - single-star long-slit
  - echelle
  - spectropolarimetry

  • -c   make a check image of the star and the slit.
  • -q   query the user for another iteration.
  • -nofo   do not execute alfosc.focus-offset
  • <slit-specifier>   unambiguous string to specify slit.
  • <exptime>   exposure time for target acquisition images.
Will first do a binned full-frame image and then another iteration on a 800x800 windowed image. The binned image is taken with 1/4 of the requested exposure time. The acquisition images are analysed interactively using slitoff, which will move the telescope and guide probe to get the star on the requested slit.
The user may request a check of the positioning by making an additional test image with the slit in the beam. In this case the slit will be left in the beam at exit of the script. The user may request an interactive query, which allows to do additional slitoff iterations, and in case a slit image is requested to do aditional slit images.
If a polarimetry slitlet is specified, the script will setup for spectropolarimetry. This script makes sure that the aperture and grism wheels are correctly positioned, and does not move any of the filter wheels for in case a (blocking-)filter has to be in the beam (which should be put in the beam before starting alfosc.acquisition). Exception: if a filter-wheel (cross-disperser) grism is in the beam, the filter wheel will be put to OPEN. Moves the calibration mirror out of the beam. Moves the FAPOL carriage in/out when necesary. Moves to the default internal focus for normal and specpol setups. Executes alfosc.focus-offset before the first acquisition image is taken, unless command-line flag -nofo is given. Exits with full-frame unbinned CCD settings, and autosave_on. Note: the slit specifier should be a unique string. A list of optical elements can be found here.
Usage example:
  alfosc.acquisition -c -q Slit_1.0 2   Makes acquisition with 2s exposure time, using horizontal 1.0" slit, shows check-image of the star and the slit and queries user for another iteration.
TEL
alfosc focus [-e] [-n <N>] [-nodefault] [-t <nn>] [-a <mode>][-filter] Fully automated focus script for ALFOSC.
[-n <N>]: Number, <N>, of maximal loops, default is 3.
[-t <nn>] Expose <nn> seconds. Default is 10.
[-nodefault]: Start from actual focus rather than default focus.
[-filter]: Leave current filters in the beam
[-a <mode>]: Acquisition mode. <mode> can be:
  • noacq: Use current pointing for focusing.
  • nearest: Use nearest focus field from current pointing.
  • optimal: Use nearest focus field between 60-70 degrees altitude (default)
Focus is determined without any filter in the beam (except if the -filter flag is set). Filter and any other ALFOSC instrument & detector settings will be saved before running the focus script and restored at the end.
The 'focus' command is the recommended way of focusing the telescope. In case the command fails, for instance if too few stars are detected in the image, the focus can be determined in a more interactive mode by using the commands focuspyr-setup, expose, focuspyr, focus-position (see documentation on these commands for further information).

Usage example:
  alfosc.focus -n 4 -t 15 -a nearest   Focuses the telescope using the nearest focusfield, doing 4 loops with individual exposures of 15s.

TEL
alfosc focus-offset [-e] [-d <nn>] Optics in the beam introduces a telescope focus offset (see table). The 'focus-offset' command checks what is currently in the FASU and ALFOSC filter wheels and applies the corresponding focus offset (using foc-del) when possible. The focus offset introduced by a retarder plate in polarimetry mode is also accounted for. Be very careful when using this command. Focus offset for many optical elements are not known and as a consequence the telescope may in fact not be in focus even after using this command. If the focus offset is not known, 0 will be assumed. If this occurs, a warning message will appear both in the talker window and in the sequencer window. Several warning messages may appear if several optical elements in the beam have unknown focus offsets. The final telescope focus offset applied is the sum of the offsets for the element in each wheel, and may therefore be wrong if any offset is unknown. Do not use this command in scripts unless you are absolutely sure that the focus offset are known for all optical elements to be used.
If you intentionally wish to defocus the telescope (for instance when observing very bright targets), call the script with the [-d] flag, specifying the number of focus units to defocus the telescope with, for instance
focus-offset -d 200
will defocus the telescope with 200 units with respect to optimal focus. Reasonable defocus values ranges from 50-2000 units.
TEL
alfosc slitoff [slit=<nn> | xref=<x> yref=<y>] Calculates the telescope offset required to bring a target onto a given slit and performs the required telescope offset. The slit number <slitno> refers to the position of the requested slit in the ALFOSC slit wheel. Alternatively, an (<x>,<y>) pixel position can be given as reference. The script uses the currently loaded DS9 image and assumes this corresponds to an acquisition image of the field the telescope currently is pointed at. The target is identified interactively by the user through an imexam session. TEL

In scripts, the syntax alfosc.<command> should be used.
If a part of a command is written in <angle brackets>, this is an argument that should be replaced with a value.
If a part of a command is written in [square brackets], this is an optional argument or flag.
When available, the optional flag -d will write extended debugging information to the log.
When available, the optional flag -e will show the script on standard output instead of executing the commands.
When available, the optional flag -t will only make a simulated exposure. Useful for testing scripts.

Type definitions:
DATA: All commands related to handling/modifying data (editing fits-headers, post-processing etc.).
DET: Commands related to operations with the detector.
DISP: Commands related to displaying images on the instrument computer.
INST: Commands related to operations with the instrument.
TEL: Commands related to operations with the telescope.

Back to top Last modified: January 26 2023