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Guide to observing remotely with ALFOSC

This page contains specific instructions for the Stockholm school 2014.

This page only describes things that are special for the remote observing procedure. All things related to observing with ALFOSC are documented on the main ALFOSC web pages.


  • In case of any doubts or questions, please contact the control room directly using the `skype' connection. If not available or nobody is in the control room (e.g., in the daytime) please call the control room (+34-922405660) or the service building (+34-922405663).


  • There are various things that can/should be done in preparation for the observations. For each target:
    • the required exposure time can be estimated here
    • the visibility during the night should be check, e.g., here
    • and finding charts can be prepared here (ING DSS) or here (Aladin)
    At this time one should also consider what kind of calibration is needed for the data, specifically if apart from day-time calibration, night time calibrations are needed.

    Make sure that the telescope staff knows the needed instrument setup and calibrations.

  • With all this information it is now possible to draw up an observing plan, defining the order in which you want to observe your target with approximate time-line for the observations. For this you should take in to account the time it takes to position a target, for instance onto a slit (see It also is good to define priorities for the different targets. Together with the time-line this will make it easier to decide what to do in case the observations do not proceed as fast as expected, or if the weather changes. It also is good to have some back-up targets in case the observations proceed faster than expected, or if, e.g., some of the main targets can not be observed due to strong wind from the wrong direction.

Logging in

  • Open a terminal on your computer
  • Log in to the computer at the telescope using the following command

       ssh -X

  • This is only possible from computers with a previously registered IP number.

  • You will be prompted for a password which will be supplied by the NOT staff.

Starting the control software

  • Once logged in to tessa (in the above mentioned terminal) type

       startobssys remotealfosc

    then type the TCS access-code when prompted. The TCS access-code changes every day at noon UT. For this reason the observing system needs to be restarted every day and the TCS access-code should be obtained in advance from the NOT staff on La Palma (see above for contact information).

    In case there is already a ALFOSC observing session running this command will fail. Contact the telescope to resolve this.

    The `startobssys remotealfosc' command will open a total of 8 windows (see picture here):

    • 2 `sequencer' terminals (6) and (7)
    • A CCD status windows (1)
    • The ALFOSC instrument status display (3)
    • The ALFOSC instrument control (2)
    • the TCS status display (4)
    • a `Talker' window which provides status, warning and error message for the observing system (5).
    • a small `tech-xterm' window in which the low-level communication messages with the instrument can be seen. This window can be `minimized' (8).

    The command takes some time to startup and depending on the connection it will take some time for all windows to appear.

  • To operate the system, commands can be typed in the two sequencer terminals.

    To close a sequencer terminal type 'exit' at its prompt. You can always get another sequencer terminal, using the command 'seqterm'. This is possible from any sequencer terminal window as well as any other terminal window logged in on tessa.

Starting the postprocessing image display

  • Open a terminal on your computer
  • Log in to the computer at the telescope using the following command

       ssh -X

  • This is only possible from computers with a previously registered IP number.

  • You will be prompted for a password which will be supplied by the NOT staff.
  • In the terminal window a line of text similar to this will appear:

       setdisplay 'localhost:18.0'

  • Copy and paste that line into the ALFOSC sequencer terminal
  • Type in the ALFOSC sequencer terminal


    An empty DS9 window should appear. HAVE PATIENCE. This may take some time.
    ALFOSC FITS images will be displayed in the DS9 window automatically after they have been saved.

  • For best results, choose the 'Scale' option 'zscale' in the DS9 display.
  • In the second sequencer terminal, type


    which will display a graphics window (HAVE PATIENCE) and put the cursor in imexam mode on the image loaded into the DS9 window. As new images gets loaded into the DS9, the imexam task will automatically work on these, so there is no reason to quit the imexam task after every analysis.

Accessing data

  • The data taken can be retrieved with 'ftp' from the computer
  • Read more instructions about it in here

Observing with ALFOSC

  • Target and/or (daytime) calibration observation can now been made with ALFOSC through commands in the ALFOSC sequencer windows.
  • Observing with ALFOSC and use of the sequencer system is described in detail on the ALFOSC web pages

  • Some often-used commands:
    alfosc.expose to make an exposure
    alfosc.dark to make a dark/bias
    alfosc.bin set CCD binning
    alfosc.xbeg set CCD window
    alfosc.ybeg set CCD window
    alfosc.xsize set CCD window
    alfosc.ysize set CCD window
    alfosc.resetxy to reset CCD parameters
    alfosc.object to set the OBJECT header
    alfosc.imexam to start an IRAF 'imexamine' session on the displayed image
    alfosc.teloffset to offset the object relative to CCD

  • Documentation of ALFOSC/telescope Sequencer commands and scripts

  • Note, it is recommended to set optical elements and calibration unit mirror by clicking the UIF, instead of using scripts such as alfosc.acquisition, alfosc.allopen, alfosc.wheels etc. These scripts may gave an instrument time-out (see Fault 1563 and Fault 1790)

Target catalogue

  • To be able to point the telescope to your targets you need to prepare a catalogue with the coordinates. Instruction and a web form to enter the target coordinates can be found at
    For the Tartu school use the proposal number 47-703.
  • After generating the catalogue you need to read it in to the observing system. To do this, type in any sequencer window 47_703_<catalogue-name>.cat

    where <catalogue-name> is the specific name you have given the catalogue.

Start of the night

Note that for this school the NOT staff will take twilight flat fields and focus the telescope at the start of the night, after which the remote observers are expected to start-up the system and and start observing. This will be around UT 20:40. Tartu local time is UT+3h!

  • Around sunset the local staff will power-on the telescope, open the hatches and side ports (depending on the weather conditions).

    At this time also the `skype' connection should be tested, which requires somebody to be present at both ends of the connection.

Setup the telescope

  • To set-up the telescope at the start of the night, and after every switch from another instrument (e.g. from FIES), the following commands should be executed in any sequencer window


  • The above command sets the telescope focus to the default value, so you may want to set it to the value found in the beginning of the night (ask control room if you don't know):

       tcs.focus-position 23xxx

Spectroscopy: Define the parallactic angle

At every switch from horizontal to vertical slit (and vice-versa) one of the following commands should be executed.
  • For spectroscopy with horizontal slits, define the parallactic angle with

       tcs.instrument-parallactic-angle 0

  • For spectroscopy with vertical slits, define the parallactic angle with

       tcs.instrument-parallactic-angle 90

Moving the telescope to a target

  • Select the target that you want to observe
  • Switch off autoguiding:

  • For safety reasons, always contact the NOT staff at the telescope before moving to make sure it is safe to move
  • IMAGING: To move the telescope to the object, type in the sequencer window the command <my-object-name>

    where <my-object-name> is the name of the target in the TCS catalog

  • SPECTROSCOPY: First make sure that the parallactic angle is defined correctly (see above).
    To move the telescope to the object, type in any sequencer window the commands

       tcs.find-object <my-object-name>


    where <my-object-name> is the name of the target in the TCS catalog

Assessing the data log

You can keep an eye of recorded images during the night (an 'obslog') by producing an End-of-Night report already at the start of the night and reload the content when needed:
  • Access the EON report form, providing the proposal number and date as requested.
  • Do not fill in any information at this stage, just submit the EON form.
  • Follow the URL displayed to view the online EON report. The online report includes an up-to-date listing of all images taken that night.
  • Refresh the page as often as required to update the image listing. The full URL of the page is unique and the only way of accessing the report. Do not loose it.

Assessing the data with the postprocessing system

  • Spectroscopic data will automatically be reduced by the quickspec postprocessing script which will show the reduced spectrum in a dedicated graphics window.
    This script can also be run from the the ALFOSC sequencer terminal with


  • Furthermore, any frame that is saved to disk will be displayed in the postprocessing display. If the imexam task is active on the 2nd sequencer window, you can obtain obtain plots, statistics, etc. using the imexam facilities immediately. Alternatively, use imexamin in IRAF on your downloaded image locally.

  • For the focussing and slit-acquisition procedures described below the postprocessing display will allow you to interactively point at your targets (stars/galaxies/etc.) during the procedure.

Imaging: Filter focus offsets

  • When inserting an imaging filter or spectroscopic order-blocking filter in the beam, the telescope focus might need a correction.
    Follow the procedure described on this page.

Spectroscopy: Setting the slit angle (to get 2 objects on the slit)

  • See for a description and/or follow the procedure described on this ALFOSC page. Note that in remote mode you need to use the full names alfosc.slitrot and tcs.field-rotation for the commands.

    Very important: Quit any active imexam sessions prior to running the SLITROT task

Imaging: Setting North-is-up

If the field rotation is changed, e.g., to orient a slit along 2 object (see here), the following command should be executed.
  • To set North-is-up on the CCD, set the rotator angle with

       tcs.field-rotation 90

Spectroscopy: Centering the target on a slit

  • To position a star on the slit follow the procedure given here.

    To speed-up the procedure we suggest you window the CCD by executing the focuswindow script in the sequencer window at the start.

    Very important: Quit any active imexam sessions prior to running the `slitoff' task

In situations where the speed of the network connection is slow, an alternative procedure can be used for centering the target on the slit:

  • Make an image of the field.
  • Download the image to the remote site.
  • Load the image into DS9 on a computer on the remote site.
  • Measure the X and Y positions of the target you want to center on the slit.
  • Identify the number of the slit you want to use. The slit installed in the first postion in the aperture wheel is slit number 1 and so on.
  • In a sequencer terminal on the computer 'tessa' type the following command (in this example the slit to use is number 3, the target X,Y are 980,1022)

        alfosc.remote-slitoff slit=3 xstar=980 ystar=1022

You can also use this method on binned and windowed images. Just remember to use the 'xbin'/'ybin' options to specify the binning in each direction and the 'xbeg'/'ybeg' option to specify the x and y of the beginning of the window.

The complete command, with all the possible parameters, is:

   alfosc.remote-slitoff slit=<slitnumber> xstar=<x-coord> ystar=<y-coord> xbin=<x-bin> ybin=<y-bin>

Web camera view of the NOT control room

A web page that will show an web camera image of the NOT control room is provided. It is updated every 3 seconds. The NOT staff will control where it points. The page is accessed here.

The page is password protected. The username and password can be obtained from the NOT staff.

Shutting down

Each student group is expected to shutdown the observing system at the end of their session.
  • To shut down the instrument software, type in a terminal window logged in on tessa

       shutdownobssys remotealfosc

    and wait a little while. You can use the terminal window you used for starting the software.

    Note that you can operate both the instrument and the telescope from the remote observing system. To avoid any problem always shut down the remotealfosc observing system when you are not using it!

  • As the final step, fill out the EON report, now with all details.
Back to top Last modified: 12-May-2014