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Observations with ALFOSC

Observations with ALFOSC

The Essentials



Start the ALFOSC software in Sequencer mode
  1. To start the ALFOSC software you must be logged in as obs@tessa. Choose a new desktop. If you are not logged in on tessa you can open a new terminal window and type ssh -X obs@tessa and use the usual password. Click here to see a screenshot of the user interface.

  2. In an xterm type startobssys alfosc

    A window will pop-up, asking for the TCS access code, which you can find on the status page of the TCS. Type it and press enter. If you type the wrong code a red error message appears and you must try again.

    All the ALFOSC software will now be started - the UIF, BIAS and the FAPOL control.

    The "seqterm" is used to issue commands (A). To get another window type seqterm in one of the seqterm windows (A).

    Wait until the UT clock in the first line in the BIAS Status window starts to run. The data will be saved in /data/alfosc and will have the format ALnnmm0001.fits. For example with ALph160001.fits, 'AL' is the image prefix for ALFOSC images, 'ph' is for 2006/August, '16' is for the date 16 in the month and '0001' is a running number.

  3. To start the ALFOSC electronic observation log type
       cd /data/alfosc followed by
       obslog-alfosc ALnnmm\*.fits &
    in a terminal window where "nnmm" is the image prefix of the night.

For a more comprehensive start up procedure see: Starting and stopping the ALFOSC software in Sequencer mode

Focus the telescope
If for some reason you do not have time to focus the telescope the default value for ALFOSC is 23230, which normally gives good results. To set the telescope to this value enter foc-pos 23230 into the TCS.
  1. If you were not using ALFOSC previously switch to the ALFOSC default settings by entering setup-tel-alfosc into a seqterm (A).

  2. In a seqterm write object focus (to change the file description)

  3. It is recommended to set the focus, e.g. to the default value for ALFOSC (foc-pos 23230 on the TCS) before focusing. In the TCS type foc-del 0

  4. Load catalogue into the TCS by using the command read alphot.cat in the TCS

  5. Go to a suitable standard field from the alphot.cat.

  6. Ready the instrument for focusing by entering focuspyr-setup into a seqterm.

  7. Take a 20 second exposure exp 20.

  8. The focussed image will automatically appear on the DS9 display. Each star image will be split into four components, like an "Einstein cross" oriented up-down-left-right.

  9. Type focuspyr-auto in seqterm. The focus pyramid images will be analyzed automatically, and the calculated telescope focus offset will be displayed in the talker and seqterm.

  10. If you wish to analyse the focus pyramid images interactively type focuspyr in seqterm. (This will automatically run focuspyr-auto in the image as well so offsets can be compared). Put the cursor on the upper one of the four images of one focus star in the display. Type a followed by q to measure the focus offset. Repeat this sequence on several stars to get a better estimate of the offset. With the cursor in the DS9 display, type q to escape from the focus measurement mode. The number of steps to move the telescope focus will be shown.

  11. Set the telescope focus by typing foc-pos [new focus value] into the tcs. Iterate from step 7 at least once to verify focus value.

  12. When finished, remember to
    • move the focus pyramid out of the light beam
    • reset the CCD readout window and binning to desired size by typing resetxy in a seqterm.

Observing
NB! These instructions are meant as a guide. You should follow the instructions of the ToO team.

  • If you were not using ALFOSC previously switch to the ALFOSC default settings by entering setup-tel-alfosc into a seqterm (A).
  • Bring the telescope to its previously determined focus using the foc-pos command in the TCS.
  • Remove any filters which are in the light beam by typing allopen in a seqterm.

    Confirm the field with a finding chart

    1. In a seqterm(A) write object test (for file identification).

    2. Then make a test exposure exp 5 (exposure times vary).

    3. Compare the new image to the finding chart keeping in mind that North is up and East is to the left.

    Photometry

    1. Make sure no optical elements are in the lightpath by entering: allopen

    2. Place the correct filter in the lightbeam by choosing it from the gui menu and remember to change the focus offset. foc-del XX where XX is the focus offset.

    3. Take exposures following the instructions of the ToO team.

    4. Remember to take biases and flats. If not specified take 3 flats in each filter (using easyflat 3) and 11 biases (using mdark 0 11).

    Spectroscopy

    1. Make sure no optical elements are in the lightpath by entering: allopen

    2. Center the object on the slit using the acquisition script. Example: acquisition -c -q Slit_1.0 2

    3. Take exposures following the instructions of the ToO team.
    Note on calibration frames. Calibration frames are usually done by taking spectral flats (Halogen) and frames for wavelength calibration using (He, Ne or ThAr). It is normal to take the spectra for wavelength calibration close to the science spectra (before, after and sometimes both). Depending on the grism being used exposure times for calibration frames vary. Here is an overview of suggested calibration exposure times for a 1 arcsec slit. To change the different lamps use the calibration unit marked as B in the ALFOSC screenshot.