Dept of Astrophysics
University of NSW
Sydney
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Observing Procedure

This procedure is performed each time there is a changover from observing a source to doing a pointing and vice versa. Use this page as a checklist.

Before Observing

The following is a checklist of items that should be checked before commencing observing, especially if the telescope has been previously used for cm VLBI observations.

ACC Is the ACC on and functioning properly. Is it switched to remote?
Turret Is the mm-reciever in position at the focus point?
LO Chain

Has the mm L4 synthesister box been installed in the vertex room?
Is the L2 synthesiser switched over in the vertex room?
Is the correct cable plugged into the Marconi synthesiser?
Subreflector Is the subreflector focus position correct for the frequency you are using?
After VLBI

Are the cables on the VLBI rack in the correlator room set correctly?

MAPS

Is the weather station on the MAPS rack running?
Are all indicators on the MAPS rack Green
Mushrooms Are all mushrooms onsite in the out position?
  • For detailed information on how to solve these problems see the Mopra Observing Manual.

At the start of an observing run you should manually set the coarse and fine attenuators in a_test and check that the GTP values for both polarisations are ~2.5.
In a_test:

  • set coarse / fine 'ab00'
  • atten

Where a and b are values between 1 and 7. Try to set the coarse attenuators first so that the fine attenuators are set at ~4 with a GTP of ~2.5 on both polarisations.

Setting up the Observation

  1. Set Correlator configurations:
    • In the mpcor GUI set the desired correlator confguration file
      • Pointing = ac_64_1024_2f (different frequency in both channels) Channel B must be SiO. 
      • General Use = e.g. ac_64_1024_2 (same frequency both channels).
      • Click on the "Config" button to program configuration into the correlator.

    • In the TCS GUI
      • Check the 'Auto Decode' button is active and the 'Auto Generate' Button is inactive
      • Browse to the correlator configuration file set in the previous step
      • Pointing => turn on (red square highlighted) frequency 2 on the LO panel to activate the 2nd frequency.
      • General Use => turn off frequency 2 on the LO panel. Both polarisations are set to frequency 1.
      • Check that the no. of channels set is correct and the vlsr for the source is set.
      • Note: If this is the first observation of a new line or TCS has been restarted you will need to enter in the line frequencies in MHz under each channel. CH1 should be set to the rest frequency of the line tuned in the reciever. CH2 should be set to the frequency of the SiO maser.
      • Note: A bug in TCS causes the frequency 2 button to turn on when any of the 'action panel' buttons are selected so this should be the last thing you check when before you press go.

  2. Set the schedule file
    • In the Action Panel type in the relevant schedule file name
    • Pointing => pnt_test2 for strong masers or pnt_test3 for weaker masers.
    • General Use => e.g. onof10m, onof1D.
    • click on 'load schedule', and the schedule name will convert to uppercase
    • Note: Do not browse to the file- the program will report an error when trying to load. This is a bug.


  3. Set the source name
    • If you have previously defined a catalog file:
      • In the Antenna Control panel click on the 'source name' button. A dialog box will open displaying directories and files.
      • General Use => Choose 'own' from the menu. Browse to the your catalog file e.g. c/observer/unsw_hc/cat.all
      • Pointing => Choose 'standard' from the menu. Browse to the file Sio_Point.cat in the same directory and select a pointing source near to your target. Make sure it has a known velocity.
      • Select the desired source and check the velocity has been applied to frequency 1 (and frequency 2 if doing a pointing)
      • Click on the 'Goto' button to slew to the source and begin tracking.
    • If you have not defined a catalog file:
      • Enter the RA & DEC / L & B manualy
      • Check that your offset is 'none'
      • Check your coordinate system is set correctly (e.g. J2000, B1950, Galactic)

  4. Tune the recievers.
    • On the mmdrive pc tune the recievers to the lines of interest.
    • Pointing => Ch B sould be set to SiO.
    • General Use => Ch B sould be set to 'Ch A'. 
    • See the Tuning Guide for a complete description.

  5. Perform a Tsys measurement every 30 min or before each source is observed .
    • Note: It is not necessary to do this before pointing observations.
    • After the tuning has been completed and the antenna is tracking the source, type: mm_tsys in the controller command box on the TCS GUI
    • After 2 minutes the values of tsys for both channels will appear on the 'system status' screen of the TCS GUI Record in the log file (this is necessary for flux calibration). 
    • Note: Perform a Tsys measurement more often if the weather conditions are in a state of flux.

  6. Start observing!
    • In the TCS GUI Action Panel set the number of repeats desired
    • Click on 'Start Sched' to start observing.
  7. Close the Data File!!!!!!!
    • After every source don't forget to Start observing!
      • In the TCS GUI Action Panel set the number of repeats desired
      • Click on 'Start Sched' to start observing.
      by clicking 'close file' on the TCS GUI.

Performing a Pointing

Aim to point once every hour or every time you change elevation by more than 15 degrees. The procedure for pointing is the same as the procedure above with a few additional steps added.

As before:

  • Set the correlator configuration to ac_64_1024_2f in the mpcor GUI and the TCS GUI
  • From the 'Source' button browse to the pointing source catalog and select a maser < 15 degrees away from your science object.
  • Set the schedule file to pnt_test2 or pnt_test3 depending on the strength of the maser selected.
  • Slew to your source.
  • Tune Channel B to SiO maser (86.243442 GHz ).
    • Beware of getting crashes associated with the tuning PC as you switch back and forth between frequencies. These occur particularly when the toner is placed in and out of the beam.
  • Check the last data file has been closed and frequency 2 is selected
  • Start the schedule file with 1 repeat.
  • When the schedule has completed close the file.

New Steps:

  • In an xterm on warrum open to mpccc:
    • Use the command 'mopnt' to transfer the closed data file from to Mopra
    • Wait for the transfer to complete.

  • In an empty DECterm on Mopra:
  • Type the command 'sio_point'. This will start the pointing correction program.
  • If the filename offered is correct press return to accept.
  • Examine the pointing corrections calculated.
  • If the corrections are < 8 arcseconds type accept and move to observing a science source.
  • If the corrections are > 8 but < 20 arcseconds close the file and repeat the pointing until satisfactory corrections are obtained and then move to observe a science source
  • If the corrections are > 20 arcseconds try repeating the pointing but if this does not work call for help.

Page created by Cormac Purcell and maintained by Nadia Lo. If you have any comments and suggestions, please direct your email to nlo@phys.unsw.edu.au.