Heterodyne Observations

This is a brief introduction to heterodyne observing at the CSO. It continues from the general Introduction to Observing.

• Quick Start
• After Observing

• Preparation
  • Heterodyne Systems systems description
  • Observing Time calculation
  • Source and line catalog preparation
  • Planning for Wideband Observations
    • Receiver tuning diagram
  • Tuning narrow band and Barney receivers
• Types of Observations
  • Beam Switching
  • Position Switching
  • Pointing
  • Frequency Switched Observations
  • Mapping
  • OTF mapping
• Calibration
  • Sideband Identification
• Heterodyne Data Analysis
• Troubleshooting

This guide outlines a common observing scenario, simultaneous Beam Switching observations of three CO isotopologues in the (2-1) lines. There are many possible variations.

1. Connect to the VNC desktops. Two desktops are used, one for the UIP and the other for the spectrometer displays. (This is more flexible than one large desktop.)
   mycomp> csovnc.pl -C -l user uip
mycomp> csovnc.pl -C -l user spectro
   • In the UIP desktop, there are two xterms on the right side:
     1. The upper one displays the telescope status, updated once per second.
     2. The lower one is for the UIP.
2. In the UIP xterm, log into your account then start UIP.
   kilauea% ssh user@kilauea
kilauea% uip
3. If necessary, enable control mode.
   UIP> pundit true
4. Open the shutter. Avoid the sun. When remote observing, wait until one hour after sunset.
   UIP> shutter /open
5. Create a data file.
   UIP> data yyyy-mm-dd
6. Open source and line Catalogs, if necessary.
   UIP> catalog sources
UIP> catalog lines /line
7. Start the Secondary mirror wobbler for Beam Switching. Tuning the servo takes about 5 min. For example, 120 arcsec amplitude at 0.534 Hz.
   UIP> secondary 120 0.534
   • Check the status of the servo tuning.
     UIP> secondary
8. Select the receiver and verify the teritary mirror position.
   • For the sidecab receivers, first place the telescope at 25° zenith angle.
     UIP> za 25
UIP> instrument [RX230 | RX345 | RX460 | RX690]
UIP> tertiary /sidecab
   • For the Cassegrain receivers, first remove the mirror covers and manually rotate the tertiary mirror.
     UIP> instrument [RX345X | RX805]
UIP> tertiary /cassegrain
9. If necessary, load the appropriate pointing file.
   UIP> point rx_name
10. Tune the receiver. For example, the standard tuning for three CO isotopologues.
    UIP> lo 12co2-1 /side up /if 5.28
    Older receivers require manual tuning.
    • Receiver tuning
    • Barney
11. Configure the spectrometers (FFTS1, FFTS2, AOS5).
    UIP> spec 2 /ffts2 /ffts1w 5.28 /res
    • For the older narrow band receivers, turn on the IF processor switch in the AOS5 rack.
12. Calibrate and measure the system temperature.
    UIP> cal
13. Measure the Pointing with Beam Switching.
    UIP> spec /base 2500 3500 4700 5700
UIP> five 20 /ffts1 /range 4000 4200
    • Use the Orrery to select pointing sources.
14. Take a reference spectrum of the pointing source with Beam Switching.
    UIP> chop 2
    • Maybe useful as a Calibration reference.
15. Track the target source.
    UIP> obs target
16. Calibrate and measure the system temperature.
    UIP> cal
17. Set the integration time.
    UIP> spec 10
18. Observe the target.
    • With Beam Switching.
      UIP> chop 10
    • For Position Switching, first stop the Secondary mirror wobbler.
      UIP> secondary /stop
UIP> oo 10

1. Close the shutter. This takes 10-15 min. When remote observing, please close one hour before sunrise.
   UIP> shutter /close
   • If the shutter doesn't close, follow these instructions. Please report problems to the staff.
2. Stow the telescope
   UIP> stow
   After sunrise, wait until the shutter is no more than 15% open before using the stow command. Please do not let the Sun directly illuminate any part of the telescope structure. Check the CSO webcams.
3. Stop the secondary wobbler
   UIP> sec /stop
4. Turn off the IF processor in the AOS5 rack.
5. Turn off the receiver.
   • For the 230/460 GHz receiver:
     UIP> lo /off
   • For the older receivers: shutdown procedure
   • For Barney: shutdown procedure
6. Replace the Cassegrain mirror covers.
7. Exit from the UIP.
   UIP> exit
8. Exit from your account but please do not close the UIP xterm in the VNC desktop.
9. Stow any ladders or other equipment.
10. Return the pointing log book to the shelf.
    Heterodyne observers please add your nightly pointing sheet to the end the log book and return the book to the bookshelf.
11. Please submit an Observer Report.
12. Logout from kilauea and other computers.
13. Turn off all the lights and heaters in the building. Lock both entry doors.

Drive safely!

The CSO has DSB receivers with equal gain in the two sidebands. To determine if specific lines are in the upper or the lower side band, change the LO frequency. Lines in the two sidebands will shift in opposite directions. Lines in the image sideband will shift twice as far as lines in the signal sideband.

• To change the LO by 5 MHz,
  UIP> lo /f_off 0.005

If the atmospheric transmission in the two sidebands is different, Calibration correction will be necessary.

• If the system temperature is unreasonably high for the optical depth (τ) or weather conditions.
  • Is the IF processor in the AOS5 rack on?
  • Is there a warm load or something else in the beam?
  • Are the cassegrain mirrors uncovered?
  • Is the position of the tertiary mirror correct?
  • Are the sidecab mirror positions correct? To reposition them,
    UIP> za 25
UIP> lo line /receiver rx_name /force
  • Is the line frequency close to an atmospheric line?
    Check the atmospheric transmission.
  • Is the shutter closed?
  • Is the optical depth (τ) high and the zenith angle large?
    Wait for the source to rise.
  • Is the weather worse than you thought?
  • Is the 345 GHz sidecab receiver tuned to the fifth harmonic?

• If there's no line even though the system temperature is reasonable and the source should have a bright line.
  • Is the correct pointing model displayed on the antenna status monitor?
  • Is the pointing good?
  • Is the frequency correct? Check the catalog.
  • Is the receiver tuned properly?

• If the spectrometer stops, restart it (specify the backend).
  UIP> spectrometer /restart /ffts2 …

These older documents may contain obsolete information. Use with caution.

• Cookbook 2011-06-22
• Checklist 2011-06-22