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Table of Contents
Heterodyne Observations
This is a brief introduction to heterodyne observing at the CSO. It continues from the general Introduction to Observing.
- Preparation
- Heterodyne Systems systems description
- Observing Time calculation
- Source and line catalog preparation
- Planning for Wideband Observations
- Tuning narrow band and Barney receivers
- Types of Observations
-
Quick Start
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.
- 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:
- The upper one displays the telescope status, updated once per second.
- The lower one is for the UIP.
- In the UIP xterm, log into your account then start UIP.
kilauea% ssh user@kilauea
kilauea% uip - If necessary, enable control mode.
UIP> pundit true - Open the shutter. Avoid the sun. When remote observing, wait until one hour after sunset.
UIP> shutter /open - Create a data file.
UIP> data yyyy-mm-dd - 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
- 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
- If necessary, load the appropriate pointing file.
UIP> point rx_name - 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. -
- 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.
-
- Maybe useful as a Calibration reference.
- Track the target source.
UIP> obs target - Set the integration time.
UIP> spec 10 - Observe the target.
After observing
- 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.
- Stow the telescope
UIP> stow
After sunrise, wait until the shutter is no more than 15% open before using thestowcommand. Please do not let the Sun directly illuminate any part of the telescope structure. Check the CSO webcams. - Stop the secondary wobbler
UIP> sec /stop - Turn off the IF processor in the AOS5 rack.
- Turn off the receiver.
- Replace the Cassegrain mirror covers.
- Exit from the UIP.
UIP> exit - Exit from your account but please do not close the UIP xterm in the VNC desktop.
- Stow any ladders or other equipment.
- 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. - Please submit an Observer Report.
- Logout from kilauea and other computers.
- Turn off all the lights and heaters in the building. Lock both entry doors.
Drive safely!
Sideband Identification
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.
Troubleshooting
- 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 …
