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cso:instruments:heterodyne:pointing [2013-10-31 07:19]
sradford
cso:instruments:heterodyne:pointing [2014-01-22 19:01] (current)
sradford
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 +====== Pointing ======
 +
 +Point often for the first 2--3 hours after sunset because the pointing will shift as the temperature of the telescope changes ([[http://​www.submm.caltech.edu/​%7Ehs/​memo/​shinnaga-memo04nov.pdf|thermal pointing shifts]]). Repoint no later than an hour after the initial pointing. Repoint every 2.5--3 hours thereafter.
 +
 +[[chop|Beam switching]] with the wobbling [[cso:​telescope:​secondary]] may give more consistent results, especially if the weather is marginal. Use a short subscan integration time because there are four subscans at each point. [[onoff|Position switching]] is also possible.
 +
 +Before pointing,
 +  * Check the correct pointing model is displayed on the antenna status monitor
 +  * Load recent pointing offsets from the pointing logbook \\ ''​__UIP__>​ **fazo //​az_offset//​**''​ \\ ''​__UIP__>​ **fzao //​za_offset//​**''​
 +
 +The pointing examples use <​sup>​12</​sup>​CO(2-1) and beam switching. ​
 +
 +===  Line pointing ===
 +
 +There are many more line sources -- typically evolved stars -- than bright continuum sources. But it may be necessary to tune the receiver to a bright line. The example uses <​sup>​12</​sup>​CO(2-1) and beam switching. Position switching is also possible.
 +
 +  * Tune the receiver, if necessary, and setup the spectrometer. \\ ''​__UIP__>​ **LO 12CO2-1 /IF 5.28 /SIDE UP**''​ \\ ''​__UIP__>​ **SPEC 2 /FFTS1W 5.28 /FFTS2 /​RES**''​
 +  * Choose a pointing source with the [[cso:​telescope:​orrery]]. Then track the source with the telescope. \\ ''​__UIP__>​ **OBSERVE IRC10216** ''​
 +  * Start the secondary wobbler. \\ ''​__UIP__>​ **SEC 90 0.534** ''​
 +  * Set the baseline windows. These are line free regions used to calculate the spectral baseline.\\ ''​__UIP__>​ **SPEC /BASE 2500 3500 4700 5700** ''​
 +  * Do a calibration. \\ ''​__UIP__>​ **CAL**''​
 +  * Measure the pointing. The integration range must include the line. \\ ''​__UIP__>​ **FIVE 20 /FFTS1 /RANGE 4000 4200 ** ''​
 +    * Choose a step size somewhat less than the beam size. Here the step size is 20 arc sec because the beam size is about 30 arcsec at the observing frequency.
 +  * Update the pointing corrections. If the results of the pointing fit seem dubious, use the ''​FAZO''​ and ''​FZAO''​ commands to update the corrections.
 +  * Repeat pointing measurements until convergence.
 +  * Record the pointing results in the pointing log book to share with other observers.
 +  * After pointing, remove the baseline windows. \\ ''​__UIP__>​ **SPECTROMETER /NOBASELINE **''​
 +
 +If the line is not centered in the spectrometer or if there are lines in the baseline windows, take a spectrum prior to pointing to determine the line position and the line free baseline windows. This may be difficult if the pointing is far off.
 +
 +For standard sources, it is good practice to take a reference spectrum just after pointing as a calibration comparison.
 +
 +
 +=== Continuum pointing ===
 +
 +The bright planets, Mars, Jupiter, and Saturn, are good sources. Uranus and Neptune may be (very) difficult.
 +
 +  * Tune the receiver, if necessary, and setup the spectrometer. \\ ''​__UIP__>​ **LO 12CO2-1 /IF 5.28 /SIDE UP**''​ \\ ''​__UIP__>​ **SPEC 2 /FFTS1W 5.28 /FFTS2 /​RES**''​
 +  * Choose a pointing source with the orrery. Then track it with the telescope. \\ ''​__UIP__>​ **PLANET MARS** ''​
 +  * Start the secondary wobbler. \\ ''​__UIP__>​ **SEC 90 0.534 ** ''​
 +  * Do a calibration. \\ ''​__UIP__>​ **CAL**''​
 +  * Measure the pointing. For a continuum source, integrate over the entire spectrometer bandpass. \\ ''​__UIP__>​ **FIVE 20 /FFTS1 **''​
 +    * Choose a step size somewhat less than the beam size. Here the step size is 20 arc sec because the beam size is about 30 arcsec at the observing frequency.
 +  * Update the pointing corrections. If the results of the pointing fit seem dubious, use the ''​FAZO''​ and ''​FZAO''​ commands to update the corrections.
 +  * Repeat pointing measurements until convergence.
 +  * Record the pointing results in the pointing log book to share with other observers.
 +
 +It is good practice to take a reference spectrum of the planet just after pointing to check the beam efficiency.
  
cso/instruments/heterodyne/pointing.txt · Last modified: 2014-01-22 19:01 by sradford
 
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