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Heterodyne Observing

Observing Spectral Lines


Contents:
 News
 An introduction to heterodyne observing at the JCMT
 Receivers
 Spectrometer (Correlator)
 Spectral line frequencies
 HITEC integration time calculator
 Setting up your MSBs
 Data reduction
 Comparison spectra
 Velocity considerations
 Beam maps
 Atmospheric transmission
 Special techniques

 

News:

 

An Introduction to Heterodyne Observing at the JCMT:

 

Spectral Line Receivers - "Front ends":

 

Spectrometer - "Back ends":

 

Spectral Line Frequencies:

 

Integration Time Calculator:

 

Setting up your MSBs:

 

Spectral Line Data Reduction:

 

Comparison Spectra and Telescope Efficiencies:

  • Observations of a number standard sources at frequently-observed lines are used to verify system performance during observing.
    • Average spectra: These are the average of spectra observed with the ACSIS backend under variable conditions, and judged to be of acceptable quality. Until now there are HARP spectra and RxA3 spectra available.
    • Main beam efficiencies have been derived from all ACSIS observations made with RxA3 and HARP at 230.538 and 345.796 GHz of the planets Mars, Jupiter, and Uranus.
    • Planetary flux data can also be used for calibration.

    • Older (before early 2006) DAS measurements and utilities that may still be useful:
      • Standard Spectra: These typically were taken with the DAS backend under controlled conditions during a special campaign several years ago . Although of good quality, systematic differences with newer receivers warrant caution. All receivers used have been retired since: B3, A2, B3i, and C2.
      • Representative spectra: These were also taken a few years ago and aimed to complement the standard spectra by adding data on non-standard, but frequently used frequencies. They were selected by hand as deemed 'representative', at a time that averaging large numbers of spectra was not common practice. Some frequencies are not very representative due to a lack of data. All receiver used have been retired or upgraded since: A3, B3, WC and WD
      • A web interface to our (DAS) standard spectra database is available, as is an interface to the (DAS) efficiencies database. These databases contain all observations of standard sources and planets, and derived aperture and beam efficiencies.
      • Beam efficiencies are discussed for DAS observations made of Mars, Jupiter, and Uranus with RxA3i, RxB3, RxW-C, and RxW-D.
      • Results of Moon measurements and derived Moon efficiencies are given here.
      • For archival DAS data, one can use the plot-standard command inside SPECX to see how an observation of a standard source compares with the true "standard", if a standard spectrum is available.

     

    Velocity Considerations:

     

    Heterodyne Beam Map Archive: beam maps made with the heterodyne instruments

     

    Atmospheric Transmission: check actual amount of water vapor at your observing frequency.

 

Special Techniques: Spectral line fivepoints and focus observations.

 

Staff wiki: - password protected: current performance, instructions, troubleshooting

Contact: Per Friberg. Updated: Tue Jul 15 09:49:10 HST 2014

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