An Introduction to Heterodyne Observing at the JCMT

• Spectral Line Observing guide - A guide for new ( and not so new ) users. Covers basic concepts, techniques, calibration (for more recent results see the links below) and data reduction. Note that this has not yet been updated for observing with ACSIS. HTML and postscript.

Spectral Line Receivers - "Front ends"

• Overview and current status
• HARP-B (345GHz)  16 pixel array receiver - see also current status
• Receiver A3 (230 GHz) - see also current status

• Receiver W Under Commissioning  (B- and D-band; 345 and 690 GHz)

• Receiver B3 Retired  (345 GHz) 
• Not offered with ACSIS Heterodyne polarimeter. Rover will be offered with ACSIS after commissioning.

Spectrometer - "Back ends"

• The ACSIS digital autocorrelation spectrometer has been commissioned for use with receivers HARP, Rx A and B (and W expected). Currently available observing modes can be found here.
• Special ACSIS setup configurations for the spectrometer to handle some special circumstances.
• Digital Autocorrelation Spectrometer (the DAS), see also Postscript file. Note that the DAS spectrometer has now been retired from the JCMT.
  A description of the properties and use of this versatile instrument (Note that this information is under revision, although the principles are still correct).

Getting Spectral Line Frequencies

• List of all molecular species currently known in space - by Al Wootten
• JPL spectral line catalog browser form; and explanation of use
• List of observed microwave lines (Lovas 2002 revision); see also NIST fundamental data listings
• The Cologne Database for Molecular Spectroscopy

Heterodyne Integration Time Calculator

• A web-based tool for calculating required integration times for heterodyne observations can be found here

Spectral Line Data Reduction

• A cookbook for ACSIS data reduction is available. It is still under development and we welcome feedback on how we can improve the information given within.
  There is also a quick guide.
• Reduction of ACSIS data is done with Starlink software.
  The latest version of the STARLINK package can be downloaded here (release notes)
• The DAS has been retired, and SPECX along with it although SPECX is still used for reduction of archived DAS data.
  • Data from the DAS (in GSD format).
  • SPECX (program available via this link)
    • SPECX Cookbook, for spectral line data reduction, also available in Postscript.
    • Crash Course in SPECX, for those in a hurry.
    • Full SPECX Manual (web browsable) (postscript)
    • Introduction to velocity and frequency scales in SPECX (courtesy Andy Gibb) - 160Kb postscript file..
  • One can also use CLASS for reduction of DAS data, and in a still very limited way (headers are incomplete) for ACSIS data

Comparison Spectra and Telescope Efficiencies

• Standard Spectra are used to verify system performance during observing (source list). These data cover frequently-observed lines within each observing band.
  Spectra were extracted from the data archive (according to the standard spectra requirements) only for receiver B3, and the retired receivers A2, B3i, and C2.
  One can use the plot-standard command inside SPECX to see how an observation of a standard source compares with the true "standard", if one exists.
• "Representative" spectra have been assembled (when available) to fill the information gaps in the tables of the standard spectra for all heterodyne receiver bands (A3, B3, W/C and W/D). Eventually these data should cover all standard source/transition combinations.
  Note that for a few sources/frequencies the representative spectra given here are not really representative.
  Data for HARP are being collected but results are not yet available on these webpages.
• A web interface to our (DAS) standard spectra database is available, as is an interface to the (DAS) efficiencies database. In these databases are all observations of standard sources and planets, and derived aperture and beam efficiencies (main beam efficiency for Uranus and Neptune, and for Mars, when its diameter is small) .
• Results of Moon measurements and derived Moon efficiencies are given here.
• Planetary flux data can also be used for calibration.

Special Techniques

• Currently almost all pointing and focus observations are done as Spectral line fivepoints and focus observations (ACSIS continuum observations are rather noisy because of problems that are still under investigation).
  This greatly increased the number of useful sources, especially for our remotely tuneable receivers.

Atmospheric Transmission

• Check the Atmospheric Transmission at your observing frequency for the actual amount of water vapour.

Velocity Considerations

• Velocity frames and definitions
• Velocity & frequency scales; identifying image band lines (within SPECX), (Andy Gibb, 2004)
• You can calculate the LSR Velocity to see if the telluric line might interfere with your observation if you are doing frequency switching (use topocenctric velocity for IAU Standard Solar Motion and multiply velocity with -1.0).

Beam Maps made with the Heterodyne Instruments

• A link to the heterodyne beam map archive can be found here .