Spectral Line Resources

Creating a spectral line resource is very similar to creating continuum resources as outlined above, except for the possibly difference in correlator mode, subband bandwidth and exact frequency tuning. There are some hints to spectral line features in the recipes in the previous section. In the grand scheme of end-to-end operations, resources with the requested correlator settings may be pre-filled from information submitted to the PST during the observing time allocation procedure. However, at this stage not much of this has been implemented, and in particular Doppler calculations are disabled (see section A.3).

The NRAO defaults resource catalog contains full polarization dual output pair spectra-polarimetry resources (the continuum resources). If they appeal to you, you can copy/paste them in a personal catalog just as for the continuum resources above and edit them as needed. Check the spectral line resource properties very carefully as the spectral line resources in the NRAO defaults have a fixed sky frequency whereas you probably want to use a rest frequency in combination with Doppler tracking2.3. Most likely, however, you will opt to create your own resource from scratch, just like creating a continuum resource previously. Some items that may need extra attention are described below.

The correlator mode and other details such as the observing band and frequency should have been specified during the proposal submission stage. You may have received alternate suggestions by the PSC. In short, the correlator options are OSRO1 and OSRO2.

OSRO1 is mandatory for polarization or simultaneous dual frequency observations (within the same observing band). It delivers 64 frequency channels in full polarization for two independently tunable output pairs with identical subband bandwidths. The subband bandwidth, which is the total observing bandwidth per RCP and LCP output pair, can be chosen form 31.25 kHz to 128 MHz in powers of two. This yields a frequency channel separation of the subband bandwidth divided by 64 (488 Hz to 2 MHz).

OSRO2 can be chosen if no polarization information or if no simultaneous dual line observations are required, yielding a factor four better spectral resolution when using the same subband bandwidth compared to OSRO1.

Frequency tuning and frequency type (sky or rest) need to be set in the next table. Also supply the unit with your frequency (Hz, kHz, MHz, GHz), otherwise it assumes Hz by default. Choose either output pair AC or BD and note the restriction for Ka band in section 2.2.3. Select and enter the Rest Frequency if you anticipate Doppler tracking on a spectral line (currently disabled!), or Central Frequency if you know your exact sky frequency and do not want to apply Doppler tracking. If your line is strong and you plan to apply off-line Doppler corrections, you must over sample your line with at least a factor 3 to 5 to be successful; see section A.3. Note that for Doppler tracking you need a velocity and reference frame, which you assign to the source in the SCT, or which you enter for each scan in the OPT.

Correlator integration time should be set in integer seconds equal or larger than one. The output data rate and your required field of view (limited by time averaging smearing) should guide you in what to enter.

The subband (total observing) bandwidth is selected by checking (ticking) the blue circle (\includegraphics[height=3mm]{psimg/selected.png.ps}) for the output pairs for the correlator setting you require. This bandwidth will be divided in 256 frequency channels to provide your spectral resolution.

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