Show and Edit Catalog Entries in the RCT and in the SCT

Continuum Resources

Continuum observations are generally performed using the maximum available bandwidth to obtain the best signal to noise ratio for a signal that is (mostly) independent on frequency.. Of the OSRO resources, this would be OSRO1: 256 MHz total bandwidth, delivered in two 128 MHz chunks. As an example of a continuum OSRO1 resource, click on the (\includegraphics[height=3mm]{psimg/source.png.ps}) edit icon (with fly-over help tool-tip Show/Edit properties for this catalog entry) in front of the C band resource to see the user selectable hardware and instrument options used in this resource. To get to C band when NRAO defaults is highlighted, navigate through the table, or select group 2x 128 MHz Full pol (OSRO1) in the left hand side column to remove clutter from pointing setups first.

The information displayed (figure 2.3) is the receiver selection in the table on the top (C band; 4.0 to 8.0 GHz), followed by the OSRO mode (here OSRO1; Full polarization, two subbands, 64 frequency channels). Next follows a table with the center frequency setting for two output pairs2.1(centered on a sky frequency of 4896 and 5024 MHz, where a pair consists of RCP and LCP signals). Finally, information on the correlator integration time (3 seconds), the subband observing bandwidth (128 MHz per output pair) and the frequency channel width (2.0 MHz, which is 128 MHz divided in 64 frequency channels each).

Navigate back to the NRAO defaults catalog either by clicking NRAO defaults in the catalog column tree, or by clicking Return to NRAO defaults (or 2x 128 MHz Full pol (OSRO1), depending on how you got there) at the top of the page. Please allow the web application to finish its operation and do not use the browser Back button.

OPT figure 2.3

Figure 2.3: Web browser screen shot of the OSRO1, full polarization C band resource.

Introduction

The resources for continuum (and spectra-polarimetry) OSRO1 observations and for spectral line OSRO2 observations are very similar and the differences will vanish with further commissioning of the WIDAR correlator. For now, they will be discussed separately below, but remember that all data is delivered in frequency channels. The resources in this NRAO defaults catalog are read-only, as indicated by the slanted red font, and selections are hard coded. Entries therefore appear slightly different from entries in a personal resource.

Spectral Line Resources

There is no separate example of a spectral line resource in the NRAO defaults catalog. The WIDAR correlator writes all its data in spectral line form, meaning that the continuum resources described above are already spectral line resources. However, when the scientific interest is in a specific line, typically one would want to use a spectral resolution that is better than the spectral resolution in the continuum resources above. The correlator would be set up to provide data with narrower frequency channels than 2 MHz, tuned to the line frequency when corrected for (approximate) Doppler shift. Currently, during the OSRO period, there are two possibilities to do this, depending on the requirements on polarization and width of the frequency channels:

  • For polarization measurements all polarization products are needed. The correlator must be configured as OSRO1, centered at the anticipated observing frequency. The total number of frequency channels is 128 (twice 64), and the frequency channel bandwidth can be selected to be from 2.0 MHz, in steps halving the width, down to 488 Hz. The total bandwidth will be twice 64 times the channel width.
  • If total intensity (Stokes I) is sufficient, the correlator may be configured as OSRO2, centered at the anticipated observing frequency. The total number of frequency channels is now 256, and the frequency channel bandwidth can be selected to be from 0.5 MHz, in steps halving the width, down to 122 Hz. The total bandwidth will be 256 times the channel width.

The difference in correlator configuration between OSRO1 and OSRO2 is that giving up one output pair and giving up the cross polarization products from OSRO1 each doubles the frequency channels available in OSRO2. However, if the science requires the simultaneous observation of two lines separated by more than the total bandwidth of the single output pair, the observations must be done using OSRO1 and the trade-off is using less channels per line or using a coarser spectral resolution. For example, simultaneously observing the SiO lines at 42.8 and 43.1 GHz would require OSRO1, the continuum resource2.2.

Note that at the moment Doppler calculations using a rest frequency is disabled. Check section A.3 for more information.

Connect with NRAO

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