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Spectral Setup

The Spectral Setup page contains fields to specify spectral windows, each of which samples a sources's spectrum over a particular range of frequencies. The Forms editor basically consist of panels for the spectral specification, a feedback area that gives messages when the spectral specs are in error, and a panel that contains the sources that have been defined in the Field Setup page. An example is provided in Figure 5.7. An extremely useful accompaniment to the Forms editor is the Visual Spectral Editor that is described in full detail in Chapter 9.

The first thing to select is the type of spectral observation: Spectral Line, Single Continuum or Spectral Scan. The main difference between Spectral Line and Single Continuum is that the latter is basically a shortcut to defining a maximum-bandwidth, low-resolution spectral setup that will almost certainly be used for observing a continuum only. Spectral Line gives you full flexibility in defining spectral window positions, bandwidths and spectral resolutions. Spectral Scan is also a shortcut, in this case to a collection of multiple tunings that cover a continuous array of frequency space.

In addition, the polarization products must be specified. All ALMA receivers detect linearly-polarized radiation and the two orthogonal senses of this are referred to as X and Y. In order to maximise sensitivity, dual-polarization observations correlate both the X and Y signals from each antenna, leading to both XX and YY being delivered for each spectral window. It is usually only necessary to observe in single polarization (XX) if the maximum spectral resolution is required. Full polarization observations (XX, YY, XY and YX) should be selected if the source polarization properties (magnitude and position angle of linear polarization) need to be determined. For the moment, full polarization can only be selected for sources that are no larger than one third the size of the antenna beamsize i.e. mosaics and the ACA are not available.



Subsections
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Next: Spectral Line Up: Adding Phase-1 Science Goals Previous: Field definitions   Contents
The ALMA OT Team, 2014 May 21