In each Science Goal, sources are selected in one of two ways: by specifying a rectangular field or by specifying individual pointing positions. Each involves some restrictions.

Source Science Goal restrictions

A single SG is constrained to include one set of observational parameters that apply to all sources included in that goal. This includes AR (either a single value or a range), sensitivity, LAS, and receiver band. There is no restriction on the number of SGs per proposal.

For sources distributed widely in the sky the SG will be split by the ALMA OT into different “clusters”, each grouping all sources within 10 degrees (1 degree for SGs requiring long-baseline configurations). For each grouping within the SG, the total number of pointings must be less than or equal to 150. Pointings with the ACA, if used in concert with 12-m Array observations, do not count against this 150-pointing limit.

There is no restriction on the number of Science Goals. Sources in a SG are futher subjected to the following restrictions:

1. All the sources in an SG must be defined by the same field setup – either all as rectangular fields, or all as individual positions.

2. Sources must use the same spectral setup (relative placement and properties of spectral windows).

3. For a given group of sources clustered within 10 degrees on the sky (or 1 degree for long-baseline configurations), there cannot be more than 5 separate tunings.

Rectangular field

A rectangular field (also referred to as a mosaic) is specified by a field center, the length, width and orientation of the field, and a single spacing between the pointing centers. The ALMA OT will set up a uniform mosaic pattern based on a user-specified pointing separation, and will calculate the time to reach the required sensitivity considering any overlap. Non-Nyquist spatial samplings are allowed but must be justified in the TJ. Observations are conducted using the “mosaic” observing mode. This mode repeatedly cycles through all the pointings in the mosaic so that the imaging characteristics across the map are similar.

If ACA observations are requested as part of a mosaic, then a corresponding 7-m Array mosaic will also be observed. If these include TP observations, the mosaic area(s) will be covered by the TP Array using on-the-fly mapping.

An SG may include multiple sources, each of which can have a differently sized rectangular field. The collection of mosaics is subject to the source SG restrictions given above.

Individual pointings

PIs may choose to define a “custom mosaic” by specifying a set of individual, overlapping, pointing positions. Gaps in pointings are not allowed. Custom mosaics are subject to all the source SG restrictions given above.

The interferometric data will be combined in post-processing to produce a single image. If ACA observations are requested as part of a 12-m Array SG, then the corresponding 7-m Array observations will be obtained using a Nyquist-sampled mosaic pattern that covers the 12-m Array pointings. If these include TP observations, the mosaic area(s) will be covered by the TP Array using on-the-fly mapping.

Pointings that do not overlap within a given SG must be included as different field sources within the SG.