Field Center Coordinates
This panel is visible if Individual Pointing(s) has been selected in the Source panel. The number of pointings that can be defined is nominally 150 per Science Goal, distributed between multiple sources. In practice, more pointings can be created if the source list can be split into multiple clusters. It is possible to define multiple pointings per source, but each one must overlap such that they form a single mosaic. If multiple mosaics are required, they must be placed in separate Field Sources.
- Coords Type: Field centre in relative or absolute coordinates. Relative positions are offset from the source coordinate and are recommended. Absolute coordinates can be entered for non-solar-system objects, but will be converted to offsets from the source coordinate during SB generation as absolute coordinates cannot be used with the telescope control system.
- Array Type: If both the 12- and 7-m Arrays are required, this allows the user to choose which array's pointings to display.
- Offset Unit: If relative coordinates have been selected, set the unit of the offset (usually arcsec).
- #Pointings: A count of how many pointings have been defined.
- RA and Dec: The position of each pointing should be entered in this table, usually relative to the source coordinate. Absolute coordinates are also possible, but are not recommended. No pointing can be more than 5 degrees away from the source coordinate.
At the bottom of the panel are buttons which allow a user to add and delete pointings manually, as well as to reset to a single pointing at the source position. It is also possible to import and export pointings from and to an external ASCII file. The file format is very flexible and allows a user to write out the pointing positions in either offset or absolute coordinates and will automatically do the conversion between the two i.e. one can export in a different system to what is displayed. An example of the format for absolute coordinates in sexagesimal is shown here:
RA , Dec, Coordinate Type, Coordinate Units
-- This signals end of the header
04:31:38.4369, 18:13:57.651,Absolute,Sexagesimal
04:31:40.5426, 18:13:57.650,Absolute,Sexagesimal
04:31:36.3312, 18:13:57.650,Absolute,Sexagesimal
The “Absolute” coordinate type can be combined with the units “Sexagesimal”, “Degrees” or “Radians”, whilst “Offset” pointings can be defined in “Arcsecs”, “Arcmin” or “Degrees”. Both the unit and coordinate type are case-insensitive. Galactic coordinates are not supported.
The ALMA OT Team, 2024 May 21