This keyword replaces Coordinate_Source starting with Cycle 14 Calibration and all Cycle 15 programs. Select one of the following Reference_Frame values for each target.
To be used if the coordinate reference frame is tied to the International Celestial Reference System (ICRS). Catalogs tied to the ICRS include: HST Guide Star Catalog 2 (GSC2), Hipparcos Catalog and the Tycho-2 Catalog.
To be used if the coordinate reference frame is tied to the HST Guide Star Catalog 1. Include the Plate ID (from the "Plt" column in the GSC1) with your coordinates. This includes the GSC1 special catalogs (those with ZZZ Plate IDs). If the "Plt" value is 56, then the true source is the Hipparcos Input Catalogue. In this case use Other for the Reference_Frame.
A Plate-ID should be supplied when coordinates are taken from the Guide Star Catalog 1, or measured using a GSC survey plate, or previous HST image using GSC1 coordinates (in which case the guide star plate used in the observation should be specified). This ensures that the correct plate is used for the observation and not some other, overlapping plate. If GSC1 is specified as the reference frame and no Plate-ID is supplied then the plate providing the best astrometry will be used in selecting guide stars.
To be used if the coordinates are neither GSC1 nor ICRS.
Space Telescope Science Institute http://www.stsci.edu Voice: (410) 338-1082 help@stsci.edu |