Two Astrometric Fields for UV Observations

Maíz Apellániz, Jesús
Instrument Science Report ACS 2007-09, 16 pages


I present the data for two fields that can be used to obtain accurate astrometric calibrations in the UV. The two fields are located in NGC 604 (a Scaled OB Association in M33) and NGC 6681 (a Galactic globular cluster). The coordinates are derived from multiple ACS/HRC exposures, use the Anderson and King (2004) geometric distortion solution, have typical relative uncertainties of 1 mas, and can be used to derive geometric distortion solutions for detectors with a field of view smaller than 12 . In the process of generating the astrometric fields, the long-term stability of the HRC geometric distortion solution has been successfully tested. In two future ISRs these results will be used to derive new geometric distortion solutions for the STIS NUV- and FUV-MAMA and for the ACS SBC.