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Hubble Space Telescope
Verification of Proper Motion Specifications

We remind proposers that the specification of correct HST pointing information is their responsibility; STScI cannot check this information systematically, and observations that fail because of incorrect pointing specifications will not be repeated. We continue to experience some HST observation failures caused by erroneous proper motion entries. The most frequent cause has been incorrect units for the proper motion in right ascension. Prior to Cycle 18, the required units were seconds of time per year. As of Cycle 18 Phase II, a choice of milli-arcsec/yr, arcsec/yr, or sec of time/yr is available in APT and must be selected by the proposer. This improvement has reduced inadvertent entries in the wrong units. However, some Cycle 17 programs are still active and did not benefit from this safeguard. Another pitfall may be Cycle 17 programs that have been revised with the Cycle 18 software without due attention to this point. Finally, it is essential to make certain that the specified epoch and coordinates in fact correspond; e.g., if the coordinates have been corrected for proper motion to epoch 2000 but a different plate epoch is entered, the HST pointing will be incorrect. At this time, we request that all proposers with active programs involving proper motions verify their entries for correctness, and most especially those with active Cycle 17 programs. Two additional recent improvements should be noted in this context: clearer target confirmation charts, and the inclusion of proper motion in the APT/Aladin display.