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Hubble Space Telescope
Exposure Time and S/N calculated by the ETC for the G130M/1055 and G130M/1096 Settings are NOT correct

The focus of the G130M/1055 and G130M/1096 settings were recently adjusted to increase their resolution. As a consequence, the spectral extraction height and size of the resolution element (resel) have changed. The focus changes occurred after modifications to the ETC could be accommodated and so the 21.1 ETC does not include the proper spectral extraction height or resel size for these modes. Because of these two changes, exposure times may be underestimated by as much as a factor of 4, and S/N may be overestimated by as much as a factor of 2. The ETC assumes a resel of 30 pixels and an extraction height of 47 pixels, but the true resels are smaller and depend on wavelength; the true extraction heights are larger. The ETC will be updated for phase II of Cycle 21, in the meantime the correction factors given in the Known Issues page of the ETC should be used. For more detailed information on how to determine precise corrections, users can refer to ETC Corrections for resel size and extraction height