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Hubble Space Telescope
NICMOS Exposure Time Calculator Error

In the period between July 2004 and 28 April 2005, the NICMOS Exposure Time Calculator (ETC) contained an error. The error was caused by a new delivery of the quantum efficiency (QE) curves of the detectors to the synphot database. As a result, the change in QE from Cycle 7 to post-NCS installment QE was applied twice. This error led the ETC to overestimate the detector QEs by a factor 1.2 at the longest wavelengths to a factor 1.5 to 1.7 at the shortest wavelengths, depending on the camera used. The size of the effect can be estimated from the graph below. We recommend that any calculations performed in the affected period be repeated in order to obtain the correct exposure time or signal-to-noise estimates.