The GMOS-N B600 grating sensitivity has recently degraded significantly. This overall degradation is in addition to the blue sensitivity loss reported previously. Since the new B480 grating is now available for GMOS-N, we recommend changing B600 programs to the B480 grating. The B480 grating offers a wider wavelength coverage than B600 at a a slightly reduced spectral resolution. The characteristics of all GMOS gratings are summarized here.
A comparison of the throughput for the GMOS-N B600 and B480 gratings, measured before and after the recent Gemini-North telescope shutdown and recoating of the primary mirror, is shown below. The throughput measurements are obtained from spectrophotometric standard stars observed under CC50% conditions and include the GMOS-N and telescope optics. For the B480 grating, the results show an improved throughput after the recoating of the primary mirror. For the B600 grating, the throughput improvement is largely canceled out by the grating degradation.