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Revised COS G140L 1280 CENWAVE Setting for Cycle 18
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Hubble Space Telescope
Revised COS G140L 1280 CENWAVE Setting for Cycle 18

For Cycle 18, the G140L 1230 CENWAVE setting is being replaced by a new 1280 CENWAVE setting. This change was necessary, because the FP-POS=4 position of the 1230 setting caused zero-order light to fall onto the detector. The gap in wavelength coverage between the two COS FUV detector segments shifts by 20 Å between the 1230 and 1280 settings, but is still completely filled by the G140L 1105 central wavelength setting. Please see Table 5.4 in Section 6.10 of the COS IHB for the wavelength coverage of each COS FUV spectroscopic setting, including both the new 1280 and the older 1230 settings. Note that, in the COS spectroscopic ETC, the new setting is labeled as "1250" rather than "1280"; however, the calculations performed by the ETC are correct for the new 1280 setting. In the APT phase 1 tools, the setting is correctly labeled. APT support for the new setting will be available in time to submit Cycle 18 phase 2 proposals. Cycle 17 programs should continue to use the old 1230 CENWAVE setting, but are required to avoid the use of the FP-POS=4 position with this CENWAVE.