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Calibration programs are executed each cycle to monitor the instrument's behavior. The COS team uses these calibration data and extracts telemetry information from GO data to monitor the stability and general performance of the instrument. Below are the monitoring results for the COS FUV and NUV Dark Rates.

The COS FUV dark rate is monitored regularly by taking five 1330s dark exposures every two weeks. These exposures, after excluding those that graze the SAA, are used to determine the dark rate trend vs. time for both FUVA and FUVB detector segments.

Background counts in FUV observations can come from a variety of sources including radioactive decay of atoms in the detector glass, external charged particles, and scattered light. Because COS observations can be taken in TIME-TAG mode, individual events that are identified as background events by their PHA can be screened out during calibration. Analysis of the dark rate on this page has been done using PHA limits of 2-30, the limits currently imposed by CalCOS.

For more information on the COS FUV dark rate, see ISR 2010-11 or the most recent cycle’s ISR found in the calibration summary tables.

FUVA Dark Rate vs. Time Last Updated: Orbital Variation Last Updated:
FUVB Dark Rate vs. Time Last Updated: Orbital Variation Last Updated:

The COS NUV dark rate is monitored regularly by taking two 1330s dark exposures every two weeks. These exposures, after excluding those that graze the SAA, are used to determine the dark rate trend with time. Background counts in NUV observations can come from a variety of sources including radioactive decay of atoms in the detector glass, external charged particles, scattered light, and phosphorescence from the detector window.

For more information on the COS NUV dark rate, see ISR 2010-12 or the most recent cycle’s ISR found in the calibration summary tables.

NUV Dark Rate vs. Time Last Updated: Orbital Variation Last Updated:
LAST UPDATED: 07/11/2019
Last Updated: Tue. Apr. 23, 2019 4:47PM
Last Updated: Tue. Apr. 23, 2019 4:47PM
Last Updated: Tue. Apr. 23, 2019 4:47PM
Last Updated: Fri. Aug. 10, 2018 9:43AM
Last Updated: Mon. Oct. 14, 2019 12:23PM
Last Updated: Mon. Oct. 14, 2019 12:24PM

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