COS Instrument Handbook for Cycle 24

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12.6	Cycle 18 Calibration Program

The Cycle 18 calibration program continued the calibration and monitoring observations performed in Cycle 17, including long-term programs to monitor the sensitivity and wavelength scale of both the NUV and FUV detectors. Brief descriptions of these monitoring programs are presented in Table 12.2. Table lists additional special calibration programs that were undertaken in Cycle 18. A comprehensive review of the Cycle 18 calibration program was published in COS ISR 2013-04 (Kriss et al. 2012).

Table 12.5:

Cycle 18 Calibration Program FUV Lifetime Position Calibration Program

Program ID	Title	Accuracy Achieved	Products
124141	COS Observations of Geocoronal Lyman-α Emission	G140L: S/N = 2 per pixel at 1200 å, G130M: S/N = 2 per pixel at 1213 å	List of exposures on the COS website2 that GOs may use to model and subtract Lyman-α
12426	FUV Sensitivity Characterization	S/N ~ 10/pixel	ISR, Reference file
12432	COS FUV Detector Gain Sag vs. High Voltage	1% over 2 å bands	Decision on change of voltage or lifetime position

1

Coordinated parallel with STIS calibration program 12414.

2

http://www.stsci.edu/hst/cos/calibration/airglow.html.

As described in Section 4.1.7, gain sag affects spectra obtained with the FUV detector. To address this problem the COS team performed studies to move the Aperture Mechanism so that the FUV spectra fell on a different part of the detector, called a lifetime position. This work was divided into three phases. Table 12.6 lists the programs that were used to determine the location of the new lifetime position, enable science at that location, and finally calibrate observations obtained there. The additional lifetime calibration program “Second COS FUV Lifetime Position: Wavelength Scales (FCAL1)” uses observations from programs 12805, 12806, and 12796.

Table 12.6: Lifetime Position 2 Calibration Program

	I. Identify the New Lifetime Position
12676	COS/FUV Characterization of Detector Effects
12677	COS/FUV Mapping of the Stray PtNe Light through FCA
12678	COS/FUV Characterization of Optical Effects
	II. Enable Science at the New Lifetime Position
12793	Second COS FUV Lifetime Position: FUV Detector High Voltage Sweep (FENA1)
12795	Second COS FUV Lifetime Position: Verification of Aperture and FUV Spectrum Placement (FENA2)
12796	Second COS FUV Lifetime Position: Focus Sweep Enabling Program (FENA3)
12797	Second COS FUV Lifetime Position: FUV Target Acquisition Parameter Update (FENA4)
	III. Calibrate the New Lifetime Position
12805	Second COS FUV Lifetime Position: Wavelength and Resolution Calibration (FCAL2)
12806	Second COS FUV Lifetime Position: Flux and Flat-field Calibration and TDS Transfer (FCAL3)
12807	Second COS FUV Lifetime Position: Verification of FUV BOA Operations (FCAL4)

Phase I was part of Cycle 18. Phases II and III took place during Cycle 19.